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| 2 | PUBLIC "-//W3C//DTD HTML 4.01//EN"> |
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| 3 | <html lang="en"> |
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| 4 | <head profile="http://www.w3.org/2006/03/hcard http://dublincore.org/documents/2008/08/04/dc-html/"> |
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| 6 | <title>HTTP/1.1, part 6: Caching</title><style type="text/css" title="Xml2Rfc (sans serif)"> |
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| 244 | margin-left: 0em; |
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| 245 | margin-right: 0em; |
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| 246 | } |
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| 247 | ul.ind li li { |
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| 257 | font-style: normal; |
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| 258 | text-transform: lowercase; |
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| 259 | font-variant: small-caps; |
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| 260 | } |
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| 261 | .comment { |
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| 262 | background-color: yellow; |
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| 263 | } |
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| 264 | .center { |
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| 265 | text-align: center; |
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| 266 | } |
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| 267 | .error { |
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| 268 | color: red; |
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| 269 | font-style: italic; |
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| 270 | font-weight: bold; |
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| 271 | } |
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| 272 | .figure { |
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| 273 | font-weight: bold; |
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| 274 | text-align: center; |
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| 275 | font-size: 9pt; |
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| 277 | .filename { |
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| 278 | color: #333333; |
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| 279 | font-weight: bold; |
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| 280 | font-size: 12pt; |
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| 281 | line-height: 21pt; |
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| 285 | font-weight: bold; |
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| 286 | } |
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| 287 | .hidden { |
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| 288 | display: none; |
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| 289 | } |
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| 290 | .left { |
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| 291 | text-align: left; |
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| 292 | } |
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| 293 | .right { |
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| 294 | text-align: right; |
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| 296 | .title { |
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| 297 | color: #990000; |
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| 298 | font-size: 18pt; |
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| 299 | line-height: 18pt; |
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| 300 | font-weight: bold; |
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| 301 | text-align: center; |
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| 302 | margin-top: 36pt; |
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| 303 | } |
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| 304 | .vcardline { |
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| 305 | display: block; |
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| 306 | } |
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| 307 | .warning { |
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| 308 | font-size: 14pt; |
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| 309 | background-color: yellow; |
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| 310 | } |
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| 311 | |
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| 312 | |
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| 313 | @media print { |
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| 314 | .noprint { |
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| 315 | display: none; |
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| 316 | } |
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| 317 | |
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| 318 | a { |
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| 319 | color: black; |
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| 320 | text-decoration: none; |
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| 321 | } |
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| 322 | |
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| 323 | table.header { |
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| 324 | width: 90%; |
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| 325 | } |
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| 326 | |
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| 327 | td.header { |
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| 328 | width: 50%; |
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| 329 | color: black; |
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| 330 | background-color: white; |
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| 331 | vertical-align: top; |
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| 332 | font-size: 12pt; |
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| 333 | } |
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| 334 | |
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| 335 | ul.toc a::after { |
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| 336 | content: leader('.') target-counter(attr(href), page); |
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| 337 | } |
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| 338 | |
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| 339 | ul.ind li li a { |
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| 340 | content: target-counter(attr(href), page); |
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| 341 | } |
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| 342 | |
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| 343 | .print2col { |
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| 344 | column-count: 2; |
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| 345 | -moz-column-count: 2; |
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| 346 | column-fill: auto; |
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| 347 | } |
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| 348 | } |
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| 349 | |
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| 350 | @page { |
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| 351 | @top-left { |
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| 352 | content: "Internet-Draft"; |
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| 353 | } |
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| 354 | @top-right { |
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| 355 | content: "October 2011"; |
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| 356 | } |
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| 357 | @top-center { |
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| 358 | content: "HTTP/1.1, Part 6"; |
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| 359 | } |
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| 360 | @bottom-left { |
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| 361 | content: "Fielding, et al."; |
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| 362 | } |
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| 363 | @bottom-center { |
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| 364 | content: "Expires May 3, 2012"; |
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| 365 | } |
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| 366 | @bottom-right { |
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| 367 | content: "[Page " counter(page) "]"; |
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| 368 | } |
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| 369 | } |
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| 370 | |
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| 371 | @page:first { |
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| 372 | @top-left { |
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| 373 | content: normal; |
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| 374 | } |
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| 375 | @top-right { |
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| 376 | content: normal; |
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| 377 | } |
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| 378 | @top-center { |
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| 379 | content: normal; |
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| 380 | } |
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| 381 | } |
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| 382 | </style><link rel="Contents" href="#rfc.toc"> |
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| 383 | <link rel="Author" href="#rfc.authors"> |
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| 384 | <link rel="Copyright" href="#rfc.copyrightnotice"> |
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| 385 | <link rel="Index" href="#rfc.index"> |
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| 386 | <link rel="Chapter" title="1 Introduction" href="#rfc.section.1"> |
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| 387 | <link rel="Chapter" title="2 Cache Operation" href="#rfc.section.2"> |
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| 388 | <link rel="Chapter" title="3 Header Field Definitions" href="#rfc.section.3"> |
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| 389 | <link rel="Chapter" title="4 History Lists" href="#rfc.section.4"> |
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| 390 | <link rel="Chapter" title="5 IANA Considerations" href="#rfc.section.5"> |
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| 391 | <link rel="Chapter" title="6 Security Considerations" href="#rfc.section.6"> |
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| 392 | <link rel="Chapter" title="7 Acknowledgments" href="#rfc.section.7"> |
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| 393 | <link rel="Chapter" href="#rfc.section.8" title="8 References"> |
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| 394 | <link rel="Appendix" title="A Changes from RFC 2616" href="#rfc.section.A"> |
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| 395 | <link rel="Appendix" title="B Collected ABNF" href="#rfc.section.B"> |
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| 396 | <link rel="Appendix" title="C Change Log (to be removed by RFC Editor before publication)" href="#rfc.section.C"> |
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| 397 | <meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.556, 2011-08-28 20:30:48, XSLT vendor: SAXON 8.9 from Saxonica http://www.saxonica.com/"> |
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| 398 | <link rel="schema.dct" href="http://purl.org/dc/terms/"> |
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| 399 | <meta name="dct.creator" content="Fielding, R."> |
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| 400 | <meta name="dct.creator" content="Gettys, J."> |
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| 401 | <meta name="dct.creator" content="Mogul, J."> |
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| 402 | <meta name="dct.creator" content="Frystyk, H."> |
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| 403 | <meta name="dct.creator" content="Masinter, L."> |
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| 404 | <meta name="dct.creator" content="Leach, P."> |
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| 405 | <meta name="dct.creator" content="Berners-Lee, T."> |
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| 406 | <meta name="dct.creator" content="Lafon, Y."> |
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| 407 | <meta name="dct.creator" content="Nottingham, M."> |
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| 408 | <meta name="dct.creator" content="Reschke, J. F."> |
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| 409 | <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p6-cache-latest"> |
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| 410 | <meta name="dct.issued" scheme="ISO8601" content="2011-10-31"> |
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| 411 | <meta name="dct.replaces" content="urn:ietf:rfc:2616"> |
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| 412 | <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 6 of the seven-part specification that defines the protocol referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616. Part 6 defines requirements on HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages."> |
|---|
| 413 | <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 6 of the seven-part specification that defines the protocol referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616. Part 6 defines requirements on HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages."> |
|---|
| 414 | </head> |
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| 415 | <body> |
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| 416 | <table class="header"> |
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| 417 | <tbody> |
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| 418 | <tr> |
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| 419 | <td class="left">HTTPbis Working Group</td> |
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| 420 | <td class="right">R. Fielding, Editor</td> |
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| 421 | </tr> |
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| 422 | <tr> |
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| 423 | <td class="left">Internet-Draft</td> |
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| 424 | <td class="right">Adobe</td> |
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| 425 | </tr> |
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| 426 | <tr> |
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| 427 | <td class="left">Obsoletes: <a href="http://tools.ietf.org/html/rfc2616">2616</a> (if approved) |
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| 428 | </td> |
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| 429 | <td class="right">J. Gettys</td> |
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| 430 | </tr> |
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| 431 | <tr> |
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| 432 | <td class="left">Intended status: Standards Track</td> |
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| 433 | <td class="right">Alcatel-Lucent</td> |
|---|
| 434 | </tr> |
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| 435 | <tr> |
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| 436 | <td class="left">Expires: May 3, 2012</td> |
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| 437 | <td class="right">J. Mogul</td> |
|---|
| 438 | </tr> |
|---|
| 439 | <tr> |
|---|
| 440 | <td class="left"></td> |
|---|
| 441 | <td class="right">HP</td> |
|---|
| 442 | </tr> |
|---|
| 443 | <tr> |
|---|
| 444 | <td class="left"></td> |
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| 445 | <td class="right">H. Frystyk</td> |
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| 446 | </tr> |
|---|
| 447 | <tr> |
|---|
| 448 | <td class="left"></td> |
|---|
| 449 | <td class="right">Microsoft</td> |
|---|
| 450 | </tr> |
|---|
| 451 | <tr> |
|---|
| 452 | <td class="left"></td> |
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| 453 | <td class="right">L. Masinter</td> |
|---|
| 454 | </tr> |
|---|
| 455 | <tr> |
|---|
| 456 | <td class="left"></td> |
|---|
| 457 | <td class="right">Adobe</td> |
|---|
| 458 | </tr> |
|---|
| 459 | <tr> |
|---|
| 460 | <td class="left"></td> |
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| 461 | <td class="right">P. Leach</td> |
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| 462 | </tr> |
|---|
| 463 | <tr> |
|---|
| 464 | <td class="left"></td> |
|---|
| 465 | <td class="right">Microsoft</td> |
|---|
| 466 | </tr> |
|---|
| 467 | <tr> |
|---|
| 468 | <td class="left"></td> |
|---|
| 469 | <td class="right">T. Berners-Lee</td> |
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| 470 | </tr> |
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| 471 | <tr> |
|---|
| 472 | <td class="left"></td> |
|---|
| 473 | <td class="right">W3C/MIT</td> |
|---|
| 474 | </tr> |
|---|
| 475 | <tr> |
|---|
| 476 | <td class="left"></td> |
|---|
| 477 | <td class="right">Y. Lafon, Editor</td> |
|---|
| 478 | </tr> |
|---|
| 479 | <tr> |
|---|
| 480 | <td class="left"></td> |
|---|
| 481 | <td class="right">W3C</td> |
|---|
| 482 | </tr> |
|---|
| 483 | <tr> |
|---|
| 484 | <td class="left"></td> |
|---|
| 485 | <td class="right">M. Nottingham, Editor</td> |
|---|
| 486 | </tr> |
|---|
| 487 | <tr> |
|---|
| 488 | <td class="left"></td> |
|---|
| 489 | <td class="right">Rackspace</td> |
|---|
| 490 | </tr> |
|---|
| 491 | <tr> |
|---|
| 492 | <td class="left"></td> |
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| 493 | <td class="right">J. Reschke, Editor</td> |
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| 494 | </tr> |
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| 495 | <tr> |
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| 496 | <td class="left"></td> |
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| 497 | <td class="right">greenbytes</td> |
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| 498 | </tr> |
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| 499 | <tr> |
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| 500 | <td class="left"></td> |
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| 501 | <td class="right">October 31, 2011</td> |
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| 502 | </tr> |
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| 503 | </tbody> |
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| 504 | </table> |
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| 505 | <p class="title">HTTP/1.1, part 6: Caching<br><span class="filename">draft-ietf-httpbis-p6-cache-latest</span></p> |
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| 506 | <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1> |
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| 507 | <p>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext information |
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| 508 | systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 6 of the |
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| 509 | seven-part specification that defines the protocol referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616. |
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| 510 | </p> |
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| 511 | <p>Part 6 defines requirements on HTTP caches and the associated header fields that control cache behavior or indicate cacheable |
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| 512 | response messages. |
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| 513 | </p> |
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| 514 | <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1> |
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| 515 | <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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| 516 | 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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| 517 | </p> |
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| 518 | <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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| 519 | </p> |
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| 520 | <p>The changes in this draft are summarized in <a href="#changes.since.16" title="Since draft-ietf-httpbis-p6-cache-16">Appendix C.18</a>. |
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| 521 | </p> |
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| 522 | <h1><a id="rfc.status" href="#rfc.status">Status of This Memo</a></h1> |
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| 523 | <p>This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.</p> |
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| 524 | <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute |
|---|
| 525 | 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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| 526 | </p> |
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| 527 | <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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| 528 | 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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| 529 | in progress”. |
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| 530 | </p> |
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| 531 | <p>This Internet-Draft will expire on May 3, 2012.</p> |
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| 532 | <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1> |
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| 533 | <p>Copyright © 2011 IETF Trust and the persons identified as the document authors. All rights reserved.</p> |
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| 534 | <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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| 535 | and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License |
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| 536 | 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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| 537 | BSD License. |
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| 538 | </p> |
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| 539 | <p>This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November |
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| 540 | 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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| 541 | allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) |
