source: draft-ietf-httpbis/11/draft-ietf-httpbis-p6-cache-11.xml @ 1500

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fix mime types

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1<?xml version="1.0" encoding="UTF-8"?>
2<!--
3    This XML document is the output of clean-for-DTD.xslt; a tool that strips
4    extensions to RFC2629(bis) from documents for processing with xml2rfc.
5-->
6<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
7<?rfc toc="yes" ?>
8<?rfc symrefs="yes" ?>
9<?rfc sortrefs="yes" ?>
10<?rfc compact="yes"?>
11<?rfc subcompact="no" ?>
12<?rfc linkmailto="no" ?>
13<?rfc editing="no" ?>
14<?rfc comments="yes"?>
15<?rfc inline="yes"?>
16<?rfc rfcedstyle="yes"?>
17<!DOCTYPE rfc
18  PUBLIC "" "rfc2629.dtd">
19<rfc category="std" docName="draft-ietf-httpbis-p6-cache-11" ipr="pre5378Trust200902" obsoletes="2616">
20<front>
21
22  <title abbrev="HTTP/1.1, Part 6">HTTP/1.1, part 6: Caching</title>
23
24  <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
25    <organization abbrev="Day Software">Day Software</organization>
26    <address>
27      <postal>
28        <street>23 Corporate Plaza DR, Suite 280</street>
29        <city>Newport Beach</city>
30        <region>CA</region>
31        <code>92660</code>
32        <country>USA</country>
33      </postal>
34      <phone>+1-949-706-5300</phone>
35      <facsimile>+1-949-706-5305</facsimile>
36      <email>fielding@gbiv.com</email>
37      <uri>http://roy.gbiv.com/</uri>
38    </address>
39  </author>
40
41  <author initials="J." surname="Gettys" fullname="Jim Gettys">
42    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
43    <address>
44      <postal>
45        <street>21 Oak Knoll Road</street>
46        <city>Carlisle</city>
47        <region>MA</region>
48        <code>01741</code>
49        <country>USA</country>
50      </postal>
51      <email>jg@freedesktop.org</email>
52      <uri>http://gettys.wordpress.com/</uri>
53    </address>
54  </author>
55
56  <author fullname="Jeffrey C. Mogul" initials="J." surname="Mogul">
57    <organization abbrev="HP">Hewlett-Packard Company</organization>
58    <address>
59      <postal>
60        <street>HP Labs, Large Scale Systems Group</street>
61        <street>1501 Page Mill Road, MS 1177</street>
62        <city>Palo Alto</city>
63        <region>CA</region>
64        <code>94304</code>
65        <country>USA</country>
66      </postal>
67      <email>JeffMogul@acm.org</email>
68    </address>
69  </author>
70
71  <author fullname="Henrik Frystyk Nielsen" initials="H." surname="Frystyk">
72    <organization abbrev="Microsoft">Microsoft Corporation</organization>
73    <address>
74      <postal>
75        <street>1 Microsoft Way</street>
76        <city>Redmond</city>
77        <region>WA</region>
78        <code>98052</code>
79        <country>USA</country>
80      </postal>
81      <email>henrikn@microsoft.com</email>
82    </address>
83  </author>
84
85  <author fullname="Larry Masinter" initials="L." surname="Masinter">
86    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
87    <address>
88      <postal>
89        <street>345 Park Ave</street>
90        <city>San Jose</city>
91        <region>CA</region>
92        <code>95110</code>
93        <country>USA</country>
94      </postal>
95      <email>LMM@acm.org</email>
96      <uri>http://larry.masinter.net/</uri>
97    </address>
98  </author>
99
100  <author fullname="Paul J. Leach" initials="P." surname="Leach">
101    <organization abbrev="Microsoft">Microsoft Corporation</organization>
102    <address>
103      <postal>
104        <street>1 Microsoft Way</street>
105        <city>Redmond</city>
106        <region>WA</region>
107        <code>98052</code>
108      </postal>
109      <email>paulle@microsoft.com</email>
110    </address>
111  </author>
112
113  <author fullname="Tim Berners-Lee" initials="T." surname="Berners-Lee">
114    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
115    <address>
116      <postal>
117        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
118        <street>The Stata Center, Building 32</street>
119        <street>32 Vassar Street</street>
120        <city>Cambridge</city>
121        <region>MA</region>
122        <code>02139</code>
123        <country>USA</country>
124      </postal>
125      <email>timbl@w3.org</email>
126      <uri>http://www.w3.org/People/Berners-Lee/</uri>
127    </address>
128  </author>
129
130  <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
131    <organization abbrev="W3C">World Wide Web Consortium</organization>
132    <address>
133      <postal>
134        <street>W3C / ERCIM</street>
135        <street>2004, rte des Lucioles</street>
136        <city>Sophia-Antipolis</city>
137        <region>AM</region>
138        <code>06902</code>
139        <country>France</country>
140      </postal>
141      <email>ylafon@w3.org</email>
142      <uri>http://www.raubacapeu.net/people/yves/</uri>
143    </address>
144  </author>
145
146  <author fullname="Mark Nottingham" initials="M." role="editor" surname="Nottingham">
147    <address>
148      <email>mnot@mnot.net</email>
149      <uri>http://www.mnot.net/</uri>
150    </address>
151  </author>
152
153  <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
154    <organization abbrev="greenbytes">greenbytes GmbH</organization>
155    <address>
156      <postal>
157        <street>Hafenweg 16</street>
158        <city>Muenster</city><region>NW</region><code>48155</code>
159        <country>Germany</country>
160      </postal>
161      <phone>+49 251 2807760</phone>
162      <facsimile>+49 251 2807761</facsimile>
163      <email>julian.reschke@greenbytes.de</email>
164      <uri>http://greenbytes.de/tech/webdav/</uri>
165    </address>
166  </author>
167
168  <date month="August" year="2010" day="4"/>
169  <workgroup>HTTPbis Working Group</workgroup>
170
171<abstract>
172<t>
173   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
174   distributed, collaborative, hypermedia information systems. This document
175   is Part 6 of the seven-part specification that defines the protocol
176   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616. Part 6
177   defines requirements on HTTP caches and the associated header fields that
178   control cache behavior or indicate cacheable response messages.
179</t>
180</abstract>
181
182<note title="Editorial Note (To be removed by RFC Editor)">
183   <t>
184      Discussion of this draft should take place on the HTTPBIS working group
185      mailing list (ietf-http-wg@w3.org). The current issues list is at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
186      documents (including fancy diffs) can be found at <eref target="http://tools.ietf.org/wg/httpbis/"/>.
187   </t>
188   <t>
189      The changes in this draft are summarized in <xref target="changes.since.10"/>.
190   </t>
191</note>
192
193   </front>
194   <middle>
195
196<section anchor="caching" title="Introduction">
197<t>
198   HTTP is typically used for distributed information systems, where
199   performance can be improved by the use of response caches. This document
200   defines aspects of HTTP/1.1 related to caching and reusing response
201   messages.
202</t>
203
204<section anchor="intro.purpose" title="Purpose">
205<iref item="cache"/>
206<t>
207   An HTTP cache is a local store of response messages and the
208   subsystem that controls its message storage, retrieval, and deletion. A
209   cache stores cacheable responses in order to reduce the response time and
210   network bandwidth consumption on future, equivalent requests. Any client or
211   server MAY employ a cache, though a cache cannot be used by a server that
212   is acting as a tunnel.
213</t>
214<t>
215   Caching would be useless if it did not significantly improve performance.
216   The goal of caching in HTTP/1.1 is to reuse a prior response message to
217   satisfy a current request. In some cases, a stored response can be reused
218   without the need for a network request, reducing latency and network
219   round-trips; a "freshness" mechanism is used for this purpose (see <xref target="expiration.model"/>). Even when a new request is required, it is
220   often possible to reuse all or parts of the payload of a prior response to
221   satisfy the request, thereby reducing network bandwidth usage; a
222   "validation" mechanism is used for this purpose (see <xref target="validation.model"/>).
223</t>
224</section>
225
226<section anchor="intro.terminology" title="Terminology">
227<t>
228   This specification uses a number of terms to refer to the roles played by
229   participants in, and objects of, HTTP caching.
230</t>
231<t>
232   <iref item="cacheable"/>
233   <?rfc needLines="4"?>cacheable
234   <list>
235      <t>A response is cacheable if a cache is allowed to store a copy of the
236      response message for use in answering subsequent requests. Even when a
237      response is cacheable, there might be additional constraints on whether
238      a cache can use the cached copy to satisfy a particular request.</t>
239   </list>
240</t>
241<t>
242   <iref item="explicit expiration time"/>
243   <?rfc needLines="4"?>explicit expiration time
244   <list>
245      <t>The time at which the origin server intends that a representation
246      no longer be returned by a cache without further validation.</t>
247   </list>
248</t>
249<t>
250   <iref item="heuristic expiration time"/>
251   <?rfc needLines="4"?>heuristic expiration time
252   <list>
253      <t>An expiration time assigned by a cache when no explicit expiration
254      time is available.</t>
255   </list>
256</t>
257<t>
258   <iref item="age"/>
259   <?rfc needLines="4"?>age
260   <list>
261      <t>The age of a response is the time since it was sent by, or
262      successfully validated with, the origin server.</t>
263   </list>
264</t>
265<t>
266   <iref item="first-hand"/>
267   <?rfc needLines="4"?>first-hand
268   <list>
269      <t>A response is first-hand if the freshness model is not in use; i.e.,
270      its age is 0.</t>
271   </list>
272</t>
273<t>
274   <iref item="freshness lifetime"/>
275   <?rfc needLines="4"?>freshness lifetime
276   <list>
277      <t>The length of time between the generation of a response and its
278      expiration time.</t>
279   </list>
280</t>
281<t>
282   <iref item="fresh"/>
283   <?rfc needLines="4"?>fresh
284   <list>
285      <t>A response is fresh if its age has not yet exceeded its freshness
286      lifetime.</t>
287   </list>
288</t>
289<t>
290   <iref item="stale"/>
291   <?rfc needLines="4"?>stale
292   <list>
293      <t>A response is stale if its age has passed its freshness lifetime
294      (either explicit or heuristic).</t>
295   </list>
296</t>
297<t>
298   <iref item="validator"/>
299   <?rfc needLines="4"?>validator
300   <list>
301      <t>A protocol element (e.g., an entity-tag or a Last-Modified time) that
302      is used to find out whether a stored response has an equivalent copy of
303      a representation.</t>
304   </list>
305</t>
306<t anchor="shared.and.non-shared.caches">
307   <iref item="validator"/>
308   <?rfc needLines="4"?>shared cache
309   <list>
310      <t>A cache that is accessible to more than one user. A non-shared cache
311      is dedicated to a single user.</t>
312   </list>
313</t>
314</section>
315
316<section anchor="intro.requirements" title="Requirements">
317<t>
318   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
319   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
320   document are to be interpreted as described in <xref target="RFC2119"/>.
321</t>
322<t>
323   An implementation is not compliant if it fails to satisfy one or more of
324   the "MUST" or "REQUIRED" level requirements for the protocols it
325   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
326   level and all the "SHOULD" level requirements for its protocols is said to
327   be "unconditionally compliant"; one that satisfies all the "MUST" level
328   requirements but not all the "SHOULD" level requirements for its protocols
329   is said to be "conditionally compliant".
330</t>
331</section>
332
333<section title="Syntax Notation" anchor="notation">
334   
335   
336   
337   
338   
339   
340   
341   
342   
343<t>
344   This specification uses the ABNF syntax defined in Section 1.2 of <xref target="Part1"/> (which
345   extends the syntax defined in <xref target="RFC5234"/> with a list rule).
346   <xref target="collected.abnf"/> shows the collected ABNF, with the list
347   rule expanded.
