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| 295 | font-size: 18pt; |
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| 298 | text-align: center; |
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| 299 | margin-top: 36pt; |
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| 300 | } |
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| 301 | .vcardline { |
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| 302 | display: block; |
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| 303 | } |
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| 306 | background-color: yellow; |
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| 307 | } |
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| 308 | |
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| 309 | |
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| 310 | @media print { |
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| 311 | .noprint { |
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| 312 | display: none; |
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| 313 | } |
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| 314 | |
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| 315 | a { |
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| 319 | |
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| 322 | } |
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| 323 | |
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| 324 | td.header { |
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| 325 | width: 50%; |
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| 326 | color: black; |
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| 327 | background-color: white; |
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| 328 | vertical-align: top; |
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| 329 | font-size: 12pt; |
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| 330 | } |
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| 331 | |
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| 334 | } |
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| 335 | |
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| 337 | content: target-counter(attr(href), page); |
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| 338 | } |
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| 339 | |
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| 340 | .print2col { |
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| 341 | column-count: 2; |
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| 342 | column-fill: auto; |
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| 343 | } |
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| 344 | } |
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| 345 | |
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| 346 | @page { |
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| 347 | @top-left { |
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| 348 | content: "Internet-Draft"; |
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| 349 | } |
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| 350 | @top-right { |
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| 351 | content: "January 2012"; |
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| 352 | } |
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| 353 | @top-center { |
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| 354 | content: "HTTP/1.1, Part 4"; |
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| 355 | } |
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| 356 | @bottom-left { |
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| 357 | content: "Fielding, et al."; |
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| 358 | } |
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| 359 | @bottom-center { |
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| 360 | content: "Expires July 29, 2012"; |
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| 361 | } |
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| 362 | @bottom-right { |
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| 363 | content: "[Page " counter(page) "]"; |
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| 364 | } |
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| 365 | } |
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| 366 | |
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| 367 | @page:first { |
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| 368 | @top-left { |
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| 369 | content: normal; |
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| 370 | } |
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| 371 | @top-right { |
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| 372 | content: normal; |
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| 373 | } |
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| 374 | @top-center { |
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| 375 | content: normal; |
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| 376 | } |
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| 377 | } |
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| 378 | </style><link rel="Contents" href="#rfc.toc"> |
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| 379 | <link rel="Author" href="#rfc.authors"> |
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| 380 | <link rel="Copyright" href="#rfc.copyrightnotice"> |
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| 381 | <link rel="Index" href="#rfc.index"> |
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| 382 | <link rel="Chapter" title="1 Introduction" href="#rfc.section.1"> |
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| 383 | <link rel="Chapter" title="2 Validators" href="#rfc.section.2"> |
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| 384 | <link rel="Chapter" title="3 Precondition Header Fields" href="#rfc.section.3"> |
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| 385 | <link rel="Chapter" title="4 Status Code Definitions" href="#rfc.section.4"> |
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| 386 | <link rel="Chapter" title="5 IANA Considerations" href="#rfc.section.5"> |
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| 387 | <link rel="Chapter" title="6 Security Considerations" href="#rfc.section.6"> |
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| 388 | <link rel="Chapter" title="7 Acknowledgments" href="#rfc.section.7"> |
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| 389 | <link rel="Chapter" href="#rfc.section.8" title="8 References"> |
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| 390 | <link rel="Appendix" title="A Changes from RFC 2616" href="#rfc.section.A"> |
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| 391 | <link rel="Appendix" title="B Collected ABNF" href="#rfc.section.B"> |
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| 392 | <link rel="Appendix" title="C Change Log (to be removed by RFC Editor before publication)" href="#rfc.section.C"> |
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| 393 | <link href="p3-payload.html" rel="prev"> |
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| 394 | <link href="p5-range.html" rel="next"> |
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| 395 | <meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.561, 2011-12-24 13:06:50, XSLT vendor: SAXON 8.9 from Saxonica http://www.saxonica.com/"> |
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| 396 | <link rel="schema.dct" href="http://purl.org/dc/terms/"> |
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| 397 | <meta name="dct.creator" content="Fielding, R."> |
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| 398 | <meta name="dct.creator" content="Gettys, J."> |
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| 399 | <meta name="dct.creator" content="Mogul, J."> |
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| 400 | <meta name="dct.creator" content="Frystyk, H."> |
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| 401 | <meta name="dct.creator" content="Masinter, L."> |
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| 402 | <meta name="dct.creator" content="Leach, P."> |
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| 403 | <meta name="dct.creator" content="Berners-Lee, T."> |
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| 404 | <meta name="dct.creator" content="Lafon, Y."> |
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| 405 | <meta name="dct.creator" content="Reschke, J. F."> |
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| 406 | <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p4-conditional-latest"> |
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| 407 | <meta name="dct.issued" scheme="ISO8601" content="2012-01-26"> |
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| 408 | <meta name="dct.replaces" content="urn:ietf:rfc:2616"> |
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| 409 | <meta name="dct.abstract" content="The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext 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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| 410 | <meta name="description" content="The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext 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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| 411 | </head> |
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| 412 | <body> |
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| 413 | <table class="header"> |
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| 414 | <tbody> |
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| 415 | <tr> |
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| 416 | <td class="left">HTTPbis Working Group</td> |
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| 417 | <td class="right">R. Fielding, Editor</td> |
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| 418 | </tr> |
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| 419 | <tr> |
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| 420 | <td class="left">Internet-Draft</td> |
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| 421 | <td class="right">Adobe</td> |
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| 422 | </tr> |
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| 423 | <tr> |
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| 424 | <td class="left">Obsoletes: <a href="http://tools.ietf.org/html/rfc2616">2616</a> (if approved) |
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| 425 | </td> |
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| 426 | <td class="right">J. Gettys</td> |
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| 427 | </tr> |
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| 428 | <tr> |
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| 429 | <td class="left">Intended status: Standards Track</td> |
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| 430 | <td class="right">Alcatel-Lucent</td> |
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| 431 | </tr> |
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| 432 | <tr> |
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| 433 | <td class="left">Expires: July 29, 2012</td> |
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| 434 | <td class="right">J. Mogul</td> |
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| 435 | </tr> |
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| 436 | <tr> |
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| 437 | <td class="left"></td> |
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| 438 | <td class="right">HP</td> |
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| 439 | </tr> |
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| 440 | <tr> |
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| 441 | <td class="left"></td> |
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| 442 | <td class="right">H. Frystyk</td> |
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| 443 | </tr> |
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| 444 | <tr> |
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| 445 | <td class="left"></td> |
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| 446 | <td class="right">Microsoft</td> |
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| 447 | </tr> |
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| 448 | <tr> |
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| 449 | <td class="left"></td> |
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| 450 | <td class="right">L. Masinter</td> |
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| 451 | </tr> |
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| 452 | <tr> |
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| 453 | <td class="left"></td> |
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| 454 | <td class="right">Adobe</td> |
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| 455 | </tr> |
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| 456 | <tr> |
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| 457 | <td class="left"></td> |
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| 458 | <td class="right">P. Leach</td> |
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| 459 | </tr> |
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| 460 | <tr> |
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| 461 | <td class="left"></td> |
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| 462 | <td class="right">Microsoft</td> |
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| 463 | </tr> |
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| 464 | <tr> |
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| 465 | <td class="left"></td> |
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| 466 | <td class="right">T. Berners-Lee</td> |
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| 467 | </tr> |
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| 468 | <tr> |
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| 469 | <td class="left"></td> |
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| 470 | <td class="right">W3C/MIT</td> |
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| 471 | </tr> |
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| 472 | <tr> |
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| 473 | <td class="left"></td> |
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| 474 | <td class="right">Y. Lafon, Editor</td> |
|---|
| 475 | </tr> |
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| 476 | <tr> |
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| 477 | <td class="left"></td> |
|---|
| 478 | <td class="right">W3C</td> |
|---|
| 479 | </tr> |
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| 480 | <tr> |
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| 481 | <td class="left"></td> |
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| 482 | <td class="right">J. Reschke, Editor</td> |
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| 483 | </tr> |
