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| 305 | |
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| 320 | |
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| 321 | @page { |
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| 322 | @top-left { |
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| 323 | content: "INTERNET DRAFT"; |
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| 324 | } |
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| 325 | @top-right { |
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| 326 | content: "February 2009"; |
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| 327 | } |
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| 328 | @top-center { |
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| 329 | content: "HTTP/1.1, Part 4"; |
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| 330 | } |
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| 331 | @bottom-left { |
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| 332 | content: "Fielding, et al."; |
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| 333 | } |
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| 334 | @bottom-center { |
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| 336 | } |
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| 341 | |
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| 349 | @top-center { |
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| 350 | content: normal; |
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| 351 | } |
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| 352 | } |
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| 353 | </style><link rel="Contents" href="#rfc.toc"> |
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| 354 | <link rel="Author" href="#rfc.authors"> |
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| 355 | <link rel="Copyright" href="#rfc.copyright"> |
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| 356 | <link rel="Index" href="#rfc.index"> |
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| 357 | <link rel="Chapter" title="1 Introduction" href="#rfc.section.1"> |
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| 358 | <link rel="Chapter" title="2 Entity Tags" href="#rfc.section.2"> |
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| 359 | <link rel="Chapter" title="3 Status Code Definitions" href="#rfc.section.3"> |
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| 360 | <link rel="Chapter" title="4 Weak and Strong Validators" href="#rfc.section.4"> |
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| 361 | <link rel="Chapter" title="5 Rules for When to Use Entity Tags and Last-Modified Dates" href="#rfc.section.5"> |
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| 362 | <link rel="Chapter" title="6 Header Field Definitions" href="#rfc.section.6"> |
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| 363 | <link rel="Chapter" title="7 IANA Considerations" href="#rfc.section.7"> |
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| 364 | <link rel="Chapter" title="8 Security Considerations" href="#rfc.section.8"> |
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| 365 | <link rel="Chapter" title="9 Acknowledgments" href="#rfc.section.9"> |
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| 366 | <link rel="Chapter" href="#rfc.section.10" title="10 References"> |
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| 367 | <link rel="Appendix" title="A Compatibility with Previous Versions" href="#rfc.section.A"> |
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| 368 | <link rel="Appendix" title="B Collected ABNF" href="#rfc.section.B"> |
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| 369 | <link rel="Appendix" title="C Change Log (to be removed by RFC Editor before publication)" href="#rfc.section.C"> |
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| 370 | <meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.424, 2009-02-24 16:15:29, XSLT vendor: SAXON 8.9 from Saxonica http://www.saxonica.com/"> |
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| 371 | <link rel="schema.DC" href="http://purl.org/dc/elements/1.1/"> |
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| 372 | <meta name="DC.Creator" content="Fielding, R."> |
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| 373 | <meta name="DC.Creator" content="Gettys, J."> |
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| 374 | <meta name="DC.Creator" content="Mogul, J."> |
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| 375 | <meta name="DC.Creator" content="Frystyk, H."> |
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| 376 | <meta name="DC.Creator" content="Masinter, L."> |
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| 377 | <meta name="DC.Creator" content="Leach, P."> |
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| 378 | <meta name="DC.Creator" content="Berners-Lee, T."> |
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| 379 | <meta name="DC.Creator" content="Lafon, Y."> |
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| 380 | <meta name="DC.Creator" content="Reschke, J. F."> |
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| 381 | <meta name="DC.Identifier" content="urn:ietf:id:draft-ietf-httpbis-p4-conditional-latest"> |
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| 382 | <meta name="DC.Date.Issued" scheme="ISO8601" content="2009-02"> |
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| 383 | <meta name="DC.Relation.Replaces" content="urn:ietf:rfc:2616"> |
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| 384 | <meta name="DC.Description.Abstract" content="The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 4 of the seven-part specification that defines the protocol referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616. Part 4 defines request header fields for indicating conditional requests and the rules for constructing responses to those requests."> |
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| 385 | </head> |
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| 386 | <body> |
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| 387 | <table summary="header information" class="header" border="0" cellpadding="1" cellspacing="1"> |
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| 388 | <tr> |
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| 389 | <td class="header left">HTTPbis Working Group</td> |
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| 390 | <td class="header right">R. Fielding, Editor</td> |
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| 391 | </tr> |
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| 392 | <tr> |
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| 393 | <td class="header left">Internet Draft</td> |
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| 394 | <td class="header right">Day Software</td> |
|---|
| 395 | </tr> |
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| 396 | <tr> |
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| 397 | <td class="header left"> |
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| 398 | <draft-ietf-httpbis-p4-conditional-latest> |
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| 399 | |
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| 400 | </td> |
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| 401 | <td class="header right">J. Gettys</td> |
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| 402 | </tr> |
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| 403 | <tr> |
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| 404 | <td class="header left">Obsoletes: <a href="http://tools.ietf.org/html/rfc2616">2616</a> (if approved) |
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| 405 | </td> |
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| 406 | <td class="header right">One Laptop per Child</td> |
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| 407 | </tr> |
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| 408 | <tr> |
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| 409 | <td class="header left">Intended status: Standards Track</td> |
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| 410 | <td class="header right">J. Mogul</td> |
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| 411 | </tr> |
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| 412 | <tr> |
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| 413 | <td class="header left">Expires: August 2009</td> |
|---|
| 414 | <td class="header right">HP</td> |
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| 415 | </tr> |
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| 416 | <tr> |
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| 417 | <td class="header left"></td> |
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| 418 | <td class="header right">H. Frystyk</td> |
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| 419 | </tr> |
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| 420 | <tr> |
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| 421 | <td class="header left"></td> |
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| 422 | <td class="header right">Microsoft</td> |
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| 423 | </tr> |
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| 424 | <tr> |
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| 425 | <td class="header left"></td> |
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| 426 | <td class="header right">L. Masinter</td> |
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| 427 | </tr> |
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| 428 | <tr> |
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| 429 | <td class="header left"></td> |
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| 430 | <td class="header right">Adobe Systems</td> |
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| 431 | </tr> |
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| 432 | <tr> |
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| 433 | <td class="header left"></td> |
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| 434 | <td class="header right">P. Leach</td> |
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| 435 | </tr> |
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| 436 | <tr> |
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| 437 | <td class="header left"></td> |
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| 438 | <td class="header right">Microsoft</td> |
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| 439 | </tr> |
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| 440 | <tr> |
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| 441 | <td class="header left"></td> |
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| 442 | <td class="header right">T. Berners-Lee</td> |
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| 443 | </tr> |
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| 444 | <tr> |
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| 445 | <td class="header left"></td> |
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| 446 | <td class="header right">W3C/MIT</td> |
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| 447 | </tr> |
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| 448 | <tr> |
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| 449 | <td class="header left"></td> |
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| 450 | <td class="header right">Y. Lafon, Editor</td> |
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| 451 | </tr> |
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| 452 | <tr> |
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| 453 | <td class="header left"></td> |
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| 454 | <td class="header right">W3C</td> |
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| 455 | </tr> |
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| 456 | <tr> |
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| 457 | <td class="header left"></td> |
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| 458 | <td class="header right">J. F. Reschke, Editor</td> |
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| 459 | </tr> |
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| 460 | <tr> |
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| 461 | <td class="header left"></td> |
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| 462 | <td class="header right">greenbytes</td> |
|---|
| 463 | </tr> |
|---|
| 464 | <tr> |
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| 465 | <td class="header left"></td> |
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| 466 | <td class="header right">February 28, 2009</td> |
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| 467 | </tr> |
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| 468 | </table> |