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| 542 | controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative |
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| 543 | 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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| 544 | it into languages other than English. |
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| 545 | </p> |
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| 546 | <hr class="noprint"> |
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| 547 | <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1> |
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| 548 | <ul class="toc"> |
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| 549 | <li>1. <a href="#caching">Introduction</a><ul> |
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| 550 | <li>1.1 <a href="#intro.purpose">Purpose</a></li> |
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| 551 | <li>1.2 <a href="#intro.terminology">Terminology</a></li> |
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| 552 | <li>1.3 <a href="#intro.conformance.and.error.handling">Conformance and Error Handling</a></li> |
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| 553 | <li>1.4 <a href="#notation">Syntax Notation</a><ul> |
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| 554 | <li>1.4.1 <a href="#core.rules">Core Rules</a></li> |
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| 555 | <li>1.4.2 <a href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></li> |
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| 556 | </ul> |
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| 557 | </li> |
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| 558 | <li>1.5 <a href="#delta-seconds">Delta Seconds</a></li> |
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| 559 | </ul> |
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| 560 | </li> |
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| 561 | <li>2. <a href="#caching.overview">Cache Operation</a><ul> |
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| 562 | <li>2.1 <a href="#response.cacheability">Response Cacheability</a></li> |
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| 563 | <li>2.2 <a href="#constructing.responses.from.caches">Constructing Responses from Caches</a></li> |
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| 564 | <li>2.3 <a href="#expiration.model">Freshness Model</a><ul> |
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| 565 | <li>2.3.1 <a href="#calculating.freshness.lifetime">Calculating Freshness Lifetime</a><ul> |
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| 566 | <li>2.3.1.1 <a href="#heuristic.freshness">Calculating Heuristic Freshness</a></li> |
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| 567 | </ul> |
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| 568 | </li> |
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| 569 | <li>2.3.2 <a href="#age.calculations">Calculating Age</a></li> |
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| 570 | <li>2.3.3 <a href="#serving.stale.responses">Serving Stale Responses</a></li> |
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| 571 | </ul> |
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| 572 | </li> |
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| 573 | <li>2.4 <a href="#validation.model">Validation Model</a><ul> |
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| 574 | <li>2.4.1 <a href="#freshening.responses">Freshening Responses</a></li> |
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| 575 | </ul> |
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| 576 | </li> |
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| 577 | <li>2.5 <a href="#invalidation.after.updates.or.deletions">Request Methods that Invalidate</a></li> |
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| 578 | <li>2.6 <a href="#caching.authenticated.responses">Shared Caching of Authenticated Responses</a></li> |
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| 579 | <li>2.7 <a href="#caching.negotiated.responses">Caching Negotiated Responses</a></li> |
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| 580 | <li>2.8 <a href="#combining.responses">Combining Partial Content</a></li> |
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| 581 | </ul> |
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| 582 | </li> |
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| 583 | <li>3. <a href="#header.field.definitions">Header Field Definitions</a><ul> |
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| 584 | <li>3.1 <a href="#header.age">Age</a></li> |
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| 585 | <li>3.2 <a href="#header.cache-control">Cache-Control</a><ul> |
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| 586 | <li>3.2.1 <a href="#cache-request-directive">Request Cache-Control Directives</a></li> |
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| 587 | <li>3.2.2 <a href="#cache-response-directive">Response Cache-Control Directives</a></li> |
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| 588 | <li>3.2.3 <a href="#cache.control.extensions">Cache Control Extensions</a></li> |
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| 589 | </ul> |
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| 590 | </li> |
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| 591 | <li>3.3 <a href="#header.expires">Expires</a></li> |
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| 592 | <li>3.4 <a href="#header.pragma">Pragma</a></li> |
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| 593 | <li>3.5 <a href="#header.vary">Vary</a></li> |
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| 594 | <li>3.6 <a href="#header.warning">Warning</a></li> |
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| 595 | </ul> |
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| 596 | </li> |
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| 597 | <li>4. <a href="#history.lists">History Lists</a></li> |
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| 598 | <li>5. <a href="#IANA.considerations">IANA Considerations</a><ul> |
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| 599 | <li>5.1 <a href="#cache.directive.registration">Cache Directive Registry</a></li> |
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| 600 | <li>5.2 <a href="#header.field.registration">Header Field Registration</a></li> |
|---|
| 601 | </ul> |
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| 602 | </li> |
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| 603 | <li>6. <a href="#security.considerations">Security Considerations</a></li> |
|---|
| 604 | <li>7. <a href="#acks">Acknowledgments</a></li> |
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| 605 | <li>8. <a href="#rfc.references">References</a><ul> |
|---|
| 606 | <li>8.1 <a href="#rfc.references.1">Normative References</a></li> |
|---|
| 607 | <li>8.2 <a href="#rfc.references.2">Informative References</a></li> |
|---|
| 608 | </ul> |
|---|
| 609 | </li> |
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| 610 | <li><a href="#rfc.authors">Authors' Addresses</a></li> |
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| 611 | <li>A. <a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li> |
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| 612 | <li>B. <a href="#collected.abnf">Collected ABNF</a></li> |
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| 613 | <li>C. <a href="#change.log">Change Log (to be removed by RFC Editor before publication)</a><ul> |
|---|
| 614 | <li>C.1 <a href="#rfc.section.C.1">Since RFC 2616</a></li> |
|---|
| 615 | <li>C.2 <a href="#rfc.section.C.2">Since draft-ietf-httpbis-p6-cache-00</a></li> |
|---|
| 616 | <li>C.3 <a href="#rfc.section.C.3">Since draft-ietf-httpbis-p6-cache-01</a></li> |
|---|
| 617 | <li>C.4 <a href="#changes.since.02">Since draft-ietf-httpbis-p6-cache-02</a></li> |
|---|
| 618 | <li>C.5 <a href="#changes.since.03">Since draft-ietf-httpbis-p6-cache-03</a></li> |
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| 619 | <li>C.6 <a href="#changes.since.04">Since draft-ietf-httpbis-p6-cache-04</a></li> |
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| 620 | <li>C.7 <a href="#changes.since.05">Since draft-ietf-httpbis-p6-cache-05</a></li> |
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| 621 | <li>C.8 <a href="#changes.since.06">Since draft-ietf-httpbis-p6-cache-06</a></li> |
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| 622 | <li>C.9 <a href="#changes.since.07">Since draft-ietf-httpbis-p6-cache-07</a></li> |
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| 623 | <li>C.10 <a href="#changes.since.08">Since draft-ietf-httpbis-p6-cache-08</a></li> |
|---|
| 624 | <li>C.11 <a href="#changes.since.09">Since draft-ietf-httpbis-p6-cache-09</a></li> |
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| 625 | <li>C.12 <a href="#changes.since.10">Since draft-ietf-httpbis-p6-cache-10</a></li> |
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| 626 | <li>C.13 <a href="#changes.since.11">Since draft-ietf-httpbis-p6-cache-11</a></li> |
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| 627 | <li>C.14 <a href="#changes.since.12">Since draft-ietf-httpbis-p6-cache-12</a></li> |
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| 628 | <li>C.15 <a href="#changes.since.13">Since draft-ietf-httpbis-p6-cache-13</a></li> |
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| 629 | <li>C.16 <a href="#changes.since.14">Since draft-ietf-httpbis-p6-cache-14</a></li> |
|---|
| 630 | <li>C.17 <a href="#changes.since.15">Since draft-ietf-httpbis-p6-cache-15</a></li> |
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| 631 | <li>C.18 <a href="#changes.since.16">Since draft-ietf-httpbis-p6-cache-16</a></li> |
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| 632 | </ul> |
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| 633 | </li> |
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| 634 | <li><a href="#rfc.index">Index</a></li> |
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| 635 | </ul> |
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| 636 | <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a> <a id="caching" href="#caching">Introduction</a></h1> |
|---|
| 637 | <p id="rfc.section.1.p.1">HTTP is typically used for distributed information systems, where performance can be improved by the use of response caches. |
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| 638 | This document defines aspects of HTTP/1.1 related to caching and reusing response messages. |
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| 639 | </p> |
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| 640 | <div id="rfc.iref.c.1"></div> |
|---|
| 641 | <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a> <a id="intro.purpose" href="#intro.purpose">Purpose</a></h2> |
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| 642 | <p id="rfc.section.1.1.p.1">An HTTP <dfn>cache</dfn> is a local store of response messages and the subsystem that controls its message storage, retrieval, and deletion. A cache |
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| 643 | stores cacheable responses in order to reduce the response time and network bandwidth consumption on future, equivalent requests. |
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| 644 | Any client or server <em class="bcp14">MAY</em> employ a cache, though a cache cannot be used by a server that is acting as a tunnel. |
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| 645 | </p> |
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| 646 | <p id="rfc.section.1.1.p.2">The goal of caching in HTTP/1.1 is to significantly improve performance by reusing a prior response message to satisfy a current |
|---|
| 647 | request. A stored response is considered "fresh", as defined in <a href="#expiration.model" title="Freshness Model">Section 2.3</a>, if the response can be reused without "validation" (checking with the origin server to see if the cached response remains |
|---|
| 648 | valid for this request). A fresh cache response can therefore reduce both latency and network transfers each time it is reused. |
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| 649 | When a cached response is not fresh, it might still be reusable if it can be freshened by validation (<a href="#validation.model" title="Validation Model">Section 2.4</a>) or if the origin is unavailable. |
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| 650 | </p> |
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| 651 | <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a> <a id="intro.terminology" href="#intro.terminology">Terminology</a></h2> |
|---|
| 652 | <p id="rfc.section.1.2.p.1">This specification uses a number of terms to refer to the roles played by participants in, and objects of, HTTP caching.</p> |
|---|
| 653 | <p id="rfc.section.1.2.p.2"> <span id="rfc.iref.c.2"></span> <dfn>cache</dfn> |
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| 654 | </p> |
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| 655 | <ul class="empty"> |
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| 656 | <li>A conformant implementation of a HTTP cache. Note that this implies an HTTP/1.1 cache; this specification does not define |
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| 657 | conformance for HTTP/1.0 caches. |
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| 658 | </li> |
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| 659 | </ul> |
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| 660 | <div id="shared.and.non-shared.caches"> |
|---|
| 661 | <p id="rfc.section.1.2.p.3"> <span id="rfc.iref.s.1"></span> <dfn>shared cache</dfn> |
|---|
| 662 | </p> |
|---|
| 663 | <ul class="empty"> |
|---|
| 664 | <li>A cache that stores responses to be reused by more than one user; usually (but not always) deployed as part of an intermediary.</li> |
|---|
| 665 | </ul> |
|---|
| 666 | </div> |
|---|
| 667 | <p id="rfc.section.1.2.p.4"> <span id="rfc.iref.p.1"></span> <dfn>private cache</dfn> |
|---|
| 668 | </p> |
|---|
| 669 | <ul class="empty"> |
|---|
| 670 | <li>A cache that is dedicated to a single user.</li> |
|---|
| 671 | </ul> |
|---|
| 672 | <p id="rfc.section.1.2.p.5"> <span id="rfc.iref.c.3"></span> <dfn>cacheable</dfn> |
|---|
| 673 | </p> |
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| 674 | <ul class="empty"> |
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| 675 | <li>A response is cacheable if a cache is allowed to store a copy of the response message for use in answering subsequent requests. |
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| 676 | Even when a response is cacheable, there might be additional constraints on whether a cache can use the stored copy to satisfy |
|---|
| 677 | a particular request. |
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| 678 | </li> |
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| 679 | </ul> |
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| 680 | <p id="rfc.section.1.2.p.6"> <span id="rfc.iref.e.1"></span> <dfn>explicit expiration time</dfn> |
|---|
| 681 | </p> |
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| 682 | <ul class="empty"> |
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| 683 | <li>The time at which the origin server intends that a representation no longer be returned by a cache without further validation.</li> |
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| 684 | </ul> |
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| 685 | <p id="rfc.section.1.2.p.7"> <span id="rfc.iref.h.1"></span> <dfn>heuristic expiration time</dfn> |
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| 686 | </p> |
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| 687 | <ul class="empty"> |
|---|
| 688 | <li>An expiration time assigned by a cache when no explicit expiration time is available.</li> |
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| 689 | </ul> |
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| 690 | <p id="rfc.section.1.2.p.8"> <span id="rfc.iref.a.1"></span> <dfn>age</dfn> |
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| 691 | </p> |
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| 692 | <ul class="empty"> |
|---|
| 693 | <li>The age of a response is the time since it was sent by, or successfully validated with, the origin server.</li> |
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| 694 | </ul> |
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| 695 | <p id="rfc.section.1.2.p.9"> <span id="rfc.iref.f.1"></span> <dfn>first-hand</dfn> |
|---|
| 696 | </p> |
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| 697 | <ul class="empty"> |
|---|
| 698 | <li>A response is first-hand if the freshness model is not in use; i.e., its age is 0.</li> |
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| 699 | </ul> |
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| 700 | <p id="rfc.section.1.2.p.10"> <span id="rfc.iref.f.2"></span> <dfn>freshness lifetime</dfn> |
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| 701 | </p> |
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| 702 | <ul class="empty"> |
|---|
| 703 | <li>The length of time between the generation of a response and its expiration time.</li> |
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| 704 | </ul> |
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| 705 | <p id="rfc.section.1.2.p.11"> <span id="rfc.iref.f.3"></span> <dfn>fresh</dfn> |
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| 706 | </p> |
|---|
| 707 | <ul class="empty"> |
|---|
| 708 | <li>A response is fresh if its age has not yet exceeded its freshness lifetime.</li> |
|---|
| 709 | </ul> |
|---|
| 710 | <p id="rfc.section.1.2.p.12"> <span id="rfc.iref.s.2"></span> <dfn>stale</dfn> |
|---|
| 711 | </p> |
|---|
| 712 | <ul class="empty"> |
|---|
| 713 | <li>A response is stale if its age has passed its freshness lifetime (either explicit or heuristic).</li> |
|---|
| 714 | </ul> |
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| 715 | <p id="rfc.section.1.2.p.13"> <span id="rfc.iref.v.1"></span> <dfn>validator</dfn> |
|---|
| 716 | </p> |
|---|
| 717 | <ul class="empty"> |
|---|
| 718 | <li>A protocol element (e.g., an entity-tag or a Last-Modified time) that is used to find out whether a stored response is an |
|---|
| 719 | equivalent copy of a representation. See <a href="p4-conditional.html#weak.and.strong.validators" title="Weak versus Strong">Section 2.1</a> of <a href="#Part4" id="rfc.xref.Part4.1"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>. |
|---|
| 720 | </li> |
|---|
| 721 | </ul> |
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| 722 | <p id="rfc.section.1.2.p.14"> <span id="rfc.iref.s.3"></span> <span id="rfc.iref.v.2"></span> <dfn>strong validator</dfn> |
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| 723 | </p> |
|---|
| 724 | <ul class="empty"> |
|---|
| 725 | <li>A validator that is defined by the origin server such that its current value will change if the representation body changes; |
|---|
| 726 | i.e., an entity-tag that is not marked as weak (<a href="p4-conditional.html#header.etag" title="ETag">Section 2.3</a> of <a href="#Part4" id="rfc.xref.Part4.2"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>) or, if no entity-tag is provided, a Last-Modified value that is strong in the sense defined by <a href="p4-conditional.html#lastmod.comparison" title="Comparison">Section 2.2.2</a> of <a href="#Part4" id="rfc.xref.Part4.3"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>. |
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| 727 | </li> |
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| 728 | </ul> |
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| 729 | <h2 id="rfc.section.1.3"><a href="#rfc.section.1.3">1.3</a> <a id="intro.conformance.and.error.handling" href="#intro.conformance.and.error.handling">Conformance and Error Handling</a></h2> |
|---|
| 730 | <p id="rfc.section.1.3.p.1">The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" |
|---|
| 731 | 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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| 732 | </p> |
|---|
| 733 | <p id="rfc.section.1.3.p.2">This document defines conformance criteria for several roles in HTTP communication, including Senders, Recipients, Clients, |
|---|
| 734 | 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. |
|---|
| 735 | </p> |
|---|
| 736 | <p id="rfc.section.1.3.p.3">An implementation is considered conformant if it complies with all of the requirements associated with its role(s). Note that |
|---|
| 737 | SHOULD-level requirements are relevant here, unless one of the documented exceptions is applicable. |
|---|
| 738 | </p> |
|---|
| 739 | <p id="rfc.section.1.3.p.4">This document also uses ABNF to define valid protocol elements (<a href="#notation" title="Syntax Notation">Section 1.4</a>). In addition to the prose requirements placed upon them, Senders <em class="bcp14">MUST NOT</em> generate protocol elements that are invalid. |
|---|
| 740 | </p> |
|---|
| 741 | <p id="rfc.section.1.3.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 |
|---|
| 742 | mechanisms, except in cases where it has direct impact on security. This is because different uses of the protocol require |
|---|
| 743 | different error handling strategies; for example, a Web browser may wish to transparently recover from a response where the |
|---|
| 744 | Location header field doesn't parse according to the ABNF, whereby in a systems control protocol using HTTP, this type of |
|---|
| 745 | error recovery could lead to dangerous consequences. |
|---|
| 746 | </p> |
|---|
| 747 | <h2 id="rfc.section.1.4"><a href="#rfc.section.1.4">1.4</a> <a id="notation" href="#notation">Syntax Notation</a></h2> |
|---|
| 748 | <p id="rfc.section.1.4.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. |
|---|
| 749 | </p> |
|---|
| 750 | <p id="rfc.section.1.4.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 |
|---|
| 751 | (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 |
|---|
| 752 | character). |
|---|
| 753 | </p> |
|---|
| 754 | <h3 id="rfc.section.1.4.1"><a href="#rfc.section.1.4.1">1.4.1</a> <a id="core.rules" href="#core.rules">Core Rules</a></h3> |
|---|
| 755 | <p id="rfc.section.1.4.1.p.1">The core 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>: |
|---|
| 756 | </p> |
|---|
| 757 | <div id="rfc.figure.u.1"></div><pre class="inline"> <a href="#core.rules" class="smpl">OWS</a> = <OWS, defined in <a href="#Part1" id="rfc.xref.Part1.4"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#basic.rules" title="Basic Rules">Section 1.2.2</a>> |
|---|
| 758 | <a href="#core.rules" class="smpl">quoted-string</a> = <quoted-string, 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>> |
|---|
| 759 | <a href="#core.rules" class="smpl">token</a> = <token, defined in <a href="#Part1" id="rfc.xref.Part1.6"><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>> |
|---|
| 760 | </pre><h3 id="rfc.section.1.4.2"><a href="#rfc.section.1.4.2">1.4.2</a> <a id="abnf.dependencies" href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></h3> |
