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300 | content: "INTERNET DRAFT"; |
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301 | } |
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302 | @top-right { |
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303 | content: "December 2007"; |
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304 | } |
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305 | @top-center { |
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306 | content: "HTTP/1.1"; |
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307 | } |
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308 | @bottom-left { |
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309 | content: "Fielding, et al."; |
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330 | </style><link rel="Contents" href="#rfc.toc"> |
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331 | <link rel="Author" href="#rfc.authors"> |
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332 | <link rel="Copyright" href="#rfc.copyright"> |
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333 | <link rel="Index" href="#rfc.index"> |
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334 | <link rel="Chapter" title="1 Introduction" href="#rfc.section.1"> |
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335 | <link rel="Chapter" title="2 Protocol Parameters" href="#rfc.section.2"> |
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336 | <link rel="Chapter" title="3 Entity" href="#rfc.section.3"> |
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337 | <link rel="Chapter" title="4 Content Negotiation" href="#rfc.section.4"> |
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338 | <link rel="Chapter" title="5 Header Field Definitions" href="#rfc.section.5"> |
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339 | <link rel="Chapter" title="6 IANA Considerations" href="#rfc.section.6"> |
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340 | <link rel="Chapter" title="7 Security Considerations" href="#rfc.section.7"> |
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341 | <link rel="Chapter" title="8 Acknowledgments" href="#rfc.section.8"> |
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342 | <link rel="Chapter" href="#rfc.section.9" title="9 References"> |
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343 | <link rel="Appendix" title="A Differences Between HTTP Entities and RFC 2045 Entities" href="#rfc.section.A"> |
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344 | <link rel="Appendix" title="B Additional Features" href="#rfc.section.B"> |
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345 | <link rel="Appendix" title="C Changes from RFC 2068" href="#rfc.section.C"> |
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346 | <meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.353, 2007/12/11 23:20:44, XSLT vendor: SAXON 8.9 from Saxonica http://www.saxonica.com/"> |
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347 | <link rel="schema.DC" href="http://purl.org/dc/elements/1.1/"> |
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348 | <meta name="DC.Creator" content="Fielding, R."> |
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349 | <meta name="DC.Creator" content="Gettys, J."> |
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350 | <meta name="DC.Creator" content="Mogul, J."> |
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351 | <meta name="DC.Creator" content="Frystyk, H."> |
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352 | <meta name="DC.Creator" content="Masinter, L."> |
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353 | <meta name="DC.Creator" content="Leach, P."> |
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354 | <meta name="DC.Creator" content="Berners-Lee, T."> |
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355 | <meta name="DC.Creator" content="Lafon, Y."> |
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356 | <meta name="DC.Creator" content="Reschke, J. F."> |
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357 | <meta name="DC.Identifier" content="urn:ietf:id:draft-ietf-httpbis-p3-payload-latest"> |
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358 | <meta name="DC.Date.Issued" scheme="ISO8601" content="2007-12"> |
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359 | <meta name="DC.Relation.Replaces" content="urn:ietf:rfc:2068"> |
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360 | <meta name="DC.Relation.Replaces" content="urn:ietf:rfc:2616"> |
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361 | <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 3 of the seven-part specification that defines the protocol referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616. Part 3 defines HTTP message content, metadata, and content negotiation."> |
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362 | </head> |
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363 | <body> |
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364 | <table summary="header information" class="header" border="0" cellpadding="1" cellspacing="1"> |
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365 | <tr> |
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366 | <td class="header left">Network Working Group</td> |
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367 | <td class="header right">R. Fielding, Editor</td> |
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368 | </tr> |
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369 | <tr> |
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370 | <td class="header left">Internet Draft</td> |
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371 | <td class="header right">Day Software</td> |
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372 | </tr> |
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373 | <tr> |
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374 | <td class="header left"> |
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375 | <draft-ietf-httpbis-p3-payload-latest> |
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376 | |
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377 | </td> |
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378 | <td class="header right">J. Gettys</td> |
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379 | </tr> |
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380 | <tr> |
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381 | <td class="header left">Obsoletes: <a href="http://tools.ietf.org/html/rfc2068">2068</a>, |
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382 | <a href="http://tools.ietf.org/html/rfc2616">2616</a> (if approved) |
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383 | </td> |
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384 | <td class="header right">One Laptop per Child</td> |
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385 | </tr> |
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386 | <tr> |
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387 | <td class="header left">Intended status: Standards Track</td> |
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388 | <td class="header right">J. Mogul</td> |
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389 | </tr> |
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390 | <tr> |
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391 | <td class="header left">Expires: June 2008</td> |
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392 | <td class="header right">HP</td> |
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393 | </tr> |
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394 | <tr> |
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395 | <td class="header left"></td> |
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396 | <td class="header right">H. Frystyk</td> |
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397 | </tr> |
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398 | <tr> |
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399 | <td class="header left"></td> |
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400 | <td class="header right">Microsoft</td> |
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401 | </tr> |
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402 | <tr> |
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403 | <td class="header left"></td> |
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404 | <td class="header right">L. Masinter</td> |
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405 | </tr> |