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| 469 | <p class="title">HTTP/1.1, part 4: Conditional Requests<br><span class="filename">draft-ietf-httpbis-p4-conditional-latest</span></p> |
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| 470 | <h1><a id="rfc.status" href="#rfc.status">Status of this Memo</a></h1> |
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| 471 | <p>This Internet-Draft is submitted to IETF pursuant to, and in full conformance with, the provisions of BCP 78 and BCP 79. This |
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| 472 | document may contain material from IETF Documents or IETF Contributions published or made publicly available before November |
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| 473 | 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to |
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| 474 | allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) |
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| 475 | controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative |
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| 476 | works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate |
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| 477 | it into languages other than English. |
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| 478 | </p> |
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| 479 | <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note |
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| 480 | that other groups may also distribute working documents as Internet-Drafts. |
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| 481 | </p> |
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| 482 | <p>Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other |
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| 483 | documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work |
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| 484 | in progress”. |
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| 485 | </p> |
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| 486 | <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>>. |
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| 487 | </p> |
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| 488 | <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>>. |
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| 489 | </p> |
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| 490 | <p>This Internet-Draft will expire in August 2009.</p> |
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| 491 | <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1> |
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| 492 | <p>Copyright © 2009 IETF Trust and the persons identified as the document authors. All rights reserved.</p> |
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| 493 | <p>This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date |
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| 494 | of publication of this document (<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. |
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| 495 | </p> |
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| 496 | <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1> |
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| 497 | <p>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information |
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| 498 | systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 4 of the |
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| 499 | seven-part specification that defines the protocol referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616. Part |
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| 500 | 4 defines request header fields for indicating conditional requests and the rules for constructing responses to those requests. |
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| 501 | </p> |
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| 502 | <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1> |
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| 503 | <p>Discussion of this draft should take place on the HTTPBIS working group mailing list (ietf-http-wg@w3.org). The current issues |
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| 504 | list is at <<a href="http://tools.ietf.org/wg/httpbis/trac/report/11">http://tools.ietf.org/wg/httpbis/trac/report/11</a>> and related documents (including fancy diffs) can be found at <<a href="http://tools.ietf.org/wg/httpbis/">http://tools.ietf.org/wg/httpbis/</a>>. |
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| 505 | </p> |
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| 506 | <p>The changes in this draft are summarized in <a href="#changes.since.05" title="Since draft-ietf-httpbis-p4-conditional-05">Appendix C.7</a>. |
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| 507 | </p> |
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| 508 | <hr class="noprint"> |
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| 509 | <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1> |
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| 510 | <ul class="toc"> |
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| 511 | <li class="tocline0">1. <a href="#introduction">Introduction</a><ul class="toc"> |
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| 512 | <li class="tocline1">1.1 <a href="#intro.requirements">Requirements</a></li> |
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| 513 | <li class="tocline1">1.2 <a href="#notation">Syntax Notation</a><ul class="toc"> |
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| 514 | <li class="tocline1">1.2.1 <a href="#core.rules">Core Rules</a></li> |
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| 515 | <li class="tocline1">1.2.2 <a href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></li> |
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| 516 | </ul> |
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| 517 | </li> |
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| 518 | </ul> |
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| 519 | </li> |
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| 520 | <li class="tocline0">2. <a href="#entity.tags">Entity Tags</a></li> |
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| 521 | <li class="tocline0">3. <a href="#rfc.section.3">Status Code Definitions</a><ul class="toc"> |
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| 522 | <li class="tocline1">3.1 <a href="#status.304">304 Not Modified</a></li> |
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| 523 | <li class="tocline1">3.2 <a href="#status.412">412 Precondition Failed</a></li> |
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| 524 | </ul> |
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| 525 | </li> |
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| 526 | <li class="tocline0">4. <a href="#weak.and.strong.validators">Weak and Strong Validators</a></li> |
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| 527 | <li class="tocline0">5. <a href="#rules.for.when.to.use.entity.tags.and.last-modified.dates">Rules for When to Use Entity Tags and Last-Modified Dates</a></li> |
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| 528 | <li class="tocline0">6. <a href="#header.fields">Header Field Definitions</a><ul class="toc"> |
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| 529 | <li class="tocline1">6.1 <a href="#header.etag">ETag</a></li> |
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| 530 | <li class="tocline1">6.2 <a href="#header.if-match">If-Match</a></li> |
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| 531 | <li class="tocline1">6.3 <a href="#header.if-modified-since">If-Modified-Since</a></li> |
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| 532 | <li class="tocline1">6.4 <a href="#header.if-none-match">If-None-Match</a></li> |
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| 533 | <li class="tocline1">6.5 <a href="#header.if-unmodified-since">If-Unmodified-Since</a></li> |
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| 534 | <li class="tocline1">6.6 <a href="#header.last-modified">Last-Modified</a></li> |
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| 535 | </ul> |
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| 536 | </li> |
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| 537 | <li class="tocline0">7. <a href="#IANA.considerations">IANA Considerations</a><ul class="toc"> |
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| 538 | <li class="tocline1">7.1 <a href="#message.header.registration">Message Header Registration</a></li> |
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| 539 | </ul> |
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| 540 | </li> |
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| 541 | <li class="tocline0">8. <a href="#security.considerations">Security Considerations</a></li> |
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| 542 | <li class="tocline0">9. <a href="#ack">Acknowledgments</a></li> |
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| 543 | <li class="tocline0">10. <a href="#rfc.references">References</a><ul class="toc"> |
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| 544 | <li class="tocline1">10.1 <a href="#rfc.references.1">Normative References</a></li> |
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| 545 | <li class="tocline1">10.2 <a href="#rfc.references.2">Informative References</a></li> |
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| 546 | </ul> |
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| 547 | </li> |
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| 548 | <li class="tocline0"><a href="#rfc.authors">Authors' Addresses</a></li> |
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| 549 | <li class="tocline0">A. <a href="#compatibility">Compatibility with Previous Versions</a><ul class="toc"> |
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| 550 | <li class="tocline1">A.1 <a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li> |
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| 551 | </ul> |
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| 552 | </li> |
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| 553 | <li class="tocline0">B. <a href="#collected.abnf">Collected ABNF</a></li> |
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| 554 | <li class="tocline0">C. <a href="#change.log">Change Log (to be removed by RFC Editor before publication)</a><ul class="toc"> |
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| 555 | <li class="tocline1">C.1 <a href="#rfc.section.C.1">Since RFC2616</a></li> |
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| 556 | <li class="tocline1">C.2 <a href="#rfc.section.C.2">Since draft-ietf-httpbis-p4-conditional-00</a></li> |
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| 557 | <li class="tocline1">C.3 <a href="#rfc.section.C.3">Since draft-ietf-httpbis-p4-conditional-01</a></li> |
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| 558 | <li class="tocline1">C.4 <a href="#changes.since.02">Since draft-ietf-httpbis-p4-conditional-02</a></li> |
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| 559 | <li class="tocline1">C.5 <a href="#changes.since.03">Since draft-ietf-httpbis-p4-conditional-03</a></li> |
|---|
| 560 | <li class="tocline1">C.6 <a href="#changes.since.04">Since draft-ietf-httpbis-p4-conditional-04</a></li> |
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| 561 | <li class="tocline1">C.7 <a href="#changes.since.05">Since draft-ietf-httpbis-p4-conditional-05</a></li> |
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| 562 | </ul> |
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| 563 | </li> |
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| 564 | <li class="tocline0"><a href="#rfc.index">Index</a></li> |
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| 565 | </ul> |
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| 566 | <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a> <a id="introduction" href="#introduction">Introduction</a></h1> |
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| 567 | <p id="rfc.section.1.p.1">This document defines HTTP/1.1 response metadata for indicating potential changes to payload content, including modification |
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| 568 | time stamps and opaque entity-tags, and the HTTP conditional request mechanisms that allow preconditions to be placed on a |
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| 569 | request method. Conditional GET requests allow for efficient cache updates. Other conditional request methods are used to |
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| 570 | protect against overwriting or misunderstanding the state of a resource that has been changed unbeknownst to the requesting |