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| 484 | <tr> |
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| 485 | <td class="left"></td> |
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| 486 | <td class="right">greenbytes</td> |
|---|
| 487 | </tr> |
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| 488 | <tr> |
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| 489 | <td class="left"></td> |
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| 490 | <td class="right">January 26, 2012</td> |
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| 491 | </tr> |
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| 492 | </tbody> |
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| 493 | </table> |
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| 494 | <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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| 495 | <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1> |
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| 496 | <p>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext information |
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| 497 | 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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| 498 | seven-part specification that defines the protocol referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616. |
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| 499 | </p> |
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| 500 | <p>Part 4 defines request header fields for indicating conditional requests and the rules for constructing responses to those |
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| 501 | requests. |
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| 502 | </p> |
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| 503 | <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1> |
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| 504 | <p>Discussion of this draft should take place on the HTTPBIS working group mailing list (ietf-http-wg@w3.org), which is archived |
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| 505 | at <<a href="http://lists.w3.org/Archives/Public/ietf-http-wg/">http://lists.w3.org/Archives/Public/ietf-http-wg/</a>>. |
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| 506 | </p> |
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| 507 | <p>The current issues list is at <<a href="http://tools.ietf.org/wg/httpbis/trac/report/3">http://tools.ietf.org/wg/httpbis/trac/report/3</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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| 508 | </p> |
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| 509 | <p>The changes in this draft are summarized in <a href="#changes.since.18" title="Since draft-ietf-httpbis-p4-conditional-18">Appendix C.20</a>. |
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| 510 | </p> |
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| 511 | <h1><a id="rfc.status" href="#rfc.status">Status of This Memo</a></h1> |
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| 512 | <p>This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.</p> |
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| 513 | <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute |
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| 514 | working documents as Internet-Drafts. The list of current Internet-Drafts is at <a href="http://datatracker.ietf.org/drafts/current/">http://datatracker.ietf.org/drafts/current/</a>. |
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| 515 | </p> |
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| 516 | <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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| 517 | 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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| 518 | in progress”. |
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| 519 | </p> |
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| 520 | <p>This Internet-Draft will expire on July 29, 2012.</p> |
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| 521 | <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1> |
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| 522 | <p>Copyright © 2012 IETF Trust and the persons identified as the document authors. All rights reserved.</p> |
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| 523 | <p>This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights |
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| 524 | and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License |
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| 525 | text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified |
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| 526 | BSD License. |
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| 527 | </p> |
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| 528 | <p>This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November |
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| 529 | 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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| 530 | allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) |
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| 531 | controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative |
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| 532 | 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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| 533 | it into languages other than English. |
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| 534 | </p> |
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| 535 | <hr class="noprint"> |
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| 536 | <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1> |
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| 537 | <ul class="toc"> |
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| 538 | <li>1. <a href="#introduction">Introduction</a><ul> |
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| 539 | <li>1.1 <a href="#intro.conformance.and.error.handling">Conformance and Error Handling</a></li> |
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| 540 | <li>1.2 <a href="#notation">Syntax Notation</a></li> |
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| 541 | </ul> |
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| 542 | </li> |
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| 543 | <li>2. <a href="#validators">Validators</a><ul> |
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| 544 | <li>2.1 <a href="#weak.and.strong.validators">Weak versus Strong</a></li> |
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| 545 | <li>2.2 <a href="#header.last-modified">Last-Modified</a><ul> |
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| 546 | <li>2.2.1 <a href="#lastmod.generation">Generation</a></li> |
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| 547 | <li>2.2.2 <a href="#lastmod.comparison">Comparison</a></li> |
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| 548 | </ul> |
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| 549 | </li> |
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| 550 | <li>2.3 <a href="#header.etag">ETag</a><ul> |
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| 551 | <li>2.3.1 <a href="#entity.tag.generation">Generation</a></li> |
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| 552 | <li>2.3.2 <a href="#entity.tag.comparison">Comparison</a></li> |
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| 553 | <li>2.3.3 <a href="#example.entity.tag.vs.conneg">Example: Entity-tags varying on Content-Negotiated Resources</a></li> |
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| 554 | </ul> |
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| 555 | </li> |
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| 556 | <li>2.4 <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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| 557 | </ul> |
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| 558 | </li> |
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| 559 | <li>3. <a href="#header.field.definitions">Precondition Header Fields</a><ul> |
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| 560 | <li>3.1 <a href="#header.if-match">If-Match</a></li> |
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| 561 | <li>3.2 <a href="#header.if-none-match">If-None-Match</a></li> |
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| 562 | <li>3.3 <a href="#header.if-modified-since">If-Modified-Since</a></li> |
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| 563 | <li>3.4 <a href="#header.if-unmodified-since">If-Unmodified-Since</a></li> |
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| 564 | <li>3.5 <a href="#header.if-range">If-Range</a></li> |
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| 565 | </ul> |
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| 566 | </li> |
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| 567 | <li>4. <a href="#status.code.definitions">Status Code Definitions</a><ul> |
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| 568 | <li>4.1 <a href="#status.304">304 Not Modified</a></li> |
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| 569 | <li>4.2 <a href="#status.412">412 Precondition Failed</a></li> |
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| 570 | </ul> |
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| 571 | </li> |
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| 572 | <li>5. <a href="#IANA.considerations">IANA Considerations</a><ul> |
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| 573 | <li>5.1 <a href="#status.code.registration">Status Code Registration</a></li> |
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| 574 | <li>5.2 <a href="#header.field.registration">Header Field Registration</a></li> |
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| 575 | </ul> |
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| 576 | </li> |
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| 577 | <li>6. <a href="#security.considerations">Security Considerations</a></li> |
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| 578 | <li>7. <a href="#acks">Acknowledgments</a></li> |
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| 579 | <li>8. <a href="#rfc.references">References</a><ul> |
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| 580 | <li>8.1 <a href="#rfc.references.1">Normative References</a></li> |
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| 581 | <li>8.2 <a href="#rfc.references.2">Informative References</a></li> |
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| 582 | </ul> |
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| 583 | </li> |
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| 584 | <li><a href="#rfc.authors">Authors' Addresses</a></li> |
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| 585 | <li>A. <a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li> |
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| 586 | <li>B. <a href="#collected.abnf">Collected ABNF</a></li> |
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| 587 | <li>C. <a href="#change.log">Change Log (to be removed by RFC Editor before publication)</a><ul> |
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| 588 | <li>C.1 <a href="#rfc.section.C.1">Since RFC 2616</a></li> |
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| 589 | <li>C.2 <a href="#rfc.section.C.2">Since draft-ietf-httpbis-p4-conditional-00</a></li> |
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| 590 | <li>C.3 <a href="#rfc.section.C.3">Since draft-ietf-httpbis-p4-conditional-01</a></li> |
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| 591 | <li>C.4 <a href="#changes.since.02">Since draft-ietf-httpbis-p4-conditional-02</a></li> |
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| 592 | <li>C.5 <a href="#changes.since.03">Since draft-ietf-httpbis-p4-conditional-03</a></li> |
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| 593 | <li>C.6 <a href="#changes.since.04">Since draft-ietf-httpbis-p4-conditional-04</a></li> |
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| 594 | <li>C.7 <a href="#changes.since.05">Since draft-ietf-httpbis-p4-conditional-05</a></li> |
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| 595 | <li>C.8 <a href="#changes.since.06">Since draft-ietf-httpbis-p4-conditional-06</a></li> |
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| 596 | <li>C.9 <a href="#changes.since.07">Since draft-ietf-httpbis-p4-conditional-07</a></li> |
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| 597 | <li>C.10 <a href="#changes.since.08">Since draft-ietf-httpbis-p4-conditional-08</a></li> |
|---|
| 598 | <li>C.11 <a href="#changes.since.09">Since draft-ietf-httpbis-p4-conditional-09</a></li> |
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| 599 | <li>C.12 <a href="#changes.since.10">Since draft-ietf-httpbis-p4-conditional-10</a></li> |
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| 600 | <li>C.13 <a href="#changes.since.11">Since draft-ietf-httpbis-p4-conditional-11</a></li> |
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| 601 | <li>C.14 <a href="#changes.since.12">Since draft-ietf-httpbis-p4-conditional-12</a></li> |
|---|
| 602 | <li>C.15 <a href="#changes.since.13">Since draft-ietf-httpbis-p4-conditional-13</a></li> |
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| 603 | <li>C.16 <a href="#changes.since.14">Since draft-ietf-httpbis-p4-conditional-14</a></li> |
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| 604 | <li>C.17 <a href="#changes.since.15">Since draft-ietf-httpbis-p4-conditional-15</a></li> |
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| 605 | <li>C.18 <a href="#changes.since.16">Since draft-ietf-httpbis-p4-conditional-16</a></li> |
|---|
| 606 | <li>C.19 <a href="#changes.since.17">Since draft-ietf-httpbis-p4-conditional-17</a></li> |
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| 607 | <li>C.20 <a href="#changes.since.18">Since draft-ietf-httpbis-p4-conditional-18</a></li> |
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| 608 | </ul> |
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| 609 | </li> |
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| 610 | <li><a href="#rfc.index">Index</a></li> |
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| 611 | </ul> |
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| 612 | <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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| 613 | <p id="rfc.section.1.p.1">This document defines the HTTP/1.1 conditional request mechanisms, including both metadata for indicating/observing changes |
|---|
| 614 | in resource representations and request header fields that specify preconditions on that metadata be checked before performing |
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| 615 | the request method. Conditional GET requests are the most efficient mechanism for HTTP cache updates <a href="#Part6" id="rfc.xref.Part6.1"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>. Conditionals can also be applied to state-changing methods, such as PUT and DELETE, to prevent the "lost update" problem: |
