Changeset 2726 for draft-ietf-httpbis/03/p1-messaging.html
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draft-ietf-httpbis/03/p1-messaging.html
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362 } 354 363 @bottom-right { 355 content: "[Page " counter(page) "]"; 356 } 364 content: "[Page " counter(page) "]"; 365 } 357 366 } 358 367 359 @page:first { 368 @page:first { 360 369 @top-left { 361 370 content: normal; … … 389 398 <link rel="Appendix" title="D Compatibility with Previous Versions" href="#rfc.section.D"> 390 399 <link rel="Appendix" title="E Change Log (to be removed by RFC Editor before publication)" href="#rfc.section.E"> 391 <meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1. 537, 2010-12-30 14:21:59, XSLT vendor: SAXON 8.9 from Saxonica http://www.saxonica.com/">400 <meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.640, 2014/06/13 12:42:58, XSLT vendor: SAXON 8.9 from Saxonica http://www.saxonica.com/"> 392 401 <link rel="schema.dct" href="http://purl.org/dc/terms/"> 393 402 <meta name="dct.creator" content="Fielding, R."> … … 418 427 </tr> 419 428 <tr> 420 <td class="left">Obsoletes: <a href="http ://tools.ietf.org/html/rfc2616">2616</a> (if approved)429 <td class="left">Obsoletes: <a href="https://tools.ietf.org/html/rfc2616">2616</a> (if approved) 421 430 </td> 422 431 <td class="right">J. Gettys</td> … … 489 498 </table> 490 499 <p class="title">HTTP/1.1, part 1: URIs, Connections, and Message Parsing<br><span class="filename">draft-ietf-httpbis-p1-messaging-03</span></p> 491 <h1><a id="rfc.status" href="#rfc.status">Status of this Memo</a></h1> 492 <p>By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she 493 is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 494 6 of BCP 79. 495 </p> 496 <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note 497 that other groups may also distribute working documents as Internet-Drafts. 498 </p> 499 <p>Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other 500 documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work 501 in progress”. 502 </p> 503 <p>The list of current Internet-Drafts can be accessed at <a href="http://www.ietf.org/ietf/1id-abstracts.txt">http://www.ietf.org/ietf/1id-abstracts.txt</a>. 504 </p> 505 <p>The list of Internet-Draft Shadow Directories can be accessed at <a href="http://www.ietf.org/shadow.html">http://www.ietf.org/shadow.html</a>. 506 </p> 507 <p>This Internet-Draft will expire on December 19, 2008.</p> 508 <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1> 500 <div id="rfc.status"> 501 <h1><a href="#rfc.status">Status of this Memo</a></h1> 502 <p>By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she 503 is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 504 6 of BCP 79. 505 </p> 506 <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note 507 that other groups may also distribute working documents as Internet-Drafts. 508 </p> 509 <p>Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other 510 documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work 511 in progress”. 512 </p> 513 <p>The list of current Internet-Drafts can be accessed at <a href="http://www.ietf.org/ietf/1id-abstracts.txt">http://www.ietf.org/ietf/1id-abstracts.txt</a>. 514 </p> 515 <p>The list of Internet-Draft Shadow Directories can be accessed at <a href="http://www.ietf.org/shadow.html">http://www.ietf.org/shadow.html</a>. 516 </p> 517 <p>This Internet-Draft will expire on December 19, 2008.</p> 518 </div> 519 <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1> 509 520 <p>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information 510 521 systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 1 of the … … 513 524 (URI) schemes, defines the generic message syntax and parsing requirements for HTTP message frames, and describes general 514 525 security concerns for implementations. 515 </p> 516 <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1> 526 </p> 527 <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1> 517 528 <p>Discussion of this draft should take place on the HTTPBIS working group mailing list (ietf-http-wg@w3.org). The current issues 518 529 list is at <<a href="http://www.tools.ietf.org/wg/httpbis/trac/report/11">http://www.tools.ietf.org/wg/httpbis/trac/report/11</a>> and related documents (including fancy diffs) can be found at <<a href="http://www.tools.ietf.org/wg/httpbis/">http://www.tools.ietf.org/wg/httpbis/</a>>. 519 </p> 530 </p> 520 531 <p>The changes in this draft are summarized in <a href="#changes.since.02" title="Since draft-ietf-httpbis-p1-messaging-02">Appendix E.4</a>. 521 </p> 532 </p> 522 533 <hr class="noprint"> 523 534 <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1> 524 535 <ul class="toc"> 525 <li> 1. <a href="#introduction">Introduction</a><ul>526 <li> 1.1 <a href="#intro.purpose">Purpose</a></li>527 <li> 1.2 <a href="#intro.requirements">Requirements</a></li>528 <li> 1.3 <a href="#intro.terminology">Terminology</a></li>529 <li> 1.4 <a href="#intro.overall.operation">Overall Operation</a></li>536 <li><a href="#rfc.section.1">1.</a> <a href="#introduction">Introduction</a><ul> 537 <li><a href="#rfc.section.1.1">1.1</a> <a href="#intro.purpose">Purpose</a></li> 538 <li><a href="#rfc.section.1.2">1.2</a> <a href="#intro.requirements">Requirements</a></li> 539 <li><a href="#rfc.section.1.3">1.3</a> <a href="#intro.terminology">Terminology</a></li> 540 <li><a href="#rfc.section.1.4">1.4</a> <a href="#intro.overall.operation">Overall Operation</a></li> 530 541 </ul> 531 542 </li> 532 <li> 2. <a href="#notation">Notational Conventions and Generic Grammar</a><ul>533 <li> 2.1 <a href="#notation.abnf">Augmented BNF</a></li>534 <li> 2.2 <a href="#basic.rules">Basic Rules</a></li>535 <li> 2.3 <a href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></li>543 <li><a href="#rfc.section.2">2.</a> <a href="#notation">Notational Conventions and Generic Grammar</a><ul> 544 <li><a href="#rfc.section.2.1">2.1</a> <a href="#notation.abnf">Augmented BNF</a></li> 545 <li><a href="#rfc.section.2.2">2.2</a> <a href="#basic.rules">Basic Rules</a></li> 546 <li><a href="#rfc.section.2.3">2.3</a> <a href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></li> 536 547 </ul> 537 548 </li> 538 <li> 3. <a href="#protocol.parameters">Protocol Parameters</a><ul>539 <li> 3.1 <a href="#http.version">HTTP Version</a></li>540 <li> 3.2 <a href="#uri">Uniform Resource Identifiers</a><ul>541 <li> 3.2.1 <a href="#general.syntax">General Syntax</a></li>542 <li> 3.2.2 <a href="#http.url">http URL</a></li>543 <li> 3.2.3 <a href="#uri.comparison">URI Comparison</a></li>549 <li><a href="#rfc.section.3">3.</a> <a href="#protocol.parameters">Protocol Parameters</a><ul> 550 <li><a href="#rfc.section.3.1">3.1</a> <a href="#http.version">HTTP Version</a></li> 551 <li><a href="#rfc.section.3.2">3.2</a> <a href="#uri">Uniform Resource Identifiers</a><ul> 552 <li><a href="#rfc.section.3.2.1">3.2.1</a> <a href="#general.syntax">General Syntax</a></li> 553 <li><a href="#rfc.section.3.2.2">3.2.2</a> <a href="#http.url">http URL</a></li> 554 <li><a href="#rfc.section.3.2.3">3.2.3</a> <a href="#uri.comparison">URI Comparison</a></li> 544 555 </ul> 545 556 </li> 546 <li> 3.3 <a href="#date.time.formats">Date/Time Formats</a><ul>547 <li> 3.3.1 <a href="#full.date">Full Date</a></li>557 <li><a href="#rfc.section.3.3">3.3</a> <a href="#date.time.formats">Date/Time Formats</a><ul> 558 <li><a href="#rfc.section.3.3.1">3.3.1</a> <a href="#full.date">Full Date</a></li> 548 559 </ul> 549 560 </li> 550 <li> 3.4 <a href="#transfer.codings">Transfer Codings</a><ul>551 <li> 3.4.1 <a href="#chunked.transfer.encoding">Chunked Transfer Coding</a></li>561 <li><a href="#rfc.section.3.4">3.4</a> <a href="#transfer.codings">Transfer Codings</a><ul> 562 <li><a href="#rfc.section.3.4.1">3.4.1</a> <a href="#chunked.transfer.encoding">Chunked Transfer Coding</a></li> 552 563 </ul> 553 564 </li> 554 <li> 3.5 <a href="#product.tokens">Product Tokens</a></li>565 <li><a href="#rfc.section.3.5">3.5</a> <a href="#product.tokens">Product Tokens</a></li> 555 566 </ul> 556 567 </li> 557 <li> 4. <a href="#http.message">HTTP Message</a><ul>558 <li> 4.1 <a href="#message.types">Message Types</a></li>559 <li> 4.2 <a href="#message.headers">Message Headers</a></li>560 <li> 4.3 <a href="#message.body">Message Body</a></li>561 <li> 4.4 <a href="#message.length">Message Length</a></li>562 <li> 4.5 <a href="#general.header.fields">General Header Fields</a></li>568 <li><a href="#rfc.section.4">4.</a> <a href="#http.message">HTTP Message</a><ul> 569 <li><a href="#rfc.section.4.1">4.1</a> <a href="#message.types">Message Types</a></li> 570 <li><a href="#rfc.section.4.2">4.2</a> <a href="#message.headers">Message Headers</a></li> 571 <li><a href="#rfc.section.4.3">4.3</a> <a href="#message.body">Message Body</a></li> 572 <li><a href="#rfc.section.4.4">4.4</a> <a href="#message.length">Message Length</a></li> 573 <li><a href="#rfc.section.4.5">4.5</a> <a href="#general.header.fields">General Header Fields</a></li> 563 574 </ul> 564 575 </li> 565 <li> 5. <a href="#request">Request</a><ul>566 <li> 5.1 <a href="#request-line">Request-Line</a><ul>567 <li> 5.1.1 <a href="#method">Method</a></li>568 <li> 5.1.2 <a href="#request-uri">Request-URI</a></li>576 <li><a href="#rfc.section.5">5.</a> <a href="#request">Request</a><ul> 577 <li><a href="#rfc.section.5.1">5.1</a> <a href="#request-line">Request-Line</a><ul> 578 <li><a href="#rfc.section.5.1.1">5.1.1</a> <a href="#method">Method</a></li> 579 <li><a href="#rfc.section.5.1.2">5.1.2</a> <a href="#request-uri">Request-URI</a></li> 569 580 </ul> 570 581 </li> 571 <li> 5.2 <a href="#the.resource.identified.by.a.request">The Resource Identified by a Request</a></li>582 <li><a href="#rfc.section.5.2">5.2</a> <a href="#the.resource.identified.by.a.request">The Resource Identified by a Request</a></li> 572 583 </ul> 573 584 </li> 574 <li> 6. <a href="#response">Response</a><ul>575 <li> 6.1 <a href="#status-line">Status-Line</a><ul>576 <li> 6.1.1 <a href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></li>585 <li><a href="#rfc.section.6">6.</a> <a href="#response">Response</a><ul> 586 <li><a href="#rfc.section.6.1">6.1</a> <a href="#status-line">Status-Line</a><ul> 587 <li><a href="#rfc.section.6.1.1">6.1.1</a> <a href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></li> 577 588 </ul> 578 589 </li> 579 590 </ul> 580 591 </li> 581 <li>7. <a href="#connections">Connections</a><ul> 582 <li>7.1 <a href="#persistent.connections">Persistent Connections</a><ul> 583 <li>7.1.1 <a href="#persistent.purpose">Purpose</a></li> 584 <li>7.1.2 <a href="#persistent.overall">Overall Operation</a><ul> 585 <li>7.1.2.1 <a href="#persistent.negotiation">Negotiation</a></li> 586 <li>7.1.2.2 <a href="#pipelining">Pipelining</a></li> 587 </ul> 588 </li> 589 <li>7.1.3 <a href="#persistent.proxy">Proxy Servers</a></li> 590 <li>7.1.4 <a href="#persistent.practical">Practical Considerations</a></li> 592 <li><a href="#rfc.section.7">7.</a> <a href="#connections">Connections</a><ul> 593 <li><a href="#rfc.section.7.1">7.1</a> <a href="#persistent.connections">Persistent Connections</a><ul> 594 <li><a href="#rfc.section.7.1.1">7.1.1</a> <a href="#persistent.purpose">Purpose</a></li> 595 <li><a href="#rfc.section.7.1.2">7.1.2</a> <a href="#persistent.overall">Overall Operation</a></li> 596 <li><a href="#rfc.section.7.1.3">7.1.3</a> <a href="#persistent.proxy">Proxy Servers</a></li> 597 <li><a href="#rfc.section.7.1.4">7.1.4</a> <a href="#persistent.practical">Practical Considerations</a></li> 591 598 </ul> 592 599 </li> 593 <li> 7.2 <a href="#message.transmission.requirements">Message Transmission Requirements</a><ul>594 <li> 7.2.1 <a href="#persistent.flow">Persistent Connections and Flow Control</a></li>595 <li> 7.2.2 <a href="#persistent.monitor">Monitoring Connections for Error Status Messages</a></li>596 <li> 7.2.3 <a href="#use.of.the.100.status">Use of the 100 (Continue) Status</a></li>597 <li> 7.2.4 <a href="#connection.premature">Client Behavior if Server Prematurely Closes Connection</a></li>600 <li><a href="#rfc.section.7.2">7.2</a> <a href="#message.transmission.requirements">Message Transmission Requirements</a><ul> 601 <li><a href="#rfc.section.7.2.1">7.2.1</a> <a href="#persistent.flow">Persistent Connections and Flow Control</a></li> 602 <li><a href="#rfc.section.7.2.2">7.2.2</a> <a href="#persistent.monitor">Monitoring Connections for Error Status Messages</a></li> 603 <li><a href="#rfc.section.7.2.3">7.2.3</a> <a href="#use.of.the.100.status">Use of the 100 (Continue) Status</a></li> 604 <li><a href="#rfc.section.7.2.4">7.2.4</a> <a href="#connection.premature">Client Behavior if Server Prematurely Closes Connection</a></li> 598 605 </ul> 599 606 </li> 600 607 </ul> 601 608 </li> 602 <li> 8. <a href="#header.fields">Header Field Definitions</a><ul>603 <li> 8.1 <a href="#header.connection">Connection</a></li>604 <li> 8.2 <a href="#header.content-length">Content-Length</a></li>605 <li> 8.3 <a href="#header.date">Date</a><ul>606 <li> 8.3.1 <a href="#clockless.origin.server.operation">Clockless Origin Server Operation</a></li>609 <li><a href="#rfc.section.8">8.</a> <a href="#header.fields">Header Field Definitions</a><ul> 610 <li><a href="#rfc.section.8.1">8.1</a> <a href="#header.connection">Connection</a></li> 611 <li><a href="#rfc.section.8.2">8.2</a> <a href="#header.content-length">Content-Length</a></li> 612 <li><a href="#rfc.section.8.3">8.3</a> <a href="#header.date">Date</a><ul> 613 <li><a href="#rfc.section.8.3.1">8.3.1</a> <a href="#clockless.origin.server.operation">Clockless Origin Server Operation</a></li> 607 614 </ul> 608 615 </li> 609 <li> 8.4 <a href="#header.host">Host</a></li>610 <li> 8.5 <a href="#header.te">TE</a></li>611 <li> 8.6 <a href="#header.trailer">Trailer</a></li>612 <li> 8.7 <a href="#header.transfer-encoding">Transfer-Encoding</a></li>613 <li> 8.8 <a href="#header.upgrade">Upgrade</a></li>614 <li> 8.9 <a href="#header.via">Via</a></li>616 <li><a href="#rfc.section.8.4">8.4</a> <a href="#header.host">Host</a></li> 617 <li><a href="#rfc.section.8.5">8.5</a> <a href="#header.te">TE</a></li> 618 <li><a href="#rfc.section.8.6">8.6</a> <a href="#header.trailer">Trailer</a></li> 619 <li><a href="#rfc.section.8.7">8.7</a> <a href="#header.transfer-encoding">Transfer-Encoding</a></li> 620 <li><a href="#rfc.section.8.8">8.8</a> <a href="#header.upgrade">Upgrade</a></li> 621 <li><a href="#rfc.section.8.9">8.9</a> <a href="#header.via">Via</a></li> 615 622 </ul> 616 623 </li> 617 <li> 9. <a href="#IANA.considerations">IANA Considerations</a><ul>618 <li> 9.1 <a href="#message.header.registration">Message Header Registration</a></li>624 <li><a href="#rfc.section.9">9.</a> <a href="#IANA.considerations">IANA Considerations</a><ul> 625 <li><a href="#rfc.section.9.1">9.1</a> <a href="#message.header.registration">Message Header Registration</a></li> 619 626 </ul> 620 627 </li> 621 <li> 10. <a href="#security.considerations">Security Considerations</a><ul>622 <li> 10.1 <a href="#personal.information">Personal Information</a></li>623 <li> 10.2 <a href="#abuse.of.server.log.information">Abuse of Server Log Information</a></li>624 <li> 10.3 <a href="#attack.pathname">Attacks Based On File and Path Names</a></li>625 <li> 10.4 <a href="#dns.spoofing">DNS Spoofing</a></li>626 <li> 10.5 <a href="#attack.proxies">Proxies and Caching</a></li>627 <li> 10.6 <a href="#attack.DoS">Denial of Service Attacks on Proxies</a></li>628 <li><a href="#rfc.section.10">10.</a> <a href="#security.considerations">Security Considerations</a><ul> 629 <li><a href="#rfc.section.10.1">10.1</a> <a href="#personal.information">Personal Information</a></li> 630 <li><a href="#rfc.section.10.2">10.2</a> <a href="#abuse.of.server.log.information">Abuse of Server Log Information</a></li> 631 <li><a href="#rfc.section.10.3">10.3</a> <a href="#attack.pathname">Attacks Based On File and Path Names</a></li> 632 <li><a href="#rfc.section.10.4">10.4</a> <a href="#dns.spoofing">DNS Spoofing</a></li> 633 <li><a href="#rfc.section.10.5">10.5</a> <a href="#attack.proxies">Proxies and Caching</a></li> 634 <li><a href="#rfc.section.10.6">10.6</a> <a href="#attack.DoS">Denial of Service Attacks on Proxies</a></li> 628 635 </ul> 629 636 </li> 630 <li> 11. <a href="#ack">Acknowledgments</a></li>631 <li> 12. <a href="#rfc.references">References</a><ul>632 <li> 12.1 <a href="#rfc.references.1">Normative References</a></li>633 <li> 12.2 <a href="#rfc.references.2">Informative References</a></li>637 <li><a href="#rfc.section.11">11.</a> <a href="#ack">Acknowledgments</a></li> 638 <li><a href="#rfc.section.12">12.</a> <a href="#rfc.references">References</a><ul> 639 <li><a href="#rfc.section.12.1">12.1</a> <a href="#rfc.references.1">Normative References</a></li> 640 <li><a href="#rfc.section.12.2">12.2</a> <a href="#rfc.references.2">Informative References</a></li> 634 641 </ul> 635 642 </li> 636 <li><a href="#rfc.authors">Authors' Addresses</a></li> 637 <li>A. <a href="#internet.media.type.http">Internet Media Types</a><ul> 638 <li>A.1 <a href="#internet.media.type.message.http">Internet Media Type message/http</a></li> 639 <li>A.2 <a href="#internet.media.type.application.http">Internet Media Type application/http</a></li> 643 <li><a href="#rfc.section.A">A.</a> <a href="#internet.media.type.http">Internet Media Types</a><ul> 644 <li><a href="#rfc.section.A.1">A.1</a> <a href="#internet.media.type.message.http">Internet Media Type message/http</a></li> 645 <li><a href="#rfc.section.A.2">A.2</a> <a href="#internet.media.type.application.http">Internet Media Type application/http</a></li> 640 646 </ul> 641 647 </li> 642 <li> B. <a href="#tolerant.applications">Tolerant Applications</a></li>643 <li> C. <a href="#conversion.of.date.formats">Conversion of Date Formats</a></li>644 <li> D. <a href="#compatibility">Compatibility with Previous Versions</a><ul>645 <li> D.1 <a href="#changes.from.1.0">Changes from HTTP/1.0</a><ul>646 <li> D.1.1 <a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses</a></li>648 <li><a href="#rfc.section.B">B.</a> <a href="#tolerant.applications">Tolerant Applications</a></li> 649 <li><a href="#rfc.section.C">C.</a> <a href="#conversion.of.date.formats">Conversion of Date Formats</a></li> 650 <li><a href="#rfc.section.D">D.</a> <a href="#compatibility">Compatibility with Previous Versions</a><ul> 651 <li><a href="#rfc.section.D.1">D.1</a> <a href="#changes.from.1.0">Changes from HTTP/1.0</a><ul> 652 <li><a href="#rfc.section.D.1.1">D.1.1</a> <a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses</a></li> 647 653 </ul> 648 654 </li> 649 <li> D.2 <a href="#compatibility.with.http.1.0.persistent.connections">Compatibility with HTTP/1.0 Persistent Connections</a></li>650 <li> D.3 <a href="#changes.from.rfc.2068">Changes from RFC 2068</a></li>651 <li> D.4 <a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li>655 <li><a href="#rfc.section.D.2">D.2</a> <a href="#compatibility.with.http.1.0.persistent.connections">Compatibility with HTTP/1.0 Persistent Connections</a></li> 656 <li><a href="#rfc.section.D.3">D.3</a> <a href="#changes.from.rfc.2068">Changes from RFC 2068</a></li> 657 <li><a href="#rfc.section.D.4">D.4</a> <a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li> 652 658 </ul> 653 659 </li> 654 <li> E. <a href="#change.log">Change Log (to be removed by RFC Editor before publication)</a><ul>655 <li> E.1 <a href="#rfc.section.E.1">Since RFC2616</a></li>656 <li> E.2 <a href="#rfc.section.E.2">Since draft-ietf-httpbis-p1-messaging-00</a></li>657 <li> E.3 <a href="#rfc.section.E.3">Since draft-ietf-httpbis-p1-messaging-01</a></li>658 <li> E.4 <a href="#changes.since.02">Since draft-ietf-httpbis-p1-messaging-02</a></li>660 <li><a href="#rfc.section.E">E.</a> <a href="#change.log">Change Log (to be removed by RFC Editor before publication)</a><ul> 661 <li><a href="#rfc.section.E.1">E.1</a> <a href="#rfc.section.E.1">Since RFC2616</a></li> 662 <li><a href="#rfc.section.E.2">E.2</a> <a href="#rfc.section.E.2">Since draft-ietf-httpbis-p1-messaging-00</a></li> 663 <li><a href="#rfc.section.E.3">E.3</a> <a href="#rfc.section.E.3">Since draft-ietf-httpbis-p1-messaging-01</a></li> 664 <li><a href="#rfc.section.E.4">E.4</a> <a href="#changes.since.02">Since draft-ietf-httpbis-p1-messaging-02</a></li> 659 665 </ul> 660 666 </li> 661 667 <li><a href="#rfc.index">Index</a></li> 668 <li><a href="#rfc.authors">Authors' Addresses</a></li> 662 669 <li><a href="#rfc.ipr">Intellectual Property and Copyright Statements</a></li> 663 670 </ul> 664 <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a> <a id="introduction" href="#introduction">Introduction</a></h1> 665 <p id="rfc.section.1.p.1">The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information 666 systems. HTTP has been in use by the World-Wide Web global information initiative since 1990. The first version of HTTP, commonly 667 referred to as HTTP/0.9, was a simple protocol for raw data transfer across the Internet with only a single method and no 668 metadata. HTTP/1.0, as defined by <a href="#RFC1945" id="rfc.xref.RFC1945.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.0">[RFC1945]</cite></a>, improved the protocol by allowing messages to be in the format of MIME-like messages, containing metadata about the data 669 transferred and modifiers on the request/response semantics. However, HTTP/1.0 did not sufficiently take into consideration 670 the effects of hierarchical proxies, caching, the need for persistent connections, or name-based virtual hosts. In addition, 671 the proliferation of incompletely-implemented applications calling themselves "HTTP/1.0" necessitated a protocol version change 672 in order for two communicating applications to determine each other's true capabilities. 673 </p> 674 <p id="rfc.section.1.p.2">This document is Part 1 of the seven-part specification that defines the protocol referred to as "HTTP/1.1", obsoleting <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>. HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent requirements that enable reliable implementations 675 and adding only those new features that will either be safely ignored by an HTTP/1.0 recipient or only sent when communicating 676 with a party advertising compliance with HTTP/1.1. Part 1 defines those aspects of HTTP/1.1 related to overall network operation, 677 message framing, interaction with transport protocols, and URI schemes. 678 </p> 679 <p id="rfc.section.1.p.3">This document is currently disorganized in order to minimize the changes between drafts and enable reviewers to see the smaller 680 errata changes. The next draft will reorganize the sections to better reflect the content. In particular, the sections will 681 be organized according to the typical process of deciding when to use HTTP (URI schemes), overall network operation, connection 682 management, message framing, and generic message parsing. The current mess reflects how widely dispersed these topics and 683 associated requirements had become in <a href="#RFC2616" id="rfc.xref.RFC2616.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>. 684 </p> 685 <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a> <a id="intro.purpose" href="#intro.purpose">Purpose</a></h2> 686 <p id="rfc.section.1.1.p.1">Practical information systems require more functionality than simple retrieval, including search, front-end update, and annotation. 687 HTTP allows an open-ended set of methods and headers that indicate the purpose of a request <a href="#RFC2324" id="rfc.xref.RFC2324.1"><cite title="Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)">[RFC2324]</cite></a>. It builds on the discipline of reference provided by the Uniform Resource Identifier (URI) <a href="#RFC1630" id="rfc.xref.RFC1630.1"><cite title="Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network as used in the World-Wide Web">[RFC1630]</cite></a>, as a location (URL) <a href="#RFC1738" id="rfc.xref.RFC1738.1"><cite title="Uniform Resource Locators (URL)">[RFC1738]</cite></a> or name (URN) <a href="#RFC1737" id="rfc.xref.RFC1737.1"><cite title="Functional Requirements for Uniform Resource Names">[RFC1737]</cite></a>, for indicating the resource to which a method is to be applied. Messages are passed in a format similar to that used by 688 Internet mail <a href="#RFC2822" id="rfc.xref.RFC2822.1"><cite title="Internet Message Format">[RFC2822]</cite></a> as defined by the Multipurpose Internet Mail Extensions (MIME) <a href="#RFC2045" id="rfc.xref.RFC2045.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a>. 689 </p> 690 <p id="rfc.section.1.1.p.2">HTTP is also used as a generic protocol for communication between user agents and proxies/gateways to other Internet systems, 691 including those supported by the SMTP <a href="#RFC2821" id="rfc.xref.RFC2821.1"><cite title="Simple Mail Transfer Protocol">[RFC2821]</cite></a>, NNTP <a href="#RFC3977" id="rfc.xref.RFC3977.1"><cite title="Network News Transfer Protocol (NNTP)">[RFC3977]</cite></a>, FTP <a href="#RFC959" id="rfc.xref.RFC959.1"><cite title="File Transfer Protocol">[RFC959]</cite></a>, Gopher <a href="#RFC1436" id="rfc.xref.RFC1436.1"><cite title="The Internet Gopher Protocol (a distributed document search and retrieval protocol)">[RFC1436]</cite></a>, and WAIS <a href="#WAIS" id="rfc.xref.WAIS.1"><cite title="WAIS Interface Protocol Prototype Functional Specification (v1.5)">[WAIS]</cite></a> protocols. In this way, HTTP allows basic hypermedia access to resources available from diverse applications. 692 </p> 693 <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a> <a id="intro.requirements" href="#intro.requirements">Requirements</a></h2> 694 <p id="rfc.section.1.2.p.1">The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" 695 in this document are to be interpreted as described in <a href="#RFC2119" id="rfc.xref.RFC2119.1"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[RFC2119]</cite></a>. 696 </p> 697 <p id="rfc.section.1.2.p.2">An implementation is not compliant if it fails to satisfy one or more of the <em class="bcp14">MUST</em> or <em class="bcp14">REQUIRED</em> level requirements for the protocols it implements. An implementation that satisfies all the <em class="bcp14">MUST</em> or <em class="bcp14">REQUIRED</em> level and all the <em class="bcp14">SHOULD</em> level requirements for its protocols is said to be "unconditionally compliant"; one that satisfies all the <em class="bcp14">MUST</em> level requirements but not all the <em class="bcp14">SHOULD</em> level requirements for its protocols is said to be "conditionally compliant." 698 </p> 699 <h2 id="rfc.section.1.3"><a href="#rfc.section.1.3">1.3</a> <a id="intro.terminology" href="#intro.terminology">Terminology</a></h2> 700 <p id="rfc.section.1.3.p.1">This specification uses a number of terms to refer to the roles played by participants in, and objects of, the HTTP communication.</p> 701 <p id="rfc.section.1.3.p.2"> <span id="rfc.iref.c.1"></span> <dfn>connection</dfn> 702 </p> 703 <ul class="empty"> 704 <li>A transport layer virtual circuit established between two programs for the purpose of communication.</li> 705 </ul> 706 <p id="rfc.section.1.3.p.3"> <span id="rfc.iref.m.1"></span> <dfn>message</dfn> 707 </p> 708 <ul class="empty"> 709 <li>The basic unit of HTTP communication, consisting of a structured sequence of octets matching the syntax defined in <a href="#http.message" title="HTTP Message">Section 4</a> and transmitted via the connection. 710 </li> 711 </ul> 712 <p id="rfc.section.1.3.p.4"> <span id="rfc.iref.r.1"></span> <dfn>request</dfn> 713 </p> 714 <ul class="empty"> 715 <li>An HTTP request message, as defined in <a href="#request" title="Request">Section 5</a>. 716 </li> 717 </ul> 718 <p id="rfc.section.1.3.p.5"> <span id="rfc.iref.r.2"></span> <dfn>response</dfn> 719 </p> 720 <ul class="empty"> 721 <li>An HTTP response message, as defined in <a href="#response" title="Response">Section 6</a>. 722 </li> 723 </ul> 724 <p id="rfc.section.1.3.p.6"> <span id="rfc.iref.r.3"></span> <dfn>resource</dfn> 725 </p> 726 <ul class="empty"> 727 <li>A network data object or service that can be identified by a URI, as defined in <a href="#uri" title="Uniform Resource Identifiers">Section 3.2</a>. Resources may be available in multiple representations (e.g. multiple languages, data formats, size, and resolutions) or 728 vary in other ways. 729 </li> 730 </ul> 731 <p id="rfc.section.1.3.p.7"> <span id="rfc.iref.e.1"></span> <dfn>entity</dfn> 732 </p> 733 <ul class="empty"> 734 <li>The information transferred as the payload of a request or response. An entity consists of metainformation in the form of 735 entity-header fields and content in the form of an entity-body, as described in <a href="p3-payload.html#entity" title="Entity">Section 4</a> of <a href="#Part3" id="rfc.xref.Part3.1"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>. 736 </li> 737 </ul> 738 <p id="rfc.section.1.3.p.8"> <span id="rfc.iref.r.4"></span> <dfn>representation</dfn> 739 </p> 740 <ul class="empty"> 741 <li>An entity included with a response that is subject to content negotiation, as described in <a href="p3-payload.html#content.negotiation" title="Content Negotiation">Section 5</a> of <a href="#Part3" id="rfc.xref.Part3.2"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>. There may exist multiple representations associated with a particular response status. 742 </li> 743 </ul> 744 <p id="rfc.section.1.3.p.9"> <span id="rfc.iref.c.2"></span> <dfn>content negotiation</dfn> 745 </p> 746 <ul class="empty"> 747 <li>The mechanism for selecting the appropriate representation when servicing a request, as described in <a href="p3-payload.html#content.negotiation" title="Content Negotiation">Section 5</a> of <a href="#Part3" id="rfc.xref.Part3.3"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>. The representation of entities in any response can be negotiated (including error responses). 748 </li> 749 </ul> 750 <p id="rfc.section.1.3.p.10"> <span id="rfc.iref.v.1"></span> <dfn>variant</dfn> 751 </p> 752 <ul class="empty"> 753 <li>A resource may have one, or more than one, representation(s) associated with it at any given instant. Each of these representations 754 is termed a `variant'. Use of the term `variant' does not necessarily imply that the resource is subject to content negotiation. 755 </li> 756 </ul> 757 <p id="rfc.section.1.3.p.11"> <span id="rfc.iref.c.3"></span> <dfn>client</dfn> 758 </p> 759 <ul class="empty"> 760 <li>A program that establishes connections for the purpose of sending requests.</li> 761 </ul> 762 <p id="rfc.section.1.3.p.12"> <span id="rfc.iref.u.1"></span> <dfn>user agent</dfn> 763 </p> 764 <ul class="empty"> 765 <li>The client which initiates a request. These are often browsers, editors, spiders (web-traversing robots), or other end user 766 tools. 767 </li> 768 </ul> 769 <p id="rfc.section.1.3.p.13"> <span id="rfc.iref.s.1"></span> <dfn>server</dfn> 770 </p> 771 <ul class="empty"> 772 <li>An application program that accepts connections in order to service requests by sending back responses. Any given program 773 may be capable of being both a client and a server; our use of these terms refers only to the role being performed by the 774 program for a particular connection, rather than to the program's capabilities in general. Likewise, any server may act as 775 an origin server, proxy, gateway, or tunnel, switching behavior based on the nature of each request. 776 </li> 777 </ul> 778 <p id="rfc.section.1.3.p.14"> <span id="rfc.iref.o.1"></span> <dfn>origin server</dfn> 779 </p> 780 <ul class="empty"> 781 <li>The server on which a given resource resides or is to be created.</li> 782 </ul> 783 <p id="rfc.section.1.3.p.15"> <span id="rfc.iref.p.1"></span> <dfn>proxy</dfn> 784 </p> 785 <ul class="empty"> 786 <li>An intermediary program which acts as both a server and a client for the purpose of making requests on behalf of other clients. 787 Requests are serviced internally or by passing them on, with possible translation, to other servers. A proxy <em class="bcp14">MUST</em> implement both the client and server requirements of this specification. A "transparent proxy" is a proxy that does not modify 788 the request or response beyond what is required for proxy authentication and identification. A "non-transparent proxy" is 789 a proxy that modifies the request or response in order to provide some added service to the user agent, such as group annotation 790 services, media type transformation, protocol reduction, or anonymity filtering. Except where either transparent or non-transparent 791 behavior is explicitly stated, the HTTP proxy requirements apply to both types of proxies. 792 </li> 793 </ul> 794 <p id="rfc.section.1.3.p.16"> <span id="rfc.iref.g.1"></span> <dfn>gateway</dfn> 795 </p> 796 <ul class="empty"> 797 <li>A server which acts as an intermediary for some other server. Unlike a proxy, a gateway receives requests as if it were the 798 origin server for the requested resource; the requesting client may not be aware that it is communicating with a gateway. 799 </li> 800 </ul> 801 <p id="rfc.section.1.3.p.17"> <span id="rfc.iref.t.1"></span> <dfn>tunnel</dfn> 802 </p> 803 <ul class="empty"> 804 <li>An intermediary program which is acting as a blind relay between two connections. Once active, a tunnel is not considered 805 a party to the HTTP communication, though the tunnel may have been initiated by an HTTP request. The tunnel ceases to exist 806 when both ends of the relayed connections are closed. 807 </li> 808 </ul> 809 <p id="rfc.section.1.3.p.18"> <span id="rfc.iref.c.4"></span> <dfn>cache</dfn> 810 </p> 811 <ul class="empty"> 812 <li>A program's local store of response messages and the subsystem that controls its message storage, retrieval, and deletion. 813 A cache stores cacheable responses in order to reduce the response time and network bandwidth consumption on future, equivalent 814 requests. Any client or server may include a cache, though a cache cannot be used by a server that is acting as a tunnel. 815 </li> 816 </ul> 817 <p id="rfc.section.1.3.p.19"> <span id="rfc.iref.c.5"></span> <dfn>cacheable</dfn> 818 </p> 819 <ul class="empty"> 820 <li>A response is cacheable if a cache is allowed to store a copy of the response message for use in answering subsequent requests. 821 The rules for determining the cacheability of HTTP responses are defined in <a href="p6-cache.html#caching" title="Introduction">Section 1</a> of <a href="#Part6" id="rfc.xref.Part6.1"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>. Even if a resource is cacheable, there may be additional constraints on whether a cache can use the cached copy for a particular 822 request. 823 </li> 824 </ul> 825 <p id="rfc.section.1.3.p.20"> <span id="rfc.iref.u.2"></span> <span id="rfc.iref.d.1"></span> <dfn>upstream</dfn>/<dfn>downstream</dfn> 826 </p> 827 <ul class="empty"> 828 <li>Upstream and downstream describe the flow of a message: all messages flow from upstream to downstream.</li> 829 </ul> 830 <p id="rfc.section.1.3.p.21"> <span id="rfc.iref.i.1"></span> <span id="rfc.iref.o.2"></span> <dfn>inbound</dfn>/<dfn>outbound</dfn> 831 </p> 832 <ul class="empty"> 833 <li>Inbound and outbound refer to the request and response paths for messages: "inbound" means "traveling toward the origin server", 834 and "outbound" means "traveling toward the user agent" 835 </li> 836 </ul> 837 <h2 id="rfc.section.1.4"><a href="#rfc.section.1.4">1.4</a> <a id="intro.overall.operation" href="#intro.overall.operation">Overall Operation</a></h2> 838 <p id="rfc.section.1.4.p.1">HTTP is a request/response protocol. A client sends a request to the server in the form of a request method, URI, and protocol 839 version, followed by a MIME-like message containing request modifiers, client information, and possible body content over 840 a connection with a server. The server responds with a status line, including the message's protocol version and a success 841 or error code, followed by a MIME-like message containing server information, entity metainformation, and possible entity-body 842 content. The relationship between HTTP and MIME is described in <a href="p3-payload.html#differences.between.http.entities.and.rfc.2045.entities" title="Differences Between HTTP Entities and RFC 2045 Entities">Appendix A</a> of <a href="#Part3" id="rfc.xref.Part3.4"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>. 843 </p> 844 <p id="rfc.section.1.4.p.2">Most HTTP communication is initiated by a user agent and consists of a request to be applied to a resource on some origin 845 server. In the simplest case, this may be accomplished via a single connection (v) between the user agent (UA) and the origin 846 server (O). 847 </p> 848 <div id="rfc.figure.u.1"></div><pre class="drawing"> request chain ------------------------> 671 <div id="introduction"> 672 <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a> <a href="#introduction">Introduction</a></h1> 673 <p id="rfc.section.1.p.1">The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information 674 systems. HTTP has been in use by the World-Wide Web global information initiative since 1990. The first version of HTTP, commonly 675 referred to as HTTP/0.9, was a simple protocol for raw data transfer across the Internet with only a single method and no 676 metadata. HTTP/1.0, as defined by <a href="#RFC1945" id="rfc.xref.RFC1945.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.0">[RFC1945]</cite></a>, improved the protocol by allowing messages to be in the format of MIME-like messages, containing metadata about the data 677 transferred and modifiers on the request/response semantics. However, HTTP/1.0 did not sufficiently take into consideration 678 the effects of hierarchical proxies, caching, the need for persistent connections, or name-based virtual hosts. In addition, 679 the proliferation of incompletely-implemented applications calling themselves "HTTP/1.0" necessitated a protocol version change 680 in order for two communicating applications to determine each other's true capabilities. 681 </p> 682 <p id="rfc.section.1.p.2">This document is Part 1 of the seven-part specification that defines the protocol referred to as "HTTP/1.1", obsoleting <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>. HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent requirements that enable reliable implementations 683 and adding only those new features that will either be safely ignored by an HTTP/1.0 recipient or only sent when communicating 684 with a party advertising compliance with HTTP/1.1. Part 1 defines those aspects of HTTP/1.1 related to overall network operation, 685 message framing, interaction with transport protocols, and URI schemes. 686 </p> 687 <p id="rfc.section.1.p.3">This document is currently disorganized in order to minimize the changes between drafts and enable reviewers to see the smaller 688 errata changes. The next draft will reorganize the sections to better reflect the content. In particular, the sections will 689 be organized according to the typical process of deciding when to use HTTP (URI schemes), overall network operation, connection 690 management, message framing, and generic message parsing. The current mess reflects how widely dispersed these topics and 691 associated requirements had become in <a href="#RFC2616" id="rfc.xref.RFC2616.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>. 692 </p> 693 <div id="intro.purpose"> 694 <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a> <a href="#intro.purpose">Purpose</a></h2> 695 <p id="rfc.section.1.1.p.1">Practical information systems require more functionality than simple retrieval, including search, front-end update, and annotation. 696 HTTP allows an open-ended set of methods and headers that indicate the purpose of a request <a href="#RFC2324" id="rfc.xref.RFC2324.1"><cite title="Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)">[RFC2324]</cite></a>. It builds on the discipline of reference provided by the Uniform Resource Identifier (URI) <a href="#RFC1630" id="rfc.xref.RFC1630.1"><cite title="Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network as used in the World-Wide Web">[RFC1630]</cite></a>, as a location (URL) <a href="#RFC1738" id="rfc.xref.RFC1738.1"><cite title="Uniform Resource Locators (URL)">[RFC1738]</cite></a> or name (URN) <a href="#RFC1737" id="rfc.xref.RFC1737.1"><cite title="Functional Requirements for Uniform Resource Names">[RFC1737]</cite></a>, for indicating the resource to which a method is to be applied. Messages are passed in a format similar to that used by 697 Internet mail <a href="#RFC2822" id="rfc.xref.RFC2822.1"><cite title="Internet Message Format">[RFC2822]</cite></a> as defined by the Multipurpose Internet Mail Extensions (MIME) <a href="#RFC2045" id="rfc.xref.RFC2045.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a>. 698 </p> 699 <p id="rfc.section.1.1.p.2">HTTP is also used as a generic protocol for communication between user agents and proxies/gateways to other Internet systems, 700 including those supported by the SMTP <a href="#RFC2821" id="rfc.xref.RFC2821.1"><cite title="Simple Mail Transfer Protocol">[RFC2821]</cite></a>, NNTP <a href="#RFC3977" id="rfc.xref.RFC3977.1"><cite title="Network News Transfer Protocol (NNTP)">[RFC3977]</cite></a>, FTP <a href="#RFC959" id="rfc.xref.RFC959.1"><cite title="File Transfer Protocol">[RFC959]</cite></a>, Gopher <a href="#RFC1436" id="rfc.xref.RFC1436.1"><cite title="The Internet Gopher Protocol (a distributed document search and retrieval protocol)">[RFC1436]</cite></a>, and WAIS <a href="#WAIS" id="rfc.xref.WAIS.1"><cite title="WAIS Interface Protocol Prototype Functional Specification (v1.5)">[WAIS]</cite></a> protocols. In this way, HTTP allows basic hypermedia access to resources available from diverse applications. 701 </p> 702 </div> 703 <div id="intro.requirements"> 704 <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a> <a href="#intro.requirements">Requirements</a></h2> 705 <p id="rfc.section.1.2.p.1">The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" 706 in this document are to be interpreted as described in <a href="#RFC2119" id="rfc.xref.RFC2119.1"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[RFC2119]</cite></a>. 707 </p> 708 <p id="rfc.section.1.2.p.2">An implementation is not compliant if it fails to satisfy one or more of the <em class="bcp14">MUST</em> or <em class="bcp14">REQUIRED</em> level requirements for the protocols it implements. An implementation that satisfies all the <em class="bcp14">MUST</em> or <em class="bcp14">REQUIRED</em> level and all the <em class="bcp14">SHOULD</em> level requirements for its protocols is said to be "unconditionally compliant"; one that satisfies all the <em class="bcp14">MUST</em> level requirements but not all the <em class="bcp14">SHOULD</em> level requirements for its protocols is said to be "conditionally compliant." 709 </p> 710 </div> 711 <div id="intro.terminology"> 712 <h2 id="rfc.section.1.3"><a href="#rfc.section.1.3">1.3</a> <a href="#intro.terminology">Terminology</a></h2> 713 <p id="rfc.section.1.3.p.1">This specification uses a number of terms to refer to the roles played by participants in, and objects of, the HTTP communication.</p> 714 <p id="rfc.section.1.3.p.2"><span id="rfc.iref.c.1"></span> <dfn>connection</dfn> 715 </p> 716 <ul class="empty"> 717 <li>A transport layer virtual circuit established between two programs for the purpose of communication.</li> 718 </ul> 719 <p id="rfc.section.1.3.p.3"><span id="rfc.iref.m.1"></span> <dfn>message</dfn> 720 </p> 721 <ul class="empty"> 722 <li>The basic unit of HTTP communication, consisting of a structured sequence of octets matching the syntax defined in <a href="#http.message" title="HTTP Message">Section 4</a> and transmitted via the connection. 