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| 571 | client. |
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| 572 | </p> |
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| 573 | <p id="rfc.section.1.p.2">This document is currently disorganized in order to minimize the changes between drafts and enable reviewers to see the smaller |
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| 574 | errata changes. The next draft will reorganize the sections to better reflect the content. In particular, the sections on |
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| 575 | resource metadata will be discussed first and then followed by each conditional request-header, concluding with a definition |
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| 576 | of precedence and the expectation of ordering strong validator checks before weak validator checks. It is likely that more |
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| 577 | content from <a href="#Part6" id="rfc.xref.Part6.1"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a> will migrate to this part, where appropriate. The current mess reflects how widely dispersed these topics and associated requirements |
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| 578 | had become in <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>. |
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| 579 | </p> |
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| 580 | <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a> <a id="intro.requirements" href="#intro.requirements">Requirements</a></h2> |
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| 581 | <p id="rfc.section.1.1.p.1">The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" |
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| 582 | 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>. |
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| 583 | </p> |
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| 584 | <p id="rfc.section.1.1.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." |
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| 585 | </p> |
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| 586 | <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a> <a id="notation" href="#notation">Syntax Notation</a></h2> |
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| 587 | <p id="rfc.section.1.2.p.1">This specification uses the ABNF syntax defined in <a href="p1-messaging.html#notation" title="Syntax Notation">Section 1.2</a> of <a href="#Part1" id="rfc.xref.Part1.1"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. The following core rules are included by reference, as defined in <a href="#RFC5234" id="rfc.xref.RFC5234.1"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>, <a href="http://tools.ietf.org/html/rfc5234#appendix-B.1">Appendix B.1</a>: ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote), HEXDIG |
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| 588 | (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit sequence of data), SP (space), VCHAR (any visible USASCII character), |
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| 589 | and WSP (whitespace). |
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| 590 | </p> |
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| 591 | <h3 id="rfc.section.1.2.1"><a href="#rfc.section.1.2.1">1.2.1</a> <a id="core.rules" href="#core.rules">Core Rules</a></h3> |
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| 592 | <p id="rfc.section.1.2.1.p.1">The core rules below are defined in <a href="p1-messaging.html#basic.rules" title="Basic Rules">Section 1.2.2</a> of <a href="#Part1" id="rfc.xref.Part1.2"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>: |
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| 593 | </p> |
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| 594 | <div id="rfc.figure.u.1"></div><pre class="inline"> <a href="#core.rules" class="smpl">quoted-string</a> = <quoted-string, defined in <a href="#Part1" id="rfc.xref.Part1.3"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#basic.rules" title="Basic Rules">Section 1.2.2</a>> |
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| 595 | <a href="#core.rules" class="smpl">OWS</a> = <OWS, defined in <a href="#Part1" id="rfc.xref.Part1.4"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#basic.rules" title="Basic Rules">Section 1.2.2</a>> |
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| 596 | </pre><h3 id="rfc.section.1.2.2"><a href="#rfc.section.1.2.2">1.2.2</a> <a id="abnf.dependencies" href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></h3> |
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| 597 | <p id="rfc.section.1.2.2.p.1">The ABNF rules below are defined in other parts:</p> |
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| 598 | <div id="rfc.figure.u.2"></div><pre class="inline"> <a href="#abnf.dependencies" class="smpl">HTTP-date</a> = <HTTP-date, defined in <a href="#Part1" id="rfc.xref.Part1.5"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#full.date" title="Full Date">Section 3.2.1</a>> |
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| 599 | </pre><h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a> <a id="entity.tags" href="#entity.tags">Entity Tags</a></h1> |
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| 600 | <p id="rfc.section.2.p.1">Entity tags are used for comparing two or more entities from the same requested resource. HTTP/1.1 uses entity tags in the |
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| 601 | ETag (<a href="#header.etag" id="rfc.xref.header.etag.1" title="ETag">Section 6.1</a>), If-Match (<a href="#header.if-match" id="rfc.xref.header.if-match.1" title="If-Match">Section 6.2</a>), If-None-Match (<a href="#header.if-none-match" id="rfc.xref.header.if-none-match.1" title="If-None-Match">Section 6.4</a>), and If-Range (<a href="p5-range.html#header.if-range" title="If-Range">Section 5.3</a> of <a href="#Part5" id="rfc.xref.Part5.1"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>) header fields. The definition of how they are used and compared as cache validators is in <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section 4</a>. An entity tag consists of an opaque quoted string, possibly prefixed by a weakness indicator. |
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| 602 | </p> |
|---|
| 603 | <div id="rfc.figure.u.3"></div><pre class="inline"><span id="rfc.iref.g.1"></span><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span> <a href="#entity.tags" class="smpl">entity-tag</a> = [ <a href="#entity.tags" class="smpl">weak</a> ] <a href="#entity.tags" class="smpl">opaque-tag</a> |
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| 604 | <a href="#entity.tags" class="smpl">weak</a> = "W/" |
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| 605 | <a href="#entity.tags" class="smpl">opaque-tag</a> = <a href="#core.rules" class="smpl">quoted-string</a> |
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| 606 | </pre><p id="rfc.section.2.p.3">A "strong entity tag" <em class="bcp14">MAY</em> be shared by two entities of a resource only if they are equivalent by octet equality. |
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| 607 | </p> |
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| 608 | <p id="rfc.section.2.p.4">A "weak entity tag," indicated by the "W/" prefix, <em class="bcp14">MAY</em> be shared by two entities of a resource only if the entities are equivalent and could be substituted for each other with no |
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| 609 | significant change in semantics. A weak entity tag can only be used for weak comparison. |
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| 610 | </p> |
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| 611 | <p id="rfc.section.2.p.5">An entity tag <em class="bcp14">MUST</em> be unique across all versions of all entities associated with a particular resource. A given entity tag value <em class="bcp14">MAY</em> be used for entities obtained by requests on different URIs. The use of the same entity tag value in conjunction with entities |
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| 612 | obtained by requests on different URIs does not imply the equivalence of those entities. |
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| 613 | </p> |
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| 614 | <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a> Status Code Definitions |
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| 615 | </h1> |
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| 616 | <div id="rfc.iref.3"></div> |
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| 617 | <div id="rfc.iref.s.1"></div> |
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| 618 | <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a> <a id="status.304" href="#status.304">304 Not Modified</a></h2> |
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| 619 | <p id="rfc.section.3.1.p.1">If the client has performed a conditional GET request and access is allowed, but the document has not been modified, the server <em class="bcp14">SHOULD</em> respond with this status code. The 304 response <em class="bcp14">MUST NOT</em> contain a message-body, and thus is always terminated by the first empty line after the header fields. |
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| 620 | </p> |
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| 621 | <p id="rfc.section.3.1.p.2">The response <em class="bcp14">MUST</em> include the following header fields: |
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| 622 | </p> |
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| 623 | <ul> |
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| 624 | <li> |
|---|
| 625 | <p>Date, unless its omission is required by <a href="p1-messaging.html#clockless.origin.server.operation" title="Clockless Origin Server Operation">Section 8.3.1</a> of <a href="#Part1" id="rfc.xref.Part1.6"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. |
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| 626 | </p> |
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| 627 | <p>If a clockless origin server obeys these rules, and proxies and clients add their own Date to any response received without |
|---|
| 628 | one (as already specified by <a href="p1-messaging.html#header.date" title="Date">Section 8.3</a> of <a href="#Part1" id="rfc.xref.Part1.7"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, caches will operate correctly. |
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| 629 | </p> |
|---|
| 630 | </li> |
|---|
| 631 | <li> |
|---|
| 632 | <p>ETag and/or Content-Location, if the header would have been sent in a 200 response to the same request.</p> |
|---|
| 633 | </li> |
|---|
| 634 | <li> |
|---|
| 635 | <p>Expires, Cache-Control, and/or Vary, if the field-value might differ from that sent in any previous response for the same |
|---|
| 636 | variant. |
|---|
| 637 | </p> |
|---|
| 638 | </li> |
|---|
| 639 | </ul> |
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| 640 | <p id="rfc.section.3.1.p.3">If the conditional GET used a strong cache validator (see <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section 4</a>), the response <em class="bcp14">SHOULD NOT</em> include other entity-headers. Otherwise (i.e., the conditional GET used a weak validator), the response <em class="bcp14">MUST NOT</em> include other entity-headers; this prevents inconsistencies between cached entity-bodies and updated headers. |
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| 641 | </p> |
|---|
| 642 | <p id="rfc.section.3.1.p.4">If a 304 response indicates an entity not currently cached, then the cache <em class="bcp14">MUST</em> disregard the response and repeat the request without the conditional. |
|---|
| 643 | </p> |
|---|
| 644 | <p id="rfc.section.3.1.p.5">If a cache uses a received 304 response to update a cache entry, the cache <em class="bcp14">MUST</em> update the entry to reflect any new field values given in the response. |
|---|
| 645 | </p> |
|---|
| 646 | <div id="rfc.iref.4"></div> |
|---|
| 647 | <div id="rfc.iref.s.2"></div> |
|---|
| 648 | <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a> <a id="status.412" href="#status.412">412 Precondition Failed</a></h2> |
|---|
| 649 | <p id="rfc.section.3.2.p.1">The precondition given in one or more of the request-header fields evaluated to false when it was tested on the server. This |
|---|
| 650 | response code allows the client to place preconditions on the current resource metainformation (header field data) and thus |
|---|
| 651 | prevent the requested method from being applied to a resource other than the one intended. |
|---|
| 652 | </p> |
|---|
| 653 | <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a> <a id="weak.and.strong.validators" href="#weak.and.strong.validators">Weak and Strong Validators</a></h1> |
|---|