|---|
| 761 | <p id="rfc.section.1.4.2.p.1">The ABNF rules below are defined in other parts:</p> |
|---|
| 762 | <div id="rfc.figure.u.2"></div><pre class="inline"> <a href="#abnf.dependencies" class="smpl">field-name</a> = <field-name, defined in <a href="#Part1" id="rfc.xref.Part1.7"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#header.fields" title="Header Fields">Section 3.2</a>> |
|---|
| 763 | <a href="#abnf.dependencies" class="smpl">HTTP-date</a> = <HTTP-date, defined in <a href="#Part2" id="rfc.xref.Part2.1"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>, <a href="p2-semantics.html#http.date" title="Date/Time Formats">Section 8</a>> |
|---|
| 764 | <a href="#abnf.dependencies" class="smpl">port</a> = <port, defined in <a href="#Part1" id="rfc.xref.Part1.8"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#uri" title="Uniform Resource Identifiers">Section 2.7</a>> |
|---|
| 765 | <a href="#abnf.dependencies" class="smpl">pseudonym</a> = <pseudonym, defined in <a href="#Part1" id="rfc.xref.Part1.9"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#header.via" title="Via">Section 8.8</a>> |
|---|
| 766 | <a href="#abnf.dependencies" class="smpl">uri-host</a> = <uri-host, defined in <a href="#Part1" id="rfc.xref.Part1.10"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#uri" title="Uniform Resource Identifiers">Section 2.7</a>> |
|---|
| 767 | </pre><h2 id="rfc.section.1.5"><a href="#rfc.section.1.5">1.5</a> <a id="delta-seconds" href="#delta-seconds">Delta Seconds</a></h2> |
|---|
| 768 | <p id="rfc.section.1.5.p.1">The delta-seconds rule specifies a non-negative integer, representing time in seconds.</p> |
|---|
| 769 | <div id="rfc.figure.u.3"></div><pre class="inline"><span id="rfc.iref.g.1"></span> <a href="#delta-seconds" class="smpl">delta-seconds</a> = 1*<a href="#notation" class="smpl">DIGIT</a> |
|---|
| 770 | </pre><p id="rfc.section.1.5.p.3">If an implementation receives a delta-seconds value larger than the largest positive integer it can represent, or if any of |
|---|
| 771 | its subsequent calculations overflows, it <em class="bcp14">MUST</em> consider the value to be 2147483648 (2<sup>31</sup>). Recipients parsing a delta-seconds value <em class="bcp14">MUST</em> use an arithmetic type of at least 31 bits of range, and senders <em class="bcp14">MUST NOT</em> send delta-seconds with a value greater than 2147483648. |
|---|
| 772 | </p> |
|---|
| 773 | <div id="rfc.iref.c.4"></div> |
|---|
| 774 | <div id="rfc.iref.c.5"></div> |
|---|
| 775 | <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a> <a id="caching.overview" href="#caching.overview">Cache Operation</a></h1> |
|---|
| 776 | <p id="rfc.section.2.p.1">Proper cache operation preserves the semantics of HTTP transfers (<a href="#Part2" id="rfc.xref.Part2.2"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) while eliminating the transfer of information already held in the cache. Although caching is an entirely <em class="bcp14">OPTIONAL</em> feature of HTTP, we assume that reusing the cached response is desirable and that such reuse is the default behavior when |
|---|
| 777 | no requirement or locally-desired configuration prevents it. Therefore, HTTP cache requirements are focused on preventing |
|---|
| 778 | a cache from either storing a non-reusable response or reusing a stored response inappropriately. |
|---|
| 779 | </p> |
|---|
| 780 | <p id="rfc.section.2.p.2">Each <dfn>cache entry</dfn> consists of a cache key and one or more HTTP responses corresponding to prior requests that used the same key. The most common |
|---|
| 781 | form of cache entry is a successful result of a retrieval request: i.e., a 200 (OK) response containing a representation of |
|---|
| 782 | the resource identified by the request target. However, it is also possible to cache negative results (e.g., 404 not found), |
|---|
| 783 | incomplete results (e.g., 206 partial content), and responses to safe methods other than GET if the method's definition allows |
|---|
| 784 | such caching and defines something suitable for use as a cache key. |
|---|
| 785 | </p> |
|---|
| 786 | <p id="rfc.section.2.p.3">The default <dfn>cache key</dfn> consists of the request method and target URI. However, since HTTP caches in common use today are typically limited to caching |
|---|
| 787 | responses to GET, most implementations simply decline other methods and use only the URI as the key. |
|---|
| 788 | </p> |
|---|
| 789 | <p id="rfc.section.2.p.4">If a request target is subject to content negotiation, its cache entry might consist of multiple stored responses, each differentiated |
|---|
| 790 | by a secondary key for the values of the original request's selecting header fields (<a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section 2.7</a>). |
|---|
| 791 | </p> |
|---|
| 792 | <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a> <a id="response.cacheability" href="#response.cacheability">Response Cacheability</a></h2> |
|---|
| 793 | <p id="rfc.section.2.1.p.1">A cache <em class="bcp14">MUST NOT</em> store a response to any request, unless: |
|---|
| 794 | </p> |
|---|
| 795 | <ul> |
|---|
| 796 | <li>The request method is understood by the cache and defined as being cacheable, and</li> |
|---|
| 797 | <li>the response status code is understood by the cache, and</li> |
|---|
| 798 | <li>the "no-store" cache directive (see <a href="#header.cache-control" id="rfc.xref.header.cache-control.1" title="Cache-Control">Section 3.2</a>) does not appear in request or response header fields, and |
|---|
| 799 | </li> |
|---|
| 800 | <li>the "private" cache response directive (see <a href="#cache-response-directive" title="Response Cache-Control Directives">Section 3.2.2</a> does not appear in the response, if the cache is shared, and |
|---|
| 801 | </li> |
|---|
| 802 | <li>the "Authorization" header field (see <a href="p7-auth.html#header.authorization" title="Authorization">Section 4.1</a> of <a href="#Part7" id="rfc.xref.Part7.1"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a>) does not appear in the request, if the cache is shared, unless the response explicitly allows it (see <a href="#caching.authenticated.responses" title="Shared Caching of Authenticated Responses">Section 2.6</a>), and |
|---|
| 803 | </li> |
|---|
| 804 | <li>the response either: |
|---|
| 805 | <ul> |
|---|
| 806 | <li>contains an Expires header field (see <a href="#header.expires" id="rfc.xref.header.expires.1" title="Expires">Section 3.3</a>), or |
|---|
| 807 | </li> |
|---|
| 808 | <li>contains a max-age response cache directive (see <a href="#cache-response-directive" title="Response Cache-Control Directives">Section 3.2.2</a>), or |
|---|
| 809 | </li> |
|---|
| 810 | <li>contains a s-maxage response cache directive and the cache is shared, or</li> |
|---|
| 811 | <li>contains a Cache Control Extension (see <a href="#cache.control.extensions" title="Cache Control Extensions">Section 3.2.3</a>) that allows it to be cached, or |
|---|
| 812 | </li> |
|---|
| 813 | <li>has a status code that can be served with heuristic freshness (see <a href="#heuristic.freshness" title="Calculating Heuristic Freshness">Section 2.3.1.1</a>). |
|---|
| 814 | </li> |
|---|
| 815 | </ul> |
|---|
| 816 | </li> |
|---|
| 817 | </ul> |
|---|
| 818 | <p id="rfc.section.2.1.p.2">Note that any of the requirements listed above can be overridden by a cache-control extension; see <a href="#cache.control.extensions" title="Cache Control Extensions">Section 3.2.3</a>. |
|---|
| 819 | </p> |
|---|
| 820 | <p id="rfc.section.2.1.p.3">In this context, a cache has "understood" a request method or a response status code if it recognizes it and implements any |
|---|
| 821 | cache-specific behavior. |
|---|
| 822 | </p> |
|---|
| 823 | <p id="rfc.section.2.1.p.4">Note that, in normal operation, most caches will not store a response that has neither a cache validator nor an explicit expiration |
|---|
| 824 | time, as such responses are not usually useful to store. However, caches are not prohibited from storing such responses. |
|---|
| 825 | </p> |
|---|
| 826 | <p id="rfc.section.2.1.p.5">A response message is considered complete when all of the octets indicated by the message framing (<a href="#Part1" id="rfc.xref.Part1.11"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) are received prior to the connection being closed. If the request is GET, the response status is 200 (OK), and the entire |
|---|
| 827 | response header block has been received, a cache <em class="bcp14">MAY</em> store an incomplete response message-body if the cache entry is recorded as incomplete. Likewise, a 206 (Partial Content) |
|---|
| 828 | response <em class="bcp14">MAY</em> be stored as if it were an incomplete 200 (OK) cache entry. However, a cache <em class="bcp14">MUST NOT</em> store incomplete or partial content responses if it does not support the Range and Content-Range header fields or if it does |
|---|
| 829 | not understand the range units used in those fields. |
|---|
| 830 | </p> |
|---|
| 831 | <p id="rfc.section.2.1.p.6">A cache <em class="bcp14">MAY</em> complete a stored incomplete response by making a subsequent range request (<a href="#Part5" id="rfc.xref.Part5.1"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>) and combining the successful response with the stored entry, as defined in <a href="#combining.responses" title="Combining Partial Content">Section 2.8</a>. A cache <em class="bcp14">MUST NOT</em> use an incomplete response to answer requests unless the response has been made complete or the request is partial and specifies |
|---|
| 832 | a range that is wholly within the incomplete response. A cache <em class="bcp14">MUST NOT</em> send a partial response to a client without explicitly marking it as such using the 206 (Partial Content) status code. |
|---|
| 833 | </p> |
|---|
| 834 | <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a> <a id="constructing.responses.from.caches" href="#constructing.responses.from.caches">Constructing Responses from Caches</a></h2> |
|---|
| 835 | <p id="rfc.section.2.2.p.1">For a presented request, a cache <em class="bcp14">MUST NOT</em> return a stored response, unless: |
|---|
| 836 | </p> |
|---|
| 837 | <ul> |
|---|
| 838 | <li>The presented effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.12"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) and that of the stored response match, and |
|---|
| 839 | </li> |
|---|
| 840 | <li>the request method associated with the stored response allows it to be used for the presented request, and</li> |
|---|
| 841 | <li>selecting header fields nominated by the stored response (if any) match those presented (see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section 2.7</a>), and |
|---|
| 842 | </li> |
|---|
| 843 | <li>the presented request and stored response are free from directives that would prevent its use (see <a href="#header.cache-control" id="rfc.xref.header.cache-control.2" title="Cache-Control">Section 3.2</a> and <a href="#header.pragma" id="rfc.xref.header.pragma.1" title="Pragma">Section 3.4</a>), and |
|---|
| 844 | </li> |
|---|
| 845 | <li>the stored response is either: |
|---|
| 846 | <ul> |
|---|
| 847 | <li>fresh (see <a href="#expiration.model" title="Freshness Model">Section 2.3</a>), or |
|---|
| 848 | </li> |
|---|
| 849 | <li>allowed to be served stale (see <a href="#serving.stale.responses" title="Serving Stale Responses">Section 2.3.3</a>), or |
|---|
| 850 | </li> |
|---|
| 851 | <li>successfully validated (see <a href="#validation.model" title="Validation Model">Section 2.4</a>). |
|---|
| 852 | </li> |
|---|
| 853 | </ul> |
|---|
| 854 | </li> |
|---|
| 855 | </ul> |
|---|
| 856 | <p id="rfc.section.2.2.p.2">Note that any of the requirements listed above can be overridden by a cache-control extension; see <a href="#cache.control.extensions" title="Cache Control Extensions">Section 3.2.3</a>. |
|---|
| 857 | </p> |
|---|
| 858 | <p id="rfc.section.2.2.p.3">When a stored response is used to satisfy a request without validation, a cache <em class="bcp14">MUST</em> include a single Age header field (<a href="#header.age" id="rfc.xref.header.age.1" title="Age">Section 3.1</a>) in the response with a value equal to the stored response's current_age; see <a href="#age.calculations" title="Calculating Age">Section 2.3.2</a>. |
|---|
| 859 | </p> |
|---|
| 860 | <p id="rfc.section.2.2.p.4">A cache <em class="bcp14">MUST</em> write through requests with methods that are unsafe (<a href="p2-semantics.html#safe.methods" title="Safe Methods">Section 6.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.3"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) to the origin server; i.e., a cache must not generate a reply to such a request before having forwarded the request and |
|---|
| 861 | having received a corresponding response. |
|---|
| 862 | </p> |
|---|
| 863 | <p id="rfc.section.2.2.p.5">Also, note that unsafe requests might invalidate already stored responses; see <a href="#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section 2.5</a>. |
|---|
| 864 | </p> |
|---|
| 865 | <p id="rfc.section.2.2.p.6">When more than one suitable response is stored, a cache <em class="bcp14">MUST</em> use the most recent response (as determined by the Date header field). It can also forward a request with "Cache-Control: |
|---|
| 866 | max-age=0" or "Cache-Control: no-cache" to disambiguate which response to use. |
|---|
| 867 | </p> |
|---|
| 868 | <p id="rfc.section.2.2.p.7">A cache that does not have a clock available <em class="bcp14">MUST NOT</em> use stored responses without revalidating them on every use. A cache, especially a shared cache, <em class="bcp14">SHOULD</em> use a mechanism, such as NTP <a href="#RFC1305" id="rfc.xref.RFC1305.1"><cite title="Network Time Protocol (Version 3) Specification, Implementation">[RFC1305]</cite></a>, to synchronize its clock with a reliable external standard. |
|---|
| 869 | </p> |
|---|
| 870 | <h2 id="rfc.section.2.3"><a href="#rfc.section.2.3">2.3</a> <a id="expiration.model" href="#expiration.model">Freshness Model</a></h2> |
|---|
| 871 | <p id="rfc.section.2.3.p.1">When a response is "fresh" in the cache, it can be used to satisfy subsequent requests without contacting the origin server, |
|---|
| 872 | thereby improving efficiency. |
|---|
| 873 | </p> |
|---|
| 874 | <p id="rfc.section.2.3.p.2">The primary mechanism for determining freshness is for an origin server to provide an explicit expiration time in the future, |
|---|
| 875 | using either the Expires header field (<a href="#header.expires" id="rfc.xref.header.expires.2" title="Expires">Section 3.3</a>) or the max-age response cache directive (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section 3.2.2</a>). Generally, origin servers will assign future explicit expiration times to responses in the belief that the representation |
|---|
| 876 | is not likely to change in a semantically significant way before the expiration time is reached. |
|---|
| 877 | </p> |
|---|
| 878 | <p id="rfc.section.2.3.p.3">If an origin server wishes to force a cache to validate every request, it can assign an explicit expiration time in the past |
|---|
| 879 | to indicate that the response is already stale. Compliant caches will normally validate the cached response before reusing |
|---|
| 880 | it for subsequent requests (see <a href="#serving.stale.responses" title="Serving Stale Responses">Section 2.3.3</a>). |
|---|
| 881 | </p> |
|---|
| 882 | <p id="rfc.section.2.3.p.4">Since origin servers do not always provide explicit expiration times, a cache <em class="bcp14">MAY</em> assign a heuristic expiration time when an explicit time is not specified, employing algorithms that use other header field |
|---|
| 883 | values (such as the Last-Modified time) to estimate a plausible expiration time. This specification does not provide specific |
|---|
| 884 | algorithms, but does impose worst-case constraints on their results. |
|---|
| 885 | </p> |
|---|
| 886 | <div id="rfc.figure.u.4"></div> |
|---|
| 887 | <p>The calculation to determine if a response is fresh is:</p> <pre class="text"> response_is_fresh = (freshness_lifetime > current_age) |
|---|
| 888 | </pre> <p id="rfc.section.2.3.p.6">The freshness_lifetime is defined in <a href="#calculating.freshness.lifetime" title="Calculating Freshness Lifetime">Section 2.3.1</a>; the current_age is defined in <a href="#age.calculations" title="Calculating Age">Section 2.3.2</a>. |
|---|
| 889 | </p> |
|---|
| 890 | <p id="rfc.section.2.3.p.7">Additionally, clients might need to influence freshness calculation. They can do this using several request cache directives, |
|---|
| 891 | with the effect of either increasing or loosening constraints on freshness. See <a href="#cache-request-directive" title="Request Cache-Control Directives">Section 3.2.1</a>. |
|---|
| 892 | </p> |
|---|
| 893 | <p id="rfc.section.2.3.p.8">Note that freshness applies only to cache operation; it cannot be used to force a user agent to refresh its display or reload |
|---|
| 894 | a resource. See <a href="#history.lists" title="History Lists">Section 4</a> for an explanation of the difference between caches and history mechanisms. |
|---|
| 895 | </p> |
|---|
| 896 | <h3 id="rfc.section.2.3.1"><a href="#rfc.section.2.3.1">2.3.1</a> <a id="calculating.freshness.lifetime" href="#calculating.freshness.lifetime">Calculating Freshness Lifetime</a></h3> |
|---|
| 897 | <p id="rfc.section.2.3.1.p.1">A cache can calculate the freshness lifetime (denoted as freshness_lifetime) of a response by using the first match of: </p> |
|---|
| 898 | <ul> |
|---|
| 899 | <li>If the cache is shared and the s-maxage response cache directive (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section 3.2.2</a>) is present, use its value, or |
|---|
| 900 | </li> |
|---|
| 901 | <li>If the max-age response cache directive (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section 3.2.2</a>) is present, use its value, or |
|---|
| 902 | </li> |
|---|
| 903 | <li>If the Expires response header field (<a href="#header.expires" id="rfc.xref.header.expires.3" title="Expires">Section 3.3</a>) is present, use its value minus the value of the Date response header field, or |
|---|
| 904 | </li> |
|---|
| 905 | <li>Otherwise, no explicit expiration time is present in the response. A heuristic freshness lifetime might be applicable; see <a href="#heuristic.freshness" title="Calculating Heuristic Freshness">Section 2.3.1.1</a>. |
|---|
| 906 | </li> |
|---|
| 907 | </ul> |
|---|
| 908 | <p id="rfc.section.2.3.1.p.2">Note that this calculation is not vulnerable to clock skew, since all of the information comes from the origin server.</p> |
|---|
| 909 | <h4 id="rfc.section.2.3.1.1"><a href="#rfc.section.2.3.1.1">2.3.1.1</a> <a id="heuristic.freshness" href="#heuristic.freshness">Calculating Heuristic Freshness</a></h4> |
|---|
| 910 | <p id="rfc.section.2.3.1.1.p.1">If no explicit expiration time is present in a stored response that has a status code whose definition allows heuristic freshness |
|---|
| 911 | to be used (including the following in <a href="p2-semantics.html#status.codes" title="Status Code Definitions">Section 7</a> of <a href="#Part2" id="rfc.xref.Part2.4"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>: 200, 203, 206, 300, 301 and 410), a cache <em class="bcp14">MAY</em> calculate a heuristic expiration time. A cache <em class="bcp14">MUST NOT</em> use heuristics to determine freshness for responses with status codes that do not explicitly allow it. |
|---|
| 912 | </p> |
|---|
| 913 | <p id="rfc.section.2.3.1.1.p.2">When a heuristic is used to calculate freshness lifetime, a cache <em class="bcp14">SHOULD</em> attach a Warning header field with a 113 warn-code to the response if its current_age is more than 24 hours and such a warning |
|---|
| 914 | is not already present. |
|---|
| 915 | </p> |
|---|
| 916 | <p id="rfc.section.2.3.1.1.p.3">Also, if the response has a Last-Modified header field (<a href="p4-conditional.html#header.last-modified" title="Last-Modified">Section 2.2</a> of <a href="#Part4" id="rfc.xref.Part4.4"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>), caches are encouraged to use a heuristic expiration value that is no more than some fraction of the interval since that |
|---|
| 917 | time. A typical setting of this fraction might be 10%. |
|---|
| 918 | </p> |
|---|
| 919 | <div class="note" id="rfc.section.2.3.1.1.p.4"> |
|---|
| 920 | <p> <b>Note:</b> RFC 2616 (<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-13.9">Section 13.9</a>) required that caches do not calculate heuristic freshness for URIs with query components (i.e., those containing '?'). In |
|---|
| 921 | practice, this has not been widely implemented. Therefore, servers are encouraged to send explicit directives (e.g., Cache-Control: |
|---|
| 922 | no-cache) if they wish to preclude caching. |
|---|
| 923 | </p> |
|---|
| 924 | </div> |
|---|
| 925 | <h3 id="rfc.section.2.3.2"><a href="#rfc.section.2.3.2">2.3.2</a> <a id="age.calculations" href="#age.calculations">Calculating Age</a></h3> |
|---|
| 926 | <p id="rfc.section.2.3.2.p.1">HTTP/1.1 uses the Age header field to convey the estimated age of the response message when obtained from a cache. The Age |
|---|
| 927 | field value is the cache's estimate of the amount of time since the response was generated or validated by the origin server. |
|---|
| 928 | In essence, the Age value is the sum of the time that the response has been resident in each of the caches along the path |
|---|
| 929 | from the origin server, plus the amount of time it has been in transit along network paths. |
|---|
| 930 | </p> |
|---|
| 931 | <p id="rfc.section.2.3.2.p.2">The following data is used for the age calculation:</p> |
|---|
| 932 | <p id="rfc.section.2.3.2.p.3"> <dfn>age_value</dfn> |
|---|
| 933 | </p> |
|---|
| 934 | <ul class="empty"> |
|---|
| 935 | <li>The term "age_value" denotes the value of the Age header field (<a href="#header.age" id="rfc.xref.header.age.2" title="Age">Section 3.1</a>), in a form appropriate for arithmetic operation; or 0, if not available. |
|---|
| 936 | </li> |
|---|
| 937 | </ul> |
|---|
| 938 | <p id="rfc.section.2.3.2.p.4"> <dfn>date_value</dfn> |
|---|
| 939 | </p> |
|---|
| 940 | <ul class="empty"> |
|---|
| 941 | <li>HTTP/1.1 requires origin servers to send a Date header field, if possible, with every response, giving the time at which the |
|---|
| 942 | response was generated. The term "date_value" denotes the value of the Date header field, in a form appropriate for arithmetic |
|---|
| 943 | operations. See <a href="p2-semantics.html#header.date" title="Date">Section 9.2</a> of <a href="#Part2" id="rfc.xref.Part2.5"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a> for the definition of the Date header field, and for requirements regarding responses without it. |
|---|
| 944 | </li> |
|---|
| 945 | </ul> |
|---|
| 946 | <p id="rfc.section.2.3.2.p.5"> <dfn>now</dfn> |
|---|
| 947 | </p> |
|---|
| 948 | <ul class="empty"> |
|---|