348</t>
349<t>
350   The following core rules are included by reference, as defined in <xref target="RFC5234"/>, Appendix B.1: ALPHA (letters), CR (carriage
351   return), CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double
352   quote), HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit
353   sequence of data), SP (space), VCHAR (any visible USASCII character), and
354   WSP (whitespace).
355</t>
356
357<section title="Core Rules" anchor="core.rules">
358   
359   
360   
361<t>
362   The core rules below are defined in Section 1.2.2 of <xref target="Part1"/>:
363</t>
364<figure><artwork type="abnf2616"><![CDATA[
365  quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>
366  token         = <token, defined in [Part1], Section 1.2.2>
367  OWS           = <OWS, defined in [Part1], Section 1.2.2>
368]]></artwork></figure>
369</section>
370
371<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
372   
373   
374   
375   
376   
377<t>
378   The ABNF rules below are defined in other parts:
379</t>
380<figure><artwork type="abnf2616"><![CDATA[
381  field-name    = <field-name, defined in [Part1], Section 3.2>
382  HTTP-date     = <HTTP-date, defined in [Part1], Section 6.1>
383  port          = <port, defined in [Part1], Section 2.6>
384  pseudonym     = <pseudonym, defined in [Part1], Section 9.9>
385  uri-host      = <uri-host, defined in [Part1], Section 2.6>
386]]></artwork></figure>
387</section>
388
389</section>
390</section>
391
392<section anchor="caching.overview" title="Cache Operation">
393
394<section anchor="response.cacheability" title="Response Cacheability">
395<t>
396   A cache MUST NOT store a response to any request, unless:
397   <list style="symbols">
398      <t>The request method is understood by the cache and defined as being
399      cacheable, and</t>
400      <t>the response status code is understood by the cache, and</t>
401      <t>the "no-store" cache directive (see <xref target="header.cache-control"/>) does not appear in request or response
402      headers, and</t>
403      <t>the "private" cache response directive (see <xref target="cache-response-directive"/> does not appear in the response, if
404      the cache is shared, and</t>
405      <t>the "Authorization" header (see Section 3.1 of <xref target="Part7"/>) does not
406      appear in the request, if the cache is shared, unless the response
407      explicitly allows it (see <xref target="caching.authenticated.responses"/>), and</t>
408      <t>the response either:
409         <list style="symbols">
410            <t>contains an Expires header (see <xref target="header.expires"/>), or</t>
411            <t>contains a max-age response cache directive (see <xref target="cache-response-directive"/>), or</t>
412            <t>contains a s-maxage response cache directive and the cache is
413            shared, or</t>
414            <t>contains a Cache Control Extension (see <xref target="cache.control.extensions"/>) that allows it to be cached,
415            or</t>
416            <t>has a status code that can be served with heuristic freshness
417            (see <xref target="heuristic.freshness"/>).</t>
418         </list>
419      </t>
420   </list>
421</t>
422<t>
423   In this context, a cache has "understood" a request method or a response
424   status code if it recognises it and implements any cache-specific
425   behaviour. In particular, 206 Partial Content responses cannot be cached by
426   an implementation that does not handle partial content (see <xref target="errors.or.incomplete.response.cache.behavior"/>).
427</t>
428<t>
429   Note that in normal operation, most caches will not store a response that
430   has neither a cache validator nor an explicit expiration time, as such
431   responses are not usually useful to store. However, caches are not
432   prohibited from storing such responses.
433</t>
434
435<section anchor="errors.or.incomplete.response.cache.behavior" title="Storing Partial and Incomplete Responses">
436<t>
437   A cache that receives an incomplete response (for example, with fewer bytes
438   of data than specified in a Content-Length header) can store the response,
439   but MUST treat it as a partial response <xref target="Part5"/>. Partial responses can
440   be combined as described in Section 4 of <xref target="Part5"/>; the result might be a
441   full response or might still be partial. A cache MUST NOT return a
442   partial response to a client without explicitly marking it as such using
443   the 206 (Partial Content) status code.
444</t>
445<t>
446   A cache that does not support the Range and Content-Range headers
447   MUST NOT store incomplete or partial responses.
448</t>
449</section>
450
451</section>
452
453
454<section anchor="constructing.responses.from.caches" title="Constructing Responses from Caches">
455<t>
456   For a presented request, a cache MUST NOT return a stored response,
457   unless:
458   <list style="symbols">
459      <t>The presented effective request URI (Section 4.3 of <xref target="Part1"/>) and
460      that of the stored response match, and</t>
461      <t>the request method associated with the stored response allows it to
462      be used for the presented request, and</t>
463      <t>selecting request-headers nominated by the stored response (if any)
464      match those presented (see <xref target="caching.negotiated.responses"/>), and</t>
465      <t>the presented request and stored response are free from directives
466      that would prevent its use (see <xref target="header.cache-control"/>
467      and <xref target="header.pragma"/>), and</t>
468      <t>the stored response is either:
469         <list style="symbols">
470            <t>fresh (see <xref target="expiration.model"/>), or</t>
471            <t>allowed to be served stale (see <xref target="serving.stale.responses"/>), or</t>
472            <t>successfully validated (see <xref target="validation.model"/>).</t>
473         </list>
474      </t>
475  </list>
476</t>
477<t>
478   When a stored response is used to satisfy a request without validation,
479   caches MUST include a single Age header field (<xref target="header.age"/>) in the response with a value equal to the stored response's
480   current_age; see <xref target="age.calculations"/>.
481</t>
482<t>
483   Requests with methods that are unsafe (Section 7.1.1 of <xref target="Part2"/>) MUST be written
484   through the cache to the origin server; i.e., a cache must not reply to
485   such a request before having forwarded the request and having received a
486   corresponding response.
487</t>
488<t>
489   Also, note that unsafe requests might invalidate already stored responses;
490   see <xref target="invalidation.after.updates.or.deletions"/>.
491</t>
492<t>
493   Caches MUST use the most recent response (as determined by the Date
494   header) when more than one suitable response is stored. They can also
495   forward a request with "Cache-Control: max-age=0" or "Cache-Control:
496   no-cache" to disambiguate which response to use.
497</t>
498</section>
499
500<section anchor="expiration.model" title="Freshness Model">
501<t>
502   When a response is "fresh" in the cache, it can be used to satisfy
503   subsequent requests without contacting the origin server, thereby improving
504   efficiency.
505</t>
506<t>
507   The primary mechanism for determining freshness is for an origin server to
508   provide an explicit expiration time in the future, using either the Expires
509   header (<xref target="header.expires"/>) or the max-age response cache
510   directive (<xref target="cache-response-directive"/>). Generally, origin
511   servers will assign future explicit expiration times to responses in the
512   belief that the representation is not likely to change in a semantically
513   significant way before the expiration time is reached.
514</t>
515<t>
516   If an origin server wishes to force a cache to validate every request, it
517   can assign an explicit expiration time in the past to indicate that the
518   response is already stale.  Compliant caches will validate the cached response
519   before reusing it for subsequent requests.
520</t>
521<t>
522   Since origin servers do not always provide explicit expiration times, HTTP
523   caches MAY assign heuristic expiration times when explicit times are not
524   specified, employing algorithms that use other header values (such as the
525   Last-Modified time) to estimate a plausible expiration time. The HTTP/1.1
526   specification does not provide specific algorithms, but does impose
527   worst-case constraints on their results.
528</t>
529<figure>
530<preamble>
531  The calculation to determine if a response is fresh is:
532</preamble>
533<artwork type="code"><![CDATA[
534   response_is_fresh = (freshness_lifetime > current_age)
535]]></artwork>
536</figure>
537<t>
538   The freshness_lifetime is defined in <xref target="calculating.freshness.lifetime"/>; the current_age is defined in
539   <xref target="age.calculations"/>.
540</t>
541<t>
542   Additionally, clients might need to influence freshness calculation. They
543   can do this using several request cache directives, with the effect of
544   either increasing or loosening constraints on freshness. See <xref target="cache-request-directive"/>.
545</t>
546<t>
547   <cref anchor="ISSUE-no-req-for-directives">there are not requirements
548   directly applying to cache-request-directives and freshness.</cref>
549</t>
550<t>
551   Note that freshness applies only to cache operation; it cannot be used to
552   force a user agent to refresh its display or reload a resource. See <xref target="history.lists"/> for an explanation of the difference between
553   caches and history mechanisms.
554</t>
555
556<section anchor="calculating.freshness.lifetime" title="Calculating Freshness Lifetime">
557<t>
558   A cache can calculate the freshness lifetime (denoted as
559   freshness_lifetime) of a response by using the first match of:
560   <list style="symbols">
561      <t>If the cache is shared and the s-maxage response cache directive
562      (<xref target="cache-response-directive"/>) is present, use its value,
563      or</t>
564      <t>If the max-age response cache directive (<xref target="cache-response-directive"/>) is present, use its value, or</t>
565      <t>If the Expires response header (<xref target="header.expires"/>) is
566      present, use its value minus the value of the Date response header,
567      or</t>
568      <t>Otherwise, no explicit expiration time is present in the response. A
569      heuristic freshness lifetime might be applicable; see <xref target="heuristic.freshness"/>.</t>
570   </list>
571</t>
572<t>
573   Note that this calculation is not vulnerable to clock skew, since all of
574   the information comes from the origin server.
575</t>
576
577<section anchor="heuristic.freshness" title="Calculating Heuristic Freshness">
578<t>
579   If no explicit expiration time is present in a stored response that has a
580   status code whose definition allows heuristic freshness to be used
581   (including the following in Section 8 of <xref target="Part2"/>: 200, 203, 206, 300, 301 and
582   410), a heuristic expiration time MAY be calculated. Heuristics
583   MUST NOT be used for response status codes that do not explicitly allow
584   it.
585</t>
586<t>
587   When a heuristic is used to calculate freshness lifetime, the cache
588   SHOULD attach a Warning header with a 113 warn-code to the response if
589   its current_age is more than 24 hours and such a warning is not already
590   present.
591</t>
592<t>
593   Also, if the response has a Last-Modified header (Section 6.6 of <xref target="Part4"/>),
594   the heuristic expiration value SHOULD be no more than some fraction of
595   the interval since that time. A typical setting of this fraction might be
596   10%.
597</t>
598<t><list>
599   <t>
600      Note: RFC 2616 (<xref target="RFC2616"/>, Section 13.9) required that caches do not calculate heuristic
601      freshness for URLs with query components (i.e., those containing '?').
602      In practice, this has not been widely implemented. Therefore, servers
603      are encouraged to send explicit directives (e.g., Cache-Control:
604      no-cache) if they wish to preclude caching.
605   </t>
606</list></t>
607</section>
608</section>
609
610<section anchor="age.calculations" title="Calculating Age">
611<t>
612   HTTP/1.1 uses the Age response-header to convey the estimated age of the
613   response message when obtained from a cache. The Age field value is the
614   cache's estimate of the amount of time since the response was generated or
615   validated by the origin server. In essence, the Age value is the sum of the
616   time that the response has been resident in each of the caches along the
617   path from the origin server, plus the amount of time it has been in transit
618   along network paths.
619</t>
620<t>
621   The following data is used for the age calculation:
622</t>
623<t>
624   <?rfc needLines="4"?>age_value
625   <list>
626      <t>
627         The term "age_value" denotes the value of the Age header (<xref target="header.age"/>), in a form appropriate for arithmetic
628         operation; or 0, if not available.
629      </t>
630   </list>
631</t>
632<t>
633   <?rfc needLines="4"?>date_value
634   <list>
635      <t>
636         HTTP/1.1 requires origin servers to send a Date header, if possible,
637         with every response, giving the time at which the response was
638         generated. The term "date_value" denotes the value of the Date
639         header, in a form appropriate for arithmetic operations. See
640         Section 9.3 of <xref target="Part1"/> for the definition of the Date header, and for
641         requirements regarding responses without a Date response header.
642      </t>
643   </list>
644</t>
645<t>
646   <?rfc needLines="4"?>now
647   <list>
648      <t>
649         The term "now" means "the current value of the clock at the host
650         performing the calculation". Hosts that use HTTP, but especially
651         hosts running origin servers and caches, SHOULD use NTP (<xref target="RFC1305"/>) or some similar protocol to synchronize their
652         clocks to a globally accurate time standard.
653      </t>
654   </list>
655</t>
656<t>
657   <?rfc needLines="4"?>request_time
658   <list>
659      <t>
660         The current value of the clock at the host at the time the request
661         resulting in the stored response was made.