|---|
| 616 | one client accidentally overwriting the work of another client that has been acting in parallel. |
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| 617 | </p> |
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| 618 | <p id="rfc.section.1.p.2">Conditional request preconditions are based on the state of the target resource as a whole (its current value set) or the |
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| 619 | state as observed in a previously obtained representation (one value in that set). A resource might have multiple current |
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| 620 | representations, each with its own observable state. The conditional request mechanisms assume that the mapping of requests |
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| 621 | to corresponding representations will be consistent over time if the server intends to take advantage of conditionals. Regardless, |
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| 622 | if the mapping is inconsistent and the server is unable to select the appropriate representation, then no harm will result |
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| 623 | when the precondition evaluates to false. |
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| 624 | </p> |
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| 625 | <p id="rfc.section.1.p.3"><span id="rfc.iref.s.1"></span> We use the term "<dfn>selected representation</dfn>" to refer to the current representation of the target resource that would have been selected in a successful response if |
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| 626 | the same request had used the method GET and had excluded all of the conditional request header fields. The conditional request |
|---|
| 627 | preconditions are evaluated by comparing the values provided in the request header fields to the current metadata for the |
|---|
| 628 | selected representation. |
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| 629 | </p> |
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| 630 | <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a> <a id="intro.conformance.and.error.handling" href="#intro.conformance.and.error.handling">Conformance and Error Handling</a></h2> |
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| 631 | <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" |
|---|
| 632 | 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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| 633 | </p> |
|---|
| 634 | <p id="rfc.section.1.1.p.2">This document defines conformance criteria for several roles in HTTP communication, including Senders, Recipients, Clients, |
|---|
| 635 | Servers, User-Agents, Origin Servers, Intermediaries, Proxies and Gateways. See <a href="p1-messaging.html#architecture" title="Architecture">Section 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> for definitions of these terms. |
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| 636 | </p> |
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| 637 | <p id="rfc.section.1.1.p.3">An implementation is considered conformant if it complies with all of the requirements associated with its role(s). Note that |
|---|
| 638 | SHOULD-level requirements are relevant here, unless one of the documented exceptions is applicable. |
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| 639 | </p> |
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| 640 | <p id="rfc.section.1.1.p.4">This document also uses ABNF to define valid protocol elements (<a href="#notation" title="Syntax Notation">Section 1.2</a>). In addition to the prose requirements placed upon them, Senders <em class="bcp14">MUST NOT</em> generate protocol elements that are invalid. |
|---|
| 641 | </p> |
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| 642 | <p id="rfc.section.1.1.p.5">Unless noted otherwise, Recipients <em class="bcp14">MAY</em> take steps to recover a usable protocol element from an invalid construct. However, HTTP does not define specific error handling |
|---|
| 643 | mechanisms, except in cases where it has direct impact on security. This is because different uses of the protocol require |
|---|
| 644 | different error handling strategies; for example, a Web browser may wish to transparently recover from a response where the |
|---|
| 645 | Location header field doesn't parse according to the ABNF, whereby in a systems control protocol using HTTP, this type of |
|---|
| 646 | error recovery could lead to dangerous consequences. |
|---|
| 647 | </p> |
|---|
| 648 | <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a> <a id="notation" href="#notation">Syntax Notation</a></h2> |
|---|
| 649 | <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.Part1.2"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> (which extends the syntax defined in <a href="#RFC5234" id="rfc.xref.RFC5234.1"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a> with a list rule). <a href="#collected.abnf" title="Collected ABNF">Appendix B</a> shows the collected ABNF, with the list rule expanded. |
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| 650 | </p> |
|---|
| 651 | <p id="rfc.section.1.2.p.2">The following core rules are included by reference, as defined in <a href="#RFC5234" id="rfc.xref.RFC5234.2"><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 |
|---|
| 652 | (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit sequence of data), SP (space), and VCHAR (any visible US-ASCII |
|---|
| 653 | character). |
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| 654 | </p> |
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| 655 | <p id="rfc.section.1.2.p.3">The ABNF rules below are 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> and <a href="#Part2" id="rfc.xref.Part2.1"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>: |
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| 656 | </p> |
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| 657 | <div id="rfc.figure.u.1"></div><pre class="inline"> <a href="#notation" 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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| 658 | <a href="#notation" class="smpl">obs-text</a> = <obs-text, 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#field.rules" title="Common Field ABNF Rules">Section 3.2.3</a>> |
|---|
| 659 | <a href="#notation" class="smpl">HTTP-date</a> = <HTTP-date, defined in <a href="#Part2" id="rfc.xref.Part2.2"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>, <a href="p2-semantics.html#http.date" title="Date/Time Formats">Section 8</a>> |
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| 660 | </pre><div id="rfc.iref.m.1"></div> |
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| 661 | <div id="rfc.iref.v.1"></div> |
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| 662 | <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a> <a id="validators" href="#validators">Validators</a></h1> |
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| 663 | <p id="rfc.section.2.p.1">This specification defines two forms of metadata that are commonly used to observe resource state and test for preconditions: |
|---|
| 664 | modification dates and opaque entity tags. Additional metadata that reflects resource state has been defined by various extensions |
|---|
| 665 | of HTTP, such as WebDAV <a href="#RFC4918" id="rfc.xref.RFC4918.1"><cite title="HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)">[RFC4918]</cite></a>, that are beyond the scope of this specification. A resource metadata value is referred to as a "<dfn>validator</dfn>" when it is used within a precondition. |
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| 666 | </p> |
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| 667 | <div id="rfc.iref.v.2"></div> |
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| 668 | <div id="rfc.iref.v.3"></div> |
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| 669 | <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a> <a id="weak.and.strong.validators" href="#weak.and.strong.validators">Weak versus Strong</a></h2> |
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| 670 | <p id="rfc.section.2.1.p.1">Validators come in two flavors: strong or weak. Weak validators are easy to generate but are far less useful for comparisons. |
|---|
| 671 | Strong validators are ideal for comparisons but can be very difficult (and occasionally impossible) to generate efficiently. |
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| 672 | Rather than impose that all forms of resource adhere to the same strength of validator, HTTP exposes the type of validator |
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| 673 | in use and imposes restrictions on when weak validators can be used as preconditions. |
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| 674 | </p> |
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| 675 | <p id="rfc.section.2.1.p.2">A "strong validator" is a representation metadata value that <em class="bcp14">MUST</em> be changed to a new, previously unused or guaranteed unique, value whenever a change occurs to the representation data such |
|---|
| 676 | that a change would be observable in the payload body of a 200 response to GET. A strong validator <em class="bcp14">MAY</em> be changed for other reasons, such as when a semantically significant part of the representation metadata is changed (e.g., |
|---|
| 677 | Content-Type), but it is in the best interests of the origin server to only change the value when it is necessary to invalidate |
|---|
| 678 | the stored responses held by remote caches and authoring tools. A strong validator <em class="bcp14">MUST</em> be unique across all representations of a given resource, such that no two representations of that resource share the same |
|---|
| 679 | validator unless their payload body would be identical. |
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| 680 | </p> |
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| 681 | <p id="rfc.section.2.1.p.3">Cache entries might persist for arbitrarily long periods, regardless of expiration times. Thus, a cache might attempt to validate |
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| 682 | an entry using a validator that it obtained in the distant past. A strong validator <em class="bcp14">MUST</em> be unique across all versions of all representations associated with a particular resource over time. However, there is no |
|---|
| 683 | implication of uniqueness across representations of different resources (i.e., the same strong validator might be in use for |
|---|
| 684 | representations of multiple resources at the same time and does not imply that those representations are equivalent). |
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| 685 | </p> |
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| 686 | <p id="rfc.section.2.1.p.4">There are a variety of strong validators used in practice. The best are based on strict revision control, wherein each change |
|---|
| 687 | to a representation always results in a unique node name and revision identifier being assigned before the representation |
|---|
| 688 | is made accessible to GET. A cryptographic hash function applied to the representation data is also sufficient if the data |
|---|
| 689 | is available prior to the response header fields being sent and the digest does not need to be recalculated every time a validation |
|---|
| 690 | request is received. However, if a resource has distinct representations that differ only in their metadata, such as might |
|---|
| 691 | occur with content negotiation over media types that happen to share the same data format, then a server <em class="bcp14">SHOULD</em> incorporate additional information in the validator to distinguish those representations and avoid confusing cache behavior. |
|---|
| 692 | </p> |
|---|
| 693 | <p id="rfc.section.2.1.p.5">In contrast, a "weak validator" is a representation metadata value that might not be changed for every change to the representation |
|---|
| 694 | data. This weakness might be due to limitations in how the value is calculated, such as clock resolution or an inability to |
|---|
| 695 | ensure uniqueness for all possible representations of the resource, or due to a desire by the resource owner to group representations |
|---|
| 696 | by some self-determined set of equivalency rather than unique sequences of data. A weak entity-tag <em class="bcp14">SHOULD</em> change whenever the origin server considers prior representations to be unacceptable as a substitute for the current representation. |
|---|
| 697 | In other words, a weak entity-tag <em class="bcp14">SHOULD</em> change whenever the origin server wants caches to invalidate old responses. |
|---|
| 698 | </p> |
|---|
| 699 | <p id="rfc.section.2.1.p.6">For example, the representation of a weather report that changes in content every second, based on dynamic measurements, might |
|---|
| 700 | be grouped into sets of equivalent representations (from the origin server's perspective) with the same weak validator in |
|---|
| 701 | order to allow cached representations to be valid for a reasonable period of time (perhaps adjusted dynamically based on server |
|---|
| 702 | load or weather quality). Likewise, a representation's modification time, if defined with only one-second resolution, might |
|---|
| 703 | be a weak validator if it is possible for the representation to be modified twice during a single second and retrieved between |
|---|
| 704 | those modifications. |
|---|
| 705 | </p> |
|---|
| 706 | <p id="rfc.section.2.1.p.7">A "use" of a validator occurs when either a client generates a request and includes the validator in a precondition or when |
|---|
| 707 | a server compares two validators. Weak validators are only usable in contexts that do not depend on exact equality of a representation's |
|---|
| 708 | payload body. Strong validators are usable and preferred for all conditional requests, including cache validation, partial |
|---|
| 709 | content ranges, and "lost update" avoidance. |
|---|
| 710 | </p> |
|---|
| 711 | <div id="rfc.iref.l.1"></div> |
|---|
| 712 | <div id="rfc.iref.h.1"></div> |
|---|
| 713 | <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a> <a id="header.last-modified" href="#header.last-modified">Last-Modified</a></h2> |
|---|
| 714 | <p id="rfc.section.2.2.p.1">The "Last-Modified" header field indicates the date and time at which the origin server believes the selected representation |
|---|
| 715 | was last modified. |
|---|
| 716 | </p> |
|---|
| 717 | <div id="rfc.figure.u.2"></div><pre class="inline"><span id="rfc.iref.g.1"></span> <a href="#header.last-modified" class="smpl">Last-Modified</a> = <a href="#notation" class="smpl">HTTP-date</a> |
|---|
| 718 | </pre><p id="rfc.section.2.2.p.3">An example of its use is</p> |
|---|
| 719 | <div id="rfc.figure.u.3"></div><pre class="text"> Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT |
|---|
| 720 | </pre><h3 id="rfc.section.2.2.1"><a href="#rfc.section.2.2.1">2.2.1</a> <a id="lastmod.generation" href="#lastmod.generation">Generation</a></h3> |