| 654 | <p id="rfc.section.4.p.1">Since both origin servers and caches will compare two validators to decide if they represent the same or different entities, |
|---|
| 655 | one normally would expect that if the entity (the entity-body or any entity-headers) changes in any way, then the associated |
|---|
| 656 | validator would change as well. If this is true, then we call this validator a "strong validator." |
|---|
| 657 | </p> |
|---|
| 658 | <p id="rfc.section.4.p.2">However, there might be cases when a server prefers to change the validator only on semantically significant changes, and |
|---|
| 659 | not when insignificant aspects of the entity change. A validator that does not always change when the resource changes is |
|---|
| 660 | a "weak validator." |
|---|
| 661 | </p> |
|---|
| 662 | <p id="rfc.section.4.p.3">Entity tags are normally "strong validators," but the protocol provides a mechanism to tag an entity tag as "weak." One can |
|---|
| 663 | think of a strong validator as one that changes whenever the bits of an entity changes, while a weak value changes whenever |
|---|
| 664 | the meaning of an entity changes. Alternatively, one can think of a strong validator as part of an identifier for a specific |
|---|
| 665 | entity, while a weak validator is part of an identifier for a set of semantically equivalent entities. |
|---|
| 666 | </p> |
|---|
| 667 | <dl class="empty"> |
|---|
| 668 | <dd> <b>Note:</b> One example of a strong validator is an integer that is incremented in stable storage every time an entity is changed. |
|---|
| 669 | </dd> |
|---|
| 670 | <dd>An entity's modification time, if represented with one-second resolution, could be a weak validator, since it is possible |
|---|
| 671 | that the resource might be modified twice during a single second. |
|---|
| 672 | </dd> |
|---|
| 673 | <dd>Support for weak validators is optional. However, weak validators allow for more efficient caching of equivalent objects; |
|---|
| 674 | for example, a hit counter on a site is probably good enough if it is updated every few days or weeks, and any value during |
|---|
| 675 | that period is likely "good enough" to be equivalent. |
|---|
| 676 | </dd> |
|---|
| 677 | </dl> |
|---|
| 678 | <p id="rfc.section.4.p.4">A "use" of a validator is either when a client generates a request and includes the validator in a validating header field, |
|---|
| 679 | or when a server compares two validators. |
|---|
| 680 | </p> |
|---|
| 681 | <p id="rfc.section.4.p.5">Strong validators are usable in any context. Weak validators are only usable in contexts that do not depend on exact equality |
|---|
| 682 | of an entity. For example, either kind is usable for a conditional GET of a full entity. However, only a strong validator |
|---|
| 683 | is usable for a sub-range retrieval, since otherwise the client might end up with an internally inconsistent entity. |
|---|
| 684 | </p> |
|---|
| 685 | <p id="rfc.section.4.p.6">Clients <em class="bcp14">MUST NOT</em> use weak validators in range requests (<a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>). |
|---|
| 686 | </p> |
|---|
| 687 | <p id="rfc.section.4.p.7">The only function that HTTP/1.1 defines on validators is comparison. There are two validator comparison functions, depending |
|---|
| 688 | on whether the comparison context allows the use of weak validators or not: |
|---|
| 689 | </p> |
|---|
| 690 | <ul> |
|---|
| 691 | <li>The strong comparison function: in order to be considered equal, both opaque-tags <em class="bcp14">MUST</em> be identical character-by-character, and both <em class="bcp14">MUST NOT</em> be weak. |
|---|
| 692 | </li> |
|---|
| 693 | <li>The weak comparison function: in order to be considered equal, both opaque-tags <em class="bcp14">MUST</em> be identical character-by-character. |
|---|
| 694 | </li> |
|---|
| 695 | </ul> |
|---|
| 696 | <p id="rfc.section.4.p.8">The example below shows the results for a set of entity tag pairs, and both the weak and strong comparison function results:</p> |
|---|
| 697 | <div id="rfc.table.u.1"> |
|---|
| 698 | <table summary="" class="tt full" cellpadding="3" cellspacing="0"> |
|---|
| 699 | <thead> |
|---|
| 700 | <tr> |
|---|
| 701 | <th>ETag 1</th> |
|---|
| 702 | <th>ETag 2</th> |
|---|
| 703 | <th>Strong Comparison</th> |
|---|
| 704 | <th>Weak Comparison</th> |
|---|
| 705 | </tr> |
|---|
| 706 | </thead> |
|---|
| 707 | <tbody> |
|---|
| 708 | <tr> |
|---|
| 709 | <td>W/"1"</td> |
|---|
| 710 | <td>W/"1"</td> |
|---|
| 711 | <td>no match</td> |
|---|
| 712 | <td>match</td> |
|---|
| 713 | </tr> |
|---|
| 714 | <tr> |
|---|
| 715 | <td>W/"1"</td> |
|---|
| 716 | <td>W/"2"</td> |
|---|
| 717 | <td>no match</td> |
|---|
| 718 | <td>no match</td> |
|---|
| 719 | </tr> |
|---|
| 720 | <tr> |
|---|
| 721 | <td>W/"1"</td> |
|---|
| 722 | <td>"1"</td> |
|---|
| 723 | <td>no match</td> |
|---|
| 724 | <td>match</td> |
|---|
| 725 | </tr> |
|---|
| 726 | <tr> |
|---|
| 727 | <td>"1"</td> |
|---|
| 728 | <td>"1"</td> |
|---|
| 729 | <td>match</td> |
|---|
| 730 | <td>match</td> |
|---|
| 731 | </tr> |
|---|
| 732 | </tbody> |
|---|
| 733 | </table> |
|---|
| 734 | </div> |
|---|
| 735 | <p id="rfc.section.4.p.9">An entity tag is strong unless it is explicitly tagged as weak. <a href="#entity.tags" title="Entity Tags">Section 2</a> gives the syntax for entity tags. |
|---|
| 736 | </p> |
|---|
| 737 | <p id="rfc.section.4.p.10">A Last-Modified time, when used as a validator in a request, is implicitly weak unless it is possible to deduce that it is |
|---|
| 738 | strong, using the following rules: |
|---|
| 739 | </p> |
|---|
| 740 | <ul> |
|---|
| 741 | <li>The validator is being compared by an origin server to the actual current validator for the entity and,</li> |
|---|
| 742 | <li>That origin server reliably knows that the associated entity did not change twice during the second covered by the presented |
|---|
| 743 | validator. |
|---|
| 744 | </li> |
|---|
| 745 | </ul> |
|---|
| 746 | <p id="rfc.section.4.p.11">or </p> |
|---|
| 747 | <ul> |
|---|
| 748 | <li>The validator is about to be used by a client in an If-Modified-Since or If-Unmodified-Since header, because the client has |
|---|
| 749 | a cache entry for the associated entity, and |
|---|
| 750 | </li> |
|---|
| 751 | <li>That cache entry includes a Date value, which gives the time when the origin server sent the original response, and</li> |
|---|
| 752 | <li>The presented Last-Modified time is at least 60 seconds before the Date value.</li> |
|---|
| 753 | </ul> |
|---|
| 754 | <p id="rfc.section.4.p.12">or </p> |
|---|
| 755 | <ul> |
|---|
| 756 | <li>The validator is being compared by an intermediate cache to the validator stored in its cache entry for the entity, and</li> |
|---|
| 757 | <li>That cache entry includes a Date value, which gives the time when the origin server sent the original response, and</li> |
|---|
| 758 | <li>The presented Last-Modified time is at least 60 seconds before the Date value.</li> |
|---|
| 759 | </ul> |
|---|
| 760 | <p id="rfc.section.4.p.13">This method relies on the fact that if two different responses were sent by the origin server during the same second, but |
|---|
| 761 | both had the same Last-Modified time, then at least one of those responses would have a Date value equal to its Last-Modified |
|---|
| 762 | time. The arbitrary 60-second limit guards against the possibility that the Date and Last-Modified values are generated from |
|---|
| 763 | different clocks, or at somewhat different times during the preparation of the response. An implementation <em class="bcp14">MAY</em> use a value larger than 60 seconds, if it is believed that 60 seconds is too short. |
|---|
| 764 | </p> |
|---|
| 765 | <p id="rfc.section.4.p.14">If a client wishes to perform a sub-range retrieval on a value for which it has only a Last-Modified time and no opaque validator, |
|---|
| 766 | it <em class="bcp14">MAY</em> do this only if the Last-Modified time is strong in the sense described here. |
|---|
| 767 | </p> |
|---|
| 768 | <p id="rfc.section.4.p.15">A cache or origin server receiving a conditional range request (<a href="#Part5" id="rfc.xref.Part5.3"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>) <em class="bcp14">MUST</em> use the strong comparison function to evaluate the condition. |
|---|
| 769 | </p> |
|---|
| 770 | <p id="rfc.section.4.p.16">These rules allow HTTP/1.1 caches and clients to safely perform sub-range retrievals on values that have been obtained from |
|---|
| 771 | HTTP/1.0 servers. |
|---|
| 772 | </p> |
|---|
| 773 | <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a> <a id="rules.for.when.to.use.entity.tags.and.last-modified.dates" href="#rules.for.when.to.use.entity.tags.and.last-modified.dates">Rules for When to Use Entity Tags and Last-Modified Dates</a></h1> |
|---|
| 774 | <p id="rfc.section.5.p.1">We adopt a set of rules and recommendations for origin servers, clients, and caches regarding when various validator types |
|---|
| 775 | ought to be used, and for what purposes. |
|---|
| 776 | </p> |
|---|
| 777 | <p id="rfc.section.5.p.2">HTTP/1.1 origin servers: </p> |
|---|
| 778 | <ul> |
|---|
| 779 | <li><em class="bcp14">SHOULD</em> send an entity tag validator unless it is not feasible to generate one. |
|---|
| 780 | </li> |
|---|
| 781 | <li><em class="bcp14">MAY</em> send a weak entity tag instead of a strong entity tag, if performance considerations support the use of weak entity tags, |
|---|
| 782 | or if it is unfeasible to send a strong entity tag. |
|---|
| 783 | </li> |
|---|
| 784 | <li><em class="bcp14">SHOULD</em> send a Last-Modified value if it is feasible to send one, unless the risk of a breakdown in semantic transparency that could |
|---|
| 785 | result from using this date in an If-Modified-Since header would lead to serious problems. |
|---|
| 786 | </li> |
|---|
| 787 | </ul> |
|---|
| 788 | <p id="rfc.section.5.p.3">In other words, the preferred behavior for an HTTP/1.1 origin server is to send both a strong entity tag and a Last-Modified |
|---|
| 789 | value. |
|---|
| 790 | </p> |
|---|
| 791 | <p id="rfc.section.5.p.4">In order to be legal, a strong entity tag <em class="bcp14">MUST</em> change whenever the associated entity changes in any way. A weak entity tag <em class="bcp14">SHOULD</em> change whenever the associated entity changes in a semantically significant way. |
|---|
| 792 | </p> |
|---|
| 793 | <dl class="empty"> |
|---|
| 794 | <dd> <b>Note:</b> in order to provide semantically transparent caching, an origin server must avoid reusing a specific strong entity tag value |
|---|
| 795 | for two different entities, or reusing a specific weak entity tag value for two semantically different entities. Cache entries |
|---|
| 796 | might persist for arbitrarily long periods, regardless of expiration times, so it might be inappropriate to expect that a |
|---|
| 797 | cache will never again attempt to validate an entry using a validator that it obtained at some point in the past. |
|---|
| 798 | </dd> |
|---|
| 799 | </dl> |
|---|
| 800 | <p id="rfc.section.5.p.5">HTTP/1.1 clients: </p> |
|---|
| 801 | <ul> |
|---|
| 802 | <li>If an entity tag has been provided by the origin server, <em class="bcp14">MUST</em> use that entity tag in any cache-conditional request (using If-Match or If-None-Match). |
|---|
| 803 | </li> |
|---|
| 804 | <li>If only a Last-Modified value has been provided by the origin server, <em class="bcp14">SHOULD</em> use that value in non-subrange cache-conditional requests (using If-Modified-Since). |
|---|
| 805 | </li> |
|---|
| 806 | <li>If only a Last-Modified value has been provided by an HTTP/1.0 origin server, <em class="bcp14">MAY</em> use that value in subrange cache-conditional requests (using If-Unmodified-Since:). The user agent <em class="bcp14">SHOULD</em> provide a way to disable this, in case of difficulty. |
|---|
| 807 | </li> |
|---|
| 808 | <li>If both an entity tag and a Last-Modified value have been provided by the origin server, <em class="bcp14">SHOULD</em> use both validators in cache-conditional requests. This allows both HTTP/1.0 and HTTP/1.1 caches to respond appropriately. |
|---|
| 809 | </li> |
|---|
| 810 | </ul> |
|---|
| 811 | <p id="rfc.section.5.p.6">An HTTP/1.1 origin server, upon receiving a conditional request that includes both a Last-Modified date (e.g., in an If-Modified-Since |
|---|
| 812 | or If-Unmodified-Since header field) and one or more entity tags (e.g., in an If-Match, If-None-Match, or If-Range header |
|---|
| 813 | field) as cache validators, <em class="bcp14">MUST NOT</em> return a response status of 304 (Not Modified) unless doing so is consistent with all of the conditional header fields in |
|---|
| 814 | the request. |
|---|
| 815 | </p> |
|---|
| 816 | <p id="rfc.section.5.p.7">An HTTP/1.1 caching proxy, upon receiving a conditional request that includes both a Last-Modified date and one or more entity |
|---|
| 817 | tags as cache validators, <em class="bcp14">MUST NOT</em> return a locally cached response to the client unless that cached response is consistent with all of the conditional header |