662      </t>
663   </list>
664</t>
665<t>
666   <?rfc needLines="4"?>response_time
667   <list>
668      <t>
669         The current value of the clock at the host at the time the response
670         was received.
671      </t>
672   </list>
673</t>
674<t>
675   A response's age can be calculated in two entirely independent ways:
676   <list style="numbers">
677      <t>the "apparent_age": response_time minus date_value, if the local
678      clock is reasonably well synchronized to the origin server's clock. If
679      the result is negative, the result is replaced by zero.</t>
680      <t>the "corrected_age_value", if all of the caches along the response
681      path implement HTTP/1.1; note this value MUST be interpreted relative
682      to the time the request was initiated, not the time that the response
683      was received.</t>
684   </list>
685</t>
686<figure>
687<artwork type="code"><![CDATA[
688  apparent_age = max(0, response_time - date_value);
689
690  response_delay = response_time - request_time;
691  corrected_age_value = age_value + response_delay; 
692]]></artwork>
693</figure>
694<figure>
695<preamble>These are combined as</preamble>
696<artwork type="code"><![CDATA[
697  corrected_initial_age = max(apparent_age, corrected_age_value);
698]]></artwork></figure>
699<t>
700   The current_age of a stored response can then be calculated by adding the
701   amount of time (in seconds) since the stored response was last validated by
702   the origin server to the corrected_initial_age.
703</t>
704<figure><artwork type="code"><![CDATA[
705  resident_time = now - response_time;
706  current_age = corrected_initial_age + resident_time;
707]]></artwork></figure>
708</section>
709
710<section anchor="serving.stale.responses" title="Serving Stale Responses">
711<t>
712   A "stale" response is one that either has explicit expiry information or is
713   allowed to have heuristic expiry calculated, but is not fresh according to
714   the calculations in <xref target="expiration.model"/>.
715</t>
716<t>
717   Caches MUST NOT return a stale response if it is prohibited by an
718   explicit in-protocol directive (e.g., by a "no-store" or "no-cache" cache
719   directive, a "must-revalidate" cache-response-directive, or an applicable
720   "s-maxage" or "proxy-revalidate" cache-response-directive; see <xref target="cache-response-directive"/>).
721</t>
722<t>
723   Caches SHOULD NOT return stale responses unless they are disconnected
724   (i.e., it cannot contact the origin server or otherwise find a forward
725   path) or otherwise explicitly allowed (e.g., the max-stale request
726   directive; see <xref target="cache-request-directive"/>).
727</t>
728<t>
729   Stale responses SHOULD have a Warning header with the 110 warn-code (see
730   <xref target="header.warning"/>). Likewise, the 112 warn-code SHOULD be
731   sent on stale responses if the cache is disconnected.
732</t>
733<t>
734   If a cache receives a first-hand response (either an entire response, or a
735   304 (Not Modified) response) that it would normally forward to the
736   requesting client, and the received response is no longer fresh, the cache
737   SHOULD forward it to the requesting client without adding a new Warning
738   (but without removing any existing Warning headers). A cache SHOULD NOT
739   attempt to validate a response simply because that response became stale in
740   transit.
741</t>
742</section>
743</section>
744
745<section anchor="validation.model" title="Validation Model">
746<t>
747   When a cache has one or more stored responses for a requested URI, but
748   cannot serve any of them (e.g., because they are not fresh, or one cannot
749   be selected; see <xref target="caching.negotiated.responses"/>), it can use
750   the conditional request mechanism <xref target="Part4"/> in the forwarded request to
751   give the origin server an opportunity to both select a valid stored
752   response to be used, and to update it. This process is known as
753   "validating" or "revalidating" the stored response.
754</t>
755<t>
756   When sending such a conditional request, the cache SHOULD add an
757   If-Modified-Since header whose value is that of the Last-Modified header
758   from the selected (see <xref target="caching.negotiated.responses"/>)
759   stored response, if available.
760</t>
761<t>
762   Additionally, the cache SHOULD add an If-None-Match header whose value is
763   that of the ETag header(s) from all responses stored for the requested URI,
764   if present. However, if any of the stored responses contains only partial
765   content, its entity-tag SHOULD NOT be included in the If-None-Match
766   header field unless the request is for a range that would be fully
767   satisfied by that stored response.
768</t>
769<t>
770   A 304 (Not Modified) response status code indicates that the stored
771   response can be updated and reused; see <xref target="combining.headers"/>.
772</t>
773<t>
774   A full response (i.e., one with a response body) indicates that none of the
775   stored responses nominated in the conditional request is suitable. Instead,
776   the full response SHOULD be used to satisfy the request and MAY replace
777   the stored response.
778</t>
779<t>
780   If a cache receives a 5xx response while attempting to validate a response,
781   it MAY either forward this response to the requesting client, or act as
782   if the server failed to respond. In the latter case, it MAY return a
783   previously stored response (see <xref target="serving.stale.responses"/>).
784</t>
785</section>
786
787<section anchor="invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">
788<t>
789   Because unsafe methods (Section 7.1.1 of <xref target="Part2"/>) have the potential for changing
790   state on the origin server, intervening caches can use them to keep their
791   contents up-to-date.
792</t>
793<t>
794   The following HTTP methods MUST cause a cache to invalidate the effective
795   Request URI (Section 4.3 of <xref target="Part1"/>) as well as the URI(s) in the Location
796   and Content-Location headers (if present):
797   <list style="symbols">
798      <t>PUT</t>
799      <t>DELETE</t>
800      <t>POST</t>
801   </list>
802</t>
803<t>
804   An invalidation based on a URI from a Location or Content-Location header
805   MUST NOT be performed if the host part of that URI differs from the host
806   part in the effective request URI (Section 4.3 of <xref target="Part1"/>). This helps
807   prevent denial of service attacks.
808</t>
809<t>
810   A cache that passes through requests for methods it does not understand
811   SHOULD invalidate the effective request URI (Section 4.3 of <xref target="Part1"/>).
812</t>
813<t>
814   Here, "invalidate" means that the cache will either remove all stored
815   responses related to the effective request URI, or will mark these as
816   "invalid" and in need of a mandatory validation before they can be returned
817   in response to a subsequent request.
818</t>
819<t>
820   Note that this does not guarantee that all appropriate responses are
821   invalidated. For example, the request that caused the change at the origin
822   server might not have gone through the cache where a response is stored.
823</t>
824</section>
825
826<section anchor="caching.authenticated.responses" title="Shared Caching of Authenticated Responses">
827
828<t>
829   Shared caches MUST NOT use a cached response to a request with an
830   Authorization header (Section 3.1 of <xref target="Part7"/>) to satisfy any subsequent
831   request unless a cache directive that allows such responses to be stored is
832   present in the response.
833</t>
834
835<t>
836   In this specification, the following Cache-Control response directives
837   (<xref target="cache-response-directive"/>) have such an effect:
838   must-revalidate, public, s-maxage.
839</t>
840
841<t>
842   Note that cached responses that contain the "must-revalidate" and/or
843   "s-maxage" response directives are not allowed to be served stale (<xref target="serving.stale.responses"/>) by shared caches. In particular, a
844   response with either "max-age=0, must-revalidate" or "s-maxage=0" cannot be
845   used to satisfy a subsequent request without revalidating it on the origin
846   server.
847</t>
848</section>
849
850<section anchor="caching.negotiated.responses" title="Caching Negotiated Responses">
851<t>
852   When a cache receives a request that can be satisfied by a stored response
853   that has a Vary header field (<xref target="header.vary"/>), it MUST NOT
854   use that response unless all of the selecting request-headers nominated by
855   the Vary header match in both the original request (i.e., that associated
856   with the stored response), and the presented request.
857</t>
858<t>
859   The selecting request-headers from two requests are defined to match if and
860   only if those in the first request can be transformed to those in the
861   second request by applying any of the following:
862   <list style="symbols">
863      <t>
864         adding or removing whitespace, where allowed in the header's syntax
865      </t>
866      <t>
867         combining multiple message-header fields with the same field name
868         (see Section 3.2 of <xref target="Part1"/>)
869      </t>
870      <t>
871         normalizing both header values in a way that is known to have
872         identical semantics, according to the header's specification (e.g.,
873         re-ordering field values when order is not significant;
874         case-normalization, where values are defined to be case-insensitive)
875      </t>
876  </list>
877</t>
878<t>
879   If (after any normalization that might take place) a header field is absent
880   from a request, it can only match another request if it is also absent
881   there.
882</t>
883<t>
884   A Vary header field-value of "*" always fails to match, and subsequent
885   requests to that resource can only be properly interpreted by the origin
886   server.
887</t>
888<t>
889   The stored response with matching selecting request-headers is known as the
890   selected response.
891</t>
892<t>
893   If no selected response is available, the cache MAY forward the presented
894   request to the origin server in a conditional request; see <xref target="validation.model"/>.
895</t>
896</section>
897
898<section anchor="combining.headers" title="Combining Responses">
899<t>
900   When a cache receives a 304 (Not Modified) response or a 206 (Partial
901   Content) response (in this section, the "new" response"), it needs to
902   created an updated response by combining the stored response with the new
903   one, so that the updated response can be used to satisfy the request, and
904   potentially update the cached response.
905</t>
906<t>
907   If the new response contains an ETag, it identifies the stored response to
908   use. <cref anchor="TODO-mention-CL">might need language about
909   Content-Location here</cref><cref anchor="TODO-select-for-combine">Shouldn't this be the selected
910   response?</cref>
911</t>
912<t>
913   If the new response's status code is 206 (partial content), both the stored
914   and new responses MUST have validators, and those validators MUST match
915   using the strong comparison function (see Section 4 of <xref target="Part4"/>). Otherwise,
916   the responses MUST NOT be combined.
917</t>
918<t>
919   The stored response headers are used as those of the updated response,
920   except that
921   <list style="symbols">
922      <t>any stored Warning headers with warn-code 1xx (see <xref target="header.warning"/>) MUST be deleted.</t>
923      <t>any stored Warning headers with warn-code 2xx MUST be retained.</t>
924      <t>any other headers provided in the new response MUST replace all
925      instances of the corresponding headers from the stored response.</t>
926   </list>
927</t>
928<t>
929   The updated response headers MUST be used to replace those of the stored
930   response in cache (unless the stored response is removed from cache). In
931   the case of a 206 response, the combined representation MAY be stored.
932</t>
933</section>
934
935</section>
936
937<section anchor="header.fields" title="Header Field Definitions">
938<t>
939   This section defines the syntax and semantics of HTTP/1.1 header fields
940   related to caching.
941</t>
942
943<section anchor="header.age" title="Age">
944   <iref item="Age header" primary="true"/>
945   <iref item="Headers" primary="true" subitem="Age"/>
946   
947   
948   
949<t>
950   The "Age" response-header field conveys the sender's estimate of the amount
951   of time since the response was generated or successfully validated at the
952   origin server. Age values are calculated as specified in <xref target="age.calculations"/>.
953</t>
954<figure><iref primary="true" item="Grammar" subitem="Age"/><iref primary="true" item="Grammar" subitem="Age-v"/><artwork type="abnf2616"><![CDATA[
955  Age   = "Age" ":" OWS Age-v
956  Age-v = delta-seconds
957]]></artwork></figure>
958<t anchor="rule.delta-seconds">
959 
960  Age field-values are non-negative integers, representing time in seconds.
961</t>
962<figure><iref item="Grammar" primary="true" subitem="delta-seconds"/><artwork type="abnf2616"><![CDATA[
963  delta-seconds  = 1*DIGIT
964]]></artwork></figure>
965<t>
966   If a cache receives a value larger than the largest positive integer it can
967   represent, or if any of its age calculations overflows, it MUST transmit
968   an Age header with a field-value of 2147483648 (2^31). Caches
969   SHOULD use an arithmetic type of at least 31 bits of range.
970</t>
971<t>
972   The presence of an Age header field in a response implies that a response
973   is not first-hand. However, the converse is not true, since HTTP/1.0 caches
974   might not implement the Age header field.
975</t>
976</section>
977
978<section anchor="header.cache-control" title="Cache-Control">
979   <iref item="Cache-Control header" primary="true"/>
980   <iref item="Headers" primary="true" subitem="Cache-Control"/>
981   
982   
983   
984   
985   
986   
987<t>
988   The "Cache-Control" general-header field is used to specify directives for
989   caches along the request/response chain. Such cache directives are
990   unidirectional in that the presence of a directive in a request does not
991   imply that the same directive is to be given in the response.