|---|
| 721 | <p id="rfc.section.2.2.1.p.1">Origin servers <em class="bcp14">SHOULD</em> send Last-Modified for any selected representation for which a last modification date can be reasonably and consistently determined, |
|---|
| 722 | since its use in conditional requests and evaluating cache freshness (<a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) results in a substantial reduction of HTTP traffic on the Internet and can be a significant factor in improving service |
|---|
| 723 | scalability and reliability. |
|---|
| 724 | </p> |
|---|
| 725 | <p id="rfc.section.2.2.1.p.2">A representation is typically the sum of many parts behind the resource interface. The last-modified time would usually be |
|---|
| 726 | the most recent time that any of those parts were changed. How that value is determined for any given resource is an implementation |
|---|
| 727 | detail beyond the scope of this specification. What matters to HTTP is how recipients of the Last-Modified header field can |
|---|
| 728 | use its value to make conditional requests and test the validity of locally cached responses. |
|---|
| 729 | </p> |
|---|
| 730 | <p id="rfc.section.2.2.1.p.3">An origin server <em class="bcp14">SHOULD</em> obtain the Last-Modified value of the representation as close as possible to the time that it generates the Date field-value |
|---|
| 731 | for its response. This allows a recipient to make an accurate assessment of the representation's modification time, especially |
|---|
| 732 | if the representation changes near the time that the response is generated. |
|---|
| 733 | </p> |
|---|
| 734 | <p id="rfc.section.2.2.1.p.4">An origin server with a clock <em class="bcp14">MUST NOT</em> send a Last-Modified date that is later than the server's time of message origination (Date). If the last modification time |
|---|
| 735 | is derived from implementation-specific metadata that evaluates to some time in the future, according to the origin server's |
|---|
| 736 | clock, then the origin server <em class="bcp14">MUST</em> replace that value with the message origination date. This prevents a future modification date from having an adverse impact |
|---|
| 737 | on cache validation. |
|---|
| 738 | </p> |
|---|
| 739 | <p id="rfc.section.2.2.1.p.5">An origin server without a clock <em class="bcp14">MUST NOT</em> assign Last-Modified values to a response unless these values were associated with the resource by some other system or user |
|---|
| 740 | with a reliable clock. |
|---|
| 741 | </p> |
|---|
| 742 | <h3 id="rfc.section.2.2.2"><a href="#rfc.section.2.2.2">2.2.2</a> <a id="lastmod.comparison" href="#lastmod.comparison">Comparison</a></h3> |
|---|
| 743 | <p id="rfc.section.2.2.2.p.1">A Last-Modified time, when used as a validator in a request, is implicitly weak unless it is possible to deduce that it is |
|---|
| 744 | strong, using the following rules: |
|---|
| 745 | </p> |
|---|
| 746 | <ul> |
|---|
| 747 | <li>The validator is being compared by an origin server to the actual current validator for the representation and,</li> |
|---|
| 748 | <li>That origin server reliably knows that the associated representation did not change twice during the second covered by the |
|---|
| 749 | presented validator. |
|---|
| 750 | </li> |
|---|
| 751 | </ul> |
|---|
| 752 | <p id="rfc.section.2.2.2.p.2">or </p> |
|---|
| 753 | <ul> |
|---|
| 754 | <li>The validator is about to be used by a client in an If-Modified-Since, If-Unmodified-Since header field, because the client |
|---|
| 755 | has a cache entry, or If-Range for the associated representation, and |
|---|
| 756 | </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.2.2.2.p.3">or </p> |
|---|
| 761 | <ul> |
|---|
| 762 | <li>The validator is being compared by an intermediate cache to the validator stored in its cache entry for the representation, |
|---|
| 763 | and |
|---|
| 764 | </li> |
|---|
| 765 | <li>That cache entry includes a Date value, which gives the time when the origin server sent the original response, and</li> |
|---|
| 766 | <li>The presented Last-Modified time is at least 60 seconds before the Date value.</li> |
|---|
| 767 | </ul> |
|---|
| 768 | <p id="rfc.section.2.2.2.p.4">This method relies on the fact that if two different responses were sent by the origin server during the same second, but |
|---|
| 769 | both had the same Last-Modified time, then at least one of those responses would have a Date value equal to its Last-Modified |
|---|
| 770 | time. The arbitrary 60-second limit guards against the possibility that the Date and Last-Modified values are generated from |
|---|
| 771 | 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. |
|---|
| 772 | </p> |
|---|
| 773 | <div id="rfc.iref.e.1"></div> |
|---|
| 774 | <div id="rfc.iref.h.2"></div> |
|---|
| 775 | <h2 id="rfc.section.2.3"><a href="#rfc.section.2.3">2.3</a> <a id="header.etag" href="#header.etag">ETag</a></h2> |
|---|
| 776 | <p id="rfc.section.2.3.p.1">The ETag header field provides the current entity-tag for the selected representation. An entity-tag is an opaque validator |
|---|
| 777 | for differentiating between multiple representations of the same resource, regardless of whether those multiple representations |
|---|
| 778 | are due to resource state changes over time, content negotiation resulting in multiple representations being valid at the |
|---|
| 779 | same time, or both. An entity-tag consists of an opaque quoted string, possibly prefixed by a weakness indicator. |
|---|
| 780 | </p> |
|---|
| 781 | <div id="rfc.figure.u.4"></div><pre class="inline"><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span><span id="rfc.iref.g.4"></span><span id="rfc.iref.g.5"></span><span id="rfc.iref.g.6"></span> <a href="#header.etag" class="smpl">ETag</a> = <a href="#header.etag" class="smpl">entity-tag</a> |
|---|
| 782 | |
|---|
| 783 | <a href="#header.etag" class="smpl">entity-tag</a> = [ <a href="#header.etag" class="smpl">weak</a> ] <a href="#header.etag" class="smpl">opaque-tag</a> |
|---|
| 784 | <a href="#header.etag" class="smpl">weak</a> = %x57.2F ; "W/", case-sensitive |
|---|
| 785 | <a href="#header.etag" class="smpl">opaque-tag</a> = <a href="#notation" class="smpl">DQUOTE</a> *<a href="#header.etag" class="smpl">etagc</a> <a href="#notation" class="smpl">DQUOTE</a> |
|---|
| 786 | <a href="#header.etag" class="smpl">etagc</a> = %x21 / %x23-7E / <a href="#notation" class="smpl">obs-text</a> |
|---|
| 787 | ; <a href="#notation" class="smpl">VCHAR</a> except double quotes, plus obs-text |
|---|
| 788 | </pre><div class="note" id="rfc.section.2.3.p.3"> |
|---|
| 789 | <p> <b>Note:</b> Previously, opaque-tag was defined to be a quoted-string (<a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>, <a href="http://tools.ietf.org/html/rfc2616#section-3.11">Section 3.11</a>), thus some recipients might perform backslash unescaping. Servers therefore ought to avoid backslash characters in entity |
|---|
| 790 | tags. |
|---|
| 791 | </p> |
|---|
| 792 | </div> |
|---|
| 793 | <p id="rfc.section.2.3.p.4">An entity-tag can be more reliable for validation than a modification date in situations where it is inconvenient to store |
|---|
| 794 | modification dates, where the one-second resolution of HTTP date values is not sufficient, or where modification dates are |
|---|
| 795 | not consistently maintained. |
|---|
| 796 | </p> |
|---|
| 797 | <div id="rfc.figure.u.5"></div> |
|---|
| 798 | <p>Examples:</p> <pre class="text"> ETag: "xyzzy" |
|---|
| 799 | ETag: W/"xyzzy" |
|---|
| 800 | ETag: "" |
|---|
| 801 | </pre><p id="rfc.section.2.3.p.6">An entity-tag can be either a weak or strong validator, with strong being the default. If an origin server provides an entity-tag |
|---|
| 802 | for a representation and the generation of that entity-tag does not satisfy the requirements for a strong validator (<a href="#weak.and.strong.validators" title="Weak versus Strong">Section 2.1</a>), then that entity-tag <em class="bcp14">MUST</em> be marked as weak by prefixing its opaque value with "W/" (case-sensitive). |
|---|
| 803 | </p> |
|---|
| 804 | <h3 id="rfc.section.2.3.1"><a href="#rfc.section.2.3.1">2.3.1</a> <a id="entity.tag.generation" href="#entity.tag.generation">Generation</a></h3> |
|---|
| 805 | <p id="rfc.section.2.3.1.p.1">The principle behind entity-tags is that only the service author knows the implementation of a resource well enough to select |
|---|
| 806 | the most accurate and efficient validation mechanism for that resource, and that any such mechanism can be mapped to a simple |
|---|
| 807 | sequence of octets for easy comparison. Since the value is opaque, there is no need for the client to be aware of how each |
|---|
| 808 | entity-tag is constructed. |
|---|
| 809 | </p> |
|---|
| 810 | <p id="rfc.section.2.3.1.p.2">For example, a resource that has implementation-specific versioning applied to all changes might use an internal revision |
|---|
| 811 | number, perhaps combined with a variance identifier for content negotiation, to accurately differentiate between representations. |
|---|
| 812 | Other implementations might use a stored hash of representation content, a combination of various filesystem attributes, or |
|---|
| 813 | a modification timestamp that has sub-second resolution. |
|---|
| 814 | </p> |
|---|
| 815 | <p id="rfc.section.2.3.1.p.3">Origin servers <em class="bcp14">SHOULD</em> send ETag for any selected representation for which detection of changes can be reasonably and consistently determined, since |
|---|
| 816 | the entity-tag's use in conditional requests and evaluating cache freshness (<a href="#Part6" id="rfc.xref.Part6.3"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) can result in a substantial reduction of HTTP network traffic and can be a significant factor in improving service scalability |
|---|
| 817 | and reliability. |
|---|
| 818 | </p> |
|---|
| 819 | <h3 id="rfc.section.2.3.2"><a href="#rfc.section.2.3.2">2.3.2</a> <a id="entity.tag.comparison" href="#entity.tag.comparison">Comparison</a></h3> |
|---|
| 820 | <p id="rfc.section.2.3.2.p.1">There are two entity-tag comparison functions, depending on whether the comparison context allows the use of weak validators |
|---|
| 821 | or not: |
|---|
| 822 | </p> |
|---|
| 823 | <ul> |
|---|
| 824 | <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. |
|---|
| 825 | </li> |
|---|
| 826 | <li>The weak comparison function: in order to be considered equal, both opaque-tags <em class="bcp14">MUST</em> be identical character-by-character, but either or both of them <em class="bcp14">MAY</em> be tagged as "weak" without affecting the result. |
|---|
| 827 | </li> |
|---|
| 828 | </ul> |
|---|
| 829 | <p id="rfc.section.2.3.2.p.2">The example below shows the results for a set of entity-tag pairs, and both the weak and strong comparison function results:</p> |
|---|
| 830 | <div id="rfc.table.u.1"> |
|---|
| 831 | <table class="tt full left" cellpadding="3" cellspacing="0"> |
|---|
| 832 | <thead> |
|---|
| 833 | <tr> |
|---|
| 834 | <th>ETag 1</th> |
|---|
| 835 | <th>ETag 2</th> |
|---|
| 836 | <th>Strong Comparison</th> |
|---|
| 837 | <th>Weak Comparison</th> |
|---|
| 838 | </tr> |
|---|
| 839 | </thead> |
|---|
| 840 | <tbody> |
|---|
| 841 | <tr> |
|---|
| 842 | <td class="left">W/"1"</td> |
|---|
| 843 | <td class="left">W/"1"</td> |
|---|
| 844 | <td class="left">no match</td> |
|---|
| 845 | <td class="left">match</td> |
|---|
| 846 | </tr> |
|---|
| 847 | <tr> |
|---|
| 848 | <td class="left">W/"1"</td> |
|---|
| 849 | <td class="left">W/"2"</td> |
|---|
| 850 | <td class="left">no match</td> |
|---|
| 851 | <td class="left">no match</td> |
|---|
| 852 | </tr> |
|---|
| 853 | <tr> |
|---|
| 854 | <td class="left">W/"1"</td> |
|---|
| 855 | <td class="left">"1"</td> |
|---|
| 856 | <td class="left">no match</td> |
|---|
| 857 | <td class="left">match</td> |
|---|
| 858 | </tr> |
|---|
| 859 | <tr> |
|---|
| 860 | <td class="left">"1"</td> |
|---|
| 861 | <td class="left">"1"</td> |
|---|
| 862 | <td class="left">match</td> |
|---|
| 863 | <td class="left">match</td> |
|---|
| 864 | </tr> |
|---|
| 865 | </tbody> |
|---|
| 866 | </table> |
|---|
| 867 | </div> |
|---|
| 868 | <h3 id="rfc.section.2.3.3"><a href="#rfc.section.2.3.3">2.3.3</a> <a id="example.entity.tag.vs.conneg" href="#example.entity.tag.vs.conneg">Example: Entity-tags varying on Content-Negotiated Resources</a></h3> |
|---|
| 869 | <p id="rfc.section.2.3.3.p.1">Consider a resource that is subject to content negotiation (<a href="p3-payload.html#content.negotiation" title="Content Negotiation">Section 5</a> of <a href="#Part3" id="rfc.xref.Part3.1"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>), and where the representations returned upon a GET request vary based on the Accept-Encoding request header field (<a href="p3-payload.html#header.accept-encoding" title="Accept-Encoding">Section 6.3</a> of <a href="#Part3" id="rfc.xref.Part3.2"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>): |
|---|
| 870 | </p> |
|---|
| 871 | <div id="rfc.figure.u.6"></div> |
|---|
| 872 | <p>>> Request:</p><pre class="text2">GET /index HTTP/1.1 |
|---|
| 873 | Host: www.example.com |
|---|
| 874 | Accept-Encoding: gzip |
|---|
| 875 | |
|---|
| 876 | </pre><p id="rfc.section.2.3.3.p.3">In this case, the response might or might not use the gzip content coding. If it does not, the response might look like:</p> |
|---|
| 877 | <div id="rfc.figure.u.7"></div> |
|---|
| 878 | <p>>> Response:</p><pre class="text">HTTP/1.1 200 OK |
|---|
| 879 | Date: Thu, 26 Mar 2010 00:05:00 GMT |
|---|
| 880 | ETag: "123-a" |
|---|
| 881 | Content-Length: 70 |
|---|
| 882 | Vary: Accept-Encoding |
|---|
| 883 | Content-Type: text/plain |
|---|
| 884 | |
|---|
| 885 | <span id="exbody">Hello World! |
|---|
| 886 | Hello World! |
|---|
| 887 | Hello World! |
|---|
| 888 | Hello World! |
|---|
| 889 | Hello World! |
|---|
| 890 | </span></pre><p id="rfc.section.2.3.3.p.5">An alternative representation that does use gzip content coding would be:</p> |
|---|
| 891 | <div id="rfc.figure.u.8"></div> |
|---|
| 892 | <p>>> Response:</p><pre class="text">HTTP/1.1 200 OK |
|---|
| 893 | Date: Thu, 26 Mar 2010 00:05:00 GMT |
|---|
| 894 | ETag: "123-b" |
|---|
| 895 | Content-Length: 43 |
|---|
| 896 | Vary: Accept-Encoding |
|---|
| 897 | Content-Type: text/plain |
|---|
| 898 | Content-Encoding: gzip |
|---|
| 899 | |
|---|
| 900 | <em>...binary data...</em></pre><div class="note" id="rfc.section.2.3.3.p.7"> |
|---|
| 901 | <p> <b>Note:</b> Content codings are a property of the representation, so therefore an entity-tag of an encoded representation must be distinct |
|---|
| 902 | from an unencoded representation to prevent conflicts during cache updates and range requests. In contrast, transfer codings |
|---|
| 903 | (<a href="p1-messaging.html#transfer.codings" title="Transfer Codings">Section 5.1</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>) apply only during message transfer and do not require distinct entity-tags. |
|---|
| 904 | </p> |
|---|
| 905 | </div> |
|---|
| 906 | <h2 id="rfc.section.2.4"><a href="#rfc.section.2.4">2.4</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></h2> |