|---|
| 818 | fields in the request. |
|---|
| 819 | </p> |
|---|
| 820 | <dl class="empty"> |
|---|
| 821 | <dd> <b>Note:</b> The general principle behind these rules is that HTTP/1.1 servers and clients should transmit as much non-redundant information |
|---|
| 822 | as is available in their responses and requests. HTTP/1.1 systems receiving this information will make the most conservative |
|---|
| 823 | assumptions about the validators they receive. |
|---|
| 824 | </dd> |
|---|
| 825 | <dd>HTTP/1.0 clients and caches will ignore entity tags. Generally, last-modified values received or used by these systems will |
|---|
| 826 | support transparent and efficient caching, and so HTTP/1.1 origin servers should provide Last-Modified values. In those rare |
|---|
| 827 | cases where the use of a Last-Modified value as a validator by an HTTP/1.0 system could result in a serious problem, then |
|---|
| 828 | HTTP/1.1 origin servers should not provide one. |
|---|
| 829 | </dd> |
|---|
| 830 | </dl> |
|---|
| 831 | <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a> <a id="header.fields" href="#header.fields">Header Field Definitions</a></h1> |
|---|
| 832 | <p id="rfc.section.6.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to conditional requests.</p> |
|---|
| 833 | <p id="rfc.section.6.p.2">For entity-header fields, both sender and recipient refer to either the client or the server, depending on who sends and who |
|---|
| 834 | receives the entity. |
|---|
| 835 | </p> |
|---|
| 836 | <div id="rfc.iref.e.1"></div> |
|---|
| 837 | <div id="rfc.iref.h.1"></div> |
|---|
| 838 | <h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a> <a id="header.etag" href="#header.etag">ETag</a></h2> |
|---|
| 839 | <p id="rfc.section.6.1.p.1">The response-header field "ETag" provides the current value of the entity tag (see <a href="#entity.tags" title="Entity Tags">Section 2</a>) for the requested variant. The headers used with entity tags are described in Sections <a href="#header.if-match" id="rfc.xref.header.if-match.2" title="If-Match">6.2</a> and <a href="#header.if-none-match" id="rfc.xref.header.if-none-match.2" title="If-None-Match">6.4</a> of this document, and in <a href="p5-range.html#header.if-range" title="If-Range">Section 5.3</a> of <a href="#Part5" id="rfc.xref.Part5.4"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>. The entity tag <em class="bcp14">MAY</em> be used for comparison with other entities from the same resource (see <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section 4</a>). |
|---|
| 840 | </p> |
|---|
| 841 | <div id="rfc.figure.u.4"></div><pre class="inline"><span id="rfc.iref.g.4"></span><span id="rfc.iref.g.5"></span> <a href="#header.etag" class="smpl">ETag</a> = "ETag" ":" <a href="#core.rules" class="smpl">OWS</a> <a href="#header.etag" class="smpl">ETag-v</a> |
|---|
| 842 | <a href="#header.etag" class="smpl">ETag-v</a> = <a href="#entity.tags" class="smpl">entity-tag</a> |
|---|
| 843 | </pre><div id="rfc.figure.u.5"></div> |
|---|
| 844 | <p>Examples:</p> <pre class="text"> ETag: "xyzzy" |
|---|
| 845 | ETag: W/"xyzzy" |
|---|
| 846 | ETag: "" |
|---|
| 847 | </pre><p id="rfc.section.6.1.p.4">The ETag response-header field value, an entity tag, provides for an "opaque" cache validator. This might allow more reliable |
|---|
| 848 | validation in situations where it is inconvenient to store modification dates, where the one-second resolution of HTTP date |
|---|
| 849 | values is not sufficient, or where the origin server wishes to avoid certain paradoxes that might arise from the use of modification |
|---|
| 850 | dates. |
|---|
| 851 | </p> |
|---|
| 852 | <p id="rfc.section.6.1.p.5">The principle behind entity tags is that only the service author knows the semantics of a resource well enough to select an |
|---|
| 853 | appropriate cache validation mechanism, and the specification of any validator comparison function more complex than byte-equality |
|---|
| 854 | would open up a can of worms. Thus, comparisons of any other headers (except Last-Modified, for compatibility with HTTP/1.0) |
|---|
| 855 | are never used for purposes of validating a cache entry. |
|---|
| 856 | </p> |
|---|
| 857 | <div id="rfc.iref.i.1"></div> |
|---|
| 858 | <div id="rfc.iref.h.2"></div> |
|---|
| 859 | <h2 id="rfc.section.6.2"><a href="#rfc.section.6.2">6.2</a> <a id="header.if-match" href="#header.if-match">If-Match</a></h2> |
|---|
| 860 | <p id="rfc.section.6.2.p.1">The request-header field "If-Match" is used with a method to make it conditional. A client that has one or more entities previously |
|---|
| 861 | obtained from the resource can verify that one of those entities is current by including a list of their associated entity |
|---|
| 862 | tags in the If-Match header field. Entity tags are defined in <a href="#entity.tags" title="Entity Tags">Section 2</a>. The purpose of this feature is to allow efficient updates of cached information with a minimum amount of transaction overhead. |
|---|
| 863 | It is also used, on updating requests, to prevent inadvertent modification of the wrong version of a resource. As a special |
|---|
| 864 | case, the value "*" matches any current entity of the resource. |
|---|
| 865 | </p> |
|---|
| 866 | <div id="rfc.figure.u.6"></div><pre class="inline"><span id="rfc.iref.g.6"></span><span id="rfc.iref.g.7"></span> <a href="#header.if-match" class="smpl">If-Match</a> = "If-Match" ":" <a href="#core.rules" class="smpl">OWS</a> <a href="#header.if-match" class="smpl">If-Match-v</a> |
|---|
| 867 | <a href="#header.if-match" class="smpl">If-Match-v</a> = "*" / 1#<a href="#entity.tags" class="smpl">entity-tag</a> |
|---|
| 868 | </pre><p id="rfc.section.6.2.p.3">If any of the entity tags match the entity tag of the entity that would have been returned in the response to a similar GET |
|---|
| 869 | request (without the If-Match header) on that resource, or if "*" is given and any current entity exists for that resource, |
|---|
| 870 | then the server <em class="bcp14">MAY</em> perform the requested method as if the If-Match header field did not exist. |
|---|
| 871 | </p> |
|---|
| 872 | <p id="rfc.section.6.2.p.4">A server <em class="bcp14">MUST</em> use the strong comparison function (see <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section 4</a>) to compare the entity tags in If-Match. |
|---|
| 873 | </p> |
|---|
| 874 | <p id="rfc.section.6.2.p.5">If none of the entity tags match, or if "*" is given and no current entity exists, the server <em class="bcp14">MUST NOT</em> perform the requested method, and <em class="bcp14">MUST</em> return a 412 (Precondition Failed) response. This behavior is most useful when the client wants to prevent an updating method, |
|---|
| 875 | such as PUT, from modifying a resource that has changed since the client last retrieved it. |
|---|
| 876 | </p> |
|---|
| 877 | <p id="rfc.section.6.2.p.6">If the request would, without the If-Match header field, result in anything other than a 2xx or 412 status, then the If-Match |
|---|
| 878 | header <em class="bcp14">MUST</em> be ignored. |
|---|
| 879 | </p> |
|---|
| 880 | <p id="rfc.section.6.2.p.7">The meaning of "If-Match: *" is that the method <em class="bcp14">SHOULD</em> be performed if the representation selected by the origin server (or by a cache, possibly using the Vary mechanism, see <a href="p6-cache.html#header.vary" title="Vary">Section 15.5</a> of <a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) exists, and <em class="bcp14">MUST NOT</em> be performed if the representation does not exist. |
|---|
| 881 | </p> |
|---|
| 882 | <p id="rfc.section.6.2.p.8">A request intended to update a resource (e.g., a PUT) <em class="bcp14">MAY</em> include an If-Match header field to signal that the request method <em class="bcp14">MUST NOT</em> be applied if the entity corresponding to the If-Match value (a single entity tag) is no longer a representation of that resource. |
|---|
| 883 | This allows the user to indicate that they do not wish the request to be successful if the resource has been changed without |
|---|
| 884 | their knowledge. Examples: |
|---|
| 885 | </p> |
|---|
| 886 | <div id="rfc.figure.u.7"></div><pre class="text"> If-Match: "xyzzy" |
|---|
| 887 | If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz" |
|---|
| 888 | If-Match: * |
|---|
| 889 | </pre><p id="rfc.section.6.2.p.10">The result of a request having both an If-Match header field and either an If-None-Match or an If-Modified-Since header fields |
|---|
| 890 | is undefined by this specification. |
|---|
| 891 | </p> |
|---|
| 892 | <div id="rfc.iref.i.2"></div> |
|---|
| 893 | <div id="rfc.iref.h.3"></div> |
|---|
| 894 | <h2 id="rfc.section.6.3"><a href="#rfc.section.6.3">6.3</a> <a id="header.if-modified-since" href="#header.if-modified-since">If-Modified-Since</a></h2> |
|---|
| 895 | <p id="rfc.section.6.3.p.1">The request-header field "If-Modified-Since" is used with a method to make it conditional: if the requested variant has not |
|---|
| 896 | been modified since the time specified in this field, an entity will not be returned from the server; instead, a 304 (Not |
|---|
| 897 | Modified) response will be returned without any message-body. |
|---|
| 898 | </p> |
|---|
| 899 | <div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.8"></span><span id="rfc.iref.g.9"></span> <a href="#header.if-modified-since" class="smpl">If-Modified-Since</a> = "If-Modified-Since" ":" <a href="#core.rules" class="smpl">OWS</a> |
|---|
| 900 | <a href="#header.if-modified-since" class="smpl">If-Modified-Since-v</a> |
|---|
| 901 | <a href="#header.if-modified-since" class="smpl">If-Modified-Since-v</a> = <a href="#abnf.dependencies" class="smpl">HTTP-date</a> |
|---|
| 902 | </pre><p id="rfc.section.6.3.p.3">An example of the field is:</p> |
|---|
| 903 | <div id="rfc.figure.u.9"></div><pre class="text"> If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT |
|---|
| 904 | </pre><p id="rfc.section.6.3.p.5">A GET method with an If-Modified-Since header and no Range header requests that the identified entity be transferred only |
|---|
| 905 | if it has been modified since the date given by the If-Modified-Since header. The algorithm for determining this includes |
|---|
| 906 | the following cases: |
|---|
| 907 | </p> |
|---|
| 908 | <ol> |
|---|
| 909 | <li>If the request would normally result in anything other than a 200 (OK) status, or if the passed If-Modified-Since date is |
|---|
| 910 | invalid, the response is exactly the same as for a normal GET. A date which is later than the server's current time is invalid. |
|---|
| 911 | </li> |
|---|
| 912 | <li>If the variant has been modified since the If-Modified-Since date, the response is exactly the same as for a normal GET.</li> |
|---|
| 913 | <li>If the variant has not been modified since a valid If-Modified-Since date, the server <em class="bcp14">SHOULD</em> return a 304 (Not Modified) response. |
|---|
| 914 | </li> |
|---|
| 915 | </ol> |
|---|
| 916 | <p id="rfc.section.6.3.p.6">The purpose of this feature is to allow efficient updates of cached information with a minimum amount of transaction overhead. </p> |
|---|
| 917 | <dl class="empty"> |
|---|
| 918 | <dd> <b>Note:</b> The Range request-header field modifies the meaning of If-Modified-Since; see <a href="p5-range.html#header.range" title="Range">Section 5.4</a> of <a href="#Part5" id="rfc.xref.Part5.5"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a> for full details. |
|---|
| 919 | </dd> |
|---|
| 920 | <dd> <b>Note:</b> If-Modified-Since times are interpreted by the server, whose clock might not be synchronized with the client. |
|---|
| 921 | </dd> |
|---|
| 922 | <dd> <b>Note:</b> When handling an If-Modified-Since header field, some servers will use an exact date comparison function, rather than a less-than |
|---|
| 923 | function, for deciding whether to send a 304 (Not Modified) response. To get best results when sending an If-Modified-Since |
|---|
| 924 | header field for cache validation, clients are advised to use the exact date string received in a previous Last-Modified header |
|---|
| 925 | field whenever possible. |
|---|
| 926 | </dd> |
|---|
| 927 | <dd> <b>Note:</b> If a client uses an arbitrary date in the If-Modified-Since header instead of a date taken from the Last-Modified header for |
|---|
| 928 | the same request, the client should be aware of the fact that this date is interpreted in the server's understanding of time. |
|---|
| 929 | The client should consider unsynchronized clocks and rounding problems due to the different encodings of time between the |
|---|
| 930 | client and server. This includes the possibility of race conditions if the document has changed between the time it was first |
|---|
| 931 | requested and the If-Modified-Since date of a subsequent request, and the possibility of clock-skew-related problems if the |
|---|