723 </li> 724 </ul> 725 <p id="rfc.section.1.3.p.4"><span id="rfc.iref.r.1"></span> <dfn>request</dfn> 726 </p> 727 <ul class="empty"> 728 <li>An HTTP request message, as defined in <a href="#request" title="Request">Section 5</a>. 729 </li> 730 </ul> 731 <p id="rfc.section.1.3.p.5"><span id="rfc.iref.r.2"></span> <dfn>response</dfn> 732 </p> 733 <ul class="empty"> 734 <li>An HTTP response message, as defined in <a href="#response" title="Response">Section 6</a>. 735 </li> 736 </ul> 737 <p id="rfc.section.1.3.p.6"><span id="rfc.iref.r.3"></span> <dfn>resource</dfn> 738 </p> 739 <ul class="empty"> 740 <li>A network data object or service that can be identified by a URI, as defined in <a href="#uri" title="Uniform Resource Identifiers">Section 3.2</a>. Resources may be available in multiple representations (e.g. multiple languages, data formats, size, and resolutions) or 741 vary in other ways. 742 </li> 743 </ul> 744 <p id="rfc.section.1.3.p.7"><span id="rfc.iref.e.1"></span> <dfn>entity</dfn> 745 </p> 746 <ul class="empty"> 747 <li>The information transferred as the payload of a request or response. An entity consists of metainformation in the form of 748 entity-header fields and content in the form of an entity-body, as described in <a href="p3-payload.html#entity" title="Entity">Section 4</a> of <a href="#Part3" id="rfc.xref.Part3.1"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>. 749 </li> 750 </ul> 751 <p id="rfc.section.1.3.p.8"><span id="rfc.iref.r.4"></span> <dfn>representation</dfn> 752 </p> 753 <ul class="empty"> 754 <li>An entity included with a response that is subject to content negotiation, as described in <a href="p3-payload.html#content.negotiation" title="Content Negotiation">Section 5</a> of <a href="#Part3" id="rfc.xref.Part3.2"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>. There may exist multiple representations associated with a particular response status. 755 </li> 756 </ul> 757 <p id="rfc.section.1.3.p.9"><span id="rfc.iref.c.2"></span> <dfn>content negotiation</dfn> 758 </p> 759 <ul class="empty"> 760 <li>The mechanism for selecting the appropriate representation when servicing a request, as described in <a href="p3-payload.html#content.negotiation" title="Content Negotiation">Section 5</a> of <a href="#Part3" id="rfc.xref.Part3.3"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>. The representation of entities in any response can be negotiated (including error responses). 761 </li> 762 </ul> 763 <p id="rfc.section.1.3.p.10"><span id="rfc.iref.v.1"></span> <dfn>variant</dfn> 764 </p> 765 <ul class="empty"> 766 <li>A resource may have one, or more than one, representation(s) associated with it at any given instant. Each of these representations 767 is termed a `variant'. Use of the term `variant' does not necessarily imply that the resource is subject to content negotiation. 768 </li> 769 </ul> 770 <p id="rfc.section.1.3.p.11"><span id="rfc.iref.c.3"></span> <dfn>client</dfn> 771 </p> 772 <ul class="empty"> 773 <li>A program that establishes connections for the purpose of sending requests.</li> 774 </ul> 775 <p id="rfc.section.1.3.p.12"><span id="rfc.iref.u.1"></span> <dfn>user agent</dfn> 776 </p> 777 <ul class="empty"> 778 <li>The client which initiates a request. These are often browsers, editors, spiders (web-traversing robots), or other end user 779 tools. 780 </li> 781 </ul> 782 <p id="rfc.section.1.3.p.13"><span id="rfc.iref.s.1"></span> <dfn>server</dfn> 783 </p> 784 <ul class="empty"> 785 <li>An application program that accepts connections in order to service requests by sending back responses. Any given program 786 may be capable of being both a client and a server; our use of these terms refers only to the role being performed by the 787 program for a particular connection, rather than to the program's capabilities in general. Likewise, any server may act as 788 an origin server, proxy, gateway, or tunnel, switching behavior based on the nature of each request. 789 </li> 790 </ul> 791 <p id="rfc.section.1.3.p.14"><span id="rfc.iref.o.1"></span> <dfn>origin server</dfn> 792 </p> 793 <ul class="empty"> 794 <li>The server on which a given resource resides or is to be created.</li> 795 </ul> 796 <p id="rfc.section.1.3.p.15"><span id="rfc.iref.p.1"></span> <dfn>proxy</dfn> 797 </p> 798 <ul class="empty"> 799 <li>An intermediary program which acts as both a server and a client for the purpose of making requests on behalf of other clients. 800 Requests are serviced internally or by passing them on, with possible translation, to other servers. A proxy <em class="bcp14">MUST</em> implement both the client and server requirements of this specification. A "transparent proxy" is a proxy that does not modify 801 the request or response beyond what is required for proxy authentication and identification. A "non-transparent proxy" is 802 a proxy that modifies the request or response in order to provide some added service to the user agent, such as group annotation 803 services, media type transformation, protocol reduction, or anonymity filtering. Except where either transparent or non-transparent 804 behavior is explicitly stated, the HTTP proxy requirements apply to both types of proxies. 805 </li> 806 </ul> 807 <p id="rfc.section.1.3.p.16"><span id="rfc.iref.g.1"></span> <dfn>gateway</dfn> 808 </p> 809 <ul class="empty"> 810 <li>A server which acts as an intermediary for some other server. Unlike a proxy, a gateway receives requests as if it were the 811 origin server for the requested resource; the requesting client may not be aware that it is communicating with a gateway. 812 </li> 813 </ul> 814 <p id="rfc.section.1.3.p.17"><span id="rfc.iref.t.1"></span> <dfn>tunnel</dfn> 815 </p> 816 <ul class="empty"> 817 <li>An intermediary program which is acting as a blind relay between two connections. Once active, a tunnel is not considered 818 a party to the HTTP communication, though the tunnel may have been initiated by an HTTP request. The tunnel ceases to exist 819 when both ends of the relayed connections are closed. 820 </li> 821 </ul> 822 <p id="rfc.section.1.3.p.18"><span id="rfc.iref.c.4"></span> <dfn>cache</dfn> 823 </p> 824 <ul class="empty"> 825 <li>A program's local store of response messages and the subsystem that controls its message storage, retrieval, and deletion. 826 A cache stores cacheable responses in order to reduce the response time and network bandwidth consumption on future, equivalent 827 requests. Any client or server may include a cache, though a cache cannot be used by a server that is acting as a tunnel. 828 </li> 829 </ul> 830 <p id="rfc.section.1.3.p.19"><span id="rfc.iref.c.5"></span> <dfn>cacheable</dfn> 831 </p> 832 <ul class="empty"> 833 <li>A response is cacheable if a cache is allowed to store a copy of the response message for use in answering subsequent requests. 834 The rules for determining the cacheability of HTTP responses are defined in <a href="p6-cache.html#caching" title="Introduction">Section 1</a> of <a href="#Part6" id="rfc.xref.Part6.1"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>. Even if a resource is cacheable, there may be additional constraints on whether a cache can use the cached copy for a particular 835 request. 836 </li> 837 </ul> 838 <p id="rfc.section.1.3.p.20"><span id="rfc.iref.u.2"></span> <span id="rfc.iref.d.1"></span> <dfn>upstream</dfn>/<dfn>downstream</dfn> 839 </p> 840 <ul class="empty"> 841 <li>Upstream and downstream describe the flow of a message: all messages flow from upstream to downstream.</li> 842 </ul> 843 <p id="rfc.section.1.3.p.21"><span id="rfc.iref.i.1"></span> <span id="rfc.iref.o.2"></span> <dfn>inbound</dfn>/<dfn>outbound</dfn> 844 </p> 845 <ul class="empty"> 846 <li>Inbound and outbound refer to the request and response paths for messages: "inbound" means "traveling toward the origin server", 847 and "outbound" means "traveling toward the user agent" 848 </li> 849 </ul> 850 </div> 851 <div id="intro.overall.operation"> 852 <h2 id="rfc.section.1.4"><a href="#rfc.section.1.4">1.4</a> <a href="#intro.overall.operation">Overall Operation</a></h2> 853 <p id="rfc.section.1.4.p.1">HTTP is a request/response protocol. A client sends a request to the server in the form of a request method, URI, and protocol 854 version, followed by a MIME-like message containing request modifiers, client information, and possible body content over 855 a connection with a server. The server responds with a status line, including the message's protocol version and a success 856 or error code, followed by a MIME-like message containing server information, entity metainformation, and possible entity-body 857 content. The relationship between HTTP and MIME is described in <a href="p3-payload.html#differences.between.http.entities.and.rfc.2045.entities" title="Differences Between HTTP Entities and RFC 2045 Entities">Appendix A</a> of <a href="#Part3" id="rfc.xref.Part3.4"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>. 858 </p> 859 <p id="rfc.section.1.4.p.2">Most HTTP communication is initiated by a user agent and consists of a request to be applied to a resource on some origin 860 server. In the simplest case, this may be accomplished via a single connection (v) between the user agent (UA) and the origin 861 server (O). 862 </p> 863 <div id="rfc.figure.u.1"></div><pre class="drawing"> request chain ------------------------> 849 864 UA -------------------v------------------- O 850 865 <----------------------- response chain 851 866 </pre><p id="rfc.section.1.4.p.4">A more complicated situation occurs when one or more intermediaries are present in the request/response chain. There are three 852 common forms of intermediary: proxy, gateway, and tunnel. A proxy is a forwarding agent, receiving requests for a URI in its853 absolute form, rewriting all or part of the message, and forwarding the reformatted request toward the server identified by854 the URI. A gateway is a receiving agent, acting as a layer above some other server(s) and, if necessary, translating the requests855 to the underlying server's protocol. A tunnel acts as a relay point between two connections without changing the messages;856 tunnels are used when the communication needs to pass through an intermediary (such as a firewall) even when the intermediary857 cannot understand the contents of the messages.858 </p>859 <div id="rfc.figure.u.2"></div><pre class="drawing"> request chain -------------------------------------->867 common forms of intermediary: proxy, gateway, and tunnel. A proxy is a forwarding agent, receiving requests for a URI in its 868 absolute form, rewriting all or part of the message, and forwarding the reformatted request toward the server identified by 869 the URI. A gateway is a receiving agent, acting as a layer above some other server(s) and, if necessary, translating the requests 870 to the underlying server's protocol. A tunnel acts as a relay point between two connections without changing the messages; 871 tunnels are used when the communication needs to pass through an intermediary (such as a firewall) even when the intermediary 872 cannot understand the contents of the messages. 873 </p> 874 <div id="rfc.figure.u.2"></div><pre class="drawing"> request chain --------------------------------------> 860 875 UA -----v----- A -----v----- B -----v----- C -----v----- O 861 876 <------------------------------------- response chain 862 877 </pre><p id="rfc.section.1.4.p.6">The figure above shows three intermediaries (A, B, and C) between the user agent and origin server. A request or response 863 message that travels the whole chain will pass through four separate connections. This distinction is important because some864 HTTP communication options may apply only to the connection with the nearest, non-tunnel neighbor, only to the end-points865 of the chain, or to all connections along the chain. Although the diagram is linear, each participant may be engaged in multiple,866 simultaneous communications. For example, B may be receiving requests from many clients other than A, and/or forwarding requests867 to servers other than C, at the same time that it is handling A's request.868 </p>869 <p id="rfc.section.1.4.p.7">Any party to the communication which is not acting as a tunnel may employ an internal cache for handling requests. The effect870 of a cache is that the request/response chain is shortened if one of the participants along the chain has a cached response871 applicable to that request. The following illustrates the resulting chain if B has a cached copy of an earlier response from872 O (via C) for a request which has not been cached by UA or A.873 </p>874 <div id="rfc.figure.u.3"></div><pre class="drawing"> request chain ---------->878 message that travels the whole chain will pass through four separate connections. This distinction is important because some 879 HTTP communication options may apply only to the connection with the nearest, non-tunnel neighbor, only to the end-points 880 of the chain, or to all connections along the chain. Although the diagram is linear, each participant may be engaged in multiple, 881 simultaneous communications. For example, B may be receiving requests from many clients other than A, and/or forwarding requests 882 to servers other than C, at the same time that it is handling A's request. 883 </p> 884 <p id="rfc.section.1.4.p.7">Any party to the communication which is not acting as a tunnel may employ an internal cache for handling requests. The effect 885 of a cache is that the request/response chain is shortened if one of the participants along the chain has a cached response 886 applicable to that request. The following illustrates the resulting chain if B has a cached copy of an earlier response from 887 O (via C) for a request which has not been cached by UA or A. 888 </p> 889 <div id="rfc.figure.u.3"></div><pre class="drawing"> request chain ----------> 875 890 UA -----v----- A -----v----- B - - - - - - C - - - - - - O 876 891 <--------- response chain 877 892 </pre><p id="rfc.section.1.4.p.9">Not all responses are usefully cacheable, and some requests may contain modifiers which place special requirements on cache 878 behavior. HTTP requirements for cache behavior and cacheable responses are defined in <a href="p6-cache.html#caching" title="Introduction">Section 1</a> of <a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>. 879 </p> 880 <p id="rfc.section.1.4.p.10">In fact, there are a wide variety of architectures and configurations of caches and proxies currently being experimented with 881 or deployed across the World Wide Web. These systems include national hierarchies of proxy caches to save transoceanic bandwidth, 882 systems that broadcast or multicast cache entries, organizations that distribute subsets of cached data via CD-ROM, and so 883 on. HTTP systems are used in corporate intranets over high-bandwidth links, and for access via PDAs with low-power radio links 884 and intermittent connectivity. The goal of HTTP/1.1 is to support the wide diversity of configurations already deployed while 885 introducing protocol constructs that meet the needs of those who build web applications that require high reliability and, 886 failing that, at least reliable indications of failure. 887 </p> 888 <p id="rfc.section.1.4.p.11">HTTP communication usually takes place over TCP/IP connections. The default port is TCP 80 (<<a href="http://www.iana.org/assignments/port-numbers">http://www.iana.org/assignments/port-numbers</a>>), but other ports can be used. This does not preclude HTTP from being implemented on top of any other protocol on the Internet, 889 or on other networks. HTTP only presumes a reliable transport; any protocol that provides such guarantees can be used; the 890 mapping of the HTTP/1.1 request and response structures onto the transport data units of the protocol in question is outside 891 the scope of this specification. 892 </p> 893 <p id="rfc.section.1.4.p.12">In HTTP/1.0, most implementations used a new connection for each request/response exchange. In HTTP/1.1, a connection may 894 be used for one or more request/response exchanges, although connections may be closed for a variety of reasons (see <a href="#persistent.connections" title="Persistent Connections">Section 7.1</a>). 895 </p> 896 <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a> <a id="notation" href="#notation">Notational Conventions and Generic Grammar</a></h1> 897 <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a> <a id="notation.abnf" href="#notation.abnf">Augmented BNF</a></h2> 898 <p id="rfc.section.2.1.p.1">All of the mechanisms specified in this document are described in both prose and an augmented Backus-Naur Form (BNF) similar 899 to that used by <a href="#RFC822ABNF" id="rfc.xref.RFC822ABNF.1"><cite title="Standard for the format of ARPA Internet text messages">[RFC822ABNF]</cite></a>. Implementors will need to be familiar with the notation in order to understand this specification. The augmented BNF includes 900 the following constructs: 901 </p> 902 <p id="rfc.section.2.1.p.2">name = definition </p> 903 <ul class="empty"> 904 <li>The name of a rule is simply the name itself (without any enclosing "<" and ">") and is separated from its definition by the 905 equal "=" character. White space is only significant in that indentation of continuation lines is used to indicate a rule 906 definition that spans more than one line. Certain basic rules are in uppercase, such as SP, LWS, HTAB, CRLF, DIGIT, ALPHA, 907 etc. Angle brackets are used within definitions whenever their presence will facilitate discerning the use of rule names. 908 </li> 909 </ul> 910 <p id="rfc.section.2.1.p.3">"literal" </p> 911 <ul class="empty"> 912 <li>Quotation marks surround literal text. Unless stated otherwise, the text is case-insensitive.</li> 913 </ul> 914 <p id="rfc.section.2.1.p.4">rule1 | rule2 </p> 915 <ul class="empty"> 916 <li>Elements separated by a bar ("|") are alternatives, e.g., "yes | no" will accept yes or no.</li> 917 </ul> 918 <p id="rfc.section.2.1.p.5">(rule1 rule2) </p> 919 <ul class="empty"> 920 <li>Elements enclosed in parentheses are treated as a single element. Thus, "(elem (foo | bar) elem)" allows the token sequences 921 "elem foo elem" and "elem bar elem". 922 </li> 923 </ul> 924 <p id="rfc.section.2.1.p.6">*rule </p> 925 <ul class="empty"> 926 <li>The character "*" preceding an element indicates repetition. The full form is "<n>*<m>element" indicating at least <n> and 927 at most <m> occurrences of element. Default values are 0 and infinity so that "*(element)" allows any number, including zero; 928 "1*element" requires at least one; and "1*2element" allows one or two. 929 </li> 930 </ul> 931 <p id="rfc.section.2.1.p.7">[rule] </p> 932 <ul class="empty"> 933 <li>Square brackets enclose optional elements; "[foo bar]" is equivalent to "*1(foo bar)".</li> 934 </ul> 935 <p id="rfc.section.2.1.p.8">N rule </p> 936 <ul class="empty"> 937 <li>Specific repetition: "<n>(element)" is equivalent to "<n>*<n>(element)"; that is, exactly <n> occurrences of (element). Thus 938 2DIGIT is a 2-digit number, and 3ALPHA is a string of three alphabetic characters. 939 </li> 940 </ul> 941 <p id="rfc.section.2.1.p.9">#rule </p> 942 <ul class="empty"> 943 <li>A construct "#" is defined, similar to "*", for defining lists of elements. The full form is "<n>#<m>element" indicating at 944 least <n> and at most <m> elements, each separated by one or more commas (",") and <em class="bcp14">OPTIONAL</em> linear white space (LWS). This makes the usual form of lists very easy; a rule such as 945 <div id="rfc.figure.u.4"></div><pre class="text"> ( *<a href="#rule.LWS" class="smpl">LWS</a> element *( *<a href="#rule.LWS" class="smpl">LWS</a> "," *<a href="#rule.LWS" class="smpl">LWS</a> element ))</pre> </li> 946 <li>can be shown as 947 <div id="rfc.figure.u.5"></div><pre class="text"> 1#element</pre> </li> 948 <li>Wherever this construct is used, null elements are allowed, but do not contribute to the count of elements present. That is, 949 "(element), , (element) " is permitted, but counts as only two elements. Therefore, where at least one element is required, 950 at least one non-null element <em class="bcp14">MUST</em> be present. Default values are 0 and infinity so that "#element" allows any number, including zero; "1#element" requires at 951 least one; and "1#2element" allows one or two. 952 </li> 953 </ul> 954 <p id="rfc.section.2.1.p.10">; comment </p> 955 <ul class="empty"> 956 <li>A semi-colon, set off some distance to the right of rule text, starts a comment that continues to the end of line. This is 957 a simple way of including useful notes in parallel with the specifications. 958 </li> 959 </ul> 960 <div id="implied.LWS"> 961 <p id="rfc.section.2.1.p.11"> <span id="rfc.iref.i.2"></span> implied *LWS 962 </p> 963 <ul class="empty"> 964 <li>The grammar described by this specification is word-based. Except where noted otherwise, linear white space (LWS) can be included 965 between any two adjacent words (token or quoted-string), and between adjacent words and separators, without changing the interpretation 966 of a field. At least one delimiter (LWS and/or separators) <em class="bcp14">MUST</em> exist between any two tokens (for the definition of "token" below), since they would otherwise be interpreted as a single 967 token. 968 </li> 969 </ul> 893 behavior. HTTP requirements for cache behavior and cacheable responses are defined in <a href="p6-cache.html#caching" title="Introduction">Section 1</a> of <a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>. 894 </p> 895 <p id="rfc.section.1.4.p.10">In fact, there are a wide variety of architectures and configurations of caches and proxies currently being experimented with 896 or deployed across the World Wide Web. These systems include national hierarchies of proxy caches to save transoceanic bandwidth, 897 systems that broadcast or multicast cache entries, organizations that distribute subsets of cached data via CD-ROM, and so 898 on. HTTP systems are used in corporate intranets over high-bandwidth links, and for access via PDAs with low-power radio links 899 and intermittent connectivity. The goal of HTTP/1.1 is to support the wide diversity of configurations already deployed while 900 introducing protocol constructs that meet the needs of those who build web applications that require high reliability and, 901 failing that, at least reliable indications of failure. 902 </p> 903 <p id="rfc.section.1.4.p.11">HTTP communication usually takes place over TCP/IP connections. The default port is TCP 80 (<<a href="http://www.iana.org/assignments/port-numbers">http://www.iana.org/assignments/port-numbers</a>>), but other ports can be used. This does not preclude HTTP from being implemented on top of any other protocol on the Internet, 904 or on other networks. HTTP only presumes a reliable transport; any protocol that provides such guarantees can be used; the 905 mapping of the HTTP/1.1 request and response structures onto the transport data units of the protocol in question is outside 906 the scope of this specification. 907 </p> 908 <p id="rfc.section.1.4.p.12">In HTTP/1.0, most implementations used a new connection for each request/response exchange. In HTTP/1.1, a connection may 909 be used for one or more request/response exchanges, although connections may be closed for a variety of reasons (see <a href="#persistent.connections" title="Persistent Connections">Section 7.1</a>). 910 </p> 911 </div> 970 912 </div> 971 <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a> <a id="basic.rules" href="#basic.rules">Basic Rules</a></h2> 972 <div id="core.rules"> 973 <p id="rfc.section.2.2.p.1"> The following rules are used throughout this specification to describe basic parsing constructs. The US-ASCII coded character 974 set is defined by ANSI X3.4-1986 <a href="#USASCII" id="rfc.xref.USASCII.1"><cite title="Coded Character Set -- 7-bit American Standard Code for Information Interchange">[USASCII]</cite></a>. 975 </p> 976 </div> 977 <div id="rfc.figure.u.6"></div><pre class="inline"><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span><span id="rfc.iref.g.4"></span><span id="rfc.iref.g.5"></span><span id="rfc.iref.g.6"></span><span id="rfc.iref.g.7"></span><span id="rfc.iref.g.8"></span><span id="rfc.iref.g.9"></span><span id="rfc.iref.g.10"></span><span id="rfc.iref.g.11"></span> <a href="#core.rules" class="smpl">OCTET</a> = %x00-FF 913 <div id="notation"> 914 <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a> <a href="#notation">Notational Conventions and Generic Grammar</a></h1> 915 <div id="notation.abnf"> 916 <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a> <a href="#notation.abnf">Augmented BNF</a></h2> 917 <p id="rfc.section.2.1.p.1">All of the mechanisms specified in this document are described in both prose and an augmented Backus-Naur Form (BNF) similar 918 to that used by <a href="#RFC822ABNF" id="rfc.xref.RFC822ABNF.1"><cite title="Standard for the format of ARPA Internet text messages">[RFC822ABNF]</cite></a>. Implementors will need to be familiar with the notation in order to understand this specification. The augmented BNF includes 919 the following constructs: 920 </p> 921 <p id="rfc.section.2.1.p.2">name = definition </p> 922 <ul class="empty"> 923 <li>The name of a rule is simply the name itself (without any enclosing "<" and ">") and is separated from its definition by the 924 equal "=" character. White space is only significant in that indentation of continuation lines is used to indicate a rule 925 definition that spans more than one line. Certain basic rules are in uppercase, such as SP, LWS, HTAB, CRLF, DIGIT, ALPHA, 926 etc. Angle brackets are used within definitions whenever their presence will facilitate discerning the use of rule names. 927 </li> 928 </ul> 929 <p id="rfc.section.2.1.p.3">"literal" </p> 930 <ul class="empty"> 931 <li>Quotation marks surround literal text. Unless stated otherwise, the text is case-insensitive.</li> 932 </ul> 933 <p id="rfc.section.2.1.p.4">rule1 | rule2 </p> 934 <ul class="empty"> 935 <li>Elements separated by a bar ("|") are alternatives, e.g., "yes | no" will accept yes or no.</li> 936 </ul> 937 <p id="rfc.section.2.1.p.5">(rule1 rule2) </p> 938 <ul class="empty"> 939 <li>Elements enclosed in parentheses are treated as a single element. Thus, "(elem (foo | bar) elem)" allows the token sequences 940 "elem foo elem" and "elem bar elem". 941 </li> 942 </ul> 943 <p id="rfc.section.2.1.p.6">*rule </p> 944 <ul class="empty"> 945 <li>The character "*" preceding an element indicates repetition. The full form is "<n>*<m>element" indicating at least <n> and 946 at most <m> occurrences of element. Default values are 0 and infinity so that "*(element)" allows any number, including zero; 947 "1*element" requires at least one; and "1*2element" allows one or two. 948 </li> 949 </ul> 950 <p id="rfc.section.2.1.p.7">[rule] </p> 951 <ul class="empty"> 952 <li>Square brackets enclose optional elements; "[foo bar]" is equivalent to "*1(foo bar)".</li> 953 </ul> 954 <p id="rfc.section.2.1.p.8">N rule </p> 955 <ul class="empty"> 956 <li>Specific repetition: "<n>(element)" is equivalent to "<n>*<n>(element)"; that is, exactly <n> occurrences of (element). Thus 957 2DIGIT is a 2-digit number, and 3ALPHA is a string of three alphabetic characters. 958 </li> 959 </ul> 960 <p id="rfc.section.2.1.p.9">#rule </p> 961 <ul class="empty"> 962 <li>A construct "#" is defined, similar to "*", for defining lists of elements. The full form is "<n>#<m>element" indicating at 963 least <n> and at most <m> elements, each separated by one or more commas (",") and <em class="bcp14">OPTIONAL</em> linear white space (LWS). This makes the usual form of lists very easy; a rule such as <span id="rfc.figure.u.4"></span><pre class="text"> ( *<a href="#rule.LWS" class="smpl">LWS</a> element *( *<a href="#rule.LWS" class="smpl">LWS</a> "," *<a href="#rule.LWS" class="smpl">LWS</a> element ))</pre> </li> 964 <li>can be shown as <span id="rfc.figure.u.5"></span><pre class="text"> 1#element</pre> </li> 965 <li>Wherever this construct is used, null elements are allowed, but do not contribute to the count of elements present. That is, 966 "(element), , (element) " is permitted, but counts as only two elements. Therefore, where at least one element is required, 967 at least one non-null element <em class="bcp14">MUST</em> be present. Default values are 0 and infinity so that "#element" allows any number, including zero; "1#element" requires at 968 least one; and "1#2element" allows one or two. 969 </li> 970 </ul> 971 <p id="rfc.section.2.1.p.10">; comment </p> 972 <ul class="empty"> 973 <li>A semi-colon, set off some distance to the right of rule text, starts a comment that continues to the end of line. This is 974 a simple way of including useful notes in parallel with the specifications. 975 </li> 976 </ul> 977 <div id="implied.LWS"> 978 <p id="rfc.section.2.1.p.11"><span id="rfc.iref.i.2"></span> implied *LWS 979 </p> 980 <ul class="empty"> 981 <li>The grammar described by this specification is word-based. Except where noted otherwise, linear white space (LWS) can be included 982 between any two adjacent words (token or quoted-string), and between adjacent words and separators, without changing the interpretation 983 of a field. At least one delimiter (LWS and/or separators) <em class="bcp14">MUST</em> exist between any two tokens (for the definition of "token" below), since they would otherwise be interpreted as a single 984 token. 985 </li> 986 </ul> 987 </div> 988 </div> 989 <div id="basic.rules"> 990 <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a> <a href="#basic.rules">Basic Rules</a></h2> 991 <div id="core.rules"> 992 <p id="rfc.section.2.2.p.1"> The following rules are used throughout this specification to describe basic parsing constructs. The US-ASCII coded character 993 set is defined by ANSI X3.4-1986 <a href="#USASCII" id="rfc.xref.USASCII.1"><cite title="Coded Character Set -- 7-bit American Standard Code for Information Interchange">[USASCII]</cite></a>. 994 </p> 995 </div> 996 <div id="rfc.figure.u.6"></div><pre class="inline"><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span><span id="rfc.iref.g.4"></span><span id="rfc.iref.g.5"></span><span id="rfc.iref.g.6"></span><span id="rfc.iref.g.7"></span><span id="rfc.iref.g.8"></span><span id="rfc.iref.g.9"></span><span id="rfc.iref.g.10"></span><span id="rfc.iref.g.11"></span> <a href="#core.rules" class="smpl">OCTET</a> = %x00-FF 978 997 ; any 8-bit sequence of data 979 998 <a href="#core.rules" class="smpl">CHAR</a> = %x01-7F … … 996 1015 ; US-ASCII double-quote mark (34) 997 1016 </pre><div id="rule.CRLF"> 998 <p id="rfc.section.2.2.p.3">HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all protocol elements except the entity-body (see <a href="#tolerant.applications" title="Tolerant Applications">Appendix B</a> for tolerant applications). The end-of-line marker within an entity-body is defined by its associated media type, as described999 in <a href="p3-payload.html#media.types" title="Media Types">Section 3.3</a> of <a href="#Part3" id="rfc.xref.Part3.5"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>.1000 </p>1001 </div>1002 <div id="rfc.figure.u.7"></div><pre class="inline"><span id="rfc.iref.g.12"></span> <a href="#rule.CRLF" class="smpl">CRLF</a> = <a href="#core.rules" class="smpl">CR</a> LF1017 <p id="rfc.section.2.2.p.3"> HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all protocol elements except the entity-body (see <a href="#tolerant.applications" title="Tolerant Applications">Appendix B</a> for tolerant applications). The end-of-line marker within an entity-body is defined by its associated media type, as described 1018 in <a href="p3-payload.html#media.types" title="Media Types">Section 3.3</a> of <a href="#Part3" id="rfc.xref.Part3.5"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>. 1019 </p> 1020 </div> 1021 <div id="rfc.figure.u.7"></div><pre class="inline"><span id="rfc.iref.g.12"></span> <a href="#rule.CRLF" class="smpl">CRLF</a> = <a href="#core.rules" class="smpl">CR</a> LF 1003 1022 </pre><div id="rule.LWS"> 1004 <p id="rfc.section.2.2.p.5">HTTP/1.1 header field values can be folded onto multiple lines if the continuation line begins with a space or horizontal1005 tab. All linear white space, including folding, has the same semantics as SP. A recipient <em class="bcp14">MAY</em> replace any linear white space with a single SP before interpreting the field value or forwarding the message downstream.1006 </p>1007 </div>1008 <div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.13"></span> <a href="#rule.LWS" class="smpl">LWS</a> = [<a href="#rule.CRLF" class="smpl">CRLF</a>] 1*( <a href="#core.rules" class="smpl">SP</a> | <a href="#core.rules" class="smpl">HTAB</a> )1023 <p id="rfc.section.2.2.p.5"> HTTP/1.1 header field values can be folded onto multiple lines if the continuation line begins with a space or horizontal 1024 tab. All linear white space, including folding, has the same semantics as SP. A recipient <em class="bcp14">MAY</em> replace any linear white space with a single SP before interpreting the field value or forwarding the message downstream. 1025 </p> 1026 </div> 1027 <div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.13"></span> <a href="#rule.LWS" class="smpl">LWS</a> = [<a href="#rule.CRLF" class="smpl">CRLF</a>] 1*( <a href="#core.rules" class="smpl">SP</a> | <a href="#core.rules" class="smpl">HTAB</a> ) 1009 1028 </pre><div id="rule.TEXT"> 1010 <p id="rfc.section.2.2.p.7">The TEXT rule is only used for descriptive field contents and values that are not intended to be interpreted by the message1011 parser. Words of *TEXT <em class="bcp14">MAY</em> contain characters from character sets other than ISO-8859-1 <a href="#ISO-8859-1" id="rfc.xref.ISO-8859-1.1"><cite title="Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1">[ISO-8859-1]</cite></a> only when encoded according to the rules of <a href="#RFC2047" id="rfc.xref.RFC2047.1"><cite title="MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text">[RFC2047]</cite></a>.1012 </p>1013 </div>1014 <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.14"></span> <a href="#rule.TEXT" class="smpl">TEXT</a> = %x20-7E | %x80-FF | <a href="#rule.LWS" class="smpl">LWS</a>1029 <p id="rfc.section.2.2.p.7"> The TEXT rule is only used for descriptive field contents and values that are not intended to be interpreted by the message 1030 parser. Words of *TEXT <em class="bcp14">MAY</em> contain characters from character sets other than ISO-8859-1 <a href="#ISO-8859-1" id="rfc.xref.ISO-8859-1.1"><cite title="Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1">[ISO-8859-1]</cite></a> only when encoded according to the rules of <a href="#RFC2047" id="rfc.xref.RFC2047.1"><cite title="MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text">[RFC2047]</cite></a>. 1031 </p> 1032 </div> 1033 <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.14"></span> <a href="#rule.TEXT" class="smpl">TEXT</a> = %x20-7E | %x80-FF | <a href="#rule.LWS" class="smpl">LWS</a> 1015 1034 ; any <a href="#core.rules" class="smpl">OCTET</a> except <a href="#core.rules" class="smpl">CTL</a>s, but including <a href="#rule.LWS" class="smpl">LWS</a> 1016 1035 </pre><p id="rfc.section.2.2.p.9">A CRLF is allowed in the definition of TEXT only as part of a header field continuation. It is expected that the folding LWS 1017 will be replaced with a single SP before interpretation of the TEXT value.1018 </p>1019 <div id="rule.HEX">1020 <p id="rfc.section.2.2.p.10">Hexadecimal numeric characters are used in several protocol elements.</p>1021 </div>1022 <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.15"></span> <a href="#rule.HEX" class="smpl">HEX</a> = "A" | "B" | "C" | "D" | "E" | "F"1036 will be replaced with a single SP before interpretation of the TEXT value. 1037 </p> 1038 <div id="rule.HEX"> 1039 <p id="rfc.section.2.2.p.10"> Hexadecimal numeric characters are used in several protocol elements.</p> 1040 </div> 1041 <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.15"></span> <a href="#rule.HEX" class="smpl">HEX</a> = "A" | "B" | "C" | "D" | "E" | "F" 1023 1042 | "a" | "b" | "c" | "d" | "e" | "f" | <a href="#core.rules" class="smpl">DIGIT</a> 1024 1043 </pre><div id="rule.token.separators"> 1025 <p id="rfc.section.2.2.p.12">Many HTTP/1.1 header field values consist of words separated by LWS or special characters. These special characters <em class="bcp14">MUST</em> be in a quoted string to be used within a parameter value (as defined in <a href="#transfer.codings" title="Transfer Codings">Section 3.4</a>).1026 </p>1027 </div>1028 <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.16"></span><span id="rfc.iref.g.17"></span><span id="rfc.iref.g.18"></span> <a href="#rule.token.separators" class="smpl">separators</a> = "(" | ")" | "<" | ">" | "@"1044 <p id="rfc.section.2.2.p.12"> Many HTTP/1.1 header field values consist of words separated by LWS or special characters. These special characters <em class="bcp14">MUST</em> be in a quoted string to be used within a parameter value (as defined in <a href="#transfer.codings" title="Transfer Codings">Section 3.4</a>). 1045 </p> 1046 </div> 1047 <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.16"></span><span id="rfc.iref.g.17"></span><span id="rfc.iref.g.18"></span> <a href="#rule.token.separators" class="smpl">separators</a> = "(" | ")" | "<" | ">" | "@" 1029 1048 | "," | ";" | ":" | "\" | <a href="#core.rules" class="smpl">DQUOTE</a> 1030 1049 | "/" | "[" | "]" | "?" | "=" … … 1038 1057 <a href="#rule.token.separators" class="smpl">token</a> = 1*<a href="#rule.token.separators" class="smpl">tchar</a> 1039 1058 </pre><div id="rule.comment"> 1040 <p id="rfc.section.2.2.p.14">Comments can be included in some HTTP header fields by surrounding the comment text with parentheses. Comments are only allowed1041 in fields containing "comment" as part of their field value definition. In all other fields, parentheses are considered part1042 of the field value.1043 </p>1044 </div>1045 <div id="rfc.figure.u.12"></div><pre class="inline"><span id="rfc.iref.g.19"></span><span id="rfc.iref.g.20"></span> <a href="#rule.comment" class="smpl">comment</a> = "(" *( <a href="#rule.comment" class="smpl">ctext</a> | <a href="#rule.quoted-pair" class="smpl">quoted-pair</a> | <a href="#rule.comment" class="smpl">comment</a> ) ")"1059 <p id="rfc.section.2.2.p.14"> Comments can be included in some HTTP header fields by surrounding the comment text with parentheses. Comments are only allowed 1060 in fields containing "comment" as part of their field value definition. In all other fields, parentheses are considered part 1061 of the field value. 1062 </p> 1063 </div> 1064 <div id="rfc.figure.u.12"></div><pre class="inline"><span id="rfc.iref.g.19"></span><span id="rfc.iref.g.20"></span> <a href="#rule.comment" class="smpl">comment</a> = "(" *( <a href="#rule.comment" class="smpl">ctext</a> | <a href="#rule.quoted-pair" class="smpl">quoted-pair</a> | <a href="#rule.comment" class="smpl">comment</a> ) ")" 1046 1065 <a href="#rule.comment" class="smpl">ctext</a> = <any <a href="#rule.TEXT" class="smpl">TEXT</a> excluding "(" and ")"> 1047 1066 </pre><div id="rule.quoted-string"> 1048 <p id="rfc.section.2.2.p.16">A string of text is parsed as a single word if it is quoted using double-quote marks.</p>1049 </div>1050 <div id="rfc.figure.u.13"></div><pre class="inline"><span id="rfc.iref.g.21"></span><span id="rfc.iref.g.22"></span> <a href="#rule.quoted-string" class="smpl">quoted-string</a> = ( <a href="#core.rules" class="smpl">DQUOTE</a> *(<a href="#rule.quoted-string" class="smpl">qdtext</a> | <a href="#rule.quoted-pair" class="smpl">quoted-pair</a> ) <a href="#core.rules" class="smpl">DQUOTE</a> )1067 <p id="rfc.section.2.2.p.16"> A string of text is parsed as a single word if it is quoted using double-quote marks.</p> 1068 </div> 1069 <div id="rfc.figure.u.13"></div><pre class="inline"><span id="rfc.iref.g.21"></span><span id="rfc.iref.g.22"></span> <a href="#rule.quoted-string" class="smpl">quoted-string</a> = ( <a href="#core.rules" class="smpl">DQUOTE</a> *(<a href="#rule.quoted-string" class="smpl">qdtext</a> | <a href="#rule.quoted-pair" class="smpl">quoted-pair</a> ) <a href="#core.rules" class="smpl">DQUOTE</a> ) 1051 1070 <a href="#rule.quoted-string" class="smpl">qdtext</a> = <any <a href="#rule.TEXT" class="smpl">TEXT</a> excluding <a href="#core.rules" class="smpl">DQUOTE</a> and "\"> 1052 1071 </pre><div id="rule.quoted-pair"> 1053 <p id="rfc.section.2.2.p.18">The backslash character ("\") <em class="bcp14">MAY</em> be used as a single-character quoting mechanism only within quoted-string and comment constructs.1054 </p>1055 </div>1056 <div id="rfc.figure.u.14"></div><pre class="inline"><span id="rfc.iref.g.23"></span><span id="rfc.iref.g.24"></span> <a href="#rule.quoted-pair" class="smpl">quoted-text</a> = %x01-09 |1072 <p id="rfc.section.2.2.p.18"> The backslash character ("\") <em class="bcp14">MAY</em> be used as a single-character quoting mechanism only within quoted-string and comment constructs. 1073 </p> 1074 </div> 1075 <div id="rfc.figure.u.14"></div><pre class="inline"><span id="rfc.iref.g.23"></span><span id="rfc.iref.g.24"></span> <a href="#rule.quoted-pair" class="smpl">quoted-text</a> = %x01-09 | 1057 1076 %x0B-0C | 1058 1077 %x0E-FF ; Characters excluding NUL, <a href="#core.rules" class="smpl">CR</a> and <a href="#core.rules" class="smpl">LF</a> 1059 1078 <a href="#rule.quoted-pair" class="smpl">quoted-pair</a> = "\" <a href="#rule.quoted-pair" class="smpl">quoted-text</a> 1060 </pre><h2 id="rfc.section.2.3"><a href="#rfc.section.2.3">2.3</a> <a id="abnf.dependencies" href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></h2> 1061 <p id="rfc.section.2.3.p.1">The ABNF rules below are defined in other parts:</p> 1062 <div id="rfc.figure.u.15"></div><pre class="inline"> <a href="#abnf.dependencies" class="smpl">request-header</a> = <request-header, defined in <a href="#Part2" id="rfc.xref.Part2.1"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>, <a href="p2-semantics.html#request.header.fields" title="Request Header Fields">Section 4</a>> 1079 </pre></div> 1080 <div id="abnf.dependencies"> 1081 <h2 id="rfc.section.2.3"><a href="#rfc.section.2.3">2.3</a> <a href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></h2> 1082 <p id="rfc.section.2.3.p.1">The ABNF rules below are defined in other parts:</p> 1083 <div id="rfc.figure.u.15"></div><pre class="inline"> <a href="#abnf.dependencies" class="smpl">request-header</a> = <request-header, defined in <a href="#Part2" id="rfc.xref.Part2.1"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>, <a href="p2-semantics.html#request.header.fields" title="Request Header Fields">Section 4</a>> 1063 1084 <a href="#abnf.dependencies" class="smpl">response-header</a> = <response-header, defined in <a href="#Part2" id="rfc.xref.Part2.2"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>, <a href="p2-semantics.html#response.header.fields" title="Response Header Fields">Section 6</a>> 1064 1085 </pre><div id="rfc.figure.u.16"></div><pre class="inline"> <a href="#abnf.dependencies" class="smpl">accept-params</a> = <accept-params, defined in <a href="#Part3" id="rfc.xref.Part3.6"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>, <a href="p3-payload.html#header.accept" title="Accept">Section 6.1</a>> … … 1068 1089 <a href="#abnf.dependencies" class="smpl">Pragma</a> = <Pragma, defined in <a href="#Part6" id="rfc.xref.Part6.4"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>, <a href="p6-cache.html#header.pragma" title="Pragma">Section 16.4</a>> 1069 1090 <a href="#abnf.dependencies" class="smpl">Warning</a> = <Warning, defined in <a href="#Part6" id="rfc.xref.Part6.5"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>, <a href="p6-cache.html#header.warning" title="Warning">Section 16.6</a>> 1070 </pre><h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a> <a id="protocol.parameters" href="#protocol.parameters">Protocol Parameters</a></h1> 1071 <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a> <a id="http.version" href="#http.version">HTTP Version</a></h2> 1072 <p id="rfc.section.3.1.p.1">HTTP uses a "<major>.