|---|
| 907 | <p id="rfc.section.2.4.p.1">We adopt a set of rules and recommendations for origin servers, clients, and caches regarding when various validator types |
|---|
| 908 | ought to be used, and for what purposes. |
|---|
| 909 | </p> |
|---|
| 910 | <p id="rfc.section.2.4.p.2">HTTP/1.1 origin servers: </p> |
|---|
| 911 | <ul> |
|---|
| 912 | <li><em class="bcp14">SHOULD</em> send an entity-tag validator unless it is not feasible to generate one. |
|---|
| 913 | </li> |
|---|
| 914 | <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, |
|---|
| 915 | or if it is unfeasible to send a strong entity-tag. |
|---|
| 916 | </li> |
|---|
| 917 | <li><em class="bcp14">SHOULD</em> send a Last-Modified value if it is feasible to send one. |
|---|
| 918 | </li> |
|---|
| 919 | </ul> |
|---|
| 920 | <p id="rfc.section.2.4.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 |
|---|
| 921 | value. |
|---|
| 922 | </p> |
|---|
| 923 | <p id="rfc.section.2.4.p.4">HTTP/1.1 clients: </p> |
|---|
| 924 | <ul> |
|---|
| 925 | <li><em class="bcp14">MUST</em> use that entity-tag in any cache-conditional request (using If-Match or If-None-Match) if an entity-tag has been provided |
|---|
| 926 | by the origin server. |
|---|
| 927 | </li> |
|---|
| 928 | <li><em class="bcp14">SHOULD</em> use the Last-Modified value in non-subrange cache-conditional requests (using If-Modified-Since) if only a Last-Modified value |
|---|
| 929 | has been provided by the origin server. |
|---|
| 930 | </li> |
|---|
| 931 | <li><em class="bcp14">MAY</em> use the Last-Modified value in subrange cache-conditional requests (using If-Unmodified-Since) if only a Last-Modified value |
|---|
| 932 | has been provided by an HTTP/1.0 origin server. The user agent <em class="bcp14">SHOULD</em> provide a way to disable this, in case of difficulty. |
|---|
| 933 | </li> |
|---|
| 934 | <li><em class="bcp14">SHOULD</em> use both validators in cache-conditional requests if both an entity-tag and a Last-Modified value have been provided by the |
|---|
| 935 | origin server. This allows both HTTP/1.0 and HTTP/1.1 caches to respond appropriately. |
|---|
| 936 | </li> |
|---|
| 937 | </ul> |
|---|
| 938 | <p id="rfc.section.2.4.p.5">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 |
|---|
| 939 | 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 |
|---|
| 940 | field) as cache validators, <em class="bcp14">MUST NOT</em> return a response status code of 304 (Not Modified) unless doing so is consistent with all of the conditional header fields |
|---|
| 941 | in the request. |
|---|
| 942 | </p> |
|---|
| 943 | <p id="rfc.section.2.4.p.6">An HTTP/1.1 caching proxy, upon receiving a conditional request that includes both a Last-Modified date and one or more entity-tags |
|---|
| 944 | 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 |
|---|
| 945 | fields in the request. |
|---|
| 946 | </p> |
|---|
| 947 | <ul class="empty"> |
|---|
| 948 | <li> <b>Note:</b> The general principle behind these rules is that HTTP/1.1 servers and clients ought to transmit as much non-redundant information |
|---|
| 949 | as is available in their responses and requests. HTTP/1.1 systems receiving this information will make the most conservative |
|---|
| 950 | assumptions about the validators they receive. |
|---|
| 951 | </li> |
|---|
| 952 | <li>HTTP/1.0 clients and caches might ignore entity-tags. Generally, last-modified values received or used by these systems will |
|---|
| 953 | support transparent and efficient caching, and so HTTP/1.1 origin servers should provide Last-Modified values. In those rare |
|---|
| 954 | 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 |
|---|
| 955 | HTTP/1.1 origin servers should not provide one. |
|---|
| 956 | </li> |
|---|
| 957 | </ul> |
|---|
| 958 | <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a> <a id="header.field.definitions" href="#header.field.definitions">Precondition Header Fields</a></h1> |
|---|
| 959 | <p id="rfc.section.3.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields for applying preconditions on requests.</p> |
|---|
| 960 | <div id="rfc.iref.i.1"></div> |
|---|
| 961 | <div id="rfc.iref.h.3"></div> |
|---|
| 962 | <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a> <a id="header.if-match" href="#header.if-match">If-Match</a></h2> |
|---|
| 963 | <p id="rfc.section.3.1.p.1">The "If-Match" header field <em class="bcp14">MAY</em> be used to make a request method conditional on the current existence or value of an entity-tag for one or more representations |
|---|
| 964 | of the target resource. If-Match is generally useful for resource update requests, such as PUT requests, as a means for protecting |
|---|
| 965 | against accidental overwrites when multiple clients are acting in parallel on the same resource (i.e., the "lost update" problem). |
|---|
| 966 | An If-Match field-value of "*" places the precondition on the existence of any current representation for the target resource. |
|---|
| 967 | </p> |
|---|
| 968 | <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.7"></span> <a href="#header.if-match" class="smpl">If-Match</a> = "*" / 1#<a href="#header.etag" class="smpl">entity-tag</a> |
|---|
| 969 | </pre><p id="rfc.section.3.1.p.3">If any of the entity-tags listed in the If-Match field value match (as per <a href="#entity.tag.comparison" title="Comparison">Section 2.3.2</a>) the entity-tag of the selected representation for the target resource, or if "*" is given and any current representation |
|---|
| 970 | exists for the target resource, then the server <em class="bcp14">MAY</em> perform the request method as if the If-Match header field was not present. |
|---|
| 971 | </p> |
|---|
| 972 | <p id="rfc.section.3.1.p.4">If none of the entity-tags match, or if "*" is given and no current representation exists, the server <em class="bcp14">MUST NOT</em> perform the requested method. Instead, the server <em class="bcp14">MUST</em> respond with the 412 (Precondition Failed) status code. |
|---|
| 973 | </p> |
|---|
| 974 | <p id="rfc.section.3.1.p.5">If the request would, without the If-Match header field, result in anything other than a 2xx or 412 status code, then the |
|---|
| 975 | If-Match header field <em class="bcp14">MUST</em> be ignored. |
|---|
| 976 | </p> |
|---|
| 977 | <p id="rfc.section.3.1.p.6">Examples:</p> |
|---|
| 978 | <div id="rfc.figure.u.10"></div><pre class="text"> If-Match: "xyzzy" |
|---|
| 979 | If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz" |
|---|
| 980 | If-Match: * |
|---|
| 981 | </pre><p id="rfc.section.3.1.p.8">The result of a request having both an If-Match header field and either an If-None-Match or an If-Modified-Since header field |
|---|
| 982 | is undefined by this specification. |
|---|
| 983 | </p> |
|---|
| 984 | <div id="rfc.iref.i.2"></div> |
|---|
| 985 | <div id="rfc.iref.h.4"></div> |
|---|
| 986 | <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a> <a id="header.if-none-match" href="#header.if-none-match">If-None-Match</a></h2> |
|---|
| 987 | <p id="rfc.section.3.2.p.1">The "If-None-Match" header field <em class="bcp14">MAY</em> be used to make a request method conditional on not matching any of the current entity-tag values for representations of the |
|---|
| 988 | target resource. If-None-Match is primarily used in conditional GET requests to enable efficient updates of cached information |
|---|
| 989 | with a minimum amount of transaction overhead. A client that has one or more representations previously obtained from the |
|---|
| 990 | target resource can send If-None-Match with a list of the associated entity-tags in the hope of receiving a 304 response if |
|---|
| 991 | at least one of those representations matches the selected representation. |
|---|
| 992 | </p> |
|---|
| 993 | <p id="rfc.section.3.2.p.2">If-None-Match MAY also be used with a value of "*" to prevent an unsafe request method (e.g., PUT) from inadvertently modifying |
|---|
| 994 | an existing representation of the target resource when the client believes that the resource does not have a current representation. |
|---|
| 995 | This is a variation on the "lost update" problem that might arise if more than one client attempts to create an initial representation |
|---|
| 996 | for the target resource. |
|---|
| 997 | </p> |
|---|
| 998 | <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.8"></span> <a href="#header.if-none-match" class="smpl">If-None-Match</a> = "*" / 1#<a href="#header.etag" class="smpl">entity-tag</a> |
|---|
| 999 | </pre><p id="rfc.section.3.2.p.4">If any of the entity-tags listed in the If-None-Match field-value match (as per <a href="#entity.tag.comparison" title="Comparison">Section 2.3.2</a>) the entity-tag of the selected representation, or if "*" is given and any current representation exists for that resource, |
|---|
| 1000 | then the server <em class="bcp14">MUST NOT</em> perform the requested method. Instead, if the request method was GET or HEAD, the server <em class="bcp14">SHOULD</em> respond with a 304 (Not Modified) status code, including the cache-related header fields (particularly ETag) of the selected |
|---|
| 1001 | representation that has a matching entity-tag. For all other request methods, the server <em class="bcp14">MUST</em> respond with a 412 (Precondition Failed) status code. |
|---|
| 1002 | </p> |
|---|
| 1003 | <p id="rfc.section.3.2.p.5">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. |
|---|
| 1004 | </p> |
|---|
| 1005 | <p id="rfc.section.3.2.p.6">If the request would, without the If-None-Match header field, result in anything other than a 2xx or 304 status code, then |
|---|
| 1006 | the If-None-Match header field <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 2.4</a> for a discussion of server behavior when both If-Modified-Since and If-None-Match appear in the same request.) |
|---|
| 1007 | </p> |
|---|
| 1008 | <p id="rfc.section.3.2.p.7">Examples:</p> |
|---|
| 1009 | <div id="rfc.figure.u.12"></div><pre class="text"> If-None-Match: "xyzzy" |
|---|
| 1010 | If-None-Match: W/"xyzzy" |
|---|
| 1011 | If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz" |
|---|
| 1012 | If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz" |
|---|
| 1013 | If-None-Match: * |
|---|
| 1014 | </pre><p id="rfc.section.3.2.p.9">The result of a request having both an If-None-Match header field and either an If-Match or an If-Unmodified-Since header |
|---|
| 1015 | field is undefined by this specification. |
|---|
| 1016 | </p> |
|---|
| 1017 | <div id="rfc.iref.i.3"></div> |
|---|
| 1018 | <div id="rfc.iref.h.5"></div> |
|---|
| 1019 | <h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a> <a id="header.if-modified-since" href="#header.if-modified-since">If-Modified-Since</a></h2> |
|---|
| 1020 | <p id="rfc.section.3.3.p.1">The "If-Modified-Since" header field <em class="bcp14">MAY</em> be used to make a request method conditional by modification date: if the selected representation has not been modified since |
|---|
| 1021 | the time specified in this field, then do not perform the request method; instead, respond as detailed below. |
|---|
| 1022 | </p> |
|---|
| 1023 | <div id="rfc.figure.u.13"></div><pre class="inline"><span id="rfc.iref.g.9"></span> <a href="#header.if-modified-since" class="smpl">If-Modified-Since</a> = <a href="#notation" class="smpl">HTTP-date</a> |
|---|
| 1024 | </pre><p id="rfc.section.3.3.p.3">An example of the field is:</p> |
|---|
| 1025 | <div id="rfc.figure.u.14"></div><pre class="text"> If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT |
|---|
| 1026 | </pre><p id="rfc.section.3.3.p.5">A GET method with an If-Modified-Since header field and no Range header field requests that the selected representation be |
|---|
| 1027 | transferred only if it has been modified since the date given by the If-Modified-Since header field. The algorithm for determining |
|---|
| 1028 | this includes the following cases: |
|---|
| 1029 | </p> |
|---|
| 1030 | <ol> |
|---|
| 1031 | <li>If the request would normally result in anything other than a 200 (OK) status code, or if the passed If-Modified-Since date |
|---|
| 1032 | is invalid, the response is exactly the same as for a normal GET. A date which is later than the server's current time is |
|---|
| 1033 | invalid. |
|---|
| 1034 | </li> |
|---|
| 1035 | <li>If the selected representation has been modified since the If-Modified-Since date, the response is exactly the same as for |
|---|
| 1036 | a normal GET. |
|---|
| 1037 | </li> |
|---|
| 1038 | <li>If the selected representation has not been modified since a valid If-Modified-Since date, the server <em class="bcp14">SHOULD</em> return a 304 (Not Modified) response. |
|---|
| 1039 | </li> |
|---|
| 1040 | </ol> |
|---|
| 1041 | <p id="rfc.section.3.3.p.6">The purpose of this feature is to allow efficient updates of cached information with a minimum amount of transaction overhead. </p> |
|---|
| 1042 | <ul class="empty"> |
|---|
| 1043 | <li> <b>Note:</b> The Range 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.Part5.1"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a> for full details. |
|---|
| 1044 | </li> |
|---|
| 1045 | <li> <b>Note:</b> If-Modified-Since times are interpreted by the server, whose clock might not be synchronized with the client. |
|---|
| 1046 | </li> |
|---|
| 1047 | <li> <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 |
|---|
| 1048 | function, for deciding whether to send a 304 (Not Modified) response. To get best results when sending an If-Modified-Since |
|---|
| 1049 | header field for cache validation, clients are advised to use the exact date string received in a previous Last-Modified header |
|---|
| 1050 | field whenever possible. |
|---|
| 1051 | </li> |
|---|
| 1052 | <li> <b>Note:</b> If a client uses an arbitrary date in the If-Modified-Since header field instead of a date taken from the Last-Modified header |
|---|
| 1053 | field for the same request, the client needs to be aware that this date is interpreted in the server's understanding of time. |
|---|
| 1054 | Unsynchronized clocks and rounding problems, due to the different encodings of time between the client and server, are concerns. |
|---|
| 1055 | This includes the possibility of race conditions if the document has changed between the time it was first requested and the |
|---|
| 1056 | If-Modified-Since date of a subsequent request, and the possibility of clock-skew-related problems if the If-Modified-Since |
|---|
| 1057 | date is derived from the client's clock without correction to the server's clock. Corrections for different time bases between |
|---|
| 1058 | client and server are at best approximate due to network latency. |
|---|
| 1059 | </li> |
|---|
| 1060 | </ul> |
|---|
| 1061 | <p id="rfc.section.3.3.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 |
|---|
| 1062 | field is undefined by this specification. |
|---|
| 1063 | </p> |
|---|
| 1064 | <div id="rfc.iref.i.4"></div> |
|---|
| 1065 | <div id="rfc.iref.h.6"></div> |
|---|
| 1066 | <h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a> <a id="header.if-unmodified-since" href="#header.if-unmodified-since">If-Unmodified-Since</a></h2> |
|---|