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406 | <tr> |
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407 | <td class="header left"></td> |
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408 | <td class="header right">Adobe Systems</td> |
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409 | </tr> |
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410 | <tr> |
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411 | <td class="header left"></td> |
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412 | <td class="header right">P. Leach</td> |
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413 | </tr> |
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414 | <tr> |
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415 | <td class="header left"></td> |
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416 | <td class="header right">Microsoft</td> |
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417 | </tr> |
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418 | <tr> |
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419 | <td class="header left"></td> |
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420 | <td class="header right">T. Berners-Lee</td> |
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421 | </tr> |
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422 | <tr> |
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423 | <td class="header left"></td> |
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424 | <td class="header right">W3C/MIT</td> |
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425 | </tr> |
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426 | <tr> |
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427 | <td class="header left"></td> |
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428 | <td class="header right">Y. Lafon, Editor</td> |
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429 | </tr> |
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430 | <tr> |
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431 | <td class="header left"></td> |
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432 | <td class="header right">W3C</td> |
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433 | </tr> |
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434 | <tr> |
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435 | <td class="header left"></td> |
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436 | <td class="header right">J. F. Reschke, Editor</td> |
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437 | </tr> |
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438 | <tr> |
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439 | <td class="header left"></td> |
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440 | <td class="header right">greenbytes</td> |
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441 | </tr> |
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442 | <tr> |
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443 | <td class="header left"></td> |
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444 | <td class="header right">December 2007</td> |
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445 | </tr> |
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446 | </table> |
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447 | <p class="title">HTTP/1.1, part 3: Message Payload and Content Negotiation<br><span class="filename">draft-ietf-httpbis-p3-payload-latest</span></p> |
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448 | <h1><a id="rfc.status" href="#rfc.status">Status of this Memo</a></h1> |
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449 | <p>By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she |
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450 | is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section |
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451 | 6 of BCP 79. |
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452 | </p> |
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453 | <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note |
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454 | that other groups may also distribute working documents as Internet-Drafts. |
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455 | </p> |
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456 | <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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457 | 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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458 | in progress”. |
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459 | </p> |
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460 | <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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461 | </p> |
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462 | <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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463 | </p> |
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464 | <p>This Internet-Draft will expire in June 2008.</p> |
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465 | <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1> |
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466 | <p>Copyright © The IETF Trust (2007). All Rights Reserved.</p> |
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467 | <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1> |
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468 | <p>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information |
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469 | systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 3 of the |
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470 | seven-part specification that defines the protocol referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616. Part |
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471 | 3 defines HTTP message content, metadata, and content negotiation. |
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472 | </p> |
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473 | <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1> |
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474 | <p>This version of the HTTP specification contains only minimal editorial changes from <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a> (abstract, introductory paragraph, and authors' addresses). All other changes are due to partitioning the original into seven |
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475 | mostly independent parts. The intent is for readers of future drafts to able to use draft 00 as the basis for comparison when |
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476 | the WG makes later changes to the specification text. This draft will shortly be followed by draft 01 (containing the first |
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477 | round of changes that have already been agreed to on the mailing list). There is no point in reviewing this draft other than |
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478 | to verify that the partitioning has been done correctly. Roy T. Fielding, Yves Lafon, and Julian Reschke will be the editors |
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479 | after draft 00 is submitted. |
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480 | </p> |
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481 | <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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482 | list is at <<a href="http://www3.tools.ietf.org/wg/httpbis/trac/report/11">http://www3.tools.ietf.org/wg/httpbis/trac/report/11</a>> and related documents (including fancy diffs) can be found at <<a href="http://www3.tools.ietf.org/wg/httpbis/">http://www3.tools.ietf.org/wg/httpbis/</a>>. |
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483 | </p> |
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484 | <hr class="noprint"> |
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485 | <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1> |
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486 | <ul class="toc"> |
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487 | <li class="tocline0">1. <a href="#introduction">Introduction</a><ul class="toc"> |
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488 | <li class="tocline1">1.1 <a href="#intro.requirements">Requirements</a></li> |
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489 | </ul> |
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490 | </li> |