<minor>" numbering scheme to indicate versions of the protocol. The protocol versioning policy is intended 1073 to allow the sender to indicate the format of a message and its capacity for understanding further HTTP communication, rather 1074 than the features obtained via that communication. No change is made to the version number for the addition of message components 1075 which do not affect communication behavior or which only add to extensible field values. The <minor> number is incremented 1076 when the changes made to the protocol add features which do not change the general message parsing algorithm, but which may 1077 add to the message semantics and imply additional capabilities of the sender. The <major> number is incremented when the format 1078 of a message within the protocol is changed. See <a href="#RFC2145" id="rfc.xref.RFC2145.1"><cite title="Use and Interpretation of HTTP Version Numbers">[RFC2145]</cite></a> for a fuller explanation. 1079 </p> 1080 <p id="rfc.section.3.1.p.2">The version of an HTTP message is indicated by an HTTP-Version field in the first line of the message. HTTP-Version is case-sensitive.</p> 1081 <div id="rfc.figure.u.18"></div><pre class="inline"><span id="rfc.iref.g.25"></span><span id="rfc.iref.g.26"></span> <a href="#http.version" class="smpl">HTTP-Version</a> = <a href="#http.version" class="smpl">HTTP-Prot-Name</a> "/" 1*<a href="#core.rules" class="smpl">DIGIT</a> "." 1*<a href="#core.rules" class="smpl">DIGIT</a> 1091 </pre></div> 1092 </div> 1093 <div id="protocol.parameters"> 1094 <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a> <a href="#protocol.parameters">Protocol Parameters</a></h1> 1095 <div id="http.version"> 1096 <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a> <a href="#http.version">HTTP Version</a></h2> 1097 <p id="rfc.section.3.1.p.1">HTTP uses a "<major>.<minor>" numbering scheme to indicate versions of the protocol. The protocol versioning policy is intended 1098 to allow the sender to indicate the format of a message and its capacity for understanding further HTTP communication, rather 1099 than the features obtained via that communication. No change is made to the version number for the addition of message components 1100 which do not affect communication behavior or which only add to extensible field values. The <minor> number is incremented 1101 when the changes made to the protocol add features which do not change the general message parsing algorithm, but which may 1102 add to the message semantics and imply additional capabilities of the sender. The <major> number is incremented when the format 1103 of a message within the protocol is changed. See <a href="#RFC2145" id="rfc.xref.RFC2145.1"><cite title="Use and Interpretation of HTTP Version Numbers">[RFC2145]</cite></a> for a fuller explanation. 1104 </p> 1105 <p id="rfc.section.3.1.p.2">The version of an HTTP message is indicated by an HTTP-Version field in the first line of the message. HTTP-Version is case-sensitive.</p> 1106 <div id="rfc.figure.u.18"></div><pre class="inline"><span id="rfc.iref.g.25"></span><span id="rfc.iref.g.26"></span> <a href="#http.version" class="smpl">HTTP-Version</a> = <a href="#http.version" class="smpl">HTTP-Prot-Name</a> "/" 1*<a href="#core.rules" class="smpl">DIGIT</a> "." 1*<a href="#core.rules" class="smpl">DIGIT</a> 1082 1107 <a href="#http.version" class="smpl">HTTP-Prot-Name</a> = %x48.54.54.50 ; "HTTP", case-sensitive 1083 1108 </pre><p id="rfc.section.3.1.p.4">Note that the major and minor numbers <em class="bcp14">MUST</em> be treated as separate integers and that each <em class="bcp14">MAY</em> be incremented higher than a single digit. Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is lower than HTTP/12.3. 1084 Leading zeros <em class="bcp14">MUST</em> be ignored by recipients and <em class="bcp14">MUST NOT</em> be sent. 1085 </p> 1086 <p id="rfc.section.3.1.p.5">An application that sends a request or response message that includes HTTP-Version of "HTTP/1.1" <em class="bcp14">MUST</em> be at least conditionally compliant with this specification. Applications that are at least conditionally compliant with this 1087 specification <em class="bcp14">SHOULD</em> use an HTTP-Version of "HTTP/1.1" in their messages, and <em class="bcp14">MUST</em> do so for any message that is not compatible with HTTP/1.0. For more details on when to send specific HTTP-Version values, 1088 see <a href="#RFC2145" id="rfc.xref.RFC2145.2"><cite title="Use and Interpretation of HTTP Version Numbers">[RFC2145]</cite></a>. 1089 </p> 1090 <p id="rfc.section.3.1.p.6">The HTTP version of an application is the highest HTTP version for which the application is at least conditionally compliant.</p> 1091 <p id="rfc.section.3.1.p.7">Proxy and gateway applications need to be careful when forwarding messages in protocol versions different from that of the 1092 application. Since the protocol version indicates the protocol capability of the sender, a proxy/gateway <em class="bcp14">MUST NOT</em> send a message with a version indicator which is greater than its actual version. If a higher version request is received, 1093 the proxy/gateway <em class="bcp14">MUST</em> either downgrade the request version, or respond with an error, or switch to tunnel behavior. 1094 </p> 1095 <p id="rfc.section.3.1.p.8">Due to interoperability problems with HTTP/1.0 proxies discovered since the publication of <a href="#RFC2068" id="rfc.xref.RFC2068.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, caching proxies <em class="bcp14">MUST</em>, gateways <em class="bcp14">MAY</em>, and tunnels <em class="bcp14">MUST NOT</em> upgrade the request to the highest version they support. The proxy/gateway's response to that request <em class="bcp14">MUST</em> be in the same major version as the request. 1096 </p> 1097 <p id="rfc.section.3.1.p.9"> </p> 1098 <ul class="empty"> 1099 <li> <b>Note:</b> Converting between versions of HTTP may involve modification of header fields required or forbidden by the versions involved. 1100 </li> 1101 </ul> 1102 <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a> <a id="uri" href="#uri">Uniform Resource Identifiers</a></h2> 1103 <p id="rfc.section.3.2.p.1">URIs have been known by many names: WWW addresses, Universal Document Identifiers, Universal Resource Identifiers <a href="#RFC1630" id="rfc.xref.RFC1630.2"><cite title="Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network as used in the World-Wide Web">[RFC1630]</cite></a>, and finally the combination of Uniform Resource Locators (URL) <a href="#RFC1738" id="rfc.xref.RFC1738.2"><cite title="Uniform Resource Locators (URL)">[RFC1738]</cite></a> and Names (URN) <a href="#RFC1737" id="rfc.xref.RFC1737.2"><cite title="Functional Requirements for Uniform Resource Names">[RFC1737]</cite></a>. As far as HTTP is concerned, Uniform Resource Identifiers are simply formatted strings which identify--via name, location, 1104 or any other characteristic--a resource. 1105 </p> 1106 <h3 id="rfc.section.3.2.1"><a href="#rfc.section.3.2.1">3.2.1</a> <a id="general.syntax" href="#general.syntax">General Syntax</a></h3> 1107 <p id="rfc.section.3.2.1.p.1">URIs in HTTP can be represented in absolute form or relative to some known base URI <a href="#RFC1808" id="rfc.xref.RFC1808.1"><cite title="Relative Uniform Resource Locators">[RFC1808]</cite></a>, depending upon the context of their use. The two forms are differentiated by the fact that absolute URIs always begin with 1108 a scheme name followed by a colon. For definitive information on URL syntax and semantics, see "Uniform Resource Identifiers 1109 (URI): Generic Syntax and Semantics," <a href="#RFC2396" id="rfc.xref.RFC2396.1"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a> (which replaces <a href="#RFC1738" id="rfc.xref.RFC1738.3"><cite title="Uniform Resource Locators (URL)">[RFC1738]</cite></a> and <a href="#RFC1808" id="rfc.xref.RFC1808.2"><cite title="Relative Uniform Resource Locators">[RFC1808]</cite></a>). This specification adopts the definitions of "URI-reference", "absoluteURI", "fragment", "relativeURI", "port", "host", 1110 "abs_path", "query", and "authority" from that specification: 1111 </p> 1112 <div id="rfc.figure.u.19"></div><pre class="inline"><span id="rfc.iref.g.27"></span><span id="rfc.iref.g.28"></span><span id="rfc.iref.g.29"></span><span id="rfc.iref.g.30"></span><span id="rfc.iref.g.31"></span><span id="rfc.iref.g.32"></span><span id="rfc.iref.g.33"></span> <a href="#general.syntax" class="smpl">absoluteURI</a> = <absoluteURI, defined in <a href="#RFC2396" id="rfc.xref.RFC2396.2"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>, <a href="http://tools.ietf.org/html/rfc2396#section-3">Section 3</a>> 1113 <a href="#general.syntax" class="smpl">authority</a> = <authority, defined in <a href="#RFC2396" id="rfc.xref.RFC2396.3"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>, <a href="http://tools.ietf.org/html/rfc2396#section-3.2">Section 3.2</a>> 1114 <a href="#general.syntax" class="smpl">fragment</a> = <fragment, defined in <a href="#RFC2396" id="rfc.xref.RFC2396.4"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>, <a href="http://tools.ietf.org/html/rfc2396#section-4.1">Section 4.1</a>> 1115 <a href="#general.syntax" class="smpl">path-absolute</a> = <abs_path, defined in <a href="#RFC2396" id="rfc.xref.RFC2396.5"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>, <a href="http://tools.ietf.org/html/rfc2396#section-3">Section 3</a>> 1116 <a href="#general.syntax" class="smpl">port</a> = <port, defined in <a href="#RFC2396" id="rfc.xref.RFC2396.6"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>, <a href="http://tools.ietf.org/html/rfc2396#section-3.2.2">Section 3.2.2</a>> 1117 <a href="#general.syntax" class="smpl">query</a> = <query, defined in <a href="#RFC2396" id="rfc.xref.RFC2396.7"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>, <a href="http://tools.ietf.org/html/rfc2396#section-3.4">Section 3.4</a>> 1118 <a href="#general.syntax" class="smpl">relativeURI</a> = <relativeURI, defined in <a href="#RFC2396" id="rfc.xref.RFC2396.8"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>, <a href="http://tools.ietf.org/html/rfc2396#section-5">Section 5</a>> 1119 <a href="#general.syntax" class="smpl">uri-host</a> = <host, defined in <a href="#RFC2396" id="rfc.xref.RFC2396.9"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>, <a href="http://tools.ietf.org/html/rfc2396#section-3.2.2">Section 3.2.2</a>> 1109 Leading zeros <em class="bcp14">MUST</em> be ignored by recipients and <em class="bcp14">MUST NOT</em> be sent. 1110 </p> 1111 <p id="rfc.section.3.1.p.5">An application that sends a request or response message that includes HTTP-Version of "HTTP/1.1" <em class="bcp14">MUST</em> be at least conditionally compliant with this specification. Applications that are at least conditionally compliant with this 1112 specification <em class="bcp14">SHOULD</em> use an HTTP-Version of "HTTP/1.1" in their messages, and <em class="bcp14">MUST</em> do so for any message that is not compatible with HTTP/1.0. For more details on when to send specific HTTP-Version values, 1113 see <a href="#RFC2145" id="rfc.xref.RFC2145.2"><cite title="Use and Interpretation of HTTP Version Numbers">[RFC2145]</cite></a>. 1114 </p> 1115 <p id="rfc.section.3.1.p.6">The HTTP version of an application is the highest HTTP version for which the application is at least conditionally compliant.</p> 1116 <p id="rfc.section.3.1.p.7">Proxy and gateway applications need to be careful when forwarding messages in protocol versions different from that of the 1117 application. Since the protocol version indicates the protocol capability of the sender, a proxy/gateway <em class="bcp14">MUST NOT</em> send a message with a version indicator which is greater than its actual version. If a higher version request is received, 1118 the proxy/gateway <em class="bcp14">MUST</em> either downgrade the request version, or respond with an error, or switch to tunnel behavior. 1119 </p> 1120 <p id="rfc.section.3.1.p.8">Due to interoperability problems with HTTP/1.0 proxies discovered since the publication of <a href="#RFC2068" id="rfc.xref.RFC2068.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, caching proxies <em class="bcp14">MUST</em>, gateways <em class="bcp14">MAY</em>, and tunnels <em class="bcp14">MUST NOT</em> upgrade the request to the highest version they support. The proxy/gateway's response to that request <em class="bcp14">MUST</em> be in the same major version as the request. 1121 </p> 1122 <p id="rfc.section.3.1.p.9"></p> 1123 <ul class="empty"> 1124 <li><b>Note:</b> Converting between versions of HTTP may involve modification of header fields required or forbidden by the versions involved. 1125 </li> 1126 </ul> 1127 </div> 1128 <div id="uri"> 1129 <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a> <a href="#uri">Uniform Resource Identifiers</a></h2> 1130 <p id="rfc.section.3.2.p.1">URIs have been known by many names: WWW addresses, Universal Document Identifiers, Universal Resource Identifiers <a href="#RFC1630" id="rfc.xref.RFC1630.2"><cite title="Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network as used in the World-Wide Web">[RFC1630]</cite></a>, and finally the combination of Uniform Resource Locators (URL) <a href="#RFC1738" id="rfc.xref.RFC1738.2"><cite title="Uniform Resource Locators (URL)">[RFC1738]</cite></a> and Names (URN) <a href="#RFC1737" id="rfc.xref.RFC1737.2"><cite title="Functional Requirements for Uniform Resource Names">[RFC1737]</cite></a>. As far as HTTP is concerned, Uniform Resource Identifiers are simply formatted strings which identify--via name, location, 1131 or any other characteristic--a resource. 1132 </p> 1133 <div id="general.syntax"> 1134 <h3 id="rfc.section.3.2.1"><a href="#rfc.section.3.2.1">3.2.1</a> <a href="#general.syntax">General Syntax</a></h3> 1135 <p id="rfc.section.3.2.1.p.1">URIs in HTTP can be represented in absolute form or relative to some known base URI <a href="#RFC1808" id="rfc.xref.RFC1808.1"><cite title="Relative Uniform Resource Locators">[RFC1808]</cite></a>, depending upon the context of their use. The two forms are differentiated by the fact that absolute URIs always begin with 1136 a scheme name followed by a colon. For definitive information on URL syntax and semantics, see "Uniform Resource Identifiers 1137 (URI): Generic Syntax and Semantics," <a href="#RFC2396" id="rfc.xref.RFC2396.1"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a> (which replaces <a href="#RFC1738" id="rfc.xref.RFC1738.3"><cite title="Uniform Resource Locators (URL)">[RFC1738]</cite></a> and <a href="#RFC1808" id="rfc.xref.RFC1808.2"><cite title="Relative Uniform Resource Locators">[RFC1808]</cite></a>). This specification adopts the definitions of "URI-reference", "absoluteURI", "fragment", "relativeURI", "port", "host", 1138 "abs_path", "query", and "authority" from that specification: 1139 </p> 1140 <div id="rfc.figure.u.19"></div><pre class="inline"><span id="rfc.iref.g.27"></span><span id="rfc.iref.g.28"></span><span id="rfc.iref.g.29"></span><span id="rfc.iref.g.30"></span><span id="rfc.iref.g.31"></span><span id="rfc.iref.g.32"></span><span id="rfc.iref.g.33"></span> <a href="#general.syntax" class="smpl">absoluteURI</a> = <absoluteURI, defined in <a href="#RFC2396" id="rfc.xref.RFC2396.2"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>, <a href="https://tools.ietf.org/html/rfc2396#section-3">Section 3</a>> 1141 <a href="#general.syntax" class="smpl">authority</a> = <authority, defined in <a href="#RFC2396" id="rfc.xref.RFC2396.3"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>, <a href="https://tools.ietf.org/html/rfc2396#section-3.2">Section 3.2</a>> 1142 <a href="#general.syntax" class="smpl">fragment</a> = <fragment, defined in <a href="#RFC2396" id="rfc.xref.RFC2396.4"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>, <a href="https://tools.ietf.org/html/rfc2396#section-4.1">Section 4.1</a>> 1143 <a href="#general.syntax" class="smpl">path-absolute</a> = <abs_path, defined in <a href="#RFC2396" id="rfc.xref.RFC2396.5"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>, <a href="https://tools.ietf.org/html/rfc2396#section-3">Section 3</a>> 1144 <a href="#general.syntax" class="smpl">port</a> = <port, defined in <a href="#RFC2396" id="rfc.xref.RFC2396.6"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>, <a href="https://tools.ietf.org/html/rfc2396#section-3.2.2">Section 3.2.2</a>> 1145 <a href="#general.syntax" class="smpl">query</a> = <query, defined in <a href="#RFC2396" id="rfc.xref.RFC2396.7"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>, <a href="https://tools.ietf.org/html/rfc2396#section-3.4">Section 3.4</a>> 1146 <a href="#general.syntax" class="smpl">relativeURI</a> = <relativeURI, defined in <a href="#RFC2396" id="rfc.xref.RFC2396.8"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>, <a href="https://tools.ietf.org/html/rfc2396#section-5">Section 5</a>> 1147 <a href="#general.syntax" class="smpl">uri-host</a> = <host, defined in <a href="#RFC2396" id="rfc.xref.RFC2396.9"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>, <a href="https://tools.ietf.org/html/rfc2396#section-3.2.2">Section 3.2.2</a>> 1120 1148 </pre><p id="rfc.section.3.2.1.p.3">HTTP does not place any a priori limit on the length of a URI. Servers <em class="bcp14">MUST</em> be able to handle the URI of any resource they serve, and <em class="bcp14">SHOULD</em> be able to handle URIs of unbounded length if they provide GET-based forms that could generate such URIs. A server <em class="bcp14">SHOULD</em> return 414 (Request-URI Too Long) status if a URI is longer than the server can handle (see <a href="p2-semantics.html#status.414" title="414 Request-URI Too Long">Section 9.4.15</a> of <a href="#Part2" id="rfc.xref.Part2.3"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). 1121 </p> 1122 <p id="rfc.section.3.2.1.p.4"> </p> 1123 <ul class="empty"> 1124 <li> <b>Note:</b> Servers ought to be cautious about depending on URI lengths above 255 bytes, because some older client or proxy implementations 1125 might not properly support these lengths. 1126 </li> 1127 </ul> 1128 <h3 id="rfc.section.3.2.2"><a href="#rfc.section.3.2.2">3.2.2</a> <a id="http.url" href="#http.url">http URL</a></h3> 1129 <p id="rfc.section.3.2.2.p.1">The "http" scheme is used to locate network resources via the HTTP protocol. This section defines the scheme-specific syntax 1130 and semantics for http URLs. 1131 </p> 1132 <div id="rfc.figure.u.20"></div><pre class="inline"><span id="rfc.iref.g.34"></span> <a href="#http.url" class="smpl">http-URL</a> = "http:" "//" <a href="#general.syntax" class="smpl">uri-host</a> [ ":" <a href="#general.syntax" class="smpl">port</a> ] 1149 </p> 1150 <p id="rfc.section.3.2.1.p.4"></p> 1151 <ul class="empty"> 1152 <li><b>Note:</b> Servers ought to be cautious about depending on URI lengths above 255 bytes, because some older client or proxy implementations 1153 might not properly support these lengths. 1154 </li> 1155 </ul> 1156 </div> 1157 <div id="http.url"> 1158 <h3 id="rfc.section.3.2.2"><a href="#rfc.section.3.2.2">3.2.2</a> <a href="#http.url">http URL</a></h3> 1159 <p id="rfc.section.3.2.2.p.1">The "http" scheme is used to locate network resources via the HTTP protocol. This section defines the scheme-specific syntax 1160 and semantics for http URLs. 1161 </p> 1162 <div id="rfc.figure.u.20"></div><pre class="inline"><span id="rfc.iref.g.34"></span> <a href="#http.url" class="smpl">http-URL</a> = "http:" "//" <a href="#general.syntax" class="smpl">uri-host</a> [ ":" <a href="#general.syntax" class="smpl">port</a> ] 1133 1163 [ <a href="#general.syntax" class="smpl">path-absolute</a> [ "?" <a href="#general.syntax" class="smpl">query</a> ]] 1134 1164 </pre><p id="rfc.section.3.2.2.p.3">If the port is empty or not given, port 80 is assumed. The semantics are that the identified resource is located at the server 1135 listening for TCP connections on that port of that host, and the Request-URI for the resource is path-absolute (<a href="#request-uri" title="Request-URI">Section 5.1.2</a>). The use of IP addresses in URLs <em class="bcp14">SHOULD</em> be avoided whenever possible (see <a href="#RFC1900" id="rfc.xref.RFC1900.1"><cite title="Renumbering Needs Work">[RFC1900]</cite></a>). If the path-absolute is not present in the URL, it <em class="bcp14">MUST</em> be given as "/" when used as a Request-URI for a resource (<a href="#request-uri" title="Request-URI">Section 5.1.2</a>). If a proxy receives a host name which is not a fully qualified domain name, it <em class="bcp14">MAY</em> add its domain to the host name it received. If a proxy receives a fully qualified domain name, the proxy <em class="bcp14">MUST NOT</em> change the host name. 1136 </p> 1137 <h3 id="rfc.section.3.2.3"><a href="#rfc.section.3.2.3">3.2.3</a> <a id="uri.comparison" href="#uri.comparison">URI Comparison</a></h3> 1138 <p id="rfc.section.3.2.3.p.1">When comparing two URIs to decide if they match or not, a client <em class="bcp14">SHOULD</em> use a case-sensitive octet-by-octet comparison of the entire URIs, with these exceptions: 1139 </p> 1140 <ul> 1141 <li>A port that is empty or not given is equivalent to the default port for that URI-reference;</li> 1142 <li>Comparisons of host names <em class="bcp14">MUST</em> be case-insensitive; 1143 </li> 1144 <li>Comparisons of scheme names <em class="bcp14">MUST</em> be case-insensitive; 1145 </li> 1146 <li>An empty path-absolute is equivalent to an path-absolute of "/".</li> 1147 </ul> 1148 <p id="rfc.section.3.2.3.p.2">Characters other than those in the "reserved" set (see <a href="#RFC2396" id="rfc.xref.RFC2396.10"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>) are equivalent to their ""%" HEX HEX" encoding. 1149 </p> 1150 <p id="rfc.section.3.2.3.p.3">For example, the following three URIs are equivalent:</p> 1151 <div id="rfc.figure.u.21"></div><pre class="text"> http://example.com:80/~smith/home.html 1165 listening for TCP connections on that port of that host, and the Request-URI for the resource is path-absolute (<a href="#request-uri" title="Request-URI">Section 5.1.2</a>). The use of IP addresses in URLs <em class="bcp14">SHOULD</em> be avoided whenever possible (see <a href="#RFC1900" id="rfc.xref.RFC1900.1"><cite title="Renumbering Needs Work">[RFC1900]</cite></a>). If the path-absolute is not present in the URL, it <em class="bcp14">MUST</em> be given as "/" when used as a Request-URI for a resource (<a href="#request-uri" title="Request-URI">Section 5.1.2</a>). If a proxy receives a host name which is not a fully qualified domain name, it <em class="bcp14">MAY</em> add its domain to the host name it received. If a proxy receives a fully qualified domain name, the proxy <em class="bcp14">MUST NOT</em> change the host name. 1166 </p> 1167 </div> 1168 <div id="uri.comparison"> 1169 <h3 id="rfc.section.3.2.3"><a href="#rfc.section.3.2.3">3.2.3</a> <a href="#uri.comparison">URI Comparison</a></h3> 1170 <p id="rfc.section.3.2.3.p.1">When comparing two URIs to decide if they match or not, a client <em class="bcp14">SHOULD</em> use a case-sensitive octet-by-octet comparison of the entire URIs, with these exceptions: 1171 </p> 1172 <ul> 1173 <li>A port that is empty or not given is equivalent to the default port for that URI-reference;</li> 1174 <li>Comparisons of host names <em class="bcp14">MUST</em> be case-insensitive; 1175 </li> 1176 <li>Comparisons of scheme names <em class="bcp14">MUST</em> be case-insensitive; 1177 </li> 1178 <li>An empty path-absolute is equivalent to an path-absolute of "/".</li> 1179 </ul> 1180 <p id="rfc.section.3.2.3.p.2">Characters other than those in the "reserved" set (see <a href="#RFC2396" id="rfc.xref.RFC2396.10"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>) are equivalent to their ""%" HEX HEX" encoding. 1181 </p> 1182 <p id="rfc.section.3.2.3.p.3">For example, the following three URIs are equivalent:</p> 1183 <div id="rfc.figure.u.21"></div><pre class="text"> http://example.com:80/~smith/home.html 1152 1184 http://EXAMPLE.com/%7Esmith/home.html 1153 1185 http://EXAMPLE.com:/%7esmith/home.html 1154 </pre><h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a> <a id="date.time.formats" href="#date.time.formats">Date/Time Formats</a></h2> 1155 <h3 id="rfc.section.3.3.1"><a href="#rfc.section.3.3.1">3.3.1</a> <a id="full.date" href="#full.date">Full Date</a></h3> 1156 <p id="rfc.section.3.3.1.p.1">HTTP applications have historically allowed three different formats for the representation of date/time stamps:</p> 1157 <div id="rfc.figure.u.22"></div><pre class="text"> Sun, 06 Nov 1994 08:49:37 GMT ; RFC 822, updated by RFC 1123 1186 </pre></div> 1187 </div> 1188 <div id="date.time.formats"> 1189 <h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a> <a href="#date.time.formats">Date/Time Formats</a></h2> 1190 <div id="full.date"> 1191 <h3 id="rfc.section.3.3.1"><a href="#rfc.section.3.3.1">3.3.1</a> <a href="#full.date">Full Date</a></h3> 1192 <p id="rfc.section.3.3.1.p.1">HTTP applications have historically allowed three different formats for the representation of date/time stamps:</p> 1193 <div id="rfc.figure.u.22"></div><pre class="text"> Sun, 06 Nov 1994 08:49:37 GMT ; RFC 822, updated by RFC 1123 1158 1194 Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format 1159 1195 Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format 1160 1196 </pre><p id="rfc.section.3.3.1.p.3">The first format is preferred as an Internet standard and represents a fixed-length subset of that defined by <a href="#RFC1123" id="rfc.xref.RFC1123.1"><cite title="Requirements for Internet Hosts - Application and Support">[RFC1123]</cite></a> (an update to <a href="#RFC822" id="rfc.xref.RFC822.1"><cite title="Standard for the format of ARPA Internet text messages">[RFC822]</cite></a>). The other formats are described here only for compatibility with obsolete implementations. HTTP/1.1 clients and servers 1161 that parse the date value <em class="bcp14">MUST</em> accept all three formats (for compatibility with HTTP/1.0), though they <em class="bcp14">MUST</em> only generate the RFC 1123 format for representing HTTP-date values in header fields. See <a href="#tolerant.applications" title="Tolerant Applications">Appendix B</a> for further information.1162 </p>1163 <ul class="empty">1164 <li><b>Note:</b> Recipients of date values are encouraged to be robust in accepting date values that may have been sent by non-HTTP applications,1165 as is sometimes the case when retrieving or posting messages via proxies/gateways to SMTP or NNTP.1166 </li>1167 </ul>1168 <p id="rfc.section.3.3.1.p.5">All HTTP date/time stamps <em class="bcp14">MUST</em> be represented in Greenwich Mean Time (GMT), without exception. For the purposes of HTTP, GMT is exactly equal to UTC (Coordinated1169 Universal Time). This is indicated in the first two formats by the inclusion of "GMT" as the three-letter abbreviation for1170 time zone, and <em class="bcp14">MUST</em> be assumed when reading the asctime format. HTTP-date is case sensitive and <em class="bcp14">MUST NOT</em> include additional LWS beyond that specifically included as SP in the grammar.1171 </p>1172 <div id="rfc.figure.u.23"></div><pre class="inline"><span id="rfc.iref.g.35"></span><span id="rfc.iref.g.36"></span><span id="rfc.iref.g.37"></span><span id="rfc.iref.g.38"></span><span id="rfc.iref.g.39"></span><span id="rfc.iref.g.40"></span><span id="rfc.iref.g.41"></span><span id="rfc.iref.g.42"></span><span id="rfc.iref.g.43"></span><span id="rfc.iref.g.44"></span><span id="rfc.iref.g.45"></span><span id="rfc.iref.g.46"></span> <a href="#full.date" class="smpl">HTTP-date</a> = <a href="#full.date" class="smpl">rfc1123-date</a> | <a href="#full.date" class="smpl">obsolete-date</a>1197 that parse the date value <em class="bcp14">MUST</em> accept all three formats (for compatibility with HTTP/1.0), though they <em class="bcp14">MUST</em> only generate the RFC 1123 format for representing HTTP-date values in header fields. See <a href="#tolerant.applications" title="Tolerant Applications">Appendix B</a> for further information. 1198 </p> 1199 <ul class="empty"> 1200 <li><b>Note:</b> Recipients of date values are encouraged to be robust in accepting date values that may have been sent by non-HTTP applications, 1201 as is sometimes the case when retrieving or posting messages via proxies/gateways to SMTP or NNTP. 1202 </li> 1203 </ul> 1204 <p id="rfc.section.3.3.1.p.5">All HTTP date/time stamps <em class="bcp14">MUST</em> be represented in Greenwich Mean Time (GMT), without exception. For the purposes of HTTP, GMT is exactly equal to UTC (Coordinated 1205 Universal Time). This is indicated in the first two formats by the inclusion of "GMT" as the three-letter abbreviation for 1206 time zone, and <em class="bcp14">MUST</em> be assumed when reading the asctime format. HTTP-date is case sensitive and <em class="bcp14">MUST NOT</em> include additional LWS beyond that specifically included as SP in the grammar. 1207 </p> 1208 <div id="rfc.figure.u.23"></div><pre class="inline"><span id="rfc.iref.g.35"></span><span id="rfc.iref.g.36"></span><span id="rfc.iref.g.37"></span><span id="rfc.iref.g.38"></span><span id="rfc.iref.g.39"></span><span id="rfc.iref.g.40"></span><span id="rfc.iref.g.41"></span><span id="rfc.iref.g.42"></span><span id="rfc.iref.g.43"></span><span id="rfc.iref.g.44"></span><span id="rfc.iref.g.45"></span><span id="rfc.iref.g.46"></span> <a href="#full.date" class="smpl">HTTP-date</a> = <a href="#full.date" class="smpl">rfc1123-date</a> | <a href="#full.date" class="smpl">obsolete-date</a> 1173 1209 <a href="#full.date" class="smpl">obsolete-date</a> = <a href="#full.date" class="smpl">rfc850-date</a> | <a href="#full.date" class="smpl">asctime-date</a> 1174 1210 <a href="#full.date" class="smpl">rfc1123-date</a> = <a href="#full.date" class="smpl">wkday</a> "," <a href="#core.rules" class="smpl">SP</a> date1 <a href="#core.rules" class="smpl">SP</a> time <a href="#core.rules" class="smpl">SP</a> "GMT" … … 1190 1226 | "May" | "Jun" | "Jul" | "Aug" 1191 1227 | "Sep" | "Oct" | "Nov" | "Dec" 1192 </pre><p id="rfc.section.3.3.1.p.7"> <b>Note:</b> HTTP requirements for the date/time stamp format apply only to their usage within the protocol stream. Clients and servers 1193 are not required to use these formats for user presentation, request logging, etc. 1194 </p> 1195 <h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a> <a id="transfer.codings" href="#transfer.codings">Transfer Codings</a></h2> 1196 <p id="rfc.section.3.4.p.1">Transfer-coding values are used to indicate an encoding transformation that has been, can be, or may need to be applied to 1197 an entity-body in order to ensure "safe transport" through the network. This differs from a content coding in that the transfer-coding 1198 is a property of the message, not of the original entity. 1199 </p> 1200 <div id="rfc.figure.u.24"></div><pre class="inline"><span id="rfc.iref.g.47"></span><span id="rfc.iref.g.48"></span> <a href="#transfer.codings" class="smpl">transfer-coding</a> = "chunked" | <a href="#transfer.codings" class="smpl">transfer-extension</a> 1228 </pre><p id="rfc.section.3.3.1.p.7"><b>Note:</b> HTTP requirements for the date/time stamp format apply only to their usage within the protocol stream. Clients and servers 1229 are not required to use these formats for user presentation, request logging, etc. 1230 </p> 1231 </div> 1232 </div> 1233 <div id="transfer.codings"> 1234 <h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a> <a href="#transfer.codings">Transfer Codings</a></h2> 1235 <p id="rfc.section.3.4.p.1">Transfer-coding values are used to indicate an encoding transformation that has been, can be, or may need to be applied to 1236 an entity-body in order to ensure "safe transport" through the network. This differs from a content coding in that the transfer-coding 1237 is a property of the message, not of the original entity. 1238 </p> 1239 <div id="rfc.figure.u.24"></div><pre class="inline"><span id="rfc.iref.g.47"></span><span id="rfc.iref.g.48"></span> <a href="#transfer.codings" class="smpl">transfer-coding</a> = "chunked" | <a href="#transfer.codings" class="smpl">transfer-extension</a> 1201 1240 <a href="#transfer.codings" class="smpl">transfer-extension</a> = <a href="#rule.token.separators" class="smpl">token</a> *( ";" <a href="#transfer.codings" class="smpl">parameter</a> ) 1202 1241 </pre><div id="rule.parameter"> 1203 <p id="rfc.section.3.4.p.3">Parameters are in the form of attribute/value pairs.</p>1204 </div>1205 <div id="rfc.figure.u.25"></div><pre class="inline"><span id="rfc.iref.g.49"></span><span id="rfc.iref.g.50"></span><span id="rfc.iref.g.51"></span> <a href="#transfer.codings" class="smpl">parameter</a> = <a href="#rule.parameter" class="smpl">attribute</a> "=" <a href="#rule.parameter" class="smpl">value</a>1242 <p id="rfc.section.3.4.p.3"> Parameters are in the form of attribute/value pairs.</p> 1243 </div> 1244 <div id="rfc.figure.u.25"></div><pre class="inline"><span id="rfc.iref.g.49"></span><span id="rfc.iref.g.50"></span><span id="rfc.iref.g.51"></span> <a href="#transfer.codings" class="smpl">parameter</a> = <a href="#rule.parameter" class="smpl">attribute</a> "=" <a href="#rule.parameter" class="smpl">value</a> 1206 1245 <a href="#rule.parameter" class="smpl">attribute</a> = <a href="#rule.token.separators" class="smpl">token</a> 1207 1246 <a href="#rule.parameter" class="smpl">value</a> = <a href="#rule.token.separators" class="smpl">token</a> | <a href="#rule.quoted-string" class="smpl">quoted-string</a> 1208 1247 </pre><p id="rfc.section.3.4.p.5">All transfer-coding values are case-insensitive. HTTP/1.1 uses transfer-coding values in the TE header field (<a href="#header.te" id="rfc.xref.header.te.1" title="TE">Section 8.5</a>) and in the Transfer-Encoding header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.1" title="Transfer-Encoding">Section 8.7</a>). 1209 </p> 1210 <p id="rfc.section.3.4.p.6">Whenever a transfer-coding is applied to a message-body, the set of transfer-codings <em class="bcp14">MUST</em> include "chunked", unless the message is terminated by closing the connection. When the "chunked" transfer-coding is used, 1211 it <em class="bcp14">MUST</em> be the last transfer-coding applied to the message-body. The "chunked" transfer-coding <em class="bcp14">MUST NOT</em> be applied more than once to a message-body. These rules allow the recipient to determine the transfer-length of the message 1212 (<a href="#message.length" title="Message Length">Section 4.4</a>). 1213 </p> 1214 <p id="rfc.section.3.4.p.7">Transfer-codings are analogous to the Content-Transfer-Encoding values of MIME <a href="#RFC2045" id="rfc.xref.RFC2045.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a>, which were designed to enable safe transport of binary data over a 7-bit transport service. However, safe transport has 1215 a different focus for an 8bit-clean transfer protocol. In HTTP, the only unsafe characteristic of message-bodies is the difficulty 1216 in determining the exact body length (<a href="#message.length" title="Message Length">Section 4.4</a>), or the desire to encrypt data over a shared transport. 1217 </p> 1218 <p id="rfc.section.3.4.p.8">The Internet Assigned Numbers Authority (IANA) acts as a registry for transfer-coding value tokens. Initially, the registry 1219 contains the following tokens: "chunked" (<a href="#chunked.transfer.encoding" title="Chunked Transfer Coding">Section 3.4.1</a>), "gzip", "compress", and "deflate" (<a href="p3-payload.html#content.codings" title="Content Codings">Section 3.2</a> of <a href="#Part3" id="rfc.xref.Part3.9"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>). 1220 </p> 1221 <p id="rfc.section.3.4.p.9">New transfer-coding value tokens <em class="bcp14">SHOULD</em> be registered in the same way as new content-coding value tokens (<a href="p3-payload.html#content.codings" title="Content Codings">Section 3.2</a> of <a href="#Part3" id="rfc.xref.Part3.10"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>). 1222 </p> 1223 <p id="rfc.section.3.4.p.10">A server which receives an entity-body with a transfer-coding it does not understand <em class="bcp14">SHOULD</em> return 501 (Not Implemented), and close the connection. A server <em class="bcp14">MUST NOT</em> send transfer-codings to an HTTP/1.0 client. 1224 </p> 1225 <h3 id="rfc.section.3.4.1"><a href="#rfc.section.3.4.1">3.4.1</a> <a id="chunked.transfer.encoding" href="#chunked.transfer.encoding">Chunked Transfer Coding</a></h3> 1226 <p id="rfc.section.3.4.1.p.1">The chunked encoding modifies the body of a message in order to transfer it as a series of chunks, each with its own size 1227 indicator, followed by an <em class="bcp14">OPTIONAL</em> trailer containing entity-header fields. This allows dynamically produced content to be transferred along with the information 1228 necessary for the recipient to verify that it has received the full message. 1229 </p> 1230 <div id="rfc.figure.u.26"></div><pre class="inline"><span id="rfc.iref.g.52"></span><span id="rfc.iref.g.53"></span><span id="rfc.iref.g.54"></span><span id="rfc.iref.g.55"></span><span id="rfc.iref.g.56"></span><span id="rfc.iref.g.57"></span><span id="rfc.iref.g.58"></span><span id="rfc.iref.g.59"></span><span id="rfc.iref.g.60"></span> <a href="#chunked.transfer.encoding" class="smpl">Chunked-Body</a> = *<a href="#chunked.transfer.encoding" class="smpl">chunk</a> 1248 </p> 1249 <p id="rfc.section.3.4.p.6">Whenever a transfer-coding is applied to a message-body, the set of transfer-codings <em class="bcp14">MUST</em> include "chunked", unless the message is terminated by closing the connection. When the "chunked" transfer-coding is used, 1250 it <em class="bcp14">MUST</em> be the last transfer-coding applied to the message-body. The "chunked" transfer-coding <em class="bcp14">MUST NOT</em> be applied more than once to a message-body. These rules allow the recipient to determine the transfer-length of the message 1251 (<a href="#message.length" title="Message Length">Section 4.4</a>). 1252 </p> 1253 <p id="rfc.section.3.4.p.7">Transfer-codings are analogous to the Content-Transfer-Encoding values of MIME <a href="#RFC2045" id="rfc.xref.RFC2045.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a>, which were designed to enable safe transport of binary data over a 7-bit transport service. However, safe transport has 1254 a different focus for an 8bit-clean transfer protocol. In HTTP, the only unsafe characteristic of message-bodies is the difficulty 1255 in determining the exact body length (<a href="#message.length" title="Message Length">Section 4.4</a>), or the desire to encrypt data over a shared transport. 1256 </p> 1257 <p id="rfc.section.3.4.p.8">The Internet Assigned Numbers Authority (IANA) acts as a registry for transfer-coding value tokens. Initially, the registry 1258 contains the following tokens: "chunked" (<a href="#chunked.transfer.encoding" title="Chunked Transfer Coding">Section 3.4.1</a>), "gzip", "compress", and "deflate" (<a href="p3-payload.html#content.codings" title="Content Codings">Section 3.2</a> of <a href="#Part3" id="rfc.xref.Part3.9"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>). 1259 </p> 1260 <p id="rfc.section.3.4.p.9">New transfer-coding value tokens <em class="bcp14">SHOULD</em> be registered in the same way as new content-coding value tokens (<a href="p3-payload.html#content.codings" title="Content Codings">Section 3.2</a> of <a href="#Part3" id="rfc.xref.Part3.10"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>). 1261 </p> 1262 <p id="rfc.section.3.4.p.10">A server which receives an entity-body with a transfer-coding it does not understand <em class="bcp14">SHOULD</em> return 501 (Not Implemented), and close the connection. A server <em class="bcp14">MUST NOT</em> send transfer-codings to an HTTP/1.0 client. 1263 </p> 1264 <div id="chunked.transfer.encoding"> 1265 <h3 id="rfc.section.3.4.1"><a href="#rfc.section.3.4.1">3.4.1</a> <a href="#chunked.transfer.encoding">Chunked Transfer Coding</a></h3> 1266 <p id="rfc.section.3.4.1.p.1">The chunked encoding modifies the body of a message in order to transfer it as a series of chunks, each with its own size 1267 indicator, followed by an <em class="bcp14">OPTIONAL</em> trailer containing entity-header fields. This allows dynamically produced content to be transferred along with the information 1268 necessary for the recipient to verify that it has received the full message. 1269 </p> 1270 <div id="rfc.figure.u.26"></div><pre class="inline"><span id="rfc.iref.g.52"></span><span id="rfc.iref.g.53"></span><span id="rfc.iref.g.54"></span><span id="rfc.iref.g.55"></span><span id="rfc.iref.g.56"></span><span id="rfc.iref.g.57"></span><span id="rfc.iref.g.58"></span><span id="rfc.iref.g.59"></span><span id="rfc.iref.g.60"></span> <a href="#chunked.transfer.encoding" class="smpl">Chunked-Body</a> = *<a href="#chunked.transfer.encoding" class="smpl">chunk</a> 1231 1271 <a href="#chunked.transfer.encoding" class="smpl">last-chunk</a> 1232 1272 <a href="#chunked.transfer.encoding" class="smpl">trailer-part</a> … … 1244 1284 <a href="#chunked.transfer.encoding" class="smpl">trailer-part</a> = *(<a href="#abnf.dependencies" class="smpl">entity-header</a> <a href="#rule.CRLF" class="smpl">CRLF</a>) 1245 1285 </pre><p id="rfc.section.3.4.1.p.3">The chunk-size field is a string of hex digits indicating the size of the chunk-data in octets. The chunked encoding is ended 1246 by any chunk whose size is zero, followed by the trailer, which is terminated by an empty line.1247 </p>1248 <p id="rfc.section.3.4.1.p.4">The trailer allows the sender to include additional HTTP header fields at the end of the message. The Trailer header field1249 can be used to indicate which header fields are included in a trailer (see <a href="#header.trailer" id="rfc.xref.header.trailer.1" title="Trailer">Section 8.6</a>).1250 </p>1251 <p id="rfc.section.3.4.1.p.5">A server using chunked transfer-coding in a response <em class="bcp14">MUST NOT</em> use the trailer for any header fields unless at least one of the following is true:1252 </p>1253 <ol>1254 <li>the request included a TE header field that indicates "trailers" is acceptable in the transfer-coding of the response, as1255 described in <a href="#header.te" id="rfc.xref.header.te.2" title="TE">Section 8.5</a>; or,1256 </li>1257 <li>the server is the origin server for the response, the trailer fields consist entirely of optional metadata, and the recipient1258 could use the message (in a manner acceptable to the origin server) without receiving this metadata. In other words, the origin1259 server is willing to accept the possibility that the trailer fields might be silently discarded along the path to the client.1260 </li>1261 </ol>1262 <p id="rfc.section.3.4.1.p.6">This requirement prevents an interoperability failure when the message is being received by an HTTP/1.1 (or later) proxy and1263 forwarded to an HTTP/1.0 recipient. It avoids a situation where compliance with the protocol would have necessitated a possibly1264 infinite buffer on the proxy.1265 </p>1266 <p id="rfc.section.3.4.1.p.7">A process for decoding the "chunked" transfer-coding can be represented in pseudo-code as:</p>1267 <div id="rfc.figure.u.27"></div><pre class="text"> length := 01286 by any chunk whose size is zero, followed by the trailer, which is terminated by an empty line. 1287 </p> 1288 <p id="rfc.section.3.4.1.p.4">The trailer allows the sender to include additional HTTP header fields at the end of the message. The Trailer header field 1289 can be used to indicate which header fields are included in a trailer (see <a href="#header.trailer" id="rfc.xref.header.trailer.1" title="Trailer">Section 8.6</a>). 