992</t>
993<t>
994   HTTP/1.1 caches MUST obey the requirements of the Cache-Control
995   directives defined in this section. See <xref target="cache.control.extensions"/> for information about how Cache-Control
996   directives defined elsewhere are handled.
997</t>
998<t><list>
999   <t>
1000       Note: HTTP/1.0 caches might not implement Cache-Control and
1001       might only implement Pragma: no-cache (see <xref target="header.pragma"/>).
1002   </t>
1003</list></t>
1004<t>
1005   Cache directives MUST be passed through by a proxy or gateway
1006   application, regardless of their significance to that application, since
1007   the directives might be applicable to all recipients along the
1008   request/response chain. It is not possible to target a directive to a
1009   specific cache.
1010</t>
1011<figure><iref primary="true" item="Grammar" subitem="Cache-Control"/><iref primary="true" item="Grammar" subitem="Cache-Control-v"/><iref primary="true" item="Grammar" subitem="cache-extension"/><artwork type="abnf2616"><![CDATA[
1012  Cache-Control   = "Cache-Control" ":" OWS Cache-Control-v
1013  Cache-Control-v = 1#cache-directive
1014
1015  cache-directive = cache-request-directive
1016     / cache-response-directive
1017
1018  cache-extension = token [ "=" ( token / quoted-string ) ]
1019]]></artwork></figure>
1020
1021<section anchor="cache-request-directive" title="Request Cache-Control Directives">
1022   
1023
1024<figure><iref item="Grammar" primary="true" subitem="cache-request-directive"/><artwork type="abnf2616"><![CDATA[
1025  cache-request-directive =
1026       "no-cache"
1027     / "no-store"
1028     / "max-age" "=" delta-seconds
1029     / "max-stale" [ "=" delta-seconds ]
1030     / "min-fresh" "=" delta-seconds
1031     / "no-transform"
1032     / "only-if-cached"
1033     / cache-extension
1034]]></artwork></figure>
1035
1036<t>
1037   <?rfc needLines="4"?>no-cache
1038   <iref item="Cache Directives" primary="true" subitem="no-cache"/>
1039   <iref item="no-cache" primary="true" subitem="Cache Directive"/>
1040   <list>
1041      <t>The no-cache request directive indicates that a stored response
1042      MUST NOT be used to satisfy the request without successful validation
1043      on the origin server.</t> 
1044   </list>
1045</t>
1046<t>
1047   <?rfc needLines="4"?>no-store
1048   <iref item="Cache Directives" primary="true" subitem="no-store"/>
1049   <iref item="no-store" primary="true" subitem="Cache Directive"/>
1050   <list>
1051      <t>The no-store request directive indicates that a cache MUST NOT
1052      store any part of either this request or any response to it. This
1053      directive applies to both non-shared and shared caches. "MUST NOT
1054      store" in this context means that the cache MUST NOT intentionally
1055      store the information in non-volatile storage, and MUST make a
1056      best-effort attempt to remove the information from volatile storage as
1057      promptly as possible after forwarding it.</t>
1058      <t>This directive is NOT a reliable or sufficient mechanism for ensuring
1059      privacy. In particular, malicious or compromised caches might not
1060      recognize or obey this directive, and communications networks might be
1061      vulnerable to eavesdropping.</t>
1062   </list>
1063</t>
1064<t>
1065   <?rfc needLines="4"?>max-age
1066   <iref item="Cache Directives" primary="true" subitem="max-age"/>
1067   <iref item="max-age" primary="true" subitem="Cache Directive"/>
1068   <list>
1069      <t>The max-age request directive indicates that the client is willing to
1070      accept a response whose age is no greater than the specified time in
1071      seconds. Unless the max-stale request directive is also present, the
1072      client is not willing to accept a stale response.</t>
1073   </list>
1074</t>
1075<t>
1076   <?rfc needLines="4"?>max-stale
1077   <iref item="Cache Directives" primary="true" subitem="max-stale"/>
1078   <iref item="max-stale" primary="true" subitem="Cache Directive"/>
1079   <list>
1080      <t>The max-stale request directive indicates that the client is willing
1081      to accept a response that has exceeded its expiration time. If max-stale
1082      is assigned a value, then the client is willing to accept a response
1083      that has exceeded its expiration time by no more than the specified
1084      number of seconds. If no value is assigned to max-stale, then the client
1085      is willing to accept a stale response of any age.</t>
1086   </list>
1087</t>
1088<t>
1089   <?rfc needLines="4"?>min-fresh
1090   <iref item="Cache Directives" primary="true" subitem="min-fresh"/>
1091   <iref item="min-fresh" primary="true" subitem="Cache Directive"/>
1092   <list>
1093      <t>The min-fresh request directive indicates that the client is willing
1094      to accept a response whose freshness lifetime is no less than its
1095      current age plus the specified time in seconds. That is, the client
1096      wants a response that will still be fresh for at least the specified
1097      number of seconds.</t>
1098   </list>
1099</t>
1100<t>
1101   <?rfc needLines="4"?>no-transform
1102   <iref item="Cache Directives" primary="true" subitem="no-transform"/>
1103   <iref item="no-transform" primary="true" subitem="Cache Directive"/>
1104   <list>
1105      <t>The no-transform request directive indicates that an intermediate
1106      cache or proxy MUST NOT change the Content-Encoding, Content-Range or
1107      Content-Type request headers, nor the request representation.</t>
1108   </list>
1109</t>
1110<t>
1111   <?rfc needLines="4"?>only-if-cached
1112   <iref item="Cache Directives" primary="true" subitem="only-if-cached"/>
1113   <iref item="only-if-cached" primary="true" subitem="Cache Directive"/>
1114   <list>
1115      <t>The only-if-cached request directive indicates that the client only
1116      wishes to return a stored response. If it receives this directive, a
1117      cache SHOULD either respond using a stored response that is consistent
1118      with the other constraints of the request, or respond with a 504
1119      (Gateway Timeout) status code. If a group of caches is being operated as
1120      a unified system with good internal connectivity, such a request MAY
1121      be forwarded within that group of caches.</t>
1122   </list>
1123</t>
1124</section>
1125
1126<section anchor="cache-response-directive" title="Response Cache-Control Directives">
1127   
1128
1129<figure><iref item="Grammar" primary="true" subitem="cache-response-directive"/><artwork type="abnf2616"><![CDATA[
1130  cache-response-directive =
1131       "public"
1132     / "private" [ "=" DQUOTE 1#field-name DQUOTE ]
1133     / "no-cache" [ "=" DQUOTE 1#field-name DQUOTE ]
1134     / "no-store"
1135     / "no-transform"
1136     / "must-revalidate"
1137     / "proxy-revalidate"
1138     / "max-age" "=" delta-seconds
1139     / "s-maxage" "=" delta-seconds
1140     / cache-extension
1141]]></artwork></figure>
1142
1143<t>
1144   <?rfc needLines="4"?>public
1145   <iref item="Cache Directives" primary="true" subitem="public"/>
1146   <iref item="public" primary="true" subitem="Cache Directive"/>
1147   <list>
1148      <t>The public response directive indicates that the response MAY be
1149      cached, even if it would normally be non-cacheable or cacheable only
1150      within a non-shared cache. (See also Authorization,
1151      Section 3.1 of <xref target="Part7"/>, for additional details.) </t>
1152  </list>
1153</t>
1154<t>
1155   <?rfc needLines="4"?>private
1156   <iref item="Cache Directives" primary="true" subitem="private"/>
1157   <iref item="private" primary="true" subitem="Cache Directive"/>
1158   <list>
1159      <t>The private response directive indicates that the response message is
1160      intended for a single user and MUST NOT be stored by a shared cache. A
1161      private (non-shared) cache MAY store the response.</t>
1162      <t>If the private response directive specifies one or more field-names,
1163      this requirement is limited to the field-values associated with the
1164      listed response headers. That is, the specified field-names(s)
1165      MUST NOT be stored by a shared cache, whereas the remainder of the
1166      response message MAY be.</t>
1167      <t> Note: This usage of the word private only controls where
1168      the response can be stored; it cannot ensure the privacy of the message
1169      content. Also, private response directives with field-names are often
1170      handled by implementations as if an unqualified private directive was
1171      received; i.e., the special handling for the qualified form is not
1172      widely implemented.</t>
1173   </list>
1174</t>
1175<t>
1176   <?rfc needLines="4"?>no-cache
1177   <iref item="Cache Directives" primary="true" subitem="no-cache"/>
1178   <iref item="no-cache" primary="true" subitem="Cache Directive"/>
1179   <list>
1180      <t>The no-cache response directive indicates that the response MUST NOT
1181      be used to satisfy a subsequent request without successful validation on
1182      the origin server. This allows an origin server to prevent a cache from
1183      using it to satisfy a request without contacting it, even by caches that
1184      have been configured to return stale responses.</t>
1185      <t>If the no-cache response directive specifies one or more field-names,
1186      this requirement is limited to the field-values associated with the
1187      listed response headers. That is, the specified field-name(s) MUST NOT
1188      be sent in the response to a subsequent request without successful
1189      validation on the origin server. This allows an origin server to prevent
1190      the re-use of certain header fields in a response, while still allowing
1191      caching of the rest of the response.</t>
1192      <t> Note: Most HTTP/1.0 caches will not recognize or obey
1193      this directive. Also, no-cache response directives with field-names are
1194      often handled by implementations as if an unqualified no-cache directive
1195      was received; i.e., the special handling for the qualified form is not
1196      widely implemented. </t>
1197   </list>
1198</t>
1199<t>
1200   <?rfc needLines="4"?>no-store
1201   <iref item="Cache Directives" primary="true" subitem="no-store"/>
1202   <iref item="no-store" primary="true" subitem="Cache Directive"/>
1203   <list>
1204      <t>The no-store response directive indicates that a cache MUST NOT
1205      store any part of either the immediate request or response. This
1206      directive applies to both non-shared and shared caches. "MUST NOT
1207      store" in this context means that the cache MUST NOT intentionally
1208      store the information in non-volatile storage, and MUST make a
1209      best-effort attempt to remove the information from volatile storage as
1210      promptly as possible after forwarding it.</t>
1211      <t>This directive is NOT a reliable or sufficient mechanism for ensuring
1212      privacy. In particular, malicious or compromised caches might not
1213      recognize or obey this directive, and communications networks might be
1214      vulnerable to eavesdropping.</t>
1215   </list>
1216</t>
1217<t>
1218   <?rfc needLines="4"?>must-revalidate
1219   <iref item="Cache Directives" primary="true" subitem="must-revalidate"/>
1220   <iref item="must-revalidate" primary="true" subitem="Cache Directive"/>
1221   <list>
1222      <t>The must-revalidate response directive indicates that once it has
1223      become stale, the response MUST NOT be used to satisfy subsequent
1224      requests without successful validation on the origin server.</t>
1225      <t>The must-revalidate directive is necessary to support reliable
1226      operation for certain protocol features. In all circumstances an
1227      HTTP/1.1 cache MUST obey the must-revalidate directive; in particular,
1228      if the cache cannot reach the origin server for any reason, it MUST
1229      generate a 504 (Gateway Timeout) response.</t>
1230      <t>Servers SHOULD send the must-revalidate directive if and only if
1231      failure to validate a request on the representation could result in
1232      incorrect operation, such as a silently unexecuted financial
1233      transaction.</t>
1234   </list>
1235</t>
1236<t>
1237   <?rfc needLines="4"?>proxy-revalidate
1238   <iref item="Cache Directives" primary="true" subitem="proxy-revalidate"/>
1239   <iref item="proxy-revalidate" primary="true" subitem="Cache Directive"/>
1240   <list>
1241      <t>The proxy-revalidate response directive has the same meaning as the
1242      must-revalidate response directive, except that it does not apply to
1243      non-shared caches.</t>
1244   </list>
1245</t>
1246<t>
1247   <?rfc needLines="4"?>max-age
1248   <iref item="Cache Directives" primary="true" subitem="max-age"/>
1249   <iref item="max-age" primary="true" subitem="Cache Directive"/>
1250   <list>
1251      <t>The max-age response directive indicates that response is to be
1252      considered stale after its age is greater than the specified number of
1253      seconds.</t>
1254   </list>
1255</t>
1256<t>
1257   <?rfc needLines="4"?>s-maxage
1258   <iref item="Cache Directives" primary="true" subitem="s-maxage"/>
1259   <iref item="s-maxage" primary="true" subitem="Cache Directive"/>
1260   <list>
1261      <t>The s-maxage response directive indicates that, in shared caches, the
1262      maximum age specified by this directive overrides the maximum age
1263      specified by either the max-age directive or the Expires header. The
1264      s-maxage directive also implies the semantics of the proxy-revalidate
1265      response directive.</t>
1266   </list>
1267</t>
1268<t>
1269   <?rfc needLines="4"?>no-transform
1270   <iref item="Cache Directives" primary="true" subitem="no-transform"/>
1271   <iref item="no-transform" primary="true" subitem="Cache Directive"/>
1272   <list>
1273      <t>The no-transform response directive indicates that an intermediate
1274      cache or proxy MUST NOT change the Content-Encoding, Content-Range or
1275      Content-Type response headers, nor the response representation.</t>
1276   </list>
1277</t>
1278
1279</section>
1280
1281<section anchor="cache.control.extensions" title="Cache Control Extensions">
1282<t>
1283   The Cache-Control header field can be extended through the use of one or
1284   more cache-extension tokens, each with an optional value. Informational
1285   extensions (those that do not require a change in cache behavior) can be
1286   added without changing the semantics of other directives. Behavioral
1287   extensions are designed to work by acting as modifiers to the existing base
1288   of cache directives. Both the new directive and the standard directive are
1289   supplied, such that applications that do not understand the new directive
1290   will default to the behavior specified by the standard directive, and those
1291   that understand the new directive will recognize it as modifying the
1292   requirements associated with the standard directive. In this way,
1293   extensions to the cache-control directives can be made without requiring
1294   changes to the base protocol.