| 932 | If-Modified-Since date is derived from the client's clock without correction to the server's clock. Corrections for different |
|---|
| 933 | time bases between client and server are at best approximate due to network latency. |
|---|
| 934 | </dd> |
|---|
| 935 | </dl> |
|---|
| 936 | <p id="rfc.section.6.3.p.7">The result of a request having both an If-Modified-Since header field and either an If-Match or an If-Unmodified-Since header |
|---|
| 937 | fields is undefined by this specification. |
|---|
| 938 | </p> |
|---|
| 939 | <div id="rfc.iref.i.3"></div> |
|---|
| 940 | <div id="rfc.iref.h.4"></div> |
|---|
| 941 | <h2 id="rfc.section.6.4"><a href="#rfc.section.6.4">6.4</a> <a id="header.if-none-match" href="#header.if-none-match">If-None-Match</a></h2> |
|---|
| 942 | <p id="rfc.section.6.4.p.1">The request-header field "If-None-Match" is used with a method to make it conditional. A client that has one or more entities |
|---|
| 943 | previously obtained from the resource can verify that none of those entities is current by including a list of their associated |
|---|
| 944 | entity tags in the If-None-Match header field. The purpose of this feature is to allow efficient updates of cached information |
|---|
| 945 | with a minimum amount of transaction overhead. It is also used to prevent a method (e.g. PUT) from inadvertently modifying |
|---|
| 946 | an existing resource when the client believes that the resource does not exist. |
|---|
| 947 | </p> |
|---|
| 948 | <p id="rfc.section.6.4.p.2">As a special case, the value "*" matches any current entity of the resource.</p> |
|---|
| 949 | <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.10"></span><span id="rfc.iref.g.11"></span> <a href="#header.if-none-match" class="smpl">If-None-Match</a> = "If-None-Match" ":" <a href="#core.rules" class="smpl">OWS</a> <a href="#header.if-none-match" class="smpl">If-None-Match-v</a> |
|---|
| 950 | <a href="#header.if-none-match" class="smpl">If-None-Match-v</a> = "*" / 1#<a href="#entity.tags" class="smpl">entity-tag</a> |
|---|
| 951 | </pre><p id="rfc.section.6.4.p.4">If any of the entity tags match the entity tag of the entity that would have been returned in the response to a similar GET |
|---|
| 952 | request (without the If-None-Match header) on that resource, or if "*" is given and any current entity exists for that resource, |
|---|
| 953 | then the server <em class="bcp14">MUST NOT</em> perform the requested method, unless required to do so because the resource's modification date fails to match that supplied |
|---|
| 954 | in an If-Modified-Since header field in the request. Instead, if the request method was GET or HEAD, the server <em class="bcp14">SHOULD</em> respond with a 304 (Not Modified) response, including the cache-related header fields (particularly ETag) of one of the entities |
|---|
| 955 | that matched. For all other request methods, the server <em class="bcp14">MUST</em> respond with a status of 412 (Precondition Failed). |
|---|
| 956 | </p> |
|---|
| 957 | <p id="rfc.section.6.4.p.5">See <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section 4</a> for rules on how to determine if two entity tags match. |
|---|
| 958 | </p> |
|---|
| 959 | <p id="rfc.section.6.4.p.6">If none of the entity tags match, then the server <em class="bcp14">MAY</em> perform the requested method as if the If-None-Match header field did not exist, but <em class="bcp14">MUST</em> also ignore any If-Modified-Since header field(s) in the request. That is, if no entity tags match, then the server <em class="bcp14">MUST NOT</em> return a 304 (Not Modified) response. |
|---|
| 960 | </p> |
|---|
| 961 | <p id="rfc.section.6.4.p.7">If the request would, without the If-None-Match header field, result in anything other than a 2xx or 304 status, then the |
|---|
| 962 | If-None-Match header <em class="bcp14">MUST</em> be ignored. (See <a href="#rules.for.when.to.use.entity.tags.and.last-modified.dates" title="Rules for When to Use Entity Tags and Last-Modified Dates">Section 5</a> for a discussion of server behavior when both If-Modified-Since and If-None-Match appear in the same request.) |
|---|
| 963 | </p> |
|---|
| 964 | <p id="rfc.section.6.4.p.8">The meaning of "If-None-Match: *" is that the method <em class="bcp14">MUST NOT</em> be performed if the representation selected by the origin server (or by a cache, possibly using the Vary mechanism, see <a href="p6-cache.html#header.vary" title="Vary">Section 15.5</a> of <a href="#Part6" id="rfc.xref.Part6.3"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) exists, and <em class="bcp14">SHOULD</em> be performed if the representation does not exist. This feature is intended to be useful in preventing races between PUT operations. |
|---|
| 965 | </p> |
|---|
| 966 | <p id="rfc.section.6.4.p.9">Examples:</p> |
|---|
| 967 | <div id="rfc.figure.u.11"></div><pre class="text"> If-None-Match: "xyzzy" |
|---|
| 968 | If-None-Match: W/"xyzzy" |
|---|
| 969 | If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz" |
|---|
| 970 | If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz" |
|---|
| 971 | If-None-Match: * |
|---|
| 972 | </pre><p id="rfc.section.6.4.p.11">The result of a request having both an If-None-Match header field and either an If-Match or an If-Unmodified-Since header |
|---|
| 973 | fields is undefined by this specification. |
|---|
| 974 | </p> |
|---|
| 975 | <div id="rfc.iref.i.4"></div> |
|---|
| 976 | <div id="rfc.iref.h.5"></div> |
|---|
| 977 | <h2 id="rfc.section.6.5"><a href="#rfc.section.6.5">6.5</a> <a id="header.if-unmodified-since" href="#header.if-unmodified-since">If-Unmodified-Since</a></h2> |
|---|
| 978 | <p id="rfc.section.6.5.p.1">The request-header field "If-Unmodified-Since" is used with a method to make it conditional. If the requested resource has |
|---|
| 979 | not been modified since the time specified in this field, the server <em class="bcp14">SHOULD</em> perform the requested operation as if the If-Unmodified-Since header were not present. |
|---|
| 980 | </p> |
|---|
| 981 | <p id="rfc.section.6.5.p.2">If the requested variant has been modified since the specified time, the server <em class="bcp14">MUST NOT</em> perform the requested operation, and <em class="bcp14">MUST</em> return a 412 (Precondition Failed). |
|---|
| 982 | </p> |
|---|
| 983 | <div id="rfc.figure.u.12"></div><pre class="inline"><span id="rfc.iref.g.12"></span><span id="rfc.iref.g.13"></span> <a href="#header.if-unmodified-since" class="smpl">If-Unmodified-Since</a> = "If-Unmodified-Since" ":" <a href="#core.rules" class="smpl">OWS</a> |
|---|
| 984 | <a href="#header.if-unmodified-since" class="smpl">If-Unmodified-Since-v</a> |
|---|
| 985 | <a href="#header.if-unmodified-since" class="smpl">If-Unmodified-Since-v</a> = <a href="#abnf.dependencies" class="smpl">HTTP-date</a> |
|---|
| 986 | </pre><p id="rfc.section.6.5.p.4">An example of the field is:</p> |
|---|
| 987 | <div id="rfc.figure.u.13"></div><pre class="text"> If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT |
|---|
| 988 | </pre><p id="rfc.section.6.5.p.6">If the request normally (i.e., without the If-Unmodified-Since header) would result in anything other than a 2xx or 412 status, |
|---|
| 989 | the If-Unmodified-Since header <em class="bcp14">SHOULD</em> be ignored. |
|---|
| 990 | </p> |
|---|
| 991 | <p id="rfc.section.6.5.p.7">If the specified date is invalid, the header is ignored.</p> |
|---|
| 992 | <p id="rfc.section.6.5.p.8">The result of a request having both an If-Unmodified-Since header field and either an If-None-Match or an If-Modified-Since |
|---|
| 993 | header fields is undefined by this specification. |
|---|
| 994 | </p> |
|---|
| 995 | <div id="rfc.iref.l.1"></div> |
|---|
| 996 | <div id="rfc.iref.h.6"></div> |
|---|
| 997 | <h2 id="rfc.section.6.6"><a href="#rfc.section.6.6">6.6</a> <a id="header.last-modified" href="#header.last-modified">Last-Modified</a></h2> |
|---|
| 998 | <p id="rfc.section.6.6.p.1">The entity-header field "Last-Modified" indicates the date and time at which the origin server believes the variant was last |
|---|
| 999 | modified. |
|---|
| 1000 | </p> |
|---|
| 1001 | <div id="rfc.figure.u.14"></div><pre class="inline"><span id="rfc.iref.g.14"></span><span id="rfc.iref.g.15"></span> <a href="#header.last-modified" class="smpl">Last-Modified</a> = "Last-Modified" ":" <a href="#core.rules" class="smpl">OWS</a> <a href="#header.last-modified" class="smpl">Last-Modified-v</a> |
|---|
| 1002 | <a href="#header.last-modified" class="smpl">Last-Modified-v</a> = <a href="#abnf.dependencies" class="smpl">HTTP-date</a> |
|---|
| 1003 | </pre><p id="rfc.section.6.6.p.3">An example of its use is</p> |
|---|
| 1004 | <div id="rfc.figure.u.15"></div><pre class="text"> Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT |
|---|
| 1005 | </pre><p id="rfc.section.6.6.p.5">The exact meaning of this header field depends on the implementation of the origin server and the nature of the original resource. |
|---|
| 1006 | For files, it may be just the file system last-modified time. For entities with dynamically included parts, it may be the |
|---|
| 1007 | most recent of the set of last-modify times for its component parts. For database gateways, it may be the last-update time |
|---|
| 1008 | stamp of the record. For virtual objects, it may be the last time the internal state changed. |
|---|
| 1009 | </p> |
|---|
| 1010 | <p id="rfc.section.6.6.p.6">An origin server <em class="bcp14">MUST NOT</em> send a Last-Modified date which is later than the server's time of message origination. In such cases, where the resource's |
|---|
| 1011 | last modification would indicate some time in the future, the server <em class="bcp14">MUST</em> replace that date with the message origination date. |
|---|
| 1012 | </p> |
|---|
| 1013 | <p id="rfc.section.6.6.p.7">An origin server <em class="bcp14">SHOULD</em> obtain the Last-Modified value of the entity as close as possible to the time that it generates the Date value of its response. |
|---|
| 1014 | This allows a recipient to make an accurate assessment of the entity's modification time, especially if the entity changes |
|---|
| 1015 | near the time that the response is generated. |
|---|
| 1016 | </p> |
|---|
| 1017 | <p id="rfc.section.6.6.p.8">HTTP/1.1 servers <em class="bcp14">SHOULD</em> send Last-Modified whenever feasible. |
|---|
| 1018 | </p> |
|---|
| 1019 | <p id="rfc.section.6.6.p.9">The Last-Modified entity-header field value is often used as a cache validator. In simple terms, a cache entry is considered |
|---|
| 1020 | to be valid if the entity has not been modified since the Last-Modified value. |
|---|
| 1021 | </p> |
|---|
| 1022 | <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a> <a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1> |
|---|
| 1023 | <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a> <a id="message.header.registration" href="#message.header.registration">Message Header Registration</a></h2> |
|---|
| 1024 | <p id="rfc.section.7.1.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>): |
|---|
| 1025 | </p> |
|---|
| 1026 | <div id="rfc.table.1"> |
|---|
| 1027 | <div id="iana.header.registration.table"></div> |
|---|
| 1028 | <table summary="" class="tt full" cellpadding="3" cellspacing="0"> |
|---|
| 1029 | <thead> |
|---|
| 1030 | <tr> |
|---|
| 1031 | <th>Header Field Name</th> |
|---|
| 1032 | <th>Protocol</th> |
|---|
| 1033 | <th>Status</th> |
|---|
| 1034 | <th>Reference</th> |
|---|
| 1035 | </tr> |
|---|
| 1036 | </thead> |
|---|
| 1037 | <tbody> |
|---|
| 1038 | <tr> |
|---|
| 1039 | <td>ETag</td> |
|---|
| 1040 | <td>http</td> |
|---|
| 1041 | <td>standard</td> |
|---|
| 1042 | <td> <a href="#header.etag" id="rfc.xref.header.etag.2" title="ETag">Section 6.1</a> |
|---|
| 1043 | </td> |
|---|
| 1044 | </tr> |
|---|
| 1045 | <tr> |
|---|
| 1046 | <td>If-Match</td> |
|---|
| 1047 | <td>http</td> |
|---|
| 1048 | <td>standard</td> |
|---|
| 1049 | <td> <a href="#header.if-match" id="rfc.xref.header.if-match.3" title="If-Match">Section 6.2</a> |
|---|
| 1050 | </td> |
|---|
| 1051 | </tr> |
|---|
| 1052 | <tr> |
|---|
| 1053 | <td>If-Modified-Since</td> |
|---|
| 1054 | <td>http</td> |
|---|
| 1055 | <td>standard</td> |
|---|
| 1056 | <td> <a href="#header.if-modified-since" id="rfc.xref.header.if-modified-since.1" title="If-Modified-Since">Section 6.3</a> |
|---|
| 1057 | </td> |
|---|
| 1058 | </tr> |
|---|
| 1059 | <tr> |
|---|
| 1060 | <td>If-None-Match</td> |
|---|
| 1061 | <td>http</td> |
|---|
| 1062 | <td>standard</td> |
|---|
| 1063 | <td> <a href="#header.if-none-match" id="rfc.xref.header.if-none-match.3" title="If-None-Match">Section 6.4</a> |
|---|
| 1064 | </td> |
|---|
| 1065 | </tr> |
|---|
| 1066 | <tr> |
|---|
| 1067 | <td>If-Unmodified-Since</td> |
|---|
| 1068 | <td>http</td> |
|---|
| 1069 | <td>standard</td> |
|---|
| 1070 | <td> <a href="#header.if-unmodified-since" id="rfc.xref.header.if-unmodified-since.1" title="If-Unmodified-Since">Section 6.5</a> |
|---|
| 1071 | </td> |
|---|
| 1072 | </tr> |
|---|
| 1073 | <tr> |