| 1067 | <p id="rfc.section.3.4.p.1">The "If-Unmodified-Since" header field <em class="bcp14">MAY</em> be used to make a request method conditional by modification date: if the selected representation has been modified since |
|---|
| 1068 | the time specified in this field, then the server <em class="bcp14">MUST NOT</em> perform the requested operation and <em class="bcp14">MUST</em> instead respond with the 412 (Precondition Failed) status code. If the selected representation has not been modified since |
|---|
| 1069 | the time specified in this field, the server <em class="bcp14">SHOULD</em> perform the request method as if the If-Unmodified-Since header field were not present. |
|---|
| 1070 | </p> |
|---|
| 1071 | <div id="rfc.figure.u.15"></div><pre class="inline"><span id="rfc.iref.g.10"></span> <a href="#header.if-unmodified-since" class="smpl">If-Unmodified-Since</a> = <a href="#notation" class="smpl">HTTP-date</a> |
|---|
| 1072 | </pre><p id="rfc.section.3.4.p.3">An example of the field is:</p> |
|---|
| 1073 | <div id="rfc.figure.u.16"></div><pre class="text"> If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT |
|---|
| 1074 | </pre><p id="rfc.section.3.4.p.5">If the request normally (i.e., without the If-Unmodified-Since header field) would result in anything other than a 2xx or |
|---|
| 1075 | 412 status code, the If-Unmodified-Since header field <em class="bcp14">SHOULD</em> be ignored. |
|---|
| 1076 | </p> |
|---|
| 1077 | <p id="rfc.section.3.4.p.6">If the specified date is invalid, the header field <em class="bcp14">MUST</em> be ignored. |
|---|
| 1078 | </p> |
|---|
| 1079 | <p id="rfc.section.3.4.p.7">The result of a request having both an If-Unmodified-Since header field and either an If-None-Match or an If-Modified-Since |
|---|
| 1080 | header field is undefined by this specification. |
|---|
| 1081 | </p> |
|---|
| 1082 | <h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a> <a id="header.if-range" href="#header.if-range">If-Range</a></h2> |
|---|
| 1083 | <p id="rfc.section.3.5.p.1">The If-Range header field provides a special conditional request mechanism that is similar to If-Match and If-Unmodified-Since |
|---|
| 1084 | but specific to HTTP range requests. If-Range is defined in <a href="p5-range.html#header.if-range" title="If-Range">Section 5.3</a> of <a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>. |
|---|
| 1085 | </p> |
|---|
| 1086 | <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a> <a id="status.code.definitions" href="#status.code.definitions">Status Code Definitions</a></h1> |
|---|
| 1087 | <div id="rfc.iref.27"></div> |
|---|
| 1088 | <div id="rfc.iref.s.2"></div> |
|---|
| 1089 | <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a> <a id="status.304" href="#status.304">304 Not Modified</a></h2> |
|---|
| 1090 | <p id="rfc.section.4.1.p.1">The 304 status code indicates that a conditional GET request has been received and would have resulted in a 200 (OK) response |
|---|
| 1091 | if it were not for the fact that the condition has evaluated to false. In other words, there is no need for the server to |
|---|
| 1092 | transfer a representation of the target resource because the client's request indicates that it already has a valid representation, |
|---|
| 1093 | as indicated by the 304 response header fields, and is therefore redirecting the client to make use of that stored representation |
|---|
| 1094 | as if it were the payload of a 200 response. 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. |
|---|
| 1095 | </p> |
|---|
| 1096 | <p id="rfc.section.4.1.p.2">A 304 response <em class="bcp14">MUST</em> include a Date header field (<a href="p2-semantics.html#header.date" title="Date">Section 9.2</a> of <a href="#Part2" id="rfc.xref.Part2.3"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) unless the origin server does not have a clock that can provide a reasonable approximation of the current time. If a 200 |
|---|
| 1097 | response to the same request would have included any of the header fields Cache-Control, Content-Location, ETag, Expires, |
|---|
| 1098 | Last-Modified, or Vary, then those same header fields <em class="bcp14">MUST</em> be sent in a 304 response. |
|---|
| 1099 | </p> |
|---|
| 1100 | <p id="rfc.section.4.1.p.3">Since the goal of a 304 response is to minimize information transfer when the recipient already has one or more cached representations, |
|---|
| 1101 | the response <em class="bcp14">SHOULD NOT</em> include representation metadata other than the above listed fields unless said metadata exists for the purpose of guiding |
|---|
| 1102 | cache updates (e.g., future HTTP extensions). |
|---|
| 1103 | </p> |
|---|
| 1104 | <p id="rfc.section.4.1.p.4">If the recipient of a 304 response does not have a cached representation corresponding to the entity-tag indicated by the |
|---|
| 1105 | 304 response, then the recipient <em class="bcp14">MUST NOT</em> use the 304 to update its own cache. If this conditional request originated with an outbound client, such as a user agent |
|---|
| 1106 | with its own cache sending a conditional GET to a shared proxy, then the 304 response <em class="bcp14">MAY</em> be forwarded to the outbound client. Otherwise, the recipient <em class="bcp14">MUST</em> disregard the 304 response and repeat the request without any preconditions. |
|---|
| 1107 | </p> |
|---|
| 1108 | <p id="rfc.section.4.1.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. |
|---|
| 1109 | </p> |
|---|
| 1110 | <div id="rfc.iref.28"></div> |
|---|
| 1111 | <div id="rfc.iref.s.3"></div> |
|---|
| 1112 | <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a> <a id="status.412" href="#status.412">412 Precondition Failed</a></h2> |
|---|
| 1113 | <p id="rfc.section.4.2.p.1">The 412 status code indicates that one or more preconditions given in the request header fields evaluated to false when tested |
|---|
| 1114 | on the server. This response code allows the client to place preconditions on the current resource state (its current representations |
|---|
| 1115 | and metadata) and thus prevent the request method from being applied if the target resource is in an unexpected state. |
|---|
| 1116 | </p> |
|---|
| 1117 | <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a> <a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1> |
|---|
| 1118 | <h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a> <a id="status.code.registration" href="#status.code.registration">Status Code Registration</a></h2> |
|---|
| 1119 | <p id="rfc.section.5.1.p.1">The HTTP Status Code Registry located at <<a href="http://www.iana.org/assignments/http-status-codes">http://www.iana.org/assignments/http-status-codes</a>> shall be updated with the registrations below: |
|---|
| 1120 | </p> |
|---|
| 1121 | <div id="rfc.table.1"> |
|---|
| 1122 | <div id="iana.status.code.registration.table"></div> |
|---|
| 1123 | <table class="tt full left" cellpadding="3" cellspacing="0"> |
|---|
| 1124 | <thead> |
|---|
| 1125 | <tr> |
|---|
| 1126 | <th>Value</th> |
|---|
| 1127 | <th>Description</th> |
|---|
| 1128 | <th>Reference</th> |
|---|
| 1129 | </tr> |
|---|
| 1130 | </thead> |
|---|
| 1131 | <tbody> |
|---|
| 1132 | <tr> |
|---|
| 1133 | <td class="left">304</td> |
|---|
| 1134 | <td class="left">Not Modified</td> |
|---|
| 1135 | <td class="left"> <a href="#status.304" id="rfc.xref.status.304.1" title="304 Not Modified">Section 4.1</a> |
|---|
| 1136 | </td> |
|---|
| 1137 | </tr> |
|---|
| 1138 | <tr> |
|---|
| 1139 | <td class="left">412</td> |
|---|
| 1140 | <td class="left">Precondition Failed</td> |
|---|
| 1141 | <td class="left"> <a href="#status.412" id="rfc.xref.status.412.1" title="412 Precondition Failed">Section 4.2</a> |
|---|
| 1142 | </td> |
|---|
| 1143 | </tr> |
|---|
| 1144 | </tbody> |
|---|
| 1145 | </table> |
|---|
| 1146 | </div> |
|---|
| 1147 | <h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a> <a id="header.field.registration" href="#header.field.registration">Header Field Registration</a></h2> |
|---|
| 1148 | <p id="rfc.section.5.2.p.1">The Message Header Field 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>> shall 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>): |
|---|
| 1149 | </p> |
|---|
| 1150 | <div id="rfc.table.2"> |
|---|
| 1151 | <div id="iana.header.registration.table"></div> |
|---|
| 1152 | <table class="tt full left" cellpadding="3" cellspacing="0"> |
|---|
| 1153 | <thead> |
|---|
| 1154 | <tr> |
|---|
| 1155 | <th>Header Field Name</th> |
|---|
| 1156 | <th>Protocol</th> |
|---|
| 1157 | <th>Status</th> |
|---|
| 1158 | <th>Reference</th> |
|---|
| 1159 | </tr> |
|---|
| 1160 | </thead> |
|---|
| 1161 | <tbody> |
|---|
| 1162 | <tr> |
|---|
| 1163 | <td class="left">ETag</td> |
|---|
| 1164 | <td class="left">http</td> |
|---|
| 1165 | <td class="left">standard</td> |
|---|
| 1166 | <td class="left"> <a href="#header.etag" id="rfc.xref.header.etag.1" title="ETag">Section 2.3</a> |
|---|
| 1167 | </td> |
|---|
| 1168 | </tr> |
|---|
| 1169 | <tr> |
|---|
| 1170 | <td class="left">If-Match</td> |
|---|
| 1171 | <td class="left">http</td> |
|---|
| 1172 | <td class="left">standard</td> |
|---|
| 1173 | <td class="left"> <a href="#header.if-match" id="rfc.xref.header.if-match.1" title="If-Match">Section 3.1</a> |
|---|
| 1174 | </td> |
|---|
| 1175 | </tr> |
|---|
| 1176 | <tr> |
|---|
| 1177 | <td class="left">If-Modified-Since</td> |
|---|
| 1178 | <td class="left">http</td> |
|---|
| 1179 | <td class="left">standard</td> |
|---|
| 1180 | <td class="left"> <a href="#header.if-modified-since" id="rfc.xref.header.if-modified-since.1" title="If-Modified-Since">Section 3.3</a> |
|---|
| 1181 | </td> |
|---|
| 1182 | </tr> |
|---|
| 1183 | <tr> |
|---|
| 1184 | <td class="left">If-None-Match</td> |
|---|
| 1185 | <td class="left">http</td> |
|---|
| 1186 | <td class="left">standard</td> |
|---|
| 1187 | <td class="left"> <a href="#header.if-none-match" id="rfc.xref.header.if-none-match.1" title="If-None-Match">Section 3.2</a> |
|---|
| 1188 | </td> |
|---|
| 1189 | </tr> |
|---|
| 1190 | <tr> |
|---|
| 1191 | <td class="left">If-Unmodified-Since</td> |
|---|
| 1192 | <td class="left">http</td> |
|---|
| 1193 | <td class="left">standard</td> |
|---|
| 1194 | <td class="left"> <a href="#header.if-unmodified-since" id="rfc.xref.header.if-unmodified-since.1" title="If-Unmodified-Since">Section 3.4</a> |
|---|
| 1195 | </td> |
|---|
| 1196 | </tr> |
|---|
| 1197 | <tr> |
|---|
| 1198 | <td class="left">Last-Modified</td> |
|---|
| 1199 | <td class="left">http</td> |
|---|
| 1200 | <td class="left">standard</td> |
|---|
| 1201 | <td class="left"> <a href="#header.last-modified" id="rfc.xref.header.last-modified.1" title="Last-Modified">Section 2.2</a> |
|---|
| 1202 | </td> |
|---|
| 1203 | </tr> |
|---|
| 1204 | </tbody> |
|---|
| 1205 | </table> |
|---|
| 1206 | </div> |
|---|
| 1207 | <p id="rfc.section.5.2.p.2">The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p> |
|---|
| 1208 | <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a> <a id="security.considerations" href="#security.considerations">Security Considerations</a></h1> |
|---|
| 1209 | <p id="rfc.section.6.p.1">No additional security considerations have been identified beyond those applicable to HTTP in general <a href="#Part1" id="rfc.xref.Part1.7"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. |
|---|
| 1210 | </p> |
|---|
| 1211 | <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a> <a id="acks" href="#acks">Acknowledgments</a></h1> |
|---|
| 1212 | <p id="rfc.section.7.p.1">See <a href="p1-messaging.html#acks" title="Acknowledgments">Section 11</a> of <a href="#Part1" id="rfc.xref.Part1.8"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. |
|---|
| 1213 | </p> |
|---|
| 1214 | <h1 id="rfc.references"><a id="rfc.section.8" href="#rfc.section.8">8.</a> References |
|---|
| 1215 | </h1> |
|---|
| 1216 | <h2 id="rfc.references.1"><a href="#rfc.section.8.1" id="rfc.section.8.1">8.1</a> Normative References |
|---|
| 1217 | </h2> |
|---|
| 1218 | <table> |
|---|
| 1219 | <tr> |
|---|
| 1220 | <td class="reference"><b id="Part1">[Part1]</b></td> |
|---|
| 1221 | <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a>, <a href="mailto:jg@freedesktop.org" title="Alcatel-Lucent Bell Labs">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-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), January 2012. |
|---|
| 1222 | </td> |
|---|
| 1223 | </tr> |
|---|
| 1224 | <tr> |
|---|
| 1225 | <td class="reference"><b id="Part2">[Part2]</b></td> |
|---|
| 1226 | <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a>, <a href="mailto:jg@freedesktop.org" title="Alcatel-Lucent Bell Labs">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p2-semantics-latest">HTTP/1.1, part 2: Message Semantics</a>”, Internet-Draft draft-ietf-httpbis-p2-semantics-latest (work in progress), January 2012. |
|---|
| 1227 | </td> |
|---|
| 1228 | </tr> |
|---|
| 1229 | <tr> |
|---|
| 1230 | <td class="reference"><b id="Part3">[Part3]</b></td> |
|---|
| 1231 | <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a>, <a href="mailto:jg@freedesktop.org" title="Alcatel-Lucent Bell Labs">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p3-payload-latest">HTTP/1.1, part 3: Message Payload and Content Negotiation</a>”, Internet-Draft draft-ietf-httpbis-p3-payload-latest (work in progress), January 2012. |
|---|
| 1232 | </td> |
|---|
| 1233 | </tr> |
|---|
| 1234 | <tr> |
|---|
| 1235 | <td class="reference"><b id="Part5">[Part5]</b></td> |
|---|
| 1236 | <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a>, <a href="mailto:jg@freedesktop.org" title="Alcatel-Lucent Bell Labs">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p5-range-latest">HTTP/1.1, part 5: Range Requests and Partial Responses</a>”, Internet-Draft draft-ietf-httpbis-p5-range-latest (work in progress), January 2012. |
|---|
| 1237 | </td> |
|---|
| 1238 | </tr> |
|---|
| 1239 | <tr> |
|---|
| 1240 | <td class="reference"><b id="Part6">[Part6]</b></td> |
|---|
| 1241 | <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a>, <a href="mailto:jg@freedesktop.org" title="Alcatel-Lucent Bell Labs">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">Berners-Lee, T.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, <a href="mailto:mnot@mnot.net" title="Rackspace">Nottingham, M., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-latest">HTTP/1.1, part 6: Caching</a>”, Internet-Draft draft-ietf-httpbis-p6-cache-latest (work in progress), January 2012. |
|---|
| 1242 | </td> |
|---|
| 1243 | </tr> |
|---|
| 1244 | <tr> |
|---|
| 1245 | <td class="reference"><b id="RFC2119">[RFC2119]</b></td> |
|---|
| 1246 | <td class="top"><a href="mailto:sob@harvard.edu" title="Harvard University">Bradner, S.</a>, “<a href="http://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>”, BCP 14, RFC 2119, March 1997. |
|---|
| 1247 | </td> |
|---|
| 1248 | </tr> |
|---|
| 1249 | <tr> |
|---|
| 1250 | <td class="reference"><b id="RFC5234">[RFC5234]</b></td> |
|---|
| 1251 | <td class="top"><a href="mailto:dcrocker@bbiw.net" title="Brandenburg InternetWorking">Crocker, D., Ed.</a> and <a href="mailto:paul.overell@thus.net" 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. |
|---|
| 1252 | </td> |
|---|
| 1253 | </tr> |
|---|
| 1254 | </table> |
|---|