1295</t>
1296<t>
1297   This extension mechanism depends on an HTTP cache obeying all of the
1298   cache-control directives defined for its native HTTP-version, obeying
1299   certain extensions, and ignoring all directives that it does not
1300   understand.
1301</t>
1302<t>
1303   For example, consider a hypothetical new response directive called
1304   "community" that acts as a modifier to the private directive. We define
1305   this new directive to mean that, in addition to any non-shared cache, any
1306   cache that is shared only by members of the community named within its
1307   value may cache the response. An origin server wishing to allow the UCI
1308   community to use an otherwise private response in their shared cache(s)
1309   could do so by including
1310</t>
1311<figure><artwork type="example"><![CDATA[
1312  Cache-Control: private, community="UCI"
1313]]></artwork></figure>
1314<t>
1315   A cache seeing this header field will act correctly even if the cache does
1316   not understand the community cache-extension, since it will also see and
1317   understand the private directive and thus default to the safe behavior.
1318</t>
1319<t>
1320   Unrecognized cache directives MUST be ignored; it is assumed that any
1321   cache directive likely to be unrecognized by an HTTP/1.1 cache will be
1322   combined with standard directives (or the response's default cacheability)
1323   such that the cache behavior will remain minimally correct even if the
1324   cache does not understand the extension(s).
1325</t>
1326<t>
1327   The HTTP Cache Directive Registry defines the name space for the cache
1328   directives.
1329</t>
1330<t>
1331   Registrations MUST include the following fields:
1332   <list style="symbols">
1333      <t>Cache Directive Name</t>
1334      <t>Pointer to specification text</t>
1335   </list>
1336</t>
1337<t>
1338   Values to be added to this name space are subject to IETF review (<xref target="RFC5226"/>, Section 4.1).
1339</t>
1340<t>
1341   The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-cache-directives"/>.
1342</t>
1343</section>
1344
1345</section>
1346
1347<section anchor="header.expires" title="Expires">
1348   <iref item="Expires header" primary="true"/>
1349   <iref item="Headers" primary="true" subitem="Expires"/>
1350   
1351   
1352<t>
1353   The "Expires" header field gives the date/time after which the
1354   response is considered stale. See <xref target="expiration.model"/> for
1355   further discussion of the freshness model.
1356</t>
1357<t>
1358   The presence of an Expires field does not imply that the original resource
1359   will change or cease to exist at, before, or after that time.
1360</t>
1361<t>
1362   The field-value is an absolute date and time as defined by HTTP-date in
1363   Section 6.1 of <xref target="Part1"/>; it MUST be sent in rfc1123-date format.
1364</t>
1365<figure><iref primary="true" item="Grammar" subitem="Expires"/><iref primary="true" item="Grammar" subitem="Expires-v"/><artwork type="abnf2616"><![CDATA[
1366  Expires   = "Expires" ":" OWS Expires-v
1367  Expires-v = HTTP-date
1368]]></artwork></figure>
1369<figure>
1370  <preamble>For example</preamble>
1371<artwork type="example"><![CDATA[
1372  Expires: Thu, 01 Dec 1994 16:00:00 GMT
1373]]></artwork></figure>
1374<t><list>
1375   <t>
1376       Note: If a response includes a Cache-Control field with the
1377       max-age directive (see <xref target="cache-response-directive"/>),
1378       that directive overrides the Expires field. Likewise, the s-maxage
1379       directive overrides Expires in shared caches.
1380   </t>
1381</list></t>
1382<t>
1383   HTTP/1.1 servers SHOULD NOT send Expires dates more than one year in the
1384   future.
1385</t>
1386<t>
1387   HTTP/1.1 clients and caches MUST treat other invalid date formats,
1388   especially including the value "0", as in the past (i.e., "already
1389   expired").
1390</t>
1391</section>
1392
1393<section anchor="header.pragma" title="Pragma">
1394   <iref item="Pragma header" primary="true"/>
1395   <iref item="Headers" primary="true" subitem="Pragma"/>
1396   
1397   
1398   
1399   
1400<t>
1401   The "Pragma" general-header field is used to include
1402   implementation-specific directives that might apply to any recipient along
1403   the request/response chain. All pragma directives specify optional behavior
1404   from the viewpoint of the protocol; however, some systems MAY require
1405   that behavior be consistent with the directives.
1406</t>
1407<figure><iref primary="true" item="Grammar" subitem="Pragma"/><iref primary="true" item="Grammar" subitem="Pragma-v"/><iref primary="true" item="Grammar" subitem="pragma-directive"/><iref primary="true" item="Grammar" subitem="extension-pragma"/><artwork type="abnf2616"><![CDATA[
1408  Pragma            = "Pragma" ":" OWS Pragma-v
1409  Pragma-v          = 1#pragma-directive
1410  pragma-directive  = "no-cache" / extension-pragma
1411  extension-pragma  = token [ "=" ( token / quoted-string ) ]
1412]]></artwork></figure>
1413<t>
1414   When the no-cache directive is present in a request message, an application
1415   SHOULD forward the request toward the origin server even if it has a
1416   cached copy of what is being requested. This pragma directive has the same
1417   semantics as the no-cache response directive (see <xref target="cache-response-directive"/>) and is defined here for backward
1418   compatibility with HTTP/1.0. Clients SHOULD include both header fields
1419   when a no-cache request is sent to a server not known to be HTTP/1.1
1420   compliant. HTTP/1.1 caches SHOULD treat "Pragma: no-cache" as if the
1421   client had sent "Cache-Control: no-cache".
1422</t>
1423<t><list>
1424   <t>
1425      Note: Because the meaning of "Pragma: no-cache" as a
1426      response-header field is not actually specified, it does not provide a
1427      reliable replacement for "Cache-Control: no-cache" in a response.
1428   </t>
1429</list></t>
1430<t>
1431   This mechanism is deprecated; no new Pragma directives will be defined in
1432   HTTP.
1433</t>
1434</section>
1435
1436<section anchor="header.vary" title="Vary">
1437   <iref item="Vary header" primary="true"/>
1438   <iref item="Headers" primary="true" subitem="Vary"/>
1439   
1440   
1441<t>
1442   The "Vary" response-header field conveys the set of request-header fields
1443   that were used to select the representation.
1444</t>
1445<t>
1446   Caches use this information, in part, to determine whether a stored
1447   response can be used to satisfy a given request; see <xref target="caching.negotiated.responses"/>. determines, while the response is
1448   fresh, whether a cache is permitted to use the response to reply to a
1449   subsequent request without validation; see <xref target="caching.negotiated.responses"/>.
1450</t>
1451<t>
1452   In uncacheable or stale responses, the Vary field value advises the user
1453   agent about the criteria that were used to select the representation.
1454</t>
1455<figure><iref primary="true" item="Grammar" subitem="Vary"/><iref primary="true" item="Grammar" subitem="Vary-v"/><artwork type="abnf2616"><![CDATA[
1456  Vary   = "Vary" ":" OWS Vary-v
1457  Vary-v = "*" / 1#field-name
1458]]></artwork></figure>
1459<t>
1460   The set of header fields named by the Vary field value is known as the
1461   selecting request-headers.
1462</t>
1463<t>
1464   Servers SHOULD include a Vary header field with any cacheable response
1465   that is subject to server-driven negotiation. Doing so allows a cache to
1466   properly interpret future requests on that resource and informs the user
1467   agent about the presence of negotiation on that resource. A server MAY
1468   include a Vary header field with a non-cacheable response that is subject
1469   to server-driven negotiation, since this might provide the user agent with
1470   useful information about the dimensions over which the response varies at
1471   the time of the response.
1472</t>
1473<t>
1474   A Vary field value of "*" signals that unspecified parameters not limited
1475   to the request-headers (e.g., the network address of the client), play a
1476   role in the selection of the response representation; therefore, a cache
1477   cannot determine whether this response is appropriate. The "*" value
1478   MUST NOT be generated by a proxy server.
1479</t>
1480<t>
1481   The field-names given are not limited to the set of standard request-header
1482   fields defined by this specification. Field names are case-insensitive.
1483</t>
1484</section>
1485
1486<section anchor="header.warning" title="Warning">
1487   <iref item="Warning header" primary="true"/>
1488   <iref item="Headers" primary="true" subitem="Warning"/>
1489   
1490   
1491   
1492   
1493   
1494   
1495   
1496<t>
1497   The "Warning" general-header field is used to carry additional information
1498   about the status or transformation of a message that might not be reflected
1499   in the message. This information is typically used to warn about possible
1500   incorrectness introduced by caching operations or transformations applied
1501   to the payload of the message.
1502</t>
1503<t>
1504   Warnings can be used for other purposes, both cache-related and otherwise.
1505   The use of a warning, rather than an error status code, distinguishes these
1506   responses from true failures.
1507</t>
1508<t>
1509   Warning headers can in general be applied to any message, however some
1510   warn-codes are specific to caches and can only be applied to response
1511   messages.
1512</t>
1513<figure><iref primary="true" item="Grammar" subitem="Warning"/><iref primary="true" item="Grammar" subitem="Warning-v"/><iref primary="true" item="Grammar" subitem="warning-value"/><iref primary="true" item="Grammar" subitem="warn-code"/><iref primary="true" item="Grammar" subitem="warn-agent"/><iref primary="true" item="Grammar" subitem="warn-text"/><iref primary="true" item="Grammar" subitem="warn-date"/><artwork type="abnf2616"><![CDATA[
1514  Warning    = "Warning" ":" OWS Warning-v
1515  Warning-v  = 1#warning-value
1516 
1517  warning-value = warn-code SP warn-agent SP warn-text
1518                                        [SP warn-date]
1519 
1520  warn-code  = 3DIGIT
1521  warn-agent = ( uri-host [ ":" port ] ) / pseudonym
1522                  ; the name or pseudonym of the server adding
1523                  ; the Warning header, for use in debugging
1524  warn-text  = quoted-string
1525  warn-date  = DQUOTE HTTP-date DQUOTE
1526]]></artwork></figure>
1527<t>
1528   Multiple warnings can be attached to a response (either by the origin
1529   server or by a cache), including multiple warnings with the same code
1530   number, only differing in warn-text.