1290 </p> 1291 <p id="rfc.section.3.4.1.p.5">A server using chunked transfer-coding in a response <em class="bcp14">MUST NOT</em> use the trailer for any header fields unless at least one of the following is true: 1292 </p> 1293 <ol> 1294 <li>the request included a TE header field that indicates "trailers" is acceptable in the transfer-coding of the response, as 1295 described in <a href="#header.te" id="rfc.xref.header.te.2" title="TE">Section 8.5</a>; or, 1296 </li> 1297 <li>the server is the origin server for the response, the trailer fields consist entirely of optional metadata, and the recipient 1298 could use the message (in a manner acceptable to the origin server) without receiving this metadata. In other words, the origin 1299 server is willing to accept the possibility that the trailer fields might be silently discarded along the path to the client. 1300 </li> 1301 </ol> 1302 <p id="rfc.section.3.4.1.p.6">This requirement prevents an interoperability failure when the message is being received by an HTTP/1.1 (or later) proxy and 1303 forwarded to an HTTP/1.0 recipient. It avoids a situation where compliance with the protocol would have necessitated a possibly 1304 infinite buffer on the proxy. 1305 </p> 1306 <p id="rfc.section.3.4.1.p.7">A process for decoding the "chunked" transfer-coding can be represented in pseudo-code as:</p> 1307 <div id="rfc.figure.u.27"></div><pre class="text"> length := 0 1268 1308 read chunk-size, chunk-extension (if any) and CRLF 1269 1309 while (chunk-size > 0) { … … 1281 1321 Remove "chunked" from Transfer-Encoding 1282 1322 </pre><p id="rfc.section.3.4.1.p.9">All HTTP/1.1 applications <em class="bcp14">MUST</em> be able to receive and decode the "chunked" transfer-coding, and <em class="bcp14">MUST</em> ignore chunk-extension extensions they do not understand. 1283 </p> 1284 <h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a> <a id="product.tokens" href="#product.tokens">Product Tokens</a></h2> 1285 <p id="rfc.section.3.5.p.1">Product tokens are used to allow communicating applications to identify themselves by software name and version. Most fields 1286 using product tokens also allow sub-products which form a significant part of the application to be listed, separated by white 1287 space. By convention, the products are listed in order of their significance for identifying the application. 1288 </p> 1289 <div id="rfc.figure.u.28"></div><pre class="inline"><span id="rfc.iref.g.61"></span><span id="rfc.iref.g.62"></span> <a href="#product.tokens" class="smpl">product</a> = <a href="#rule.token.separators" class="smpl">token</a> ["/" <a href="#product.tokens" class="smpl">product-version</a>] 1323 </p> 1324 </div> 1325 </div> 1326 <div id="product.tokens"> 1327 <h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a> <a href="#product.tokens">Product Tokens</a></h2> 1328 <p id="rfc.section.3.5.p.1">Product tokens are used to allow communicating applications to identify themselves by software name and version. Most fields 1329 using product tokens also allow sub-products which form a significant part of the application to be listed, separated by white 1330 space. By convention, the products are listed in order of their significance for identifying the application. 1331 </p> 1332 <div id="rfc.figure.u.28"></div><pre class="inline"><span id="rfc.iref.g.61"></span><span id="rfc.iref.g.62"></span> <a href="#product.tokens" class="smpl">product</a> = <a href="#rule.token.separators" class="smpl">token</a> ["/" <a href="#product.tokens" class="smpl">product-version</a>] 1290 1333 <a href="#product.tokens" class="smpl">product-version</a> = <a href="#rule.token.separators" class="smpl">token</a> 1291 1334 </pre><p id="rfc.section.3.5.p.3">Examples:</p> 1292 <div id="rfc.figure.u.29"></div><pre class="text"> User-Agent: CERN-LineMode/2.15 libwww/2.17b31335 <div id="rfc.figure.u.29"></div><pre class="text"> User-Agent: CERN-LineMode/2.15 libwww/2.17b3 1293 1336 Server: Apache/0.8.4 1294 1337 </pre><p id="rfc.section.3.5.p.5">Product tokens <em class="bcp14">SHOULD</em> be short and to the point. They <em class="bcp14">MUST NOT</em> be used for advertising or other non-essential information. Although any token character <em class="bcp14">MAY</em> appear in a product-version, this token <em class="bcp14">SHOULD</em> only be used for a version identifier (i.e., successive versions of the same product <em class="bcp14">SHOULD</em> only differ in the product-version portion of the product value). 1295 </p> 1296 <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a> <a id="http.message" href="#http.message">HTTP Message</a></h1> 1297 <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a> <a id="message.types" href="#message.types">Message Types</a></h2> 1298 <p id="rfc.section.4.1.p.1">HTTP messages consist of requests from client to server and responses from server to client.</p> 1299 <div id="rfc.figure.u.30"></div><pre class="inline"><span id="rfc.iref.g.63"></span> <a href="#message.types" class="smpl">HTTP-message</a> = <a href="#request" class="smpl">Request</a> | <a href="#response" class="smpl">Response</a> ; HTTP/1.1 messages 1338 </p> 1339 </div> 1340 </div> 1341 <div id="http.message"> 1342 <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a> <a href="#http.message">HTTP Message</a></h1> 1343 <div id="message.types"> 1344 <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a> <a href="#message.types">Message Types</a></h2> 1345 <p id="rfc.section.4.1.p.1">HTTP messages consist of requests from client to server and responses from server to client.</p> 1346 <div id="rfc.figure.u.30"></div><pre class="inline"><span id="rfc.iref.g.63"></span> <a href="#message.types" class="smpl">HTTP-message</a> = <a href="#request" class="smpl">Request</a> | <a href="#response" class="smpl">Response</a> ; HTTP/1.1 messages 1300 1347 </pre><p id="rfc.section.4.1.p.3">Request (<a href="#request" title="Request">Section 5</a>) and Response (<a href="#response" title="Response">Section 6</a>) messages use the generic message format of <a href="#RFC2822" id="rfc.xref.RFC2822.2"><cite title="Internet Message Format">[RFC2822]</cite></a> for transferring entities (the payload of the message). Both types of message consist of a start-line, zero or more header 1301 fields (also known as "headers"), an empty line (i.e., a line with nothing preceding the CRLF) indicating the end of the header1302 fields, and possibly a message-body.1303 </p>1304 <div id="rfc.figure.u.31"></div><pre class="inline"><span id="rfc.iref.g.64"></span><span id="rfc.iref.g.65"></span> <a href="#message.types" class="smpl">generic-message</a> = <a href="#message.types" class="smpl">start-line</a>1348 fields (also known as "headers"), an empty line (i.e., a line with nothing preceding the CRLF) indicating the end of the header 1349 fields, and possibly a message-body. 1350 </p> 1351 <div id="rfc.figure.u.31"></div><pre class="inline"><span id="rfc.iref.g.64"></span><span id="rfc.iref.g.65"></span> <a href="#message.types" class="smpl">generic-message</a> = <a href="#message.types" class="smpl">start-line</a> 1305 1352 *(<a href="#message.headers" class="smpl">message-header</a> <a href="#rule.CRLF" class="smpl">CRLF</a>) 1306 1353 <a href="#rule.CRLF" class="smpl">CRLF</a> … … 1308 1355 <a href="#message.types" class="smpl">start-line</a> = <a href="#request-line" class="smpl">Request-Line</a> | <a href="#status-line" class="smpl">Status-Line</a> 1309 1356 </pre><p id="rfc.section.4.1.p.5">In the interest of robustness, servers <em class="bcp14">SHOULD</em> ignore any empty line(s) received where a Request-Line is expected. In other words, if the server is reading the protocol 1310 stream at the beginning of a message and receives a CRLF first, it should ignore the CRLF. 1311 </p> 1312 <p id="rfc.section.4.1.p.6">Certain buggy HTTP/1.0 client implementations generate extra CRLF's after a POST request. To restate what is explicitly forbidden 1313 by the BNF, an HTTP/1.1 client <em class="bcp14">MUST NOT</em> preface or follow a request with an extra CRLF. 1314 </p> 1315 <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a> <a id="message.headers" href="#message.headers">Message Headers</a></h2> 1316 <p id="rfc.section.4.2.p.1">HTTP header fields, which include general-header (<a href="#general.header.fields" title="General Header Fields">Section 4.5</a>), request-header (<a href="p2-semantics.html#request.header.fields" title="Request Header Fields">Section 4</a> of <a href="#Part2" id="rfc.xref.Part2.4"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>), response-header (<a href="p2-semantics.html#response.header.fields" title="Response Header Fields">Section 6</a> of <a href="#Part2" id="rfc.xref.Part2.5"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>), and entity-header (<a href="p3-payload.html#entity.header.fields" title="Entity Header Fields">Section 4.1</a> of <a href="#Part3" id="rfc.xref.Part3.11"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>) fields, follow the same generic format as that given in <a href="http://tools.ietf.org/html/rfc2822#section-2.1">Section 2.1</a> of <a href="#RFC2822" id="rfc.xref.RFC2822.3"><cite title="Internet Message Format">[RFC2822]</cite></a>. Each header field consists of a name followed by a colon (":") and the field value. Field names are case-insensitive. The 1317 field value <em class="bcp14">MAY</em> be preceded by any amount of LWS, though a single SP is preferred. Header fields can be extended over multiple lines by preceding 1318 each extra line with at least one SP or HTAB. Applications ought to follow "common form", where one is known or indicated, 1319 when generating HTTP constructs, since there might exist some implementations that fail to accept anything beyond the common 1320 forms. 1321 </p> 1322 <div id="rfc.figure.u.32"></div><pre class="inline"><span id="rfc.iref.g.66"></span><span id="rfc.iref.g.67"></span><span id="rfc.iref.g.68"></span><span id="rfc.iref.g.69"></span> <a href="#message.headers" class="smpl">message-header</a> = <a href="#message.headers" class="smpl">field-name</a> ":" [ <a href="#message.headers" class="smpl">field-value</a> ] 1357 stream at the beginning of a message and receives a CRLF first, it should ignore the CRLF. 1358 </p> 1359 <p id="rfc.section.4.1.p.6">Certain buggy HTTP/1.0 client implementations generate extra CRLF's after a POST request. To restate what is explicitly forbidden 1360 by the BNF, an HTTP/1.1 client <em class="bcp14">MUST NOT</em> preface or follow a request with an extra CRLF. 1361 </p> 1362 </div> 1363 <div id="message.headers"> 1364 <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a> <a href="#message.headers">Message Headers</a></h2> 1365 <p id="rfc.section.4.2.p.1">HTTP header fields, which include general-header (<a href="#general.header.fields" title="General Header Fields">Section 4.5</a>), request-header (<a href="p2-semantics.html#request.header.fields" title="Request Header Fields">Section 4</a> of <a href="#Part2" id="rfc.xref.Part2.4"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>), response-header (<a href="p2-semantics.html#response.header.fields" title="Response Header Fields">Section 6</a> of <a href="#Part2" id="rfc.xref.Part2.5"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>), and entity-header (<a href="p3-payload.html#entity.header.fields" title="Entity Header Fields">Section 4.1</a> of <a href="#Part3" id="rfc.xref.Part3.11"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>) fields, follow the same generic format as that given in <a href="https://tools.ietf.org/html/rfc2822#section-2.1">Section 2.1</a> of <a href="#RFC2822" id="rfc.xref.RFC2822.3"><cite title="Internet Message Format">[RFC2822]</cite></a>. Each header field consists of a name followed by a colon (":") and the field value. Field names are case-insensitive. The 1366 field value <em class="bcp14">MAY</em> be preceded by any amount of LWS, though a single SP is preferred. Header fields can be extended over multiple lines by preceding 1367 each extra line with at least one SP or HTAB. Applications ought to follow "common form", where one is known or indicated, 1368 when generating HTTP constructs, since there might exist some implementations that fail to accept anything beyond the common 1369 forms. 1370 </p> 1371 <div id="rfc.figure.u.32"></div><pre class="inline"><span id="rfc.iref.g.66"></span><span id="rfc.iref.g.67"></span><span id="rfc.iref.g.68"></span><span id="rfc.iref.g.69"></span> <a href="#message.headers" class="smpl">message-header</a> = <a href="#message.headers" class="smpl">field-name</a> ":" [ <a href="#message.headers" class="smpl">field-value</a> ] 1323 1372 <a href="#message.headers" class="smpl">field-name</a> = <a href="#rule.token.separators" class="smpl">token</a> 1324 1373 <a href="#message.headers" class="smpl">field-value</a> = *( <a href="#message.headers" class="smpl">field-content</a> | <a href="#rule.LWS" class="smpl">LWS</a> ) … … 1328 1377 ; of <a href="#rule.token.separators" class="smpl">token</a>, <a href="#rule.token.separators" class="smpl">separators</a>, and <a href="#rule.quoted-string" class="smpl">quoted-string</a> 1329 1378 </pre><p id="rfc.section.4.2.p.3">The field-content does not include any leading or trailing LWS: linear white space occurring before the first non-whitespace 1330 character of the field-value or after the last non-whitespace character of the field-value. Such leading or trailing LWS <em class="bcp14">MAY</em> be removed without changing the semantics of the field value. Any LWS that occurs between field-content <em class="bcp14">MAY</em> be replaced with a single SP before interpreting the field value or forwarding the message downstream. 1331 </p> 1332 <p id="rfc.section.4.2.p.4">The order in which header fields with differing field names are received is not significant. However, it is "good practice" 1333 to send general-header fields first, followed by request-header or response-header fields, and ending with the entity-header 1334 fields. 1335 </p> 1336 <p id="rfc.section.4.2.p.5">Multiple message-header fields with the same field-name <em class="bcp14">MAY</em> be present in a message if and only if the entire field-value for that header field is defined as a comma-separated list [i.e., 1337 #(values)]. It <em class="bcp14">MUST</em> be possible to combine the multiple header fields into one "field-name: field-value" pair, without changing the semantics 1338 of the message, by appending each subsequent field-value to the first, each separated by a comma. The order in which header 1339 fields with the same field-name are received is therefore significant to the interpretation of the combined field value, and 1340 thus a proxy <em class="bcp14">MUST NOT</em> change the order of these field values when a message is forwarded. 1341 </p> 1342 <h2 id="rfc.section.4.3"><a href="#rfc.section.4.3">4.3</a> <a id="message.body" href="#message.body">Message Body</a></h2> 1343 <p id="rfc.section.4.3.p.1">The message-body (if any) of an HTTP message is used to carry the entity-body associated with the request or response. The 1344 message-body differs from the entity-body only when a transfer-coding has been applied, as indicated by the Transfer-Encoding 1345 header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.2" title="Transfer-Encoding">Section 8.7</a>). 1346 </p> 1347 <div id="rfc.figure.u.33"></div><pre class="inline"><span id="rfc.iref.g.70"></span> <a href="#message.body" class="smpl">message-body</a> = <a href="#abnf.dependencies" class="smpl">entity-body</a> 1379 character of the field-value or after the last non-whitespace character of the field-value. Such leading or trailing LWS <em class="bcp14">MAY</em> be removed without changing the semantics of the field value. Any LWS that occurs between field-content <em class="bcp14">MAY</em> be replaced with a single SP before interpreting the field value or forwarding the message downstream. 1380 </p> 1381 <p id="rfc.section.4.2.p.4">The order in which header fields with differing field names are received is not significant. However, it is "good practice" 1382 to send general-header fields first, followed by request-header or response-header fields, and ending with the entity-header 1383 fields. 1384 </p> 1385 <p id="rfc.section.4.2.p.5">Multiple message-header fields with the same field-name <em class="bcp14">MAY</em> be present in a message if and only if the entire field-value for that header field is defined as a comma-separated list [i.e., 1386 #(values)]. It <em class="bcp14">MUST</em> be possible to combine the multiple header fields into one "field-name: field-value" pair, without changing the semantics 1387 of the message, by appending each subsequent field-value to the first, each separated by a comma. The order in which header 1388 fields with the same field-name are received is therefore significant to the interpretation of the combined field value, and 1389 thus a proxy <em class="bcp14">MUST NOT</em> change the order of these field values when a message is forwarded. 1390 </p> 1391 </div> 1392 <div id="message.body"> 1393 <h2 id="rfc.section.4.3"><a href="#rfc.section.4.3">4.3</a> <a href="#message.body">Message Body</a></h2> 1394 <p id="rfc.section.4.3.p.1">The message-body (if any) of an HTTP message is used to carry the entity-body associated with the request or response. The 1395 message-body differs from the entity-body only when a transfer-coding has been applied, as indicated by the Transfer-Encoding 1396 header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.2" title="Transfer-Encoding">Section 8.7</a>). 1397 </p> 1398 <div id="rfc.figure.u.33"></div><pre class="inline"><span id="rfc.iref.g.70"></span> <a href="#message.body" class="smpl">message-body</a> = <a href="#abnf.dependencies" class="smpl">entity-body</a> 1348 1399 | <entity-body encoded as per <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a>> 1349 1400 </pre><p id="rfc.section.4.3.p.3">Transfer-Encoding <em class="bcp14">MUST</em> be used to indicate any transfer-codings applied by an application to ensure safe and proper transfer of the message. Transfer-Encoding 1350 is a property of the message, not of the entity, and thus <em class="bcp14">MAY</em> be added or removed by any application along the request/response chain. (However, <a href="#transfer.codings" title="Transfer Codings">Section 3.4</a> places restrictions on when certain transfer-codings may be used.) 1351 </p> 1352 <p id="rfc.section.4.3.p.4">The rules for when a message-body is allowed in a message differ for requests and responses.</p> 1353 <p id="rfc.section.4.3.p.5">The presence of a message-body in a request is signaled by the inclusion of a Content-Length or Transfer-Encoding header field 1354 in the request's message-headers. A message-body <em class="bcp14">MUST NOT</em> be included in a request if the specification of the request method (<a href="p2-semantics.html#method" title="Method">Section 3</a> of <a href="#Part2" id="rfc.xref.Part2.6"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) explicitly disallows an entity-body in requests. When a request message contains both a message-body of non-zero length 1355 and a method that does not define any semantics for that request message-body, then an origin server <em class="bcp14">SHOULD</em> either ignore the message-body or respond with an appropriate error message (e.g., 413). A proxy or gateway, when presented 1356 the same request, <em class="bcp14">SHOULD</em> either forward the request inbound with the message-body or ignore the message-body when determining a response. 1357 </p> 1358 <p id="rfc.section.4.3.p.6">For response messages, whether or not a message-body is included with a message is dependent on both the request method and 1359 the response status code (<a href="#status.code.and.reason.phrase" title="Status Code and Reason Phrase">Section 6.1.1</a>). All responses to the HEAD request method <em class="bcp14">MUST NOT</em> include a message-body, even though the presence of entity-header fields might lead one to believe they do. All 1xx (informational), 1360 204 (No Content), and 304 (Not Modified) responses <em class="bcp14">MUST NOT</em> include a message-body. All other responses do include a message-body, although it <em class="bcp14">MAY</em> be of zero length. 1361 </p> 1362 <h2 id="rfc.section.4.4"><a href="#rfc.section.4.4">4.4</a> <a id="message.length" href="#message.length">Message Length</a></h2> 1363 <p id="rfc.section.4.4.p.1">The transfer-length of a message is the length of the message-body as it appears in the message; that is, after any transfer-codings 1364 have been applied. When a message-body is included with a message, the transfer-length of that body is determined by one of 1365 the following (in order of precedence): 1366 </p> 1367 <p id="rfc.section.4.4.p.2"> </p> 1368 <ol> 1369 <li> 1370 <p>Any response message which "<em class="bcp14">MUST NOT</em>" include a message-body (such as the 1xx, 204, and 304 responses and any response to a HEAD request) is always terminated 1371 by the first empty line after the header fields, regardless of the entity-header fields present in the message. 1372 </p> 1373 </li> 1374 <li> 1375 <p>If a Transfer-Encoding header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.3" title="Transfer-Encoding">Section 8.7</a>) is present, then the transfer-length is defined by use of the "chunked" transfer-coding (<a href="#transfer.codings" title="Transfer Codings">Section 3.4</a>), unless the message is terminated by closing the connection. 1376 </p> 1377 </li> 1378 <li> 1379 <p>If a Content-Length header field (<a href="#header.content-length" id="rfc.xref.header.content-length.1" title="Content-Length">Section 8.2</a>) is present, its decimal value in OCTETs represents both the entity-length and the transfer-length. The Content-Length header 1380 field <em class="bcp14">MUST NOT</em> be sent if these two lengths are different (i.e., if a Transfer-Encoding header field is present). If a message is received 1381 with both a Transfer-Encoding header field and a Content-Length header field, the latter <em class="bcp14">MUST</em> be ignored. 1382 </p> 1383 </li> 1384 <li> 1385 <p>If the message uses the media type "multipart/byteranges", and the transfer-length is not otherwise specified, then this self-delimiting 1386 media type defines the transfer-length. This media type <em class="bcp14">MUST NOT</em> be used unless the sender knows that the recipient can parse it; the presence in a request of a Range header with multiple 1387 byte-range specifiers from a 1.1 client implies that the client can parse multipart/byteranges responses. 1388 </p> 1389 <ul class="empty"> 1390 <li>A range header might be forwarded by a 1.0 proxy that does not understand multipart/byteranges; in this case the server <em class="bcp14">MUST</em> delimit the message using methods defined in items 1, 3 or 5 of this section. 1391 </li> 1392 </ul> 1393 </li> 1394 <li> 1395 <p>By the server closing the connection. (Closing the connection cannot be used to indicate the end of a request body, since 1396 that would leave no possibility for the server to send back a response.) 1397 </p> 1398 </li> 1399 </ol> 1400 <p id="rfc.section.4.4.p.3">For compatibility with HTTP/1.0 applications, HTTP/1.1 requests containing a message-body <em class="bcp14">MUST</em> include a valid Content-Length header field unless the server is known to be HTTP/1.1 compliant. If a request contains a message-body 1401 and a Content-Length is not given, the server <em class="bcp14">SHOULD</em> respond with 400 (Bad Request) if it cannot determine the length of the message, or with 411 (Length Required) if it wishes 1402 to insist on receiving a valid Content-Length. 1403 </p> 1404 <p id="rfc.section.4.4.p.4">All HTTP/1.1 applications that receive entities <em class="bcp14">MUST</em> accept the "chunked" transfer-coding (<a href="#transfer.codings" title="Transfer Codings">Section 3.4</a>), thus allowing this mechanism to be used for messages when the message length cannot be determined in advance. 1405 </p> 1406 <p id="rfc.section.4.4.p.5">Messages <em class="bcp14">MUST NOT</em> include both a Content-Length header field and a transfer-coding. If the message does include a transfer-coding, the Content-Length <em class="bcp14">MUST</em> be ignored. 1407 </p> 1408 <p id="rfc.section.4.4.p.6">When a Content-Length is given in a message where a message-body is allowed, its field value <em class="bcp14">MUST</em> exactly match the number of OCTETs in the message-body. HTTP/1.1 user agents <em class="bcp14">MUST</em> notify the user when an invalid length is received and detected. 1409 </p> 1410 <h2 id="rfc.section.4.5"><a href="#rfc.section.4.5">4.5</a> <a id="general.header.fields" href="#general.header.fields">General Header Fields</a></h2> 1411 <p id="rfc.section.4.5.p.1">There are a few header fields which have general applicability for both request and response messages, but which do not apply 1412 to the entity being transferred. These header fields apply only to the message being transmitted. 1413 </p> 1414 <div id="rfc.figure.u.34"></div><pre class="inline"><span id="rfc.iref.g.71"></span> <a href="#general.header.fields" class="smpl">general-header</a> = <a href="#abnf.dependencies" class="smpl">Cache-Control</a> ; <a href="#Part6" id="rfc.xref.Part6.6"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>, <a href="p6-cache.html#header.cache-control" title="Cache-Control">Section 16.2</a> 1401 is a property of the message, not of the entity, and thus <em class="bcp14">MAY</em> be added or removed by any application along the request/response chain. (However, <a href="#transfer.codings" title="Transfer Codings">Section 3.4</a> places restrictions on when certain transfer-codings may be used.) 1402 </p> 1403 <p id="rfc.section.4.3.p.4">The rules for when a message-body is allowed in a message differ for requests and responses.</p> 1404 <p id="rfc.section.4.3.p.5">The presence of a message-body in a request is signaled by the inclusion of a Content-Length or Transfer-Encoding header field 1405 in the request's message-headers. A message-body <em class="bcp14">MUST NOT</em> be included in a request if the specification of the request method (<a href="p2-semantics.html#method" title="Method">Section 3</a> of <a href="#Part2" id="rfc.xref.Part2.6"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) explicitly disallows an entity-body in requests. When a request message contains both a message-body of non-zero length 1406 and a method that does not define any semantics for that request message-body, then an origin server <em class="bcp14">SHOULD</em> either ignore the message-body or respond with an appropriate error message (e.g., 413). A proxy or gateway, when presented 1407 the same request, <em class="bcp14">SHOULD</em> either forward the request inbound with the message-body or ignore the message-body when determining a response. 1408 </p> 1409 <p id="rfc.section.4.3.p.6">For response messages, whether or not a message-body is included with a message is dependent on both the request method and 1410 the response status code (<a href="#status.code.and.reason.phrase" title="Status Code and Reason Phrase">Section 6.1.1</a>). All responses to the HEAD request method <em class="bcp14">MUST NOT</em> include a message-body, even though the presence of entity-header fields might lead one to believe they do. All 1xx (informational), 1411 204 (No Content), and 304 (Not Modified) responses <em class="bcp14">MUST NOT</em> include a message-body. All other responses do include a message-body, although it <em class="bcp14">MAY</em> be of zero length. 1412 </p> 1413 </div> 1414 <div id="message.length"> 1415 <h2 id="rfc.section.4.4"><a href="#rfc.section.4.4">4.4</a> <a href="#message.length">Message Length</a></h2> 1416 <p id="rfc.section.4.4.p.1">The transfer-length of a message is the length of the message-body as it appears in the message; that is, after any transfer-codings 1417 have been applied. When a message-body is included with a message, the transfer-length of that body is determined by one of 1418 the following (in order of precedence): 1419 </p> 1420 <p id="rfc.section.4.4.p.2"></p> 1421 <ol> 1422 <li> 1423 <p>Any response message which "<em class="bcp14">MUST NOT</em>" include a message-body (such as the 1xx, 204, and 304 responses and any response to a HEAD request) is always terminated 1424 by the first empty line after the header fields, regardless of the entity-header fields present in the message. 1425 </p> 1426 </li> 1427 <li> 1428 <p>If a Transfer-Encoding header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.3" title="Transfer-Encoding">Section 8.7</a>) is present, then the transfer-length is defined by use of the "chunked" transfer-coding (<a href="#transfer.codings" title="Transfer Codings">Section 3.4</a>), unless the message is terminated by closing the connection. 1429 </p> 1430 </li> 1431 <li> 1432 <p>If a Content-Length header field (<a href="#header.content-length" id="rfc.xref.header.content-length.1" title="Content-Length">Section 8.2</a>) is present, its decimal value in OCTETs represents both the entity-length and the transfer-length. The Content-Length header 1433 field <em class="bcp14">MUST NOT</em> be sent if these two lengths are different (i.e., if a Transfer-Encoding header field is present). If a message is received 1434 with both a Transfer-Encoding header field and a Content-Length header field, the latter <em class="bcp14">MUST</em> be ignored. 1435 </p> 1436 </li> 1437 <li> 1438 <p>If the message uses the media type "multipart/byteranges", and the transfer-length is not otherwise specified, then this self-delimiting 1439 media type defines the transfer-length. This media type <em class="bcp14">MUST NOT</em> be used unless the sender knows that the recipient can parse it; the presence in a request of a Range header with multiple 1440 byte-range specifiers from a 1.1 client implies that the client can parse multipart/byteranges responses. 1441 </p> 1442 <ul class="empty"> 1443 <li>A range header might be forwarded by a 1.0 proxy that does not understand multipart/byteranges; in this case the server <em class="bcp14">MUST</em> delimit the message using methods defined in items 1, 3 or 5 of this section. 1444 </li> 1445 </ul> 1446 </li> 1447 <li> 1448 <p>By the server closing the connection. (Closing the connection cannot be used to indicate the end of a request body, since 1449 that would leave no possibility for the server to send back a response.) 1450 </p> 1451 </li> 1452 </ol> 1453 <p id="rfc.section.4.4.p.3">For compatibility with HTTP/1.0 applications, HTTP/1.1 requests containing a message-body <em class="bcp14">MUST</em> include a valid Content-Length header field unless the server is known to be HTTP/1.1 compliant. If a request contains a message-body 1454 and a Content-Length is not given, the server <em class="bcp14">SHOULD</em> respond with 400 (Bad Request) if it cannot determine the length of the message, or with 411 (Length Required) if it wishes 1455 to insist on receiving a valid Content-Length. 1456 </p> 1457 <p id="rfc.section.4.4.p.4">All HTTP/1.1 applications that receive entities <em class="bcp14">MUST</em> accept the "chunked" transfer-coding (<a href="#transfer.codings" title="Transfer Codings">Section 3.4</a>), thus allowing this mechanism to be used for messages when the message length cannot be determined in advance. 1458 </p> 1459 <p id="rfc.section.4.4.p.5">Messages <em class="bcp14">MUST NOT</em> include both a Content-Length header field and a transfer-coding. If the message does include a transfer-coding, the Content-Length <em class="bcp14">MUST</em> be ignored. 1460 </p> 1461 <p id="rfc.section.4.4.p.6">When a Content-Length is given in a message where a message-body is allowed, its field value <em class="bcp14">MUST</em> exactly match the number of OCTETs in the message-body. HTTP/1.1 user agents <em class="bcp14">MUST</em> notify the user when an invalid length is received and detected. 1462 </p> 1463 </div> 1464 <div id="general.header.fields"> 1465 <h2 id="rfc.section.4.5"><a href="#rfc.section.4.5">4.5</a> <a href="#general.header.fields">General Header Fields</a></h2> 1466 <p id="rfc.section.4.5.p.1">There are a few header fields which have general applicability for both request and response messages, but which do not apply 1467 to the entity being transferred. These header fields apply only to the message being transmitted. 1468 </p> 1469 <div id="rfc.figure.u.34"></div><pre class="inline"><span id="rfc.iref.g.71"></span> <a href="#general.header.fields" class="smpl">general-header</a> = <a href="#abnf.dependencies" class="smpl">Cache-Control</a> ; <a href="#Part6" id="rfc.xref.Part6.6"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>, <a href="p6-cache.html#header.cache-control" title="Cache-Control">Section 16.2</a> 1415 1470 | <a href="#header.connection" class="smpl">Connection</a> ; <a href="#header.connection" id="rfc.xref.header.connection.1" title="Connection">Section 8.1</a> 1416 1471 | <a href="#header.date" class="smpl">Date</a> ; <a href="#header.date" id="rfc.xref.header.date.1" title="Date">Section 8.3</a> … … 1422 1477 | <a href="#abnf.dependencies" class="smpl">Warning</a> ; <a href="#Part6" id="rfc.xref.Part6.8"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>, <a href="p6-cache.html#header.warning" title="Warning">Section 16.6</a> 1423 1478 </pre><p id="rfc.section.4.5.p.3">General-header field names can be extended reliably only in combination with a change in the protocol version. However, new 1424 or experimental header fields may be given the semantics of general header fields if all parties in the communication recognize 1425 them to be general-header fields. Unrecognized header fields are treated as entity-header fields. 1426 </p> 1427 <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a> <a id="request" href="#request">Request</a></h1> 1428 <p id="rfc.section.5.p.1">A request message from a client to a server includes, within the first line of that message, the method to be applied to the 1429 resource, the identifier of the resource, and the protocol version in use. 1430 </p> 1431 <div id="rfc.figure.u.35"></div><pre class="inline"><span id="rfc.iref.g.72"></span> <a href="#request" class="smpl">Request</a> = <a href="#request-line" class="smpl">Request-Line</a> ; <a href="#request-line" title="Request-Line">Section 5.1</a> 1479 or experimental header fields may be given the semantics of general header fields if all parties in the communication recognize 1480 them to be general-header fields. Unrecognized header fields are treated as entity-header fields. 1481 </p> 1482 </div> 1483 </div> 1484 <div id="request"> 1485 <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a> <a href="#request">Request</a></h1> 1486 <p id="rfc.section.5.p.1">A request message from a client to a server includes, within the first line of that message, the method to be applied to the 1487 resource, the identifier of the resource, and the protocol version in use. 1488 </p> 1489 <div id="rfc.figure.u.35"></div><pre class="inline"><span id="rfc.iref.g.72"></span> <a href="#request" class="smpl">Request</a> = <a href="#request-line" class="smpl">Request-Line</a> ; <a href="#request-line" title="Request-Line">Section 5.1</a> 1432 1490 *(( <a href="#general.header.fields" class="smpl">general-header</a> ; <a href="#general.header.fields" title="General Header Fields">Section 4.5</a> 1433 1491 | <a href="#abnf.dependencies" class="smpl">request-header</a> ; <a href="#Part2" id="rfc.xref.Part2.7"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>, <a href="p2-semantics.html#request.header.fields" title="Request Header Fields">Section 4</a> … … 1435 1493 <a href="#rule.CRLF" class="smpl">CRLF</a> 1436 1494 [ <a href="#message.body" class="smpl">message-body</a> ] ; <a href="#message.body" title="Message Body">Section 4.3</a> 1437 </pre><h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a> <a id="request-line" href="#request-line">Request-Line</a></h2> 1438 <p id="rfc.section.5.1.p.1">The Request-Line begins with a method token, followed by the Request-URI and the protocol version, and ending with CRLF. The 1439 elements are separated by SP characters. No CR or LF is allowed except in the final CRLF sequence. 1440 </p> 1441 <div id="rfc.figure.u.36"></div><pre class="inline"><span id="rfc.iref.g.73"></span> <a href="#request-line" class="smpl">Request-Line</a> = <a href="#method" class="smpl">Method</a> <a href="#core.rules" class="smpl">SP</a> <a href="#request-uri" class="smpl">Request-URI</a> <a href="#core.rules" class="smpl">SP</a> <a href="#http.version" class="smpl">HTTP-Version</a> <a href="#rule.CRLF" class="smpl">CRLF</a> 1442 </pre><h3 id="rfc.section.5.1.1"><a href="#rfc.section.5.1.1">5.1.1</a> <a id="method" href="#method">Method</a></h3> 1443 <p id="rfc.section.5.1.1.p.1">The Method token indicates the method to be performed on the resource identified by the Request-URI. The method is case-sensitive.</p> 1444 <div id="rfc.figure.u.37"></div><pre class="inline"><span id="rfc.iref.g.74"></span><span id="rfc.iref.g.75"></span> <a href="#method" class="smpl">Method</a> = <a href="#rule.token.separators" class="smpl">token</a> 1445 </pre><h3 id="rfc.section.5.1.2"><a href="#rfc.section.5.1.2">5.1.2</a> <a id="request-uri" href="#request-uri">Request-URI</a></h3> 1446 <p id="rfc.section.5.1.2.p.1">The Request-URI is a Uniform Resource Identifier (<a href="#uri" title="Uniform Resource Identifiers">Section 3.2</a>) and identifies the resource upon which to apply the request. 1447 </p> 1448 <div id="rfc.figure.u.38"></div><pre class="inline"><span id="rfc.iref.g.76"></span> <a href="#request-uri" class="smpl">Request-URI</a> = "*" 1495 </pre><div id="request-line"> 1496 <h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a> <a href="#request-line">Request-Line</a></h2> 1497 <p id="rfc.section.5.1.p.1">The Request-Line begins with a method token, followed by the Request-URI and the protocol version, and ending with CRLF. The 1498 elements are separated by SP characters. No CR or LF is allowed except in the final CRLF sequence. 1499 </p> 1500 <div id="rfc.figure.u.36"></div><pre class="inline"><span id="rfc.iref.g.73"></span> <a href="#request-line" class="smpl">Request-Line</a> = <a href="#method" class="smpl">Method</a> <a href="#core.rules" class="smpl">SP</a> <a href="#request-uri" class="smpl">Request-URI</a> <a href="#core.rules" class="smpl">SP</a> <a href="#http.version" class="smpl">HTTP-Version</a> <a href="#rule.CRLF" class="smpl">CRLF</a> 1501 </pre><div id="method"> 1502 <h3 id="rfc.section.5.1.1"><a href="#rfc.section.5.1.1">5.1.1</a> <a href="#method">Method</a></h3> 1503 <p id="rfc.section.5.1.1.p.1">The Method token indicates the method to be performed on the resource identified by the Request-URI. The method is case-sensitive.</p> 1504 <div id="rfc.figure.u.37"></div><pre class="inline"><span id="rfc.iref.g.74"></span><span id="rfc.iref.g.75"></span> <a href="#method" class="smpl">Method</a> = <a href="#rule.token.separators" class="smpl">token</a> 1505 </pre></div> 1506 <div id="request-uri"> 1507 <h3 id="rfc.section.5.1.2"><a href="#rfc.section.5.1.2">5.1.2</a> <a href="#request-uri">Request-URI</a></h3> 1508 <p id="rfc.section.5.1.2.p.1">The Request-URI is a Uniform Resource Identifier (<a href="#uri" title="Uniform Resource Identifiers">Section 3.2</a>) and identifies the resource upon which to apply the request. 1509 </p> 1510 <div id="rfc.figure.u.38"></div><pre class="inline"><span id="rfc.iref.g.76"></span> <a href="#request-uri" class="smpl">Request-URI</a> = "*" 1449 1511 | <a href="#general.syntax" class="smpl">absoluteURI</a> 1450 1512 | ( <a href="#general.syntax" class="smpl">path-absolute</a> [ "?" <a href="#general.syntax" class="smpl">query</a> ] ) 1451 1513 | <a href="#general.syntax" class="smpl">authority</a> 1452 1514 </pre><p id="rfc.section.5.1.2.p.3">The four options for Request-URI are dependent on the nature of the request. The asterisk "*" means that the request does 1453 not apply to a particular resource, but to the server itself, and is only allowed when the method used does not necessarily1454 apply to a resource. One example would be1455 </p>1456 <div id="rfc.figure.u.39"></div><pre class="text"> OPTIONS * HTTP/1.11515 not apply to a particular resource, but to the server itself, and is only allowed when the method used does not necessarily 1516 apply to a resource. One example would be 1517 </p> 1518 <div id="rfc.figure.u.39"></div><pre class="text"> OPTIONS * HTTP/1.1 1457 1519 </pre><p id="rfc.section.5.1.2.p.5">The absoluteURI form is <em class="bcp14">REQUIRED</em> when the request is being made to a proxy. The proxy is requested to forward the request or service it from a valid cache, 1458 and return the response. Note that the proxy <em class="bcp14">MAY</em> forward the request on to another proxy or directly to the server specified by the absoluteURI. In order to avoid request1459 loops, a proxy <em class="bcp14">MUST</em> be able to recognize all of its server names, including any aliases, local variations, and the numeric IP address. An example1460 Request-Line would be:1461 </p>1462 <div id="rfc.figure.u.40"></div><pre class="text"> GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.11520 and return the response. Note that the proxy <em class="bcp14">MAY</em> forward the request on to another proxy or directly to the server specified by the absoluteURI. In order to avoid request 1521 loops, a proxy <em class="bcp14">MUST</em> be able to recognize all of its server names, including any aliases, local variations, and the numeric IP address. An example 1522 Request-Line would be: 1523 </p> 1524 <div id="rfc.figure.u.40"></div><pre class="text"> GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1 1463 1525 </pre><p id="rfc.section.5.1.2.p.7">To allow for transition to absoluteURIs in all requests in future versions of HTTP, all HTTP/1.1 servers <em class="bcp14">MUST</em> accept the absoluteURI form in requests, even though HTTP/1.1 clients will only generate them in requests to proxies. 1464 </p>1465 <p id="rfc.section.5.1.2.p.8">The authority form is only used by the CONNECT method (<a href="p2-semantics.html#CONNECT" title="CONNECT">Section 8.9</a> of <a href="#Part2" id="rfc.xref.Part2.8"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>).1466 </p>1467 <p id="rfc.section.5.1.2.p.9">The most common form of Request-URI is that used to identify a resource on an origin server or gateway. In this case the absolute1468 path of the URI <em class="bcp14">MUST</em> be transmitted (see <a href="#general.syntax" title="General Syntax">Section 3.2.1</a>, path-absolute) as the Request-URI, and the network location of the URI (authority) <em class="bcp14">MUST</em> be transmitted in a Host header field. For example, a client wishing to retrieve the resource above directly from the origin1469 server would create a TCP connection to port 80 of the host "www.example.org" and send the lines:1470 </p>1471 <div id="rfc.figure.u.41"></div><pre class="text"> GET /pub/WWW/TheProject.html HTTP/1.11526 </p> 1527 <p id="rfc.section.5.1.2.p.8">The authority form is only used by the CONNECT method (<a href="p2-semantics.html#CONNECT" title="CONNECT">Section 8.9</a> of <a href="#Part2" id="rfc.xref.Part2.8"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). 