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491 | <li class="tocline0">2. <a href="#protocol.parameters">Protocol Parameters</a><ul class="toc"> |
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492 | <li class="tocline1">2.1 <a href="#character.sets">Character Sets</a><ul class="toc"> |
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493 | <li class="tocline1">2.1.1 <a href="#missing.charset">Missing Charset</a></li> |
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494 | </ul> |
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495 | </li> |
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496 | <li class="tocline1">2.2 <a href="#content.codings">Content Codings</a></li> |
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497 | <li class="tocline1">2.3 <a href="#media.types">Media Types</a><ul class="toc"> |
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498 | <li class="tocline1">2.3.1 <a href="#canonicalization.and.text.defaults">Canonicalization and Text Defaults</a></li> |
---|
499 | <li class="tocline1">2.3.2 <a href="#multipart.types">Multipart Types</a></li> |
---|
500 | </ul> |
---|
501 | </li> |
---|
502 | <li class="tocline1">2.4 <a href="#quality.values">Quality Values</a></li> |
---|
503 | <li class="tocline1">2.5 <a href="#language.tags">Language Tags</a></li> |
---|
504 | </ul> |
---|
505 | </li> |
---|
506 | <li class="tocline0">3. <a href="#entity">Entity</a><ul class="toc"> |
---|
507 | <li class="tocline1">3.1 <a href="#entity.header.fields">Entity Header Fields</a></li> |
---|
508 | <li class="tocline1">3.2 <a href="#entity.body">Entity Body</a><ul class="toc"> |
---|
509 | <li class="tocline1">3.2.1 <a href="#type">Type</a></li> |
---|
510 | <li class="tocline1">3.2.2 <a href="#entity.length">Entity Length</a></li> |
---|
511 | </ul> |
---|
512 | </li> |
---|
513 | </ul> |
---|
514 | </li> |
---|
515 | <li class="tocline0">4. <a href="#content.negotiation">Content Negotiation</a><ul class="toc"> |
---|
516 | <li class="tocline1">4.1 <a href="#server-driven.negotiation">Server-driven Negotiation</a></li> |
---|
517 | <li class="tocline1">4.2 <a href="#agent-driven.negotiation">Agent-driven Negotiation</a></li> |
---|
518 | <li class="tocline1">4.3 <a href="#transparent.negotiation">Transparent Negotiation</a></li> |
---|
519 | </ul> |
---|
520 | </li> |
---|
521 | <li class="tocline0">5. <a href="#header.fields">Header Field Definitions</a><ul class="toc"> |
---|
522 | <li class="tocline1">5.1 <a href="#header.accept">Accept</a></li> |
---|
523 | <li class="tocline1">5.2 <a href="#header.accept-charset">Accept-Charset</a></li> |
---|
524 | <li class="tocline1">5.3 <a href="#header.accept-encoding">Accept-Encoding</a></li> |
---|
525 | <li class="tocline1">5.4 <a href="#header.accept-language">Accept-Language</a></li> |
---|
526 | <li class="tocline1">5.5 <a href="#header.content-encoding">Content-Encoding</a></li> |
---|
527 | <li class="tocline1">5.6 <a href="#header.content-language">Content-Language</a></li> |
---|
528 | <li class="tocline1">5.7 <a href="#header.content-location">Content-Location</a></li> |
---|
529 | <li class="tocline1">5.8 <a href="#header.content-md5">Content-MD5</a></li> |
---|
530 | <li class="tocline1">5.9 <a href="#header.content-type">Content-Type</a></li> |
---|
531 | </ul> |
---|
532 | </li> |
---|
533 | <li class="tocline0">6. <a href="#IANA.considerations">IANA Considerations</a></li> |
---|
534 | <li class="tocline0">7. <a href="#security.considerations">Security Considerations</a><ul class="toc"> |
---|
535 | <li class="tocline1">7.1 <a href="#privacy.issues.connected.to.accept.headers">Privacy Issues Connected to Accept Headers</a></li> |
---|
536 | <li class="tocline1">7.2 <a href="#content-disposition.issues">Content-Disposition Issues</a></li> |
---|
537 | </ul> |
---|
538 | </li> |
---|
539 | <li class="tocline0">8. <a href="#ack">Acknowledgments</a></li> |
---|
540 | <li class="tocline0">9. <a href="#rfc.references">References</a></li> |
---|
541 | <li class="tocline0"><a href="#rfc.authors">Authors' Addresses</a></li> |
---|
542 | <li class="tocline0">A. <a href="#differences.between.http.entities.and.rfc.2045.entities">Differences Between HTTP Entities and RFC 2045 Entities</a><ul class="toc"> |
---|
543 | <li class="tocline1">A.1 <a href="#mime-version">MIME-Version</a></li> |
---|
544 | <li class="tocline1">A.2 <a href="#conversion.to.canonical.form">Conversion to Canonical Form</a></li> |
---|
545 | <li class="tocline1">A.3 <a href="#introduction.of.content-encoding">Introduction of Content-Encoding</a></li> |
---|
546 | <li class="tocline1">A.4 <a href="#no.content-transfer-encoding">No Content-Transfer-Encoding</a></li> |
---|
547 | <li class="tocline1">A.5 <a href="#introduction.of.transfer-encoding">Introduction of Transfer-Encoding</a></li> |
---|
548 | <li class="tocline1">A.6 <a href="#mhtml.line.length">MHTML and Line Length Limitations</a></li> |
---|
549 | </ul> |
---|
550 | </li> |
---|
551 | <li class="tocline0">B. <a href="#additional.features">Additional Features</a><ul class="toc"> |
---|
552 | <li class="tocline1">B.1 <a href="#content-disposition">Content-Disposition</a></li> |
---|
553 | </ul> |
---|
554 | </li> |
---|
555 | <li class="tocline0">C. <a href="#changes.from.rfc.2068">Changes from RFC 2068</a></li> |
---|
556 | <li class="tocline0"><a href="#rfc.ipr">Intellectual Property and Copyright Statements</a></li> |
---|
557 | <li class="tocline0"><a href="#rfc.index">Index</a></li> |
---|
558 | </ul> |
---|
559 | <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a> <a id="introduction" href="#introduction">Introduction</a></h1> |
---|
560 | <p id="rfc.section.1.p.1">This document will define aspects of HTTP related to the payload of messages (message content), including metadata and media |
---|
561 | types, along with HTTP content negotiation. Right now it only includes the extracted relevant sections of RFC 2616 without |
---|
562 | edit. |
---|
563 | </p> |
---|
564 | <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> |
---|
565 | <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" |
---|
566 | 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>. |
---|
567 | </p> |
---|
568 | <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." |
---|
569 | </p> |
---|
570 | <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a> <a id="protocol.parameters" href="#protocol.parameters">Protocol Parameters</a></h1> |
---|
571 | <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a> <a id="character.sets" href="#character.sets">Character Sets</a></h2> |
---|
572 | <p id="rfc.section.2.1.p.1">HTTP uses the same definition of the term "character set" as that described for MIME:</p> |
---|
573 | <p id="rfc.section.2.1.p.2">The term "character set" is used in this document to refer to a method used with one or more tables to convert a sequence |
---|
574 | of octets into a sequence of characters. Note that unconditional conversion in the other direction is not required, in that |
---|
575 | not all characters may be available in a given character set and a character set may provide more than one sequence of octets |
---|
576 | to represent a particular character. This definition is intended to allow various kinds of character encoding, from simple |
---|
577 | single-table mappings such as US-ASCII to complex table switching methods such as those that use ISO-2022's techniques. However, |
---|
578 | the definition associated with a MIME character set name <em class="bcp14">MUST</em> fully specify the mapping to be performed from octets to characters. In particular, use of external profiling information |
---|
579 | to determine the exact mapping is not permitted. |
---|
580 | </p> |
---|
581 | <dl class="empty"> |
---|
582 | <dd> <b>Note:</b> This use of the term "character set" is more commonly referred to as a "character encoding." However, since HTTP and MIME |
---|
583 | share the same registry, it is important that the terminology also be shared. |
---|
584 | </dd> |
---|
585 | </dl> |
---|
586 | <p id="rfc.section.2.1.p.4">HTTP character sets are identified by case-insensitive tokens. The complete set of tokens is defined by the IANA Character |
---|
587 | Set registry (<<a href="http://www.iana.org/assignments/character-sets">http://www.iana.org/assignments/character-sets</a>>). |
---|
588 | </p> |
---|
589 | <div id="rfc.figure.u.1"></div><pre class="inline"><span id="rfc.iref.g.1"></span> charset = token |
---|
590 | </pre><p id="rfc.section.2.1.p.6">Although HTTP allows an arbitrary token to be used as a charset value, any token that has a predefined value within the IANA |
---|