1531</t>
1532<t>
1533   When this occurs, the user agent SHOULD inform the user of as many of
1534   them as possible, in the order that they appear in the response.
1535</t>
1536<t>
1537   Systems that generate multiple Warning headers SHOULD order them with
1538   this user agent behavior in mind. New Warning headers SHOULD be added
1539   after any existing Warning headers.
1540</t>
1541<t>
1542   Warnings are assigned three digit warn-codes. The first digit indicates
1543   whether the Warning is required to be deleted from a stored response after
1544   validation:
1545   <list style="symbols">
1546      <t>1xx Warnings describe the freshness or validation status of the
1547      response, and so MUST be deleted by caches after validation. They can
1548      only be generated by a cache when validating a cached entry, and
1549      MUST NOT be generated in any other situation.</t>
1550      <t>2xx Warnings describe some aspect of the representation that is not
1551      rectified by a validation (for example, a lossy compression of the
1552      representation) and MUST NOT be deleted by caches after validation,
1553      unless a full response is returned, in which case they MUST be.</t>
1554   </list>
1555</t>
1556<t>
1557   If an implementation sends a message with one or more Warning headers to a
1558   receiver whose version is HTTP/1.0 or lower, then the sender MUST include
1559   in each warning-value a warn-date that matches the Date header in the
1560   message.
1561</t>
1562<t>
1563   If an implementation receives a message with a warning-value that includes
1564   a warn-date, and that warn-date is different from the Date value in the
1565   response, then that warning-value MUST be deleted from the message before
1566   storing, forwarding, or using it. (preventing the consequences of naive
1567   caching of Warning header fields.) If all of the warning-values are deleted
1568   for this reason, the Warning header MUST be deleted as well.
1569</t>
1570<t>
1571   The following warn-codes are defined by this specification, each with a
1572   recommended warn-text in English, and a description of its meaning.
1573</t>
1574<t>
1575<?rfc needLines="4"?>
1576   110 Response is stale
1577   <list>
1578      <t>SHOULD be included whenever the returned response is stale.</t>
1579   </list>
1580</t>
1581<t>
1582<?rfc needLines="4"?>
1583   111 Revalidation failed
1584   <list>
1585      <t>SHOULD be included if a cache returns a stale response because an
1586      attempt to validate the response failed, due to an inability to reach
1587      the server.</t>
1588   </list>
1589</t>
1590<t>
1591<?rfc needLines="4"?>
1592   112 Disconnected operation
1593   <list>
1594      <t>SHOULD be included if the cache is intentionally disconnected from
1595      the rest of the network for a period of time.</t>
1596   </list>
1597</t>
1598<t>
1599<?rfc needLines="4"?>
1600   113 Heuristic expiration
1601   <list>
1602      <t>SHOULD be included if the cache heuristically chose a freshness
1603      lifetime greater than 24 hours and the response's age is greater than 24
1604      hours.</t>
1605   </list>
1606</t>
1607<t>
1608<?rfc needLines="4"?>
1609   199 Miscellaneous warning
1610   <list>
1611      <t>The warning text can include arbitrary information to be presented to
1612      a human user, or logged. A system receiving this warning MUST NOT take
1613      any automated action, besides presenting the warning to the user.</t>
1614   </list>
1615</t>
1616<t>
1617<?rfc needLines="4"?>
1618   214 Transformation applied
1619   <list>
1620      <t>MUST be added by an intermediate proxy if it applies any
1621      transformation to the representation, such as changing the
1622      content-coding, media-type, or modifying the representation data, unless
1623      this Warning code already appears in the response.</t>
1624   </list>
1625</t>
1626<t>
1627<?rfc needLines="4"?>
1628   299 Miscellaneous persistent warning
1629   <list>
1630      <t>The warning text can include arbitrary information to be presented to
1631      a human user, or logged. A system receiving this warning MUST NOT take
1632      any automated action.</t>
1633   </list>
1634</t>
1635</section>
1636
1637</section>
1638
1639<section anchor="history.lists" title="History Lists">
1640<t>
1641   User agents often have history mechanisms, such as "Back" buttons and
1642   history lists, that can be used to redisplay a representation retrieved
1643   earlier in a session.
1644</t>
1645<t>
1646   The freshness model (<xref target="expiration.model"/>) does not
1647   necessarily apply to history mechanisms. I.e., a history mechanism can
1648   display a previous representation even if it has expired.
1649</t>
1650<t>
1651   This does not prohibit the history mechanism from telling the user that a
1652   view might be stale, or from honoring cache directives (e.g.,
1653   Cache-Control: no-store).
1654</t>
1655</section>
1656
1657
1658<section anchor="IANA.considerations" title="IANA Considerations">
1659
1660<section title="Cache Directive Registry" anchor="cache.directive.registration">
1661<t>
1662   The registration procedure for HTTP Cache Directives is defined by <xref target="cache.control.extensions"/> of this document.
1663</t>
1664<t>
1665   The HTTP Cache Directive Registry shall be created at <eref target="http://www.iana.org/assignments/http-cache-directives"/> and be
1666   populated with the registrations below:
1667</t>
1668
1669<!--AUTOGENERATED FROM extract-cache-directives-defs.xslt, do not edit manually-->
1670<texttable align="left" suppress-title="true" anchor="iana.cache.directive.registration.table">
1671   <ttcol>Cache Directive</ttcol>
1672   <ttcol>Reference</ttcol>
1673
1674   <c>max-age</c>
1675   <c>
1676      <xref target="cache-request-directive"/>, <xref target="cache-response-directive"/>
1677   </c>
1678   <c>max-stale</c>
1679   <c>
1680      <xref target="cache-request-directive"/>
1681   </c>
1682   <c>min-fresh</c>
1683   <c>
1684      <xref target="cache-request-directive"/>
1685   </c>
1686   <c>must-revalidate</c>
1687   <c>
1688      <xref target="cache-response-directive"/>
1689   </c>
1690   <c>no-cache</c>
1691   <c>
1692      <xref target="cache-request-directive"/>, <xref target="cache-response-directive"/>
1693   </c>
1694   <c>no-store</c>
1695   <c>
1696      <xref target="cache-request-directive"/>, <xref target="cache-response-directive"/>
1697   </c>
1698   <c>no-transform</c>
1699   <c>
1700      <xref target="cache-request-directive"/>, <xref target="cache-response-directive"/>
1701   </c>
1702   <c>only-if-cached</c>
1703   <c>
1704      <xref target="cache-request-directive"/>
1705   </c>
1706   <c>private</c>
1707   <c>
1708      <xref target="cache-response-directive"/>
1709   </c>
1710   <c>proxy-revalidate</c>
1711   <c>
1712      <xref target="cache-response-directive"/>
1713   </c>
1714   <c>public</c>
1715   <c>
1716      <xref target="cache-response-directive"/>
1717   </c>
1718   <c>s-maxage</c>
1719   <c>
1720      <xref target="cache-response-directive"/>
1721   </c>
1722   <c>stale-if-error</c>
1723   <c>
1724      <xref target="RFC5861"/>, Section 4
1725   </c>
1726   <c>stale-while-revalidate</c>
1727   <c>
1728      <xref target="RFC5861"/>, Section 3
1729   </c>
1730</texttable>
1731<!--(END)-->
1732
1733</section>
1734
1735<section title="Header Field Registration" anchor="header.field.registration">
1736<t>
1737  The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/>
1738  shall be updated with the permanent registrations below (see <xref target="RFC3864"/>):
1739</t>
1740
1741<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1742<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1743   <ttcol>Header Field Name</ttcol>
1744   <ttcol>Protocol</ttcol>
1745   <ttcol>Status</ttcol>
1746   <ttcol>Reference</ttcol>
1747
1748   <c>Age</c>
1749   <c>http</c>
1750   <c>standard</c>
1751   <c>
1752      <xref target="header.age"/>
1753   </c>
1754   <c>Cache-Control</c>
1755   <c>http</c>
1756   <c>standard</c>
1757   <c>
1758      <xref target="header.cache-control"/>
1759   </c>
1760   <c>Expires</c>
1761   <c>http</c>
1762   <c>standard</c>
1763   <c>
1764      <xref target="header.expires"/>
1765   </c>
1766   <c>Pragma</c>
1767   <c>http</c>
1768   <c>standard</c>
1769   <c>
1770      <xref target="header.pragma"/>
1771   </c>
1772   <c>Vary</c>
1773   <c>http</c>
1774   <c>standard</c>
1775   <c>
1776      <xref target="header.vary"/>
1777   </c>
1778   <c>Warning</c>
1779   <c>http</c>
1780   <c>standard</c>
1781   <c>
1782      <xref target="header.warning"/>
1783   </c>
1784</texttable>
1785<!--(END)-->
1786
1787<t>
1788   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task
1789   Force".
1790</t>
1791</section>
1792
1793</section>
1794
1795<section anchor="security.considerations" title="Security Considerations">
1796<t>
1797   Caches expose additional potential vulnerabilities, since the contents of
1798   the cache represent an attractive target for malicious exploitation.
1799   Because cache contents persist after an HTTP request is complete, an attack
1800   on the cache can reveal information long after a user believes that the
1801   information has been removed from the network. Therefore, cache contents
1802   need to be protected as sensitive information.
