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4HTTPbis Working Group                                   R. Fielding, Ed.
5Internet-Draft                                              Day Software
6Obsoletes: 2616 (if approved)                                  J. Gettys
7Intended status: Standards Track                          Alcatel-Lucent
8Expires: January 13, 2011                                       J. Mogul
9                                                                      HP
10                                                              H. Frystyk
11                                                               Microsoft
12                                                             L. Masinter
13                                                           Adobe Systems
14                                                                P. Leach
15                                                               Microsoft
16                                                          T. Berners-Lee
17                                                                 W3C/MIT
18                                                           Y. Lafon, Ed.
19                                                                     W3C
20                                                         J. Reschke, Ed.
21                                                              greenbytes
22                                                           July 12, 2010
23
24
25                 HTTP/1.1, part 4: Conditional Requests
26                  draft-ietf-httpbis-p4-conditional-10
27
28Abstract
29
30   The Hypertext Transfer Protocol (HTTP) is an application-level
31   protocol for distributed, collaborative, hypermedia information
32   systems.  HTTP has been in use by the World Wide Web global
33   information initiative since 1990.  This document is Part 4 of the
34   seven-part specification that defines the protocol referred to as
35   "HTTP/1.1" and, taken together, obsoletes RFC 2616.  Part 4 defines
36   request header fields for indicating conditional requests and the
37   rules for constructing responses to those requests.
38
39Editorial Note (To be removed by RFC Editor)
40
41   Discussion of this draft should take place on the HTTPBIS working
42   group mailing list (ietf-http-wg@w3.org).  The current issues list is
43   at <http://tools.ietf.org/wg/httpbis/trac/report/3> and related
44   documents (including fancy diffs) can be found at
45   <http://tools.ietf.org/wg/httpbis/>.
46
47   The changes in this draft are summarized in Appendix C.11.
48
49Status of This Memo
50
51   This Internet-Draft is submitted in full conformance with the
52
53
54
55Fielding, et al.        Expires January 13, 2011                [Page 1]
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57Internet-Draft              HTTP/1.1, Part 4                   July 2010
58
59
60   provisions of BCP 78 and BCP 79.
61
62   Internet-Drafts are working documents of the Internet Engineering
63   Task Force (IETF).  Note that other groups may also distribute
64   working documents as Internet-Drafts.  The list of current Internet-
65   Drafts is at http://datatracker.ietf.org/drafts/current/.
66
67   Internet-Drafts are draft documents valid for a maximum of six months
68   and may be updated, replaced, or obsoleted by other documents at any
69   time.  It is inappropriate to use Internet-Drafts as reference
70   material or to cite them other than as "work in progress."
71
72   This Internet-Draft will expire on January 13, 2011.
73
74Copyright Notice
75
76   Copyright (c) 2010 IETF Trust and the persons identified as the
77   document authors.  All rights reserved.
78
79   This document is subject to BCP 78 and the IETF Trust's Legal
80   Provisions Relating to IETF Documents
81   (http://trustee.ietf.org/license-info) in effect on the date of
82   publication of this document.  Please review these documents
83   carefully, as they describe your rights and restrictions with respect
84   to this document.  Code Components extracted from this document must
85   include Simplified BSD License text as described in Section 4.e of
86   the Trust Legal Provisions and are provided without warranty as
87   described in the Simplified BSD License.
88
89   This document may contain material from IETF Documents or IETF
90   Contributions published or made publicly available before November
91   10, 2008.  The person(s) controlling the copyright in some of this
92   material may not have granted the IETF Trust the right to allow
93   modifications of such material outside the IETF Standards Process.
94   Without obtaining an adequate license from the person(s) controlling
95   the copyright in such materials, this document may not be modified
96   outside the IETF Standards Process, and derivative works of it may
97   not be created outside the IETF Standards Process, except to format
98   it for publication as an RFC or to translate it into languages other
99   than English.