| 949 | <li>The term "now" means "the current value of the clock at the host performing the calculation". A cache <em class="bcp14">SHOULD</em> use NTP (<a href="#RFC1305" id="rfc.xref.RFC1305.2"><cite title="Network Time Protocol (Version 3) Specification, Implementation">[RFC1305]</cite></a>) or some similar protocol to synchronize its clocks to a globally accurate time standard. |
|---|
| 950 | </li> |
|---|
| 951 | </ul> |
|---|
| 952 | <p id="rfc.section.2.3.2.p.6"> <dfn>request_time</dfn> |
|---|
| 953 | </p> |
|---|
| 954 | <ul class="empty"> |
|---|
| 955 | <li>The current value of the clock at the host at the time the request resulting in the stored response was made.</li> |
|---|
| 956 | </ul> |
|---|
| 957 | <p id="rfc.section.2.3.2.p.7"> <dfn>response_time</dfn> |
|---|
| 958 | </p> |
|---|
| 959 | <ul class="empty"> |
|---|
| 960 | <li>The current value of the clock at the host at the time the response was received.</li> |
|---|
| 961 | </ul> |
|---|
| 962 | <p id="rfc.section.2.3.2.p.8">A response's age can be calculated in two entirely independent ways: </p> |
|---|
| 963 | <ol> |
|---|
| 964 | <li>the "apparent_age": response_time minus date_value, if the local clock is reasonably well synchronized to the origin server's |
|---|
| 965 | clock. If the result is negative, the result is replaced by zero. |
|---|
| 966 | </li> |
|---|
| 967 | <li>the "corrected_age_value", if all of the caches along the response path implement HTTP/1.1. A cache <em class="bcp14">MUST</em> interpret this value relative to the time the request was initiated, not the time that the response was received. |
|---|
| 968 | </li> |
|---|
| 969 | </ol> |
|---|
| 970 | <div id="rfc.figure.u.5"></div> <pre class="text"> apparent_age = max(0, response_time - date_value); |
|---|
| 971 | |
|---|
| 972 | response_delay = response_time - request_time; |
|---|
| 973 | corrected_age_value = age_value + response_delay; |
|---|
| 974 | </pre> <div id="rfc.figure.u.6"></div> |
|---|
| 975 | <p>These are combined as</p> <pre class="text"> corrected_initial_age = max(apparent_age, corrected_age_value); |
|---|
| 976 | </pre><p id="rfc.section.2.3.2.p.11">The current_age of a stored response can then be calculated by adding the amount of time (in seconds) since the stored response |
|---|
| 977 | was last validated by the origin server to the corrected_initial_age. |
|---|
| 978 | </p> |
|---|
| 979 | <div id="rfc.figure.u.7"></div><pre class="text"> resident_time = now - response_time; |
|---|
| 980 | current_age = corrected_initial_age + resident_time; |
|---|
| 981 | </pre><p id="rfc.section.2.3.2.p.13">Additionally, to avoid common problems in date parsing:</p> |
|---|
| 982 | <p id="rfc.section.2.3.2.p.14"> </p> |
|---|
| 983 | <ul> |
|---|
| 984 | <li>HTTP/1.1 clients and caches <em class="bcp14">SHOULD</em> assume that an RFC-850 date which appears to be more than 50 years in the future is in fact in the past (this helps solve |
|---|
| 985 | the "year 2000" problem). |
|---|
| 986 | </li> |
|---|
| 987 | <li>Although all date formats are specified to be case-sensitive, recipients <em class="bcp14">SHOULD</em> match day, week and timezone names case-insensitively. |
|---|
| 988 | </li> |
|---|
| 989 | <li>An HTTP/1.1 implementation <em class="bcp14">MAY</em> internally represent a parsed Expires date as earlier than the proper value, but <em class="bcp14">MUST NOT</em> internally represent a parsed Expires date as later than the proper value. |
|---|
| 990 | </li> |
|---|
| 991 | <li>All expiration-related calculations <em class="bcp14">MUST</em> be done in GMT. The local time zone <em class="bcp14">MUST NOT</em> influence the calculation or comparison of an age or expiration time. |
|---|
| 992 | </li> |
|---|
| 993 | <li>If an HTTP header field incorrectly carries a date value with a time zone other than GMT, it <em class="bcp14">MUST</em> be converted into GMT using the most conservative possible conversion. |
|---|
| 994 | </li> |
|---|
| 995 | </ul> |
|---|
| 996 | <h3 id="rfc.section.2.3.3"><a href="#rfc.section.2.3.3">2.3.3</a> <a id="serving.stale.responses" href="#serving.stale.responses">Serving Stale Responses</a></h3> |
|---|
| 997 | <p id="rfc.section.2.3.3.p.1">A "stale" response is one that either has explicit expiry information or is allowed to have heuristic expiry calculated, but |
|---|
| 998 | is not fresh according to the calculations in <a href="#expiration.model" title="Freshness Model">Section 2.3</a>. |
|---|
| 999 | </p> |
|---|
| 1000 | <p id="rfc.section.2.3.3.p.2">A cache <em class="bcp14">MUST NOT</em> return a stale response if it is prohibited by an explicit in-protocol directive (e.g., by a "no-store" or "no-cache" cache |
|---|
| 1001 | directive, a "must-revalidate" cache-response-directive, or an applicable "s-maxage" or "proxy-revalidate" cache-response-directive; |
|---|
| 1002 | see <a href="#cache-response-directive" title="Response Cache-Control Directives">Section 3.2.2</a>). |
|---|
| 1003 | </p> |
|---|
| 1004 | <p id="rfc.section.2.3.3.p.3">A cache <em class="bcp14">MUST NOT</em> return stale responses unless it is disconnected (i.e., it cannot contact the origin server or otherwise find a forward path) |
|---|
| 1005 | or doing so is explicitly allowed (e.g., by the max-stale request directive; see <a href="#cache-request-directive" title="Request Cache-Control Directives">Section 3.2.1</a>). |
|---|
| 1006 | </p> |
|---|
| 1007 | <p id="rfc.section.2.3.3.p.4">A cache <em class="bcp14">SHOULD</em> append a Warning header field with the 110 warn-code (see <a href="#header.warning" id="rfc.xref.header.warning.1" title="Warning">Section 3.6</a>) to stale responses. Likewise, a cache <em class="bcp14">SHOULD</em> add the 112 warn-code to stale responses if the cache is disconnected. |
|---|
| 1008 | </p> |
|---|
| 1009 | <p id="rfc.section.2.3.3.p.5">If a cache receives a first-hand response (either an entire response, or a 304 (Not Modified) response) that it would normally |
|---|
| 1010 | forward to the requesting client, and the received response is no longer fresh, the cache can forward it to the requesting |
|---|
| 1011 | client without adding a new Warning (but without removing any existing Warning header fields). A cache shouldn't attempt to |
|---|
| 1012 | validate a response simply because that response became stale in transit. |
|---|
| 1013 | </p> |
|---|
| 1014 | <h2 id="rfc.section.2.4"><a href="#rfc.section.2.4">2.4</a> <a id="validation.model" href="#validation.model">Validation Model</a></h2> |
|---|
| 1015 | <p id="rfc.section.2.4.p.1">When a cache has one or more stored responses for a requested URI, but cannot serve any of them (e.g., because they are not |
|---|
| 1016 | fresh, or one cannot be selected; see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section 2.7</a>), it can use the conditional request mechanism <a href="#Part4" id="rfc.xref.Part4.5"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a> in the forwarded request to give the origin server an opportunity to both select a valid stored response to be used, and to |
|---|
| 1017 | update it. This process is known as "validating" or "revalidating" the stored response. |
|---|
| 1018 | </p> |
|---|
| 1019 | <p id="rfc.section.2.4.p.2">When sending such a conditional request, a cache adds an If-Modified-Since header field whose value is that of the Last-Modified |
|---|
| 1020 | header field from the selected (see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section 2.7</a>) stored response, if available. |
|---|
| 1021 | </p> |
|---|
| 1022 | <p id="rfc.section.2.4.p.3">Additionally, a cache can add an If-None-Match header field whose value is that of the ETag header field(s) from all responses |
|---|
| 1023 | stored for the requested URI, if present. However, if any of the stored responses contains only partial content, the cache |
|---|
| 1024 | shouldn't include its entity-tag in the If-None-Match header field unless the request is for a range that would be fully satisfied |
|---|
| 1025 | by that stored response. |
|---|
| 1026 | </p> |
|---|
| 1027 | <p id="rfc.section.2.4.p.4">Cache handling of a response to a conditional request is dependent upon its status code:</p> |
|---|
| 1028 | <p id="rfc.section.2.4.p.5"> </p> |
|---|
| 1029 | <ul> |
|---|
| 1030 | <li>A 304 (Not Modified) response status code indicates that the stored response can be updated and reused; see <a href="#freshening.responses" title="Freshening Responses">Section 2.4.1</a>. |
|---|
| 1031 | </li> |
|---|
| 1032 | <li>A full response (i.e., one with a response body) indicates that none of the stored responses nominated in the conditional |
|---|
| 1033 | request is suitable. Instead, the cache can use the full response to satisfy the request and <em class="bcp14">MAY</em> replace the stored response(s). |
|---|
| 1034 | </li> |
|---|
| 1035 | <li>However, if a cache receives a 5xx response while attempting to validate a response, it can either forward this response to |
|---|
| 1036 | the requesting client, or act as if the server failed to respond. In the latter case, it can return a previously stored response |
|---|
| 1037 | (see <a href="#serving.stale.responses" title="Serving Stale Responses">Section 2.3.3</a>). |
|---|
| 1038 | </li> |
|---|
| 1039 | </ul> |
|---|
| 1040 | <h3 id="rfc.section.2.4.1"><a href="#rfc.section.2.4.1">2.4.1</a> <a id="freshening.responses" href="#freshening.responses">Freshening Responses</a></h3> |
|---|
| 1041 | <p id="rfc.section.2.4.1.p.1">When a cache receives a 304 (Not Modified) response and already has one or more stored 200 (OK) responses for the same cache |
|---|
| 1042 | key, the cache needs to identify which of the stored responses are updated by this new response and then update the stored |
|---|
| 1043 | response(s) with the new information provided in the 304 response. |
|---|
| 1044 | </p> |
|---|
| 1045 | <ul> |
|---|
| 1046 | <li>If the new response contains a strong validator, then that strong validator identifies the selected representation. All of |
|---|
| 1047 | the stored responses with the same strong validator are selected. If none of the stored responses contain the same strong |
|---|
| 1048 | validator, then this new response corresponds to a new selected representation and <em class="bcp14">MUST NOT</em> update the existing stored responses. |
|---|
| 1049 | </li> |
|---|
| 1050 | <li>If the new response contains a weak validator and that validator corresponds to one of the cache's stored responses, then |
|---|
| 1051 | the most recent of those matching stored responses is selected. |
|---|
| 1052 | </li> |
|---|
| 1053 | <li>If the new response does not include any form of validator, there is only one stored response, and that stored response also |
|---|
| 1054 | lacks a validator, then that stored response is selected. |
|---|
| 1055 | </li> |
|---|
| 1056 | </ul> |
|---|
| 1057 | <p id="rfc.section.2.4.1.p.2">If a stored response is selected for update, the cache <em class="bcp14">MUST</em>: |
|---|
| 1058 | </p> |
|---|
| 1059 | <ul> |
|---|
| 1060 | <li>delete any Warning header fields in the stored response with warn-code 1xx (see <a href="#header.warning" id="rfc.xref.header.warning.2" title="Warning">Section 3.6</a>); |
|---|
| 1061 | </li> |
|---|
| 1062 | <li>retain any Warning header fields in the stored response with warn-code 2xx; and,</li> |
|---|
| 1063 | <li>use other header fields provided in the 304 response to replace all instances of the corresponding header fields in the stored |
|---|
| 1064 | response. |
|---|
| 1065 | </li> |
|---|
| 1066 | </ul> |
|---|
| 1067 | <h2 id="rfc.section.2.5"><a href="#rfc.section.2.5">2.5</a> <a id="invalidation.after.updates.or.deletions" href="#invalidation.after.updates.or.deletions">Request Methods that Invalidate</a></h2> |
|---|
| 1068 | <p id="rfc.section.2.5.p.1">Because unsafe request methods (<a href="p2-semantics.html#safe.methods" title="Safe Methods">Section 6.1.1</a> of <a href="#Part2" id="rfc.xref.Part2.6"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>) such as PUT, POST or DELETE have the potential for changing state on the origin server, intervening caches can use them |
|---|
| 1069 | to keep their contents up-to-date. |
|---|
| 1070 | </p> |
|---|
| 1071 | <p id="rfc.section.2.5.p.2">A cache <em class="bcp14">MUST</em> invalidate the effective Request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.13"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) as well as the URI(s) in the Location and Content-Location header fields (if present) when a non-error response to a request |
|---|
| 1072 | with an unsafe method is received. |
|---|
| 1073 | </p> |
|---|
| 1074 | <p id="rfc.section.2.5.p.3">However, a cache <em class="bcp14">MUST NOT</em> invalidate a URI from a Location or Content-Location header field if the host part of that URI differs from the host part |
|---|
| 1075 | in the effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.14"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>). This helps prevent denial of service attacks. |
|---|
| 1076 | </p> |
|---|
| 1077 | <p id="rfc.section.2.5.p.4">A cache <em class="bcp14">MUST</em> invalidate the effective request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.15"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) when it receives a non-error response to a request with a method whose safety is unknown. |
|---|
| 1078 | </p> |
|---|
| 1079 | <p id="rfc.section.2.5.p.5">Here, a "non-error response" is one with a 2xx or 3xx status code. "Invalidate" means that the cache will either remove all |
|---|
| 1080 | stored responses related to the effective request URI, or will mark these as "invalid" and in need of a mandatory validation |
|---|
| 1081 | before they can be returned in response to a subsequent request. |
|---|
| 1082 | </p> |
|---|
| 1083 | <p id="rfc.section.2.5.p.6">Note that this does not guarantee that all appropriate responses are invalidated. For example, the request that caused the |
|---|
| 1084 | change at the origin server might not have gone through the cache where a response is stored. |
|---|
| 1085 | </p> |
|---|
| 1086 | <h2 id="rfc.section.2.6"><a href="#rfc.section.2.6">2.6</a> <a id="caching.authenticated.responses" href="#caching.authenticated.responses">Shared Caching of Authenticated Responses</a></h2> |
|---|
| 1087 | <p id="rfc.section.2.6.p.1">A shared cache <em class="bcp14">MUST NOT</em> use a cached response to a request with an Authorization header field (<a href="p7-auth.html#header.authorization" title="Authorization">Section 4.1</a> of <a href="#Part7" id="rfc.xref.Part7.2"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a>) to satisfy any subsequent request unless a cache directive that allows such responses to be stored is present in the response. |
|---|
| 1088 | </p> |
|---|
| 1089 | <p id="rfc.section.2.6.p.2">In this specification, the following Cache-Control response directives (<a href="#cache-response-directive" title="Response Cache-Control Directives">Section 3.2.2</a>) have such an effect: must-revalidate, public, s-maxage. |
|---|
| 1090 | </p> |
|---|
| 1091 | <p id="rfc.section.2.6.p.3">Note that cached responses that contain the "must-revalidate" and/or "s-maxage" response directives are not allowed to be |
|---|
| 1092 | served stale (<a href="#serving.stale.responses" title="Serving Stale Responses">Section 2.3.3</a>) by shared caches. In particular, a response with either "max-age=0, must-revalidate" or "s-maxage=0" cannot be used to satisfy |
|---|
| 1093 | a subsequent request without revalidating it on the origin server. |
|---|
| 1094 | </p> |
|---|
| 1095 | <h2 id="rfc.section.2.7"><a href="#rfc.section.2.7">2.7</a> <a id="caching.negotiated.responses" href="#caching.negotiated.responses">Caching Negotiated Responses</a></h2> |
|---|
| 1096 | <p id="rfc.section.2.7.p.1">When a cache receives a request that can be satisfied by a stored response that has a Vary header field (<a href="#header.vary" id="rfc.xref.header.vary.1" title="Vary">Section 3.5</a>), it <em class="bcp14">MUST NOT</em> use that response unless all of the selecting header fields nominated by the Vary header field match in both the original |
|---|
| 1097 | request (i.e., that associated with the stored response), and the presented request. |
|---|
| 1098 | </p> |
|---|
| 1099 | <p id="rfc.section.2.7.p.2">The selecting header fields from two requests are defined to match if and only if those in the first request can be transformed |
|---|
| 1100 | to those in the second request by applying any of the following: |
|---|
| 1101 | </p> |
|---|
| 1102 | <ul> |
|---|
| 1103 | <li>adding or removing whitespace, where allowed in the header field's syntax</li> |
|---|
| 1104 | <li>combining multiple header fields with the same field name (see <a href="p1-messaging.html#header.fields" title="Header Fields">Section 3.2</a> of <a href="#Part1" id="rfc.xref.Part1.16"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) |
|---|
| 1105 | </li> |
|---|
| 1106 | <li>normalizing both header field values in a way that is known to have identical semantics, according to the header field's specification |
|---|
| 1107 | (e.g., re-ordering field values when order is not significant; case-normalization, where values are defined to be case-insensitive) |
|---|
| 1108 | </li> |
|---|
| 1109 | </ul> |
|---|
| 1110 | <p id="rfc.section.2.7.p.3">If (after any normalization that might take place) a header field is absent from a request, it can only match another request |
|---|
| 1111 | if it is also absent there. |
|---|
| 1112 | </p> |
|---|
| 1113 | <p id="rfc.section.2.7.p.4">A Vary header field-value of "*" always fails to match, and subsequent requests to that resource can only be properly interpreted |
|---|
| 1114 | by the origin server. |
|---|
| 1115 | </p> |
|---|
| 1116 | <p id="rfc.section.2.7.p.5">The stored response with matching selecting header fields is known as the selected response.</p> |
|---|
| 1117 | <p id="rfc.section.2.7.p.6">If multiple selected responses are available, the most recent response (as determined by the Date header field) is used; see <a href="#constructing.responses.from.caches" title="Constructing Responses from Caches">Section 2.2</a>. |
|---|
| 1118 | </p> |
|---|
| 1119 | <p id="rfc.section.2.7.p.7">If no selected response is available, the cache can forward the presented request to the origin server in a conditional request; |
|---|
| 1120 | see <a href="#validation.model" title="Validation Model">Section 2.4</a>. |
|---|
| 1121 | </p> |
|---|
| 1122 | <h2 id="rfc.section.2.8"><a href="#rfc.section.2.8">2.8</a> <a id="combining.responses" href="#combining.responses">Combining Partial Content</a></h2> |
|---|
| 1123 | <p id="rfc.section.2.8.p.1">A response might transfer only a partial representation if the connection closed prematurely or if the request used one or |
|---|
| 1124 | more Range specifiers (<a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>). After several such transfers, a cache might have received several ranges of the same representation. A cache <em class="bcp14">MAY</em> combine these ranges into a single stored response, and reuse that response to satisfy later requests, if they all share the |
|---|
| 1125 | same strong validator and the cache complies with the client requirements in <a href="p5-range.html#combining.byte.ranges" title="Combining Ranges">Section 4</a> of <a href="#Part5" id="rfc.xref.Part5.3"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>. |
|---|
| 1126 | </p> |
|---|
| 1127 | <p id="rfc.section.2.8.p.2">When combining the new response with one or more stored responses, a cache <em class="bcp14">MUST</em>: |
|---|
| 1128 | </p> |
|---|
| 1129 | <ul> |
|---|
| 1130 | <li>delete any Warning header fields in the stored response with warn-code 1xx (see <a href="#header.warning" id="rfc.xref.header.warning.3" title="Warning">Section 3.6</a>); |
|---|
| 1131 | </li> |
|---|
| 1132 | <li>retain any Warning header fields in the stored response with warn-code 2xx; and,</li> |
|---|
| 1133 | <li>use other header fields provided in the new response, aside from Content-Range, to replace all instances of the corresponding |
|---|
| 1134 | header fields in the stored response. |
|---|
| 1135 | </li> |
|---|
| 1136 | </ul> |
|---|
| 1137 | <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a> <a id="header.field.definitions" href="#header.field.definitions">Header Field Definitions</a></h1> |
|---|
| 1138 | <p id="rfc.section.3.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to caching.</p> |
|---|
| 1139 | <div id="rfc.iref.a.2"></div> |
|---|
| 1140 | <div id="rfc.iref.h.2"></div> |
|---|
| 1141 | <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a> <a id="header.age" href="#header.age">Age</a></h2> |
|---|
| 1142 | <p id="rfc.section.3.1.p.1">The "Age" header field conveys the sender's estimate of the amount of time since the response was generated or successfully |
|---|
| 1143 | validated at the origin server. Age values are calculated as specified in <a href="#age.calculations" title="Calculating Age">Section 2.3.2</a>. |
|---|
| 1144 | </p> |
|---|
| 1145 | <div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.2"></span> <a href="#header.age" class="smpl">Age</a> = <a href="#delta-seconds" class="smpl">delta-seconds</a> |
|---|
| 1146 | </pre><p id="rfc.section.3.1.p.3">Age field-values are non-negative integers, representing time in seconds (see <a href="#delta-seconds" title="Delta Seconds">Section 1.5</a>). |
|---|
| 1147 | </p> |
|---|
| 1148 | <p id="rfc.section.3.1.p.4">The presence of an Age header field in a response implies that a response is not first-hand. However, the converse is not |
|---|
| 1149 | true, since HTTP/1.0 caches might not implement the Age header field. |
|---|
| 1150 | </p> |
|---|
| 1151 | <div id="rfc.iref.c.6"></div> |
|---|
| 1152 | <div id="rfc.iref.h.3"></div> |
|---|
| 1153 | <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a> <a id="header.cache-control" href="#header.cache-control">Cache-Control</a></h2> |
|---|
| 1154 | <p id="rfc.section.3.2.p.1">The "Cache-Control" header field is used to specify directives for caches along the request/response chain. Such cache directives |
|---|
| 1155 | are unidirectional in that the presence of a directive in a request does not imply that the same directive is to be given |
|---|
| 1156 | in the response. |
|---|
| 1157 | </p> |
|---|
| 1158 | <p id="rfc.section.3.2.p.2">A cache <em class="bcp14">MUST</em> obey the requirements of the Cache-Control directives defined in this section. See <a href="#cache.control.extensions" title="Cache Control Extensions">Section 3.2.3</a> for information about how Cache-Control directives defined elsewhere are handled. |
|---|
| 1159 | </p> |
|---|
| 1160 | <div class="note" id="rfc.section.3.2.p.3"> |
|---|
| 1161 | <p> <b>Note:</b> HTTP/1.0 caches might not implement Cache-Control and might only implement Pragma: no-cache (see <a href="#header.pragma" id="rfc.xref.header.pragma.2" title="Pragma">Section 3.4</a>). |
|---|
| 1162 | </p> |
|---|
| 1163 | </div> |
|---|
| 1164 | <p id="rfc.section.3.2.p.4">A proxy, whether or not it implements a cache, <em class="bcp14">MUST</em> pass cache directives through in forwarded messages, regardless of their significance to that application, since the directives |
|---|
| 1165 | might be applicable to all recipients along the request/response chain. It is not possible to target a directive to a specific |
|---|