| 1255 | <h2 id="rfc.references.2"><a href="#rfc.section.8.2" id="rfc.section.8.2">8.2</a> Informative References |
|---|
| 1256 | </h2> |
|---|
| 1257 | <table> |
|---|
| 1258 | <tr> |
|---|
| 1259 | <td class="reference"><b id="RFC2616">[RFC2616]</b></td> |
|---|
| 1260 | <td class="top"><a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="W3C">Gettys, J.</a>, <a href="mailto:mogul@wrl.dec.com" title="Compaq Computer Corporation">Mogul, J.</a>, <a href="mailto:frystyk@w3.org" title="MIT Laboratory for Computer Science">Frystyk, H.</a>, <a href="mailto:masinter@parc.xerox.com" title="Xerox Corporation">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, and <a href="mailto:timbl@w3.org" title="W3C">T. Berners-Lee</a>, “<a href="http://tools.ietf.org/html/rfc2616">Hypertext Transfer Protocol -- HTTP/1.1</a>”, RFC 2616, June 1999. |
|---|
| 1261 | </td> |
|---|
| 1262 | </tr> |
|---|
| 1263 | <tr> |
|---|
| 1264 | <td class="reference"><b id="RFC3864">[RFC3864]</b></td> |
|---|
| 1265 | <td class="top"><a href="mailto:GK-IETF@ninebynine.org" title="Nine by Nine">Klyne, G.</a>, <a href="mailto:mnot@pobox.com" title="BEA Systems">Nottingham, M.</a>, and <a href="mailto:JeffMogul@acm.org" title="HP Labs">J. Mogul</a>, “<a href="http://tools.ietf.org/html/rfc3864">Registration Procedures for Message Header Fields</a>”, BCP 90, RFC 3864, September 2004. |
|---|
| 1266 | </td> |
|---|
| 1267 | </tr> |
|---|
| 1268 | <tr> |
|---|
| 1269 | <td class="reference"><b id="RFC4918">[RFC4918]</b></td> |
|---|
| 1270 | <td class="top"><a href="mailto:ldusseault@commerce.net" title="CommerceNet">Dusseault, L., Ed.</a>, “<a href="http://tools.ietf.org/html/rfc4918">HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)</a>”, RFC 4918, June 2007. |
|---|
| 1271 | </td> |
|---|
| 1272 | </tr> |
|---|
| 1273 | </table> |
|---|
| 1274 | <div class="avoidbreak"> |
|---|
| 1275 | <h1 id="rfc.authors"><a href="#rfc.authors">Authors' Addresses</a></h1> |
|---|
| 1276 | <address class="vcard"><span class="vcardline"><span class="fn">Roy T. Fielding</span> |
|---|
| 1277 | (editor) |
|---|
| 1278 | <span class="n hidden"><span class="family-name">Fielding</span><span class="given-name">Roy T.</span></span></span><span class="org vcardline">Adobe Systems Incorporated</span><span class="adr"><span class="street-address vcardline">345 Park Ave</span><span class="vcardline"><span class="locality">San Jose</span>, <span class="region">CA</span> <span class="postal-code">95110</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">Email: <a href="mailto:fielding@gbiv.com"><span class="email">fielding@gbiv.com</span></a></span><span class="vcardline">URI: <a href="http://roy.gbiv.com/" class="url">http://roy.gbiv.com/</a></span></address> |
|---|
| 1279 | <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">Alcatel-Lucent Bell Labs</span><span class="adr"><span class="street-address vcardline">21 Oak Knoll Road</span><span class="vcardline"><span class="locality">Carlisle</span>, <span class="region">MA</span> <span class="postal-code">01741</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">Email: <a href="mailto:jg@freedesktop.org"><span class="email">jg@freedesktop.org</span></a></span><span class="vcardline">URI: <a href="http://gettys.wordpress.com/" class="url">http://gettys.wordpress.com/</a></span></address> |
|---|
| 1280 | <address class="vcard"><span class="vcardline"><span class="fn">Jeffrey C. Mogul</span><span class="n hidden"><span class="family-name">Mogul</span><span class="given-name">Jeffrey C.</span></span></span><span class="org vcardline">Hewlett-Packard Company</span><span class="adr"><span class="street-address vcardline">HP Labs, Large Scale Systems Group</span><span class="street-address vcardline">1501 Page Mill Road, MS 1177</span><span class="vcardline"><span class="locality">Palo Alto</span>, <span class="region">CA</span> <span class="postal-code">94304</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">Email: <a href="mailto:JeffMogul@acm.org"><span class="email">JeffMogul@acm.org</span></a></span></address> |
|---|
| 1281 | <address class="vcard"><span class="vcardline"><span class="fn">Henrik Frystyk Nielsen</span><span class="n hidden"><span class="family-name">Frystyk</span></span></span><span class="org vcardline">Microsoft Corporation</span><span class="adr"><span class="street-address vcardline">1 Microsoft Way</span><span class="vcardline"><span class="locality">Redmond</span>, <span class="region">WA</span> <span class="postal-code">98052</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">Email: <a href="mailto:henrikn@microsoft.com"><span class="email">henrikn@microsoft.com</span></a></span></address> |
|---|
| 1282 | <address class="vcard"><span class="vcardline"><span class="fn">Larry Masinter</span><span class="n hidden"><span class="family-name">Masinter</span><span class="given-name">Larry</span></span></span><span class="org vcardline">Adobe Systems Incorporated</span><span class="adr"><span class="street-address vcardline">345 Park Ave</span><span class="vcardline"><span class="locality">San Jose</span>, <span class="region">CA</span> <span class="postal-code">95110</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">Email: <a href="mailto:LMM@acm.org"><span class="email">LMM@acm.org</span></a></span><span class="vcardline">URI: <a href="http://larry.masinter.net/" class="url">http://larry.masinter.net/</a></span></address> |
|---|
| 1283 | <address class="vcard"><span class="vcardline"><span class="fn">Paul J. Leach</span><span class="n hidden"><span class="family-name">Leach</span><span class="given-name">Paul J.</span></span></span><span class="org vcardline">Microsoft Corporation</span><span class="adr"><span class="street-address vcardline">1 Microsoft Way</span><span class="vcardline"><span class="locality">Redmond</span>, <span class="region">WA</span> <span class="postal-code">98052</span></span></span><span class="vcardline">Email: <a href="mailto:paulle@microsoft.com"><span class="email">paulle@microsoft.com</span></a></span></address> |
|---|
| 1284 | <address class="vcard"><span class="vcardline"><span class="fn">Tim Berners-Lee</span><span class="n hidden"><span class="family-name">Berners-Lee</span><span class="given-name">Tim</span></span></span><span class="org vcardline">World Wide Web Consortium</span><span class="adr"><span class="street-address vcardline">MIT Computer Science and Artificial Intelligence Laboratory</span><span class="street-address vcardline">The Stata Center, Building 32</span><span class="street-address vcardline">32 Vassar Street</span><span class="vcardline"><span class="locality">Cambridge</span>, <span class="region">MA</span> <span class="postal-code">02139</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">Email: <a href="mailto:timbl@w3.org"><span class="email">timbl@w3.org</span></a></span><span class="vcardline">URI: <a href="http://www.w3.org/People/Berners-Lee/" class="url">http://www.w3.org/People/Berners-Lee/</a></span></address> |
|---|
| 1285 | <address class="vcard"><span class="vcardline"><span class="fn">Yves Lafon</span> |
|---|
| 1286 | (editor) |
|---|
| 1287 | <span class="n hidden"><span class="family-name">Lafon</span><span class="given-name">Yves</span></span></span><span class="org vcardline">World Wide Web Consortium</span><span class="adr"><span class="street-address vcardline">W3C / ERCIM</span><span class="street-address vcardline">2004, rte des Lucioles</span><span class="vcardline"><span class="locality">Sophia-Antipolis</span>, <span class="region">AM</span> <span class="postal-code">06902</span></span><span class="country-name vcardline">France</span></span><span class="vcardline">Email: <a href="mailto:ylafon@w3.org"><span class="email">ylafon@w3.org</span></a></span><span class="vcardline">URI: <a href="http://www.raubacapeu.net/people/yves/" class="url">http://www.raubacapeu.net/people/yves/</a></span></address> |
|---|
| 1288 | <address class="vcard"><span class="vcardline"><span class="fn">Julian F. Reschke</span> |
|---|
| 1289 | (editor) |
|---|
| 1290 | <span class="n hidden"><span class="family-name">Reschke</span><span class="given-name">Julian F.</span></span></span><span class="org vcardline">greenbytes GmbH</span><span class="adr"><span class="street-address vcardline">Hafenweg 16</span><span class="vcardline"><span class="locality">Muenster</span>, <span class="region">NW</span> <span class="postal-code">48155</span></span><span class="country-name vcardline">Germany</span></span><span class="vcardline tel">Phone: <a href="tel:+492512807760"><span class="value">+49 251 2807760</span></a></span><span class="vcardline tel"><span class="type">Fax</span>: <a href="fax:+492512807761"><span class="value">+49 251 2807761</span></a></span><span class="vcardline">Email: <a href="mailto:julian.reschke@greenbytes.de"><span class="email">julian.reschke@greenbytes.de</span></a></span><span class="vcardline">URI: <a href="http://greenbytes.de/tech/webdav/" class="url">http://greenbytes.de/tech/webdav/</a></span></address> |
|---|
| 1291 | </div> |
|---|
| 1292 | <h1 id="rfc.section.A" class="np"><a href="#rfc.section.A">A.</a> <a id="changes.from.rfc.2616" href="#changes.from.rfc.2616">Changes from RFC 2616</a></h1> |
|---|
| 1293 | <p id="rfc.section.A.p.1">Allow weak entity-tags in all requests except range requests (Sections <a href="#weak.and.strong.validators" title="Weak versus Strong">2.1</a> and <a href="#header.if-none-match" id="rfc.xref.header.if-none-match.2" title="If-None-Match">3.2</a>). |
|---|
| 1294 | </p> |
|---|
| 1295 | <p id="rfc.section.A.p.2">Change ETag header field ABNF not to use quoted-string, thus avoiding escaping issues. (<a href="#header.etag" id="rfc.xref.header.etag.2" title="ETag">Section 2.3</a>) |
|---|
| 1296 | </p> |
|---|
| 1297 | <p id="rfc.section.A.p.3">Change ABNF productions for header fields to only define the field value. (<a href="#header.field.definitions" title="Precondition Header Fields">Section 3</a>) |
|---|
| 1298 | </p> |
|---|
| 1299 | <h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a> <a id="collected.abnf" href="#collected.abnf">Collected ABNF</a></h1> |
|---|
| 1300 | <div id="rfc.figure.u.17"></div> <pre class="inline"><a href="#header.etag" class="smpl">ETag</a> = entity-tag |
|---|
| 1301 | |
|---|
| 1302 | <a href="#notation" class="smpl">HTTP-date</a> = <HTTP-date, defined in [Part2], Section 8> |
|---|
| 1303 | |
|---|
| 1304 | <a href="#header.if-match" class="smpl">If-Match</a> = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS |
|---|
| 1305 | entity-tag ] ) ) |
|---|
| 1306 | <a href="#header.if-modified-since" class="smpl">If-Modified-Since</a> = HTTP-date |
|---|
| 1307 | <a href="#header.if-none-match" class="smpl">If-None-Match</a> = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS |
|---|
| 1308 | entity-tag ] ) ) |
|---|
| 1309 | <a href="#header.if-unmodified-since" class="smpl">If-Unmodified-Since</a> = HTTP-date |
|---|
| 1310 | |
|---|
| 1311 | <a href="#header.last-modified" class="smpl">Last-Modified</a> = HTTP-date |
|---|
| 1312 | |
|---|
| 1313 | <a href="#notation" class="smpl">OWS</a> = <OWS, defined in [Part1], Section 1.2.2> |
|---|
| 1314 | |
|---|
| 1315 | <a href="#header.etag" class="smpl">entity-tag</a> = [ weak ] opaque-tag |
|---|
| 1316 | <a href="#header.etag" class="smpl">etagc</a> = "!" / %x23-7E ; '#'-'~' |
|---|
| 1317 | / obs-text |
|---|
| 1318 | |
|---|
| 1319 | <a href="#notation" class="smpl">obs-text</a> = <obs-text, defined in [Part1], Section 3.2.3> |
|---|
| 1320 | <a href="#header.etag" class="smpl">opaque-tag</a> = DQUOTE *etagc DQUOTE |
|---|
| 1321 | |
|---|
| 1322 | <a href="#header.etag" class="smpl">weak</a> = %x57.2F ; W/ |
|---|
| 1323 | </pre> <div id="rfc.figure.u.18"></div> |
|---|
| 1324 | <p>ABNF diagnostics:</p><pre class="inline">; ETag defined but not used |
|---|
| 1325 | ; If-Match defined but not used |
|---|
| 1326 | ; If-Modified-Since defined but not used |
|---|
| 1327 | ; If-None-Match defined but not used |
|---|
| 1328 | ; If-Unmodified-Since defined but not used |
|---|
| 1329 | ; Last-Modified defined but not used |
|---|
| 1330 | </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> |
|---|
| 1331 | <h2 id="rfc.section.C.1"><a href="#rfc.section.C.1">C.1</a> Since RFC 2616 |
|---|
| 1332 | </h2> |
|---|
| 1333 | <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>. |
|---|
| 1334 | </p> |
|---|
| 1335 | <h2 id="rfc.section.C.2"><a href="#rfc.section.C.2">C.2</a> Since draft-ietf-httpbis-p4-conditional-00 |
|---|
| 1336 | </h2> |
|---|
| 1337 | <p id="rfc.section.C.2.p.1">Closed issues: </p> |
|---|
| 1338 | <ul> |
|---|
| 1339 | <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" |
|---|
| 1340 | </li> |
|---|
| 1341 | </ul> |
|---|
| 1342 | <p id="rfc.section.C.2.p.2">Other changes: </p> |
|---|
| 1343 | <ul> |
|---|
| 1344 | <li>Move definitions of 304 and 412 condition codes from Part2.</li> |
|---|
| 1345 | </ul> |
|---|
| 1346 | <h2 id="rfc.section.C.3"><a href="#rfc.section.C.3">C.3</a> Since draft-ietf-httpbis-p4-conditional-01 |
|---|
| 1347 | </h2> |
|---|
| 1348 | <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>>): |
|---|
| 1349 | </p> |
|---|
| 1350 | <ul> |
|---|
| 1351 | <li>Add explicit references to BNF syntax and rules imported from other parts of the specification.</li> |
|---|
| 1352 | </ul> |
|---|
| 1353 | <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> |
|---|
| 1354 | <p id="rfc.section.C.4.p.1">Closed issues: </p> |
|---|
| 1355 | <ul> |
|---|
| 1356 | <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" |
|---|
| 1357 | </li> |
|---|
| 1358 | </ul> |
|---|
| 1359 | <p id="rfc.section.C.4.p.2">Ongoing work on IANA Message Header Field Registration (<<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/40">http://tools.ietf.org/wg/httpbis/trac/ticket/40</a>>): |
|---|
| 1360 | </p> |
|---|
| 1361 | <ul> |
|---|
| 1362 | <li>Reference RFC 3984, and update header field registrations for header fields defined in this document.</li> |
|---|
| 1363 | </ul> |
|---|
| 1364 | <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> |
|---|
| 1365 | <p id="rfc.section.C.5.p.1">Closed issues: </p> |
|---|
| 1366 | <ul> |
|---|
| 1367 | <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" |
|---|
| 1368 | </li> |
|---|
| 1369 | <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" |
|---|
| 1370 | </li> |
|---|
| 1371 | <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" |
|---|
| 1372 | </li> |
|---|
| 1373 | </ul> |
|---|
| 1374 | <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> |
|---|
| 1375 | <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>>): |
|---|
| 1376 | </p> |
|---|
| 1377 | <ul> |
|---|
| 1378 | <li>Use "/" instead of "|" for alternatives.</li> |
|---|
| 1379 | <li>Introduce new ABNF rules for "bad" whitespace ("BWS"), optional whitespace ("OWS") and required whitespace ("RWS").</li> |
|---|
| 1380 | <li>Rewrite ABNFs to spell out whitespace rules, factor out header field value format definitions.</li> |
|---|
| 1381 | </ul> |
|---|
| 1382 | <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> |
|---|
| 1383 | <p id="rfc.section.C.7.p.1">Final 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>>): |
|---|
| 1384 | </p> |
|---|
| 1385 | <ul> |
|---|