591 | Character Set registry <em class="bcp14">MUST</em> represent the character set defined by that registry. Applications <em class="bcp14">SHOULD</em> limit their use of character sets to those defined by the IANA registry. |
---|
592 | </p> |
---|
593 | <p id="rfc.section.2.1.p.7">HTTP uses charset in two contexts: within an Accept-Charset request header (in which the charset value is an unquoted token) |
---|
594 | and as the value of a parameter in a Content-type header (within a request or response), in which case the parameter value |
---|
595 | of the charset parameter may be quoted. |
---|
596 | </p> |
---|
597 | <p id="rfc.section.2.1.p.8">Implementors should be aware of IETF character set requirements <a href="#RFC2279" id="rfc.xref.RFC2279.1"><cite title="UTF-8, a transformation format of ISO 10646">[RFC2279]</cite></a> <a href="#RFC2277" id="rfc.xref.RFC2277.1"><cite title="IETF Policy on Character Sets and Languages">[RFC2277]</cite></a>. |
---|
598 | </p> |
---|
599 | <h3 id="rfc.section.2.1.1"><a href="#rfc.section.2.1.1">2.1.1</a> <a id="missing.charset" href="#missing.charset">Missing Charset</a></h3> |
---|
600 | <p id="rfc.section.2.1.1.p.1">Some HTTP/1.0 software has interpreted a Content-Type header without charset parameter incorrectly to mean "recipient should |
---|
601 | guess." Senders wishing to defeat this behavior <em class="bcp14">MAY</em> include a charset parameter even when the charset is ISO-8859-1 and <em class="bcp14">SHOULD</em> do so when it is known that it will not confuse the recipient. |
---|
602 | </p> |
---|
603 | <p id="rfc.section.2.1.1.p.2">Unfortunately, some older HTTP/1.0 clients did not deal properly with an explicit charset parameter. HTTP/1.1 recipients <em class="bcp14">MUST</em> respect the charset label provided by the sender; and those user agents that have a provision to "guess" a charset <em class="bcp14">MUST</em> use the charset from the content-type field if they support that charset, rather than the recipient's preference, when initially |
---|
604 | displaying a document. See <a href="#canonicalization.and.text.defaults" title="Canonicalization and Text Defaults">Section 2.3.1</a>. |
---|
605 | </p> |
---|
606 | <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a> <a id="content.codings" href="#content.codings">Content Codings</a></h2> |
---|
607 | <p id="rfc.section.2.2.p.1">Content coding values indicate an encoding transformation that has been or can be applied to an entity. Content codings are |
---|
608 | primarily used to allow a document to be compressed or otherwise usefully transformed without losing the identity of its underlying |
---|
609 | media type and without loss of information. Frequently, the entity is stored in coded form, transmitted directly, and only |
---|
610 | decoded by the recipient. |
---|
611 | </p> |
---|
612 | <div id="rfc.figure.u.2"></div><pre class="inline"><span id="rfc.iref.g.2"></span> content-coding = token |
---|
613 | </pre><p id="rfc.section.2.2.p.3">All content-coding values are case-insensitive. HTTP/1.1 uses content-coding values in the Accept-Encoding (<a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.1" title="Accept-Encoding">Section 5.3</a>) and Content-Encoding (<a href="#header.content-encoding" id="rfc.xref.header.content-encoding.1" title="Content-Encoding">Section 5.5</a>) header fields. Although the value describes the content-coding, what is more important is that it indicates what decoding |
---|
614 | mechanism will be required to remove the encoding. |
---|
615 | </p> |
---|
616 | <p id="rfc.section.2.2.p.4">The Internet Assigned Numbers Authority (IANA) acts as a registry for content-coding value tokens. Initially, the registry |
---|
617 | contains the following tokens: |
---|
618 | </p> |
---|
619 | <p id="rfc.section.2.2.p.5">gzip<span id="rfc.iref.g.3"></span> |
---|
620 | </p> |
---|
621 | <dl class="empty"> |
---|
622 | <dd>An encoding format produced by the file compression program "gzip" (GNU zip) as described in RFC 1952 <a href="#RFC1952" id="rfc.xref.RFC1952.1"><cite title="GZIP file format specification version 4.3">[RFC1952]</cite></a>. This format is a Lempel-Ziv coding (LZ77) with a 32 bit CRC. |
---|
623 | </dd> |
---|
624 | </dl> |
---|
625 | <p id="rfc.section.2.2.p.6">compress<span id="rfc.iref.c.1"></span> |
---|
626 | </p> |
---|
627 | <dl class="empty"> |
---|
628 | <dd>The encoding format produced by the common UNIX file compression program "compress". This format is an adaptive Lempel-Ziv-Welch |
---|
629 | coding (LZW). |
---|
630 | </dd> |
---|
631 | <dd>Use of program names for the identification of encoding formats is not desirable and is discouraged for future encodings. |
---|
632 | Their use here is representative of historical practice, not good design. For compatibility with previous implementations |
---|
633 | of HTTP, applications <em class="bcp14">SHOULD</em> consider "x-gzip" and "x-compress" to be equivalent to "gzip" and "compress" respectively. |
---|
634 | </dd> |
---|
635 | </dl> |
---|
636 | <p id="rfc.section.2.2.p.7">deflate<span id="rfc.iref.d.1"></span> |
---|
637 | </p> |
---|
638 | <dl class="empty"> |
---|
639 | <dd>The "zlib" format defined in RFC 1950 <a href="#RFC1950" id="rfc.xref.RFC1950.1"><cite title="ZLIB Compressed Data Format Specification version 3.3">[RFC1950]</cite></a> in combination with the "deflate" compression mechanism described in RFC 1951 <a href="#RFC1951" id="rfc.xref.RFC1951.1"><cite title="DEFLATE Compressed Data Format Specification version 1.3">[RFC1951]</cite></a>. |
---|
640 | </dd> |
---|
641 | </dl> |
---|
642 | <p id="rfc.section.2.2.p.8">identity<span id="rfc.iref.i.1"></span> |
---|
643 | </p> |
---|
644 | <dl class="empty"> |
---|
645 | <dd>The default (identity) encoding; the use of no transformation whatsoever. This content-coding is used only in the Accept-Encoding |
---|
646 | header, and <em class="bcp14">SHOULD NOT</em> be used in the Content-Encoding header. |
---|
647 | </dd> |
---|
648 | </dl> |
---|
649 | <p id="rfc.section.2.2.p.9">New content-coding value tokens <em class="bcp14">SHOULD</em> be registered; to allow interoperability between clients and servers, specifications of the content coding algorithms needed |
---|
650 | to implement a new value <em class="bcp14">SHOULD</em> be publicly available and adequate for independent implementation, and conform to the purpose of content coding defined in |
---|
651 | this section. |
---|
652 | </p> |
---|
653 | <h2 id="rfc.section.2.3"><a href="#rfc.section.2.3">2.3</a> <a id="media.types" href="#media.types">Media Types</a></h2> |
---|
654 | <p id="rfc.section.2.3.p.1">HTTP uses Internet Media Types <a href="#RFC4288" id="rfc.xref.RFC4288.1"><cite title="Media Type Specifications and Registration Procedures">[RFC4288]</cite></a> in the Content-Type (<a href="#header.content-type" id="rfc.xref.header.content-type.1" title="Content-Type">Section 5.9</a>) and Accept (<a href="#header.accept" id="rfc.xref.header.accept.1" title="Accept">Section 5.1</a>) header fields in order to provide open and extensible data typing and type negotiation. |
---|
655 | </p> |
---|
656 | <div id="rfc.figure.u.3"></div><pre class="inline"><span id="rfc.iref.g.4"></span><span id="rfc.iref.g.5"></span><span id="rfc.iref.g.6"></span> media-type = type "/" subtype *( ";" parameter ) |
---|
657 | type = token |
---|
658 | subtype = token |
---|
659 | </pre><p id="rfc.section.2.3.p.3">Parameters <em class="bcp14">MAY</em> follow the type/subtype in the form of attribute/value pairs. |
---|
660 | </p> |
---|
661 | <div id="rfc.figure.u.4"></div><pre class="inline"><span id="rfc.iref.g.7"></span><span id="rfc.iref.g.8"></span><span id="rfc.iref.g.9"></span> parameter = attribute "=" value |
---|
662 | attribute = token |
---|
663 | value = token | quoted-string |
---|
664 | </pre><p id="rfc.section.2.3.p.5">The type, subtype, and parameter attribute names are case-insensitive. Parameter values might or might not be case-sensitive, |
---|
665 | depending on the semantics of the parameter name. Linear white space (LWS) <em class="bcp14">MUST NOT</em> be used between the type and subtype, nor between an attribute and its value. The presence or absence of a parameter might |
---|
666 | be significant to the processing of a media-type, depending on its definition within the media type registry. |
---|
667 | </p> |
---|
668 | <p id="rfc.section.2.3.p.6">Note that some older HTTP applications do not recognize media type parameters. When sending data to older HTTP applications, |
---|
669 | implementations <em class="bcp14">SHOULD</em> only use media type parameters when they are required by that type/subtype definition. |
---|
670 | </p> |
---|