| 1166 | cache. |
|---|
| 1167 | </p> |
|---|
| 1168 | <p id="rfc.section.3.2.p.5">Cache directives are identified by a token, to be compared case-insensitively, and have an optional argument.</p> |
|---|
| 1169 | <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.3"></span><span id="rfc.iref.g.4"></span> <a href="#header.cache-control" class="smpl">Cache-Control</a> = 1#<a href="#header.cache-control" class="smpl">cache-directive</a> |
|---|
| 1170 | |
|---|
| 1171 | <a href="#header.cache-control" class="smpl">cache-directive</a> = <a href="#header.cache-control" class="smpl">cache-request-directive</a> |
|---|
| 1172 | / <a href="#header.cache-control" class="smpl">cache-response-directive</a> |
|---|
| 1173 | |
|---|
| 1174 | <a href="#header.cache-control" class="smpl">cache-extension</a> = <a href="#core.rules" class="smpl">token</a> [ "=" ( <a href="#core.rules" class="smpl">token</a> / <a href="#core.rules" class="smpl">quoted-string</a> ) ] |
|---|
| 1175 | </pre><h3 id="rfc.section.3.2.1"><a href="#rfc.section.3.2.1">3.2.1</a> <a id="cache-request-directive" href="#cache-request-directive">Request Cache-Control Directives</a></h3> |
|---|
| 1176 | <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.5"></span> <a href="#header.cache-control" class="smpl">cache-request-directive</a> = |
|---|
| 1177 | "no-cache" |
|---|
| 1178 | / "no-store" |
|---|
| 1179 | / "max-age" "=" <a href="#delta-seconds" class="smpl">delta-seconds</a> |
|---|
| 1180 | / "max-stale" [ "=" <a href="#delta-seconds" class="smpl">delta-seconds</a> ] |
|---|
| 1181 | / "min-fresh" "=" <a href="#delta-seconds" class="smpl">delta-seconds</a> |
|---|
| 1182 | / "no-transform" |
|---|
| 1183 | / "only-if-cached" |
|---|
| 1184 | / <a href="#header.cache-control" class="smpl">cache-extension</a> |
|---|
| 1185 | </pre><p id="rfc.section.3.2.1.p.2"> <dfn>no-cache</dfn> <span id="rfc.iref.c.7"></span> <span id="rfc.iref.n.1"></span> |
|---|
| 1186 | </p> |
|---|
| 1187 | <ul class="empty"> |
|---|
| 1188 | <li>The no-cache request directive indicates that a cache <em class="bcp14">MUST NOT</em> use a stored response to satisfy the request without successful validation on the origin server. |
|---|
| 1189 | </li> |
|---|
| 1190 | </ul> |
|---|
| 1191 | <p id="rfc.section.3.2.1.p.3"> <dfn>no-store</dfn> <span id="rfc.iref.c.8"></span> <span id="rfc.iref.n.2"></span> |
|---|
| 1192 | </p> |
|---|
| 1193 | <ul class="empty"> |
|---|
| 1194 | <li>The no-store request directive indicates that a cache <em class="bcp14">MUST NOT</em> store any part of either this request or any response to it. This directive applies to both private and shared caches. "<em class="bcp14">MUST NOT</em> store" in this context means that the cache <em class="bcp14">MUST NOT</em> intentionally store the information in non-volatile storage, and <em class="bcp14">MUST</em> make a best-effort attempt to remove the information from volatile storage as promptly as possible after forwarding it. |
|---|
| 1195 | </li> |
|---|
| 1196 | <li>This directive is NOT a reliable or sufficient mechanism for ensuring privacy. In particular, malicious or compromised caches |
|---|
| 1197 | might not recognize or obey this directive, and communications networks might be vulnerable to eavesdropping. |
|---|
| 1198 | </li> |
|---|
| 1199 | <li>Note that if a request containing this directive is satisfied from a cache, the no-store request directive does not apply |
|---|
| 1200 | to the already stored response. |
|---|
| 1201 | </li> |
|---|
| 1202 | </ul> |
|---|
| 1203 | <p id="rfc.section.3.2.1.p.4"> <dfn>max-age</dfn> <span id="rfc.iref.c.9"></span> <span id="rfc.iref.m.1"></span> |
|---|
| 1204 | </p> |
|---|
| 1205 | <ul class="empty"> |
|---|
| 1206 | <li>The max-age request directive indicates that the client is unwilling to accept a response whose age is greater than the specified |
|---|
| 1207 | number of seconds. Unless the max-stale request directive is also present, the client is not willing to accept a stale response. |
|---|
| 1208 | </li> |
|---|
| 1209 | </ul> |
|---|
| 1210 | <p id="rfc.section.3.2.1.p.5"> <dfn>max-stale</dfn> <span id="rfc.iref.c.10"></span> <span id="rfc.iref.m.2"></span> |
|---|
| 1211 | </p> |
|---|
| 1212 | <ul class="empty"> |
|---|
| 1213 | <li>The max-stale request directive indicates that the client is willing to accept a response that has exceeded its expiration |
|---|
| 1214 | time. If max-stale is assigned a value, then the client is willing to accept a response that has exceeded its expiration time |
|---|
| 1215 | by no more than the specified number of seconds. If no value is assigned to max-stale, then the client is willing to accept |
|---|
| 1216 | a stale response of any age. |
|---|
| 1217 | </li> |
|---|
| 1218 | </ul> |
|---|
| 1219 | <p id="rfc.section.3.2.1.p.6"> <dfn>min-fresh</dfn> <span id="rfc.iref.c.11"></span> <span id="rfc.iref.m.3"></span> |
|---|
| 1220 | </p> |
|---|
| 1221 | <ul class="empty"> |
|---|
| 1222 | <li>The min-fresh request directive indicates that the client is willing to accept a response whose freshness lifetime is no less |
|---|
| 1223 | than its current age plus the specified time in seconds. That is, the client wants a response that will still be fresh for |
|---|
| 1224 | at least the specified number of seconds. |
|---|
| 1225 | </li> |
|---|
| 1226 | </ul> |
|---|
| 1227 | <p id="rfc.section.3.2.1.p.7"> <dfn>no-transform</dfn> <span id="rfc.iref.c.12"></span> <span id="rfc.iref.n.3"></span> |
|---|
| 1228 | </p> |
|---|
| 1229 | <ul class="empty"> |
|---|
| 1230 | <li>The no-transform request directive indicates that an intermediary (whether or not it implements a cache) <em class="bcp14">MUST NOT</em> change the Content-Encoding, Content-Range or Content-Type request header fields, nor the request representation. |
|---|
| 1231 | </li> |
|---|
| 1232 | </ul> |
|---|
| 1233 | <p id="rfc.section.3.2.1.p.8"> <dfn>only-if-cached</dfn> <span id="rfc.iref.c.13"></span> <span id="rfc.iref.o.1"></span> |
|---|
| 1234 | </p> |
|---|
| 1235 | <ul class="empty"> |
|---|
| 1236 | <li>The only-if-cached request directive indicates that the client only wishes to obtain a stored response. If it receives this |
|---|
| 1237 | directive, a cache <em class="bcp14">SHOULD</em> either respond using a stored response that is consistent with the other constraints of the request, or respond with a 504 |
|---|
| 1238 | (Gateway Timeout) status code. If a group of caches is being operated as a unified system with good internal connectivity, |
|---|
| 1239 | a member cache <em class="bcp14">MAY</em> forward such a request within that group of caches. |
|---|
| 1240 | </li> |
|---|
| 1241 | </ul> |
|---|
| 1242 | <h3 id="rfc.section.3.2.2"><a href="#rfc.section.3.2.2">3.2.2</a> <a id="cache-response-directive" href="#cache-response-directive">Response Cache-Control Directives</a></h3> |
|---|
| 1243 | <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.6"></span> <a href="#header.cache-control" class="smpl">cache-response-directive</a> = |
|---|
| 1244 | "public" |
|---|
| 1245 | / "private" [ "=" <a href="#notation" class="smpl">DQUOTE</a> 1#<a href="#abnf.dependencies" class="smpl">field-name</a> <a href="#notation" class="smpl">DQUOTE</a> ] |
|---|
| 1246 | / "no-cache" [ "=" <a href="#notation" class="smpl">DQUOTE</a> 1#<a href="#abnf.dependencies" class="smpl">field-name</a> <a href="#notation" class="smpl">DQUOTE</a> ] |
|---|
| 1247 | / "no-store" |
|---|
| 1248 | / "no-transform" |
|---|
| 1249 | / "must-revalidate" |
|---|
| 1250 | / "proxy-revalidate" |
|---|
| 1251 | / "max-age" "=" <a href="#delta-seconds" class="smpl">delta-seconds</a> |
|---|
| 1252 | / "s-maxage" "=" <a href="#delta-seconds" class="smpl">delta-seconds</a> |
|---|
| 1253 | / <a href="#header.cache-control" class="smpl">cache-extension</a> |
|---|
| 1254 | </pre><p id="rfc.section.3.2.2.p.2"> <dfn>public</dfn> <span id="rfc.iref.c.14"></span> <span id="rfc.iref.p.2"></span> |
|---|
| 1255 | </p> |
|---|
| 1256 | <ul class="empty"> |
|---|
| 1257 | <li>The public response directive indicates that a response whose associated request contains an 'Authentication' header <em class="bcp14">MAY</em> be stored (see <a href="#caching.authenticated.responses" title="Shared Caching of Authenticated Responses">Section 2.6</a>). |
|---|
| 1258 | </li> |
|---|
| 1259 | </ul> |
|---|
| 1260 | <p id="rfc.section.3.2.2.p.3"> <dfn>private</dfn> <span id="rfc.iref.c.15"></span> <span id="rfc.iref.p.3"></span> |
|---|
| 1261 | </p> |
|---|
| 1262 | <ul class="empty"> |
|---|
| 1263 | <li>The private response directive indicates that the response message is intended for a single user and <em class="bcp14">MUST NOT</em> be stored by a shared cache. A private cache <em class="bcp14">MAY</em> store the response. |
|---|
| 1264 | </li> |
|---|
| 1265 | <li>If the private response directive specifies one or more field-names, this requirement is limited to the field-values associated |
|---|
| 1266 | with the listed response header fields. That is, a shared cache <em class="bcp14">MUST NOT</em> store the specified field-names(s), whereas it <em class="bcp14">MAY</em> store the remainder of the response message. |
|---|
| 1267 | </li> |
|---|
| 1268 | <li> <b>Note:</b> This usage of the word private only controls where the response can be stored; it cannot ensure the privacy of the message |
|---|
| 1269 | content. Also, private response directives with field-names are often handled by implementations as if an unqualified private |
|---|
| 1270 | directive was received; i.e., the special handling for the qualified form is not widely implemented. |
|---|
| 1271 | </li> |
|---|
| 1272 | </ul> |
|---|
| 1273 | <p id="rfc.section.3.2.2.p.4"> <dfn>no-cache</dfn> <span id="rfc.iref.c.16"></span> <span id="rfc.iref.n.4"></span> |
|---|
| 1274 | </p> |
|---|
| 1275 | <ul class="empty"> |
|---|
| 1276 | <li>The no-cache response directive indicates that the response MUST NOT be used to satisfy a subsequent request without successful |
|---|
| 1277 | validation on the origin server. This allows an origin server to prevent a cache from using it to satisfy a request without |
|---|
| 1278 | contacting it, even by caches that have been configured to return stale responses. |
|---|
| 1279 | </li> |
|---|
| 1280 | <li>If the no-cache response directive specifies one or more field-names, this requirement is limited to the field-values associated |
|---|
| 1281 | with the listed response header fields. That is, a cache <em class="bcp14">MUST NOT</em> send the specified field-name(s) in the response to a subsequent request without successful validation on the origin server. |
|---|
| 1282 | This allows an origin server to prevent the re-use of certain header fields in a response, while still allowing caching of |
|---|
| 1283 | the rest of the response. |
|---|
| 1284 | </li> |
|---|
| 1285 | <li> <b>Note:</b> Most HTTP/1.0 caches will not recognize or obey this directive. Also, no-cache response directives with field-names are often |
|---|
| 1286 | handled by implementations as if an unqualified no-cache directive was received; i.e., the special handling for the qualified |
|---|
| 1287 | form is not widely implemented. |
|---|
| 1288 | </li> |
|---|
| 1289 | </ul> |
|---|
| 1290 | <p id="rfc.section.3.2.2.p.5"> <dfn>no-store</dfn> <span id="rfc.iref.c.17"></span> <span id="rfc.iref.n.5"></span> |
|---|
| 1291 | </p> |
|---|
| 1292 | <ul class="empty"> |
|---|
| 1293 | <li>The no-store response directive indicates that a cache <em class="bcp14">MUST NOT</em> store any part of either the immediate request or response. This directive applies to both private and shared caches. "<em class="bcp14">MUST NOT</em> store" in this context means that the cache <em class="bcp14">MUST NOT</em> intentionally store the information in non-volatile storage, and <em class="bcp14">MUST</em> make a best-effort attempt to remove the information from volatile storage as promptly as possible after forwarding it. |
|---|
| 1294 | </li> |
|---|
| 1295 | <li>This directive is NOT a reliable or sufficient mechanism for ensuring privacy. In particular, malicious or compromised caches |
|---|
| 1296 | might not recognize or obey this directive, and communications networks might be vulnerable to eavesdropping. |
|---|
| 1297 | </li> |
|---|
| 1298 | </ul> |
|---|
| 1299 | <p id="rfc.section.3.2.2.p.6"> <dfn>must-revalidate</dfn> <span id="rfc.iref.c.18"></span> <span id="rfc.iref.m.4"></span> |
|---|
| 1300 | </p> |
|---|
| 1301 | <ul class="empty"> |
|---|
| 1302 | <li>The must-revalidate response directive indicates that once it has become stale, a cache <em class="bcp14">MUST NOT</em> use the response to satisfy subsequent requests without successful validation on the origin server. |
|---|
| 1303 | </li> |
|---|
| 1304 | <li>The must-revalidate directive is necessary to support reliable operation for certain protocol features. In all circumstances |
|---|
| 1305 | a cache <em class="bcp14">MUST</em> obey the must-revalidate directive; in particular, if a cache cannot reach the origin server for any reason, it <em class="bcp14">MUST</em> generate a 504 (Gateway Timeout) response. |
|---|
| 1306 | </li> |
|---|
| 1307 | <li>The must-revalidate directive ought to be used by servers if and only if failure to validate a request on the representation |
|---|
| 1308 | could result in incorrect operation, such as a silently unexecuted financial transaction. |
|---|
| 1309 | </li> |
|---|
| 1310 | </ul> |
|---|
| 1311 | <p id="rfc.section.3.2.2.p.7"> <dfn>proxy-revalidate</dfn> <span id="rfc.iref.c.19"></span> <span id="rfc.iref.p.4"></span> |
|---|
| 1312 | </p> |
|---|
| 1313 | <ul class="empty"> |
|---|
| 1314 | <li>The proxy-revalidate response directive has the same meaning as the must-revalidate response directive, except that it does |
|---|
| 1315 | not apply to private caches. |
|---|
| 1316 | </li> |
|---|
| 1317 | </ul> |
|---|
| 1318 | <p id="rfc.section.3.2.2.p.8"> <dfn>max-age</dfn> <span id="rfc.iref.c.20"></span> <span id="rfc.iref.m.5"></span> |
|---|
| 1319 | </p> |
|---|
| 1320 | <ul class="empty"> |
|---|
| 1321 | <li>The max-age response directive indicates that the response is to be considered stale after its age is greater than the specified |
|---|
| 1322 | number of seconds. |
|---|
| 1323 | </li> |
|---|
| 1324 | </ul> |
|---|
| 1325 | <p id="rfc.section.3.2.2.p.9"> <dfn>s-maxage</dfn> <span id="rfc.iref.c.21"></span> <span id="rfc.iref.s.4"></span> |
|---|
| 1326 | </p> |
|---|
| 1327 | <ul class="empty"> |
|---|
| 1328 | <li>The s-maxage response directive indicates that, in shared caches, the maximum age specified by this directive overrides the |
|---|
| 1329 | maximum age specified by either the max-age directive or the Expires header field. The s-maxage directive also implies the |
|---|
| 1330 | semantics of the proxy-revalidate response directive. |
|---|
| 1331 | </li> |
|---|
| 1332 | </ul> |
|---|
| 1333 | <p id="rfc.section.3.2.2.p.10"> <dfn>no-transform</dfn> <span id="rfc.iref.c.22"></span> <span id="rfc.iref.n.6"></span> |
|---|
| 1334 | </p> |
|---|
| 1335 | <ul class="empty"> |
|---|
| 1336 | <li>The no-transform response directive indicates that an intermediary (regardless of whether it implements a cache) <em class="bcp14">MUST NOT</em> change the Content-Encoding, Content-Range or Content-Type response header fields, nor the response representation. |
|---|
| 1337 | </li> |
|---|
| 1338 | </ul> |
|---|
| 1339 | <h3 id="rfc.section.3.2.3"><a href="#rfc.section.3.2.3">3.2.3</a> <a id="cache.control.extensions" href="#cache.control.extensions">Cache Control Extensions</a></h3> |
|---|
| 1340 | <p id="rfc.section.3.2.3.p.1">The Cache-Control header field can be extended through the use of one or more cache-extension tokens, each with an optional |
|---|
| 1341 | value. Informational extensions (those that do not require a change in cache behavior) can be added without changing the semantics |
|---|
| 1342 | of other directives. Behavioral extensions are designed to work by acting as modifiers to the existing base of cache directives. |
|---|
| 1343 | Both the new directive and the standard directive are supplied, such that applications that do not understand the new directive |
|---|
| 1344 | will default to the behavior specified by the standard directive, and those that understand the new directive will recognize |
|---|
| 1345 | it as modifying the requirements associated with the standard directive. In this way, extensions to the cache-control directives |
|---|
| 1346 | can be made without requiring changes to the base protocol. |
|---|
| 1347 | </p> |
|---|
| 1348 | <p id="rfc.section.3.2.3.p.2">This extension mechanism depends on an HTTP cache obeying all of the cache-control directives defined for its native HTTP-version, |
|---|
| 1349 | obeying certain extensions, and ignoring all directives that it does not understand. |
|---|
| 1350 | </p> |
|---|
| 1351 | <p id="rfc.section.3.2.3.p.3">For example, consider a hypothetical new response directive called "community" that acts as a modifier to the private directive. |
|---|
| 1352 | We define this new directive to mean that, in addition to any private cache, any cache that is shared only by members of the |
|---|
| 1353 | community named within its value may cache the response. An origin server wishing to allow the UCI community to use an otherwise |
|---|
| 1354 | private response in their shared cache(s) could do so by including |
|---|
| 1355 | </p> |
|---|
| 1356 | <div id="rfc.figure.u.12"></div><pre class="text"> Cache-Control: private, community="UCI" |
|---|
| 1357 | </pre><p id="rfc.section.3.2.3.p.5">A cache seeing this header field will act correctly even if the cache does not understand the community cache-extension, since |
|---|
| 1358 | it will also see and understand the private directive and thus default to the safe behavior. |
|---|
| 1359 | </p> |
|---|
| 1360 | <p id="rfc.section.3.2.3.p.6">A cache <em class="bcp14">MUST</em> ignore unrecognized cache directives; it is assumed that any cache directive likely to be unrecognized by an HTTP/1.1 cache |
|---|
| 1361 | will be combined with standard directives (or the response's default cacheability) such that the cache behavior will remain |
|---|
| 1362 | minimally correct even if the cache does not understand the extension(s). |
|---|
| 1363 | </p> |
|---|
| 1364 | <p id="rfc.section.3.2.3.p.7">The HTTP Cache Directive Registry defines the name space for the cache directives.</p> |
|---|
| 1365 | <p id="rfc.section.3.2.3.p.8">A registration <em class="bcp14">MUST</em> include the following fields: |
|---|
| 1366 | </p> |
|---|
| 1367 | <ul> |
|---|
| 1368 | <li>Cache Directive Name</li> |
|---|
| 1369 | <li>Pointer to specification text</li> |
|---|
| 1370 | </ul> |
|---|
| 1371 | <p id="rfc.section.3.2.3.p.9">Values to be added to this name space are subject to IETF review (<a href="#RFC5226" id="rfc.xref.RFC5226.1"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>, <a href="http://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a>). |
|---|
| 1372 | </p> |
|---|
| 1373 | <p id="rfc.section.3.2.3.p.10">The registry itself is maintained at <<a href="http://www.iana.org/assignments/http-cache-directives">http://www.iana.org/assignments/http-cache-directives</a>>. |
|---|
| 1374 | </p> |
|---|
| 1375 | <div id="rfc.iref.e.2"></div> |
|---|
| 1376 | <div id="rfc.iref.h.4"></div> |
|---|
| 1377 | <h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a> <a id="header.expires" href="#header.expires">Expires</a></h2> |
|---|
| 1378 | <p id="rfc.section.3.3.p.1">The "Expires" header field gives the date/time after which the response is considered stale. See <a href="#expiration.model" title="Freshness Model">Section 2.3</a> for further discussion of the freshness model. |
|---|
| 1379 | </p> |
|---|
| 1380 | <p id="rfc.section.3.3.p.2">The presence of an Expires field does not imply that the original resource will change or cease to exist at, before, or after |
|---|
| 1381 | that time. |
|---|
| 1382 | </p> |
|---|
| 1383 | <p id="rfc.section.3.3.p.3">The field-value is an absolute date and time as defined by HTTP-date in <a href="p2-semantics.html#http.date" title="Date/Time Formats">Section 8</a> of <a href="#Part2" id="rfc.xref.Part2.7"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>; a sender <em class="bcp14">MUST</em> use the rfc1123-date format. |
|---|
| 1384 | </p> |
|---|
| 1385 | <div id="rfc.figure.u.13"></div><pre class="inline"><span id="rfc.iref.g.7"></span> <a href="#header.expires" class="smpl">Expires</a> = <a href="#abnf.dependencies" class="smpl">HTTP-date</a> |
|---|
| 1386 | </pre><div id="rfc.figure.u.14"></div> |
|---|
| 1387 | <p>For example</p> <pre class="text"> Expires: Thu, 01 Dec 1994 16:00:00 GMT |
|---|
| 1388 | </pre><p id="rfc.section.3.3.p.6">A cache <em class="bcp14">MUST</em> treat other invalid date formats, especially including the value "0", as in the past (i.e., "already expired"). |
|---|
| 1389 | </p> |
|---|
| 1390 | <div class="note" id="rfc.section.3.3.p.7"> |
|---|
| 1391 | <p> <b>Note:</b> If a response includes a Cache-Control field with the max-age directive (see <a href="#cache-response-directive" title="Response Cache-Control Directives">Section 3.2.2</a>), that directive overrides the Expires field. Likewise, the s-maxage directive overrides Expires in shared caches. |
|---|
| 1392 | </p> |
|---|
| 1393 | </div> |
|---|
| 1394 | <p id="rfc.section.3.3.p.8">Historically, HTTP required the Expires field-value to be no more than a year in the future. While longer freshness lifetimes |
|---|
| 1395 | are no longer prohibited, extremely large values have been demonstrated to cause problems (e.g., clock overflows due to use |
|---|
| 1396 | of 32-bit integers for time values), and most caches will evict a response far sooner than that. Therefore, senders ought |
|---|
| 1397 | not produce them. |
|---|
| 1398 | </p> |
|---|
| 1399 | <p id="rfc.section.3.3.p.9">An origin server without a clock <em class="bcp14">MUST NOT</em> assign Expires values to a response unless these values were associated with the resource by a system or user with a reliable |
|---|
| 1400 | clock. It <em class="bcp14">MAY</em> assign an Expires value that is known, at or before server configuration time, to be in the past (this allows "pre-expiration" |
|---|
| 1401 | of responses without storing separate Expires values for each resource). |
|---|
| 1402 | </p> |
|---|
| 1403 | <div id="rfc.iref.p.5"></div> |
|---|
| 1404 | <div id="rfc.iref.h.5"></div> |
|---|
| 1405 | <h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a> <a id="header.pragma" href="#header.pragma">Pragma</a></h2> |
|---|
| 1406 | <p id="rfc.section.3.4.p.1">The "Pragma" header field allows backwards compatibility with HTTP/1.0 caches, so that clients can specify a "no-cache" request |
|---|
| 1407 | that they will understand (as Cache-Control was not defined until HTTP/1.1). When the Cache-Control header is also present |
|---|
| 1408 | and understood in a request, Pragma is ignored. |
|---|
| 1409 | </p> |
|---|
| 1410 | <p id="rfc.section.3.4.p.2">In HTTP/1.0, Pragma was defined as an extensible field for implementation-specified directives for recipients. This specification |
|---|
| 1411 | deprecates such extensions to improve interoperability. |
|---|