100
101
102
103
104
105
106
107
108
109
110
111Fielding, et al.        Expires January 13, 2011                [Page 2]
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113Internet-Draft              HTTP/1.1, Part 4                   July 2010
114
115
116Table of Contents
117
118   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
119     1.1.  Requirements . . . . . . . . . . . . . . . . . . . . . . .  4
120     1.2.  Syntax Notation  . . . . . . . . . . . . . . . . . . . . .  4
121       1.2.1.  Core Rules . . . . . . . . . . . . . . . . . . . . . .  5
122       1.2.2.  ABNF Rules defined in other Parts of the
123               Specification  . . . . . . . . . . . . . . . . . . . .  5
124   2.  Entity Tags  . . . . . . . . . . . . . . . . . . . . . . . . .  5
125     2.1.  Example: Entity Tags varying on Content-Negotiated
126           Resources  . . . . . . . . . . . . . . . . . . . . . . . .  6
127   3.  Status Code Definitions  . . . . . . . . . . . . . . . . . . .  7
128     3.1.  304 Not Modified . . . . . . . . . . . . . . . . . . . . .  7
129     3.2.  412 Precondition Failed  . . . . . . . . . . . . . . . . .  8
130   4.  Weak and Strong Validators . . . . . . . . . . . . . . . . . .  8
131   5.  Rules for When to Use Entity Tags and Last-Modified Dates  . . 11
132   6.  Header Field Definitions . . . . . . . . . . . . . . . . . . . 12
133     6.1.  ETag . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
134     6.2.  If-Match . . . . . . . . . . . . . . . . . . . . . . . . . 13
135     6.3.  If-Modified-Since  . . . . . . . . . . . . . . . . . . . . 14
136     6.4.  If-None-Match  . . . . . . . . . . . . . . . . . . . . . . 16
137     6.5.  If-Unmodified-Since  . . . . . . . . . . . . . . . . . . . 17
138     6.6.  Last-Modified  . . . . . . . . . . . . . . . . . . . . . . 18
139   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 19
140     7.1.  Status Code Registration . . . . . . . . . . . . . . . . . 19
141     7.2.  Message Header Registration  . . . . . . . . . . . . . . . 19
142   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
143   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 19
144   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
145     10.1. Normative References . . . . . . . . . . . . . . . . . . . 19
146     10.2. Informative References . . . . . . . . . . . . . . . . . . 20
147   Appendix A.  Compatibility with Previous Versions  . . . . . . . . 20
148     A.1.  Changes from RFC 2616  . . . . . . . . . . . . . . . . . . 20
149   Appendix B.  Collected ABNF  . . . . . . . . . . . . . . . . . . . 21
150   Appendix C.  Change Log (to be removed by RFC Editor before
151                publication)  . . . . . . . . . . . . . . . . . . . . 21
152     C.1.  Since RFC2616  . . . . . . . . . . . . . . . . . . . . . . 21
153     C.2.  Since draft-ietf-httpbis-p4-conditional-00 . . . . . . . . 22
154     C.3.  Since draft-ietf-httpbis-p4-conditional-01 . . . . . . . . 22
155     C.4.  Since draft-ietf-httpbis-p4-conditional-02 . . . . . . . . 22
156     C.5.  Since draft-ietf-httpbis-p4-conditional-03 . . . . . . . . 22
157     C.6.  Since draft-ietf-httpbis-p4-conditional-04 . . . . . . . . 23
158     C.7.  Since draft-ietf-httpbis-p4-conditional-05 . . . . . . . . 23
159     C.8.  Since draft-ietf-httpbis-p4-conditional-06 . . . . . . . . 23
160     C.9.  Since draft-ietf-httpbis-p4-conditional-07 . . . . . . . . 23
161     C.10. Since draft-ietf-httpbis-p4-conditional-08 . . . . . . . . 23
162     C.11. Since draft-ietf-httpbis-p4-conditional-09 . . . . . . . . 23
163   Index  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
164
165
166
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169Internet-Draft              HTTP/1.1, Part 4                   July 2010
170
171
1721.  Introduction
173
174   This document defines HTTP/1.1 response metadata for indicating
175   potential changes to payload content, including modification time
176   stamps and opaque entity-tags, and the HTTP conditional request
177   mechanisms that allow preconditions to be placed on a request method.