1803</t>
1804</section>
1805
1806<section anchor="ack" title="Acknowledgments">
1807<t>
1808   Much of the content and presentation of the caching design is due to
1809   suggestions and comments from individuals including: Shel Kaphan, Paul
1810   Leach, Koen Holtman, David Morris, and Larry Masinter.
1811</t>
1812</section>
1813
1814</middle>
1815
1816<back>
1817<references title="Normative References">
1818
1819  <reference anchor="Part1">
1820    <front>
1821      <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1822      <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
1823        <organization abbrev="Day Software">Day Software</organization>
1824        <address><email>fielding@gbiv.com</email></address>
1825      </author>
1826      <author fullname="Jim Gettys" initials="J." surname="Gettys">
1827        <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1828        <address><email>jg@freedesktop.org</email></address>
1829      </author>
1830      <author fullname="Jeffrey C. Mogul" initials="J." surname="Mogul">
1831        <organization abbrev="HP">Hewlett-Packard Company</organization>
1832        <address><email>JeffMogul@acm.org</email></address>
1833      </author>
1834      <author fullname="Henrik Frystyk Nielsen" initials="H." surname="Frystyk">
1835        <organization abbrev="Microsoft">Microsoft Corporation</organization>
1836        <address><email>henrikn@microsoft.com</email></address>
1837      </author>
1838      <author fullname="Larry Masinter" initials="L." surname="Masinter">
1839        <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1840        <address><email>LMM@acm.org</email></address>
1841      </author>
1842      <author fullname="Paul J. Leach" initials="P." surname="Leach">
1843        <organization abbrev="Microsoft">Microsoft Corporation</organization>
1844        <address><email>paulle@microsoft.com</email></address>
1845      </author>
1846      <author fullname="Tim Berners-Lee" initials="T." surname="Berners-Lee">
1847        <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1848        <address><email>timbl@w3.org</email></address>
1849      </author>
1850      <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
1851        <organization abbrev="W3C">World Wide Web Consortium</organization>
1852        <address><email>ylafon@w3.org</email></address>
1853      </author>
1854      <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
1855        <organization abbrev="greenbytes">greenbytes GmbH</organization>
1856        <address><email>julian.reschke@greenbytes.de</email></address>
1857      </author>
1858      <date month="August" year="2010"/>
1859    </front>
1860    <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-11"/>
1861   
1862  </reference>
1863
1864  <reference anchor="Part2">
1865    <front>
1866      <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
1867      <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
1868        <organization abbrev="Day Software">Day Software</organization>
1869        <address><email>fielding@gbiv.com</email></address>
1870      </author>
1871      <author fullname="Jim Gettys" initials="J." surname="Gettys">
1872        <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1873        <address><email>jg@freedesktop.org</email></address>
1874      </author>
1875      <author fullname="Jeffrey C. Mogul" initials="J." surname="Mogul">
1876        <organization abbrev="HP">Hewlett-Packard Company</organization>
1877        <address><email>JeffMogul@acm.org</email></address>
1878      </author>
1879      <author fullname="Henrik Frystyk Nielsen" initials="H." surname="Frystyk">
1880        <organization abbrev="Microsoft">Microsoft Corporation</organization>
1881        <address><email>henrikn@microsoft.com</email></address>
1882      </author>
1883      <author fullname="Larry Masinter" initials="L." surname="Masinter">
1884        <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1885        <address><email>LMM@acm.org</email></address>
1886      </author>
1887      <author fullname="Paul J. Leach" initials="P." surname="Leach">
1888        <organization abbrev="Microsoft">Microsoft Corporation</organization>
1889        <address><email>paulle@microsoft.com</email></address>
1890      </author>
1891      <author fullname="Tim Berners-Lee" initials="T." surname="Berners-Lee">
1892        <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1893        <address><email>timbl@w3.org</email></address>
1894      </author>
1895      <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
1896        <organization abbrev="W3C">World Wide Web Consortium</organization>
1897        <address><email>ylafon@w3.org</email></address>
1898      </author>
1899      <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
1900        <organization abbrev="greenbytes">greenbytes GmbH</organization>
1901        <address><email>julian.reschke@greenbytes.de</email></address>
1902      </author>
1903      <date month="August" year="2010"/>
1904    </front>
1905    <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-11"/>
1906   
1907  </reference>
1908
1909  <reference anchor="Part4">
1910    <front>
1911      <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
1912      <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
1913        <organization abbrev="Day Software">Day Software</organization>
1914        <address><email>fielding@gbiv.com</email></address>
1915      </author>
1916      <author fullname="Jim Gettys" initials="J." surname="Gettys">
1917        <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1918        <address><email>jg@freedesktop.org</email></address>
1919      </author>
1920      <author fullname="Jeffrey C. Mogul" initials="J." surname="Mogul">
1921        <organization abbrev="HP">Hewlett-Packard Company</organization>
1922        <address><email>JeffMogul@acm.org</email></address>
1923      </author>
1924      <author fullname="Henrik Frystyk Nielsen" initials="H." surname="Frystyk">
1925        <organization abbrev="Microsoft">Microsoft Corporation</organization>
1926        <address><email>henrikn@microsoft.com</email></address>
1927      </author>
1928      <author fullname="Larry Masinter" initials="L." surname="Masinter">
1929        <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1930        <address><email>LMM@acm.org</email></address>
1931      </author>
1932      <author fullname="Paul J. Leach" initials="P." surname="Leach">
1933        <organization abbrev="Microsoft">Microsoft Corporation</organization>
1934        <address><email>paulle@microsoft.com</email></address>
1935      </author>
1936      <author fullname="Tim Berners-Lee" initials="T." surname="Berners-Lee">
1937        <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1938        <address><email>timbl@w3.org</email></address>
1939      </author>
1940      <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
1941        <organization abbrev="W3C">World Wide Web Consortium</organization>
1942        <address><email>ylafon@w3.org</email></address>
1943      </author>
1944      <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
1945        <organization abbrev="greenbytes">greenbytes GmbH</organization>
1946        <address><email>julian.reschke@greenbytes.de</email></address>
1947      </author>
1948      <date month="August" year="2010"/>
1949    </front>
1950    <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-11"/>
1951   
1952  </reference>
1953
1954  <reference anchor="Part5">
1955    <front>
1956      <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1957      <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
1958        <organization abbrev="Day Software">Day Software</organization>
1959        <address><email>fielding@gbiv.com</email></address>
1960      </author>
1961      <author fullname="Jim Gettys" initials="J." surname="Gettys">
1962        <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1963        <address><email>jg@freedesktop.org</email></address>
1964      </author>
1965      <author fullname="Jeffrey C. Mogul" initials="J." surname="Mogul">
1966        <organization abbrev="HP">Hewlett-Packard Company</organization>
1967        <address><email>JeffMogul@acm.org</email></address>
1968      </author>
1969      <author fullname="Henrik Frystyk Nielsen" initials="H." surname="Frystyk">
1970        <organization abbrev="Microsoft">Microsoft Corporation</organization>
1971        <address><email>henrikn@microsoft.com</email></address>
1972      </author>
1973      <author fullname="Larry Masinter" initials="L." surname="Masinter">
1974        <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
1975        <address><email>LMM@acm.org</email></address>
1976      </author>
1977      <author fullname="Paul J. Leach" initials="P." surname="Leach">
1978        <organization abbrev="Microsoft">Microsoft Corporation</organization>
1979        <address><email>paulle@microsoft.com</email></address>
1980      </author>
1981      <author fullname="Tim Berners-Lee" initials="T." surname="Berners-Lee">
1982        <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1983        <address><email>timbl@w3.org</email></address>
1984      </author>
1985      <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
1986        <organization abbrev="W3C">World Wide Web Consortium</organization>
1987        <address><email>ylafon@w3.org</email></address>
1988      </author>
1989      <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
1990        <organization abbrev="greenbytes">greenbytes GmbH</organization>
1991        <address><email>julian.reschke@greenbytes.de</email></address>
1992      </author>
1993      <date month="August" year="2010"/>
1994    </front>
1995    <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-11"/>
1996   
1997  </reference>
1998
1999  <reference anchor="Part7">
2000    <front>
2001      <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
2002      <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
2003        <organization abbrev="Day Software">Day Software</organization>
2004        <address><email>fielding@gbiv.com</email></address>
2005      </author>
2006      <author fullname="Jim Gettys" initials="J." surname="Gettys">
2007        <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
2008        <address><email>jg@freedesktop.org</email></address>
2009      </author>
2010      <author fullname="Jeffrey C. Mogul" initials="J." surname="Mogul">
2011        <organization abbrev="HP">Hewlett-Packard Company</organization>
2012        <address><email>JeffMogul@acm.org</email></address>
2013      </author>
2014      <author fullname="Henrik Frystyk Nielsen" initials="H." surname="Frystyk">
2015        <organization abbrev="Microsoft">Microsoft Corporation</organization>
2016        <address><email>henrikn@microsoft.com</email></address>
2017      </author>
2018      <author fullname="Larry Masinter" initials="L." surname="Masinter">
2019        <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
2020        <address><email>LMM@acm.org</email></address>
2021      </author>
2022      <author fullname="Paul J. Leach" initials="P." surname="Leach">
2023        <organization abbrev="Microsoft">Microsoft Corporation</organization>
2024        <address><email>paulle@microsoft.com</email></address>
2025      </author>
2026      <author fullname="Tim Berners-Lee" initials="T." surname="Berners-Lee">
2027        <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
2028        <address><email>timbl@w3.org</email></address>
2029      </author>
2030      <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
2031        <organization abbrev="W3C">World Wide Web Consortium</organization>
2032        <address><email>ylafon@w3.org</email></address>
2033      </author>
2034      <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
2035        <organization abbrev="greenbytes">greenbytes GmbH</organization>
2036        <address><email>julian.reschke@greenbytes.de</email></address>
2037      </author>
2038      <date month="August" year="2010"/>
2039    </front>
2040    <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-11"/>
2041   
2042  </reference>
2043
2044  <reference anchor="RFC2119">
2045    <front>
2046      <title>Key words for use in RFCs to Indicate Requirement Levels</title>
2047      <author fullname="Scott Bradner" initials="S." surname="Bradner">
2048        <organization>Harvard University</organization>
2049        <address><email>sob@harvard.edu</email></address>
2050      </author>
2051      <date month="March" year="1997"/>
2052    </front>
2053    <seriesInfo name="BCP" value="14"/>
2054    <seriesInfo name="RFC" value="2119"/>
2055  </reference>
2056
2057  <reference anchor="RFC5234">
2058    <front>
2059      <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
2060      <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
2061        <organization>Brandenburg InternetWorking</organization>
2062        <address>
2063          <email>dcrocker@bbiw.net</email>
2064        </address> 
2065      </author>
2066      <author initials="P." surname="Overell" fullname="Paul Overell">
2067        <organization>THUS plc.</organization>
2068        <address>
2069          <email>paul.overell@thus.net</email>
2070        </address>
2071      </author>
2072      <date month="January" year="2008"/>
2073    </front>
2074    <seriesInfo name="STD" value="68"/>
2075    <seriesInfo name="RFC" value="5234"/>
2076  </reference>
2077 
2078</references>
2079
2080<references title="Informative References">
2081
2082  <reference anchor="RFC1305">
2083    <front>
2084      <title>Network Time Protocol (Version 3) Specification, Implementation</title>
2085      <author fullname="David L. Mills" initials="D." surname="Mills">
2086        <organization>University of Delaware, Electrical Engineering Department</organization>
2087        <address><email>mills@udel.edu</email></address>
2088      </author>
2089      <date month="March" year="1992"/>
2090    </front>
2091    <seriesInfo name="RFC" value="1305"/>
2092  </reference>
2093
2094  <reference anchor="RFC2616">
2095    <front>
2096      <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
2097      <author fullname="R. Fielding" initials="R." surname="Fielding">
2098        <organization>University of California, Irvine</organization>
2099        <address><email>fielding@ics.uci.edu</email></address>
2100      </author>
2101      <author fullname="J. Gettys" initials="J." surname="Gettys">
2102        <organization>W3C</organization>
2103        <address><email>jg@w3.org</email></address>
2104      </author>
2105      <author fullname="J. Mogul" initials="J." surname="Mogul">
2106        <organization>Compaq Computer Corporation</organization>
2107        <address><email>mogul@wrl.dec.com</email></address>
2108      </author>
2109      <author fullname="H. Frystyk" initials="H." surname="Frystyk">
2110        <organization>MIT Laboratory for Computer Science</organization>
2111        <address><email>frystyk@w3.org</email></address>
2112      </author>
2113      <author fullname="L. Masinter" initials="L." surname="Masinter">
2114        <organization>Xerox Corporation</organization>
2115        <address><email>masinter@parc.xerox.com</email></address>
2116      </author>
2117      <author fullname="P. Leach" initials="P." surname="Leach">
2118        <organization>Microsoft Corporation</organization>
2119        <address><email>paulle@microsoft.com</email></address>
2120      </author>
2121      <author fullname="T. Berners-Lee" initials="T." surname="Berners-Lee">
2122        <organization>W3C</organization>
2123        <address><email>timbl@w3.org</email></address>
2124      </author>
2125      <date month="June" year="1999"/>
2126    </front>
2127    <seriesInfo name="RFC" value="2616"/>
2128  </reference>
2129
2130  <reference anchor="RFC3864">
2131    <front>
2132      <title>Registration Procedures for Message Header Fields</title>
2133      <author fullname="G. Klyne" initials="G." surname="Klyne">
2134        <organization>Nine by Nine</organization>
2135        <address><email>GK-IETF@ninebynine.org</email></address>
2136      </author>
2137      <author fullname="M. Nottingham" initials="M." surname="Nottingham">
2138        <organization>BEA Systems</organization>
2139        <address><email>mnot@pobox.com</email></address>
2140      </author>
2141      <author fullname="J. Mogul" initials="J." surname="Mogul">
2142        <organization>HP Labs</organization>
2143        <address><email>JeffMogul@acm.org</email></address>
2144      </author>
2145      <date month="September" year="2004"/>
2146    </front>
2147    <seriesInfo name="BCP" value="90"/>
2148    <seriesInfo name="RFC" value="3864"/>
2149  </reference>
2150
2151  <reference anchor="RFC5226">
2152    <front>
2153      <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
2154      <author initials="T." surname="Narten" fullname="T. Narten">
2155        <organization>IBM</organization>
2156        <address><email>narten@us.ibm.com</email></address>
2157      </author>
2158      <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
2159        <organization>Google</organization>
2160        <address><email>Harald@Alvestrand.no</email></address>
2161      </author>
2162      <date year="2008" month="May"/>
2163    </front>
2164    <seriesInfo name="BCP" value="26"/>
2165    <seriesInfo name="RFC" value="5226"/>
2166  </reference>
2167
2168  <reference anchor="RFC5861">
2169    <front>
2170      <title abbrev="HTTP stale controls">HTTP Cache-Control Extensions for Stale Content</title>
2171      <author initials="M." surname="Nottingham" fullname="Mark Nottingham">
2172        <organization>Yahoo! Inc.</organization>
2173        <address><email>mnot@yahoo-inc.com</email></address>
2174      </author>
2175      <date month="April" year="2010"/>
2176    </front>
2177    <seriesInfo name="RFC" value="5861"/>
2178  </reference>
2179
2180</references>
2181
2182<section anchor="changes.from.rfc.2616" title="Changes from RFC 2616">
2183<t>
2184  Make the specified age calculation algorithm less conservative.
2185  (<xref target="age.calculations"/>)
2186</t>
2187<t>
2188  Remove requirement to consider Content-Location in successful responses
2189  in order to determine the appropriate response to use.