| 1412 | </p> |
|---|
| 1413 | <div id="rfc.figure.u.15"></div><pre class="inline"><span id="rfc.iref.g.8"></span><span id="rfc.iref.g.9"></span><span id="rfc.iref.g.10"></span> <a href="#header.pragma" class="smpl">Pragma</a> = 1#<a href="#header.pragma" class="smpl">pragma-directive</a> |
|---|
| 1414 | <a href="#header.pragma" class="smpl">pragma-directive</a> = "no-cache" / <a href="#header.pragma" class="smpl">extension-pragma</a> |
|---|
| 1415 | <a href="#header.pragma" class="smpl">extension-pragma</a> = <a href="#core.rules" class="smpl">token</a> [ "=" ( <a href="#core.rules" class="smpl">token</a> / <a href="#core.rules" class="smpl">quoted-string</a> ) ] |
|---|
| 1416 | </pre><p id="rfc.section.3.4.p.4">When the Cache-Control header is not present in a request, the no-cache request pragma-directive <em class="bcp14">MUST</em> have the same effect on caches as if "Cache-Control: no-cache" were present (see <a href="#cache-request-directive" title="Request Cache-Control Directives">Section 3.2.1</a>). |
|---|
| 1417 | </p> |
|---|
| 1418 | <p id="rfc.section.3.4.p.5">When sending a no-cache request, a client ought to include both the pragma and cache-control directives, unless Cache-Control: |
|---|
| 1419 | no-cache is purposefully omitted to target other Cache-Control response directives at HTTP/1.1 caches. For example: |
|---|
| 1420 | </p> |
|---|
| 1421 | <div id="rfc.figure.u.16"></div> <pre class="text">GET / HTTP/1.1 |
|---|
| 1422 | Host: www.example.com |
|---|
| 1423 | Cache-Control: max-age=30 |
|---|
| 1424 | Pragma: no-cache |
|---|
| 1425 | |
|---|
| 1426 | </pre> <p id="rfc.section.3.4.p.7">will constrain HTTP/1.1 caches to serve a response no older than 30 seconds, while precluding implementations that do not |
|---|
| 1427 | understand Cache-Control from serving a cached response. |
|---|
| 1428 | </p> |
|---|
| 1429 | <div class="note" id="rfc.section.3.4.p.8"> |
|---|
| 1430 | <p> <b>Note:</b> Because the meaning of "Pragma: no-cache" in responses is not specified, it does not provide a reliable replacement for "Cache-Control: |
|---|
| 1431 | no-cache" in them. |
|---|
| 1432 | </p> |
|---|
| 1433 | </div> |
|---|
| 1434 | <div id="rfc.iref.v.3"></div> |
|---|
| 1435 | <div id="rfc.iref.h.6"></div> |
|---|
| 1436 | <h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a> <a id="header.vary" href="#header.vary">Vary</a></h2> |
|---|
| 1437 | <p id="rfc.section.3.5.p.1">The "Vary" header field conveys the set of header fields that were used to select the representation.</p> |
|---|
| 1438 | <p id="rfc.section.3.5.p.2">Caches use this information, in part, to determine whether a stored response can be used to satisfy a given request; see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section 2.7</a>. determines, while the response is fresh, whether a cache is permitted to use the response to reply to a subsequent request |
|---|
| 1439 | without validation; see <a href="#caching.negotiated.responses" title="Caching Negotiated Responses">Section 2.7</a>. |
|---|
| 1440 | </p> |
|---|
| 1441 | <p id="rfc.section.3.5.p.3">In uncacheable or stale responses, the Vary field value advises the user agent about the criteria that were used to select |
|---|
| 1442 | the representation. |
|---|
| 1443 | </p> |
|---|
| 1444 | <div id="rfc.figure.u.17"></div><pre class="inline"><span id="rfc.iref.g.11"></span> <a href="#header.vary" class="smpl">Vary</a> = "*" / 1#<a href="#abnf.dependencies" class="smpl">field-name</a> |
|---|
| 1445 | </pre><p id="rfc.section.3.5.p.5">The set of header fields named by the Vary field value is known as the selecting header fields.</p> |
|---|
| 1446 | <p id="rfc.section.3.5.p.6">A server <em class="bcp14">SHOULD</em> include a Vary header field with any cacheable response that is subject to server-driven negotiation. Doing so allows a cache |
|---|
| 1447 | to properly interpret future requests on that resource and informs the user agent about the presence of negotiation on that |
|---|
| 1448 | resource. A server <em class="bcp14">MAY</em> include a Vary header field with a non-cacheable response that is subject to server-driven negotiation, since this might provide |
|---|
| 1449 | the user agent with useful information about the dimensions over which the response varies at the time of the response. |
|---|
| 1450 | </p> |
|---|
| 1451 | <p id="rfc.section.3.5.p.7">A Vary field value of "*" signals that unspecified parameters not limited to the header fields (e.g., the network address |
|---|
| 1452 | of the client), play a role in the selection of the response representation; therefore, a cache cannot determine whether this |
|---|
| 1453 | response is appropriate. A proxy <em class="bcp14">MUST NOT</em> generate the "*" value. |
|---|
| 1454 | </p> |
|---|
| 1455 | <p id="rfc.section.3.5.p.8">The field-names given are not limited to the set of standard header fields defined by this specification. Field names are |
|---|
| 1456 | case-insensitive. |
|---|
| 1457 | </p> |
|---|
| 1458 | <div id="rfc.iref.w.1"></div> |
|---|
| 1459 | <div id="rfc.iref.h.7"></div> |
|---|
| 1460 | <h2 id="rfc.section.3.6"><a href="#rfc.section.3.6">3.6</a> <a id="header.warning" href="#header.warning">Warning</a></h2> |
|---|
| 1461 | <p id="rfc.section.3.6.p.1">The "Warning" header field is used to carry additional information about the status or transformation of a message that might |
|---|
| 1462 | not be reflected in the message. This information is typically used to warn about possible incorrectness introduced by caching |
|---|
| 1463 | operations or transformations applied to the payload of the message. |
|---|
| 1464 | </p> |
|---|
| 1465 | <p id="rfc.section.3.6.p.2">Warnings can be used for other purposes, both cache-related and otherwise. The use of a warning, rather than an error status |
|---|
| 1466 | code, distinguishes these responses from true failures. |
|---|
| 1467 | </p> |
|---|
| 1468 | <p id="rfc.section.3.6.p.3">Warning header fields can in general be applied to any message, however some warn-codes are specific to caches and can only |
|---|
| 1469 | be applied to response messages. |
|---|
| 1470 | </p> |
|---|
| 1471 | <div id="rfc.figure.u.18"></div><pre class="inline"><span id="rfc.iref.g.12"></span><span id="rfc.iref.g.13"></span><span id="rfc.iref.g.14"></span><span id="rfc.iref.g.15"></span><span id="rfc.iref.g.16"></span><span id="rfc.iref.g.17"></span> <a href="#header.warning" class="smpl">Warning</a> = 1#<a href="#header.warning" class="smpl">warning-value</a> |
|---|
| 1472 | |
|---|
| 1473 | <a href="#header.warning" class="smpl">warning-value</a> = <a href="#header.warning" class="smpl">warn-code</a> <a href="#notation" class="smpl">SP</a> <a href="#header.warning" class="smpl">warn-agent</a> <a href="#notation" class="smpl">SP</a> <a href="#header.warning" class="smpl">warn-text</a> |
|---|
| 1474 | [<a href="#notation" class="smpl">SP</a> <a href="#header.warning" class="smpl">warn-date</a>] |
|---|
| 1475 | |
|---|
| 1476 | <a href="#header.warning" class="smpl">warn-code</a> = 3<a href="#notation" class="smpl">DIGIT</a> |
|---|
| 1477 | <a href="#header.warning" class="smpl">warn-agent</a> = ( <a href="#abnf.dependencies" class="smpl">uri-host</a> [ ":" <a href="#abnf.dependencies" class="smpl">port</a> ] ) / <a href="#abnf.dependencies" class="smpl">pseudonym</a> |
|---|
| 1478 | ; the name or pseudonym of the server adding |
|---|
| 1479 | ; the Warning header field, for use in debugging |
|---|
| 1480 | <a href="#header.warning" class="smpl">warn-text</a> = <a href="#core.rules" class="smpl">quoted-string</a> |
|---|
| 1481 | <a href="#header.warning" class="smpl">warn-date</a> = <a href="#notation" class="smpl">DQUOTE</a> <a href="#abnf.dependencies" class="smpl">HTTP-date</a> <a href="#notation" class="smpl">DQUOTE</a> |
|---|
| 1482 | </pre><p id="rfc.section.3.6.p.5">Multiple warnings can be attached to a response (either by the origin server or by a cache), including multiple warnings with |
|---|
| 1483 | the same code number, only differing in warn-text. |
|---|
| 1484 | </p> |
|---|
| 1485 | <p id="rfc.section.3.6.p.6">When this occurs, the user agent <em class="bcp14">SHOULD</em> inform the user of as many of them as possible, in the order that they appear in the response. |
|---|
| 1486 | </p> |
|---|
| 1487 | <p id="rfc.section.3.6.p.7">Systems that generate multiple Warning header fields are encouraged to order them with this user agent behavior in mind. New |
|---|
| 1488 | Warning header fields are added after any existing Warning headers fields. |
|---|
| 1489 | </p> |
|---|
| 1490 | <p id="rfc.section.3.6.p.8">Warnings are assigned three digit warn-codes. The first digit indicates whether the Warning is required to be deleted from |
|---|
| 1491 | a stored response after validation: |
|---|
| 1492 | </p> |
|---|
| 1493 | <ul> |
|---|
| 1494 | <li>1xx Warnings describe the freshness or validation status of the response, and so <em class="bcp14">MUST</em> be deleted by a cache after validation. They can only be generated by a cache when validating a cached entry, and <em class="bcp14">MUST NOT</em> be generated in any other situation. |
|---|
| 1495 | </li> |
|---|
| 1496 | <li>2xx Warnings describe some aspect of the representation that is not rectified by a validation (for example, a lossy compression |
|---|
| 1497 | of the representation) and <em class="bcp14">MUST NOT</em> be deleted by a cache after validation, unless a full response is returned, in which case they <em class="bcp14">MUST</em> be. |
|---|
| 1498 | </li> |
|---|
| 1499 | </ul> |
|---|
| 1500 | <p id="rfc.section.3.6.p.9">If an implementation sends a message with one or more Warning header fields to a receiver whose version is HTTP/1.0 or lower, |
|---|
| 1501 | then the sender <em class="bcp14">MUST</em> include in each warning-value a warn-date that matches the Date header field in the message. |
|---|
| 1502 | </p> |
|---|
| 1503 | <p id="rfc.section.3.6.p.10">If a system receives a message with a warning-value that includes a warn-date, and that warn-date is different from the Date |
|---|
| 1504 | value in the response, then that warning-value <em class="bcp14">MUST</em> be deleted from the message before storing, forwarding, or using it. (preventing the consequences of naive caching of Warning |
|---|
| 1505 | header fields.) If all of the warning-values are deleted for this reason, the Warning header field <em class="bcp14">MUST</em> be deleted as well. |
|---|
| 1506 | </p> |
|---|
| 1507 | <p id="rfc.section.3.6.p.11">The following warn-codes are defined by this specification, each with a recommended warn-text in English, and a description |
|---|
| 1508 | of its meaning. |
|---|
| 1509 | </p> |
|---|
| 1510 | <p id="rfc.section.3.6.p.12"> 110 Response is stale </p> |
|---|
| 1511 | <ul class="empty"> |
|---|
| 1512 | <li>A cache <em class="bcp14">SHOULD</em> include this whenever the returned response is stale. |
|---|
| 1513 | </li> |
|---|
| 1514 | </ul> |
|---|
| 1515 | <p id="rfc.section.3.6.p.13"> 111 Revalidation failed </p> |
|---|
| 1516 | <ul class="empty"> |
|---|
| 1517 | <li>A cache <em class="bcp14">SHOULD</em> include this when returning a stale response because an attempt to validate the response failed, due to an inability to reach |
|---|
| 1518 | the server. |
|---|
| 1519 | </li> |
|---|
| 1520 | </ul> |
|---|
| 1521 | <p id="rfc.section.3.6.p.14"> 112 Disconnected operation </p> |
|---|
| 1522 | <ul class="empty"> |
|---|
| 1523 | <li>A cache <em class="bcp14">SHOULD</em> include this if it is intentionally disconnected from the rest of the network for a period of time. |
|---|
| 1524 | </li> |
|---|
| 1525 | </ul> |
|---|
| 1526 | <p id="rfc.section.3.6.p.15"> 113 Heuristic expiration </p> |
|---|
| 1527 | <ul class="empty"> |
|---|
| 1528 | <li>A cache <em class="bcp14">SHOULD</em> include this if it heuristically chose a freshness lifetime greater than 24 hours and the response's age is greater than 24 |
|---|
| 1529 | hours. |
|---|
| 1530 | </li> |
|---|
| 1531 | </ul> |
|---|
| 1532 | <p id="rfc.section.3.6.p.16"> 199 Miscellaneous warning </p> |
|---|
| 1533 | <ul class="empty"> |
|---|
| 1534 | <li>The warning text can include arbitrary information to be presented to a human user, or logged. A system receiving this warning <em class="bcp14">MUST NOT</em> take any automated action, besides presenting the warning to the user. |
|---|
| 1535 | </li> |
|---|
| 1536 | </ul> |
|---|
| 1537 | <p id="rfc.section.3.6.p.17"> 214 Transformation applied </p> |
|---|
| 1538 | <ul class="empty"> |
|---|
| 1539 | <li><em class="bcp14">MUST</em> be added by a proxy if it applies any transformation to the representation, such as changing the content-coding, media-type, |
|---|
| 1540 | or modifying the representation data, unless this Warning code already appears in the response. |
|---|
| 1541 | </li> |
|---|
| 1542 | </ul> |
|---|
| 1543 | <p id="rfc.section.3.6.p.18"> 299 Miscellaneous persistent warning </p> |
|---|
| 1544 | <ul class="empty"> |
|---|
| 1545 | <li>The warning text can include arbitrary information to be presented to a human user, or logged. A system receiving this warning <em class="bcp14">MUST NOT</em> take any automated action. |
|---|
| 1546 | </li> |
|---|
| 1547 | </ul> |
|---|
| 1548 | <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a> <a id="history.lists" href="#history.lists">History Lists</a></h1> |
|---|
| 1549 | <p id="rfc.section.4.p.1">User agents often have history mechanisms, such as "Back" buttons and history lists, that can be used to redisplay a representation |
|---|
| 1550 | retrieved earlier in a session. |
|---|
| 1551 | </p> |
|---|
| 1552 | <p id="rfc.section.4.p.2">The freshness model (<a href="#expiration.model" title="Freshness Model">Section 2.3</a>) does not necessarily apply to history mechanisms. I.e., a history mechanism can display a previous representation even if |
|---|
| 1553 | it has expired. |
|---|
| 1554 | </p> |
|---|
| 1555 | <p id="rfc.section.4.p.3">This does not prohibit the history mechanism from telling the user that a view might be stale, or from honoring cache directives |
|---|
| 1556 | (e.g., Cache-Control: no-store). |
|---|
| 1557 | </p> |
|---|
| 1558 | <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a> <a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1> |
|---|
| 1559 | <h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a> <a id="cache.directive.registration" href="#cache.directive.registration">Cache Directive Registry</a></h2> |
|---|
| 1560 | <p id="rfc.section.5.1.p.1">The registration procedure for HTTP Cache Directives is defined by <a href="#cache.control.extensions" title="Cache Control Extensions">Section 3.2.3</a> of this document. |
|---|
| 1561 | </p> |
|---|
| 1562 | <p id="rfc.section.5.1.p.2">The HTTP Cache Directive Registry shall be created at <<a href="http://www.iana.org/assignments/http-cache-directives">http://www.iana.org/assignments/http-cache-directives</a>> and be populated with the registrations below: |
|---|
| 1563 | </p> |
|---|
| 1564 | <div id="rfc.table.1"> |
|---|
| 1565 | <div id="iana.cache.directive.registration.table"></div> |
|---|
| 1566 | <table class="tt full left" cellpadding="3" cellspacing="0"> |
|---|
| 1567 | <thead> |
|---|
| 1568 | <tr> |
|---|
| 1569 | <th>Cache Directive</th> |
|---|
| 1570 | <th>Reference</th> |
|---|
| 1571 | </tr> |
|---|
| 1572 | </thead> |
|---|
| 1573 | <tbody> |
|---|
| 1574 | <tr> |
|---|
| 1575 | <td class="left">max-age</td> |
|---|
| 1576 | <td class="left"> <a href="#cache-request-directive" title="Request Cache-Control Directives">Section 3.2.1</a>, <a href="#cache-response-directive" title="Response Cache-Control Directives">Section 3.2.2</a> |
|---|
| 1577 | </td> |
|---|
| 1578 | </tr> |
|---|
| 1579 | <tr> |
|---|
| 1580 | <td class="left">max-stale</td> |
|---|
| 1581 | <td class="left"> <a href="#cache-request-directive" title="Request Cache-Control Directives">Section 3.2.1</a> |
|---|
| 1582 | </td> |
|---|
| 1583 | </tr> |
|---|
| 1584 | <tr> |
|---|
| 1585 | <td class="left">min-fresh</td> |
|---|
| 1586 | <td class="left"> <a href="#cache-request-directive" title="Request Cache-Control Directives">Section 3.2.1</a> |
|---|
| 1587 | </td> |
|---|
| 1588 | </tr> |
|---|
| 1589 | <tr> |
|---|
| 1590 | <td class="left">must-revalidate</td> |
|---|
| 1591 | <td class="left"> <a href="#cache-response-directive" title="Response Cache-Control Directives">Section 3.2.2</a> |
|---|
| 1592 | </td> |
|---|
| 1593 | </tr> |
|---|
| 1594 | <tr> |
|---|
| 1595 | <td class="left">no-cache</td> |
|---|
| 1596 | <td class="left"> <a href="#cache-request-directive" title="Request Cache-Control Directives">Section 3.2.1</a>, <a href="#cache-response-directive" title="Response Cache-Control Directives">Section 3.2.2</a> |
|---|
| 1597 | </td> |
|---|
| 1598 | </tr> |
|---|
| 1599 | <tr> |
|---|
| 1600 | <td class="left">no-store</td> |
|---|
| 1601 | <td class="left"> <a href="#cache-request-directive" title="Request Cache-Control Directives">Section 3.2.1</a>, <a href="#cache-response-directive" title="Response Cache-Control Directives">Section 3.2.2</a> |
|---|
| 1602 | </td> |
|---|
| 1603 | </tr> |
|---|
| 1604 | <tr> |
|---|
| 1605 | <td class="left">no-transform</td> |
|---|
| 1606 | <td class="left"> <a href="#cache-request-directive" title="Request Cache-Control Directives">Section 3.2.1</a>, <a href="#cache-response-directive" title="Response Cache-Control Directives">Section 3.2.2</a> |
|---|
| 1607 | </td> |
|---|
| 1608 | </tr> |
|---|
| 1609 | <tr> |
|---|
| 1610 | <td class="left">only-if-cached</td> |
|---|
| 1611 | <td class="left"> <a href="#cache-request-directive" title="Request Cache-Control Directives">Section 3.2.1</a> |
|---|
| 1612 | </td> |
|---|
| 1613 | </tr> |
|---|
| 1614 | <tr> |
|---|
| 1615 | <td class="left">private</td> |
|---|
| 1616 | <td class="left"> <a href="#cache-response-directive" title="Response Cache-Control Directives">Section 3.2.2</a> |
|---|
| 1617 | </td> |
|---|
| 1618 | </tr> |
|---|
| 1619 | <tr> |
|---|
| 1620 | <td class="left">proxy-revalidate</td> |
|---|
| 1621 | <td class="left"> <a href="#cache-response-directive" title="Response Cache-Control Directives">Section 3.2.2</a> |
|---|
| 1622 | </td> |
|---|
| 1623 | </tr> |
|---|
| 1624 | <tr> |
|---|
| 1625 | <td class="left">public</td> |
|---|
| 1626 | <td class="left"> <a href="#cache-response-directive" title="Response Cache-Control Directives">Section 3.2.2</a> |
|---|
| 1627 | </td> |
|---|
| 1628 | </tr> |
|---|
| 1629 | <tr> |
|---|
| 1630 | <td class="left">s-maxage</td> |
|---|
| 1631 | <td class="left"> <a href="#cache-response-directive" title="Response Cache-Control Directives">Section 3.2.2</a> |
|---|
| 1632 | </td> |
|---|
| 1633 | </tr> |
|---|
| 1634 | <tr> |
|---|
| 1635 | <td class="left">stale-if-error</td> |
|---|
| 1636 | <td class="left"> <a href="#RFC5861" id="rfc.xref.RFC5861.1"><cite title="HTTP Cache-Control Extensions for Stale Content">[RFC5861]</cite></a>, <a href="http://tools.ietf.org/html/rfc5861#section-4">Section 4</a> |
|---|
| 1637 | </td> |
|---|
| 1638 | </tr> |
|---|
| 1639 | <tr> |
|---|
| 1640 | <td class="left">stale-while-revalidate</td> |
|---|
| 1641 | <td class="left"> <a href="#RFC5861" id="rfc.xref.RFC5861.2"><cite title="HTTP Cache-Control Extensions for Stale Content">[RFC5861]</cite></a>, <a href="http://tools.ietf.org/html/rfc5861#section-3">Section 3</a> |
|---|
| 1642 | </td> |
|---|
| 1643 | </tr> |
|---|
| 1644 | </tbody> |
|---|
| 1645 | </table> |
|---|
| 1646 | </div> |
|---|
| 1647 | <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> |
|---|
| 1648 | <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>): |
|---|
| 1649 | </p> |
|---|
| 1650 | <div id="rfc.table.2"> |
|---|
| 1651 | <div id="iana.header.registration.table"></div> |
|---|
| 1652 | <table class="tt full left" cellpadding="3" cellspacing="0"> |
|---|
| 1653 | <thead> |
|---|
| 1654 | <tr> |
|---|
| 1655 | <th>Header Field Name</th> |
|---|
| 1656 | <th>Protocol</th> |
|---|
| 1657 | <th>Status</th> |
|---|
| 1658 | <th>Reference</th> |
|---|
| 1659 | </tr> |
|---|
| 1660 | </thead> |
|---|
| 1661 | <tbody> |
|---|
| 1662 | <tr> |
|---|
| 1663 | <td class="left">Age</td> |
|---|
| 1664 | <td class="left">http</td> |
|---|
| 1665 | <td class="left">standard</td> |
|---|
| 1666 | <td class="left"> <a href="#header.age" id="rfc.xref.header.age.3" title="Age">Section 3.1</a> |
|---|
| 1667 | </td> |
|---|
| 1668 | </tr> |
|---|
| 1669 | <tr> |
|---|
| 1670 | <td class="left">Cache-Control</td> |
|---|
| 1671 | <td class="left">http</td> |
|---|
| 1672 | <td class="left">standard</td> |
|---|
| 1673 | <td class="left"> <a href="#header.cache-control" id="rfc.xref.header.cache-control.3" title="Cache-Control">Section 3.2</a> |
|---|
| 1674 | </td> |
|---|
| 1675 | </tr> |
|---|
| 1676 | <tr> |
|---|
| 1677 | <td class="left">Expires</td> |
|---|
| 1678 | <td class="left">http</td> |
|---|
| 1679 | <td class="left">standard</td> |
|---|
| 1680 | <td class="left"> <a href="#header.expires" id="rfc.xref.header.expires.4" title="Expires">Section 3.3</a> |
|---|
| 1681 | </td> |
|---|
| 1682 | </tr> |
|---|
| 1683 | <tr> |
|---|
| 1684 | <td class="left">Pragma</td> |
|---|
| 1685 | <td class="left">http</td> |
|---|
| 1686 | <td class="left">standard</td> |
|---|
| 1687 | <td class="left"> <a href="#header.pragma" id="rfc.xref.header.pragma.3" title="Pragma">Section 3.4</a> |
|---|
| 1688 | </td> |
|---|
| 1689 | </tr> |
|---|
| 1690 | <tr> |
|---|
| 1691 | <td class="left">Vary</td> |
|---|
| 1692 | <td class="left">http</td> |
|---|
| 1693 | <td class="left">standard</td> |
|---|
| 1694 | <td class="left"> <a href="#header.vary" id="rfc.xref.header.vary.2" title="Vary">Section 3.5</a> |
|---|
| 1695 | </td> |
|---|
| 1696 | </tr> |
|---|
| 1697 | <tr> |
|---|
| 1698 | <td class="left">Warning</td> |
|---|
| 1699 | <td class="left">http</td> |
|---|
| 1700 | <td class="left">standard</td> |
|---|
| 1701 | <td class="left"> <a href="#header.warning" id="rfc.xref.header.warning.4" title="Warning">Section 3.6</a> |
|---|
| 1702 | </td> |
|---|
| 1703 | </tr> |
|---|
| 1704 | </tbody> |
|---|
| 1705 | </table> |
|---|
| 1706 | </div> |
|---|
| 1707 | <p id="rfc.section.5.2.p.2">The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p> |
|---|
| 1708 | <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a> <a id="security.considerations" href="#security.considerations">Security Considerations</a></h1> |
|---|
| 1709 | <p id="rfc.section.6.p.1">Caches expose additional potential vulnerabilities, since the contents of the cache represent an attractive target for malicious |
|---|
| 1710 | exploitation. Because cache contents persist after an HTTP request is complete, an attack on the cache can reveal information |
|---|
| 1711 | long after a user believes that the information has been removed from the network. Therefore, cache contents need to be protected |
|---|
| 1712 | as sensitive information. |
|---|
| 1713 | </p> |
|---|
| 1714 | <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a> <a id="acks" href="#acks">Acknowledgments</a></h1> |
|---|
| 1715 | <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.Part1.17"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. |
|---|
| 1716 | </p> |
|---|