178   Conditional GET requests allow for efficient cache updates.  Other
179   conditional request methods are used to protect against overwriting
180   or misunderstanding the state of a resource that has been changed
181   unbeknownst to the requesting client.
182
183   This document is currently disorganized in order to minimize the
184   changes between drafts and enable reviewers to see the smaller errata
185   changes.  The next draft will reorganize the sections to better
186   reflect the content.  In particular, the sections on resource
187   metadata will be discussed first and then followed by each
188   conditional request-header, concluding with a definition of
189   precedence and the expectation of ordering strong validator checks
190   before weak validator checks.  It is likely that more content from
191   [Part6] will migrate to this part, where appropriate.  The current
192   mess reflects how widely dispersed these topics and associated
193   requirements had become in [RFC2616].
194
1951.1.  Requirements
196
197   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
198   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
199   document are to be interpreted as described in [RFC2119].
200
201   An implementation is not compliant if it fails to satisfy one or more
202   of the "MUST" or "REQUIRED" level requirements for the protocols it
203   implements.  An implementation that satisfies all the "MUST" or
204   "REQUIRED" level and all the "SHOULD" level requirements for its
205   protocols is said to be "unconditionally compliant"; one that
206   satisfies all the "MUST" level requirements but not all the "SHOULD"
207   level requirements for its protocols is said to be "conditionally
208   compliant".
209
2101.2.  Syntax Notation
211
212   This specification uses the ABNF syntax defined in Section 1.2 of
213   [Part1] (which extends the syntax defined in [RFC5234] with a list
214   rule).  Appendix B shows the collected ABNF, with the list rule
215   expanded.
216
217   The following core rules are included by reference, as defined in
218   [RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF
219   (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),
220
221
222
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227
228   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit
229   sequence of data), SP (space), VCHAR (any visible USASCII character),
230   and WSP (whitespace).
231
2321.2.1.  Core Rules
233
234   The core rules below are defined in Section 1.2.2 of [Part1]:
235
236     quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>
237     OWS           = <OWS, defined in [Part1], Section 1.2.2>
238
2391.2.2.  ABNF Rules defined in other Parts of the Specification
240
241   The ABNF rules below are defined in other parts:
242
243     HTTP-date     = <HTTP-date, defined in [Part1], Section 6.1>
244
2452.  Entity Tags
246
247   Entity tags are used for comparing two or more entities from the same
248   requested resource.  HTTP/1.1 uses entity tags in the ETag
249   (Section 6.1), If-Match (Section 6.2), If-None-Match (Section 6.4),
250   and If-Range (Section 5.3 of [Part5]) header fields.  The definition
251   of how they are used and compared as cache validators is in
252   Section 4.  An entity tag consists of an opaque quoted string,
253   possibly prefixed by a weakness indicator.
254
255     entity-tag = [ weak ] opaque-tag
256     weak       = %x57.2F ; "W/", case-sensitive
257     opaque-tag = quoted-string
258
259   A "strong entity tag" MAY be shared by two entities of a resource
260   only if they are equivalent by octet equality.
261
262   A "weak entity tag," indicated by the "W/" prefix, MAY be shared by
263   two entities of a resource only if the entities are equivalent and
264   could be substituted for each other with no significant change in
265   semantics.  A weak entity tag can only be used for weak comparison.
266
267   An entity tag MUST be unique across all versions of all entities
268   associated with a particular resource.  A given entity tag value MAY
269   be used for entities obtained by requests on different URIs.  The use
270   of the same entity tag value in conjunction with entities obtained by
271   requests on different URIs does not imply the equivalence of those
272   entities.
273
274
275
276
277
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283
2842.1.  Example: Entity Tags varying on Content-Negotiated Resources
285
286   Consider a resource that is subject to content negotiation (Section 4
287   of [Part3]), and where the representations returned upon a GET
288   request vary based on the Accept-Encoding request header field
289   (Section 5.3 of [Part3]):
290
291   >> Request:
292
293     GET /index HTTP/1.1
294     Host: www.example.com
295     Accept-Encoding: gzip
296
297
298   In this case, the response may use the gzip Content Coding or not.
299   If it does, it might look like that:
300
301   >> Response:
302
303     HTTP/1.1 200 OK
304     Date: Thu, 26 Mar 2010 00:05:00 GMT
305     ETag: "123-a"
306     Content-Length: 70
307     Vary: Accept-Encoding
308     Content-Type: text/plain
309
310     Hello World!
311     Hello World!
312     Hello World!
313     Hello World!
314     Hello World!
315
316   A variant that does use gzip Content Coding would be:
317
318   >> Response:
319
320     HTTP/1.1 200 OK
321     Date: Thu, 26 Mar 2010 00:05:00 GMT
322     ETag: "123-b"
323     Content-Length: 43
324     Vary: Accept-Encoding
325     Content-Type: text/plain
326     Content-Encoding: gzip
327
328     ...binary data...
329
330
331
332
333
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339
340      Note: Content Codings are a property of the response entity, thus
341      affect the Entity Tag. An alternative are Transfer Codings
342      (Section 6.2 of [Part1]) which apply only to the transfer of the
343      message, and thus do not require assigning distinct entity tags.
344
3453.  Status Code Definitions
346
3473.1.  304 Not Modified
348
349   If the client has performed a conditional GET request and access is
350   allowed, but the document has not been modified, the server SHOULD
351   respond with this status code.  The 304 response MUST NOT contain a
352   message-body, and thus is always terminated by the first empty line
353   after the header fields.
354
355   The response MUST include the following header fields:
356
357   o  Date, unless its omission is required by Section 9.3.1 of [Part1].
358
359      If a clockless origin server obeys these rules, and proxies and
360      clients add their own Date to any response received without one
361      (as already specified by Section 9.3 of [Part1], caches will
362      operate correctly.
363
364   o  ETag and/or Content-Location, if the header would have been sent
365      in a 200 response to the same request.
366
367   o  Expires, Cache-Control, and/or Vary, if the field-value might
368      differ from that sent in any previous response for the same
369      variant.
370
371   If the conditional GET used a strong cache validator (see Section 4),
372   the response SHOULD NOT include other entity-headers.  Otherwise
373   (i.e., the conditional GET used a weak validator), the response MUST
374   NOT include other entity-headers; this prevents inconsistencies
375   between cached entity-bodies and updated headers.
376
377   If a 304 response indicates an entity not currently cached, then the
378   cache MUST disregard the response and repeat the request without the
379   conditional.
380
381   If a cache uses a received 304 response to update a cache entry, the
382   cache MUST update the entry to reflect any new field values given in
383   the response.
384
385
386
387
388
389
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395
3963.2.  412 Precondition Failed
397
398   The precondition given in one or more of the request-header fields
399   evaluated to false when it was tested on the server.  This response
400   code allows the client to place preconditions on the current resource
401   metainformation (header field data) and thus prevent the requested
402   method from being applied to a resource other than the one intended.
403
4044.  Weak and Strong Validators
405
406   Since both origin servers and caches will compare two validators to
407   decide if they represent the same or different entities, one normally
408   would expect that if the entity (the entity-body or any entity-
409   headers) changes in any way, then the associated validator would
410   change as well.  If this is true, then we call this validator a
411   "strong validator."
412
413   However, there might be cases when a server prefers to change the
414   validator only on semantically significant changes, and not when
415   insignificant aspects of the entity change.  A validator that does
416   not always change when the resource changes is a "weak validator."
417
418   Entity tags are normally "strong validators," but the protocol
419   provides a mechanism to tag an entity tag as "weak."  One can think
420   of a strong validator as one that changes whenever the bits of an
421   entity changes, while a weak value changes whenever the meaning of an
422   entity changes.  Alternatively, one can think of a strong validator
423   as part of an identifier for a specific entity, while a weak
424   validator is part of an identifier for a set of semantically
425   equivalent entities.
426
427      Note: One example of a strong validator is an integer that is
428      incremented in stable storage every time an entity is changed.
429
430      An entity's modification time, if represented with one-second
431      resolution, could be a weak validator, since it is possible that
432      the resource might be modified twice during a single second.
433
434      Support for weak validators is optional.  However, weak validators
435      allow for more efficient caching of equivalent objects; for
436      example, a hit counter on a site is probably good enough if it is
437      updated every few days or weeks, and any value during that period
438      is likely "good enough" to be equivalent.