671 | <p id="rfc.section.2.3.p.7">Media-type values are registered with the Internet Assigned Number Authority (IANA). The media type registration process is |
---|
672 | outlined in RFC 4288 <a href="#RFC4288" id="rfc.xref.RFC4288.2"><cite title="Media Type Specifications and Registration Procedures">[RFC4288]</cite></a>. Use of non-registered media types is discouraged. |
---|
673 | </p> |
---|
674 | <h3 id="rfc.section.2.3.1"><a href="#rfc.section.2.3.1">2.3.1</a> <a id="canonicalization.and.text.defaults" href="#canonicalization.and.text.defaults">Canonicalization and Text Defaults</a></h3> |
---|
675 | <p id="rfc.section.2.3.1.p.1">Internet media types are registered with a canonical form. An entity-body transferred via HTTP messages <em class="bcp14">MUST</em> be represented in the appropriate canonical form prior to its transmission except for "text" types, as defined in the next |
---|
676 | paragraph. |
---|
677 | </p> |
---|
678 | <p id="rfc.section.2.3.1.p.2">When in canonical form, media subtypes of the "text" type use CRLF as the text line break. HTTP relaxes this requirement and |
---|
679 | allows the transport of text media with plain CR or LF alone representing a line break when it is done consistently for an |
---|
680 | entire entity-body. HTTP applications <em class="bcp14">MUST</em> accept CRLF, bare CR, and bare LF as being representative of a line break in text media received via HTTP. In addition, if |
---|
681 | the text is represented in a character set that does not use octets 13 and 10 for CR and LF respectively, as is the case for |
---|
682 | some multi-byte character sets, HTTP allows the use of whatever octet sequences are defined by that character set to represent |
---|
683 | the equivalent of CR and LF for line breaks. This flexibility regarding line breaks applies only to text media in the entity-body; |
---|
684 | a bare CR or LF <em class="bcp14">MUST NOT</em> be substituted for CRLF within any of the HTTP control structures (such as header fields and multipart boundaries). |
---|
685 | </p> |
---|
686 | <p id="rfc.section.2.3.1.p.3">If an entity-body is encoded with a content-coding, the underlying data <em class="bcp14">MUST</em> be in a form defined above prior to being encoded. |
---|
687 | </p> |
---|
688 | <p id="rfc.section.2.3.1.p.4">The "charset" parameter is used with some media types to define the character set (<a href="#character.sets" title="Character Sets">Section 2.1</a>) of the data. When no explicit charset parameter is provided by the sender, media subtypes of the "text" type are defined |
---|
689 | to have a default charset value of "ISO-8859-1" when received via HTTP. Data in character sets other than "ISO-8859-1" or |
---|
690 | its subsets <em class="bcp14">MUST</em> be labeled with an appropriate charset value. See <a href="#missing.charset" title="Missing Charset">Section 2.1.1</a> for compatibility problems. |
---|
691 | </p> |
---|
692 | <h3 id="rfc.section.2.3.2"><a href="#rfc.section.2.3.2">2.3.2</a> <a id="multipart.types" href="#multipart.types">Multipart Types</a></h3> |
---|
693 | <p id="rfc.section.2.3.2.p.1">MIME provides for a number of "multipart" types -- encapsulations of one or more entities within a single message-body. All |
---|
694 | multipart types share a common syntax, as defined in section <a href="http://tools.ietf.org/html/rfc2046#section-5.1.1" id="rfc.xref.RFC2046.1">5.1.1</a> of RFC 2046 <a href="#RFC2046" id="rfc.xref.RFC2046.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[RFC2046]</cite></a>, and <em class="bcp14">MUST</em> include a boundary parameter as part of the media type value. The message body is itself a protocol element and <em class="bcp14">MUST</em> therefore use only CRLF to represent line breaks between body-parts. Unlike in RFC 2046, the epilogue of any multipart message <em class="bcp14">MUST</em> be empty; HTTP applications <em class="bcp14">MUST NOT</em> transmit the epilogue (even if the original multipart contains an epilogue). These restrictions exist in order to preserve |
---|
695 | the self-delimiting nature of a multipart message-body, wherein the "end" of the message-body is indicated by the ending multipart |
---|
696 | boundary. |
---|
697 | </p> |
---|
698 | <p id="rfc.section.2.3.2.p.2">In general, HTTP treats a multipart message-body no differently than any other media type: strictly as payload. The one exception |
---|
699 | is the "multipart/byteranges" type (<a href="p5-range.html#internet.media.type.multipart.byteranges" title="Internet Media Type multipart/byteranges">Appendix A</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>) when it appears in a 206 (Partial Content) response. In all other cases, an HTTP user agent <em class="bcp14">SHOULD</em> follow the same or similar behavior as a MIME user agent would upon receipt of a multipart type. The MIME header fields within |
---|
700 | each body-part of a multipart message-body do not have any significance to HTTP beyond that defined by their MIME semantics. |
---|
701 | </p> |
---|
702 | <p id="rfc.section.2.3.2.p.3">In general, an HTTP user agent <em class="bcp14">SHOULD</em> follow the same or similar behavior as a MIME user agent would upon receipt of a multipart type. If an application receives |
---|
703 | an unrecognized multipart subtype, the application <em class="bcp14">MUST</em> treat it as being equivalent to "multipart/mixed". |
---|
704 | </p> |
---|
705 | <dl class="empty"> |
---|
706 | <dd> <b>Note:</b> The "multipart/form-data" type has been specifically defined for carrying form data suitable for processing via the POST request |
---|
707 | method, as described in RFC 1867 <a href="#RFC1867" id="rfc.xref.RFC1867.1"><cite title="Form-based File Upload in HTML">[RFC1867]</cite></a>. |
---|
708 | </dd> |
---|
709 | </dl> |
---|
710 | <h2 id="rfc.section.2.4"><a href="#rfc.section.2.4">2.4</a> <a id="quality.values" href="#quality.values">Quality Values</a></h2> |
---|
711 | <p id="rfc.section.2.4.p.1">HTTP content negotiation (<a href="#content.negotiation" title="Content Negotiation">Section 4</a>) uses short "floating point" numbers to indicate the relative importance ("weight") of various negotiable parameters. A weight |
---|
712 | is normalized to a real number in the range 0 through 1, where 0 is the minimum and 1 the maximum value. If a parameter has |
---|
713 | a quality value of 0, then content with this parameter is `not acceptable' for the client. HTTP/1.1 applications <em class="bcp14">MUST NOT</em> generate more than three digits after the decimal point. User configuration of these values <em class="bcp14">SHOULD</em> also be limited in this fashion. |
---|
714 | </p> |
---|
715 | <div id="rfc.figure.u.5"></div><pre class="inline"><span id="rfc.iref.g.10"></span> qvalue = ( "0" [ "." 0*3DIGIT ] ) |
---|
716 | | ( "1" [ "." 0*3("0") ] ) |
---|
717 | </pre><p id="rfc.section.2.4.p.3">"Quality values" is a misnomer, since these values merely represent relative degradation in desired quality.</p> |
---|
718 | <h2 id="rfc.section.2.5"><a href="#rfc.section.2.5">2.5</a> <a id="language.tags" href="#language.tags">Language Tags</a></h2> |
---|
719 | <p id="rfc.section.2.5.p.1">A language tag identifies a natural language spoken, written, or otherwise conveyed by human beings for communication of information |
---|
720 | to other human beings. Computer languages are explicitly excluded. HTTP uses language tags within the Accept-Language and |
---|
721 | Content-Language fields. |
---|
722 | </p> |
---|
723 | <p id="rfc.section.2.5.p.2">The syntax and registry of HTTP language tags is the same as that defined by RFC 1766 <a href="#RFC1766" id="rfc.xref.RFC1766.1"><cite title="Tags for the Identification of Languages">[RFC1766]</cite></a>. In summary, a language tag is composed of 1 or more parts: A primary language tag and a possibly empty series of subtags: |
---|
724 | </p> |
---|
725 | <div id="rfc.figure.u.6"></div><pre class="inline"><span id="rfc.iref.g.11"></span><span id="rfc.iref.g.12"></span><span id="rfc.iref.g.13"></span> language-tag = primary-tag *( "-" subtag ) |
---|
726 | primary-tag = 1*8ALPHA |
---|
727 | subtag = 1*8ALPHA |
---|
728 | </pre><p id="rfc.section.2.5.p.4">White space is not allowed within the tag and all tags are case-insensitive. The name space of language tags is administered |
---|
729 | by the IANA. Example tags include: |
---|
730 | </p> |
---|
731 | <div id="rfc.figure.u.7"></div><pre class="text"> en, en-US, en-cockney, i-cherokee, x-pig-latin |
---|
732 | </pre><p id="rfc.section.2.5.p.6">where any two-letter primary-tag is an ISO-639 language abbreviation and any two-letter initial subtag is an ISO-3166 country |
---|