1528 </p> 1529 <p id="rfc.section.5.1.2.p.9">The most common form of Request-URI is that used to identify a resource on an origin server or gateway. In this case the absolute 1530 path of the URI <em class="bcp14">MUST</em> be transmitted (see <a href="#general.syntax" title="General Syntax">Section 3.2.1</a>, path-absolute) as the Request-URI, and the network location of the URI (authority) <em class="bcp14">MUST</em> be transmitted in a Host header field. For example, a client wishing to retrieve the resource above directly from the origin 1531 server would create a TCP connection to port 80 of the host "www.example.org" and send the lines: 1532 </p> 1533 <div id="rfc.figure.u.41"></div><pre class="text"> GET /pub/WWW/TheProject.html HTTP/1.1 1472 1534 Host: www.example.org 1473 1535 </pre><p id="rfc.section.5.1.2.p.11">followed by the remainder of the Request. Note that the absolute path cannot be empty; if none is present in the original 1474 URI, it <em class="bcp14">MUST</em> be given as "/" (the server root). 1475 </p> 1476 <p id="rfc.section.5.1.2.p.12">The Request-URI is transmitted in the format specified in <a href="#general.syntax" title="General Syntax">Section 3.2.1</a>. If the Request-URI is encoded using the "% HEX HEX" encoding <a href="#RFC2396" id="rfc.xref.RFC2396.11"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>, the origin server <em class="bcp14">MUST</em> decode the Request-URI in order to properly interpret the request. Servers <em class="bcp14">SHOULD</em> respond to invalid Request-URIs with an appropriate status code. 1477 </p> 1478 <p id="rfc.section.5.1.2.p.13">A transparent proxy <em class="bcp14">MUST NOT</em> rewrite the "path-absolute" part of the received Request-URI when forwarding it to the next inbound server, except as noted 1479 above to replace a null path-absolute with "/". 1480 </p> 1481 <p id="rfc.section.5.1.2.p.14"> </p> 1482 <ul class="empty"> 1483 <li> <b>Note:</b> The "no rewrite" rule prevents the proxy from changing the meaning of the request when the origin server is improperly using 1484 a non-reserved URI character for a reserved purpose. Implementors should be aware that some pre-HTTP/1.1 proxies have been 1485 known to rewrite the Request-URI. 1486 </li> 1487 </ul> 1488 <h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a> <a id="the.resource.identified.by.a.request" href="#the.resource.identified.by.a.request">The Resource Identified by a Request</a></h2> 1489 <p id="rfc.section.5.2.p.1">The exact resource identified by an Internet request is determined by examining both the Request-URI and the Host header field.</p> 1490 <p id="rfc.section.5.2.p.2">An origin server that does not allow resources to differ by the requested host <em class="bcp14">MAY</em> ignore the Host header field value when determining the resource identified by an HTTP/1.1 request. (But see <a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses">Appendix D.1.1</a> for other requirements on Host support in HTTP/1.1.) 1491 </p> 1492 <p id="rfc.section.5.2.p.3">An origin server that does differentiate resources based on the host requested (sometimes referred to as virtual hosts or 1493 vanity host names) <em class="bcp14">MUST</em> use the following rules for determining the requested resource on an HTTP/1.1 request: 1494 </p> 1495 <ol> 1496 <li>If Request-URI is an absoluteURI, the host is part of the Request-URI. Any Host header field value in the request <em class="bcp14">MUST</em> be ignored. 1497 </li> 1498 <li>If the Request-URI is not an absoluteURI, and the request includes a Host header field, the host is determined by the Host 1499 header field value. 1500 </li> 1501 <li>If the host as determined by rule 1 or 2 is not a valid host on the server, the response <em class="bcp14">MUST</em> be a 400 (Bad Request) error message. 1502 </li> 1503 </ol> 1504 <p id="rfc.section.5.2.p.4">Recipients of an HTTP/1.0 request that lacks a Host header field <em class="bcp14">MAY</em> attempt to use heuristics (e.g., examination of the URI path for something unique to a particular host) in order to determine 1505 what exact resource is being requested. 1506 </p> 1507 <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a> <a id="response" href="#response">Response</a></h1> 1508 <p id="rfc.section.6.p.1">After receiving and interpreting a request message, a server responds with an HTTP response message.</p> 1509 <div id="rfc.figure.u.42"></div><pre class="inline"><span id="rfc.iref.g.77"></span> <a href="#response" class="smpl">Response</a> = <a href="#status-line" class="smpl">Status-Line</a> ; <a href="#status-line" title="Status-Line">Section 6.1</a> 1536 URI, it <em class="bcp14">MUST</em> be given as "/" (the server root). 1537 </p> 1538 <p id="rfc.section.5.1.2.p.12">The Request-URI is transmitted in the format specified in <a href="#general.syntax" title="General Syntax">Section 3.2.1</a>. If the Request-URI is encoded using the "% HEX HEX" encoding <a href="#RFC2396" id="rfc.xref.RFC2396.11"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[RFC2396]</cite></a>, the origin server <em class="bcp14">MUST</em> decode the Request-URI in order to properly interpret the request. Servers <em class="bcp14">SHOULD</em> respond to invalid Request-URIs with an appropriate status code. 1539 </p> 1540 <p id="rfc.section.5.1.2.p.13">A transparent proxy <em class="bcp14">MUST NOT</em> rewrite the "path-absolute" part of the received Request-URI when forwarding it to the next inbound server, except as noted 1541 above to replace a null path-absolute with "/". 1542 </p> 1543 <p id="rfc.section.5.1.2.p.14"></p> 1544 <ul class="empty"> 1545 <li><b>Note:</b> The "no rewrite" rule prevents the proxy from changing the meaning of the request when the origin server is improperly using 1546 a non-reserved URI character for a reserved purpose. Implementors should be aware that some pre-HTTP/1.1 proxies have been 1547 known to rewrite the Request-URI. 1548 </li> 1549 </ul> 1550 </div> 1551 </div> 1552 <div id="the.resource.identified.by.a.request"> 1553 <h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a> <a href="#the.resource.identified.by.a.request">The Resource Identified by a Request</a></h2> 1554 <p id="rfc.section.5.2.p.1">The exact resource identified by an Internet request is determined by examining both the Request-URI and the Host header field.</p> 1555 <p id="rfc.section.5.2.p.2">An origin server that does not allow resources to differ by the requested host <em class="bcp14">MAY</em> ignore the Host header field value when determining the resource identified by an HTTP/1.1 request. (But see <a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses">Appendix D.1.1</a> for other requirements on Host support in HTTP/1.1.) 1556 </p> 1557 <p id="rfc.section.5.2.p.3">An origin server that does differentiate resources based on the host requested (sometimes referred to as virtual hosts or 1558 vanity host names) <em class="bcp14">MUST</em> use the following rules for determining the requested resource on an HTTP/1.1 request: 1559 </p> 1560 <ol> 1561 <li>If Request-URI is an absoluteURI, the host is part of the Request-URI. Any Host header field value in the request <em class="bcp14">MUST</em> be ignored. 1562 </li> 1563 <li>If the Request-URI is not an absoluteURI, and the request includes a Host header field, the host is determined by the Host 1564 header field value. 1565 </li> 1566 <li>If the host as determined by rule 1 or 2 is not a valid host on the server, the response <em class="bcp14">MUST</em> be a 400 (Bad Request) error message. 1567 </li> 1568 </ol> 1569 <p id="rfc.section.5.2.p.4">Recipients of an HTTP/1.0 request that lacks a Host header field <em class="bcp14">MAY</em> attempt to use heuristics (e.g., examination of the URI path for something unique to a particular host) in order to determine 1570 what exact resource is being requested. 1571 </p> 1572 </div> 1573 </div> 1574 <div id="response"> 1575 <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a> <a href="#response">Response</a></h1> 1576 <p id="rfc.section.6.p.1">After receiving and interpreting a request message, a server responds with an HTTP response message.</p> 1577 <div id="rfc.figure.u.42"></div><pre class="inline"><span id="rfc.iref.g.77"></span> <a href="#response" class="smpl">Response</a> = <a href="#status-line" class="smpl">Status-Line</a> ; <a href="#status-line" title="Status-Line">Section 6.1</a> 1510 1578 *(( <a href="#general.header.fields" class="smpl">general-header</a> ; <a href="#general.header.fields" title="General Header Fields">Section 4.5</a> 1511 1579 | <a href="#abnf.dependencies" class="smpl">response-header</a> ; <a href="#Part2" id="rfc.xref.Part2.9"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>, <a href="p2-semantics.html#response.header.fields" title="Response Header Fields">Section 6</a> … … 1513 1581 <a href="#rule.CRLF" class="smpl">CRLF</a> 1514 1582 [ <a href="#message.body" class="smpl">message-body</a> ] ; <a href="#message.body" title="Message Body">Section 4.3</a> 1515 </pre><h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a> <a id="status-line" href="#status-line">Status-Line</a></h2> 1516 <p id="rfc.section.6.1.p.1">The first line of a Response message is the Status-Line, consisting of the protocol version followed by a numeric status code 1517 and its associated textual phrase, with each element separated by SP characters. No CR or LF is allowed except in the final 1518 CRLF sequence. 1519 </p> 1520 <div id="rfc.figure.u.43"></div><pre class="inline"><span id="rfc.iref.g.78"></span> <a href="#status-line" class="smpl">Status-Line</a> = <a href="#http.version" class="smpl">HTTP-Version</a> <a href="#core.rules" class="smpl">SP</a> <a href="#status.code.and.reason.phrase" class="smpl">Status-Code</a> <a href="#core.rules" class="smpl">SP</a> <a href="#status.code.and.reason.phrase" class="smpl">Reason-Phrase</a> <a href="#rule.CRLF" class="smpl">CRLF</a> 1521 </pre><h3 id="rfc.section.6.1.1"><a href="#rfc.section.6.1.1">6.1.1</a> <a id="status.code.and.reason.phrase" href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></h3> 1522 <p id="rfc.section.6.1.1.p.1">The Status-Code element is a 3-digit integer result code of the attempt to understand and satisfy the request. These codes 1523 are fully defined in <a href="p2-semantics.html#status.codes" title="Status Code Definitions">Section 9</a> of <a href="#Part2" id="rfc.xref.Part2.10"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>. The Reason Phrase exists for the sole purpose of providing a textual description associated with the numeric status code, 1524 out of deference to earlier Internet application protocols that were more frequently used with interactive text clients. A 1525 client <em class="bcp14">SHOULD</em> ignore the content of the Reason Phrase. 1526 </p> 1527 <p id="rfc.section.6.1.1.p.2">The first digit of the Status-Code defines the class of response. The last two digits do not have any categorization role. 1528 There are 5 values for the first digit: 1529 </p> 1530 <ul> 1531 <li>1xx: Informational - Request received, continuing process</li> 1532 <li>2xx: Success - The action was successfully received, understood, and accepted</li> 1533 <li>3xx: Redirection - Further action must be taken in order to complete the request</li> 1534 <li>4xx: Client Error - The request contains bad syntax or cannot be fulfilled</li> 1535 <li>5xx: Server Error - The server failed to fulfill an apparently valid request</li> 1536 </ul> 1537 <div id="rfc.figure.u.44"></div><pre class="inline"><span id="rfc.iref.g.79"></span><span id="rfc.iref.g.80"></span><span id="rfc.iref.g.81"></span> <a href="#status.code.and.reason.phrase" class="smpl">Status-Code</a> = 3<a href="#core.rules" class="smpl">DIGIT</a> 1583 </pre><div id="status-line"> 1584 <h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a> <a href="#status-line">Status-Line</a></h2> 1585 <p id="rfc.section.6.1.p.1">The first line of a Response message is the Status-Line, consisting of the protocol version followed by a numeric status code 1586 and its associated textual phrase, with each element separated by SP characters. No CR or LF is allowed except in the final 1587 CRLF sequence. 1588 </p> 1589 <div id="rfc.figure.u.43"></div><pre class="inline"><span id="rfc.iref.g.78"></span> <a href="#status-line" class="smpl">Status-Line</a> = <a href="#http.version" class="smpl">HTTP-Version</a> <a href="#core.rules" class="smpl">SP</a> <a href="#status.code.and.reason.phrase" class="smpl">Status-Code</a> <a href="#core.rules" class="smpl">SP</a> <a href="#status.code.and.reason.phrase" class="smpl">Reason-Phrase</a> <a href="#rule.CRLF" class="smpl">CRLF</a> 1590 </pre><div id="status.code.and.reason.phrase"> 1591 <h3 id="rfc.section.6.1.1"><a href="#rfc.section.6.1.1">6.1.1</a> <a href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></h3> 1592 <p id="rfc.section.6.1.1.p.1">The Status-Code element is a 3-digit integer result code of the attempt to understand and satisfy the request. These codes 1593 are fully defined in <a href="p2-semantics.html#status.codes" title="Status Code Definitions">Section 9</a> of <a href="#Part2" id="rfc.xref.Part2.10"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>. The Reason Phrase exists for the sole purpose of providing a textual description associated with the numeric status code, 1594 out of deference to earlier Internet application protocols that were more frequently used with interactive text clients. A 1595 client <em class="bcp14">SHOULD</em> ignore the content of the Reason Phrase. 1596 </p> 1597 <p id="rfc.section.6.1.1.p.2">The first digit of the Status-Code defines the class of response. The last two digits do not have any categorization role. 1598 There are 5 values for the first digit: 1599 </p> 1600 <ul> 1601 <li>1xx: Informational - Request received, continuing process</li> 1602 <li>2xx: Success - The action was successfully received, understood, and accepted</li> 1603 <li>3xx: Redirection - Further action must be taken in order to complete the request</li> 1604 <li>4xx: Client Error - The request contains bad syntax or cannot be fulfilled</li> 1605 <li>5xx: Server Error - The server failed to fulfill an apparently valid request</li> 1606 </ul> 1607 <div id="rfc.figure.u.44"></div><pre class="inline"><span id="rfc.iref.g.79"></span><span id="rfc.iref.g.80"></span><span id="rfc.iref.g.81"></span> <a href="#status.code.and.reason.phrase" class="smpl">Status-Code</a> = 3<a href="#core.rules" class="smpl">DIGIT</a> 1538 1608 <a href="#status.code.and.reason.phrase" class="smpl">Reason-Phrase</a> = *<<a href="#rule.TEXT" class="smpl">TEXT</a>, excluding <a href="#core.rules" class="smpl">CR</a>, <a href="#core.rules" class="smpl">LF</a>> 1539 </pre><h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a> <a id="connections" href="#connections">Connections</a></h1> 1540 <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a> <a id="persistent.connections" href="#persistent.connections">Persistent Connections</a></h2> 1541 <h3 id="rfc.section.7.1.1"><a href="#rfc.section.7.1.1">7.1.1</a> <a id="persistent.purpose" href="#persistent.purpose">Purpose</a></h3> 1542 <p id="rfc.section.7.1.1.p.1">Prior to persistent connections, a separate TCP connection was established to fetch each URL, increasing the load on HTTP 1543 servers and causing congestion on the Internet. The use of inline images and other associated data often require a client 1544 to make multiple requests of the same server in a short amount of time. Analysis of these performance problems and results 1545 from a prototype implementation are available <a href="#Pad1995" id="rfc.xref.Pad1995.1"><cite title="Improving HTTP Latency">[Pad1995]</cite></a> <a href="#Spe" id="rfc.xref.Spe.1"><cite title="Analysis of HTTP Performance Problems">[Spe]</cite></a>. Implementation experience and measurements of actual HTTP/1.1 (<cite title="Hypertext Transfer Protocol -- HTTP/1.1" id="rfc.xref.RFC2068.2">RFC 2068</cite>) implementations show good results <a href="#Nie1997" id="rfc.xref.Nie1997.1"><cite title="Network Performance Effects of HTTP/1.1, CSS1, and PNG">[Nie1997]</cite></a>. Alternatives have also been explored, for example, T/TCP <a href="#Tou1998" id="rfc.xref.Tou1998.1"><cite title="Analysis of HTTP Performance">[Tou1998]</cite></a>. 1546 </p> 1547 <p id="rfc.section.7.1.1.p.2">Persistent HTTP connections have a number of advantages: </p> 1548 <ul> 1549 <li>By opening and closing fewer TCP connections, CPU time is saved in routers and hosts (clients, servers, proxies, gateways, 1550 tunnels, or caches), and memory used for TCP protocol control blocks can be saved in hosts. 1551 </li> 1552 <li>HTTP requests and responses can be pipelined on a connection. Pipelining allows a client to make multiple requests without 1553 waiting for each response, allowing a single TCP connection to be used much more efficiently, with much lower elapsed time. 1554 </li> 1555 <li>Network congestion is reduced by reducing the number of packets caused by TCP opens, and by allowing TCP sufficient time to 1556 determine the congestion state of the network. 1557 </li> 1558 <li>Latency on subsequent requests is reduced since there is no time spent in TCP's connection opening handshake.</li> 1559 <li>HTTP can evolve more gracefully, since errors can be reported without the penalty of closing the TCP connection. Clients using 1560 future versions of HTTP might optimistically try a new feature, but if communicating with an older server, retry with old 1561 semantics after an error is reported. 1562 </li> 1563 </ul> 1564 <p id="rfc.section.7.1.1.p.3">HTTP implementations <em class="bcp14">SHOULD</em> implement persistent connections. 1565 </p> 1566 <h3 id="rfc.section.7.1.2"><a href="#rfc.section.7.1.2">7.1.2</a> <a id="persistent.overall" href="#persistent.overall">Overall Operation</a></h3> 1567 <p id="rfc.section.7.1.2.p.1">A significant difference between HTTP/1.1 and earlier versions of HTTP is that persistent connections are the default behavior 1568 of any HTTP connection. That is, unless otherwise indicated, the client <em class="bcp14">SHOULD</em> assume that the server will maintain a persistent connection, even after error responses from the server. 1569 </p> 1570 <p id="rfc.section.7.1.2.p.2">Persistent connections provide a mechanism by which a client and a server can signal the close of a TCP connection. This signaling 1571 takes place using the Connection header field (<a href="#header.connection" id="rfc.xref.header.connection.2" title="Connection">Section 8.1</a>). Once a close has been signaled, the client <em class="bcp14">MUST NOT</em> send any more requests on that connection. 1572 </p> 1573 <h4 id="rfc.section.7.1.2.1"><a href="#rfc.section.7.1.2.1">7.1.2.1</a> <a id="persistent.negotiation" href="#persistent.negotiation">Negotiation</a></h4> 1574 <p id="rfc.section.7.1.2.1.p.1">An HTTP/1.1 server <em class="bcp14">MAY</em> assume that a HTTP/1.1 client intends to maintain a persistent connection unless a Connection header including the connection-token 1575 "close" was sent in the request. If the server chooses to close the connection immediately after sending the response, it <em class="bcp14">SHOULD</em> send a Connection header including the connection-token close. 1576 </p> 1577 <p id="rfc.section.7.1.2.1.p.2">An HTTP/1.1 client <em class="bcp14">MAY</em> expect a connection to remain open, but would decide to keep it open based on whether the response from a server contains 1578 a Connection header with the connection-token close. In case the client does not want to maintain a connection for more than 1579 that request, it <em class="bcp14">SHOULD</em> send a Connection header including the connection-token close. 1580 </p> 1581 <p id="rfc.section.7.1.2.1.p.3">If either the client or the server sends the close token in the Connection header, that request becomes the last one for the 1582 connection. 1583 </p> 1584 <p id="rfc.section.7.1.2.1.p.4">Clients and servers <em class="bcp14">SHOULD NOT</em> assume that a persistent connection is maintained for HTTP versions less than 1.1 unless it is explicitly signaled. See <a href="#compatibility.with.http.1.0.persistent.connections" title="Compatibility with HTTP/1.0 Persistent Connections">Appendix D.2</a> for more information on backward compatibility with HTTP/1.0 clients. 1585 </p> 1586 <p id="rfc.section.7.1.2.1.p.5">In order to remain persistent, all messages on the connection <em class="bcp14">MUST</em> have a self-defined message length (i.e., one not defined by closure of the connection), as described in <a href="#message.length" title="Message Length">Section 4.4</a>. 1587 </p> 1588 <h4 id="rfc.section.7.1.2.2"><a href="#rfc.section.7.1.2.2">7.1.2.2</a> <a id="pipelining" href="#pipelining">Pipelining</a></h4> 1589 <p id="rfc.section.7.1.2.2.p.1">A client that supports persistent connections <em class="bcp14">MAY</em> "pipeline" its requests (i.e., send multiple requests without waiting for each response). A server <em class="bcp14">MUST</em> send its responses to those requests in the same order that the requests were received. 1590 </p> 1591 <p id="rfc.section.7.1.2.2.p.2">Clients which assume persistent connections and pipeline immediately after connection establishment <em class="bcp14">SHOULD</em> be prepared to retry their connection if the first pipelined attempt fails. If a client does such a retry, it <em class="bcp14">MUST NOT</em> pipeline before it knows the connection is persistent. Clients <em class="bcp14">MUST</em> also be prepared to resend their requests if the server closes the connection before sending all of the corresponding responses. 1592 </p> 1593 <p id="rfc.section.7.1.2.2.p.3">Clients <em class="bcp14">SHOULD NOT</em> pipeline requests using non-idempotent methods or non-idempotent sequences of methods (see <a href="p2-semantics.html#idempotent.methods" title="Idempotent Methods">Section 8.1.2</a> of <a href="#Part2" id="rfc.xref.Part2.11"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). Otherwise, a premature termination of the transport connection could lead to indeterminate results. A client wishing to 1594 send a non-idempotent request <em class="bcp14">SHOULD</em> wait to send that request until it has received the response status for the previous request. 1595 </p> 1596 <h3 id="rfc.section.7.1.3"><a href="#rfc.section.7.1.3">7.1.3</a> <a id="persistent.proxy" href="#persistent.proxy">Proxy Servers</a></h3> 1597 <p id="rfc.section.7.1.3.p.1">It is especially important that proxies correctly implement the properties of the Connection header field as specified in <a href="#header.connection" id="rfc.xref.header.connection.3" title="Connection">Section 8.1</a>. 1598 </p> 1599 <p id="rfc.section.7.1.3.p.2">The proxy server <em class="bcp14">MUST</em> signal persistent connections separately with its clients and the origin servers (or other proxy servers) that it connects 1600 to. Each persistent connection applies to only one transport link. 1601 </p> 1602 <p id="rfc.section.7.1.3.p.3">A proxy server <em class="bcp14">MUST NOT</em> establish a HTTP/1.1 persistent connection with an HTTP/1.0 client (but see <a href="#RFC2068" id="rfc.xref.RFC2068.3"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a> for information and discussion of the problems with the Keep-Alive header implemented by many HTTP/1.0 clients). 1603 </p> 1604 <h3 id="rfc.section.7.1.4"><a href="#rfc.section.7.1.4">7.1.4</a> <a id="persistent.practical" href="#persistent.practical">Practical Considerations</a></h3> 1605 <p id="rfc.section.7.1.4.p.1">Servers will usually have some time-out value beyond which they will no longer maintain an inactive connection. Proxy servers 1606 might make this a higher value since it is likely that the client will be making more connections through the same server. 1607 The use of persistent connections places no requirements on the length (or existence) of this time-out for either the client 1608 or the server. 1609 </p> 1610 <p id="rfc.section.7.1.4.p.2">When a client or server wishes to time-out it <em class="bcp14">SHOULD</em> issue a graceful close on the transport connection. Clients and servers <em class="bcp14">SHOULD</em> both constantly watch for the other side of the transport close, and respond to it as appropriate. If a client or server does 1611 not detect the other side's close promptly it could cause unnecessary resource drain on the network. 1612 </p> 1613 <p id="rfc.section.7.1.4.p.3">A client, server, or proxy <em class="bcp14">MAY</em> close the transport connection at any time. For example, a client might have started to send a new request at the same time 1614 that the server has decided to close the "idle" connection. From the server's point of view, the connection is being closed 1615 while it was idle, but from the client's point of view, a request is in progress. 1616 </p> 1617 <p id="rfc.section.7.1.4.p.4">This means that clients, servers, and proxies <em class="bcp14">MUST</em> be able to recover from asynchronous close events. Client software <em class="bcp14">SHOULD</em> reopen the transport connection and retransmit the aborted sequence of requests without user interaction so long as the request 1618 sequence is idempotent (see <a href="p2-semantics.html#idempotent.methods" title="Idempotent Methods">Section 8.1.2</a> of <a href="#Part2" id="rfc.xref.Part2.12"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). Non-idempotent methods or sequences <em class="bcp14">MUST NOT</em> be automatically retried, although user agents <em class="bcp14">MAY</em> offer a human operator the choice of retrying the request(s). Confirmation by user-agent software with semantic understanding 1619 of the application <em class="bcp14">MAY</em> substitute for user confirmation. The automatic retry <em class="bcp14">SHOULD NOT</em> be repeated if the second sequence of requests fails. 1620 </p> 1621 <p id="rfc.section.7.1.4.p.5">Servers <em class="bcp14">SHOULD</em> always respond to at least one request per connection, if at all possible. Servers <em class="bcp14">SHOULD NOT</em> close a connection in the middle of transmitting a response, unless a network or client failure is suspected. 1622 </p> 1623 <p id="rfc.section.7.1.4.p.6">Clients that use persistent connections <em class="bcp14">SHOULD</em> limit the number of simultaneous connections that they maintain to a given server. A single-user client <em class="bcp14">SHOULD NOT</em> maintain more than 2 connections with any server or proxy. A proxy <em class="bcp14">SHOULD</em> use up to 2*N connections to another server or proxy, where N is the number of simultaneously active users. These guidelines 1624 are intended to improve HTTP response times and avoid congestion. 1625 </p> 1626 <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a> <a id="message.transmission.requirements" href="#message.transmission.requirements">Message Transmission Requirements</a></h2> 1627 <h3 id="rfc.section.7.2.1"><a href="#rfc.section.7.2.1">7.2.1</a> <a id="persistent.flow" href="#persistent.flow">Persistent Connections and Flow Control</a></h3> 1628 <p id="rfc.section.7.2.1.p.1">HTTP/1.1 servers <em class="bcp14">SHOULD</em> maintain persistent connections and use TCP's flow control mechanisms to resolve temporary overloads, rather than terminating 1629 connections with the expectation that clients will retry. The latter technique can exacerbate network congestion. 1630 </p> 1631 <h3 id="rfc.section.7.2.2"><a href="#rfc.section.7.2.2">7.2.2</a> <a id="persistent.monitor" href="#persistent.monitor">Monitoring Connections for Error Status Messages</a></h3> 1632 <p id="rfc.section.7.2.2.p.1">An HTTP/1.1 (or later) client sending a message-body <em class="bcp14">SHOULD</em> monitor the network connection for an error status while it is transmitting the request. If the client sees an error status, 1633 it <em class="bcp14">SHOULD</em> immediately cease transmitting the body. If the body is being sent using a "chunked" encoding (<a href="#transfer.codings" title="Transfer Codings">Section 3.4</a>), a zero length chunk and empty trailer <em class="bcp14">MAY</em> be used to prematurely mark the end of the message. If the body was preceded by a Content-Length header, the client <em class="bcp14">MUST</em> close the connection. 1634 </p> 1635 <h3 id="rfc.section.7.2.3"><a href="#rfc.section.7.2.3">7.2.3</a> <a id="use.of.the.100.status" href="#use.of.the.100.status">Use of the 100 (Continue) Status</a></h3> 1636 <p id="rfc.section.7.2.3.p.1">The purpose of the 100 (Continue) status (see <a href="p2-semantics.html#status.100" title="100 Continue">Section 9.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.13"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) is to allow a client that is sending a request message with a request body to determine if the origin server is willing 1637 to accept the request (based on the request headers) before the client sends the request body. In some cases, it might either 1638 be inappropriate or highly inefficient for the client to send the body if the server will reject the message without looking 1639 at the body. 1640 </p> 1641 <p id="rfc.section.7.2.3.p.2">Requirements for HTTP/1.1 clients: </p> 1642 <ul> 1643 <li>If a client will wait for a 100 (Continue) response before sending the request body, it <em class="bcp14">MUST</em> send an Expect request-header field (<a href="p2-semantics.html#header.expect" title="Expect">Section 10.2</a> of <a href="#Part2" id="rfc.xref.Part2.14"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) with the "100-continue" expectation. 1644 </li> 1645 <li>A client <em class="bcp14">MUST NOT</em> send an Expect request-header field (<a href="p2-semantics.html#header.expect" title="Expect">Section 10.2</a> of <a href="#Part2" id="rfc.xref.Part2.15"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) with the "100-continue" expectation if it does not intend to send a request body. 1646 </li> 1647 </ul> 1648 <p id="rfc.section.7.2.3.p.3">Because of the presence of older implementations, the protocol allows ambiguous situations in which a client may send "Expect: 1649 100-continue" without receiving either a 417 (Expectation Failed) status or a 100 (Continue) status. Therefore, when a client 1650 sends this header field to an origin server (possibly via a proxy) from which it has never seen a 100 (Continue) status, the 1651 client <em class="bcp14">SHOULD NOT</em> wait for an indefinite period before sending the request body. 1652 </p> 1653 <p id="rfc.section.7.2.3.p.4">Requirements for HTTP/1.1 origin servers: </p> 1654 <ul> 1655 <li>Upon receiving a request which includes an Expect request-header field with the "100-continue" expectation, an origin server <em class="bcp14">MUST</em> either respond with 100 (Continue) status and continue to read from the input stream, or respond with a final status code. 1656 The origin server <em class="bcp14">MUST NOT</em> wait for the request body before sending the 100 (Continue) response. If it responds with a final status code, it <em class="bcp14">MAY</em> close the transport connection or it <em class="bcp14">MAY</em> continue to read and discard the rest of the request. It <em class="bcp14">MUST NOT</em> perform the requested method if it returns a final status code. 1657 </li> 1658 <li>An origin server <em class="bcp14">SHOULD NOT</em> send a 100 (Continue) response if the request message does not include an Expect request-header field with the "100-continue" 1659 expectation, and <em class="bcp14">MUST NOT</em> send a 100 (Continue) response if such a request comes from an HTTP/1.0 (or earlier) client. There is an exception to this 1660 rule: for compatibility with <a href="#RFC2068" id="rfc.xref.RFC2068.4"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, a server <em class="bcp14">MAY</em> send a 100 (Continue) status in response to an HTTP/1.1 PUT or POST request that does not include an Expect request-header 1661 field with the "100-continue" expectation. This exception, the purpose of which is to minimize any client processing delays 1662 associated with an undeclared wait for 100 (Continue) status, applies only to HTTP/1.1 requests, and not to requests with 1663 any other HTTP-version value. 1664 </li> 1665 <li>An origin server <em class="bcp14">MAY</em> omit a 100 (Continue) response if it has already received some or all of the request body for the corresponding request. 1666 </li> 1667 <li>An origin server that sends a 100 (Continue) response <em class="bcp14">MUST</em> ultimately send a final status code, once the request body is received and processed, unless it terminates the transport connection 1668 prematurely. 1669 </li> 1670 <li>If an origin server receives a request that does not include an Expect request-header field with the "100-continue" expectation, 1671 the request includes a request body, and the server responds with a final status code before reading the entire request body 1672 from the transport connection, then the server <em class="bcp14">SHOULD NOT</em> close the transport connection until it has read the entire request, or until the client closes the connection. Otherwise, 1673 the client might not reliably receive the response message. However, this requirement is not be construed as preventing a 1674 server from defending itself against denial-of-service attacks, or from badly broken client implementations. 1675 </li> 1676 </ul> 1677 <p id="rfc.section.7.2.3.p.5">Requirements for HTTP/1.1 proxies: </p> 1678 <ul> 1679 <li>If a proxy receives a request that includes an Expect request-header field with the "100-continue" expectation, and the proxy 1680 either knows that the next-hop server complies with HTTP/1.1 or higher, or does not know the HTTP version of the next-hop 1681 server, it <em class="bcp14">MUST</em> forward the request, including the Expect header field. 1682 </li> 1683 <li>If the proxy knows that the version of the next-hop server is HTTP/1.0 or lower, it <em class="bcp14">MUST NOT</em> forward the request, and it <em class="bcp14">MUST</em> respond with a 417 (Expectation Failed) status. 1684 </li> 1685 <li>Proxies <em class="bcp14">SHOULD</em> maintain a cache recording the HTTP version numbers received from recently-referenced next-hop servers. 1686 </li> 1687 <li>A proxy <em class="bcp14">MUST NOT</em> forward a 100 (Continue) response if the request message was received from an HTTP/1.0 (or earlier) client and did not include 1688 an Expect request-header field with the "100-continue" expectation. This requirement overrides the general rule for forwarding 1689 of 1xx responses (see <a href="p2-semantics.html#status.1xx" title="Informational 1xx">Section 9.1</a> of <a href="#Part2" id="rfc.xref.Part2.16"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). 1690 </li> 1691 </ul> 1692 <h3 id="rfc.section.7.2.4"><a href="#rfc.section.7.2.4">7.2.4</a> <a id="connection.premature" href="#connection.premature">Client Behavior if Server Prematurely Closes Connection</a></h3> 1693 <p id="rfc.section.7.2.4.p.1">If an HTTP/1.1 client sends a request which includes a request body, but which does not include an Expect request-header field 1694 with the "100-continue" expectation, and if the client is not directly connected to an HTTP/1.1 origin server, and if the 1695 client sees the connection close before receiving any status from the server, the client <em class="bcp14">SHOULD</em> retry the request. If the client does retry this request, it <em class="bcp14">MAY</em> use the following "binary exponential backoff" algorithm to be assured of obtaining a reliable response: 1696 </p> 1697 <ol> 1698 <li>Initiate a new connection to the server</li> 1699 <li>Transmit the request-headers</li> 1700 <li>Initialize a variable R to the estimated round-trip time to the server (e.g., based on the time it took to establish the connection), 1701 or to a constant value of 5 seconds if the round-trip time is not available. 1702 </li> 1703 <li>Compute T = R * (2**N), where N is the number of previous retries of this request.</li> 1704 <li>Wait either for an error response from the server, or for T seconds (whichever comes first)</li> 1705 <li>If no error response is received, after T seconds transmit the body of the request.</li> 1706 <li>If client sees that the connection is closed prematurely, repeat from step 1 until the request is accepted, an error response 1707 is received, or the user becomes impatient and terminates the retry process. 1708 </li> 1709 </ol> 1710 <p id="rfc.section.7.2.4.p.2">If at any point an error status is received, the client </p> 1711 <ul> 1712 <li><em class="bcp14">SHOULD NOT</em> continue and 1713 </li> 1714 <li><em class="bcp14">SHOULD</em> close the connection if it has not completed sending the request message. 1715 </li> 1716 </ul> 1717 <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a> <a id="header.fields" href="#header.fields">Header Field Definitions</a></h1> 1718 <p id="rfc.section.8.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to message framing and transport protocols.</p> 1719 <p id="rfc.section.8.p.2">For entity-header fields, both sender and recipient refer to either the client or the server, depending on who sends and who 1720 receives the entity. 1721 </p> 1722 <div id="rfc.iref.c.6"></div> 1723 <div id="rfc.iref.h.1"></div> 1724 <h2 id="rfc.section.8.1"><a href="#rfc.section.8.1">8.1</a> <a id="header.connection" href="#header.connection">Connection</a></h2> 1725 <p id="rfc.section.8.1.p.1">The Connection general-header field allows the sender to specify options that are desired for that particular connection and <em class="bcp14">MUST NOT</em> be communicated by proxies over further connections. 1726 </p> 1727 <p id="rfc.section.8.1.p.2">The Connection header has the following grammar:</p> 1728 <div id="rfc.figure.u.45"></div><pre class="inline"><span id="rfc.iref.g.82"></span><span id="rfc.iref.g.83"></span> <a href="#header.connection" class="smpl">Connection</a> = "Connection" ":" 1#(<a href="#header.connection" class="smpl">connection-token</a>) 1609 </pre></div> 1610 </div> 1611 </div> 1612 <div id="connections"> 1613 <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a> <a href="#connections">Connections</a></h1> 1614 <div id="persistent.connections"> 1615 <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a> <a href="#persistent.connections">Persistent Connections</a></h2> 1616 <div id="persistent.purpose"> 1617 <h3 id="rfc.section.7.1.1"><a href="#rfc.section.7.1.1">7.1.1</a> <a href="#persistent.purpose">Purpose</a></h3> 1618 <p id="rfc.section.7.1.1.p.1">Prior to persistent connections, a separate TCP connection was established to fetch each URL, increasing the load on HTTP 1619 servers and causing congestion on the Internet. The use of inline images and other associated data often require a client 1620 to make multiple requests of the same server in a short amount of time. Analysis of these performance problems and results 1621 from a prototype implementation are available <a href="#Pad1995" id="rfc.xref.Pad1995.1"><cite title="Improving HTTP Latency">[Pad1995]</cite></a> <a href="#Spe" id="rfc.xref.Spe.1"><cite title="Analysis of HTTP Performance Problems">[Spe]</cite></a>. Implementation experience and measurements of actual HTTP/1.1 (<cite title="Hypertext Transfer Protocol -- HTTP/1.1" id="rfc.xref.RFC2068.2">RFC 2068</cite>) implementations show good results <a href="#Nie1997" id="rfc.xref.Nie1997.1"><cite title="Network Performance Effects of HTTP/1.1, CSS1, and PNG">[Nie1997]</cite></a>. Alternatives have also been explored, for example, T/TCP <a href="#Tou1998" id="rfc.xref.Tou1998.1"><cite title="Analysis of HTTP Performance">[Tou1998]</cite></a>. 1622 </p> 1623 <p id="rfc.section.7.1.1.p.2">Persistent HTTP connections have a number of advantages: </p> 1624 <ul> 1625 <li>By opening and closing fewer TCP connections, CPU time is saved in routers and hosts (clients, servers, proxies, gateways, 1626 tunnels, or caches), and memory used for TCP protocol control blocks can be saved in hosts. 1627 </li> 1628 <li>HTTP requests and responses can be pipelined on a connection. Pipelining allows a client to make multiple requests without 1629 waiting for each response, allowing a single TCP connection to be used much more efficiently, with much lower elapsed time. 1630 </li> 1631 <li>Network congestion is reduced by reducing the number of packets caused by TCP opens, and by allowing TCP sufficient time to 1632 determine the congestion state of the network. 1633 </li> 1634 <li>Latency on subsequent requests is reduced since there is no time spent in TCP's connection opening handshake.</li> 1635 <li>HTTP can evolve more gracefully, since errors can be reported without the penalty of closing the TCP connection. Clients using 1636 future versions of HTTP might optimistically try a new feature, but if communicating with an older server, retry with old 1637 semantics after an error is reported. 1638 </li> 1639 </ul> 1640 <p id="rfc.section.7.1.1.p.3">HTTP implementations <em class="bcp14">SHOULD</em> implement persistent connections. 1641 </p> 1642 </div> 1643 <div id="persistent.overall"> 1644 <h3 id="rfc.section.7.1.2"><a href="#rfc.section.7.1.2">7.1.2</a> <a href="#persistent.overall">Overall Operation</a></h3> 1645 <p id="rfc.section.7.1.2.p.1">A significant difference between HTTP/1.1 and earlier versions of HTTP is that persistent connections are the default behavior 1646 of any HTTP connection. That is, unless otherwise indicated, the client <em class="bcp14">SHOULD</em> assume that the server will maintain a persistent connection, even after error responses from the server. 1647 </p> 1648 <p id="rfc.section.7.1.2.p.2">Persistent connections provide a mechanism by which a client and a server can signal the close of a TCP connection. This signaling 1649 takes place using the Connection header field (<a href="#header.connection" id="rfc.xref.header.connection.2" title="Connection">Section 8.1</a>). Once a close has been signaled, the client <em class="bcp14">MUST NOT</em> send any more requests on that connection. 1650 </p> 1651 <div id="persistent.negotiation"> 1652 <h4 id="rfc.section.7.1.2.1"><a href="#rfc.section.7.1.2.1">7.1.2.1</a> <a href="#persistent.negotiation">Negotiation</a></h4> 1653 <p id="rfc.section.7.1.2.1.p.1">An HTTP/1.1 server <em class="bcp14">MAY</em> assume that a HTTP/1.1 client intends to maintain a persistent connection unless a Connection header including the connection-token 1654 "close" was sent in the request. If the server chooses to close the connection immediately after sending the response, it <em class="bcp14">SHOULD</em> send a Connection header including the connection-token close. 1655 </p> 1656 <p id="rfc.section.7.1.2.1.p.2">An HTTP/1.1 client <em class="bcp14">MAY</em> expect a connection to remain open, but would decide to keep it open based on whether the response from a server contains 1657 a Connection header with the connection-token close. In case the client does not want to maintain a connection for more than 1658 that request, it <em class="bcp14">SHOULD</em> send a Connection header including the connection-token close. 1659 </p> 1660 <p id="rfc.section.7.1.2.1.p.3">If either the client or the server sends the close token in the Connection header, that request becomes the last one for the 1661 connection. 1662 </p> 1663 <p id="rfc.section.7.1.2.1.p.4">Clients and servers <em class="bcp14">SHOULD NOT</em> assume that a persistent connection is maintained for HTTP versions less than 1.1 unless it is explicitly signaled. See <a href="#compatibility.with.http.1.0.persistent.connections" title="Compatibility with HTTP/1.0 Persistent Connections">Appendix D.2</a> for more information on backward compatibility with HTTP/1.0 clients. 1664 </p> 1665 <p id="rfc.section.7.1.2.1.p.5">In order to remain persistent, all messages on the connection <em class="bcp14">MUST</em> have a self-defined message length (i.e., one not defined by closure of the connection), as described in <a href="#message.length" title="Message Length">Section 4.4</a>. 