| 1717 | <h1 id="rfc.references"><a id="rfc.section.8" href="#rfc.section.8">8.</a> References |
|---|
| 1718 | </h1> |
|---|
| 1719 | <h2 id="rfc.references.1"><a href="#rfc.section.8.1" id="rfc.section.8.1">8.1</a> Normative References |
|---|
| 1720 | </h2> |
|---|
| 1721 | <table> |
|---|
| 1722 | <tr> |
|---|
| 1723 | <td class="reference"><b id="Part1">[Part1]</b></td> |
|---|
| 1724 | <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), October 2011. |
|---|
| 1725 | </td> |
|---|
| 1726 | </tr> |
|---|
| 1727 | <tr> |
|---|
| 1728 | <td class="reference"><b id="Part2">[Part2]</b></td> |
|---|
| 1729 | <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), October 2011. |
|---|
| 1730 | </td> |
|---|
| 1731 | </tr> |
|---|
| 1732 | <tr> |
|---|
| 1733 | <td class="reference"><b id="Part4">[Part4]</b></td> |
|---|
| 1734 | <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-p4-conditional-latest">HTTP/1.1, part 4: Conditional Requests</a>”, Internet-Draft draft-ietf-httpbis-p4-conditional-latest (work in progress), October 2011. |
|---|
| 1735 | </td> |
|---|
| 1736 | </tr> |
|---|
| 1737 | <tr> |
|---|
| 1738 | <td class="reference"><b id="Part5">[Part5]</b></td> |
|---|
| 1739 | <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), October 2011. |
|---|
| 1740 | </td> |
|---|
| 1741 | </tr> |
|---|
| 1742 | <tr> |
|---|
| 1743 | <td class="reference"><b id="Part7">[Part7]</b></td> |
|---|
| 1744 | <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-p7-auth-latest">HTTP/1.1, part 7: Authentication</a>”, Internet-Draft draft-ietf-httpbis-p7-auth-latest (work in progress), October 2011. |
|---|
| 1745 | </td> |
|---|
| 1746 | </tr> |
|---|
| 1747 | <tr> |
|---|
| 1748 | <td class="reference"><b id="RFC2119">[RFC2119]</b></td> |
|---|
| 1749 | <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. |
|---|
| 1750 | </td> |
|---|
| 1751 | </tr> |
|---|
| 1752 | <tr> |
|---|
| 1753 | <td class="reference"><b id="RFC5234">[RFC5234]</b></td> |
|---|
| 1754 | <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. |
|---|
| 1755 | </td> |
|---|
| 1756 | </tr> |
|---|
| 1757 | </table> |
|---|
| 1758 | <h2 id="rfc.references.2"><a href="#rfc.section.8.2" id="rfc.section.8.2">8.2</a> Informative References |
|---|
| 1759 | </h2> |
|---|
| 1760 | <table> |
|---|
| 1761 | <tr> |
|---|
| 1762 | <td class="reference"><b id="RFC1305">[RFC1305]</b></td> |
|---|
| 1763 | <td class="top"><a href="mailto:mills@udel.edu" title="University of Delaware, Electrical Engineering Department">Mills, D.</a>, “<a href="http://tools.ietf.org/html/rfc1305">Network Time Protocol (Version 3) Specification, Implementation</a>”, RFC 1305, March 1992. |
|---|
| 1764 | </td> |
|---|
| 1765 | </tr> |
|---|
| 1766 | <tr> |
|---|
| 1767 | <td class="reference"><b id="RFC2616">[RFC2616]</b></td> |
|---|
| 1768 | <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. |
|---|
| 1769 | </td> |
|---|
| 1770 | </tr> |
|---|
| 1771 | <tr> |
|---|
| 1772 | <td class="reference"><b id="RFC3864">[RFC3864]</b></td> |
|---|
| 1773 | <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. |
|---|
| 1774 | </td> |
|---|
| 1775 | </tr> |
|---|
| 1776 | <tr> |
|---|
| 1777 | <td class="reference"><b id="RFC5226">[RFC5226]</b></td> |
|---|
| 1778 | <td class="top"><a href="mailto:narten@us.ibm.com" title="IBM">Narten, T.</a> and <a href="mailto:Harald@Alvestrand.no" title="Google">H. Alvestrand</a>, “<a href="http://tools.ietf.org/html/rfc5226">Guidelines for Writing an IANA Considerations Section in RFCs</a>”, BCP 26, RFC 5226, May 2008. |
|---|
| 1779 | </td> |
|---|
| 1780 | </tr> |
|---|
| 1781 | <tr> |
|---|
| 1782 | <td class="reference"><b id="RFC5861">[RFC5861]</b></td> |
|---|
| 1783 | <td class="top"><a href="mailto:mnot@yahoo-inc.com" title="Yahoo! Inc.">Nottingham, M.</a>, “<a href="http://tools.ietf.org/html/rfc5861">HTTP Cache-Control Extensions for Stale Content</a>”, RFC 5861, April 2010. |
|---|
| 1784 | </td> |
|---|
| 1785 | </tr> |
|---|
| 1786 | </table> |
|---|
| 1787 | <div class="avoidbreak"> |
|---|
| 1788 | <h1 id="rfc.authors"><a href="#rfc.authors">Authors' Addresses</a></h1> |
|---|
| 1789 | <address class="vcard"><span class="vcardline"><span class="fn">Roy T. Fielding</span> |
|---|
| 1790 | (editor) |
|---|
| 1791 | <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> |
|---|
| 1792 | <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> |
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| 1793 | <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> |
|---|
| 1794 | <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> |
|---|
| 1795 | <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> |
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| 1796 | <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> |
|---|
| 1797 | <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> |
|---|
| 1798 | <address class="vcard"><span class="vcardline"><span class="fn">Yves Lafon</span> |
|---|
| 1799 | (editor) |
|---|
| 1800 | <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> |
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| 1801 | <address class="vcard"><span class="vcardline"><span class="fn">Mark Nottingham</span> |
|---|
| 1802 | (editor) |
|---|
| 1803 | <span class="n hidden"><span class="family-name">Nottingham</span><span class="given-name">Mark</span></span></span><span class="org vcardline">Rackspace</span><span class="vcardline">Email: <a href="mailto:mnot@mnot.net"><span class="email">mnot@mnot.net</span></a></span><span class="vcardline">URI: <a href="http://www.mnot.net/" class="url">http://www.mnot.net/</a></span></address> |
|---|
| 1804 | <address class="vcard"><span class="vcardline"><span class="fn">Julian F. Reschke</span> |
|---|
| 1805 | (editor) |
|---|
| 1806 | <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> |
|---|
| 1807 | </div> |
|---|
| 1808 | <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> |
|---|
| 1809 | <p id="rfc.section.A.p.1">Make the specified age calculation algorithm less conservative. (<a href="#age.calculations" title="Calculating Age">Section 2.3.2</a>) |
|---|
| 1810 | </p> |
|---|
| 1811 | <p id="rfc.section.A.p.2">Remove requirement to consider Content-Location in successful responses in order to determine the appropriate response to |
|---|
| 1812 | use. (<a href="#validation.model" title="Validation Model">Section 2.4</a>) |
|---|
| 1813 | </p> |
|---|
| 1814 | <p id="rfc.section.A.p.3">Clarify denial of service attack avoidance requirement. (<a href="#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section 2.5</a>) |
|---|
| 1815 | </p> |
|---|
| 1816 | <p id="rfc.section.A.p.4">Change ABNF productions for header fields to only define the field value. (<a href="#header.field.definitions" title="Header Field Definitions">Section 3</a>) |
|---|
| 1817 | </p> |
|---|
| 1818 | <p id="rfc.section.A.p.5">Do not mention RFC 2047 encoding and multiple languages in Warning header fields anymore, as these aspects never were implemented. |
|---|
| 1819 | (<a href="#header.warning" id="rfc.xref.header.warning.5" title="Warning">Section 3.6</a>) |
|---|
| 1820 | </p> |
|---|
| 1821 | <h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a> <a id="collected.abnf" href="#collected.abnf">Collected ABNF</a></h1> |
|---|
| 1822 | <div id="rfc.figure.u.19"></div> <pre class="inline"><a href="#header.age" class="smpl">Age</a> = delta-seconds |
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| 1823 | |
|---|
| 1824 | <a href="#header.cache-control" class="smpl">Cache-Control</a> = *( "," OWS ) cache-directive *( OWS "," [ OWS |
|---|
| 1825 | cache-directive ] ) |
|---|
| 1826 | |
|---|
| 1827 | <a href="#header.expires" class="smpl">Expires</a> = HTTP-date |
|---|
| 1828 | |
|---|
| 1829 | <a href="#abnf.dependencies" class="smpl">HTTP-date</a> = <HTTP-date, defined in [Part2], Section 8> |
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| 1830 | |
|---|
| 1831 | <a href="#core.rules" class="smpl">OWS</a> = <OWS, defined in [Part1], Section 1.2.2> |
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| 1832 | |
|---|
| 1833 | <a href="#header.pragma" class="smpl">Pragma</a> = *( "," OWS ) pragma-directive *( OWS "," [ OWS |
|---|
| 1834 | pragma-directive ] ) |
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| 1835 | |
|---|
| 1836 | <a href="#header.vary" class="smpl">Vary</a> = "*" / ( *( "," OWS ) field-name *( OWS "," [ OWS field-name ] |
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| 1837 | ) ) |
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| 1838 | |
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| 1839 | <a href="#header.warning" class="smpl">Warning</a> = *( "," OWS ) warning-value *( OWS "," [ OWS warning-value ] |
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| 1840 | ) |
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| 1841 | |
|---|
| 1842 | <a href="#header.cache-control" class="smpl">cache-directive</a> = cache-request-directive / cache-response-directive |
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| 1843 | <a href="#header.cache-control" class="smpl">cache-extension</a> = token [ "=" ( token / quoted-string ) ] |
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| 1844 | <a href="#header.cache-control" class="smpl">cache-request-directive</a> = "no-cache" / "no-store" / ( "max-age=" |
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| 1845 | delta-seconds ) / ( "max-stale" [ "=" delta-seconds ] ) / ( |
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| 1846 | "min-fresh=" delta-seconds ) / "no-transform" / "only-if-cached" / |
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| 1847 | cache-extension |
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| 1848 | <a href="#header.cache-control" class="smpl">cache-response-directive</a> = "public" / ( "private" [ "=" DQUOTE *( "," |
|---|
| 1849 | OWS ) field-name *( OWS "," [ OWS field-name ] ) DQUOTE ] ) / ( |
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| 1850 | "no-cache" [ "=" DQUOTE *( "," OWS ) field-name *( OWS "," [ OWS |
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| 1851 | field-name ] ) DQUOTE ] ) / "no-store" / "no-transform" / |
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| 1852 | "must-revalidate" / "proxy-revalidate" / ( "max-age=" delta-seconds |
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| 1853 | ) / ( "s-maxage=" delta-seconds ) / cache-extension |
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| 1854 | |
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| 1855 | <a href="#delta-seconds" class="smpl">delta-seconds</a> = 1*DIGIT |
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| 1856 | |
|---|
| 1857 | <a href="#header.pragma" class="smpl">extension-pragma</a> = token [ "=" ( token / quoted-string ) ] |
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| 1858 | |
|---|
| 1859 | <a href="#abnf.dependencies" class="smpl">field-name</a> = <field-name, defined in [Part1], Section 3.2> |
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| 1860 | |
|---|
| 1861 | <a href="#abnf.dependencies" class="smpl">port</a> = <port, defined in [Part1], Section 2.7> |
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| 1862 | <a href="#header.pragma" class="smpl">pragma-directive</a> = "no-cache" / extension-pragma |
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| 1863 | <a href="#abnf.dependencies" class="smpl">pseudonym</a> = <pseudonym, defined in [Part1], Section 8.8> |
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| 1864 | |
|---|
| 1865 | <a href="#core.rules" class="smpl">quoted-string</a> = <quoted-string, defined in [Part1], Section 3.2.3> |
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| 1866 | |
|---|
| 1867 | <a href="#core.rules" class="smpl">token</a> = <token, defined in [Part1], Section 3.2.3> |
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| 1868 | |
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| 1869 | <a href="#abnf.dependencies" class="smpl">uri-host</a> = <uri-host, defined in [Part1], Section 2.7> |
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| 1870 | |
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| 1871 | <a href="#header.warning" class="smpl">warn-agent</a> = ( uri-host [ ":" port ] ) / pseudonym |
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| 1872 | <a href="#header.warning" class="smpl">warn-code</a> = 3DIGIT |
|---|
| 1873 | <a href="#header.warning" class="smpl">warn-date</a> = DQUOTE HTTP-date DQUOTE |
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| 1874 | <a href="#header.warning" class="smpl">warn-text</a> = quoted-string |
|---|
| 1875 | <a href="#header.warning" class="smpl">warning-value</a> = warn-code SP warn-agent SP warn-text [ SP warn-date |
|---|
| 1876 | ] |
|---|
| 1877 | </pre> <div id="rfc.figure.u.20"></div> |
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| 1878 | <p>ABNF diagnostics:</p><pre class="inline">; Age defined but not used |
|---|
| 1879 | ; Cache-Control defined but not used |
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| 1880 | ; Expires defined but not used |
|---|
| 1881 | ; Pragma defined but not used |
|---|
| 1882 | ; Vary defined but not used |
|---|
| 1883 | ; Warning defined but not used |
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| 1884 | </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> |
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| 1885 | <h2 id="rfc.section.C.1"><a href="#rfc.section.C.1">C.1</a> Since RFC 2616 |
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| 1886 | </h2> |
|---|
| 1887 | <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>. |
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| 1888 | </p> |
|---|
| 1889 | <h2 id="rfc.section.C.2"><a href="#rfc.section.C.2">C.2</a> Since draft-ietf-httpbis-p6-cache-00 |
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| 1890 | </h2> |
|---|
| 1891 | <p id="rfc.section.C.2.p.1">Closed issues: </p> |
|---|
| 1892 | <ul> |
|---|
| 1893 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/9">http://tools.ietf.org/wg/httpbis/trac/ticket/9</a>>: "Trailer" (<<a href="http://purl.org/NET/http-errata#trailer-hop">http://purl.org/NET/http-errata#trailer-hop</a>>) |
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| 1894 | </li> |
|---|
| 1895 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/12">http://tools.ietf.org/wg/httpbis/trac/ticket/12</a>>: "Invalidation after Update or Delete" (<<a href="http://purl.org/NET/http-errata#invalidupd">http://purl.org/NET/http-errata#invalidupd</a>>) |
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| 1896 | </li> |
|---|
| 1897 | <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" |
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| 1898 | </li> |
|---|
| 1899 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/48">http://tools.ietf.org/wg/httpbis/trac/ticket/48</a>>: "Date reference typo" |
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| 1900 | </li> |
|---|
| 1901 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/49">http://tools.ietf.org/wg/httpbis/trac/ticket/49</a>>: "Connection header text" |
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| 1902 | </li> |
|---|
| 1903 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/65">http://tools.ietf.org/wg/httpbis/trac/ticket/65</a>>: "Informative references" |
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| 1904 | </li> |
|---|
| 1905 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/66">http://tools.ietf.org/wg/httpbis/trac/ticket/66</a>>: "ISO-8859-1 Reference" |
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| 1906 | </li> |
|---|
| 1907 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/86">http://tools.ietf.org/wg/httpbis/trac/ticket/86</a>>: "Normative up-to-date references" |
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| 1908 | </li> |
|---|
| 1909 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/87">http://tools.ietf.org/wg/httpbis/trac/ticket/87</a>>: "typo in 13.2.2" |
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| 1910 | </li> |
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| 1911 | </ul> |
|---|
| 1912 | <p id="rfc.section.C.2.p.2">Other changes: </p> |
|---|
| 1913 | <ul> |
|---|
| 1914 | <li>Use names of RFC4234 core rules DQUOTE and HTAB (work in progress on <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/36">http://tools.ietf.org/wg/httpbis/trac/ticket/36</a>>) |
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| 1915 | </li> |
|---|
| 1916 | </ul> |
|---|
| 1917 | <h2 id="rfc.section.C.3"><a href="#rfc.section.C.3">C.3</a> Since draft-ietf-httpbis-p6-cache-01 |
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| 1918 | </h2> |
|---|
| 1919 | <p id="rfc.section.C.3.p.1">Closed issues: </p> |
|---|
| 1920 | <ul> |
|---|
| 1921 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/82">http://tools.ietf.org/wg/httpbis/trac/ticket/82</a>>: "rel_path not used" |
|---|
| 1922 | </li> |
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| 1923 | </ul> |
|---|
| 1924 | <p id="rfc.section.C.3.p.2">Other changes: </p> |
|---|
| 1925 | <ul> |
|---|
| 1926 | <li>Get rid of duplicate BNF rule names ("host" -> "uri-host") (work in progress on <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/36">http://tools.ietf.org/wg/httpbis/trac/ticket/36</a>>) |
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| 1927 | </li> |
|---|
| 1928 | <li>Add explicit references to BNF syntax and rules imported from other parts of the specification.</li> |
|---|
| 1929 | </ul> |
|---|
| 1930 | <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-p6-cache-02</a></h2> |
|---|
| 1931 | <p id="rfc.section.C.4.p.1">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>>): |
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| 1932 | </p> |
|---|
| 1933 | <ul> |
|---|
| 1934 | <li>Reference RFC 3984, and update header field registrations for header fields defined in this document.</li> |
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| 1935 | </ul> |
|---|
| 1936 | <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-p6-cache-03</a></h2> |
|---|
| 1937 | <p id="rfc.section.C.5.p.1">Closed issues: </p> |
|---|
| 1938 | <ul> |
|---|
| 1939 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/106">http://tools.ietf.org/wg/httpbis/trac/ticket/106</a>>: "Vary header classification" |
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| 1940 | </li> |
|---|
| 1941 | </ul> |
|---|
| 1942 | <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-p6-cache-04</a></h2> |
|---|
| 1943 | <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>>): |
|---|
| 1944 | </p> |
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| 1945 | <ul> |
|---|
| 1946 | <li>Use "/" instead of "|" for alternatives.</li> |
|---|
| 1947 | <li>Introduce new ABNF rules for "bad" whitespace ("BWS"), optional whitespace ("OWS") and required whitespace ("RWS").</li> |
|---|
| 1948 | <li>Rewrite ABNFs to spell out whitespace rules, factor out header field value format definitions.</li> |
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| 1949 | </ul> |
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| 1950 | <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-p6-cache-05</a></h2> |
|---|
| 1951 | <p id="rfc.section.C.7.p.1">This is a total rewrite of this part of the specification.</p> |
|---|
| 1952 | <p id="rfc.section.C.7.p.2">Affected issues: </p> |
|---|
| 1953 | <ul> |
|---|
| 1954 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/54">http://tools.ietf.org/wg/httpbis/trac/ticket/54</a>>: "Definition of 1xx Warn-Codes" |
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| 1955 | </li> |
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| 1956 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/60">http://tools.ietf.org/wg/httpbis/trac/ticket/60</a>>: "Placement of 13.5.1 and 13.5.2" |
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| 1957 | </li> |
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| 1958 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/138">http://tools.ietf.org/wg/httpbis/trac/ticket/138</a>>: "The role of Warning and Semantic Transparency in Caching" |
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| 1959 | </li> |
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| 1960 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/139">http://tools.ietf.org/wg/httpbis/trac/ticket/139</a>>: "Methods and Caching" |
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| 1961 | </li> |
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| 1962 | </ul> |
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| 1963 | <p id="rfc.section.C.7.p.3">In addition: 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>>): |
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| 1964 | </p> |
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| 1965 | <ul> |
|---|
| 1966 | <li>Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.</li> |
|---|
| 1967 | </ul> |
|---|
| 1968 | <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-p6-cache-06</a></h2> |
|---|
| 1969 | <p id="rfc.section.C.8.p.1">Closed issues: </p> |
|---|
| 1970 | <ul> |
|---|
| 1971 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/161">http://tools.ietf.org/wg/httpbis/trac/ticket/161</a>>: "base for numeric protocol elements" |
|---|
| 1972 | </li> |
|---|
| 1973 | </ul> |
|---|
| 1974 | <p id="rfc.section.C.8.p.2">Affected issues: </p> |
|---|
| 1975 | <ul> |
|---|
| 1976 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/37">http://tools.ietf.org/wg/httpbis/trac/ticket/37</a>>: "Vary and non-existant headers" |
|---|
| 1977 | </li> |
|---|
| 1978 | </ul> |
|---|
| 1979 | <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-p6-cache-07</a></h2> |
|---|
| 1980 | <p id="rfc.section.C.9.p.1">Closed issues: </p> |
|---|
| 1981 | <ul> |
|---|
| 1982 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/54">http://tools.ietf.org/wg/httpbis/trac/ticket/54</a>>: "Definition of 1xx Warn-Codes" |
|---|
| 1983 | </li> |
|---|
| 1984 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/167">http://tools.ietf.org/wg/httpbis/trac/ticket/167</a>>: "Content-Location on 304 responses" |
|---|
| 1985 | </li> |
|---|
| 1986 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/169">http://tools.ietf.org/wg/httpbis/trac/ticket/169</a>>: "private and no-cache CC directives with headers" |
|---|
| 1987 | </li> |
|---|
| 1988 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/187">http://tools.ietf.org/wg/httpbis/trac/ticket/187</a>>: "RFC2047 and warn-text" |
|---|
| 1989 | </li> |
|---|
| 1990 | </ul> |
|---|
| 1991 | <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-p6-cache-08</a></h2> |
|---|
| 1992 | <p id="rfc.section.C.10.p.1">Closed issues: </p> |
|---|
| 1993 | <ul> |
|---|
| 1994 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/147">http://tools.ietf.org/wg/httpbis/trac/ticket/147</a>>: "serving negotiated responses from cache: header-specific canonicalization" |
|---|
| 1995 | </li> |
|---|
| 1996 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/197">http://tools.ietf.org/wg/httpbis/trac/ticket/197</a>>: "Effect of CC directives on history lists" |
|---|
| 1997 | </li> |
|---|
| 1998 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/291">http://tools.ietf.org/wg/httpbis/trac/ticket/291</a>>: "Cache Extensions can override no-store, etc." |