| 1386 | <li>Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.</li> |
|---|
| 1387 | </ul> |
|---|
| 1388 | <h2 id="rfc.section.C.8"><a href="#rfc.section.C.8">C.8</a> <a id="changes.since.06" href="#changes.since.06">Since draft-ietf-httpbis-p4-conditional-06</a></h2> |
|---|
| 1389 | <p id="rfc.section.C.8.p.1">Closed issues: </p> |
|---|
| 1390 | <ul> |
|---|
| 1391 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/153">http://tools.ietf.org/wg/httpbis/trac/ticket/153</a>>: "case-sensitivity of etag weakness indicator" |
|---|
| 1392 | </li> |
|---|
| 1393 | </ul> |
|---|
| 1394 | <h2 id="rfc.section.C.9"><a href="#rfc.section.C.9">C.9</a> <a id="changes.since.07" href="#changes.since.07">Since draft-ietf-httpbis-p4-conditional-07</a></h2> |
|---|
| 1395 | <p id="rfc.section.C.9.p.1">Closed issues: </p> |
|---|
| 1396 | <ul> |
|---|
| 1397 | <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" (If-Match still was defined to require strong matching) |
|---|
| 1398 | </li> |
|---|
| 1399 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/198">http://tools.ietf.org/wg/httpbis/trac/ticket/198</a>>: "move IANA registrations for optional status codes" |
|---|
| 1400 | </li> |
|---|
| 1401 | </ul> |
|---|
| 1402 | <h2 id="rfc.section.C.10"><a href="#rfc.section.C.10">C.10</a> <a id="changes.since.08" href="#changes.since.08">Since draft-ietf-httpbis-p4-conditional-08</a></h2> |
|---|
| 1403 | <p id="rfc.section.C.10.p.1">No significant changes.</p> |
|---|
| 1404 | <h2 id="rfc.section.C.11"><a href="#rfc.section.C.11">C.11</a> <a id="changes.since.09" href="#changes.since.09">Since draft-ietf-httpbis-p4-conditional-09</a></h2> |
|---|
| 1405 | <p id="rfc.section.C.11.p.1">No significant changes.</p> |
|---|
| 1406 | <h2 id="rfc.section.C.12"><a href="#rfc.section.C.12">C.12</a> <a id="changes.since.10" href="#changes.since.10">Since draft-ietf-httpbis-p4-conditional-10</a></h2> |
|---|
| 1407 | <p id="rfc.section.C.12.p.1">Closed issues: </p> |
|---|
| 1408 | <ul> |
|---|
| 1409 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/69">http://tools.ietf.org/wg/httpbis/trac/ticket/69</a>>: "Clarify 'Requested Variant'" |
|---|
| 1410 | </li> |
|---|
| 1411 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/109">http://tools.ietf.org/wg/httpbis/trac/ticket/109</a>>: "Clarify entity / representation / variant terminology" |
|---|
| 1412 | </li> |
|---|
| 1413 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/220">http://tools.ietf.org/wg/httpbis/trac/ticket/220</a>>: "consider removing the 'changes from 2068' sections" |
|---|
| 1414 | </li> |
|---|
| 1415 | </ul> |
|---|
| 1416 | <h2 id="rfc.section.C.13"><a href="#rfc.section.C.13">C.13</a> <a id="changes.since.11" href="#changes.since.11">Since draft-ietf-httpbis-p4-conditional-11</a></h2> |
|---|
| 1417 | <p id="rfc.section.C.13.p.1">None.</p> |
|---|
| 1418 | <h2 id="rfc.section.C.14"><a href="#rfc.section.C.14">C.14</a> <a id="changes.since.12" href="#changes.since.12">Since draft-ietf-httpbis-p4-conditional-12</a></h2> |
|---|
| 1419 | <p id="rfc.section.C.14.p.1">Closed issues: </p> |
|---|
| 1420 | <ul> |
|---|
| 1421 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/224">http://tools.ietf.org/wg/httpbis/trac/ticket/224</a>>: "Header Classification" |
|---|
| 1422 | </li> |
|---|
| 1423 | </ul> |
|---|
| 1424 | <h2 id="rfc.section.C.15"><a href="#rfc.section.C.15">C.15</a> <a id="changes.since.13" href="#changes.since.13">Since draft-ietf-httpbis-p4-conditional-13</a></h2> |
|---|
| 1425 | <p id="rfc.section.C.15.p.1">Closed issues: </p> |
|---|
| 1426 | <ul> |
|---|
| 1427 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/89">http://tools.ietf.org/wg/httpbis/trac/ticket/89</a>>: "If-* and entities" |
|---|
| 1428 | </li> |
|---|
| 1429 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/101">http://tools.ietf.org/wg/httpbis/trac/ticket/101</a>>: "Definition of validator weakness" |
|---|
| 1430 | </li> |
|---|
| 1431 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/276">http://tools.ietf.org/wg/httpbis/trac/ticket/276</a>>: "untangle ABNFs for header fields" |
|---|
| 1432 | </li> |
|---|
| 1433 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/269">http://tools.ietf.org/wg/httpbis/trac/ticket/269</a>>: "ETags and Quotes" |
|---|
| 1434 | </li> |
|---|
| 1435 | </ul> |
|---|
| 1436 | <h2 id="rfc.section.C.16"><a href="#rfc.section.C.16">C.16</a> <a id="changes.since.14" href="#changes.since.14">Since draft-ietf-httpbis-p4-conditional-14</a></h2> |
|---|
| 1437 | <p id="rfc.section.C.16.p.1">None.</p> |
|---|
| 1438 | <h2 id="rfc.section.C.17"><a href="#rfc.section.C.17">C.17</a> <a id="changes.since.15" href="#changes.since.15">Since draft-ietf-httpbis-p4-conditional-15</a></h2> |
|---|
| 1439 | <p id="rfc.section.C.17.p.1">Closed issues: </p> |
|---|
| 1440 | <ul> |
|---|
| 1441 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/304">http://tools.ietf.org/wg/httpbis/trac/ticket/304</a>>: "If-Range should be listed when dicussing contexts where L-M can be considered strong" |
|---|
| 1442 | </li> |
|---|
| 1443 | </ul> |
|---|
| 1444 | <h2 id="rfc.section.C.18"><a href="#rfc.section.C.18">C.18</a> <a id="changes.since.16" href="#changes.since.16">Since draft-ietf-httpbis-p4-conditional-16</a></h2> |
|---|
| 1445 | <p id="rfc.section.C.18.p.1">Closed issues: </p> |
|---|
| 1446 | <ul> |
|---|
| 1447 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/186">http://tools.ietf.org/wg/httpbis/trac/ticket/186</a>>: "Document HTTP's error-handling philosophy" |
|---|
| 1448 | </li> |
|---|
| 1449 | </ul> |
|---|
| 1450 | <h2 id="rfc.section.C.19"><a href="#rfc.section.C.19">C.19</a> <a id="changes.since.17" href="#changes.since.17">Since draft-ietf-httpbis-p4-conditional-17</a></h2> |
|---|
| 1451 | <p id="rfc.section.C.19.p.1">Closed issues: </p> |
|---|
| 1452 | <ul> |
|---|
| 1453 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/306">http://tools.ietf.org/wg/httpbis/trac/ticket/306</a>>: "does etag value really use quoted-string" |
|---|
| 1454 | </li> |
|---|
| 1455 | </ul> |
|---|
| 1456 | <h2 id="rfc.section.C.20"><a href="#rfc.section.C.20">C.20</a> <a id="changes.since.18" href="#changes.since.18">Since draft-ietf-httpbis-p4-conditional-18</a></h2> |
|---|
| 1457 | <p id="rfc.section.C.20.p.1">None yet.</p> |
|---|
| 1458 | <h1 id="rfc.index"><a href="#rfc.index">Index</a></h1> |
|---|
| 1459 | <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.M">M</a> <a href="#rfc.index.P">P</a> <a href="#rfc.index.R">R</a> <a href="#rfc.index.S">S</a> <a href="#rfc.index.V">V</a> |
|---|
| 1460 | </p> |
|---|
| 1461 | <div class="print2col"> |
|---|
| 1462 | <ul class="ind"> |
|---|
| 1463 | <li><a id="rfc.index.3" href="#rfc.index.3"><b>3</b></a><ul> |
|---|
| 1464 | <li>304 Not Modified (status code) <a href="#rfc.iref.27"><b>4.1</b></a>, <a href="#rfc.xref.status.304.1">5.1</a></li> |
|---|
| 1465 | </ul> |
|---|
| 1466 | </li> |
|---|
| 1467 | <li><a id="rfc.index.4" href="#rfc.index.4"><b>4</b></a><ul> |
|---|
| 1468 | <li>412 Precondition Failed (status code) <a href="#rfc.iref.28"><b>4.2</b></a>, <a href="#rfc.xref.status.412.1">5.1</a></li> |
|---|
| 1469 | </ul> |
|---|
| 1470 | </li> |
|---|
| 1471 | <li><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul> |
|---|
| 1472 | <li>ETag header field <a href="#rfc.iref.e.1"><b>2.3</b></a>, <a href="#rfc.xref.header.etag.1">5.2</a>, <a href="#rfc.xref.header.etag.2">A</a></li> |
|---|
| 1473 | </ul> |
|---|
| 1474 | </li> |
|---|
| 1475 | <li><a id="rfc.index.G" href="#rfc.index.G"><b>G</b></a><ul> |
|---|
| 1476 | <li><tt>Grammar</tt> |
|---|
| 1477 | <ul> |
|---|
| 1478 | <li><tt>entity-tag</tt> <a href="#rfc.iref.g.3"><b>2.3</b></a></li> |
|---|
| 1479 | <li><tt>ETag</tt> <a href="#rfc.iref.g.2"><b>2.3</b></a></li> |
|---|
| 1480 | <li><tt>etagc</tt> <a href="#rfc.iref.g.6"><b>2.3</b></a></li> |
|---|
| 1481 | <li><tt>If-Match</tt> <a href="#rfc.iref.g.7"><b>3.1</b></a></li> |
|---|
| 1482 | <li><tt>If-Modified-Since</tt> <a href="#rfc.iref.g.9"><b>3.3</b></a></li> |
|---|
| 1483 | <li><tt>If-None-Match</tt> <a href="#rfc.iref.g.8"><b>3.2</b></a></li> |
|---|
| 1484 | <li><tt>If-Unmodified-Since</tt> <a href="#rfc.iref.g.10"><b>3.4</b></a></li> |
|---|
| 1485 | <li><tt>Last-Modified</tt> <a href="#rfc.iref.g.1"><b>2.2</b></a></li> |
|---|
| 1486 | <li><tt>opaque-tag</tt> <a href="#rfc.iref.g.5"><b>2.3</b></a></li> |
|---|
| 1487 | <li><tt>weak</tt> <a href="#rfc.iref.g.4"><b>2.3</b></a></li> |
|---|
| 1488 | </ul> |
|---|
| 1489 | </li> |
|---|
| 1490 | </ul> |
|---|
| 1491 | </li> |
|---|
| 1492 | <li><a id="rfc.index.H" href="#rfc.index.H"><b>H</b></a><ul> |
|---|
| 1493 | <li>Header Fields |
|---|
| 1494 | <ul> |
|---|
| 1495 | <li>ETag <a href="#rfc.iref.h.2"><b>2.3</b></a>, <a href="#rfc.xref.header.etag.1">5.2</a>, <a href="#rfc.xref.header.etag.2">A</a></li> |
|---|
| 1496 | <li>If-Match <a href="#rfc.iref.h.3"><b>3.1</b></a>, <a href="#rfc.xref.header.if-match.1">5.2</a></li> |
|---|
| 1497 | <li>If-Modified-Since <a href="#rfc.iref.h.5"><b>3.3</b></a>, <a href="#rfc.xref.header.if-modified-since.1">5.2</a></li> |
|---|
| 1498 | <li>If-None-Match <a href="#rfc.iref.h.4"><b>3.2</b></a>, <a href="#rfc.xref.header.if-none-match.1">5.2</a>, <a href="#rfc.xref.header.if-none-match.2">A</a></li> |
|---|
| 1499 | <li>If-Unmodified-Since <a href="#rfc.iref.h.6"><b>3.4</b></a>, <a href="#rfc.xref.header.if-unmodified-since.1">5.2</a></li> |
|---|
| 1500 | <li>Last-Modified <a href="#rfc.iref.h.1"><b>2.2</b></a>, <a href="#rfc.xref.header.last-modified.1">5.2</a></li> |
|---|
| 1501 | </ul> |
|---|
| 1502 | </li> |
|---|
| 1503 | </ul> |
|---|
| 1504 | </li> |
|---|
| 1505 | <li><a id="rfc.index.I" href="#rfc.index.I"><b>I</b></a><ul> |
|---|
| 1506 | <li>If-Match header field <a href="#rfc.iref.i.1"><b>3.1</b></a>, <a href="#rfc.xref.header.if-match.1">5.2</a></li> |
|---|
| 1507 | <li>If-Modified-Since header field <a href="#rfc.iref.i.3"><b>3.3</b></a>, <a href="#rfc.xref.header.if-modified-since.1">5.2</a></li> |
|---|
| 1508 | <li>If-None-Match header field <a href="#rfc.iref.i.2"><b>3.2</b></a>, <a href="#rfc.xref.header.if-none-match.1">5.2</a>, <a href="#rfc.xref.header.if-none-match.2">A</a></li> |
|---|
| 1509 | <li>If-Unmodified-Since header field <a href="#rfc.iref.i.4"><b>3.4</b></a>, <a href="#rfc.xref.header.if-unmodified-since.1">5.2</a></li> |
|---|
| 1510 | </ul> |
|---|
| 1511 | </li> |
|---|
| 1512 | <li><a id="rfc.index.L" href="#rfc.index.L"><b>L</b></a><ul> |
|---|
| 1513 | <li>Last-Modified header field <a href="#rfc.iref.l.1"><b>2.2</b></a>, <a href="#rfc.xref.header.last-modified.1">5.2</a></li> |
|---|
| 1514 | </ul> |
|---|
| 1515 | </li> |
|---|
| 1516 | <li><a id="rfc.index.M" href="#rfc.index.M"><b>M</b></a><ul> |
|---|
| 1517 | <li>metadata <a href="#rfc.iref.m.1"><b>2</b></a></li> |
|---|
| 1518 | </ul> |
|---|
| 1519 | </li> |
|---|
| 1520 | <li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul> |
|---|
| 1521 | <li><em>Part1</em> <a href="#rfc.xref.Part1.1">1.1</a>, <a href="#rfc.xref.Part1.2">1.2</a>, <a href="#rfc.xref.Part1.3">1.2</a>, <a href="#rfc.xref.Part1.4">1.2</a>, <a href="#rfc.xref.Part1.5">1.2</a>, <a href="#rfc.xref.Part1.6">2.3.3</a>, <a href="#rfc.xref.Part1.7">6</a>, <a href="#rfc.xref.Part1.8">7</a>, <a href="#Part1"><b>8.1</b></a><ul> |
|---|
| 1522 | <li><em>Section 1.2</em> <a href="#rfc.xref.Part1.2">1.2</a></li> |
|---|
| 1523 | <li><em>Section 1.2.2</em> <a href="#rfc.xref.Part1.4">1.2</a></li> |
|---|
| 1524 | <li><em>Section 2</em> <a href="#rfc.xref.Part1.1">1.1</a></li> |
|---|
| 1525 | <li><em>Section 3.2.3</em> <a href="#rfc.xref.Part1.5">1.2</a></li> |
|---|
| 1526 | <li><em>Section 5.1</em> <a href="#rfc.xref.Part1.6">2.3.3</a></li> |
|---|
| 1527 | <li><em>Section 11</em> <a href="#rfc.xref.Part1.8">7</a></li> |
|---|
| 1528 | </ul> |
|---|
| 1529 | </li> |
|---|
| 1530 | <li><em>Part2</em> <a href="#rfc.xref.Part2.1">1.2</a>, <a href="#rfc.xref.Part2.2">1.2</a>, <a href="#rfc.xref.Part2.3">4.1</a>, <a href="#Part2"><b>8.1</b></a><ul> |
|---|
| 1531 | <li><em>Section 8</em> <a href="#rfc.xref.Part2.2">1.2</a></li> |
|---|
| 1532 | <li><em>Section 9.2</em> <a href="#rfc.xref.Part2.3">4.1</a></li> |
|---|
| 1533 | </ul> |
|---|
| 1534 | </li> |
|---|
| 1535 | <li><em>Part3</em> <a href="#rfc.xref.Part3.1">2.3.3</a>, <a href="#rfc.xref.Part3.2">2.3.3</a>, <a href="#Part3"><b>8.1</b></a><ul> |
|---|
| 1536 | <li><em>Section 5</em> <a href="#rfc.xref.Part3.1">2.3.3</a></li> |
|---|
| 1537 | <li><em>Section 6.3</em> <a href="#rfc.xref.Part3.2">2.3.3</a></li> |
|---|
| 1538 | </ul> |
|---|
| 1539 | </li> |
|---|
| 1540 | <li><em>Part5</em> <a href="#rfc.xref.Part5.1">3.3</a>, <a href="#rfc.xref.Part5.2">3.5</a>, <a href="#Part5"><b>8.1</b></a><ul> |
|---|
| 1541 | <li><em>Section 5.3</em> <a href="#rfc.xref.Part5.2">3.5</a></li> |
|---|
| 1542 | <li><em>Section 5.4</em> <a href="#rfc.xref.Part5.1">3.3</a></li> |
|---|
| 1543 | </ul> |
|---|
| 1544 | </li> |
|---|
| 1545 | <li><em>Part6</em> <a href="#rfc.xref.Part6.1">1</a>, <a href="#rfc.xref.Part6.2">2.2.1</a>, <a href="#rfc.xref.Part6.3">2.3.1</a>, <a href="#Part6"><b>8.1</b></a></li> |
|---|
| 1546 | </ul> |
|---|
| 1547 | </li> |
|---|
| 1548 | <li><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul> |
|---|
| 1549 | <li><em>RFC2119</em> <a href="#rfc.xref.RFC2119.1">1.1</a>, <a href="#RFC2119"><b>8.1</b></a></li> |
|---|
| 1550 | <li><em>RFC2616</em> <a href="#rfc.xref.RFC2616.1">2.3</a>, <a href="#RFC2616"><b>8.2</b></a>, <a href="#rfc.xref.RFC2616.2">C.1</a><ul> |
|---|
| 1551 | <li><em>Section 3.11</em> <a href="#rfc.xref.RFC2616.1">2.3</a></li> |
|---|
| 1552 | </ul> |
|---|
| 1553 | </li> |
|---|
| 1554 | <li><em>RFC3864</em> <a href="#rfc.xref.RFC3864.1">5.2</a>, <a href="#RFC3864"><b>8.2</b></a></li> |
|---|
| 1555 | <li><em>RFC4918</em> <a href="#rfc.xref.RFC4918.1">2</a>, <a href="#RFC4918"><b>8.2</b></a></li> |
|---|
| 1556 | <li><em>RFC5234</em> <a href="#rfc.xref.RFC5234.1">1.2</a>, <a href="#rfc.xref.RFC5234.2">1.2</a>, <a href="#RFC5234"><b>8.1</b></a><ul> |
|---|
| 1557 | <li><em>Appendix B.1</em> <a href="#rfc.xref.RFC5234.2">1.2</a></li> |
|---|
| 1558 | </ul> |
|---|
| 1559 | </li> |
|---|
| 1560 | </ul> |
|---|
| 1561 | </li> |
|---|
| 1562 | <li><a id="rfc.index.S" href="#rfc.index.S"><b>S</b></a><ul> |
|---|
| 1563 | <li>selected representation <a href="#rfc.iref.s.1"><b>1</b></a></li> |
|---|
| 1564 | <li>Status Codes |
|---|
| 1565 | <ul> |
|---|
| 1566 | <li>304 Not Modified <a href="#rfc.iref.s.2"><b>4.1</b></a>, <a href="#rfc.xref.status.304.1">5.1</a></li> |
|---|
| 1567 | <li>412 Precondition Failed <a href="#rfc.iref.s.3"><b>4.2</b></a>, <a href="#rfc.xref.status.412.1">5.1</a></li> |
|---|
| 1568 | </ul> |
|---|
| 1569 | </li> |
|---|
| 1570 | </ul> |
|---|
| 1571 | </li> |
|---|
| 1572 | <li><a id="rfc.index.V" href="#rfc.index.V"><b>V</b></a><ul> |
|---|
| 1573 | <li>validator <a href="#rfc.iref.v.1"><b>2</b></a><ul> |
|---|
| 1574 | <li>strong <a href="#rfc.iref.v.3"><b>2.1</b></a></li> |
|---|
| 1575 | <li>weak <a href="#rfc.iref.v.2"><b>2.1</b></a></li> |
|---|
| 1576 | </ul> |
|---|
| 1577 | </li> |
|---|
| 1578 | </ul> |
|---|
| 1579 | </li> |
|---|
| 1580 | </ul> |
|---|
| 1581 | </div> |
|---|
| 1582 | </body> |
|---|
| 1583 | </html> |
|---|
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