733 | code. (The last three tags above are not registered tags; all but the last are examples of tags which could be registered |
---|
734 | in future.) |
---|
735 | </p> |
---|
736 | <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a> <a id="entity" href="#entity">Entity</a></h1> |
---|
737 | <p id="rfc.section.3.p.1">Request and Response messages <em class="bcp14">MAY</em> transfer an entity if not otherwise restricted by the request method or response status code. An entity consists of entity-header |
---|
738 | fields and an entity-body, although some responses will only include the entity-headers. |
---|
739 | </p> |
---|
740 | <p id="rfc.section.3.p.2">In this section, both sender and recipient refer to either the client or the server, depending on who sends and who receives |
---|
741 | the entity. |
---|
742 | </p> |
---|
743 | <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a> <a id="entity.header.fields" href="#entity.header.fields">Entity Header Fields</a></h2> |
---|
744 | <p id="rfc.section.3.1.p.1">Entity-header fields define metainformation about the entity-body or, if no body is present, about the resource identified |
---|
745 | by the request. Some of this metainformation is <em class="bcp14">OPTIONAL</em>; some might be <em class="bcp14">REQUIRED</em> by portions of this specification. |
---|
746 | </p> |
---|
747 | <div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.14"></span><span id="rfc.iref.g.15"></span> entity-header = Allow ; <a href="#Part2" id="rfc.xref.Part2.1"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>, <a href="p2-semantics.html#header.allow" title="Allow">Section 10.1</a> |
---|
748 | | Content-Encoding ; <a href="#header.content-encoding" id="rfc.xref.header.content-encoding.2" title="Content-Encoding">Section 5.5</a> |
---|
749 | | Content-Language ; <a href="#header.content-language" id="rfc.xref.header.content-language.1" title="Content-Language">Section 5.6</a> |
---|
750 | | Content-Length ; <a href="#Part1" id="rfc.xref.Part1.1"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#header.content-length" title="Content-Length">Section 8.2</a> |
---|
751 | | Content-Location ; <a href="#header.content-location" id="rfc.xref.header.content-location.1" title="Content-Location">Section 5.7</a> |
---|
752 | | Content-MD5 ; <a href="#header.content-md5" id="rfc.xref.header.content-md5.1" title="Content-MD5">Section 5.8</a> |
---|
753 | | Content-Range ; <a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>, <a href="p5-range.html#header.content-range" title="Content-Range">Section 5.2</a> |
---|
754 | | Content-Type ; <a href="#header.content-type" id="rfc.xref.header.content-type.2" title="Content-Type">Section 5.9</a> |
---|
755 | | Expires ; <a href="#Part6" id="rfc.xref.Part6.1"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>, <a href="p6-cache.html#header.expires" title="Expires">Section 3.3</a> |
---|
756 | | Last-Modified ; <a href="#Part4" id="rfc.xref.Part4.1"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>, <a href="p4-conditional.html#header.last-modified" title="Last-Modified">Section 6.6</a> |
---|
757 | | extension-header |
---|
758 | |
---|
759 | extension-header = message-header |
---|
760 | </pre><p id="rfc.section.3.1.p.3">The extension-header mechanism allows additional entity-header fields to be defined without changing the protocol, but these |
---|
761 | fields cannot be assumed to be recognizable by the recipient. Unrecognized header fields <em class="bcp14">SHOULD</em> be ignored by the recipient and <em class="bcp14">MUST</em> be forwarded by transparent proxies. |
---|
762 | </p> |
---|
763 | <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a> <a id="entity.body" href="#entity.body">Entity Body</a></h2> |
---|
764 | <p id="rfc.section.3.2.p.1">The entity-body (if any) sent with an HTTP request or response is in a format and encoding defined by the entity-header fields.</p> |
---|
765 | <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.16"></span> entity-body = *OCTET |
---|
766 | </pre><p id="rfc.section.3.2.p.3">An entity-body is only present in a message when a message-body is present, as described in <a href="p1-messaging.html#message.body" title="Message Body">Section 4.3</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>. The entity-body is obtained from the message-body by decoding any Transfer-Encoding that might have been applied to ensure |
---|
767 | safe and proper transfer of the message. |
---|
768 | </p> |
---|
769 | <h3 id="rfc.section.3.2.1"><a href="#rfc.section.3.2.1">3.2.1</a> <a id="type" href="#type">Type</a></h3> |
---|
770 | <p id="rfc.section.3.2.1.p.1">When an entity-body is included with a message, the data type of that body is determined via the header fields Content-Type |
---|
771 | and Content-Encoding. These define a two-layer, ordered encoding model: |
---|
772 | </p> |
---|
773 | <div id="rfc.figure.u.10"></div><pre class="text"> entity-body := Content-Encoding( Content-Type( data ) ) |
---|
774 | </pre><p id="rfc.section.3.2.1.p.3">Content-Type specifies the media type of the underlying data. Content-Encoding may be used to indicate any additional content |
---|
775 | codings applied to the data, usually for the purpose of data compression, that are a property of the requested resource. There |
---|
776 | is no default encoding. |
---|
777 | </p> |
---|
778 | <p id="rfc.section.3.2.1.p.4">Any HTTP/1.1 message containing an entity-body <em class="bcp14">SHOULD</em> include a Content-Type header field defining the media type of that body. If and only if the media type is not given by a |
---|
779 | Content-Type field, the recipient <em class="bcp14">MAY</em> attempt to guess the media type via inspection of its content and/or the name extension(s) of the URI used to identify the |
---|
780 | resource. If the media type remains unknown, the recipient <em class="bcp14">SHOULD</em> treat it as type "application/octet-stream". |
---|
781 | </p> |
---|
782 | <h3 id="rfc.section.3.2.2"><a href="#rfc.section.3.2.2">3.2.2</a> <a id="entity.length" href="#entity.length">Entity Length</a></h3> |
---|
783 | <p id="rfc.section.3.2.2.p.1">The entity-length of a message is the length of the message-body before any transfer-codings have been applied. <a href="p1-messaging.html#message.length" title="Message Length">Section 4.4</a> of <a href="#Part1" id="rfc.xref.Part1.3"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> defines how the transfer-length of a message-body is determined. |
---|
784 | </p> |
---|
785 | <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a> <a id="content.negotiation" href="#content.negotiation">Content Negotiation</a></h1> |
---|
786 | <p id="rfc.section.4.p.1">Most HTTP responses include an entity which contains information for interpretation by a human user. Naturally, it is desirable |
---|
787 | to supply the user with the "best available" entity corresponding to the request. Unfortunately for servers and caches, not |
---|
788 | all users have the same preferences for what is "best," and not all user agents are equally capable of rendering all entity |
---|
789 | types. For that reason, HTTP has provisions for several mechanisms for "content negotiation" -- the process of selecting the |
---|
790 | best representation for a given response when there are multiple representations available. |
---|
791 | </p> |
---|
792 | <dl class="empty"> |
---|
793 | <dd> <b>Note:</b> This is not called "format negotiation" because the alternate representations may be of the same media type, but use different |
---|
794 | capabilities of that type, be in different languages, etc. |
---|
795 | </dd> |
---|
796 | </dl> |
---|
797 | <p id="rfc.section.4.p.2">Any response containing an entity-body <em class="bcp14">MAY</em> be subject to negotiation, including error responses. |
---|
798 | </p> |
---|
799 | <p id="rfc.section.4.p.3">There are two kinds of content negotiation which are possible in HTTP: server-driven and agent-driven negotiation. These two |
---|
800 | kinds of negotiation are orthogonal and thus may be used separately or in combination. One method of combination, referred |
---|
801 | to as transparent negotiation, occurs when a cache uses the agent-driven negotiation information provided by the origin server |
---|
802 | in order to provide server-driven negotiation for subsequent requests. |
---|
803 | </p> |
---|
804 | <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a> <a id="server-driven.negotiation" href="#server-driven.negotiation">Server-driven Negotiation</a></h2> |
---|
805 | <p id="rfc.section.4.1.p.1">If the selection of the best representation for a response is made by an algorithm located at the server, it is called server-driven |
---|