|---|
| 1074 | <td>Last-Modified</td> |
|---|
| 1075 | <td>http</td> |
|---|
| 1076 | <td>standard</td> |
|---|
| 1077 | <td> <a href="#header.last-modified" id="rfc.xref.header.last-modified.1" title="Last-Modified">Section 6.6</a> |
|---|
| 1078 | </td> |
|---|
| 1079 | </tr> |
|---|
| 1080 | </tbody> |
|---|
| 1081 | </table> |
|---|
| 1082 | </div> |
|---|
| 1083 | <p id="rfc.section.7.1.p.2">The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p> |
|---|
| 1084 | <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a> <a id="security.considerations" href="#security.considerations">Security Considerations</a></h1> |
|---|
| 1085 | <p id="rfc.section.8.p.1">No additional security considerations have been identified beyond those applicable to HTTP in general <a href="#Part1" id="rfc.xref.Part1.8"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. |
|---|
| 1086 | </p> |
|---|
| 1087 | <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a> <a id="ack" href="#ack">Acknowledgments</a></h1> |
|---|
| 1088 | <h1 id="rfc.references"><a id="rfc.section.10" href="#rfc.section.10">10.</a> References |
|---|
| 1089 | </h1> |
|---|
| 1090 | <h2 id="rfc.references.1"><a href="#rfc.section.10.1" id="rfc.section.10.1">10.1</a> Normative References |
|---|
| 1091 | </h2> |
|---|
| 1092 | <table summary="Normative References"> |
|---|
| 1093 | <tr> |
|---|
| 1094 | <td class="reference"><b id="Part1">[Part1]</b></td> |
|---|
| 1095 | <td class="top"><a title="Day Software">Fielding, R., Ed.</a>, <a title="One Laptop per Child">Gettys, J.</a>, <a title="Hewlett-Packard Company">Mogul, J.</a>, <a title="Microsoft Corporation">Frystyk, H.</a>, <a title="Adobe Systems, Incorporated">Masinter, L.</a>, <a title="Microsoft Corporation">Leach, P.</a>, <a title="World Wide Web Consortium">Berners-Lee, T.</a>, <a title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a title="greenbytes GmbH">J. F. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-latest">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</a>”, Internet-Draft draft-ietf-httpbis-p1-messaging-latest (work in progress), February 2009. |
|---|
| 1096 | </td> |
|---|
| 1097 | </tr> |
|---|
| 1098 | <tr> |
|---|
| 1099 | <td class="reference"><b id="Part5">[Part5]</b></td> |
|---|
| 1100 | <td class="top"><a title="Day Software">Fielding, R., Ed.</a>, <a title="One Laptop per Child">Gettys, J.</a>, <a title="Hewlett-Packard Company">Mogul, J.</a>, <a title="Microsoft Corporation">Frystyk, H.</a>, <a title="Adobe Systems, Incorporated">Masinter, L.</a>, <a title="Microsoft Corporation">Leach, P.</a>, <a title="World Wide Web Consortium">Berners-Lee, T.</a>, <a title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a title="greenbytes GmbH">J. F. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p5-range-latest">HTTP/1.1, part 5: Range Requests and Partial Responses</a>”, Internet-Draft draft-ietf-httpbis-p5-range-latest (work in progress), February 2009. |
|---|
| 1101 | </td> |
|---|
| 1102 | </tr> |
|---|
| 1103 | <tr> |
|---|
| 1104 | <td class="reference"><b id="Part6">[Part6]</b></td> |
|---|
| 1105 | <td class="top"><a title="Day Software">Fielding, R., Ed.</a>, <a title="One Laptop per Child">Gettys, J.</a>, <a title="Hewlett-Packard Company">Mogul, J.</a>, <a title="Microsoft Corporation">Frystyk, H.</a>, <a title="Adobe Systems, Incorporated">Masinter, L.</a>, <a title="Microsoft Corporation">Leach, P.</a>, <a title="World Wide Web Consortium">Berners-Lee, T.</a>, <a title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a title="greenbytes GmbH">J. F. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-latest">HTTP/1.1, part 6: Caching</a>”, Internet-Draft draft-ietf-httpbis-p6-cache-latest (work in progress), February 2009. |
|---|
| 1106 | </td> |
|---|
| 1107 | </tr> |
|---|
| 1108 | <tr> |
|---|
| 1109 | <td class="reference"><b id="RFC2119">[RFC2119]</b></td> |
|---|
| 1110 | <td class="top"><a 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. |
|---|
| 1111 | </td> |
|---|
| 1112 | </tr> |
|---|
| 1113 | <tr> |
|---|
| 1114 | <td class="reference"><b id="RFC5234">[RFC5234]</b></td> |
|---|
| 1115 | <td class="top"><a title="Brandenburg InternetWorking">Crocker, D., Ed.</a> and <a title="THUS plc.">P. Overell</a>, “<a href="http://tools.ietf.org/html/rfc5234">Augmented BNF for Syntax Specifications: ABNF</a>”, STD 68, RFC 5234, January 2008. |
|---|
| 1116 | </td> |
|---|
| 1117 | </tr> |
|---|
| 1118 | </table> |
|---|
| 1119 | <h2 id="rfc.references.2"><a href="#rfc.section.10.2" id="rfc.section.10.2">10.2</a> Informative References |
|---|
| 1120 | </h2> |
|---|
| 1121 | <table summary="Informative References"> |
|---|
| 1122 | <tr> |
|---|
| 1123 | <td class="reference"><b id="RFC2616">[RFC2616]</b></td> |
|---|
| 1124 | <td class="top"><a title="University of California, Irvine">Fielding, R.</a>, <a title="W3C">Gettys, J.</a>, <a title="Compaq Computer Corporation">Mogul, J.</a>, <a title="MIT Laboratory for Computer Science">Frystyk, H.</a>, <a title="Xerox Corporation">Masinter, L.</a>, <a title="Microsoft Corporation">Leach, P.</a>, and <a 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. |
|---|
| 1125 | </td> |
|---|
| 1126 | </tr> |
|---|
| 1127 | <tr> |
|---|
| 1128 | <td class="reference"><b id="RFC3864">[RFC3864]</b></td> |
|---|
| 1129 | <td class="top"><a title="Nine by Nine">Klyne, G.</a>, <a title="BEA Systems">Nottingham, M.</a>, and <a 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. |
|---|
| 1130 | </td> |
|---|
| 1131 | </tr> |
|---|
| 1132 | </table> |
|---|
| 1133 | <h1 id="rfc.authors"><a href="#rfc.authors">Authors' Addresses</a></h1> |
|---|
| 1134 | <address class="vcard"><span class="vcardline"><span class="fn">Roy T. Fielding</span> |
|---|
| 1135 | (editor) |
|---|
| 1136 | <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><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> |
|---|
| 1137 | <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><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> |
|---|
| 1138 | <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><span class="email">JeffMogul@acm.org</span></a></span></address> |
|---|
| 1139 | <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><span class="email">henrikn@microsoft.com</span></a></span></address> |
|---|
| 1140 | <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><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> |
|---|
| 1141 | <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><span class="email">paulle@microsoft.com</span></a></span></address> |
|---|
| 1142 | <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><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> |
|---|
| 1143 | <address class="vcard"><span class="vcardline"><span class="fn">Yves Lafon</span> |
|---|
| 1144 | (editor) |
|---|
| 1145 | <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><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> |
|---|
| 1146 | <address class="vcard"><span class="vcardline"><span class="fn">Julian F. Reschke</span> |
|---|
| 1147 | (editor) |
|---|
| 1148 | <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><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> |
|---|
| 1149 | <h1 id="rfc.section.A"><a href="#rfc.section.A">A.</a> <a id="compatibility" href="#compatibility">Compatibility with Previous Versions</a></h1> |
|---|
| 1150 | <h2 id="rfc.section.A.1"><a href="#rfc.section.A.1">A.1</a> <a id="changes.from.rfc.2616" href="#changes.from.rfc.2616">Changes from RFC 2616</a></h2> |
|---|
| 1151 | <p id="rfc.section.A.1.p.1">Allow weak entity tags in all requests except range requests (Sections <a href="#weak.and.strong.validators" title="Weak and Strong Validators">4</a> and <a href="#header.if-none-match" id="rfc.xref.header.if-none-match.4" title="If-None-Match">6.4</a>). |
|---|
| 1152 | </p> |
|---|
| 1153 | <h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a> <a id="collected.abnf" href="#collected.abnf">Collected ABNF</a></h1> |
|---|
| 1154 | <div id="rfc.figure.u.16"></div> <pre class="inline"><a href="#header.etag" class="smpl">ETag</a> = "ETag:" OWS ETag-v |
|---|
| 1155 | <a href="#header.etag" class="smpl">ETag-v</a> = entity-tag |
|---|
| 1156 | |
|---|
| 1157 | <a href="#abnf.dependencies" class="smpl">HTTP-date</a> = <HTTP-date, defined in [Part1], Section 3.2.1> |
|---|
| 1158 | |
|---|
| 1159 | <a href="#header.if-match" class="smpl">If-Match</a> = "If-Match:" OWS If-Match-v |
|---|
| 1160 | <a href="#header.if-match" class="smpl">If-Match-v</a> = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS |
|---|
| 1161 | entity-tag ] ) ) |
|---|
| 1162 | <a href="#header.if-modified-since" class="smpl">If-Modified-Since</a> = "If-Modified-Since:" OWS If-Modified-Since-v |
|---|
| 1163 | <a href="#header.if-modified-since" class="smpl">If-Modified-Since-v</a> = HTTP-date |
|---|
| 1164 | <a href="#header.if-none-match" class="smpl">If-None-Match</a> = "If-None-Match:" OWS If-None-Match-v |
|---|
| 1165 | <a href="#header.if-none-match" class="smpl">If-None-Match-v</a> = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS |
|---|
| 1166 | entity-tag ] ) ) |
|---|
| 1167 | <a href="#header.if-unmodified-since" class="smpl">If-Unmodified-Since</a> = "If-Unmodified-Since:" OWS |
|---|
| 1168 | If-Unmodified-Since-v |
|---|
| 1169 | <a href="#header.if-unmodified-since" class="smpl">If-Unmodified-Since-v</a> = HTTP-date |
|---|
| 1170 | |
|---|
| 1171 | <a href="#header.last-modified" class="smpl">Last-Modified</a> = "Last-Modified:" OWS Last-Modified-v |
|---|
| 1172 | <a href="#header.last-modified" class="smpl">Last-Modified-v</a> = HTTP-date |
|---|
| 1173 | |
|---|
| 1174 | <a href="#core.rules" class="smpl">OWS</a> = <OWS, defined in [Part1], Section 1.2.2> |
|---|
| 1175 | |
|---|
| 1176 | <a href="#entity.tags" class="smpl">entity-tag</a> = [ weak ] opaque-tag |
|---|
| 1177 | |
|---|
| 1178 | <a href="#entity.tags" class="smpl">opaque-tag</a> = quoted-string |
|---|
| 1179 | |
|---|
| 1180 | <a href="#core.rules" class="smpl">quoted-string</a> = <quoted-string, defined in [Part1], Section 1.2.2> |
|---|
| 1181 | |
|---|
| 1182 | <a href="#entity.tags" class="smpl">weak</a> = "W/" |
|---|
| 1183 | |
|---|
| 1184 | |
|---|
| 1185 | </pre> <div id="rfc.figure.u.17"></div> |
|---|
| 1186 | <p>ABNF diagnostics:</p><pre class="inline">; ETag defined but not used |
|---|
| 1187 | ; If-Match defined but not used |
|---|
| 1188 | ; If-Modified-Since defined but not used |
|---|
| 1189 | ; If-None-Match defined but not used |
|---|
| 1190 | ; If-Unmodified-Since defined but not used |
|---|
| 1191 | ; Last-Modified defined but not used |
|---|
| 1192 | </pre><h1 id="rfc.section.C"><a href="#rfc.section.C">C.</a> <a id="change.log" href="#change.log">Change Log (to be removed by RFC Editor before publication)</a></h1> |
|---|
| 1193 | <h2 id="rfc.section.C.1"><a href="#rfc.section.C.1">C.1</a> Since RFC2616 |
|---|
| 1194 | </h2> |
|---|
| 1195 | <p id="rfc.section.C.1.p.1">Extracted relevant partitions from <a href="#RFC2616" id="rfc.xref.RFC2616.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>. |
|---|
| 1196 | </p> |
|---|
| 1197 | <h2 id="rfc.section.C.2"><a href="#rfc.section.C.2">C.2</a> Since draft-ietf-httpbis-p4-conditional-00 |
|---|
| 1198 | </h2> |
|---|
| 1199 | <p id="rfc.section.C.2.p.1">Closed issues: </p> |
|---|
| 1200 | <ul> |
|---|
| 1201 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/35">http://tools.ietf.org/wg/httpbis/trac/ticket/35</a>>: "Normative and Informative references" |
|---|
| 1202 | </li> |
|---|
| 1203 | </ul> |
|---|
| 1204 | <p id="rfc.section.C.2.p.2">Other changes: </p> |
|---|
| 1205 | <ul> |
|---|
| 1206 | <li>Move definitions of 304 and 412 condition codes from Part2.</li> |
|---|
| 1207 | </ul> |
|---|
| 1208 | <h2 id="rfc.section.C.3"><a href="#rfc.section.C.3">C.3</a> Since draft-ietf-httpbis-p4-conditional-01 |
|---|
| 1209 | </h2> |
|---|
| 1210 | <p id="rfc.section.C.3.p.1">Ongoing work on ABNF conversion (<<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/36">http://tools.ietf.org/wg/httpbis/trac/ticket/36</a>>): |
|---|
| 1211 | </p> |
|---|
| 1212 | <ul> |
|---|
| 1213 | <li>Add explicit references to BNF syntax and rules imported from other parts of the specification.</li> |
|---|
| 1214 | </ul> |
|---|
| 1215 | <h2 id="rfc.section.C.4"><a href="#rfc.section.C.4">C.4</a> <a id="changes.since.02" href="#changes.since.02">Since draft-ietf-httpbis-p4-conditional-02</a></h2> |
|---|
| 1216 | <p id="rfc.section.C.4.p.1">Closed issues: </p> |
|---|
| 1217 | <ul> |
|---|
| 1218 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/116">http://tools.ietf.org/wg/httpbis/trac/ticket/116</a>>: "Weak ETags on non-GET requests" |
|---|
| 1219 | </li> |
|---|
| 1220 | </ul> |
|---|
| 1221 | <p id="rfc.section.C.4.p.2">Ongoing work on IANA Message Header Registration (<<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/40">http://tools.ietf.org/wg/httpbis/trac/ticket/40</a>>): |
|---|
| 1222 | </p> |
|---|
| 1223 | <ul> |
|---|