1666 </p> 1667 </div> 1668 <div id="pipelining"> 1669 <h4 id="rfc.section.7.1.2.2"><a href="#rfc.section.7.1.2.2">7.1.2.2</a> <a href="#pipelining">Pipelining</a></h4> 1670 <p id="rfc.section.7.1.2.2.p.1">A client that supports persistent connections <em class="bcp14">MAY</em> "pipeline" its requests (i.e., send multiple requests without waiting for each response). A server <em class="bcp14">MUST</em> send its responses to those requests in the same order that the requests were received. 1671 </p> 1672 <p id="rfc.section.7.1.2.2.p.2">Clients which assume persistent connections and pipeline immediately after connection establishment <em class="bcp14">SHOULD</em> be prepared to retry their connection if the first pipelined attempt fails. If a client does such a retry, it <em class="bcp14">MUST NOT</em> pipeline before it knows the connection is persistent. Clients <em class="bcp14">MUST</em> also be prepared to resend their requests if the server closes the connection before sending all of the corresponding responses. 1673 </p> 1674 <p id="rfc.section.7.1.2.2.p.3">Clients <em class="bcp14">SHOULD NOT</em> pipeline requests using non-idempotent methods or non-idempotent sequences of methods (see <a href="p2-semantics.html#idempotent.methods" title="Idempotent Methods">Section 8.1.2</a> of <a href="#Part2" id="rfc.xref.Part2.11"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). Otherwise, a premature termination of the transport connection could lead to indeterminate results. A client wishing to 1675 send a non-idempotent request <em class="bcp14">SHOULD</em> wait to send that request until it has received the response status for the previous request. 1676 </p> 1677 </div> 1678 </div> 1679 <div id="persistent.proxy"> 1680 <h3 id="rfc.section.7.1.3"><a href="#rfc.section.7.1.3">7.1.3</a> <a href="#persistent.proxy">Proxy Servers</a></h3> 1681 <p id="rfc.section.7.1.3.p.1">It is especially important that proxies correctly implement the properties of the Connection header field as specified in <a href="#header.connection" id="rfc.xref.header.connection.3" title="Connection">Section 8.1</a>. 1682 </p> 1683 <p id="rfc.section.7.1.3.p.2">The proxy server <em class="bcp14">MUST</em> signal persistent connections separately with its clients and the origin servers (or other proxy servers) that it connects 1684 to. Each persistent connection applies to only one transport link. 1685 </p> 1686 <p id="rfc.section.7.1.3.p.3">A proxy server <em class="bcp14">MUST NOT</em> establish a HTTP/1.1 persistent connection with an HTTP/1.0 client (but see <a href="#RFC2068" id="rfc.xref.RFC2068.3"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a> for information and discussion of the problems with the Keep-Alive header implemented by many HTTP/1.0 clients). 1687 </p> 1688 </div> 1689 <div id="persistent.practical"> 1690 <h3 id="rfc.section.7.1.4"><a href="#rfc.section.7.1.4">7.1.4</a> <a href="#persistent.practical">Practical Considerations</a></h3> 1691 <p id="rfc.section.7.1.4.p.1">Servers will usually have some time-out value beyond which they will no longer maintain an inactive connection. Proxy servers 1692 might make this a higher value since it is likely that the client will be making more connections through the same server. 1693 The use of persistent connections places no requirements on the length (or existence) of this time-out for either the client 1694 or the server. 1695 </p> 1696 <p id="rfc.section.7.1.4.p.2">When a client or server wishes to time-out it <em class="bcp14">SHOULD</em> issue a graceful close on the transport connection. Clients and servers <em class="bcp14">SHOULD</em> both constantly watch for the other side of the transport close, and respond to it as appropriate. If a client or server does 1697 not detect the other side's close promptly it could cause unnecessary resource drain on the network. 1698 </p> 1699 <p id="rfc.section.7.1.4.p.3">A client, server, or proxy <em class="bcp14">MAY</em> close the transport connection at any time. For example, a client might have started to send a new request at the same time 1700 that the server has decided to close the "idle" connection. From the server's point of view, the connection is being closed 1701 while it was idle, but from the client's point of view, a request is in progress. 1702 </p> 1703 <p id="rfc.section.7.1.4.p.4">This means that clients, servers, and proxies <em class="bcp14">MUST</em> be able to recover from asynchronous close events. Client software <em class="bcp14">SHOULD</em> reopen the transport connection and retransmit the aborted sequence of requests without user interaction so long as the request 1704 sequence is idempotent (see <a href="p2-semantics.html#idempotent.methods" title="Idempotent Methods">Section 8.1.2</a> of <a href="#Part2" id="rfc.xref.Part2.12"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). Non-idempotent methods or sequences <em class="bcp14">MUST NOT</em> be automatically retried, although user agents <em class="bcp14">MAY</em> offer a human operator the choice of retrying the request(s). Confirmation by user-agent software with semantic understanding 1705 of the application <em class="bcp14">MAY</em> substitute for user confirmation. The automatic retry <em class="bcp14">SHOULD NOT</em> be repeated if the second sequence of requests fails. 1706 </p> 1707 <p id="rfc.section.7.1.4.p.5">Servers <em class="bcp14">SHOULD</em> always respond to at least one request per connection, if at all possible. Servers <em class="bcp14">SHOULD NOT</em> close a connection in the middle of transmitting a response, unless a network or client failure is suspected. 1708 </p> 1709 <p id="rfc.section.7.1.4.p.6">Clients that use persistent connections <em class="bcp14">SHOULD</em> limit the number of simultaneous connections that they maintain to a given server. A single-user client <em class="bcp14">SHOULD NOT</em> maintain more than 2 connections with any server or proxy. A proxy <em class="bcp14">SHOULD</em> use up to 2*N connections to another server or proxy, where N is the number of simultaneously active users. These guidelines 1710 are intended to improve HTTP response times and avoid congestion. 1711 </p> 1712 </div> 1713 </div> 1714 <div id="message.transmission.requirements"> 1715 <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a> <a href="#message.transmission.requirements">Message Transmission Requirements</a></h2> 1716 <div id="persistent.flow"> 1717 <h3 id="rfc.section.7.2.1"><a href="#rfc.section.7.2.1">7.2.1</a> <a href="#persistent.flow">Persistent Connections and Flow Control</a></h3> 1718 <p id="rfc.section.7.2.1.p.1">HTTP/1.1 servers <em class="bcp14">SHOULD</em> maintain persistent connections and use TCP's flow control mechanisms to resolve temporary overloads, rather than terminating 1719 connections with the expectation that clients will retry. The latter technique can exacerbate network congestion. 1720 </p> 1721 </div> 1722 <div id="persistent.monitor"> 1723 <h3 id="rfc.section.7.2.2"><a href="#rfc.section.7.2.2">7.2.2</a> <a href="#persistent.monitor">Monitoring Connections for Error Status Messages</a></h3> 1724 <p id="rfc.section.7.2.2.p.1">An HTTP/1.1 (or later) client sending a message-body <em class="bcp14">SHOULD</em> monitor the network connection for an error status while it is transmitting the request. If the client sees an error status, 1725 it <em class="bcp14">SHOULD</em> immediately cease transmitting the body. If the body is being sent using a "chunked" encoding (<a href="#transfer.codings" title="Transfer Codings">Section 3.4</a>), a zero length chunk and empty trailer <em class="bcp14">MAY</em> be used to prematurely mark the end of the message. If the body was preceded by a Content-Length header, the client <em class="bcp14">MUST</em> close the connection. 1726 </p> 1727 </div> 1728 <div id="use.of.the.100.status"> 1729 <h3 id="rfc.section.7.2.3"><a href="#rfc.section.7.2.3">7.2.3</a> <a href="#use.of.the.100.status">Use of the 100 (Continue) Status</a></h3> 1730 <p id="rfc.section.7.2.3.p.1">The purpose of the 100 (Continue) status (see <a href="p2-semantics.html#status.100" title="100 Continue">Section 9.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.13"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) is to allow a client that is sending a request message with a request body to determine if the origin server is willing 1731 to accept the request (based on the request headers) before the client sends the request body. In some cases, it might either 1732 be inappropriate or highly inefficient for the client to send the body if the server will reject the message without looking 1733 at the body. 1734 </p> 1735 <p id="rfc.section.7.2.3.p.2">Requirements for HTTP/1.1 clients: </p> 1736 <ul> 1737 <li>If a client will wait for a 100 (Continue) response before sending the request body, it <em class="bcp14">MUST</em> send an Expect request-header field (<a href="p2-semantics.html#header.expect" title="Expect">Section 10.2</a> of <a href="#Part2" id="rfc.xref.Part2.14"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) with the "100-continue" expectation. 1738 </li> 1739 <li>A client <em class="bcp14">MUST NOT</em> send an Expect request-header field (<a href="p2-semantics.html#header.expect" title="Expect">Section 10.2</a> of <a href="#Part2" id="rfc.xref.Part2.15"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) with the "100-continue" expectation if it does not intend to send a request body. 1740 </li> 1741 </ul> 1742 <p id="rfc.section.7.2.3.p.3">Because of the presence of older implementations, the protocol allows ambiguous situations in which a client may send "Expect: 1743 100-continue" without receiving either a 417 (Expectation Failed) status or a 100 (Continue) status. Therefore, when a client 1744 sends this header field to an origin server (possibly via a proxy) from which it has never seen a 100 (Continue) status, the 1745 client <em class="bcp14">SHOULD NOT</em> wait for an indefinite period before sending the request body. 1746 </p> 1747 <p id="rfc.section.7.2.3.p.4">Requirements for HTTP/1.1 origin servers: </p> 1748 <ul> 1749 <li>Upon receiving a request which includes an Expect request-header field with the "100-continue" expectation, an origin server <em class="bcp14">MUST</em> either respond with 100 (Continue) status and continue to read from the input stream, or respond with a final status code. 1750 The origin server <em class="bcp14">MUST NOT</em> wait for the request body before sending the 100 (Continue) response. If it responds with a final status code, it <em class="bcp14">MAY</em> close the transport connection or it <em class="bcp14">MAY</em> continue to read and discard the rest of the request. It <em class="bcp14">MUST NOT</em> perform the requested method if it returns a final status code. 1751 </li> 1752 <li>An origin server <em class="bcp14">SHOULD NOT</em> send a 100 (Continue) response if the request message does not include an Expect request-header field with the "100-continue" 1753 expectation, and <em class="bcp14">MUST NOT</em> send a 100 (Continue) response if such a request comes from an HTTP/1.0 (or earlier) client. There is an exception to this 1754 rule: for compatibility with <a href="#RFC2068" id="rfc.xref.RFC2068.4"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, a server <em class="bcp14">MAY</em> send a 100 (Continue) status in response to an HTTP/1.1 PUT or POST request that does not include an Expect request-header 1755 field with the "100-continue" expectation. This exception, the purpose of which is to minimize any client processing delays 1756 associated with an undeclared wait for 100 (Continue) status, applies only to HTTP/1.1 requests, and not to requests with 1757 any other HTTP-version value. 1758 </li> 1759 <li>An origin server <em class="bcp14">MAY</em> omit a 100 (Continue) response if it has already received some or all of the request body for the corresponding request. 1760 </li> 1761 <li>An origin server that sends a 100 (Continue) response <em class="bcp14">MUST</em> ultimately send a final status code, once the request body is received and processed, unless it terminates the transport connection 1762 prematurely. 1763 </li> 1764 <li>If an origin server receives a request that does not include an Expect request-header field with the "100-continue" expectation, 1765 the request includes a request body, and the server responds with a final status code before reading the entire request body 1766 from the transport connection, then the server <em class="bcp14">SHOULD NOT</em> close the transport connection until it has read the entire request, or until the client closes the connection. Otherwise, 1767 the client might not reliably receive the response message. However, this requirement is not be construed as preventing a 1768 server from defending itself against denial-of-service attacks, or from badly broken client implementations. 1769 </li> 1770 </ul> 1771 <p id="rfc.section.7.2.3.p.5">Requirements for HTTP/1.1 proxies: </p> 1772 <ul> 1773 <li>If a proxy receives a request that includes an Expect request-header field with the "100-continue" expectation, and the proxy 1774 either knows that the next-hop server complies with HTTP/1.1 or higher, or does not know the HTTP version of the next-hop 1775 server, it <em class="bcp14">MUST</em> forward the request, including the Expect header field. 1776 </li> 1777 <li>If the proxy knows that the version of the next-hop server is HTTP/1.0 or lower, it <em class="bcp14">MUST NOT</em> forward the request, and it <em class="bcp14">MUST</em> respond with a 417 (Expectation Failed) status. 1778 </li> 1779 <li>Proxies <em class="bcp14">SHOULD</em> maintain a cache recording the HTTP version numbers received from recently-referenced next-hop servers. 1780 </li> 1781 <li>A proxy <em class="bcp14">MUST NOT</em> forward a 100 (Continue) response if the request message was received from an HTTP/1.0 (or earlier) client and did not include 1782 an Expect request-header field with the "100-continue" expectation. This requirement overrides the general rule for forwarding 1783 of 1xx responses (see <a href="p2-semantics.html#status.1xx" title="Informational 1xx">Section 9.1</a> of <a href="#Part2" id="rfc.xref.Part2.16"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). 1784 </li> 1785 </ul> 1786 </div> 1787 <div id="connection.premature"> 1788 <h3 id="rfc.section.7.2.4"><a href="#rfc.section.7.2.4">7.2.4</a> <a href="#connection.premature">Client Behavior if Server Prematurely Closes Connection</a></h3> 1789 <p id="rfc.section.7.2.4.p.1">If an HTTP/1.1 client sends a request which includes a request body, but which does not include an Expect request-header field 1790 with the "100-continue" expectation, and if the client is not directly connected to an HTTP/1.1 origin server, and if the 1791 client sees the connection close before receiving any status from the server, the client <em class="bcp14">SHOULD</em> retry the request. If the client does retry this request, it <em class="bcp14">MAY</em> use the following "binary exponential backoff" algorithm to be assured of obtaining a reliable response: 1792 </p> 1793 <ol> 1794 <li>Initiate a new connection to the server</li> 1795 <li>Transmit the request-headers</li> 1796 <li>Initialize a variable R to the estimated round-trip time to the server (e.g., based on the time it took to establish the connection), 1797 or to a constant value of 5 seconds if the round-trip time is not available. 1798 </li> 1799 <li>Compute T = R * (2**N), where N is the number of previous retries of this request.</li> 1800 <li>Wait either for an error response from the server, or for T seconds (whichever comes first)</li> 1801 <li>If no error response is received, after T seconds transmit the body of the request.</li> 1802 <li>If client sees that the connection is closed prematurely, repeat from step 1 until the request is accepted, an error response 1803 is received, or the user becomes impatient and terminates the retry process. 1804 </li> 1805 </ol> 1806 <p id="rfc.section.7.2.4.p.2">If at any point an error status is received, the client </p> 1807 <ul> 1808 <li><em class="bcp14">SHOULD NOT</em> continue and 1809 </li> 1810 <li><em class="bcp14">SHOULD</em> close the connection if it has not completed sending the request message. 1811 </li> 1812 </ul> 1813 </div> 1814 </div> 1815 </div> 1816 <div id="header.fields"> 1817 <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a> <a href="#header.fields">Header Field Definitions</a></h1> 1818 <p id="rfc.section.8.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to message framing and transport protocols.</p> 1819 <p id="rfc.section.8.p.2">For entity-header fields, both sender and recipient refer to either the client or the server, depending on who sends and who 1820 receives the entity. 1821 </p> 1822 <div id="header.connection"> 1823 <div id="rfc.iref.c.6"></div> 1824 <div id="rfc.iref.h.1"></div> 1825 <h2 id="rfc.section.8.1"><a href="#rfc.section.8.1">8.1</a> <a href="#header.connection">Connection</a></h2> 1826 <p id="rfc.section.8.1.p.1">The Connection general-header field allows the sender to specify options that are desired for that particular connection and <em class="bcp14">MUST NOT</em> be communicated by proxies over further connections. 1827 </p> 1828 <p id="rfc.section.8.1.p.2">The Connection header has the following grammar:</p> 1829 <div id="rfc.figure.u.45"></div><pre class="inline"><span id="rfc.iref.g.82"></span><span id="rfc.iref.g.83"></span> <a href="#header.connection" class="smpl">Connection</a> = "Connection" ":" 1#(<a href="#header.connection" class="smpl">connection-token</a>) 1729 1830 <a href="#header.connection" class="smpl">connection-token</a> = <a href="#rule.token.separators" class="smpl">token</a> 1730 1831 </pre><p id="rfc.section.8.1.p.4">HTTP/1.1 proxies <em class="bcp14">MUST</em> parse the Connection header field before a message is forwarded and, for each connection-token in this field, remove any header 1731 field(s) from the message with the same name as the connection-token. Connection options are signaled by the presence of a1732 connection-token in the Connection header field, not by any corresponding additional header field(s), since the additional1733 header field may not be sent if there are no parameters associated with that connection option.1734 </p>1735 <p id="rfc.section.8.1.p.5">Message headers listed in the Connection header <em class="bcp14">MUST NOT</em> include end-to-end headers, such as Cache-Control.1736 </p>1737 <p id="rfc.section.8.1.p.6">HTTP/1.1 defines the "close" connection option for the sender to signal that the connection will be closed after completion1738 of the response. For example,1739 </p>1740 <div id="rfc.figure.u.46"></div><pre class="text"> Connection: close1832 field(s) from the message with the same name as the connection-token. Connection options are signaled by the presence of a 1833 connection-token in the Connection header field, not by any corresponding additional header field(s), since the additional 1834 header field may not be sent if there are no parameters associated with that connection option. 1835 </p> 1836 <p id="rfc.section.8.1.p.5">Message headers listed in the Connection header <em class="bcp14">MUST NOT</em> include end-to-end headers, such as Cache-Control. 1837 </p> 1838 <p id="rfc.section.8.1.p.6">HTTP/1.1 defines the "close" connection option for the sender to signal that the connection will be closed after completion 1839 of the response. For example, 1840 </p> 1841 <div id="rfc.figure.u.46"></div><pre class="text"> Connection: close 1741 1842 </pre><p id="rfc.section.8.1.p.8">in either the request or the response header fields indicates that the connection <em class="bcp14">SHOULD NOT</em> be considered `persistent' (<a href="#persistent.connections" title="Persistent Connections">Section 7.1</a>) after the current request/response is complete. 1742 </p> 1743 <p id="rfc.section.8.1.p.9">An HTTP/1.1 client that does not support persistent connections <em class="bcp14">MUST</em> include the "close" connection option in every request message. 1744 </p> 1745 <p id="rfc.section.8.1.p.10">An HTTP/1.1 server that does not support persistent connections <em class="bcp14">MUST</em> include the "close" connection option in every response message that does not have a 1xx (informational) status code. 1746 </p> 1747 <p id="rfc.section.8.1.p.11">A system receiving an HTTP/1.0 (or lower-version) message that includes a Connection header <em class="bcp14">MUST</em>, for each connection-token in this field, remove and ignore any header field(s) from the message with the same name as the 1748 connection-token. This protects against mistaken forwarding of such header fields by pre-HTTP/1.1 proxies. See <a href="#compatibility.with.http.1.0.persistent.connections" title="Compatibility with HTTP/1.0 Persistent Connections">Appendix D.2</a>. 1749 </p> 1750 <div id="rfc.iref.c.7"></div> 1751 <div id="rfc.iref.h.2"></div> 1752 <h2 id="rfc.section.8.2"><a href="#rfc.section.8.2">8.2</a> <a id="header.content-length" href="#header.content-length">Content-Length</a></h2> 1753 <p id="rfc.section.8.2.p.1">The Content-Length entity-header field indicates the size of the entity-body, in decimal number of OCTETs, sent to the recipient 1754 or, in the case of the HEAD method, the size of the entity-body that would have been sent had the request been a GET. 1755 </p> 1756 <div id="rfc.figure.u.47"></div><pre class="inline"><span id="rfc.iref.g.84"></span> <a href="#header.content-length" class="smpl">Content-Length</a> = "Content-Length" ":" 1*<a href="#core.rules" class="smpl">DIGIT</a> 1843 </p> 1844 <p id="rfc.section.8.1.p.9">An HTTP/1.1 client that does not support persistent connections <em class="bcp14">MUST</em> include the "close" connection option in every request message. 1845 </p> 1846 <p id="rfc.section.8.1.p.10">An HTTP/1.1 server that does not support persistent connections <em class="bcp14">MUST</em> include the "close" connection option in every response message that does not have a 1xx (informational) status code. 1847 </p> 1848 <p id="rfc.section.8.1.p.11">A system receiving an HTTP/1.0 (or lower-version) message that includes a Connection header <em class="bcp14">MUST</em>, for each connection-token in this field, remove and ignore any header field(s) from the message with the same name as the 1849 connection-token. This protects against mistaken forwarding of such header fields by pre-HTTP/1.1 proxies. See <a href="#compatibility.with.http.1.0.persistent.connections" title="Compatibility with HTTP/1.0 Persistent Connections">Appendix D.2</a>. 1850 </p> 1851 </div> 1852 <div id="header.content-length"> 1853 <div id="rfc.iref.c.7"></div> 1854 <div id="rfc.iref.h.2"></div> 1855 <h2 id="rfc.section.8.2"><a href="#rfc.section.8.2">8.2</a> <a href="#header.content-length">Content-Length</a></h2> 1856 <p id="rfc.section.8.2.p.1">The Content-Length entity-header field indicates the size of the entity-body, in decimal number of OCTETs, sent to the recipient 1857 or, in the case of the HEAD method, the size of the entity-body that would have been sent had the request been a GET. 1858 </p> 1859 <div id="rfc.figure.u.47"></div><pre class="inline"><span id="rfc.iref.g.84"></span> <a href="#header.content-length" class="smpl">Content-Length</a> = "Content-Length" ":" 1*<a href="#core.rules" class="smpl">DIGIT</a> 1757 1860 </pre><p id="rfc.section.8.2.p.3">An example is</p> 1758 <div id="rfc.figure.u.48"></div><pre class="text"> Content-Length: 34951861 <div id="rfc.figure.u.48"></div><pre class="text"> Content-Length: 3495 1759 1862 </pre><p id="rfc.section.8.2.p.5">Applications <em class="bcp14">SHOULD</em> use this field to indicate the transfer-length of the message-body, unless this is prohibited by the rules in <a href="#message.length" title="Message Length">Section 4.4</a>. 1760 </p> 1761 <p id="rfc.section.8.2.p.6">Any Content-Length greater than or equal to zero is a valid value. <a href="#message.length" title="Message Length">Section 4.4</a> describes how to determine the length of a message-body if a Content-Length is not given. 1762 </p> 1763 <p id="rfc.section.8.2.p.7">Note that the meaning of this field is significantly different from the corresponding definition in MIME, where it is an optional 1764 field used within the "message/external-body" content-type. In HTTP, it <em class="bcp14">SHOULD</em> be sent whenever the message's length can be determined prior to being transferred, unless this is prohibited by the rules 1765 in <a href="#message.length" title="Message Length">Section 4.4</a>. 1766 </p> 1767 <div id="rfc.iref.d.2"></div> 1768 <div id="rfc.iref.h.3"></div> 1769 <h2 id="rfc.section.8.3"><a href="#rfc.section.8.3">8.3</a> <a id="header.date" href="#header.date">Date</a></h2> 1770 <p id="rfc.section.8.3.p.1">The Date general-header field represents the date and time at which the message was originated, having the same semantics 1771 as orig-date in <a href="http://tools.ietf.org/html/rfc2822#section-3.6.1">Section 3.6.1</a> of <a href="#RFC2822" id="rfc.xref.RFC2822.4"><cite title="Internet Message Format">[RFC2822]</cite></a>. The field value is an HTTP-date, as described in <a href="#full.date" title="Full Date">Section 3.3.1</a>; it <em class="bcp14">MUST</em> be sent in rfc1123-date format. 1772 </p> 1773 <div id="rfc.figure.u.49"></div><pre class="inline"><span id="rfc.iref.g.85"></span> <a href="#header.date" class="smpl">Date</a> = "Date" ":" <a href="#full.date" class="smpl">HTTP-date</a> 1863 </p> 1864 <p id="rfc.section.8.2.p.6">Any Content-Length greater than or equal to zero is a valid value. <a href="#message.length" title="Message Length">Section 4.4</a> describes how to determine the length of a message-body if a Content-Length is not given. 1865 </p> 1866 <p id="rfc.section.8.2.p.7">Note that the meaning of this field is significantly different from the corresponding definition in MIME, where it is an optional 1867 field used within the "message/external-body" content-type. In HTTP, it <em class="bcp14">SHOULD</em> be sent whenever the message's length can be determined prior to being transferred, unless this is prohibited by the rules 1868 in <a href="#message.length" title="Message Length">Section 4.4</a>. 1869 </p> 1870 </div> 1871 <div id="header.date"> 1872 <div id="rfc.iref.d.2"></div> 1873 <div id="rfc.iref.h.3"></div> 1874 <h2 id="rfc.section.8.3"><a href="#rfc.section.8.3">8.3</a> <a href="#header.date">Date</a></h2> 1875 <p id="rfc.section.8.3.p.1">The Date general-header field represents the date and time at which the message was originated, having the same semantics 1876 as orig-date in <a href="https://tools.ietf.org/html/rfc2822#section-3.6.1">Section 3.6.1</a> of <a href="#RFC2822" id="rfc.xref.RFC2822.4"><cite title="Internet Message Format">[RFC2822]</cite></a>. The field value is an HTTP-date, as described in <a href="#full.date" title="Full Date">Section 3.3.1</a>; it <em class="bcp14">MUST</em> be sent in rfc1123-date format. 1877 </p> 1878 <div id="rfc.figure.u.49"></div><pre class="inline"><span id="rfc.iref.g.85"></span> <a href="#header.date" class="smpl">Date</a> = "Date" ":" <a href="#full.date" class="smpl">HTTP-date</a> 1774 1879 </pre><p id="rfc.section.8.3.p.3">An example is</p> 1775 <div id="rfc.figure.u.50"></div><pre class="text"> Date: Tue, 15 Nov 1994 08:12:31 GMT1880 <div id="rfc.figure.u.50"></div><pre class="text"> Date: Tue, 15 Nov 1994 08:12:31 GMT 1776 1881 </pre><p id="rfc.section.8.3.p.5">Origin servers <em class="bcp14">MUST</em> include a Date header field in all responses, except in these cases: 1777 </p> 1778 <ol> 1779 <li>If the response status code is 100 (Continue) or 101 (Switching Protocols), the response <em class="bcp14">MAY</em> include a Date header field, at the server's option. 1780 </li> 1781 <li>If the response status code conveys a server error, e.g. 500 (Internal Server Error) or 503 (Service Unavailable), and it 1782 is inconvenient or impossible to generate a valid Date. 1783 </li> 1784 <li>If the server does not have a clock that can provide a reasonable approximation of the current time, its responses <em class="bcp14">MUST NOT</em> include a Date header field. In this case, the rules in <a href="#clockless.origin.server.operation" title="Clockless Origin Server Operation">Section 8.3.1</a> <em class="bcp14">MUST</em> be followed. 1785 </li> 1786 </ol> 1787 <p id="rfc.section.8.3.p.6">A received message that does not have a Date header field <em class="bcp14">MUST</em> be assigned one by the recipient if the message will be cached by that recipient or gatewayed via a protocol which requires 1788 a Date. An HTTP implementation without a clock <em class="bcp14">MUST NOT</em> cache responses without revalidating them on every use. An HTTP cache, especially a shared cache, <em class="bcp14">SHOULD</em> use a mechanism, such as NTP <a href="#RFC1305" id="rfc.xref.RFC1305.1"><cite title="Network Time Protocol (Version 3) Specification, Implementation">[RFC1305]</cite></a>, to synchronize its clock with a reliable external standard. 1789 </p> 1790 <p id="rfc.section.8.3.p.7">Clients <em class="bcp14">SHOULD</em> only send a Date header field in messages that include an entity-body, as in the case of the PUT and POST requests, and even 1791 then it is optional. A client without a clock <em class="bcp14">MUST NOT</em> send a Date header field in a request. 1792 </p> 1793 <p id="rfc.section.8.3.p.8">The HTTP-date sent in a Date header <em class="bcp14">SHOULD NOT</em> represent a date and time subsequent to the generation of the message. It <em class="bcp14">SHOULD</em> represent the best available approximation of the date and time of message generation, unless the implementation has no means 1794 of generating a reasonably accurate date and time. In theory, the date ought to represent the moment just before the entity 1795 is generated. In practice, the date can be generated at any time during the message origination without affecting its semantic 1796 value. 1797 </p> 1798 <h3 id="rfc.section.8.3.1"><a href="#rfc.section.8.3.1">8.3.1</a> <a id="clockless.origin.server.operation" href="#clockless.origin.server.operation">Clockless Origin Server Operation</a></h3> 1799 <p id="rfc.section.8.3.1.p.1">Some origin server implementations might not have a clock available. An origin server without a clock <em class="bcp14">MUST NOT</em> assign Expires or Last-Modified values to a response, unless these values were associated with the resource by a system or 1800 user with a reliable clock. It <em class="bcp14">MAY</em> assign an Expires value that is known, at or before server configuration time, to be in the past (this allows "pre-expiration" 1801 of responses without storing separate Expires values for each resource). 1802 </p> 1803 <div id="rfc.iref.h.4"></div> 1804 <div id="rfc.iref.h.5"></div> 1805 <h2 id="rfc.section.8.4"><a href="#rfc.section.8.4">8.4</a> <a id="header.host" href="#header.host">Host</a></h2> 1806 <p id="rfc.section.8.4.p.1">The Host request-header field specifies the Internet host and port number of the resource being requested, as obtained from 1807 the original URI given by the user or referring resource (generally an HTTP URL, as described in <a href="#http.url" title="http URL">Section 3.2.2</a>). The Host field value <em class="bcp14">MUST</em> represent the naming authority of the origin server or gateway given by the original URL. This allows the origin server or 1808 gateway to differentiate between internally-ambiguous URLs, such as the root "/" URL of a server for multiple host names on 1809 a single IP address. 1810 </p> 1811 <div id="rfc.figure.u.51"></div><pre class="inline"><span id="rfc.iref.g.86"></span> <a href="#header.host" class="smpl">Host</a> = "Host" ":" <a href="#general.syntax" class="smpl">uri-host</a> [ ":" <a href="#general.syntax" class="smpl">port</a> ] ; <a href="#http.url" title="http URL">Section 3.2.2</a> 1882 </p> 1883 <ol> 1884 <li>If the response status code is 100 (Continue) or 101 (Switching Protocols), the response <em class="bcp14">MAY</em> include a Date header field, at the server's option. 1885 </li> 1886 <li>If the response status code conveys a server error, e.g. 500 (Internal Server Error) or 503 (Service Unavailable), and it 1887 is inconvenient or impossible to generate a valid Date. 1888 </li> 1889 <li>If the server does not have a clock that can provide a reasonable approximation of the current time, its responses <em class="bcp14">MUST NOT</em> include a Date header field. In this case, the rules in <a href="#clockless.origin.server.operation" title="Clockless Origin Server Operation">Section 8.3.1</a> <em class="bcp14">MUST</em> be followed. 1890 </li> 1891 </ol> 1892 <p id="rfc.section.8.3.p.6">A received message that does not have a Date header field <em class="bcp14">MUST</em> be assigned one by the recipient if the message will be cached by that recipient or gatewayed via a protocol which requires 1893 a Date. An HTTP implementation without a clock <em class="bcp14">MUST NOT</em> cache responses without revalidating them on every use. An HTTP cache, especially a shared cache, <em class="bcp14">SHOULD</em> use a mechanism, such as NTP <a href="#RFC1305" id="rfc.xref.RFC1305.1"><cite title="Network Time Protocol (Version 3) Specification, Implementation">[RFC1305]</cite></a>, to synchronize its clock with a reliable external standard. 1894 </p> 1895 <p id="rfc.section.8.3.p.7">Clients <em class="bcp14">SHOULD</em> only send a Date header field in messages that include an entity-body, as in the case of the PUT and POST requests, and even 1896 then it is optional. A client without a clock <em class="bcp14">MUST NOT</em> send a Date header field in a request. 1897 </p> 1898 <p id="rfc.section.8.3.p.8">The HTTP-date sent in a Date header <em class="bcp14">SHOULD NOT</em> represent a date and time subsequent to the generation of the message. It <em class="bcp14">SHOULD</em> represent the best available approximation of the date and time of message generation, unless the implementation has no means 1899 of generating a reasonably accurate date and time. In theory, the date ought to represent the moment just before the entity 1900 is generated. In practice, the date can be generated at any time during the message origination without affecting its semantic 1901 value. 1902 </p> 1903 <div id="clockless.origin.server.operation"> 1904 <h3 id="rfc.section.8.3.1"><a href="#rfc.section.8.3.1">8.3.1</a> <a href="#clockless.origin.server.operation">Clockless Origin Server Operation</a></h3> 1905 <p id="rfc.section.8.3.1.p.1">Some origin server implementations might not have a clock available. An origin server without a clock <em class="bcp14">MUST NOT</em> assign Expires or Last-Modified values to a response, unless these values were associated with the resource by a system or 1906 user with a reliable clock. It <em class="bcp14">MAY</em> assign an Expires value that is known, at or before server configuration time, to be in the past (this allows "pre-expiration" 1907 of responses without storing separate Expires values for each resource). 1908 </p> 1909 </div> 1910 </div> 1911 <div id="header.host"> 1912 <div id="rfc.iref.h.4"></div> 1913 <div id="rfc.iref.h.5"></div> 1914 <h2 id="rfc.section.8.4"><a href="#rfc.section.8.4">8.4</a> <a href="#header.host">Host</a></h2> 1915 <p id="rfc.section.8.4.p.1">The Host request-header field specifies the Internet host and port number of the resource being requested, as obtained from 1916 the original URI given by the user or referring resource (generally an HTTP URL, as described in <a href="#http.url" title="http URL">Section 3.2.2</a>). The Host field value <em class="bcp14">MUST</em> represent the naming authority of the origin server or gateway given by the original URL. This allows the origin server or 1917 gateway to differentiate between internally-ambiguous URLs, such as the root "/" URL of a server for multiple host names on 1918 a single IP address. 1919 </p> 1920 <div id="rfc.figure.u.51"></div><pre class="inline"><span id="rfc.iref.g.86"></span> <a href="#header.host" class="smpl">Host</a> = "Host" ":" <a href="#general.syntax" class="smpl">uri-host</a> [ ":" <a href="#general.syntax" class="smpl">port</a> ] ; <a href="#http.url" title="http URL">Section 3.2.2</a> 1812 1921 </pre><p id="rfc.section.8.4.p.3">A "host" without any trailing port information implies the default port for the service requested (e.g., "80" for an HTTP 1813 URL). For example, a request on the origin server for <http://www.example.org/pub/WWW/> would properly include:1814 </p>1815 <div id="rfc.figure.u.52"></div><pre class="text"> GET /pub/WWW/ HTTP/1.11922 URL). For example, a request on the origin server for <http://www.example.org/pub/WWW/> would properly include: 1923 </p> 1924 <div id="rfc.figure.u.52"></div><pre class="text"> GET /pub/WWW/ HTTP/1.1 1816 1925 Host: www.example.org 1817 1926 </pre><p id="rfc.section.8.4.p.5">A client <em class="bcp14">MUST</em> include a Host header field in all HTTP/1.1 request messages. If the requested URI does not include an Internet host name 1818 for the service being requested, then the Host header field <em class="bcp14">MUST</em> be given with an empty value. An HTTP/1.1 proxy <em class="bcp14">MUST</em> ensure that any request message it forwards does contain an appropriate Host header field that identifies the service being 1819 requested by the proxy. All Internet-based HTTP/1.1 servers <em class="bcp14">MUST</em> respond with a 400 (Bad Request) status code to any HTTP/1.1 request message which lacks a Host header field. 1820 </p> 1821 <p id="rfc.section.8.4.p.6">See Sections <a href="#the.resource.identified.by.a.request" title="The Resource Identified by a Request">5.2</a> and <a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses">D.1.1</a> for other requirements relating to Host. 1822 </p> 1823 <div id="rfc.iref.t.2"></div> 1824 <div id="rfc.iref.h.6"></div> 1825 <h2 id="rfc.section.8.5"><a href="#rfc.section.8.5">8.5</a> <a id="header.te" href="#header.te">TE</a></h2> 1826 <p id="rfc.section.8.5.p.1">The TE request-header field indicates what extension transfer-codings it is willing to accept in the response and whether 1827 or not it is willing to accept trailer fields in a chunked transfer-coding. Its value may consist of the keyword "trailers" 1828 and/or a comma-separated list of extension transfer-coding names with optional accept parameters (as described in <a href="#transfer.codings" title="Transfer Codings">Section 3.4</a>). 1829 </p> 1830 <div id="rfc.figure.u.53"></div><pre class="inline"><span id="rfc.iref.g.87"></span><span id="rfc.iref.g.88"></span> <a href="#header.te" class="smpl">TE</a> = "TE" ":" #( <a href="#header.te" class="smpl">t-codings</a> ) 1927 for the service being requested, then the Host header field <em class="bcp14">MUST</em> be given with an empty value. An HTTP/1.1 proxy <em class="bcp14">MUST</em> ensure that any request message it forwards does contain an appropriate Host header field that identifies the service being 1928 requested by the proxy. All Internet-based HTTP/1.1 servers <em class="bcp14">MUST</em> respond with a 400 (Bad Request) status code to any HTTP/1.1 request message which lacks a Host header field. 1929 </p> 1930 <p id="rfc.section.8.4.p.6">See Sections <a href="#the.resource.identified.by.a.request" title="The Resource Identified by a Request">5.2</a> and <a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses">D.1.1</a> for other requirements relating to Host. 1931 </p> 1932 </div> 1933 <div id="header.te"> 1934 <div id="rfc.iref.t.2"></div> 1935 <div id="rfc.iref.h.6"></div> 1936 <h2 id="rfc.section.8.5"><a href="#rfc.section.8.5">8.5</a> <a href="#header.te">TE</a></h2> 1937 <p id="rfc.section.8.5.p.1">The TE request-header field indicates what extension transfer-codings it is willing to accept in the response and whether 1938 or not it is willing to accept trailer fields in a chunked transfer-coding. Its value may consist of the keyword "trailers" 1939 and/or a comma-separated list of extension transfer-coding names with optional accept parameters (as described in <a href="#transfer.codings" title="Transfer Codings">Section 3.4</a>). 1940 </p> 1941 <div id="rfc.figure.u.53"></div><pre class="inline"><span id="rfc.iref.g.87"></span><span id="rfc.iref.g.88"></span> <a href="#header.te" class="smpl">TE</a> = "TE" ":" #( <a href="#header.te" class="smpl">t-codings</a> ) 1831 1942 <a href="#header.te" class="smpl">t-codings</a> = "trailers" | ( <a href="#transfer.codings" class="smpl">transfer-extension</a> [ <a href="#abnf.dependencies" class="smpl">accept-params</a> ] ) 1832 1943 </pre><p id="rfc.section.8.5.p.3">The presence of the keyword "trailers" indicates that the client is willing to accept trailer fields in a chunked transfer-coding, 1833 as defined in <a href="#chunked.transfer.encoding" title="Chunked Transfer Coding">Section 3.4.1</a>. This keyword is reserved for use with transfer-coding values even though it does not itself represent a transfer-coding.1834 </p>1835 <p id="rfc.section.8.5.p.4">Examples of its use are:</p>1836 <div id="rfc.figure.u.54"></div><pre class="text"> TE: deflate1944 as defined in <a href="#chunked.transfer.encoding" title="Chunked Transfer Coding">Section 3.4.1</a>. This keyword is reserved for use with transfer-coding values even though it does not itself represent a transfer-coding. 1945 </p> 1946 <p id="rfc.section.8.5.p.4">Examples of its use are:</p> 1947 <div id="rfc.figure.u.54"></div><pre class="text"> TE: deflate 1837 1948 TE: 1838 1949 TE: trailers, deflate;q=0.5 1839 1950 </pre><p id="rfc.section.8.5.p.6">The TE header field only applies to the immediate connection. Therefore, the keyword <em class="bcp14">MUST</em> be supplied within a Connection header field (<a href="#header.connection" id="rfc.xref.header.connection.4" title="Connection">Section 8.1</a>) whenever TE is present in an HTTP/1.1 message. 1840 </p> 1841 <p id="rfc.section.8.5.p.7">A server tests whether a transfer-coding is acceptable, according to a TE field, using these rules: </p> 1842 <ol> 1843 <li> 1844 <p>The "chunked" transfer-coding is always acceptable. If the keyword "trailers" is listed, the client indicates that it is willing 1845 to accept trailer fields in the chunked response on behalf of itself and any downstream clients. The implication is that, 1846 if given, the client is stating that either all downstream clients are willing to accept trailer fields in the forwarded response, 1847 or that it will attempt to buffer the response on behalf of downstream recipients. 1848 </p> 1849 <p> <b>Note:</b> HTTP/1.1 does not define any means to limit the size of a chunked response such that a client can be assured of buffering 1850 the entire response. 1851 </p> 1852 </li> 1853 <li> 1854 <p>If the transfer-coding being tested is one of the transfer-codings listed in the TE field, then it is acceptable unless it 1855 is accompanied by a qvalue of 0. (As defined in <a href="p3-payload.html#quality.values" title="Quality Values">Section 3.4</a> of <a href="#Part3" id="rfc.xref.Part3.14"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>, a qvalue of 0 means "not acceptable.") 1856 </p> 1857 </li> 1858 <li> 1859 <p>If multiple transfer-codings are acceptable, then the acceptable transfer-coding with the highest non-zero qvalue is preferred. 1860 The "chunked" transfer-coding always has a qvalue of 1. 1861 </p> 1862 </li> 1863 </ol> 1864 <p id="rfc.section.8.5.p.8">If the TE field-value is empty or if no TE field is present, the only transfer-coding is "chunked". A message with no transfer-coding 1865 is always acceptable. 1866 </p> 1867 <div id="rfc.iref.t.3"></div> 1868 <div id="rfc.iref.h.7"></div> 1869 <h2 id="rfc.section.8.6"><a href="#rfc.section.8.6">8.6</a> <a id="header.trailer" href="#header.trailer">Trailer</a></h2> 1870 <p id="rfc.section.8.6.p.1">The Trailer general field value indicates that the given set of header fields is present in the trailer of a message encoded 1871 with chunked transfer-coding. 