806 | negotiation. Selection is based on the available representations of the response (the dimensions over which it can vary; e.g. |
---|
807 | language, content-coding, etc.) and the contents of particular header fields in the request message or on other information |
---|
808 | pertaining to the request (such as the network address of the client). |
---|
809 | </p> |
---|
810 | <p id="rfc.section.4.1.p.2">Server-driven negotiation is advantageous when the algorithm for selecting from among the available representations is difficult |
---|
811 | to describe to the user agent, or when the server desires to send its "best guess" to the client along with the first response |
---|
812 | (hoping to avoid the round-trip delay of a subsequent request if the "best guess" is good enough for the user). In order to |
---|
813 | improve the server's guess, the user agent <em class="bcp14">MAY</em> include request header fields (Accept, Accept-Language, Accept-Encoding, etc.) which describe its preferences for such a response. |
---|
814 | </p> |
---|
815 | <p id="rfc.section.4.1.p.3">Server-driven negotiation has disadvantages: </p> |
---|
816 | <ol> |
---|
817 | <li>It is impossible for the server to accurately determine what might be "best" for any given user, since that would require |
---|
818 | complete knowledge of both the capabilities of the user agent and the intended use for the response (e.g., does the user want |
---|
819 | to view it on screen or print it on paper?). |
---|
820 | </li> |
---|
821 | <li>Having the user agent describe its capabilities in every request can be both very inefficient (given that only a small percentage |
---|
822 | of responses have multiple representations) and a potential violation of the user's privacy. |
---|
823 | </li> |
---|
824 | <li>It complicates the implementation of an origin server and the algorithms for generating responses to a request.</li> |
---|
825 | <li>It may limit a public cache's ability to use the same response for multiple user's requests.</li> |
---|
826 | </ol> |
---|
827 | <p id="rfc.section.4.1.p.4">HTTP/1.1 includes the following request-header fields for enabling server-driven negotiation through description of user agent |
---|
828 | capabilities and user preferences: Accept (<a href="#header.accept" id="rfc.xref.header.accept.2" title="Accept">Section 5.1</a>), Accept-Charset (<a href="#header.accept-charset" id="rfc.xref.header.accept-charset.1" title="Accept-Charset">Section 5.2</a>), Accept-Encoding (<a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.2" title="Accept-Encoding">Section 5.3</a>), Accept-Language (<a href="#header.accept-language" id="rfc.xref.header.accept-language.1" title="Accept-Language">Section 5.4</a>), and User-Agent (<a href="p2-semantics.html#header.user-agent" title="User-Agent">Section 10.9</a> of <a href="#Part2" id="rfc.xref.Part2.2"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). However, an origin server is not limited to these dimensions and <em class="bcp14">MAY</em> vary the response based on any aspect of the request, including information outside the request-header fields or within extension |
---|
829 | header fields not defined by this specification. |
---|
830 | </p> |
---|
831 | <p id="rfc.section.4.1.p.5">The Vary header field <a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a> can be used to express the parameters the server uses to select a representation that is subject to server-driven negotiation. |
---|
832 | </p> |
---|
833 | <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a> <a id="agent-driven.negotiation" href="#agent-driven.negotiation">Agent-driven Negotiation</a></h2> |
---|
834 | <p id="rfc.section.4.2.p.1">With agent-driven negotiation, selection of the best representation for a response is performed by the user agent after receiving |
---|
835 | an initial response from the origin server. Selection is based on a list of the available representations of the response |
---|
836 | included within the header fields or entity-body of the initial response, with each representation identified by its own URI. |
---|
837 | Selection from among the representations may be performed automatically (if the user agent is capable of doing so) or manually |
---|
838 | by the user selecting from a generated (possibly hypertext) menu. |
---|
839 | </p> |
---|
840 | <p id="rfc.section.4.2.p.2">Agent-driven negotiation is advantageous when the response would vary over commonly-used dimensions (such as type, language, |
---|
841 | or encoding), when the origin server is unable to determine a user agent's capabilities from examining the request, and generally |
---|
842 | when public caches are used to distribute server load and reduce network usage. |
---|
843 | </p> |
---|
844 | <p id="rfc.section.4.2.p.3">Agent-driven negotiation suffers from the disadvantage of needing a second request to obtain the best alternate representation. |
---|
845 | This second request is only efficient when caching is used. In addition, this specification does not define any mechanism |
---|
846 | for supporting automatic selection, though it also does not prevent any such mechanism from being developed as an extension |
---|
847 | and used within HTTP/1.1. |
---|
848 | </p> |
---|
849 | <p id="rfc.section.4.2.p.4">HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable) status codes for enabling agent-driven negotiation when |
---|
850 | the server is unwilling or unable to provide a varying response using server-driven negotiation. |
---|
851 | </p> |
---|
852 | <h2 id="rfc.section.4.3"><a href="#rfc.section.4.3">4.3</a> <a id="transparent.negotiation" href="#transparent.negotiation">Transparent Negotiation</a></h2> |
---|
853 | <p id="rfc.section.4.3.p.1">Transparent negotiation is a combination of both server-driven and agent-driven negotiation. When a cache is supplied with |
---|
854 | a form of the list of available representations of the response (as in agent-driven negotiation) and the dimensions of variance |
---|
855 | are completely understood by the cache, then the cache becomes capable of performing server-driven negotiation on behalf of |
---|
856 | the origin server for subsequent requests on that resource. |
---|
857 | </p> |
---|
858 | <p id="rfc.section.4.3.p.2">Transparent negotiation has the advantage of distributing the negotiation work that would otherwise be required of the origin |
---|
859 | server and also removing the second request delay of agent-driven negotiation when the cache is able to correctly guess the |
---|
860 | right response. |
---|
861 | </p> |
---|
862 | <p id="rfc.section.4.3.p.3">This specification does not define any mechanism for transparent negotiation, though it also does not prevent any such mechanism |
---|
863 | from being developed as an extension that could be used within HTTP/1.1. |
---|
864 | </p> |
---|
865 | <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a> <a id="header.fields" href="#header.fields">Header Field Definitions</a></h1> |
---|
866 | <p id="rfc.section.5.p.1">This section defines the syntax and semantics of all standard HTTP/1.1 header fields. For entity-header fields, both sender |
---|
867 | and recipient refer to either the client or the server, depending on who sends and who receives the entity. |
---|
868 | </p> |
---|
869 | <div id="rfc.iref.a.1"></div> |
---|
870 | <div id="rfc.iref.h.1"></div> |
---|
871 | <h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a> <a id="header.accept" href="#header.accept">Accept</a></h2> |
---|
872 | <p id="rfc.section.5.1.p.1">The Accept request-header field can be used to specify certain media types which are acceptable for the response. Accept headers |
---|
873 | can be used to indicate that the request is specifically limited to a small set of desired types, as in the case of a request |
---|
874 | for an in-line image. |
---|
875 | </p> |
---|
876 | <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.17"></span><span id="rfc.iref.g.18"></span><span id="rfc.iref.g.19"></span><span id="rfc.iref.g.20"></span> Accept = "Accept" ":" |
---|
877 | #( media-range [ accept-params ] ) |
---|
878 | |
---|
879 | media-range = ( "*/*" |
---|
880 | | ( type "/" "*" ) |
---|
881 | | ( type "/" subtype ) |
---|
882 | ) *( ";" parameter ) |
---|
883 | accept-params = ";" "q" "=" qvalue *( accept-extension ) |
---|
884 | accept-extension = ";" token [ "=" ( token | quoted-string ) ] |
---|
885 | </pre><p id="rfc.section.5.1.p.3">The asterisk "*" character is used to group media types into ranges, with "*/*" indicating all media types and "type/*" indicating |
---|
886 | all subtypes of that type. The media-range <em class="bcp14">MAY</em> include media type parameters that are applicable to that range. |