|---|
| 1999 | </li> |
|---|
| 2000 | </ul> |
|---|
| 2001 | <p id="rfc.section.C.10.p.2">Affected issues: </p> |
|---|
| 2002 | <ul> |
|---|
| 2003 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/199">http://tools.ietf.org/wg/httpbis/trac/ticket/199</a>>: Status codes and caching |
|---|
| 2004 | </li> |
|---|
| 2005 | </ul> |
|---|
| 2006 | <p id="rfc.section.C.10.p.3">Partly resolved issues: </p> |
|---|
| 2007 | <ul> |
|---|
| 2008 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/60">http://tools.ietf.org/wg/httpbis/trac/ticket/60</a>>: "Placement of 13.5.1 and 13.5.2" |
|---|
| 2009 | </li> |
|---|
| 2010 | </ul> |
|---|
| 2011 | <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-p6-cache-09</a></h2> |
|---|
| 2012 | <p id="rfc.section.C.11.p.1">Closed issues: </p> |
|---|
| 2013 | <ul> |
|---|
| 2014 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/29">http://tools.ietf.org/wg/httpbis/trac/ticket/29</a>>: "Age calculation" |
|---|
| 2015 | </li> |
|---|
| 2016 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/168">http://tools.ietf.org/wg/httpbis/trac/ticket/168</a>>: "Clarify differences between / requirements for request and response CC directives" |
|---|
| 2017 | </li> |
|---|
| 2018 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/174">http://tools.ietf.org/wg/httpbis/trac/ticket/174</a>>: "Caching authenticated responses" |
|---|
| 2019 | </li> |
|---|
| 2020 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/208">http://tools.ietf.org/wg/httpbis/trac/ticket/208</a>>: "IANA registry for cache-control directives" |
|---|
| 2021 | </li> |
|---|
| 2022 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/211">http://tools.ietf.org/wg/httpbis/trac/ticket/211</a>>: "Heuristic caching of URLs with query components" |
|---|
| 2023 | </li> |
|---|
| 2024 | </ul> |
|---|
| 2025 | <p id="rfc.section.C.11.p.2">Partly resolved issues: </p> |
|---|
| 2026 | <ul> |
|---|
| 2027 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/196">http://tools.ietf.org/wg/httpbis/trac/ticket/196</a>>: "Term for the requested resource's URI" |
|---|
| 2028 | </li> |
|---|
| 2029 | </ul> |
|---|
| 2030 | <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-p6-cache-10</a></h2> |
|---|
| 2031 | <p id="rfc.section.C.12.p.1">Closed issues: </p> |
|---|
| 2032 | <ul> |
|---|
| 2033 | <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" |
|---|
| 2034 | </li> |
|---|
| 2035 | <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" |
|---|
| 2036 | </li> |
|---|
| 2037 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/223">http://tools.ietf.org/wg/httpbis/trac/ticket/223</a>>: "Allowing heuristic caching for new status codes" |
|---|
| 2038 | </li> |
|---|
| 2039 | <li>Clean up TODOs and prose in "Combining Responses."</li> |
|---|
| 2040 | </ul> |
|---|
| 2041 | <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-p6-cache-11</a></h2> |
|---|
| 2042 | <p id="rfc.section.C.13.p.1">Closed issues: </p> |
|---|
| 2043 | <ul> |
|---|
| 2044 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/204">http://tools.ietf.org/wg/httpbis/trac/ticket/204</a>>: "Text about clock requirement for caches belongs in p6" |
|---|
| 2045 | </li> |
|---|
| 2046 | </ul> |
|---|
| 2047 | <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-p6-cache-12</a></h2> |
|---|
| 2048 | <p id="rfc.section.C.14.p.1">Closed issues: </p> |
|---|
| 2049 | <ul> |
|---|
| 2050 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/224">http://tools.ietf.org/wg/httpbis/trac/ticket/224</a>>: "Header Classification" |
|---|
| 2051 | </li> |
|---|
| 2052 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/268">http://tools.ietf.org/wg/httpbis/trac/ticket/268</a>>: "Clarify 'public'" |
|---|
| 2053 | </li> |
|---|
| 2054 | </ul> |
|---|
| 2055 | <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-p6-cache-13</a></h2> |
|---|
| 2056 | <p id="rfc.section.C.15.p.1">Closed issues: </p> |
|---|
| 2057 | <ul> |
|---|
| 2058 | <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" |
|---|
| 2059 | </li> |
|---|
| 2060 | </ul> |
|---|
| 2061 | <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-p6-cache-14</a></h2> |
|---|
| 2062 | <p id="rfc.section.C.16.p.1">Closed issues: </p> |
|---|
| 2063 | <ul> |
|---|
| 2064 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/38">http://tools.ietf.org/wg/httpbis/trac/ticket/38</a>>: "Mismatch Vary" |
|---|
| 2065 | </li> |
|---|
| 2066 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/235">http://tools.ietf.org/wg/httpbis/trac/ticket/235</a>>: "Cache Invalidation only happens upon successful responses" |
|---|
| 2067 | </li> |
|---|
| 2068 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/282">http://tools.ietf.org/wg/httpbis/trac/ticket/282</a>>: "Recommend minimum sizes for protocol elements" |
|---|
| 2069 | </li> |
|---|
| 2070 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/289">http://tools.ietf.org/wg/httpbis/trac/ticket/289</a>>: "Proxies don't 'understand' methods" |
|---|
| 2071 | </li> |
|---|
| 2072 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/291">http://tools.ietf.org/wg/httpbis/trac/ticket/291</a>>: "Cache Extensions can override no-store, etc." |
|---|
| 2073 | </li> |
|---|
| 2074 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/292">http://tools.ietf.org/wg/httpbis/trac/ticket/292</a>>: "Pragma" |
|---|
| 2075 | </li> |
|---|
| 2076 | </ul> |
|---|
| 2077 | <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-p6-cache-15</a></h2> |
|---|
| 2078 | <p id="rfc.section.C.17.p.1">Closed issues: </p> |
|---|
| 2079 | <ul> |
|---|
| 2080 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/290">http://tools.ietf.org/wg/httpbis/trac/ticket/290</a>>: "Motivate one-year limit for Expires" |
|---|
| 2081 | </li> |
|---|
| 2082 | </ul> |
|---|
| 2083 | <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-p6-cache-16</a></h2> |
|---|
| 2084 | <p id="rfc.section.C.18.p.1">Closed issues: </p> |
|---|
| 2085 | <ul> |
|---|
| 2086 | <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" |
|---|
| 2087 | </li> |
|---|
| 2088 | <li> <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/317">http://tools.ietf.org/wg/httpbis/trac/ticket/317</a>>: "Cache-Control directive case sensitivity" |
|---|
| 2089 | </li> |
|---|
| 2090 | </ul> |
|---|
| 2091 | <h1 id="rfc.index"><a href="#rfc.index">Index</a></h1> |
|---|
| 2092 | <p class="noprint"><a href="#rfc.index.A">A</a> <a href="#rfc.index.C">C</a> <a href="#rfc.index.E">E</a> <a href="#rfc.index.F">F</a> <a href="#rfc.index.G">G</a> <a href="#rfc.index.H">H</a> <a href="#rfc.index.M">M</a> <a href="#rfc.index.N">N</a> <a href="#rfc.index.O">O</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> <a href="#rfc.index.W">W</a> |
|---|
| 2093 | </p> |
|---|
| 2094 | <div class="print2col"> |
|---|
| 2095 | <ul class="ind"> |
|---|
| 2096 | <li><a id="rfc.index.A" href="#rfc.index.A"><b>A</b></a><ul> |
|---|
| 2097 | <li>age <a href="#rfc.iref.a.1">1.2</a></li> |
|---|
| 2098 | <li>Age header field <a href="#rfc.xref.header.age.1">2.2</a>, <a href="#rfc.xref.header.age.2">2.3.2</a>, <a href="#rfc.iref.a.2"><b>3.1</b></a>, <a href="#rfc.xref.header.age.3">5.2</a></li> |
|---|
| 2099 | </ul> |
|---|
| 2100 | </li> |
|---|
| 2101 | <li><a id="rfc.index.C" href="#rfc.index.C"><b>C</b></a><ul> |
|---|
| 2102 | <li>cache <a href="#rfc.iref.c.1">1.1</a>, <a href="#rfc.iref.c.2">1.2</a></li> |
|---|
| 2103 | <li>Cache Directives |
|---|
| 2104 | <ul> |
|---|
| 2105 | <li>max-age <a href="#rfc.iref.c.9"><b>3.2.1</b></a>, <a href="#rfc.iref.c.20"><b>3.2.2</b></a></li> |
|---|
| 2106 | <li>max-stale <a href="#rfc.iref.c.10"><b>3.2.1</b></a></li> |
|---|
| 2107 | <li>min-fresh <a href="#rfc.iref.c.11"><b>3.2.1</b></a></li> |
|---|
| 2108 | <li>must-revalidate <a href="#rfc.iref.c.18"><b>3.2.2</b></a></li> |
|---|
| 2109 | <li>no-cache <a href="#rfc.iref.c.7"><b>3.2.1</b></a>, <a href="#rfc.iref.c.16"><b>3.2.2</b></a></li> |
|---|
| 2110 | <li>no-store <a href="#rfc.iref.c.8"><b>3.2.1</b></a>, <a href="#rfc.iref.c.17"><b>3.2.2</b></a></li> |
|---|
| 2111 | <li>no-transform <a href="#rfc.iref.c.12"><b>3.2.1</b></a>, <a href="#rfc.iref.c.22"><b>3.2.2</b></a></li> |
|---|
| 2112 | <li>only-if-cached <a href="#rfc.iref.c.13"><b>3.2.1</b></a></li> |
|---|
| 2113 | <li>private <a href="#rfc.iref.c.15"><b>3.2.2</b></a></li> |
|---|
| 2114 | <li>proxy-revalidate <a href="#rfc.iref.c.19"><b>3.2.2</b></a></li> |
|---|
| 2115 | <li>public <a href="#rfc.iref.c.14"><b>3.2.2</b></a></li> |
|---|
| 2116 | <li>s-maxage <a href="#rfc.iref.c.21"><b>3.2.2</b></a></li> |
|---|
| 2117 | </ul> |
|---|
| 2118 | </li> |
|---|
| 2119 | <li>cache entry <a href="#rfc.iref.c.4">2</a></li> |
|---|
| 2120 | <li>cache key <a href="#rfc.iref.c.5">2</a></li> |
|---|
| 2121 | <li>Cache-Control header field <a href="#rfc.xref.header.cache-control.1">2.1</a>, <a href="#rfc.xref.header.cache-control.2">2.2</a>, <a href="#rfc.iref.c.6"><b>3.2</b></a>, <a href="#rfc.xref.header.cache-control.3">5.2</a></li> |
|---|
| 2122 | <li>cacheable <a href="#rfc.iref.c.3">1.2</a></li> |
|---|
| 2123 | </ul> |
|---|
| 2124 | </li> |
|---|
| 2125 | <li><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul> |
|---|
| 2126 | <li>Expires header field <a href="#rfc.xref.header.expires.1">2.1</a>, <a href="#rfc.xref.header.expires.2">2.3</a>, <a href="#rfc.xref.header.expires.3">2.3.1</a>, <a href="#rfc.iref.e.2"><b>3.3</b></a>, <a href="#rfc.xref.header.expires.4">5.2</a></li> |
|---|
| 2127 | <li>explicit expiration time <a href="#rfc.iref.e.1">1.2</a></li> |
|---|
| 2128 | </ul> |
|---|
| 2129 | </li> |
|---|
| 2130 | <li><a id="rfc.index.F" href="#rfc.index.F"><b>F</b></a><ul> |
|---|
| 2131 | <li>first-hand <a href="#rfc.iref.f.1">1.2</a></li> |
|---|
| 2132 | <li>fresh <a href="#rfc.iref.f.3">1.2</a></li> |
|---|
| 2133 | <li>freshness lifetime <a href="#rfc.iref.f.2">1.2</a></li> |
|---|
| 2134 | </ul> |
|---|
| 2135 | </li> |
|---|
| 2136 | <li><a id="rfc.index.G" href="#rfc.index.G"><b>G</b></a><ul> |
|---|
| 2137 | <li><tt>Grammar</tt> |
|---|
| 2138 | <ul> |
|---|
| 2139 | <li><tt>Age</tt> <a href="#rfc.iref.g.2"><b>3.1</b></a></li> |
|---|
| 2140 | <li><tt>Cache-Control</tt> <a href="#rfc.iref.g.3"><b>3.2</b></a></li> |
|---|
| 2141 | <li><tt>cache-extension</tt> <a href="#rfc.iref.g.4"><b>3.2</b></a></li> |
|---|
| 2142 | <li><tt>cache-request-directive</tt> <a href="#rfc.iref.g.5"><b>3.2.1</b></a></li> |
|---|
| 2143 | <li><tt>cache-response-directive</tt> <a href="#rfc.iref.g.6"><b>3.2.2</b></a></li> |
|---|
| 2144 | <li><tt>delta-seconds</tt> <a href="#rfc.iref.g.1"><b>1.5</b></a></li> |
|---|
| 2145 | <li><tt>Expires</tt> <a href="#rfc.iref.g.7"><b>3.3</b></a></li> |
|---|
| 2146 | <li><tt>extension-pragma</tt> <a href="#rfc.iref.g.10"><b>3.4</b></a></li> |
|---|
| 2147 | <li><tt>Pragma</tt> <a href="#rfc.iref.g.8"><b>3.4</b></a></li> |
|---|
| 2148 | <li><tt>pragma-directive</tt> <a href="#rfc.iref.g.9"><b>3.4</b></a></li> |
|---|
| 2149 | <li><tt>Vary</tt> <a href="#rfc.iref.g.11"><b>3.5</b></a></li> |
|---|
| 2150 | <li><tt>warn-agent</tt> <a href="#rfc.iref.g.15"><b>3.6</b></a></li> |
|---|
| 2151 | <li><tt>warn-code</tt> <a href="#rfc.iref.g.14"><b>3.6</b></a></li> |
|---|
| 2152 | <li><tt>warn-date</tt> <a href="#rfc.iref.g.17"><b>3.6</b></a></li> |
|---|
| 2153 | <li><tt>warn-text</tt> <a href="#rfc.iref.g.16"><b>3.6</b></a></li> |
|---|
| 2154 | <li><tt>Warning</tt> <a href="#rfc.iref.g.12"><b>3.6</b></a></li> |
|---|
| 2155 | <li><tt>warning-value</tt> <a href="#rfc.iref.g.13"><b>3.6</b></a></li> |
|---|
| 2156 | </ul> |
|---|
| 2157 | </li> |
|---|
| 2158 | </ul> |
|---|
| 2159 | </li> |
|---|
| 2160 | <li><a id="rfc.index.H" href="#rfc.index.H"><b>H</b></a><ul> |
|---|
| 2161 | <li>Header Fields |
|---|
| 2162 | <ul> |
|---|
| 2163 | <li>Age <a href="#rfc.xref.header.age.1">2.2</a>, <a href="#rfc.xref.header.age.2">2.3.2</a>, <a href="#rfc.iref.h.2"><b>3.1</b></a>, <a href="#rfc.xref.header.age.3">5.2</a></li> |
|---|
| 2164 | <li>Cache-Control <a href="#rfc.xref.header.cache-control.1">2.1</a>, <a href="#rfc.xref.header.cache-control.2">2.2</a>, <a href="#rfc.iref.h.3"><b>3.2</b></a>, <a href="#rfc.xref.header.cache-control.3">5.2</a></li> |
|---|
| 2165 | <li>Expires <a href="#rfc.xref.header.expires.1">2.1</a>, <a href="#rfc.xref.header.expires.2">2.3</a>, <a href="#rfc.xref.header.expires.3">2.3.1</a>, <a href="#rfc.iref.h.4"><b>3.3</b></a>, <a href="#rfc.xref.header.expires.4">5.2</a></li> |
|---|
| 2166 | <li>Pragma <a href="#rfc.xref.header.pragma.1">2.2</a>, <a href="#rfc.xref.header.pragma.2">3.2</a>, <a href="#rfc.iref.h.5"><b>3.4</b></a>, <a href="#rfc.xref.header.pragma.3">5.2</a></li> |
|---|
| 2167 | <li>Vary <a href="#rfc.xref.header.vary.1">2.7</a>, <a href="#rfc.iref.h.6"><b>3.5</b></a>, <a href="#rfc.xref.header.vary.2">5.2</a></li> |
|---|
| 2168 | <li>Warning <a href="#rfc.xref.header.warning.1">2.3.3</a>, <a href="#rfc.xref.header.warning.2">2.4.1</a>, <a href="#rfc.xref.header.warning.3">2.8</a>, <a href="#rfc.iref.h.7"><b>3.6</b></a>, <a href="#rfc.xref.header.warning.4">5.2</a>, <a href="#rfc.xref.header.warning.5">A</a></li> |
|---|
| 2169 | </ul> |
|---|
| 2170 | </li> |
|---|
| 2171 | <li>heuristic expiration time <a href="#rfc.iref.h.1">1.2</a></li> |
|---|
| 2172 | </ul> |
|---|
| 2173 | </li> |
|---|
| 2174 | <li><a id="rfc.index.M" href="#rfc.index.M"><b>M</b></a><ul> |
|---|
| 2175 | <li>max-age |
|---|
| 2176 | <ul> |
|---|
| 2177 | <li>Cache Directive <a href="#rfc.iref.m.1"><b>3.2.1</b></a>, <a href="#rfc.iref.m.5"><b>3.2.2</b></a></li> |
|---|
| 2178 | </ul> |
|---|
| 2179 | </li> |
|---|
| 2180 | <li>max-stale |
|---|
| 2181 | <ul> |
|---|
| 2182 | <li>Cache Directive <a href="#rfc.iref.m.2"><b>3.2.1</b></a></li> |
|---|
| 2183 | </ul> |
|---|
| 2184 | </li> |
|---|
| 2185 | <li>min-fresh |
|---|
| 2186 | <ul> |
|---|
| 2187 | <li>Cache Directive <a href="#rfc.iref.m.3"><b>3.2.1</b></a></li> |
|---|
| 2188 | </ul> |
|---|
| 2189 | </li> |
|---|
| 2190 | <li>must-revalidate |
|---|
| 2191 | <ul> |
|---|
| 2192 | <li>Cache Directive <a href="#rfc.iref.m.4"><b>3.2.2</b></a></li> |
|---|
| 2193 | </ul> |
|---|
| 2194 | </li> |
|---|
| 2195 | </ul> |
|---|
| 2196 | </li> |
|---|
| 2197 | <li><a id="rfc.index.N" href="#rfc.index.N"><b>N</b></a><ul> |
|---|
| 2198 | <li>no-cache |
|---|
| 2199 | <ul> |
|---|
| 2200 | <li>Cache Directive <a href="#rfc.iref.n.1"><b>3.2.1</b></a>, <a href="#rfc.iref.n.4"><b>3.2.2</b></a></li> |
|---|
| 2201 | </ul> |
|---|
| 2202 | </li> |
|---|
| 2203 | <li>no-store |
|---|
| 2204 | <ul> |
|---|
| 2205 | <li>Cache Directive <a href="#rfc.iref.n.2"><b>3.2.1</b></a>, <a href="#rfc.iref.n.5"><b>3.2.2</b></a></li> |
|---|
| 2206 | </ul> |
|---|
| 2207 | </li> |
|---|
| 2208 | <li>no-transform |
|---|
| 2209 | <ul> |
|---|
| 2210 | <li>Cache Directive <a href="#rfc.iref.n.3"><b>3.2.1</b></a>, <a href="#rfc.iref.n.6"><b>3.2.2</b></a></li> |
|---|
| 2211 | </ul> |
|---|
| 2212 | </li> |
|---|
| 2213 | </ul> |
|---|
| 2214 | </li> |
|---|
| 2215 | <li><a id="rfc.index.O" href="#rfc.index.O"><b>O</b></a><ul> |
|---|
| 2216 | <li>only-if-cached |
|---|
| 2217 | <ul> |
|---|
| 2218 | <li>Cache Directive <a href="#rfc.iref.o.1"><b>3.2.1</b></a></li> |
|---|
| 2219 | </ul> |
|---|
| 2220 | </li> |
|---|
| 2221 | </ul> |
|---|
| 2222 | </li> |
|---|
| 2223 | <li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul> |
|---|
| 2224 | <li><em>Part1</em> <a href="#rfc.xref.Part1.1">1.3</a>, <a href="#rfc.xref.Part1.2">1.4</a>, <a href="#rfc.xref.Part1.3">1.4.1</a>, <a href="#rfc.xref.Part1.4">1.4.1</a>, <a href="#rfc.xref.Part1.5">1.4.1</a>, <a href="#rfc.xref.Part1.6">1.4.1</a>, <a href="#rfc.xref.Part1.7">1.4.2</a>, <a href="#rfc.xref.Part1.8">1.4.2</a>, <a href="#rfc.xref.Part1.9">1.4.2</a>, <a href="#rfc.xref.Part1.10">1.4.2</a>, <a href="#rfc.xref.Part1.11">2.1</a>, <a href="#rfc.xref.Part1.12">2.2</a>, <a href="#rfc.xref.Part1.13">2.5</a>, <a href="#rfc.xref.Part1.14">2.5</a>, <a href="#rfc.xref.Part1.15">2.5</a>, <a href="#rfc.xref.Part1.16">2.7</a>, <a href="#rfc.xref.Part1.17">7</a>, <a href="#Part1"><b>8.1</b></a><ul> |
|---|
| 2225 | <li><em>Section 1.2</em> <a href="#rfc.xref.Part1.2">1.4</a></li> |
|---|
| 2226 | <li><em>Section 1.2.2</em> <a href="#rfc.xref.Part1.4">1.4.1</a></li> |
|---|
| 2227 | <li><em>Section 2</em> <a href="#rfc.xref.Part1.1">1.3</a></li> |
|---|
| 2228 | <li><em>Section 2.7</em> <a href="#rfc.xref.Part1.8">1.4.2</a>, <a href="#rfc.xref.Part1.10">1.4.2</a></li> |
|---|
| 2229 | <li><em>Section 3.2</em> <a href="#rfc.xref.Part1.7">1.4.2</a>, <a href="#rfc.xref.Part1.16">2.7</a></li> |
|---|
| 2230 | <li><em>Section 3.2.3</em> <a href="#rfc.xref.Part1.5">1.4.1</a>, <a href="#rfc.xref.Part1.6">1.4.1</a></li> |
|---|
| 2231 | <li><em>Section 4.3</em> <a href="#rfc.xref.Part1.12">2.2</a>, <a href="#rfc.xref.Part1.13">2.5</a>, <a href="#rfc.xref.Part1.14">2.5</a>, <a href="#rfc.xref.Part1.15">2.5</a></li> |
|---|
| 2232 | <li><em>Section 8.8</em> <a href="#rfc.xref.Part1.9">1.4.2</a></li> |
|---|
| 2233 | <li><em>Section 11</em> <a href="#rfc.xref.Part1.17">7</a></li> |
|---|
| 2234 | </ul> |
|---|
| 2235 | </li> |
|---|
| 2236 | <li><em>Part2</em> <a href="#rfc.xref.Part2.1">1.4.2</a>, <a href="#rfc.xref.Part2.2">2</a>, <a href="#rfc.xref.Part2.3">2.2</a>, <a href="#rfc.xref.Part2.4">2.3.1.1</a>, <a href="#rfc.xref.Part2.5">2.3.2</a>, <a href="#rfc.xref.Part2.6">2.5</a>, <a href="#rfc.xref.Part2.7">3.3</a>, <a href="#Part2"><b>8.1</b></a><ul> |
|---|
| 2237 | <li><em>Section 6.1.1</em> <a href="#rfc.xref.Part2.3">2.2</a>, <a href="#rfc.xref.Part2.6">2.5</a></li> |
|---|
| 2238 | <li><em>Section 7</em> <a href="#rfc.xref.Part2.4">2.3.1.1</a></li> |
|---|
| 2239 | <li><em>Section 8</em> <a href="#rfc.xref.Part2.1">1.4.2</a>, <a href="#rfc.xref.Part2.7">3.3</a></li> |
|---|
| 2240 | <li><em>Section 9.2</em> <a href="#rfc.xref.Part2.5">2.3.2</a></li> |
|---|
| 2241 | </ul> |
|---|
| 2242 | </li> |
|---|
| 2243 | <li><em>Part4</em> <a href="#rfc.xref.Part4.1">1.2</a>, <a href="#rfc.xref.Part4.2">1.2</a>, <a href="#rfc.xref.Part4.3">1.2</a>, <a href="#rfc.xref.Part4.4">2.3.1.1</a>, <a href="#rfc.xref.Part4.5">2.4</a>, <a href="#Part4"><b>8.1</b></a><ul> |
|---|
| 2244 | <li><em>Section 2.1</em> <a href="#rfc.xref.Part4.1">1.2</a></li> |
|---|
| 2245 | <li><em>Section 2.2</em> <a href="#rfc.xref.Part4.4">2.3.1.1</a></li> |
|---|
| 2246 | <li><em>Section 2.2.2</em> <a href="#rfc.xref.Part4.3">1.2</a></li> |
|---|
| 2247 | <li><em>Section 2.3</em> <a href="#rfc.xref.Part4.2">1.2</a></li> |
|---|
| 2248 | </ul> |
|---|
| 2249 | </li> |
|---|
| 2250 | <li><em>Part5</em> <a href="#rfc.xref.Part5.1">2.1</a>, <a href="#rfc.xref.Part5.2">2.8</a>, <a href="#rfc.xref.Part5.3">2.8</a>, <a href="#Part5"><b>8.1</b></a><ul> |
|---|
| 2251 | <li><em>Section 4</em> <a href="#rfc.xref.Part5.3">2.8</a></li> |
|---|
| 2252 | </ul> |
|---|
| 2253 | </li> |
|---|
| 2254 | <li><em>Part7</em> <a href="#rfc.xref.Part7.1">2.1</a>, <a href="#rfc.xref.Part7.2">2.6</a>, <a href="#Part7"><b>8.1</b></a><ul> |
|---|
| 2255 | <li><em>Section 4.1</em> <a href="#rfc.xref.Part7.1">2.1</a>, <a href="#rfc.xref.Part7.2">2.6</a></li> |
|---|
| 2256 | </ul> |
|---|
| 2257 | </li> |
|---|
| 2258 | <li>Pragma header field <a href="#rfc.xref.header.pragma.1">2.2</a>, <a href="#rfc.xref.header.pragma.2">3.2</a>, <a href="#rfc.iref.p.5"><b>3.4</b></a>, <a href="#rfc.xref.header.pragma.3">5.2</a></li> |
|---|
| 2259 | <li>private |
|---|
| 2260 | <ul> |
|---|
| 2261 | <li>Cache Directive <a href="#rfc.iref.p.3"><b>3.2.2</b></a></li> |
|---|
| 2262 | </ul> |
|---|
| 2263 | </li> |
|---|
| 2264 | <li>private cache <a href="#rfc.iref.p.1">1.2</a></li> |
|---|
| 2265 | <li>proxy-revalidate |
|---|
| 2266 | <ul> |
|---|
| 2267 | <li>Cache Directive <a href="#rfc.iref.p.4"><b>3.2.2</b></a></li> |
|---|
| 2268 | </ul> |
|---|
| 2269 | </li> |
|---|
| 2270 | <li>public |
|---|
| 2271 | <ul> |
|---|
| 2272 | <li>Cache Directive <a href="#rfc.iref.p.2"><b>3.2.2</b></a></li> |
|---|
| 2273 | </ul> |
|---|
| 2274 | </li> |
|---|
| 2275 | </ul> |
|---|
| 2276 | </li> |
|---|
| 2277 | <li><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul> |
|---|
| 2278 | <li><em>RFC1305</em> <a href="#rfc.xref.RFC1305.1">2.2</a>, <a href="#rfc.xref.RFC1305.2">2.3.2</a>, <a href="#RFC1305"><b>8.2</b></a></li> |
|---|
| 2279 | <li><em>RFC2119</em> <a href="#rfc.xref.RFC2119.1">1.3</a>, <a href="#RFC2119"><b>8.1</b></a></li> |
|---|
| 2280 | <li><em>RFC2616</em> <a href="#rfc.xref.RFC2616.1">2.3.1.1</a>, <a href="#RFC2616"><b>8.2</b></a>, <a href="#rfc.xref.RFC2616.2">C.1</a><ul> |
|---|
| 2281 | <li><em>Section 13.9</em> <a href="#rfc.xref.RFC2616.1">2.3.1.1</a></li> |
|---|
| 2282 | </ul> |
|---|
| 2283 | </li> |
|---|
| 2284 | <li><em>RFC3864</em> <a href="#rfc.xref.RFC3864.1">5.2</a>, <a href="#RFC3864"><b>8.2</b></a></li> |
|---|
| 2285 | <li><em>RFC5226</em> <a href="#rfc.xref.RFC5226.1">3.2.3</a>, <a href="#RFC5226"><b>8.2</b></a><ul> |
|---|
| 2286 | <li><em>Section 4.1</em> <a href="#rfc.xref.RFC5226.1">3.2.3</a></li> |
|---|
| 2287 | </ul> |
|---|
| 2288 | </li> |
|---|
| 2289 | <li><em>RFC5234</em> <a href="#rfc.xref.RFC5234.1">1.4</a>, <a href="#rfc.xref.RFC5234.2">1.4</a>, <a href="#RFC5234"><b>8.1</b></a><ul> |
|---|
| 2290 | <li><em>Appendix B.1</em> <a href="#rfc.xref.RFC5234.2">1.4</a></li> |
|---|
| 2291 | </ul> |
|---|
| 2292 | </li> |
|---|
| 2293 | <li><em>RFC5861</em> <a href="#rfc.xref.RFC5861.1">5.1</a>, <a href="#rfc.xref.RFC5861.2">5.1</a>, <a href="#RFC5861"><b>8.2</b></a><ul> |
|---|
| 2294 | <li><em>Section 3</em> <a href="#rfc.xref.RFC5861.2">5.1</a></li> |
|---|
| 2295 | <li><em>Section 4</em> <a href="#rfc.xref.RFC5861.1">5.1</a></li> |
|---|
| 2296 | </ul> |
|---|
| 2297 | </li> |
|---|
| 2298 | </ul> |
|---|
| 2299 | </li> |
|---|
| 2300 | <li><a id="rfc.index.S" href="#rfc.index.S"><b>S</b></a><ul> |
|---|
| 2301 | <li>s-maxage |
|---|
| 2302 | <ul> |
|---|
| 2303 | <li>Cache Directive <a href="#rfc.iref.s.4"><b>3.2.2</b></a></li> |
|---|
| 2304 | </ul> |
|---|
| 2305 | </li> |
|---|
| 2306 | <li>shared cache <a href="#rfc.iref.s.1">1.2</a></li> |
|---|
| 2307 | <li>stale <a href="#rfc.iref.s.2">1.2</a></li> |
|---|
| 2308 | <li>strong validator <a href="#rfc.iref.s.3">1.2</a></li> |
|---|
| 2309 | </ul> |
|---|
| 2310 | </li> |
|---|
| 2311 | <li><a id="rfc.index.V" href="#rfc.index.V"><b>V</b></a><ul> |
|---|
| 2312 | <li>validator <a href="#rfc.iref.v.1">1.2</a><ul> |
|---|
| 2313 | <li>strong <a href="#rfc.iref.v.2">1.2</a></li> |
|---|
| 2314 | </ul> |
|---|
| 2315 | </li> |
|---|
| 2316 | <li>Vary header field <a href="#rfc.xref.header.vary.1">2.7</a>, <a href="#rfc.iref.v.3"><b>3.5</b></a>, <a href="#rfc.xref.header.vary.2">5.2</a></li> |
|---|
| 2317 | </ul> |
|---|
| 2318 | </li> |
|---|
| 2319 | <li><a id="rfc.index.W" href="#rfc.index.W"><b>W</b></a><ul> |
|---|
| 2320 | <li>Warning header field <a href="#rfc.xref.header.warning.1">2.3.3</a>, <a href="#rfc.xref.header.warning.2">2.4.1</a>, <a href="#rfc.xref.header.warning.3">2.8</a>, <a href="#rfc.iref.w.1"><b>3.6</b></a>, <a href="#rfc.xref.header.warning.4">5.2</a>, <a href="#rfc.xref.header.warning.5">A</a></li> |
|---|
| 2321 | </ul> |
|---|
| 2322 | </li> |
|---|
| 2323 | </ul> |
|---|
| 2324 | </div> |
|---|
| 2325 | </body> |
|---|
| 2326 | </html> |
|---|
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