439
440   A "use" of a validator is either when a client generates a request
441   and includes the validator in a validating header field, or when a
442   server compares two validators.
443
444
445
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451
452   Strong validators are usable in any context.  Weak validators are
453   only usable in contexts that do not depend on exact equality of an
454   entity.  For example, either kind is usable for a conditional GET of
455   a full entity.  However, only a strong validator is usable for a sub-
456   range retrieval, since otherwise the client might end up with an
457   internally inconsistent entity.
458
459   Clients MUST NOT use weak validators in range requests ([Part5]).
460
461   The only function that HTTP/1.1 defines on validators is comparison.
462   There are two validator comparison functions, depending on whether
463   the comparison context allows the use of weak validators or not:
464
465   o  The strong comparison function: in order to be considered equal,
466      both opaque-tags MUST be identical character-by-character, and
467      both MUST NOT be weak.
468
469   o  The weak comparison function: in order to be considered equal,
470      both opaque-tags MUST be identical character-by-character, but
471      either or both of them MAY be tagged as "weak" without affecting
472      the result.
473
474   The example below shows the results for a set of entity tag pairs,
475   and both the weak and strong comparison function results:
476
477   +--------+--------+-------------------+-----------------+
478   | ETag 1 | ETag 2 | Strong Comparison | Weak Comparison |
479   +--------+--------+-------------------+-----------------+
480   | W/"1"  | W/"1"  | no match          | match           |
481   | W/"1"  | W/"2"  | no match          | no match        |
482   | W/"1"  | "1"    | no match          | match           |
483   | "1"    | "1"    | match             | match           |
484   +--------+--------+-------------------+-----------------+
485
486   An entity tag is strong unless it is explicitly tagged as weak.
487   Section 2 gives the syntax for entity tags.
488
489   A Last-Modified time, when used as a validator in a request, is
490   implicitly weak unless it is possible to deduce that it is strong,
491   using the following rules:
492
493   o  The validator is being compared by an origin server to the actual
494      current validator for the entity and,
495
496   o  That origin server reliably knows that the associated entity did
497      not change twice during the second covered by the presented
498      validator.
499
500
501
502
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507
508   or
509
510   o  The validator is about to be used by a client in an If-Modified-
511      Since or If-Unmodified-Since header, because the client has a
512      cache entry for the associated entity, and
513
514   o  That cache entry includes a Date value, which gives the time when
515      the origin server sent the original response, and
516
517   o  The presented Last-Modified time is at least 60 seconds before the
518      Date value.
519
520   or
521
522   o  The validator is being compared by an intermediate cache to the
523      validator stored in its cache entry for the entity, and
524
525   o  That cache entry includes a Date value, which gives the time when
526      the origin server sent the original response, and
527
528   o  The presented Last-Modified time is at least 60 seconds before the
529      Date value.
530
531   This method relies on the fact that if two different responses were
532   sent by the origin server during the same second, but both had the
533   same Last-Modified time, then at least one of those responses would
534   have a Date value equal to its Last-Modified time.  The arbitrary 60-
535   second limit guards against the possibility that the Date and Last-
536   Modified values are generated from different clocks, or at somewhat
537   different times during the preparation of the response.  An
538   implementation MAY use a value larger than 60 seconds, if it is
539   believed that 60 seconds is too short.
540
541   If a client wishes to perform a sub-range retrieval on a value for
542   which it has only a Last-Modified time and no opaque validator, it
543   MAY do this only if the Last-Modified time is strong in the sense
544   described here.
545
546   A cache or origin server receiving a conditional range request
547   ([Part5]) MUST use the strong comparison function to evaluate the
548   condition.
549
550   These rules allow HTTP/1.1 caches and clients to safely perform sub-
551   range retrievals on values that have been obtained from HTTP/1.0
552   servers.
553
554
555
556
557
558
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563
5645.  Rules for When to Use Entity Tags and Last-Modified Dates
565
566   We adopt a set of rules and recommendations for origin servers,
567   clients, and caches regarding when various validator types ought to
568   be used, and for what purposes.