1872 </p> 1873 <div id="rfc.figure.u.55"></div><pre class="inline"><span id="rfc.iref.g.89"></span> <a href="#header.trailer" class="smpl">Trailer</a> = "Trailer" ":" 1#<a href="#message.headers" class="smpl">field-name</a> 1951 </p> 1952 <p id="rfc.section.8.5.p.7">A server tests whether a transfer-coding is acceptable, according to a TE field, using these rules: </p> 1953 <ol> 1954 <li> 1955 <p>The "chunked" transfer-coding is always acceptable. If the keyword "trailers" is listed, the client indicates that it is willing 1956 to accept trailer fields in the chunked response on behalf of itself and any downstream clients. The implication is that, 1957 if given, the client is stating that either all downstream clients are willing to accept trailer fields in the forwarded response, 1958 or that it will attempt to buffer the response on behalf of downstream recipients. 1959 </p> 1960 <p><b>Note:</b> HTTP/1.1 does not define any means to limit the size of a chunked response such that a client can be assured of buffering 1961 the entire response. 1962 </p> 1963 </li> 1964 <li> 1965 <p>If the transfer-coding being tested is one of the transfer-codings listed in the TE field, then it is acceptable unless it 1966 is accompanied by a qvalue of 0. (As defined in <a href="p3-payload.html#quality.values" title="Quality Values">Section 3.4</a> of <a href="#Part3" id="rfc.xref.Part3.14"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>, a qvalue of 0 means "not acceptable.") 1967 </p> 1968 </li> 1969 <li> 1970 <p>If multiple transfer-codings are acceptable, then the acceptable transfer-coding with the highest non-zero qvalue is preferred. 1971 The "chunked" transfer-coding always has a qvalue of 1. 1972 </p> 1973 </li> 1974 </ol> 1975 <p id="rfc.section.8.5.p.8">If the TE field-value is empty or if no TE field is present, the only transfer-coding is "chunked". A message with no transfer-coding 1976 is always acceptable. 1977 </p> 1978 </div> 1979 <div id="header.trailer"> 1980 <div id="rfc.iref.t.3"></div> 1981 <div id="rfc.iref.h.7"></div> 1982 <h2 id="rfc.section.8.6"><a href="#rfc.section.8.6">8.6</a> <a href="#header.trailer">Trailer</a></h2> 1983 <p id="rfc.section.8.6.p.1">The Trailer general field value indicates that the given set of header fields is present in the trailer of a message encoded 1984 with chunked transfer-coding. 1985 </p> 1986 <div id="rfc.figure.u.55"></div><pre class="inline"><span id="rfc.iref.g.89"></span> <a href="#header.trailer" class="smpl">Trailer</a> = "Trailer" ":" 1#<a href="#message.headers" class="smpl">field-name</a> 1874 1987 </pre><p id="rfc.section.8.6.p.3">An HTTP/1.1 message <em class="bcp14">SHOULD</em> include a Trailer header field in a message using chunked transfer-coding with a non-empty trailer. Doing so allows the recipient 1875 to know which header fields to expect in the trailer. 1876 </p> 1877 <p id="rfc.section.8.6.p.4">If no Trailer header field is present, the trailer <em class="bcp14">SHOULD NOT</em> include any header fields. See <a href="#chunked.transfer.encoding" title="Chunked Transfer Coding">Section 3.4.1</a> for restrictions on the use of trailer fields in a "chunked" transfer-coding. 1878 </p> 1879 <p id="rfc.section.8.6.p.5">Message header fields listed in the Trailer header field <em class="bcp14">MUST NOT</em> include the following header fields: 1880 </p> 1881 <ul> 1882 <li>Transfer-Encoding</li> 1883 <li>Content-Length</li> 1884 <li>Trailer</li> 1885 </ul> 1886 <div id="rfc.iref.t.4"></div> 1887 <div id="rfc.iref.h.8"></div> 1888 <h2 id="rfc.section.8.7"><a href="#rfc.section.8.7">8.7</a> <a id="header.transfer-encoding" href="#header.transfer-encoding">Transfer-Encoding</a></h2> 1889 <p id="rfc.section.8.7.p.1">The Transfer-Encoding general-header field indicates what (if any) type of transformation has been applied to the message 1890 body in order to safely transfer it between the sender and the recipient. This differs from the content-coding in that the 1891 transfer-coding is a property of the message, not of the entity. 1892 </p> 1893 <div id="rfc.figure.u.56"></div><pre class="inline"><span id="rfc.iref.g.90"></span> <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> = "Transfer-Encoding" ":" 1#<a href="#transfer.codings" class="smpl">transfer-coding</a> 1988 to know which header fields to expect in the trailer. 1989 </p> 1990 <p id="rfc.section.8.6.p.4">If no Trailer header field is present, the trailer <em class="bcp14">SHOULD NOT</em> include any header fields. See <a href="#chunked.transfer.encoding" title="Chunked Transfer Coding">Section 3.4.1</a> for restrictions on the use of trailer fields in a "chunked" transfer-coding. 1991 </p> 1992 <p id="rfc.section.8.6.p.5">Message header fields listed in the Trailer header field <em class="bcp14">MUST NOT</em> include the following header fields: 1993 </p> 1994 <ul> 1995 <li>Transfer-Encoding</li> 1996 <li>Content-Length</li> 1997 <li>Trailer</li> 1998 </ul> 1999 </div> 2000 <div id="header.transfer-encoding"> 2001 <div id="rfc.iref.t.4"></div> 2002 <div id="rfc.iref.h.8"></div> 2003 <h2 id="rfc.section.8.7"><a href="#rfc.section.8.7">8.7</a> <a href="#header.transfer-encoding">Transfer-Encoding</a></h2> 2004 <p id="rfc.section.8.7.p.1">The Transfer-Encoding general-header field indicates what (if any) type of transformation has been applied to the message 2005 body in order to safely transfer it between the sender and the recipient. This differs from the content-coding in that the 2006 transfer-coding is a property of the message, not of the entity. 2007 </p> 2008 <div id="rfc.figure.u.56"></div><pre class="inline"><span id="rfc.iref.g.90"></span> <a href="#header.transfer-encoding" class="smpl">Transfer-Encoding</a> = "Transfer-Encoding" ":" 1#<a href="#transfer.codings" class="smpl">transfer-coding</a> 1894 2009 </pre><p id="rfc.section.8.7.p.3">Transfer-codings are defined in <a href="#transfer.codings" title="Transfer Codings">Section 3.4</a>. An example is: 1895 </p>1896 <div id="rfc.figure.u.57"></div><pre class="text"> Transfer-Encoding: chunked2010 </p> 2011 <div id="rfc.figure.u.57"></div><pre class="text"> Transfer-Encoding: chunked 1897 2012 </pre><p id="rfc.section.8.7.p.5">If multiple encodings have been applied to an entity, the transfer-codings <em class="bcp14">MUST</em> be listed in the order in which they were applied. Additional information about the encoding parameters <em class="bcp14">MAY</em> be provided by other entity-header fields not defined by this specification. 1898 </p> 1899 <p id="rfc.section.8.7.p.6">Many older HTTP/1.0 applications do not understand the Transfer-Encoding header.</p> 1900 <div id="rfc.iref.u.3"></div> 1901 <div id="rfc.iref.h.9"></div> 1902 <h2 id="rfc.section.8.8"><a href="#rfc.section.8.8">8.8</a> <a id="header.upgrade" href="#header.upgrade">Upgrade</a></h2> 1903 <p id="rfc.section.8.8.p.1">The Upgrade general-header allows the client to specify what additional communication protocols it supports and would like 1904 to use if the server finds it appropriate to switch protocols. The server <em class="bcp14">MUST</em> use the Upgrade header field within a 101 (Switching Protocols) response to indicate which protocol(s) are being switched. 1905 </p> 1906 <div id="rfc.figure.u.58"></div><pre class="inline"><span id="rfc.iref.g.91"></span> <a href="#header.upgrade" class="smpl">Upgrade</a> = "Upgrade" ":" 1#<a href="#product.tokens" class="smpl">product</a> 2013 </p> 2014 <p id="rfc.section.8.7.p.6">Many older HTTP/1.0 applications do not understand the Transfer-Encoding header.</p> 2015 </div> 2016 <div id="header.upgrade"> 2017 <div id="rfc.iref.u.3"></div> 2018 <div id="rfc.iref.h.9"></div> 2019 <h2 id="rfc.section.8.8"><a href="#rfc.section.8.8">8.8</a> <a href="#header.upgrade">Upgrade</a></h2> 2020 <p id="rfc.section.8.8.p.1">The Upgrade general-header allows the client to specify what additional communication protocols it supports and would like 2021 to use if the server finds it appropriate to switch protocols. The server <em class="bcp14">MUST</em> use the Upgrade header field within a 101 (Switching Protocols) response to indicate which protocol(s) are being switched. 2022 </p> 2023 <div id="rfc.figure.u.58"></div><pre class="inline"><span id="rfc.iref.g.91"></span> <a href="#header.upgrade" class="smpl">Upgrade</a> = "Upgrade" ":" 1#<a href="#product.tokens" class="smpl">product</a> 1907 2024 </pre><p id="rfc.section.8.8.p.3">For example,</p> 1908 <div id="rfc.figure.u.59"></div><pre class="text"> Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x112025 <div id="rfc.figure.u.59"></div><pre class="text"> Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11 1909 2026 </pre><p id="rfc.section.8.8.p.5">The Upgrade header field is intended to provide a simple mechanism for transition from HTTP/1.1 to some other, incompatible 1910 protocol. It does so by allowing the client to advertise its desire to use another protocol, such as a later version of HTTP 1911 with a higher major version number, even though the current request has been made using HTTP/1.1. This eases the difficult 1912 transition between incompatible protocols by allowing the client to initiate a request in the more commonly supported protocol 1913 while indicating to the server that it would like to use a "better" protocol if available (where "better" is determined by 1914 the server, possibly according to the nature of the method and/or resource being requested). 1915 </p> 1916 <p id="rfc.section.8.8.p.6">The Upgrade header field only applies to switching application-layer protocols upon the existing transport-layer connection. 1917 Upgrade cannot be used to insist on a protocol change; its acceptance and use by the server is optional. The capabilities 1918 and nature of the application-layer communication after the protocol change is entirely dependent upon the new protocol chosen, 1919 although the first action after changing the protocol <em class="bcp14">MUST</em> be a response to the initial HTTP request containing the Upgrade header field. 1920 </p> 1921 <p id="rfc.section.8.8.p.7">The Upgrade header field only applies to the immediate connection. Therefore, the upgrade keyword <em class="bcp14">MUST</em> be supplied within a Connection header field (<a href="#header.connection" id="rfc.xref.header.connection.5" title="Connection">Section 8.1</a>) whenever Upgrade is present in an HTTP/1.1 message. 1922 </p> 1923 <p id="rfc.section.8.8.p.8">The Upgrade header field cannot be used to indicate a switch to a protocol on a different connection. For that purpose, it 1924 is more appropriate to use a 301, 302, 303, or 305 redirection response. 1925 </p> 1926 <p id="rfc.section.8.8.p.9">This specification only defines the protocol name "HTTP" for use by the family of Hypertext Transfer Protocols, as defined 1927 by the HTTP version rules of <a href="#http.version" title="HTTP Version">Section 3.1</a> and future updates to this specification. Any token can be used as a protocol name; however, it will only be useful if both 1928 the client and server associate the name with the same protocol. 1929 </p> 1930 <div id="rfc.iref.v.2"></div> 1931 <div id="rfc.iref.h.10"></div> 1932 <h2 id="rfc.section.8.9"><a href="#rfc.section.8.9">8.9</a> <a id="header.via" href="#header.via">Via</a></h2> 1933 <p id="rfc.section.8.9.p.1">The Via general-header field <em class="bcp14">MUST</em> be used by gateways and proxies to indicate the intermediate protocols and recipients between the user agent and the server 1934 on requests, and between the origin server and the client on responses. It is analogous to the "Received" field defined in <a href="http://tools.ietf.org/html/rfc2822#section-3.6.7">Section 3.6.7</a> of <a href="#RFC2822" id="rfc.xref.RFC2822.5"><cite title="Internet Message Format">[RFC2822]</cite></a> and is intended to be used for tracking message forwards, avoiding request loops, and identifying the protocol capabilities 1935 of all senders along the request/response chain. 1936 </p> 1937 <div id="rfc.figure.u.60"></div><pre class="inline"><span id="rfc.iref.g.92"></span><span id="rfc.iref.g.93"></span><span id="rfc.iref.g.94"></span><span id="rfc.iref.g.95"></span><span id="rfc.iref.g.96"></span><span id="rfc.iref.g.97"></span> <a href="#header.via" class="smpl">Via</a> = "Via" ":" 1#( <a href="#header.via" class="smpl">received-protocol</a> <a href="#header.via" class="smpl">received-by</a> [ <a href="#rule.comment" class="smpl">comment</a> ] ) 2027 protocol. It does so by allowing the client to advertise its desire to use another protocol, such as a later version of HTTP 2028 with a higher major version number, even though the current request has been made using HTTP/1.1. This eases the difficult 2029 transition between incompatible protocols by allowing the client to initiate a request in the more commonly supported protocol 2030 while indicating to the server that it would like to use a "better" protocol if available (where "better" is determined by 2031 the server, possibly according to the nature of the method and/or resource being requested). 2032 </p> 2033 <p id="rfc.section.8.8.p.6">The Upgrade header field only applies to switching application-layer protocols upon the existing transport-layer connection. 2034 Upgrade cannot be used to insist on a protocol change; its acceptance and use by the server is optional. The capabilities 2035 and nature of the application-layer communication after the protocol change is entirely dependent upon the new protocol chosen, 2036 although the first action after changing the protocol <em class="bcp14">MUST</em> be a response to the initial HTTP request containing the Upgrade header field. 2037 </p> 2038 <p id="rfc.section.8.8.p.7">The Upgrade header field only applies to the immediate connection. Therefore, the upgrade keyword <em class="bcp14">MUST</em> be supplied within a Connection header field (<a href="#header.connection" id="rfc.xref.header.connection.5" title="Connection">Section 8.1</a>) whenever Upgrade is present in an HTTP/1.1 message. 2039 </p> 2040 <p id="rfc.section.8.8.p.8">The Upgrade header field cannot be used to indicate a switch to a protocol on a different connection. For that purpose, it 2041 is more appropriate to use a 301, 302, 303, or 305 redirection response. 2042 </p> 2043 <p id="rfc.section.8.8.p.9">This specification only defines the protocol name "HTTP" for use by the family of Hypertext Transfer Protocols, as defined 2044 by the HTTP version rules of <a href="#http.version" title="HTTP Version">Section 3.1</a> and future updates to this specification. Any token can be used as a protocol name; however, it will only be useful if both 2045 the client and server associate the name with the same protocol. 2046 </p> 2047 </div> 2048 <div id="header.via"> 2049 <div id="rfc.iref.v.2"></div> 2050 <div id="rfc.iref.h.10"></div> 2051 <h2 id="rfc.section.8.9"><a href="#rfc.section.8.9">8.9</a> <a href="#header.via">Via</a></h2> 2052 <p id="rfc.section.8.9.p.1">The Via general-header field <em class="bcp14">MUST</em> be used by gateways and proxies to indicate the intermediate protocols and recipients between the user agent and the server 2053 on requests, and between the origin server and the client on responses. It is analogous to the "Received" field defined in <a href="https://tools.ietf.org/html/rfc2822#section-3.6.7">Section 3.6.7</a> of <a href="#RFC2822" id="rfc.xref.RFC2822.5"><cite title="Internet Message Format">[RFC2822]</cite></a> and is intended to be used for tracking message forwards, avoiding request loops, and identifying the protocol capabilities 2054 of all senders along the request/response chain. 2055 </p> 2056 <div id="rfc.figure.u.60"></div><pre class="inline"><span id="rfc.iref.g.92"></span><span id="rfc.iref.g.93"></span><span id="rfc.iref.g.94"></span><span id="rfc.iref.g.95"></span><span id="rfc.iref.g.96"></span><span id="rfc.iref.g.97"></span> <a href="#header.via" class="smpl">Via</a> = "Via" ":" 1#( <a href="#header.via" class="smpl">received-protocol</a> <a href="#header.via" class="smpl">received-by</a> [ <a href="#rule.comment" class="smpl">comment</a> ] ) 1938 2057 <a href="#header.via" class="smpl">received-protocol</a> = [ <a href="#header.via" class="smpl">protocol-name</a> "/" ] <a href="#header.via" class="smpl">protocol-version</a> 1939 2058 <a href="#header.via" class="smpl">protocol-name</a> = <a href="#rule.token.separators" class="smpl">token</a> … … 1942 2061 <a href="#header.via" class="smpl">pseudonym</a> = <a href="#rule.token.separators" class="smpl">token</a> 1943 2062 </pre><p id="rfc.section.8.9.p.3">The received-protocol indicates the protocol version of the message received by the server or client along each segment of 1944 the request/response chain. The received-protocol version is appended to the Via field value when the message is forwarded1945 so that information about the protocol capabilities of upstream applications remains visible to all recipients.1946 </p>1947 <p id="rfc.section.8.9.p.4">The protocol-name is optional if and only if it would be "HTTP". The received-by field is normally the host and optional port1948 number of a recipient server or client that subsequently forwarded the message. However, if the real host is considered to1949 be sensitive information, it <em class="bcp14">MAY</em> be replaced by a pseudonym. If the port is not given, it <em class="bcp14">MAY</em> be assumed to be the default port of the received-protocol.1950 </p>1951 <p id="rfc.section.8.9.p.5">Multiple Via field values represents each proxy or gateway that has forwarded the message. Each recipient <em class="bcp14">MUST</em> append its information such that the end result is ordered according to the sequence of forwarding applications.1952 </p>1953 <p id="rfc.section.8.9.p.6">Comments <em class="bcp14">MAY</em> be used in the Via header field to identify the software of the recipient proxy or gateway, analogous to the User-Agent and1954 Server header fields. However, all comments in the Via field are optional and <em class="bcp14">MAY</em> be removed by any recipient prior to forwarding the message.1955 </p>1956 <p id="rfc.section.8.9.p.7">For example, a request message could be sent from an HTTP/1.0 user agent to an internal proxy code-named "fred", which uses1957 HTTP/1.1 to forward the request to a public proxy at p.example.net, which completes the request by forwarding it to the origin1958 server at www.example.com. The request received by www.example.com would then have the following Via header field:1959 </p>1960 <div id="rfc.figure.u.61"></div><pre class="text"> Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)2063 the request/response chain. The received-protocol version is appended to the Via field value when the message is forwarded 2064 so that information about the protocol capabilities of upstream applications remains visible to all recipients. 2065 </p> 2066 <p id="rfc.section.8.9.p.4">The protocol-name is optional if and only if it would be "HTTP". The received-by field is normally the host and optional port 2067 number of a recipient server or client that subsequently forwarded the message. However, if the real host is considered to 2068 be sensitive information, it <em class="bcp14">MAY</em> be replaced by a pseudonym. If the port is not given, it <em class="bcp14">MAY</em> be assumed to be the default port of the received-protocol. 2069 </p> 2070 <p id="rfc.section.8.9.p.5">Multiple Via field values represents each proxy or gateway that has forwarded the message. Each recipient <em class="bcp14">MUST</em> append its information such that the end result is ordered according to the sequence of forwarding applications. 2071 </p> 2072 <p id="rfc.section.8.9.p.6">Comments <em class="bcp14">MAY</em> be used in the Via header field to identify the software of the recipient proxy or gateway, analogous to the User-Agent and 2073 Server header fields. However, all comments in the Via field are optional and <em class="bcp14">MAY</em> be removed by any recipient prior to forwarding the message. 2074 </p> 2075 <p id="rfc.section.8.9.p.7">For example, a request message could be sent from an HTTP/1.0 user agent to an internal proxy code-named "fred", which uses 2076 HTTP/1.1 to forward the request to a public proxy at p.example.net, which completes the request by forwarding it to the origin 2077 server at www.example.com. The request received by www.example.com would then have the following Via header field: 2078 </p> 2079 <div id="rfc.figure.u.61"></div><pre class="text"> Via: 1.0 fred, 1.1 p.example.net (Apache/1.1) 1961 2080 </pre><p id="rfc.section.8.9.p.9">Proxies and gateways used as a portal through a network firewall <em class="bcp14">SHOULD NOT</em>, by default, forward the names and ports of hosts within the firewall region. This information <em class="bcp14">SHOULD</em> only be propagated if explicitly enabled. If not enabled, the received-by host of any host behind the firewall <em class="bcp14">SHOULD</em> be replaced by an appropriate pseudonym for that host. 1962 </p>1963 <p id="rfc.section.8.9.p.10">For organizations that have strong privacy requirements for hiding internal structures, a proxy <em class="bcp14">MAY</em> combine an ordered subsequence of Via header field entries with identical received-protocol values into a single such entry.1964 For example,1965 </p>1966 <div id="rfc.figure.u.62"></div><pre class="text"> Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy2081 </p> 2082 <p id="rfc.section.8.9.p.10">For organizations that have strong privacy requirements for hiding internal structures, a proxy <em class="bcp14">MAY</em> combine an ordered subsequence of Via header field entries with identical received-protocol values into a single such entry. 2083 For example, 2084 </p> 2085 <div id="rfc.figure.u.62"></div><pre class="text"> Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy 1967 2086 </pre><p id="rfc.section.8.9.p.12">could be collapsed to</p> 1968 <div id="rfc.figure.u.63"></div><pre class="text"> Via: 1.0 ricky, 1.1 mertz, 1.0 lucy2087 <div id="rfc.figure.u.63"></div><pre class="text"> Via: 1.0 ricky, 1.1 mertz, 1.0 lucy 1969 2088 </pre><p id="rfc.section.8.9.p.14">Applications <em class="bcp14">SHOULD NOT</em> combine multiple entries unless they are all under the same organizational control and the hosts have already been replaced 1970 by pseudonyms. Applications <em class="bcp14">MUST NOT</em> combine entries which have different received-protocol values. 1971 </p> 1972 <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a> <a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1> 1973 <h2 id="rfc.section.9.1"><a href="#rfc.section.9.1">9.1</a> <a id="message.header.registration" href="#message.header.registration">Message Header Registration</a></h2> 1974 <p id="rfc.section.9.1.p.1">The Message Header Registry located at <<a href="http://www.iana.org/assignments/message-headers/message-header-index.html">http://www.iana.org/assignments/message-headers/message-header-index.html</a>> should be updated with the permanent registrations below (see <a href="#RFC3864" id="rfc.xref.RFC3864.1"><cite title="Registration Procedures for Message Header Fields">[RFC3864]</cite></a>): 1975 </p> 1976 <div id="rfc.table.u.1"> 1977 <table class="tt full center" cellpadding="3" cellspacing="0"> 1978 <thead> 1979 <tr> 1980 <th>Header Field Name</th> 1981 <th>Protocol</th> 1982 <th>Status</th> 1983 <th>Reference</th> 1984 </tr> 1985 </thead> 1986 <tbody> 1987 <tr> 1988 <td class="left">Connection</td> 1989 <td class="left">http</td> 1990 <td class="left">standard</td> 1991 <td class="left"> <a href="#header.connection" id="rfc.xref.header.connection.6" title="Connection">Section 8.1</a> 1992 </td> 1993 </tr> 1994 <tr> 1995 <td class="left">Content-Length</td> 1996 <td class="left">http</td> 1997 <td class="left">standard</td> 1998 <td class="left"> <a href="#header.content-length" id="rfc.xref.header.content-length.2" title="Content-Length">Section 8.2</a> 1999 </td> 2000 </tr> 2001 <tr> 2002 <td class="left">Date</td> 2003 <td class="left">http</td> 2004 <td class="left">standard</td> 2005 <td class="left"> <a href="#header.date" id="rfc.xref.header.date.2" title="Date">Section 8.3</a> 2006 </td> 2007 </tr> 2008 <tr> 2009 <td class="left">Host</td> 2010 <td class="left">http</td> 2011 <td class="left">standard</td> 2012 <td class="left"> <a href="#header.host" id="rfc.xref.header.host.1" title="Host">Section 8.4</a> 2013 </td> 2014 </tr> 2015 <tr> 2016 <td class="left">TE</td> 2017 <td class="left">http</td> 2018 <td class="left">standard</td> 2019 <td class="left"> <a href="#header.te" id="rfc.xref.header.te.3" title="TE">Section 8.5</a> 2020 </td> 2021 </tr> 2022 <tr> 2023 <td class="left">Trailer</td> 2024 <td class="left">http</td> 2025 <td class="left">standard</td> 2026 <td class="left"> <a href="#header.trailer" id="rfc.xref.header.trailer.3" title="Trailer">Section 8.6</a> 2027 </td> 2028 </tr> 2029 <tr> 2030 <td class="left">Transfer-Encoding</td> 2031 <td class="left">http</td> 2032 <td class="left">standard</td> 2033 <td class="left"> <a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.5" title="Transfer-Encoding">Section 8.7</a> 2034 </td> 2035 </tr> 2036 <tr> 2037 <td class="left">Upgrade</td> 2038 <td class="left">http</td> 2039 <td class="left">standard</td> 2040 <td class="left"> <a href="#header.upgrade" id="rfc.xref.header.upgrade.2" title="Upgrade">Section 8.8</a> 2041 </td> 2042 </tr> 2043 <tr> 2044 <td class="left">Via</td> 2045 <td class="left">http</td> 2046 <td class="left">standard</td> 2047 <td class="left"> <a href="#header.via" id="rfc.xref.header.via.2" title="Via">Section 8.9</a> 2048 </td> 2049 </tr> 2050 </tbody> 2051 </table> 2089 by pseudonyms. Applications <em class="bcp14">MUST NOT</em> combine entries which have different received-protocol values. 2090 </p> 2091 </div> 2052 2092 </div> 2053 <p id="rfc.section.9.1.p.2">The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p> 2054 <h1 id="rfc.section.10"><a href="#rfc.section.10">10.</a> <a id="security.considerations" href="#security.considerations">Security Considerations</a></h1> 2055 <p id="rfc.section.10.p.1">This section is meant to inform application developers, information providers, and users of the security limitations in HTTP/1.1 2056 as described by this document. The discussion does not include definitive solutions to the problems revealed, though it does 2057 make some suggestions for reducing security risks. 2058 </p> 2059 <h2 id="rfc.section.10.1"><a href="#rfc.section.10.1">10.1</a> <a id="personal.information" href="#personal.information">Personal Information</a></h2> 2060 <p id="rfc.section.10.1.p.1">HTTP clients are often privy to large amounts of personal information (e.g. the user's name, location, mail address, passwords, 2061 encryption keys, etc.), and <em class="bcp14">SHOULD</em> be very careful to prevent unintentional leakage of this information. We very strongly recommend that a convenient interface 2062 be provided for the user to control dissemination of such information, and that designers and implementors be particularly 2063 careful in this area. History shows that errors in this area often create serious security and/or privacy problems and generate 2064 highly adverse publicity for the implementor's company. 2065 </p> 2066 <h2 id="rfc.section.10.2"><a href="#rfc.section.10.2">10.2</a> <a id="abuse.of.server.log.information" href="#abuse.of.server.log.information">Abuse of Server Log Information</a></h2> 2067 <p id="rfc.section.10.2.p.1">A server is in the position to save personal data about a user's requests which might identify their reading patterns or subjects 2068 of interest. This information is clearly confidential in nature and its handling can be constrained by law in certain countries. 2069 People using HTTP to provide data are responsible for ensuring that such material is not distributed without the permission 2070 of any individuals that are identifiable by the published results. 2071 </p> 2072 <h2 id="rfc.section.10.3"><a href="#rfc.section.10.3">10.3</a> <a id="attack.pathname" href="#attack.pathname">Attacks Based On File and Path Names</a></h2> 2073 <p id="rfc.section.10.3.p.1">Implementations of HTTP origin servers <em class="bcp14">SHOULD</em> be careful to restrict the documents returned by HTTP requests to be only those that were intended by the server administrators. 2074 If an HTTP server translates HTTP URIs directly into file system calls, the server <em class="bcp14">MUST</em> take special care not to serve files that were not intended to be delivered to HTTP clients. For example, UNIX, Microsoft 2075 Windows, and other operating systems use ".." as a path component to indicate a directory level above the current one. On 2076 such a system, an HTTP server <em class="bcp14">MUST</em> disallow any such construct in the Request-URI if it would otherwise allow access to a resource outside those intended to 2077 be accessible via the HTTP server. Similarly, files intended for reference only internally to the server (such as access control 2078 files, configuration files, and script code) <em class="bcp14">MUST</em> be protected from inappropriate retrieval, since they might contain sensitive information. Experience has shown that minor 2079 bugs in such HTTP server implementations have turned into security risks. 2080 </p> 2081 <h2 id="rfc.section.10.4"><a href="#rfc.section.10.4">10.4</a> <a id="dns.spoofing" href="#dns.spoofing">DNS Spoofing</a></h2> 2082 <p id="rfc.section.10.4.p.1">Clients using HTTP rely heavily on the Domain Name Service, and are thus generally prone to security attacks based on the 2083 deliberate mis-association of IP addresses and DNS names. Clients need to be cautious in assuming the continuing validity 2084 of an IP number/DNS name association. 2085 </p> 2086 <p id="rfc.section.10.4.p.2">In particular, HTTP clients <em class="bcp14">SHOULD</em> rely on their name resolver for confirmation of an IP number/DNS name association, rather than caching the result of previous 2087 host name lookups. Many platforms already can cache host name lookups locally when appropriate, and they <em class="bcp14">SHOULD</em> be configured to do so. It is proper for these lookups to be cached, however, only when the TTL (Time To Live) information 2088 reported by the name server makes it likely that the cached information will remain useful. 2089 </p> 2090 <p id="rfc.section.10.4.p.3">If HTTP clients cache the results of host name lookups in order to achieve a performance improvement, they <em class="bcp14">MUST</em> observe the TTL information reported by DNS. 2091 </p> 2092 <p id="rfc.section.10.4.p.4">If HTTP clients do not observe this rule, they could be spoofed when a previously-accessed server's IP address changes. As 2093 network renumbering is expected to become increasingly common <a href="#RFC1900" id="rfc.xref.RFC1900.2"><cite title="Renumbering Needs Work">[RFC1900]</cite></a>, the possibility of this form of attack will grow. Observing this requirement thus reduces this potential security vulnerability. 2094 </p> 2095 <p id="rfc.section.10.4.p.5">This requirement also improves the load-balancing behavior of clients for replicated servers using the same DNS name and reduces 2096 the likelihood of a user's experiencing failure in accessing sites which use that strategy. 2097 </p> 2098 <h2 id="rfc.section.10.5"><a href="#rfc.section.10.5">10.5</a> <a id="attack.proxies" href="#attack.proxies">Proxies and Caching</a></h2> 2099 <p id="rfc.section.10.5.p.1">By their very nature, HTTP proxies are men-in-the-middle, and represent an opportunity for man-in-the-middle attacks. Compromise 2100 of the systems on which the proxies run can result in serious security and privacy problems. Proxies have access to security-related 2101 information, personal information about individual users and organizations, and proprietary information belonging to users 2102 and content providers. A compromised proxy, or a proxy implemented or configured without regard to security and privacy considerations, 2103 might be used in the commission of a wide range of potential attacks. 2104 </p> 2105 <p id="rfc.section.10.5.p.2">Proxy operators should protect the systems on which proxies run as they would protect any system that contains or transports 2106 sensitive information. In particular, log information gathered at proxies often contains highly sensitive personal information, 2107 and/or information about organizations. Log information should be carefully guarded, and appropriate guidelines for use developed 2108 and followed. (<a href="#abuse.of.server.log.information" title="Abuse of Server Log Information">Section 10.2</a>). 2109 </p> 2110 <p id="rfc.section.10.5.p.3">Proxy implementors should consider the privacy and security implications of their design and coding decisions, and of the 2111 configuration options they provide to proxy operators (especially the default configuration). 2112 </p> 2113 <p id="rfc.section.10.5.p.4">Users of a proxy need to be aware that they are no trustworthier than the people who run the proxy; HTTP itself cannot solve 2114 this problem. 2115 </p> 2116 <p id="rfc.section.10.5.p.5">The judicious use of cryptography, when appropriate, may suffice to protect against a broad range of security and privacy 2117 attacks. Such cryptography is beyond the scope of the HTTP/1.1 specification. 2118 </p> 2119 <h2 id="rfc.section.10.6"><a href="#rfc.section.10.6">10.6</a> <a id="attack.DoS" href="#attack.DoS">Denial of Service Attacks on Proxies</a></h2> 2120 <p id="rfc.section.10.6.p.1">They exist. They are hard to defend against. Research continues. Beware.</p> 2121 <h1 id="rfc.section.11"><a href="#rfc.section.11">11.</a> <a id="ack" href="#ack">Acknowledgments</a></h1> 2122 <p id="rfc.section.11.p.1">This specification makes heavy use of the augmented BNF and generic constructs defined by David H. Crocker for <a href="#RFC822ABNF" id="rfc.xref.RFC822ABNF.2"><cite title="Standard for the format of ARPA Internet text messages">[RFC822ABNF]</cite></a>. Similarly, it reuses many of the definitions provided by Nathaniel Borenstein and Ned Freed for MIME <a href="#RFC2045" id="rfc.xref.RFC2045.3"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a>. We hope that their inclusion in this specification will help reduce past confusion over the relationship between HTTP and 2123 Internet mail message formats. 2124 </p> 2125 <p id="rfc.section.11.p.2">HTTP has evolved considerably over the years. It has benefited from a large and active developer community--the many people 2126 who have participated on the www-talk mailing list--and it is that community which has been most responsible for the success 2127 of HTTP and of the World-Wide Web in general. Marc Andreessen, Robert Cailliau, Daniel W. Connolly, Bob Denny, John Franks, 2128 Jean-Francois Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob McCool, Lou Montulli, Dave Raggett, Tony Sanders, 2129 and Marc VanHeyningen deserve special recognition for their efforts in defining early aspects of the protocol. 2130 </p> 2131 <p id="rfc.section.11.p.3">This document has benefited greatly from the comments of all those participating in the HTTP-WG. In addition to those already 2132 mentioned, the following individuals have contributed to this specification: 2133 </p> 2134 <p id="rfc.section.11.p.4">Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf, Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman 2135 Czyborra, Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy, Koen Holtman, Alex Hopmann, 2136 Bob Jernigan, Shel Kaphan, Rohit Khare, John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol, Daniel LaLiberte, Ben 2137 Laurie, Paul J. Leach, Albert Lunde, John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris, Gavin Nicol, Ross 2138 Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees, Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz, Allan 2139 M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink, Simon E. Spero, Richard N. Taylor, Robert S. Thau, Bill (BearHeart) 2140 Weinman, Francois Yergeau, Mary Ellen Zurko, Josh Cohen. 2141 </p> 2142 <p id="rfc.section.11.p.5">Thanks to the "cave men" of Palo Alto. You know who you are.</p> 2143 <p id="rfc.section.11.p.6">Jim Gettys (the editor of <a href="#RFC2616" id="rfc.xref.RFC2616.3"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>) wishes particularly to thank Roy Fielding, the editor of <a href="#RFC2068" id="rfc.xref.RFC2068.5"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, along with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott 2144 Lawrence, and Larry Masinter for their help. And thanks go particularly to Jeff Mogul and Scott Lawrence for performing the 2145 "MUST/MAY/SHOULD" audit. 2146 </p> 2147 <p id="rfc.section.11.p.7">The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik Frystyk implemented RFC 2068 early, and we wish to thank 2148 them for the discovery of many of the problems that this document attempts to rectify. 2149 </p> 2093 <div id="IANA.considerations"> 2094 <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a> <a href="#IANA.considerations">IANA Considerations</a></h1> 2095 <div id="message.header.registration"> 2096 <h2 id="rfc.section.9.1"><a href="#rfc.section.9.1">9.1</a> <a href="#message.header.registration">Message Header Registration</a></h2> 2097 <p id="rfc.section.9.1.p.1">The Message Header Registry located at <<a href="http://www.iana.org/assignments/message-headers/message-header-index.html">http://www.iana.org/assignments/message-headers/message-header-index.html</a>> should be updated with the permanent registrations below (see <a href="#RFC3864" id="rfc.xref.RFC3864.1"><cite title="Registration Procedures for Message Header Fields">[RFC3864]</cite></a>): 2098 </p> 2099 <div id="rfc.table.u.1"> 2100 <table class="tt full center" cellpadding="3" cellspacing="0"> 2101 <thead> 2102 <tr> 2103 <th>Header Field Name</th> 2104 <th>Protocol</th> 2105 <th>Status</th> 2106 <th>Reference</th> 2107 </tr> 2108 </thead> 2109 <tbody> 2110 <tr> 2111 <td class="left">Connection</td> 2112 <td class="left">http</td> 2113 <td class="left">standard</td> 2114 <td class="left"><a href="#header.connection" id="rfc.xref.header.connection.6" title="Connection">Section 8.1</a> 2115 </td> 2116 </tr> 2117 <tr> 2118 <td class="left">Content-Length</td> 2119 <td class="left">http</td> 2120 <td class="left">standard</td> 2121 <td class="left"><a href="#header.content-length" id="rfc.xref.header.content-length.2" title="Content-Length">Section 8.2</a> 2122 </td> 2123 </tr> 2124 <tr> 2125 <td class="left">Date</td> 2126 <td class="left">http</td> 2127 <td class="left">standard</td> 2128 <td class="left"><a href="#header.date" id="rfc.xref.header.date.2" title="Date">Section 8.3</a> 2129 </td> 2130 </tr> 2131 <tr> 2132 <td class="left">Host</td> 2133 <td class="left">http</td> 2134 <td class="left">standard</td> 2135 <td class="left"><a href="#header.host" id="rfc.xref.header.host.1" title="Host">Section 8.4</a> 2136 </td> 2137 </tr> 2138 <tr> 2139 <td class="left">TE</td> 2140 <td class="left">http</td> 2141 <td class="left">standard</td> 2142 <td class="left"><a href="#header.te" id="rfc.xref.header.te.3" title="TE">Section 8.5</a> 2143 </td> 2144 </tr> 2145 <tr> 2146 <td class="left">Trailer</td> 2147 <td class="left">http</td> 2148 <td class="left">standard</td> 2149 <td class="left"><a href="#header.trailer" id="rfc.xref.header.trailer.3" title="Trailer">Section 8.6</a> 2150 </td> 2151 </tr> 2152 <tr> 2153 <td class="left">Transfer-Encoding</td> 2154 <td class="left">http</td> 2155 <td class="left">standard</td> 2156 <td class="left"><a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.5" title="Transfer-Encoding">Section 8.7</a> 2157 </td> 2158 </tr> 2159 <tr> 2160 <td class="left">Upgrade</td> 2161 <td class="left">http</td> 2162 <td class="left">standard</td> 2163 <td class="left"><a href="#header.upgrade" id="rfc.xref.header.upgrade.2" title="Upgrade">Section 8.8</a> 2164 </td> 2165 </tr> 2166 <tr> 2167 <td class="left">Via</td> 2168 <td class="left">http</td> 2169 <td class="left">standard</td> 2170 <td class="left"><a href="#header.via" id="rfc.xref.header.via.2" title="Via">Section 8.9</a> 2171 </td> 2172 </tr> 2173 </tbody> 2174 </table> 2175 </div> 2176 <p id="rfc.section.9.1.p.2">The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p> 2177 </div> 2178 </div> 2179 <div id="security.considerations"> 2180 <h1 id="rfc.section.10"><a href="#rfc.section.10">10.</a> <a href="#security.considerations">Security Considerations</a></h1> 2181 <p id="rfc.section.10.p.1">This section is meant to inform application developers, information providers, and users of the security limitations in HTTP/1.1 2182 as described by this document. The discussion does not include definitive solutions to the problems revealed, though it does 2183 make some suggestions for reducing security risks. 2184 </p> 2185 <div id="personal.information"> 2186 <h2 id="rfc.section.10.1"><a href="#rfc.section.10.1">10.1</a> <a href="#personal.information">Personal Information</a></h2> 2187 <p id="rfc.section.10.1.p.1">HTTP clients are often privy to large amounts of personal information (e.g. the user's name, location, mail address, passwords, 2188 encryption keys, etc.), and <em class="bcp14">SHOULD</em> be very careful to prevent unintentional leakage of this information. We very strongly recommend that a convenient interface 2189 be provided for the user to control dissemination of such information, and that designers and implementors be particularly 2190 careful in this area. History shows that errors in this area often create serious security and/or privacy problems and generate 2191 highly adverse publicity for the implementor's company. 2192 </p> 2193 </div> 2194 <div id="abuse.of.server.log.information"> 2195 <h2 id="rfc.section.10.2"><a href="#rfc.section.10.2">10.2</a> <a href="#abuse.of.server.log.information">Abuse of Server Log Information</a></h2> 2196 <p id="rfc.section.10.2.p.1">A server is in the position to save personal data about a user's requests which might identify their reading patterns or subjects 2197 of interest. This information is clearly confidential in nature and its handling can be constrained by law in certain countries. 2198 People using HTTP to provide data are responsible for ensuring that such material is not distributed without the permission 2199 of any individuals that are identifiable by the published results. 2200 </p> 2201 </div> 2202 <div id="attack.pathname"> 2203 <h2 id="rfc.section.10.3"><a href="#rfc.section.10.3">10.3</a> <a href="#attack.pathname">Attacks Based On File and Path Names</a></h2> 2204 <p id="rfc.section.10.3.p.1">Implementations of HTTP origin servers <em class="bcp14">SHOULD</em> be careful to restrict the documents returned by HTTP requests to be only those that were intended by the server administrators. 2205 If an HTTP server translates HTTP URIs directly into file system calls, the server <em class="bcp14">MUST</em> take special care not to serve files that were not intended to be delivered to HTTP clients. For example, UNIX, Microsoft 2206 Windows, and other operating systems use ".." as a path component to indicate a directory level above the current one. On 2207 such a system, an HTTP server <em class="bcp14">MUST</em> disallow any such construct in the Request-URI if it would otherwise allow access to a resource outside those intended to 2208 be accessible via the HTTP server. Similarly, files intended for reference only internally to the server (such as access control 2209 files, configuration files, and script code) <em class="bcp14">MUST</em> be protected from inappropriate retrieval, since they might contain sensitive information. Experience has shown that minor 2210 bugs in such HTTP server implementations have turned into security risks. 