| 1224 | <li>Reference RFC 3984, and update header registrations for headers defined in this document.</li> |
|---|
| 1225 | </ul> |
|---|
| 1226 | <h2 id="rfc.section.C.5"><a href="#rfc.section.C.5">C.5</a> <a id="changes.since.03" href="#changes.since.03">Since draft-ietf-httpbis-p4-conditional-03</a></h2> |
|---|
| 1227 | <p id="rfc.section.C.5.p.1">Closed issues: </p> |
|---|
| 1228 | <ul> |
|---|
| 1229 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/71">http://tools.ietf.org/wg/httpbis/trac/ticket/71</a>>: "Examples for ETag matching" |
|---|
| 1230 | </li> |
|---|
| 1231 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/124">http://tools.ietf.org/wg/httpbis/trac/ticket/124</a>>: "'entity value' undefined" |
|---|
| 1232 | </li> |
|---|
| 1233 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/126">http://tools.ietf.org/wg/httpbis/trac/ticket/126</a>>: "bogus 2068 Date header reference" |
|---|
| 1234 | </li> |
|---|
| 1235 | </ul> |
|---|
| 1236 | <h2 id="rfc.section.C.6"><a href="#rfc.section.C.6">C.6</a> <a id="changes.since.04" href="#changes.since.04">Since draft-ietf-httpbis-p4-conditional-04</a></h2> |
|---|
| 1237 | <p id="rfc.section.C.6.p.1">Ongoing work on ABNF conversion (<<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/36">http://tools.ietf.org/wg/httpbis/trac/ticket/36</a>>): |
|---|
| 1238 | </p> |
|---|
| 1239 | <ul> |
|---|
| 1240 | <li>Use "/" instead of "|" for alternatives.</li> |
|---|
| 1241 | <li>Introduce new ABNF rules for "bad" whitespace ("BWS"), optional whitespace ("OWS") and required whitespace ("RWS").</li> |
|---|
| 1242 | <li>Rewrite ABNFs to spell out whitespace rules, factor out header value format definitions.</li> |
|---|
| 1243 | </ul> |
|---|
| 1244 | <h2 id="rfc.section.C.7"><a href="#rfc.section.C.7">C.7</a> <a id="changes.since.05" href="#changes.since.05">Since draft-ietf-httpbis-p4-conditional-05</a></h2> |
|---|
| 1245 | <p id="rfc.section.C.7.p.1">Ongoing work on ABNF conversion (<<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/36">http://tools.ietf.org/wg/httpbis/trac/ticket/36</a>>): |
|---|
| 1246 | </p> |
|---|
| 1247 | <ul> |
|---|
| 1248 | <li>Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.</li> |
|---|
| 1249 | </ul> |
|---|
| 1250 | <h1 id="rfc.index"><a href="#rfc.index">Index</a></h1> |
|---|
| 1251 | <p class="noprint"><a href="#rfc.index.3">3</a> <a href="#rfc.index.4">4</a> <a href="#rfc.index.E">E</a> <a href="#rfc.index.G">G</a> <a href="#rfc.index.H">H</a> <a href="#rfc.index.I">I</a> <a href="#rfc.index.L">L</a> <a href="#rfc.index.P">P</a> <a href="#rfc.index.R">R</a> <a href="#rfc.index.S">S</a> |
|---|
| 1252 | </p> |
|---|
| 1253 | <div class="print2col"> |
|---|
| 1254 | <ul class="ind"> |
|---|
| 1255 | <li class="indline0"><a id="rfc.index.3" href="#rfc.index.3"><b>3</b></a><ul class="ind"> |
|---|
| 1256 | <li class="indline1">304 Not Modified (status code) <a class="iref" href="#rfc.iref.3"><b>3.1</b></a></li> |
|---|
| 1257 | </ul> |
|---|
| 1258 | </li> |
|---|
| 1259 | <li class="indline0"><a id="rfc.index.4" href="#rfc.index.4"><b>4</b></a><ul class="ind"> |
|---|
| 1260 | <li class="indline1">412 Precondition Failed (status code) <a class="iref" href="#rfc.iref.4"><b>3.2</b></a></li> |
|---|
| 1261 | </ul> |
|---|
| 1262 | </li> |
|---|
| 1263 | <li class="indline0"><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul class="ind"> |
|---|
| 1264 | <li class="indline1">ETag header <a class="iref" href="#rfc.xref.header.etag.1">2</a>, <a class="iref" href="#rfc.iref.e.1"><b>6.1</b></a>, <a class="iref" href="#rfc.xref.header.etag.2">7.1</a></li> |
|---|
| 1265 | </ul> |
|---|
| 1266 | </li> |
|---|
| 1267 | <li class="indline0"><a id="rfc.index.G" href="#rfc.index.G"><b>G</b></a><ul class="ind"> |
|---|
| 1268 | <li class="indline1"><tt>Grammar</tt> |
|---|
| 1269 | <ul class="ind"> |
|---|
| 1270 | <li class="indline1"><tt>entity-tag</tt> <a class="iref" href="#rfc.iref.g.1"><b>2</b></a></li> |
|---|
| 1271 | <li class="indline1"><tt>ETag</tt> <a class="iref" href="#rfc.iref.g.4"><b>6.1</b></a></li> |
|---|
| 1272 | <li class="indline1"><tt>ETag-v</tt> <a class="iref" href="#rfc.iref.g.5"><b>6.1</b></a></li> |
|---|
| 1273 | <li class="indline1"><tt>If-Match</tt> <a class="iref" href="#rfc.iref.g.6"><b>6.2</b></a></li> |
|---|
| 1274 | <li class="indline1"><tt>If-Match-v</tt> <a class="iref" href="#rfc.iref.g.7"><b>6.2</b></a></li> |
|---|
| 1275 | <li class="indline1"><tt>If-Modified-Since</tt> <a class="iref" href="#rfc.iref.g.8"><b>6.3</b></a></li> |
|---|
| 1276 | <li class="indline1"><tt>If-Modified-Since-v</tt> <a class="iref" href="#rfc.iref.g.9"><b>6.3</b></a></li> |
|---|
| 1277 | <li class="indline1"><tt>If-None-Match</tt> <a class="iref" href="#rfc.iref.g.10"><b>6.4</b></a></li> |
|---|
| 1278 | <li class="indline1"><tt>If-None-Match-v</tt> <a class="iref" href="#rfc.iref.g.11"><b>6.4</b></a></li> |
|---|
| 1279 | <li class="indline1"><tt>If-Unmodified-Since</tt> <a class="iref" href="#rfc.iref.g.12"><b>6.5</b></a></li> |
|---|
| 1280 | <li class="indline1"><tt>If-Unmodified-Since-v</tt> <a class="iref" href="#rfc.iref.g.13"><b>6.5</b></a></li> |
|---|
| 1281 | <li class="indline1"><tt>Last-Modified</tt> <a class="iref" href="#rfc.iref.g.14"><b>6.6</b></a></li> |
|---|
| 1282 | <li class="indline1"><tt>Last-Modified-v</tt> <a class="iref" href="#rfc.iref.g.15"><b>6.6</b></a></li> |
|---|
| 1283 | <li class="indline1"><tt>opaque-tag</tt> <a class="iref" href="#rfc.iref.g.3"><b>2</b></a></li> |
|---|
| 1284 | <li class="indline1"><tt>weak</tt> <a class="iref" href="#rfc.iref.g.2"><b>2</b></a></li> |
|---|
| 1285 | </ul> |
|---|
| 1286 | </li> |
|---|
| 1287 | </ul> |
|---|
| 1288 | </li> |
|---|
| 1289 | <li class="indline0"><a id="rfc.index.H" href="#rfc.index.H"><b>H</b></a><ul class="ind"> |
|---|
| 1290 | <li class="indline1">Headers |
|---|
| 1291 | <ul class="ind"> |
|---|
| 1292 | <li class="indline1">ETag <a class="iref" href="#rfc.xref.header.etag.1">2</a>, <a class="iref" href="#rfc.iref.h.1"><b>6.1</b></a>, <a class="iref" href="#rfc.xref.header.etag.2">7.1</a></li> |
|---|
| 1293 | <li class="indline1">If-Match <a class="iref" href="#rfc.xref.header.if-match.1">2</a>, <a class="iref" href="#rfc.xref.header.if-match.2">6.1</a>, <a class="iref" href="#rfc.iref.h.2"><b>6.2</b></a>, <a class="iref" href="#rfc.xref.header.if-match.3">7.1</a></li> |
|---|
| 1294 | <li class="indline1">If-Modified-Since <a class="iref" href="#rfc.iref.h.3"><b>6.3</b></a>, <a class="iref" href="#rfc.xref.header.if-modified-since.1">7.1</a></li> |
|---|
| 1295 | <li class="indline1">If-None-Match <a class="iref" href="#rfc.xref.header.if-none-match.1">2</a>, <a class="iref" href="#rfc.xref.header.if-none-match.2">6.1</a>, <a class="iref" href="#rfc.iref.h.4"><b>6.4</b></a>, <a class="iref" href="#rfc.xref.header.if-none-match.3">7.1</a>, <a class="iref" href="#rfc.xref.header.if-none-match.4">A.1</a></li> |
|---|
| 1296 | <li class="indline1">If-Unmodified-Since <a class="iref" href="#rfc.iref.h.5"><b>6.5</b></a>, <a class="iref" href="#rfc.xref.header.if-unmodified-since.1">7.1</a></li> |
|---|
| 1297 | <li class="indline1">Last-Modified <a class="iref" href="#rfc.iref.h.6"><b>6.6</b></a>, <a class="iref" href="#rfc.xref.header.last-modified.1">7.1</a></li> |
|---|
| 1298 | </ul> |
|---|
| 1299 | </li> |
|---|
| 1300 | </ul> |
|---|
| 1301 | </li> |
|---|
| 1302 | <li class="indline0"><a id="rfc.index.I" href="#rfc.index.I"><b>I</b></a><ul class="ind"> |
|---|
| 1303 | <li class="indline1">If-Match header <a class="iref" href="#rfc.xref.header.if-match.1">2</a>, <a class="iref" href="#rfc.xref.header.if-match.2">6.1</a>, <a class="iref" href="#rfc.iref.i.1"><b>6.2</b></a>, <a class="iref" href="#rfc.xref.header.if-match.3">7.1</a></li> |
|---|
| 1304 | <li class="indline1">If-Modified-Since header <a class="iref" href="#rfc.iref.i.2"><b>6.3</b></a>, <a class="iref" href="#rfc.xref.header.if-modified-since.1">7.1</a></li> |
|---|
| 1305 | <li class="indline1">If-None-Match header <a class="iref" href="#rfc.xref.header.if-none-match.1">2</a>, <a class="iref" href="#rfc.xref.header.if-none-match.2">6.1</a>, <a class="iref" href="#rfc.iref.i.3"><b>6.4</b></a>, <a class="iref" href="#rfc.xref.header.if-none-match.3">7.1</a>, <a class="iref" href="#rfc.xref.header.if-none-match.4">A.1</a></li> |
|---|
| 1306 | <li class="indline1">If-Unmodified-Since header <a class="iref" href="#rfc.iref.i.4"><b>6.5</b></a>, <a class="iref" href="#rfc.xref.header.if-unmodified-since.1">7.1</a></li> |
|---|
| 1307 | </ul> |
|---|
| 1308 | </li> |
|---|
| 1309 | <li class="indline0"><a id="rfc.index.L" href="#rfc.index.L"><b>L</b></a><ul class="ind"> |
|---|
| 1310 | <li class="indline1">Last-Modified header <a class="iref" href="#rfc.iref.l.1"><b>6.6</b></a>, <a class="iref" href="#rfc.xref.header.last-modified.1">7.1</a></li> |
|---|
| 1311 | </ul> |
|---|
| 1312 | </li> |
|---|
| 1313 | <li class="indline0"><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul class="ind"> |
|---|
| 1314 | <li class="indline1"><em>Part1</em> <a class="iref" href="#rfc.xref.Part1.1">1.2</a>, <a class="iref" href="#rfc.xref.Part1.2">1.2.1</a>, <a class="iref" href="#rfc.xref.Part1.3">1.2.1</a>, <a class="iref" href="#rfc.xref.Part1.4">1.2.1</a>, <a class="iref" href="#rfc.xref.Part1.5">1.2.2</a>, <a class="iref" href="#rfc.xref.Part1.6">3.1</a>, <a class="iref" href="#rfc.xref.Part1.7">3.1</a>, <a class="iref" href="#rfc.xref.Part1.8">8</a>, <a class="iref" href="#Part1"><b>10.1</b></a><ul class="ind"> |
|---|
| 1315 | <li class="indline1"><em>Section 1.2</em> <a class="iref" href="#rfc.xref.Part1.1">1.2</a></li> |
|---|
| 1316 | <li class="indline1"><em>Section 1.2.2</em> <a class="iref" href="#rfc.xref.Part1.2">1.2.1</a>, <a class="iref" href="#rfc.xref.Part1.3">1.2.1</a>, <a class="iref" href="#rfc.xref.Part1.4">1.2.1</a></li> |
|---|
| 1317 | <li class="indline1"><em>Section 3.2.1</em> <a class="iref" href="#rfc.xref.Part1.5">1.2.2</a></li> |
|---|
| 1318 | <li class="indline1"><em>Section 8.3.1</em> <a class="iref" href="#rfc.xref.Part1.6">3.1</a></li> |
|---|
| 1319 | <li class="indline1"><em>Section 8.3</em> <a class="iref" href="#rfc.xref.Part1.7">3.1</a></li> |
|---|
| 1320 | </ul> |
|---|
| 1321 | </li> |
|---|
| 1322 | <li class="indline1"><em>Part5</em> <a class="iref" href="#rfc.xref.Part5.1">2</a>, <a class="iref" href="#rfc.xref.Part5.2">4</a>, <a class="iref" href="#rfc.xref.Part5.3">4</a>, <a class="iref" href="#rfc.xref.Part5.4">6.1</a>, <a class="iref" href="#rfc.xref.Part5.5">6.3</a>, <a class="iref" href="#Part5"><b>10.1</b></a><ul class="ind"> |
|---|
| 1323 | <li class="indline1"><em>Section 5.3</em> <a class="iref" href="#rfc.xref.Part5.1">2</a>, <a class="iref" href="#rfc.xref.Part5.4">6.1</a></li> |
|---|
| 1324 | <li class="indline1"><em>Section 5.4</em> <a class="iref" href="#rfc.xref.Part5.5">6.3</a></li> |
|---|
| 1325 | </ul> |
|---|
| 1326 | </li> |
|---|
| 1327 | <li class="indline1"><em>Part6</em> <a class="iref" href="#rfc.xref.Part6.1">1</a>, <a class="iref" href="#rfc.xref.Part6.2">6.2</a>, <a class="iref" href="#rfc.xref.Part6.3">6.4</a>, <a class="iref" href="#Part6"><b>10.1</b></a><ul class="ind"> |
|---|
| 1328 | <li class="indline1"><em>Section 15.5</em> <a class="iref" href="#rfc.xref.Part6.2">6.2</a>, <a class="iref" href="#rfc.xref.Part6.3">6.4</a></li> |
|---|
| 1329 | </ul> |
|---|
| 1330 | </li> |
|---|
| 1331 | </ul> |
|---|
| 1332 | </li> |
|---|
| 1333 | <li class="indline0"><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul class="ind"> |
|---|
| 1334 | <li class="indline1"><em>RFC2119</em> <a class="iref" href="#rfc.xref.RFC2119.1">1.1</a>, <a class="iref" href="#RFC2119"><b>10.1</b></a></li> |
|---|
| 1335 | <li class="indline1"><em>RFC2616</em> <a class="iref" href="#rfc.xref.RFC2616.1">1</a>, <a class="iref" href="#RFC2616"><b>10.2</b></a>, <a class="iref" href="#rfc.xref.RFC2616.2">C.1</a></li> |
|---|
| 1336 | <li class="indline1"><em>RFC3864</em> <a class="iref" href="#rfc.xref.RFC3864.1">7.1</a>, <a class="iref" href="#RFC3864"><b>10.2</b></a></li> |
|---|
| 1337 | <li class="indline1"><em>RFC5234</em> <a class="iref" href="#rfc.xref.RFC5234.1">1.2</a>, <a class="iref" href="#RFC5234"><b>10.1</b></a><ul class="ind"> |
|---|
| 1338 | <li class="indline1"><em>Appendix B.1</em> <a class="iref" href="#rfc.xref.RFC5234.1">1.2</a></li> |
|---|
| 1339 | </ul> |
|---|
| 1340 | </li> |
|---|
| 1341 | </ul> |
|---|
| 1342 | </li> |
|---|
| 1343 | <li class="indline0"><a id="rfc.index.S" href="#rfc.index.S"><b>S</b></a><ul class="ind"> |
|---|
| 1344 | <li class="indline1">Status Codes |
|---|
| 1345 | <ul class="ind"> |
|---|
| 1346 | <li class="indline1">304 Not Modified <a class="iref" href="#rfc.iref.s.1"><b>3.1</b></a></li> |
|---|
| 1347 | <li class="indline1">412 Precondition Failed <a class="iref" href="#rfc.iref.s.2"><b>3.2</b></a></li> |
|---|
| 1348 | </ul> |
|---|
| 1349 | </li> |
|---|
| 1350 | </ul> |
|---|
| 1351 | </li> |
|---|
| 1352 | </ul> |
|---|
| 1353 | </div> |
|---|
| 1354 | </body> |
|---|
| 1355 | </html> |
|---|
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