---|
887 | </p> |
---|
888 | <p id="rfc.section.5.1.p.4">Each media-range <em class="bcp14">MAY</em> be followed by one or more accept-params, beginning with the "q" parameter for indicating a relative quality factor. The first |
---|
889 | "q" parameter (if any) separates the media-range parameter(s) from the accept-params. Quality factors allow the user or user |
---|
890 | agent to indicate the relative degree of preference for that media-range, using the qvalue scale from 0 to 1 (<a href="#quality.values" title="Quality Values">Section 2.4</a>). The default value is q=1. |
---|
891 | </p> |
---|
892 | <dl class="empty"> |
---|
893 | <dd> <b>Note:</b> Use of the "q" parameter name to separate media type parameters from Accept extension parameters is due to historical practice. |
---|
894 | Although this prevents any media type parameter named "q" from being used with a media range, such an event is believed to |
---|
895 | be unlikely given the lack of any "q" parameters in the IANA media type registry and the rare usage of any media type parameters |
---|
896 | in Accept. Future media types are discouraged from registering any parameter named "q". |
---|
897 | </dd> |
---|
898 | </dl> |
---|
899 | <p id="rfc.section.5.1.p.5">The example</p> |
---|
900 | <div id="rfc.figure.u.12"></div><pre class="text"> Accept: audio/*; q=0.2, audio/basic |
---|
901 | </pre><p id="rfc.section.5.1.p.7"> <em class="bcp14">SHOULD</em> be interpreted as "I prefer audio/basic, but send me any audio type if it is the best available after an 80% mark-down in |
---|
902 | quality." |
---|
903 | </p> |
---|
904 | <p id="rfc.section.5.1.p.8">If no Accept header field is present, then it is assumed that the client accepts all media types. If an Accept header field |
---|
905 | is present, and if the server cannot send a response which is acceptable according to the combined Accept field value, then |
---|
906 | the server <em class="bcp14">SHOULD</em> send a 406 (not acceptable) response. |
---|
907 | </p> |
---|
908 | <p id="rfc.section.5.1.p.9">A more elaborate example is</p> |
---|
909 | <div id="rfc.figure.u.13"></div><pre class="text"> Accept: text/plain; q=0.5, text/html, |
---|
910 | text/x-dvi; q=0.8, text/x-c |
---|
911 | </pre><p id="rfc.section.5.1.p.11">Verbally, this would be interpreted as "text/html and text/x-c are the preferred media types, but if they do not exist, then |
---|
912 | send the text/x-dvi entity, and if that does not exist, send the text/plain entity." |
---|
913 | </p> |
---|
914 | <p id="rfc.section.5.1.p.12">Media ranges can be overridden by more specific media ranges or specific media types. If more than one media range applies |
---|
915 | to a given type, the most specific reference has precedence. For example, |
---|
916 | </p> |
---|
917 | <div id="rfc.figure.u.14"></div><pre class="text"> Accept: text/*, text/html, text/html;level=1, */* |
---|
918 | </pre><p id="rfc.section.5.1.p.14">have the following precedence:</p> |
---|
919 | <div id="rfc.figure.u.15"></div><pre class="text"> 1) text/html;level=1 |
---|
920 | 2) text/html |
---|
921 | 3) text/* |
---|
922 | 4) */* |
---|
923 | </pre><p id="rfc.section.5.1.p.16">The media type quality factor associated with a given type is determined by finding the media range with the highest precedence |
---|
924 | which matches that type. For example, |
---|
925 | </p> |
---|
926 | <div id="rfc.figure.u.16"></div><pre class="text"> Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1, |
---|
927 | text/html;level=2;q=0.4, */*;q=0.5 |
---|
928 | </pre><p id="rfc.section.5.1.p.18">would cause the following values to be associated:</p> |
---|
929 | <div id="rfc.figure.u.17"></div><pre class="text"> text/html;level=1 = 1 |
---|
930 | text/html = 0.7 |
---|
931 | text/plain = 0.3 |
---|
932 | image/jpeg = 0.5 |
---|
933 | text/html;level=2 = 0.4 |
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934 | text/html;level=3 = 0.7 |
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935 | </pre><p id="rfc.section.5.1.p.20"> <b>Note:</b> A user agent might be provided with a default set of quality values for certain media ranges. However, unless the user agent |
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936 | is a closed system which cannot interact with other rendering agents, this default set ought to be configurable by the user. |
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937 | </p> |
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938 | <div id="rfc.iref.a.2"></div> |
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939 | <div id="rfc.iref.h.2"></div> |
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940 | <h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a> <a id="header.accept-charset" href="#header.accept-charset">Accept-Charset</a></h2> |
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941 | <p id="rfc.section.5.2.p.1">The Accept-Charset request-header field can be used to indicate what character sets are acceptable for the response. This |
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942 | field allows clients capable of understanding more comprehensive or special-purpose character sets to signal that capability |
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943 | to a server which is capable of representing documents in those character sets. |
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944 | </p> |
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945 | <div id="rfc.figure.u.18"></div><pre class="inline"><span id="rfc.iref.g.21"></span> Accept-Charset = "Accept-Charset" ":" |
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946 | 1#( ( charset | "*" )[ ";" "q" "=" qvalue ] ) |
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947 | </pre><p id="rfc.section.5.2.p.3">Character set values are described in <a href="#character.sets" title="Character Sets">Section 2.1</a>. Each charset <em class="bcp14">MAY</em> be given an associated quality value which represents the user's preference for that charset. The default value is q=1. An |
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948 | example is |
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949 | </p> |
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950 | <div id="rfc.figure.u.19"></div><pre class="text"> Accept-Charset: iso-8859-5, unicode-1-1;q=0.8 |
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951 | </pre><p id="rfc.section.5.2.p.5">The special value "*", if present in the Accept-Charset field, matches every character set (including ISO-8859-1) which is |
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952 | not mentioned elsewhere in the Accept-Charset field. If no "*" is present in an Accept-Charset field, then all character sets |
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953 | not explicitly mentioned get a quality value of 0, except for ISO-8859-1, which gets a quality value of 1 if not explicitly |
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954 | mentioned. |
---|
955 | </p> |
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956 | <p id="rfc.section.5.2.p.6">If no Accept-Charset header is present, the default is that any character set is acceptable. If an Accept-Charset header is |
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957 | present, and if the server cannot send a response which is acceptable according to the Accept-Charset header, then the server <em class="bcp14">SHOULD</em> send an error response with the 406 (not acceptable) status code, though the sending of an unacceptable response is also allowed. |
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958 | </p> |
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959 | <div id="rfc.iref.a.3"></div> |
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960 | <div id="rfc.iref.h.3"></div> |
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961 | <h2 id="rfc.section.5.3"><a href="#rfc.section.5.3">5.3</a> <a id="header.accept-encoding" href="#header.accept-encoding">Accept-Encoding</a></h2> |
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962 | <p id="rfc.section.5.3.p.1">The Accept-Encoding request-header field is similar to Accept, but restricts the content-codings (<a href="#content.codings" title="Content Codings">Section 2.2</a>) that are acceptable in the response. |
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963 | </p> |
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964 | <div id="rfc.figure.u.20"></div><pre class="inline"><span id="rfc.iref.g.22"></span><span id="rfc.iref.g.23"></span> Accept-Encoding = "Accept-Encoding" ":" |
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965 | |
---|