2190  (<xref target="validation.model"/>)
2191</t>
2192<t>
2193  Clarify denial of service attack avoidance requirement.
2194  (<xref target="invalidation.after.updates.or.deletions"/>)
2195</t>
2196<t>
2197  Do not mention RFC 2047 encoding and multiple languages in Warning headers
2198  anymore, as these aspects never were implemented.
2199  (<xref target="header.warning"/>)
2200</t>
2201</section>
2202
2203
2204<section title="Collected ABNF" anchor="collected.abnf">
2205<figure>
2206<artwork type="abnf" name="p6-cache.parsed-abnf"><![CDATA[
2207Age = "Age:" OWS Age-v
2208Age-v = delta-seconds
2209
2210Cache-Control = "Cache-Control:" OWS Cache-Control-v
2211Cache-Control-v = *( "," OWS ) cache-directive *( OWS "," [ OWS
2212 cache-directive ] )
2213
2214Expires = "Expires:" OWS Expires-v
2215Expires-v = HTTP-date
2216
2217HTTP-date = <HTTP-date, defined in [Part1], Section 6.1>
2218
2219OWS = <OWS, defined in [Part1], Section 1.2.2>
2220
2221Pragma = "Pragma:" OWS Pragma-v
2222Pragma-v = *( "," OWS ) pragma-directive *( OWS "," [ OWS
2223 pragma-directive ] )
2224
2225Vary = "Vary:" OWS Vary-v
2226Vary-v = "*" / ( *( "," OWS ) field-name *( OWS "," [ OWS field-name
2227 ] ) )
2228
2229Warning = "Warning:" OWS Warning-v
2230Warning-v = *( "," OWS ) warning-value *( OWS "," [ OWS warning-value
2231 ] )
2232
2233cache-directive = cache-request-directive / cache-response-directive
2234cache-extension = token [ "=" ( token / quoted-string ) ]
2235cache-request-directive = "no-cache" / "no-store" / ( "max-age="
2236 delta-seconds ) / ( "max-stale" [ "=" delta-seconds ] ) / (
2237 "min-fresh=" delta-seconds ) / "no-transform" / "only-if-cached" /
2238 cache-extension
2239cache-response-directive = "public" / ( "private" [ "=" DQUOTE *( ","
2240 OWS ) field-name *( OWS "," [ OWS field-name ] ) DQUOTE ] ) / (
2241 "no-cache" [ "=" DQUOTE *( "," OWS ) field-name *( OWS "," [ OWS
2242 field-name ] ) DQUOTE ] ) / "no-store" / "no-transform" /
2243 "must-revalidate" / "proxy-revalidate" / ( "max-age=" delta-seconds
2244 ) / ( "s-maxage=" delta-seconds ) / cache-extension
2245
2246delta-seconds = 1*DIGIT
2247
2248extension-pragma = token [ "=" ( token / quoted-string ) ]
2249
2250field-name = <field-name, defined in [Part1], Section 3.2>
2251
2252port = <port, defined in [Part1], Section 2.6>
2253pragma-directive = "no-cache" / extension-pragma
2254pseudonym = <pseudonym, defined in [Part1], Section 9.9>
2255
2256quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>
2257
2258token = <token, defined in [Part1], Section 1.2.2>
2259
2260uri-host = <uri-host, defined in [Part1], Section 2.6>
2261
2262warn-agent = ( uri-host [ ":" port ] ) / pseudonym
2263warn-code = 3DIGIT
2264warn-date = DQUOTE HTTP-date DQUOTE
2265warn-text = quoted-string
2266warning-value = warn-code SP warn-agent SP warn-text [ SP warn-date
2267 ]
2268]]></artwork>
2269</figure>
2270<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
2271; Age defined but not used
2272; Cache-Control defined but not used
2273; Expires defined but not used
2274; Pragma defined but not used
2275; Vary defined but not used
2276; Warning defined but not used
2277]]></artwork></figure></section>
2278
2279
2280<section anchor="change.log" title="Change Log (to be removed by RFC Editor before publication)">
2281
2282<section title="Since RFC2616">
2283  <t>Extracted relevant partitions from <xref target="RFC2616"/>.</t>
2284</section>
2285
2286<section title="Since draft-ietf-httpbis-p6-cache-00">
2287<t>
2288  Closed issues:
2289  <list style="symbols">
2290    <t>
2291      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/9"/>: "Trailer" (<eref target="http://purl.org/NET/http-errata#trailer-hop"/>)</t>
2292    <t>
2293      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/12"/>: "Invalidation after Update or Delete" (<eref target="http://purl.org/NET/http-errata#invalidupd"/>)</t>
2294    <t>
2295      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>: "Normative and Informative references"</t>
2296    <t>
2297      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>: "Date reference typo"</t>
2298    <t>
2299      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/49"/>: "Connection header text"</t>
2300    <t>
2301      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>: "Informative references"</t>
2302    <t>
2303      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>: "ISO-8859-1 Reference"</t>
2304    <t>
2305      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>: "Normative up-to-date references"</t>
2306    <t>
2307      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/87"/>: "typo in 13.2.2"</t>
2308  </list>
2309</t>
2310<t>
2311  Other changes:
2312  <list style="symbols">
2313    <t>Use names of RFC4234 core rules DQUOTE and HTAB (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)</t>
2314  </list>
2315</t>
2316</section>
2317
2318<section title="Since draft-ietf-httpbis-p6-cache-01">
2319<t>
2320  Closed issues:
2321  <list style="symbols">
2322    <t>
2323      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>: "rel_path not used"</t>
2324  </list>
2325</t>
2326<t>
2327  Other changes:
2328  <list style="symbols">
2329    <t>Get rid of duplicate BNF rule names ("host" -&gt; "uri-host") (work in progress
2330      on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)</t>
2331    <t>Add explicit references to BNF syntax and rules imported from other parts of the
2332      specification.</t>
2333  </list>
2334</t>
2335</section>
2336
2337<section anchor="changes.since.02" title="Since draft-ietf-httpbis-p6-cache-02">
2338<t>
2339  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
2340  <list style="symbols">
2341    <t>Reference RFC 3984, and update header registrations for headers defined in this
2342      document.</t>
2343  </list>
2344</t>
2345</section>
2346
2347<section anchor="changes.since.03" title="Since draft-ietf-httpbis-p6-cache-03">
2348<t>
2349  Closed issues:
2350  <list style="symbols">
2351    <t>
2352      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/106"/>: "Vary header classification"</t>
2353  </list>
2354</t>
2355</section>
2356
2357<section anchor="changes.since.04" title="Since draft-ietf-httpbis-p6-cache-04">
2358<t>
2359  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2360  <list style="symbols"> 
2361    <t>
2362      Use "/" instead of "|" for alternatives.
2363    </t>
2364    <t>
2365      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
2366      whitespace ("OWS") and required whitespace ("RWS").
2367    </t>
2368    <t>
2369      Rewrite ABNFs to spell out whitespace rules, factor out
2370      header value format definitions.
2371    </t>
2372  </list>
2373</t>
2374</section>
2375
2376<section anchor="changes.since.05" title="Since draft-ietf-httpbis-p6-cache-05">
2377<t>
2378  This is a total rewrite of this part of the specification.
2379</t>
2380<t>
2381  Affected issues:
2382  <list style="symbols">
2383    <t>
2384      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/54"/>: "Definition of 1xx Warn-Codes"</t>
2385    <t>
2386      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>: "Placement of 13.5.1 and 13.5.2"</t>
2387    <t>
2388      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/138"/>: "The role of Warning and Semantic Transparency in Caching"</t>
2389    <t>
2390      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>: "Methods and Caching"</t>
2391  </list>
2392</t>
2393<t>
2394  In addition: Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
2395  <list style="symbols"> 
2396    <t>
2397      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
2398    </t>
2399  </list>
2400</t>
2401</section>
2402
2403<section anchor="changes.since.06" title="Since draft-ietf-httpbis-p6-cache-06">
2404<t>
2405  Closed issues:
2406  <list style="symbols"> 
2407    <t>
2408      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
2409      "base for numeric protocol elements"
2410    </t>
2411  </list>
2412</t>
2413<t>
2414  Affected issues:
2415  <list style="symbols">
2416    <t>
2417      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/37"/>:
2418      Vary and non-existant headers
2419    </t>
2420  </list>
2421</t>
2422</section>
2423
2424<section anchor="changes.since.07" title="Since draft-ietf-httpbis-p6-cache-07">
2425<t>
2426  Closed issues:
2427  <list style="symbols"> 
2428    <t>
2429      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/54"/>:
2430      "Definition of 1xx Warn-Codes"
2431    </t>
2432    <t>
2433      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/167"/>:
2434      "Content-Location on 304 responses"
2435    </t>
2436    <t>
2437      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/169"/>:
2438      "private and no-cache CC directives with headers"
2439    </t>
2440    <t>
2441      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/187"/>:
2442      "RFC2047 and warn-text"
2443    </t>
2444  </list>
2445</t>
2446</section>
2447
2448<section anchor="changes.since.08" title="Since draft-ietf-httpbis-p6-cache-08">
2449<t>
2450  Closed issues:
2451  <list style="symbols"> 
2452    <t>
2453      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/147"/>:
2454      "serving negotiated responses from cache: header-specific canonicalization"
2455    </t>
2456    <t>
2457      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/197"/>:
2458      "Effect of CC directives on history lists"
2459    </t>
2460  </list>
2461</t>
2462<t>
2463  Affected issues:
2464  <list style="symbols">
2465    <t>
2466      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
2467      Status codes and caching
2468    </t>
2469  </list>
2470</t>
2471<t>
2472  Partly resolved issues:
2473  <list style="symbols"> 
2474    <t>
2475      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
2476      "Placement of 13.5.1 and 13.5.2"
2477    </t>
2478  </list>
2479</t>
2480</section>
2481
2482<section title="Since draft-ietf-httpbis-p6-cache-09" anchor="changes.since.09">
2483<t>
2484  Closed issues:
2485  <list style="symbols"> 
2486    <t>
2487      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/29"/>:
2488      "Age calculation"
2489    </t>
2490    <t>
2491      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/168"/>:
2492      "Clarify differences between / requirements for request and response CC directives"
2493    </t>
2494        <t>
2495                <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/174"/>:
2496                "Caching authenticated responses"
2497        </t>
2498    <t>
2499      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/208"/>:
2500      "IANA registry for cache-control directives"
2501    </t>
2502    <t>
2503      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/211"/>:
2504      "Heuristic caching of URLs with query components"
2505    </t>
2506  </list>
2507</t>
2508<t>
2509  Partly resolved issues:
2510  <list style="symbols"> 
2511    <t>
2512      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
2513      "Term for the requested resource's URI"
2514    </t>
2515  </list>
2516</t>
2517</section>
2518
2519<section title="Since draft-ietf-httpbis-p6-cache-10" anchor="changes.since.10">
2520<t>
2521  Closed issues:
2522  <list style="symbols"> 
2523    <t>
2524      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
2525      "Clarify entity / representation / variant terminology"
2526    </t>
2527    <t>
2528      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
2529      "consider removing the 'changes from 2068' sections"
2530    </t>
2531    <t>
2532      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/223"/>:
2533      "Allowing heuristic caching for new status codes"
2534    </t>
2535    <t>
2536      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/223"/>:
2537      "Allowing heuristic caching for new status codes"
2538    </t>
2539    <t>
2540      Clean up TODOs and prose in "Combining Responses."
2541    </t>
2542  </list>
2543</t>
2544</section>
2545
2546</section>
2547  </back>
2548</rfc>
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