2211 </p> 2212 </div> 2213 <div id="dns.spoofing"> 2214 <h2 id="rfc.section.10.4"><a href="#rfc.section.10.4">10.4</a> <a href="#dns.spoofing">DNS Spoofing</a></h2> 2215 <p id="rfc.section.10.4.p.1">Clients using HTTP rely heavily on the Domain Name Service, and are thus generally prone to security attacks based on the 2216 deliberate mis-association of IP addresses and DNS names. Clients need to be cautious in assuming the continuing validity 2217 of an IP number/DNS name association. 2218 </p> 2219 <p id="rfc.section.10.4.p.2">In particular, HTTP clients <em class="bcp14">SHOULD</em> rely on their name resolver for confirmation of an IP number/DNS name association, rather than caching the result of previous 2220 host name lookups. Many platforms already can cache host name lookups locally when appropriate, and they <em class="bcp14">SHOULD</em> be configured to do so. It is proper for these lookups to be cached, however, only when the TTL (Time To Live) information 2221 reported by the name server makes it likely that the cached information will remain useful. 2222 </p> 2223 <p id="rfc.section.10.4.p.3">If HTTP clients cache the results of host name lookups in order to achieve a performance improvement, they <em class="bcp14">MUST</em> observe the TTL information reported by DNS. 2224 </p> 2225 <p id="rfc.section.10.4.p.4">If HTTP clients do not observe this rule, they could be spoofed when a previously-accessed server's IP address changes. As 2226 network renumbering is expected to become increasingly common <a href="#RFC1900" id="rfc.xref.RFC1900.2"><cite title="Renumbering Needs Work">[RFC1900]</cite></a>, the possibility of this form of attack will grow. Observing this requirement thus reduces this potential security vulnerability. 2227 </p> 2228 <p id="rfc.section.10.4.p.5">This requirement also improves the load-balancing behavior of clients for replicated servers using the same DNS name and reduces 2229 the likelihood of a user's experiencing failure in accessing sites which use that strategy. 2230 </p> 2231 </div> 2232 <div id="attack.proxies"> 2233 <h2 id="rfc.section.10.5"><a href="#rfc.section.10.5">10.5</a> <a href="#attack.proxies">Proxies and Caching</a></h2> 2234 <p id="rfc.section.10.5.p.1">By their very nature, HTTP proxies are men-in-the-middle, and represent an opportunity for man-in-the-middle attacks. Compromise 2235 of the systems on which the proxies run can result in serious security and privacy problems. Proxies have access to security-related 2236 information, personal information about individual users and organizations, and proprietary information belonging to users 2237 and content providers. A compromised proxy, or a proxy implemented or configured without regard to security and privacy considerations, 2238 might be used in the commission of a wide range of potential attacks. 2239 </p> 2240 <p id="rfc.section.10.5.p.2">Proxy operators should protect the systems on which proxies run as they would protect any system that contains or transports 2241 sensitive information. In particular, log information gathered at proxies often contains highly sensitive personal information, 2242 and/or information about organizations. Log information should be carefully guarded, and appropriate guidelines for use developed 2243 and followed. (<a href="#abuse.of.server.log.information" title="Abuse of Server Log Information">Section 10.2</a>). 2244 </p> 2245 <p id="rfc.section.10.5.p.3">Proxy implementors should consider the privacy and security implications of their design and coding decisions, and of the 2246 configuration options they provide to proxy operators (especially the default configuration). 2247 </p> 2248 <p id="rfc.section.10.5.p.4">Users of a proxy need to be aware that they are no trustworthier than the people who run the proxy; HTTP itself cannot solve 2249 this problem. 2250 </p> 2251 <p id="rfc.section.10.5.p.5">The judicious use of cryptography, when appropriate, may suffice to protect against a broad range of security and privacy 2252 attacks. Such cryptography is beyond the scope of the HTTP/1.1 specification. 2253 </p> 2254 </div> 2255 <div id="attack.DoS"> 2256 <h2 id="rfc.section.10.6"><a href="#rfc.section.10.6">10.6</a> <a href="#attack.DoS">Denial of Service Attacks on Proxies</a></h2> 2257 <p id="rfc.section.10.6.p.1">They exist. They are hard to defend against. Research continues. Beware.</p> 2258 </div> 2259 </div> 2260 <div id="ack"> 2261 <h1 id="rfc.section.11"><a href="#rfc.section.11">11.</a> <a href="#ack">Acknowledgments</a></h1> 2262 <p id="rfc.section.11.p.1">This specification makes heavy use of the augmented BNF and generic constructs defined by David H. Crocker for <a href="#RFC822ABNF" id="rfc.xref.RFC822ABNF.2"><cite title="Standard for the format of ARPA Internet text messages">[RFC822ABNF]</cite></a>. Similarly, it reuses many of the definitions provided by Nathaniel Borenstein and Ned Freed for MIME <a href="#RFC2045" id="rfc.xref.RFC2045.3"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a>. We hope that their inclusion in this specification will help reduce past confusion over the relationship between HTTP and 2263 Internet mail message formats. 2264 </p> 2265 <p id="rfc.section.11.p.2">HTTP has evolved considerably over the years. It has benefited from a large and active developer community--the many people 2266 who have participated on the www-talk mailing list--and it is that community which has been most responsible for the success 2267 of HTTP and of the World-Wide Web in general. Marc Andreessen, Robert Cailliau, Daniel W. Connolly, Bob Denny, John Franks, 2268 Jean-Francois Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob McCool, Lou Montulli, Dave Raggett, Tony Sanders, 2269 and Marc VanHeyningen deserve special recognition for their efforts in defining early aspects of the protocol. 2270 </p> 2271 <p id="rfc.section.11.p.3">This document has benefited greatly from the comments of all those participating in the HTTP-WG. In addition to those already 2272 mentioned, the following individuals have contributed to this specification: 2273 </p> 2274 <p id="rfc.section.11.p.4">Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf, Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman 2275 Czyborra, Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy, Koen Holtman, Alex Hopmann, 2276 Bob Jernigan, Shel Kaphan, Rohit Khare, John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol, Daniel LaLiberte, Ben 2277 Laurie, Paul J. Leach, Albert Lunde, John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris, Gavin Nicol, Ross 2278 Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees, Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz, Allan 2279 M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink, Simon E. Spero, Richard N. Taylor, Robert S. Thau, Bill (BearHeart) 2280 Weinman, Francois Yergeau, Mary Ellen Zurko, Josh Cohen. 2281 </p> 2282 <p id="rfc.section.11.p.5">Thanks to the "cave men" of Palo Alto. You know who you are.</p> 2283 <p id="rfc.section.11.p.6">Jim Gettys (the editor of <a href="#RFC2616" id="rfc.xref.RFC2616.3"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>) wishes particularly to thank Roy Fielding, the editor of <a href="#RFC2068" id="rfc.xref.RFC2068.5"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, along with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott 2284 Lawrence, and Larry Masinter for their help. And thanks go particularly to Jeff Mogul and Scott Lawrence for performing the 2285 "MUST/MAY/SHOULD" audit. 2286 </p> 2287 <p id="rfc.section.11.p.7">The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik Frystyk implemented RFC 2068 early, and we wish to thank 2288 them for the discovery of many of the problems that this document attempts to rectify. 2289 </p> 2290 </div> 2150 2291 <h1 id="rfc.references"><a id="rfc.section.12" href="#rfc.section.12">12.</a> References 2151 2292 </h1> 2152 2293 <h2 id="rfc.references.1"><a href="#rfc.section.12.1" id="rfc.section.12.1">12.1</a> Normative References 2153 2294 </h2> 2154 <table> 2295 <table> 2155 2296 <tr> 2156 2297 <td class="reference"><b id="ISO-8859-1">[ISO-8859-1]</b></td> … … 2159 2300 <tr> 2160 2301 <td class="reference"><b id="Part2">[Part2]</b></td> 2161 <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http ://tools.ietf.org/html/draft-ietf-httpbis-p2-semantics-03">HTTP/1.1, part 2: Message Semantics</a>”, Internet-Draft draft-ietf-httpbis-p2-semantics-03 (work in progress), June 2008.2302 <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="https://tools.ietf.org/html/draft-ietf-httpbis-p2-semantics-03">HTTP/1.1, part 2: Message Semantics</a>”, Internet-Draft draft-ietf-httpbis-p2-semantics-03 (work in progress), June 2008. 2162 2303 </td> 2163 2304 </tr> 2164 2305 <tr> 2165 2306 <td class="reference"><b id="Part3">[Part3]</b></td> 2166 <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http ://tools.ietf.org/html/draft-ietf-httpbis-p3-payload-03">HTTP/1.1, part 3: Message Payload and Content Negotiation</a>”, Internet-Draft draft-ietf-httpbis-p3-payload-03 (work in progress), June 2008.2307 <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="https://tools.ietf.org/html/draft-ietf-httpbis-p3-payload-03">HTTP/1.1, part 3: Message Payload and Content Negotiation</a>”, Internet-Draft draft-ietf-httpbis-p3-payload-03 (work in progress), June 2008. 2167 2308 </td> 2168 2309 </tr> 2169 2310 <tr> 2170 2311 <td class="reference"><b id="Part5">[Part5]</b></td> 2171 <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http ://tools.ietf.org/html/draft-ietf-httpbis-p5-range-03">HTTP/1.1, part 5: Range Requests and Partial Responses</a>”, Internet-Draft draft-ietf-httpbis-p5-range-03 (work in progress), June 2008.2312 <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="https://tools.ietf.org/html/draft-ietf-httpbis-p5-range-03">HTTP/1.1, part 5: Range Requests and Partial Responses</a>”, Internet-Draft draft-ietf-httpbis-p5-range-03 (work in progress), June 2008. 2172 2313 </td> 2173 2314 </tr> 2174 2315 <tr> 2175 2316 <td class="reference"><b id="Part6">[Part6]</b></td> 2176 <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http ://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-03">HTTP/1.1, part 6: Caching</a>”, Internet-Draft draft-ietf-httpbis-p6-cache-03 (work in progress), June 2008.2317 <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="https://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-03">HTTP/1.1, part 6: Caching</a>”, Internet-Draft draft-ietf-httpbis-p6-cache-03 (work in progress), June 2008. 2177 2318 </td> 2178 2319 </tr> 2179 2320 <tr> 2180 2321 <td class="reference"><b id="RFC2045">[RFC2045]</b></td> 2181 <td class="top"><a href="mailto:ned@innosoft.com" title="Innosoft International, Inc.">Freed, N.</a> and <a href="mailto:nsb@nsb.fv.com" title="First Virtual Holdings">N. Borenstein</a>, “<a href="http ://tools.ietf.org/html/rfc2045">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</a>”, RFC 2045, November 1996.2322 <td class="top"><a href="mailto:ned@innosoft.com" title="Innosoft International, Inc.">Freed, N.</a> and <a href="mailto:nsb@nsb.fv.com" title="First Virtual Holdings">N. Borenstein</a>, “<a href="https://tools.ietf.org/html/rfc2045">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</a>”, RFC 2045, November 1996. 2182 2323 </td> 2183 2324 </tr> 2184 2325 <tr> 2185 2326 <td class="reference"><b id="RFC2047">[RFC2047]</b></td> 2186 <td class="top"><a href="mailto:moore@cs.utk.edu" title="University of Tennessee">Moore, K.</a>, “<a href="http ://tools.ietf.org/html/rfc2047">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</a>”, RFC 2047, November 1996.2327 <td class="top"><a href="mailto:moore@cs.utk.edu" title="University of Tennessee">Moore, K.</a>, “<a href="https://tools.ietf.org/html/rfc2047">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</a>”, RFC 2047, November 1996. 2187 2328 </td> 2188 2329 </tr> 2189 2330 <tr> 2190 2331 <td class="reference"><b id="RFC2119">[RFC2119]</b></td> 2191 <td class="top"><a href="mailto:sob@harvard.edu" title="Harvard University">Bradner, S.</a>, “<a href="http ://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>”, BCP 14, RFC 2119, March 1997.2332 <td class="top"><a href="mailto:sob@harvard.edu" title="Harvard University">Bradner, S.</a>, “<a href="https://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>”, BCP 14, RFC 2119, March 1997. 2192 2333 </td> 2193 2334 </tr> 2194 2335 <tr> 2195 2336 <td class="reference"><b id="RFC2396">[RFC2396]</b></td> 2196 <td class="top"><a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:fielding@ics.uci.edu" title="Department of Information and Computer Science">Fielding, R.</a>, and <a href="mailto:masinter@parc.xerox.com" title="Xerox PARC">L. Masinter</a>, “<a href="http ://tools.ietf.org/html/rfc2396">Uniform Resource Identifiers (URI): Generic Syntax</a>”, RFC 2396, August 1998.2337 <td class="top"><a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:fielding@ics.uci.edu" title="Department of Information and Computer Science">Fielding, R.</a>, and <a href="mailto:masinter@parc.xerox.com" title="Xerox PARC">L. Masinter</a>, “<a href="https://tools.ietf.org/html/rfc2396">Uniform Resource Identifiers (URI): Generic Syntax</a>”, RFC 2396, August 1998. 2197 2338 </td> 2198 2339 </tr> 2199 2340 <tr> 2200 2341 <td class="reference"><b id="RFC822ABNF">[RFC822ABNF]</b></td> 2201 <td class="top"><a href="mailto:DCrocker@UDel-Relay" title="University of Delaware, Dept. of Electrical Engineering">Crocker, D.</a>, “<a href="http ://tools.ietf.org/html/rfc822">Standard for the format of ARPA Internet text messages</a>”, STD 11, RFC 822, August 1982.2342 <td class="top"><a href="mailto:DCrocker@UDel-Relay" title="University of Delaware, Dept. of Electrical Engineering">Crocker, D.</a>, “<a href="https://tools.ietf.org/html/rfc822">Standard for the format of ARPA Internet text messages</a>”, STD 11, RFC 822, August 1982. 2202 2343 </td> 2203 2344 </tr> … … 2209 2350 <h2 id="rfc.references.2"><a href="#rfc.section.12.2" id="rfc.section.12.2">12.2</a> Informative References 2210 2351 </h2> 2211 <table> 2352 <table> 2212 2353 <tr> 2213 2354 <td class="reference"><b id="Nie1997">[Nie1997]</b></td> … … 2224 2365 <tr> 2225 2366 <td class="reference"><b id="RFC1123">[RFC1123]</b></td> 2226 <td class="top"><a href="mailto:Braden@ISI.EDU" title="University of Southern California (USC), Information Sciences Institute">Braden, R.</a>, “<a href="http ://tools.ietf.org/html/rfc1123">Requirements for Internet Hosts - Application and Support</a>”, STD 3, RFC 1123, October 1989.2367 <td class="top"><a href="mailto:Braden@ISI.EDU" title="University of Southern California (USC), Information Sciences Institute">Braden, R.</a>, “<a href="https://tools.ietf.org/html/rfc1123">Requirements for Internet Hosts - Application and Support</a>”, STD 3, RFC 1123, October 1989. 2227 2368 </td> 2228 2369 </tr> 2229 2370 <tr> 2230 2371 <td class="reference"><b id="RFC1305">[RFC1305]</b></td> 2231 <td class="top"><a href="mailto:mills@udel.edu" title="University of Delaware, Electrical Engineering Department">Mills, D.</a>, “<a href="http ://tools.ietf.org/html/rfc1305">Network Time Protocol (Version 3) Specification, Implementation</a>”, RFC 1305, March 1992.2372 <td class="top"><a href="mailto:mills@udel.edu" title="University of Delaware, Electrical Engineering Department">Mills, D.</a>, “<a href="https://tools.ietf.org/html/rfc1305">Network Time Protocol (Version 3) Specification, Implementation</a>”, RFC 1305, March 1992. 2232 2373 </td> 2233 2374 </tr> 2234 2375 <tr> 2235 2376 <td class="reference"><b id="RFC1436">[RFC1436]</b></td> 2236 <td class="top"><a href="mailto:fxa@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">Anklesaria, F.</a>, <a href="mailto:mpm@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">McCahill, M.</a>, <a href="mailto:lindner@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">Lindner, P.</a>, <a href="mailto:dmj@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">Johnson, D.</a>, <a href="mailto:daniel@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">Torrey, D.</a>, and <a href="mailto:alberti@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">B. Alberti</a>, “<a href="http ://tools.ietf.org/html/rfc1436">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</a>”, RFC 1436, March 1993.2377 <td class="top"><a href="mailto:fxa@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">Anklesaria, F.</a>, <a href="mailto:mpm@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">McCahill, M.</a>, <a href="mailto:lindner@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">Lindner, P.</a>, <a href="mailto:dmj@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">Johnson, D.</a>, <a href="mailto:daniel@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">Torrey, D.</a>, and <a href="mailto:alberti@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">B. Alberti</a>, “<a href="https://tools.ietf.org/html/rfc1436">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</a>”, RFC 1436, March 1993. 2237 2378 </td> 2238 2379 </tr> 2239 2380 <tr> 2240 2381 <td class="reference"><b id="RFC1630">[RFC1630]</b></td> 2241 <td class="top"><a href="mailto:timbl@info.cern.ch" title="CERN, World-Wide Web project">Berners-Lee, T.</a>, “<a href="http ://tools.ietf.org/html/rfc1630">Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network2382 <td class="top"><a href="mailto:timbl@info.cern.ch" title="CERN, World-Wide Web project">Berners-Lee, T.</a>, “<a href="https://tools.ietf.org/html/rfc1630">Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network 2242 2383 as used in the World-Wide Web</a>”, RFC 1630, June 1994. 2243 2384 </td> … … 2245 2386 <tr> 2246 2387 <td class="reference"><b id="RFC1737">[RFC1737]</b></td> 2247 <td class="top"><a href="mailto:masinter@parc.xerox.com" title="Xerox Palo Alto Research Center">Masinter, L.</a> and <a href="mailto:sollins@lcs.mit.edu" title="MIT Laboratory for Computer Science">K. Sollins</a>, “<a href="http ://tools.ietf.org/html/rfc1737">Functional Requirements for Uniform Resource Names</a>”, RFC 1737, December 1994.2388 <td class="top"><a href="mailto:masinter@parc.xerox.com" title="Xerox Palo Alto Research Center">Masinter, L.</a> and <a href="mailto:sollins@lcs.mit.edu" title="MIT Laboratory for Computer Science">K. Sollins</a>, “<a href="https://tools.ietf.org/html/rfc1737">Functional Requirements for Uniform Resource Names</a>”, RFC 1737, December 1994. 2248 2389 </td> 2249 2390 </tr> 2250 2391 <tr> 2251 2392 <td class="reference"><b id="RFC1738">[RFC1738]</b></td> 2252 <td class="top"><a href="mailto:timbl@info.cern.ch" title="CERN, World-Wide Web project">Berners-Lee, T.</a>, <a href="mailto:masinter@parc.xerox.com" title="Xerox PARC">Masinter, L.</a>, and <a href="mailto:mpm@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">M. McCahill</a>, “<a href="http ://tools.ietf.org/html/rfc1738">Uniform Resource Locators (URL)</a>”, RFC 1738, December 1994.2393 <td class="top"><a href="mailto:timbl@info.cern.ch" title="CERN, World-Wide Web project">Berners-Lee, T.</a>, <a href="mailto:masinter@parc.xerox.com" title="Xerox PARC">Masinter, L.</a>, and <a href="mailto:mpm@boombox.micro.umn.edu" title="University of Minnesota, Computer and Information Services">M. McCahill</a>, “<a href="https://tools.ietf.org/html/rfc1738">Uniform Resource Locators (URL)</a>”, RFC 1738, December 1994. 2253 2394 </td> 2254 2395 </tr> 2255 2396 <tr> 2256 2397 <td class="reference"><b id="RFC1808">[RFC1808]</b></td> 2257 <td class="top"><a href="mailto:fielding@ics.uci.edu" title="University of California Irvine, Department of Information and Computer Science">Fielding, R.</a>, “<a href="http ://tools.ietf.org/html/rfc1808">Relative Uniform Resource Locators</a>”, RFC 1808, June 1995.2398 <td class="top"><a href="mailto:fielding@ics.uci.edu" title="University of California Irvine, Department of Information and Computer Science">Fielding, R.</a>, “<a href="https://tools.ietf.org/html/rfc1808">Relative Uniform Resource Locators</a>”, RFC 1808, June 1995. 2258 2399 </td> 2259 2400 </tr> 2260 2401 <tr> 2261 2402 <td class="reference"><b id="RFC1900">[RFC1900]</b></td> 2262 <td class="top"><a href="mailto:brian@dxcoms.cern.ch" title="CERN, Computing and Networks Division">Carpenter, B.</a> and <a href="mailto:yakov@cisco.com" title="cisco Systems">Y. Rekhter</a>, “<a href="http ://tools.ietf.org/html/rfc1900">Renumbering Needs Work</a>”, RFC 1900, February 1996.2403 <td class="top"><a href="mailto:brian@dxcoms.cern.ch" title="CERN, Computing and Networks Division">Carpenter, B.</a> and <a href="mailto:yakov@cisco.com" title="cisco Systems">Y. Rekhter</a>, “<a href="https://tools.ietf.org/html/rfc1900">Renumbering Needs Work</a>”, RFC 1900, February 1996. 2263 2404 </td> 2264 2405 </tr> 2265 2406 <tr> 2266 2407 <td class="reference"><b id="RFC1945">[RFC1945]</b></td> 2267 <td class="top"><a href="mailto:timbl@w3.org" title="MIT, Laboratory for Computer Science">Berners-Lee, T.</a>, <a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine, Department of Information and Computer Science">Fielding, R.</a>, and <a href="mailto:frystyk@w3.org" title="W3 Consortium, MIT Laboratory for Computer Science">H. Nielsen</a>, “<a href="http ://tools.ietf.org/html/rfc1945">Hypertext Transfer Protocol -- HTTP/1.0</a>”, RFC 1945, May 1996.2408 <td class="top"><a href="mailto:timbl@w3.org" title="MIT, Laboratory for Computer Science">Berners-Lee, T.</a>, <a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine, Department of Information and Computer Science">Fielding, R.</a>, and <a href="mailto:frystyk@w3.org" title="W3 Consortium, MIT Laboratory for Computer Science">H. Nielsen</a>, “<a href="https://tools.ietf.org/html/rfc1945">Hypertext Transfer Protocol -- HTTP/1.0</a>”, RFC 1945, May 1996. 2268 2409 </td> 2269 2410 </tr> 2270 2411 <tr> 2271 2412 <td class="reference"><b id="RFC2068">[RFC2068]</b></td> 2272 <td class="top"><a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine, Department of Information and Computer Science">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="MIT Laboratory for Computer Science">Gettys, J.</a>, <a href="mailto:mogul@wrl.dec.com" title="Digital Equipment Corporation, Western Research Laboratory">Mogul, J.</a>, <a href="mailto:frystyk@w3.org" title="MIT Laboratory for Computer Science">Nielsen, H.</a>, and <a href="mailto:timbl@w3.org" title="MIT Laboratory for Computer Science">T. Berners-Lee</a>, “<a href="http ://tools.ietf.org/html/rfc2068">Hypertext Transfer Protocol -- HTTP/1.1</a>”, RFC 2068, January 1997.2413 <td class="top"><a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine, Department of Information and Computer Science">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="MIT Laboratory for Computer Science">Gettys, J.</a>, <a href="mailto:mogul@wrl.dec.com" title="Digital Equipment Corporation, Western Research Laboratory">Mogul, J.</a>, <a href="mailto:frystyk@w3.org" title="MIT Laboratory for Computer Science">Nielsen, H.</a>, and <a href="mailto:timbl@w3.org" title="MIT Laboratory for Computer Science">T. Berners-Lee</a>, “<a href="https://tools.ietf.org/html/rfc2068">Hypertext Transfer Protocol -- HTTP/1.1</a>”, RFC 2068, January 1997. 2273 2414 </td> 2274 2415 </tr> 2275 2416 <tr> 2276 2417 <td class="reference"><b id="RFC2145">[RFC2145]</b></td> 2277 <td class="top"><a href="mailto:mogul@wrl.dec.com" title="Western Research Laboratory">Mogul, J.</a>, <a href="mailto:fielding@ics.uci.edu" title="Department of Information and Computer Science">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="MIT Laboratory for Computer Science">Gettys, J.</a>, and <a href="mailto:frystyk@w3.org" title="W3 Consortium">H. Nielsen</a>, “<a href="http ://tools.ietf.org/html/rfc2145">Use and Interpretation of HTTP Version Numbers</a>”, RFC 2145, May 1997.2418 <td class="top"><a href="mailto:mogul@wrl.dec.com" title="Western Research Laboratory">Mogul, J.</a>, <a href="mailto:fielding@ics.uci.edu" title="Department of Information and Computer Science">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="MIT Laboratory for Computer Science">Gettys, J.</a>, and <a href="mailto:frystyk@w3.org" title="W3 Consortium">H. Nielsen</a>, “<a href="https://tools.ietf.org/html/rfc2145">Use and Interpretation of HTTP Version Numbers</a>”, RFC 2145, May 1997. 2278 2419 </td> 2279 2420 </tr> 2280 2421 <tr> 2281 2422 <td class="reference"><b id="RFC2324">[RFC2324]</b></td> 2282 <td class="top"><a href="mailto:masinter@parc.xerox.com" title="Xerox Palo Alto Research Center">Masinter, L.</a>, “<a href="http ://tools.ietf.org/html/rfc2324">Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)</a>”, RFC 2324, April 1998.2423 <td class="top"><a href="mailto:masinter@parc.xerox.com" title="Xerox Palo Alto Research Center">Masinter, L.</a>, “<a href="https://tools.ietf.org/html/rfc2324">Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)</a>”, RFC 2324, April 1998. 2283 2424 </td> 2284 2425 </tr> 2285 2426 <tr> 2286 2427 <td class="reference"><b id="RFC2616">[RFC2616]</b></td> 2287 <td class="top"><a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="W3C">Gettys, J.</a>, <a href="mailto:mogul@wrl.dec.com" title="Compaq Computer Corporation">Mogul, J.</a>, <a href="mailto:frystyk@w3.org" title="MIT Laboratory for Computer Science">Frystyk, H.</a>, <a href="mailto:masinter@parc.xerox.com" title="Xerox Corporation">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, and <a href="mailto:timbl@w3.org" title="W3C">T. Berners-Lee</a>, “<a href="http ://tools.ietf.org/html/rfc2616">Hypertext Transfer Protocol -- HTTP/1.1</a>”, RFC 2616, June 1999.2428 <td class="top"><a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="W3C">Gettys, J.</a>, <a href="mailto:mogul@wrl.dec.com" title="Compaq Computer Corporation">Mogul, J.</a>, <a href="mailto:frystyk@w3.org" title="MIT Laboratory for Computer Science">Frystyk, H.</a>, <a href="mailto:masinter@parc.xerox.com" title="Xerox Corporation">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, and <a href="mailto:timbl@w3.org" title="W3C">T. Berners-Lee</a>, “<a href="https://tools.ietf.org/html/rfc2616">Hypertext Transfer Protocol -- HTTP/1.1</a>”, RFC 2616, June 1999. 2288 2429 </td> 2289 2430 </tr> 2290 2431 <tr> 2291 2432 <td class="reference"><b id="RFC2821">[RFC2821]</b></td> 2292 <td class="top"><a href="mailto:klensin@research.att.com" title="AT&T Laboratories">Klensin, J.</a>, “<a href="http ://tools.ietf.org/html/rfc2821">Simple Mail Transfer Protocol</a>”, RFC 2821, April 2001.2433 <td class="top"><a href="mailto:klensin@research.att.com" title="AT&T Laboratories">Klensin, J.</a>, “<a href="https://tools.ietf.org/html/rfc2821">Simple Mail Transfer Protocol</a>”, RFC 2821, April 2001. 2293 2434 </td> 2294 2435 </tr> 2295 2436 <tr> 2296 2437 <td class="reference"><b id="RFC2822">[RFC2822]</b></td> 2297 <td class="top">Resnick, P., “<a href="http ://tools.ietf.org/html/rfc2822">Internet Message Format</a>”, RFC 2822, April 2001.2438 <td class="top">Resnick, P., “<a href="https://tools.ietf.org/html/rfc2822">Internet Message Format</a>”, RFC 2822, April 2001. 2298 2439 </td> 2299 2440 </tr> 2300 2441 <tr> 2301 2442 <td class="reference"><b id="RFC3864">[RFC3864]</b></td> 2302 <td class="top"><a href="mailto:GK-IETF@ninebynine.org" title="Nine by Nine">Klyne, G.</a>, <a href="mailto:mnot@pobox.com" title="BEA Systems">Nottingham, M.</a>, and <a href="mailto:JeffMogul@acm.org" title="HP Labs">J. Mogul</a>, “<a href="http ://tools.ietf.org/html/rfc3864">Registration Procedures for Message Header Fields</a>”, BCP 90, RFC 3864, September 2004.2443 <td class="top"><a href="mailto:GK-IETF@ninebynine.org" title="Nine by Nine">Klyne, G.</a>, <a href="mailto:mnot@pobox.com" title="BEA Systems">Nottingham, M.</a>, and <a href="mailto:JeffMogul@acm.org" title="HP Labs">J. Mogul</a>, “<a href="https://tools.ietf.org/html/rfc3864">Registration Procedures for Message Header Fields</a>”, BCP 90, RFC 3864, September 2004. 2303 2444 </td> 2304 2445 </tr> 2305 2446 <tr> 2306 2447 <td class="reference"><b id="RFC3977">[RFC3977]</b></td> 2307 <td class="top"><a href="mailto:clive@demon.net" title="THUS plc">Feather, C.</a>, “<a href="http ://tools.ietf.org/html/rfc3977">Network News Transfer Protocol (NNTP)</a>”, RFC 3977, October 2006.2448 <td class="top"><a href="mailto:clive@demon.net" title="THUS plc">Feather, C.</a>, “<a href="https://tools.ietf.org/html/rfc3977">Network News Transfer Protocol (NNTP)</a>”, RFC 3977, October 2006. 2308 2449 </td> 2309 2450 </tr> 2310 2451 <tr> 2311 2452 <td class="reference"><b id="RFC4288">[RFC4288]</b></td> 2312 <td class="top"><a href="mailto:ned.freed@mrochek.com" title="Sun Microsystems">Freed, N.</a> and <a href="mailto:klensin+ietf@jck.com">J. Klensin</a>, “<a href="http ://tools.ietf.org/html/rfc4288">Media Type Specifications and Registration Procedures</a>”, BCP 13, RFC 4288, December 2005.2453 <td class="top"><a href="mailto:ned.freed@mrochek.com" title="Sun Microsystems">Freed, N.</a> and <a href="mailto:klensin+ietf@jck.com">J. Klensin</a>, “<a href="https://tools.ietf.org/html/rfc4288">Media Type Specifications and Registration Procedures</a>”, BCP 13, RFC 4288, December 2005. 2313 2454 </td> 2314 2455 </tr> 2315 2456 <tr> 2316 2457 <td class="reference"><b id="RFC822">[RFC822]</b></td> 2317 <td class="top"><a href="mailto:DCrocker@UDel-Relay" title="University of Delaware, Dept. of Electrical Engineering">Crocker, D.</a>, “<a href="http ://tools.ietf.org/html/rfc822">Standard for the format of ARPA Internet text messages</a>”, STD 11, RFC 822, August 1982.2458 <td class="top"><a href="mailto:DCrocker@UDel-Relay" title="University of Delaware, Dept. of Electrical Engineering">Crocker, D.</a>, “<a href="https://tools.ietf.org/html/rfc822">Standard for the format of ARPA Internet text messages</a>”, STD 11, RFC 822, August 1982. 2318 2459 </td> 2319 2460 </tr> 2320 2461 <tr> 2321 2462 <td class="reference"><b id="RFC959">[RFC959]</b></td> 2322 <td class="top">Postel, J. and J. Reynolds, “<a href="http ://tools.ietf.org/html/rfc959">File Transfer Protocol</a>”, STD 9, RFC 959, October 1985.2463 <td class="top">Postel, J. and J. Reynolds, “<a href="https://tools.ietf.org/html/rfc959">File Transfer Protocol</a>”, STD 9, RFC 959, October 1985. 2323 2464 </td> 2324 2465 </tr> … … 2338 2479 </tr> 2339 2480 </table> 2340 <div class="avoidbreak"> 2341 <h1 id="rfc.authors"><a href="#rfc.authors">Authors' Addresses</a></h1> 2342 <address class="vcard"><span class="vcardline"><span class="fn">Roy T. Fielding</span> 2343 (editor) 2344 <span class="n hidden"><span class="family-name">Fielding</span><span class="given-name">Roy T.</span></span></span><span class="org vcardline">Day Software</span><span class="adr"><span class="street-address vcardline">23 Corporate Plaza DR, Suite 280</span><span class="vcardline"><span class="locality">Newport Beach</span>, <span class="region">CA</span> <span class="postal-code">92660</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline tel">Phone: <a href="tel:+1-949-706-5300"><span class="value">+1-949-706-5300</span></a></span><span class="vcardline tel"><span class="type">Fax</span>: <a href="fax:+1-949-706-5305"><span class="value">+1-949-706-5305</span></a></span><span class="vcardline">EMail: <a href="mailto:fielding@gbiv.com"><span class="email">fielding@gbiv.com</span></a></span><span class="vcardline">URI: <a href="http://roy.gbiv.com/" class="url">http://roy.gbiv.com/</a></span></address> 2345 <address class="vcard"><span class="vcardline"><span class="fn">Jim Gettys</span><span class="n hidden"><span class="family-name">Gettys</span><span class="given-name">Jim</span></span></span><span class="org vcardline">One Laptop per Child</span><span class="adr"><span class="street-address vcardline">21 Oak Knoll Road</span><span class="vcardline"><span class="locality">Carlisle</span>, <span class="region">MA</span> <span class="postal-code">01741</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">EMail: <a href="mailto:jg@laptop.org"><span class="email">jg@laptop.org</span></a></span><span class="vcardline">URI: <a href="http://www.laptop.org/" class="url">http://www.laptop.org/</a></span></address> 2346 <address class="vcard"><span class="vcardline"><span class="fn">Jeffrey C. Mogul</span><span class="n hidden"><span class="family-name">Mogul</span><span class="given-name">Jeffrey C.</span></span></span><span class="org vcardline">Hewlett-Packard Company</span><span class="adr"><span class="street-address vcardline">HP Labs, Large Scale Systems Group</span><span class="street-address vcardline">1501 Page Mill Road, MS 1177</span><span class="vcardline"><span class="locality">Palo Alto</span>, <span class="region">CA</span> <span class="postal-code">94304</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">EMail: <a href="mailto:JeffMogul@acm.org"><span class="email">JeffMogul@acm.org</span></a></span></address> 2347 <address class="vcard"><span class="vcardline"><span class="fn">Henrik Frystyk Nielsen</span><span class="n hidden"><span class="family-name">Frystyk</span></span></span><span class="org vcardline">Microsoft Corporation</span><span class="adr"><span class="street-address vcardline">1 Microsoft Way</span><span class="vcardline"><span class="locality">Redmond</span>, <span class="region">WA</span> <span class="postal-code">98052</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">EMail: <a href="mailto:henrikn@microsoft.com"><span class="email">henrikn@microsoft.com</span></a></span></address> 2348 <address class="vcard"><span class="vcardline"><span class="fn">Larry Masinter</span><span class="n hidden"><span class="family-name">Masinter</span><span class="given-name">Larry</span></span></span><span class="org vcardline">Adobe Systems, Incorporated</span><span class="adr"><span class="street-address vcardline">345 Park Ave</span><span class="vcardline"><span class="locality">San Jose</span>, <span class="region">CA</span> <span class="postal-code">95110</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">EMail: <a href="mailto:LMM@acm.org"><span class="email">LMM@acm.org</span></a></span><span class="vcardline">URI: <a href="http://larry.masinter.net/" class="url">http://larry.masinter.net/</a></span></address> 2349 <address class="vcard"><span class="vcardline"><span class="fn">Paul J. Leach</span><span class="n hidden"><span class="family-name">Leach</span><span class="given-name">Paul J.</span></span></span><span class="org vcardline">Microsoft Corporation</span><span class="adr"><span class="street-address vcardline">1 Microsoft Way</span><span class="vcardline"><span class="locality">Redmond</span>, <span class="region">WA</span> <span class="postal-code">98052</span></span></span><span class="vcardline">EMail: <a href="mailto:paulle@microsoft.com"><span class="email">paulle@microsoft.com</span></a></span></address> 2350 <address class="vcard"><span class="vcardline"><span class="fn">Tim Berners-Lee</span><span class="n hidden"><span class="family-name">Berners-Lee</span><span class="given-name">Tim</span></span></span><span class="org vcardline">World Wide Web Consortium</span><span class="adr"><span class="street-address vcardline">MIT Computer Science and Artificial Intelligence Laboratory</span><span class="street-address vcardline">The Stata Center, Building 32</span><span class="street-address vcardline">32 Vassar Street</span><span class="vcardline"><span class="locality">Cambridge</span>, <span class="region">MA</span> <span class="postal-code">02139</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">EMail: <a href="mailto:timbl@w3.org"><span class="email">timbl@w3.org</span></a></span><span class="vcardline">URI: <a href="http://www.w3.org/People/Berners-Lee/" class="url">http://www.w3.org/People/Berners-Lee/</a></span></address> 2351 <address class="vcard"><span class="vcardline"><span class="fn">Yves Lafon</span> 2352 (editor) 2353 <span class="n hidden"><span class="family-name">Lafon</span><span class="given-name">Yves</span></span></span><span class="org vcardline">World Wide Web Consortium</span><span class="adr"><span class="street-address vcardline">W3C / ERCIM</span><span class="street-address vcardline">2004, rte des Lucioles</span><span class="vcardline"><span class="locality">Sophia-Antipolis</span>, <span class="region">AM</span> <span class="postal-code">06902</span></span><span class="country-name vcardline">France</span></span><span class="vcardline">EMail: <a href="mailto:ylafon@w3.org"><span class="email">ylafon@w3.org</span></a></span><span class="vcardline">URI: <a href="http://www.raubacapeu.net/people/yves/" class="url">http://www.raubacapeu.net/people/yves/</a></span></address> 2354 <address class="vcard"><span class="vcardline"><span class="fn">Julian F. Reschke</span> 2355 (editor) 2356 <span class="n hidden"><span class="family-name">Reschke</span><span class="given-name">Julian F.</span></span></span><span class="org vcardline">greenbytes GmbH</span><span class="adr"><span class="street-address vcardline">Hafenweg 16</span><span class="vcardline"><span class="locality">Muenster</span>, <span class="region">NW</span> <span class="postal-code">48155</span></span><span class="country-name vcardline">Germany</span></span><span class="vcardline tel">Phone: <a href="tel:+492512807760"><span class="value">+49 251 2807760</span></a></span><span class="vcardline tel"><span class="type">Fax</span>: <a href="fax:+492512807761"><span class="value">+49 251 2807761</span></a></span><span class="vcardline">EMail: <a href="mailto:julian.reschke@greenbytes.de"><span class="email">julian.reschke@greenbytes.de</span></a></span><span class="vcardline">URI: <a href="http://greenbytes.de/tech/webdav/" class="url">http://greenbytes.de/tech/webdav/</a></span></address> 2481 <div id="internet.media.type.http"> 2482 <h1 id="rfc.section.A" class="np"><a href="#rfc.section.A">A.</a> <a href="#internet.media.type.http">Internet Media Types</a></h1> 2483 <p id="rfc.section.A.p.1">In addition to defining HTTP/1.1, this document serves as the specification for the Internet media type "message/http" and 2484 "application/http". The following is to be registered with IANA <a href="#RFC4288" id="rfc.xref.RFC4288.1"><cite title="Media Type Specifications and Registration Procedures">[RFC4288]</cite></a>. 2485 </p> 2486 <div id="internet.media.type.message.http"> 2487 <div id="rfc.iref.m.2"></div> 2488 <div id="rfc.iref.m.3"></div> 2489 <h2 id="rfc.section.A.1"><a href="#rfc.section.A.1">A.1</a> <a href="#internet.media.type.message.http">Internet Media Type message/http</a></h2> 2490 <p id="rfc.section.A.1.p.1">The message/http type can be used to enclose a single HTTP request or response message, provided that it obeys the MIME restrictions 2491 for all "message" types regarding line length and encodings. 2492 </p> 2493 <p id="rfc.section.A.1.p.2"></p> 2494 <dl> 2495 <dt>Type name:</dt> 2496 <dd>message</dd> 2497 <dt>Subtype name:</dt> 2498 <dd>http</dd> 2499 <dt>Required parameters:</dt> 2500 <dd>none</dd> 2501 <dt>Optional parameters:</dt> 2502 <dd>version, msgtype 2503 <dl> 2504 <dt>version:</dt> 2505 <dd>The HTTP-Version number of the enclosed message (e.g., "1.1"). If not present, the version can be determined from the first 2506 line of the body. 2507 </dd> 2508 <dt>msgtype:</dt> 2509 <dd>The message type -- "request" or "response". If not present, the type can be determined from the first line of the body.</dd> 2510 </dl> 2511 </dd> 2512 <dt>Encoding considerations:</dt> 2513 <dd>only "7bit", "8bit", or "binary" are permitted</dd> 2514 <dt>Security considerations:</dt> 2515 <dd>none</dd> 2516 <dt>Interoperability considerations:</dt> 2517 <dd>none</dd> 2518 <dt>Published specification:</dt> 2519 <dd>This specification (see <a href="#internet.media.type.message.http" title="Internet Media Type message/http">Appendix A.1</a>). 2520 </dd> 2521 <dt>Applications that use this media type:</dt> 2522 <dt>Additional information:</dt> 2523 <dd> 2524 <dl> 2525 <dt>Magic number(s):</dt> 2526 <dd>none</dd> 2527 <dt>File extension(s):</dt> 2528 <dd>none</dd> 2529 <dt>Macintosh file type code(s):</dt> 2530 <dd>none</dd> 2531 </dl> 2532 </dd> 2533 <dt>Person and email address to contact for further information:</dt> 2534 <dd>See Authors Section.</dd> 2535 <dt>Intended usage:</dt> 2536 <dd>COMMON</dd> 2537 <dt>Restrictions on usage:</dt> 2538 <dd>none</dd> 2539 <dt>Author/Change controller:</dt> 2540 <dd>IESG</dd> 2541 </dl> 2542 </div> 2543 <div id="internet.media.type.application.http"> 2544 <div id="rfc.iref.m.4"></div> 2545 <div id="rfc.iref.a.1"></div> 2546 <h2 id="rfc.section.A.2"><a href="#rfc.section.A.2">A.2</a> <a href="#internet.media.type.application.http">Internet Media Type application/http</a></h2> 2547 <p id="rfc.section.A.2.p.1">The application/http type can be used to enclose a pipeline of one or more HTTP request or response messages (not intermixed).</p> 2548 <p id="rfc.section.A.2.p.2"></p> 2549 <dl> 2550 <dt>Type name:</dt> 2551 <dd>application</dd> 2552 <dt>Subtype name:</dt> 2553 <dd>http</dd> 2554 <dt>Required parameters:</dt> 2555 <dd>none</dd> 2556 <dt>Optional parameters:</dt> 2557 <dd>version, msgtype 2558 <dl> 2559 <dt>version:</dt> 2560 <dd>The HTTP-Version number of the enclosed messages (e.g., "1.1"). If not present, the version can be determined from the first 2561 line of the body. 2562 </dd> 2563 <dt>msgtype:</dt> 2564 <dd>The message type -- "request" or "response". If not present, the type can be determined from the first line of the body.</dd> 2565 </dl> 2566 </dd> 2567 <dt>Encoding considerations:</dt> 2568 <dd>HTTP messages enclosed by this type are in "binary" format; use of an appropriate Content-Transfer-Encoding is required when 2569 transmitted via E-mail. 2570 </dd> 2571 <dt>Security considerations:</dt> 2572 <dd>none</dd> 2573 <dt>Interoperability considerations:</dt> 2574 <dd>none</dd> 2575 <dt>Published specification:</dt> 2576 <dd>This specification (see <a href="#internet.media.type.application.http" title="Internet Media Type application/http">Appendix A.2</a>). 2577 </dd> 2578 <dt>Applications that use this media type:</dt> 2579 <dt>Additional information:</dt> 2580 <dd> 2581 <dl> 2582 <dt>Magic number(s):</dt> 2583 <dd>none</dd> 2584 <dt>File extension(s):</dt> 2585 <dd>none</dd> 2586 <dt>Macintosh file type code(s):</dt> 2587 <dd>none</dd> 2588 </dl> 2589 </dd> 2590 <dt>Person and email address to contact for further information:</dt> 2591 <dd>See Authors Section.</dd> 2592 <dt>Intended usage:</dt> 2593 <dd>COMMON</dd> 2594 <dt>Restrictions on usage:</dt> 2595 <dd>none</dd> 2596 <dt>Author/Change controller:</dt> 2597 <dd>IESG</dd> 2598 </dl> 2599 </div> 2357 2600 </div> 2358 <h1 id="rfc.section.A" class="np"><a href="#rfc.section.A">A.</a> <a id="internet.media.type.http" href="#internet.media.type.http">Internet Media Types</a></h1> 2359 <p id="rfc.section.A.p.1">In addition to defining HTTP/1.1, this document serves as the specification for the Internet media type "message/http" and 2360 "application/http". The following is to be registered with IANA <a href="#RFC4288" id="rfc.xref.RFC4288.1"><cite title="Media Type Specifications and Registration Procedures">[RFC4288]</cite></a>. 2361 </p> 2362 <div id="rfc.iref.m.2"></div> 2363 <div id="rfc.iref.m.3"></div> 2364 <h2 id="rfc.section.A.1"><a href="#rfc.section.A.1">A.1</a> <a id="internet.media.type.message.http" href="#internet.media.type.message.http">Internet Media Type message/http</a></h2> 2365 <p id="rfc.section.A.1.p.1">The message/http type can be used to enclose a single HTTP request or response message, provided that it obeys the MIME restrictions 2366 for all "message" types regarding line length and encodings. 2367 </p> 2368 <p id="rfc.section.A.1.p.2"> </p> 2369