569
570   HTTP/1.1 origin servers:
571
572   o  SHOULD send an entity tag validator unless it is not feasible to
573      generate one.
574
575   o  MAY send a weak entity tag instead of a strong entity tag, if
576      performance considerations support the use of weak entity tags, or
577      if it is unfeasible to send a strong entity tag.
578
579   o  SHOULD send a Last-Modified value if it is feasible to send one,
580      unless the risk of a breakdown in semantic transparency that could
581      result from using this date in an If-Modified-Since header would
582      lead to serious problems.
583
584   In other words, the preferred behavior for an HTTP/1.1 origin server
585   is to send both a strong entity tag and a Last-Modified value.
586
587   In order to be legal, a strong entity tag MUST change whenever the
588   associated entity changes in any way.  A weak entity tag SHOULD
589   change whenever the associated entity changes in a semantically
590   significant way.
591
592      Note: In order to provide semantically transparent caching, an
593      origin server must avoid reusing a specific strong entity tag
594      value for two different entities, or reusing a specific weak
595      entity tag value for two semantically different entities.  Cache
596      entries might persist for arbitrarily long periods, regardless of
597      expiration times, so it might be inappropriate to expect that a
598      cache will never again attempt to validate an entry using a
599      validator that it obtained at some point in the past.
600
601   HTTP/1.1 clients:
602
603   o  MUST use that entity tag in any cache-conditional request (using
604      If-Match or If-None-Match) if an entity tag has been provided by
605      the origin server.
606
607   o  SHOULD use the Last-Modified value in non-subrange cache-
608      conditional requests (using If-Modified-Since) if only a Last-
609      Modified value has been provided by the origin server.
610
611
612
613
614
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619
620   o  MAY use the Last-Modified value in subrange cache-conditional
621      requests (using If-Unmodified-Since) if only a Last-Modified value
622      has been provided by an HTTP/1.0 origin server.  The user agent
623      SHOULD provide a way to disable this, in case of difficulty.
624
625   o  SHOULD use both validators in cache-conditional requests if both
626      an entity tag and a Last-Modified value have been provided by the
627      origin server.  This allows both HTTP/1.0 and HTTP/1.1 caches to
628      respond appropriately.
629
630   An HTTP/1.1 origin server, upon receiving a conditional request that
631   includes both a Last-Modified date (e.g., in an If-Modified-Since or
632   If-Unmodified-Since header field) and one or more entity tags (e.g.,
633   in an If-Match, If-None-Match, or If-Range header field) as cache
634   validators, MUST NOT return a response status of 304 (Not Modified)
635   unless doing so is consistent with all of the conditional header
636   fields in the request.
637
638   An HTTP/1.1 caching proxy, upon receiving a conditional request that
639   includes both a Last-Modified date and one or more entity tags as
640   cache validators, MUST NOT return a locally cached response to the
641   client unless that cached response is consistent with all of the
642   conditional header fields in the request.
643
644      Note: The general principle behind these rules is that HTTP/1.1
645      servers and clients should transmit as much non-redundant
646      information as is available in their responses and requests.
647      HTTP/1.1 systems receiving this information will make the most
648      conservative assumptions about the validators they receive.
649
650      HTTP/1.0 clients and caches will ignore entity tags.  Generally,
651      last-modified values received or used by these systems will
652      support transparent and efficient caching, and so HTTP/1.1 origin
653      servers should provide Last-Modified values.  In those rare cases
654      where the use of a Last-Modified value as a validator by an
655      HTTP/1.0 system could result in a serious problem, then HTTP/1.1
656      origin servers should not provide one.
657
6586.  Header Field Definitions
659
660   This section defines the syntax and semantics of HTTP/1.1 header
661   fields related to conditional requests.
662
663   For entity-header fields, both sender and recipient refer to either
664   the client or the server, depending on who sends and who receives the
665   entity.
666
667
668
669
670
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674
675
6766.1.  ETag
677
678   The "ETag" response-header field provides the current value of the
679   entity tag (see Section 2) for the requested variant, which may be
680   used for comparison with other entities from the same resource (see
681   Section 4).
682
683     ETag   = "ETag" ":" OWS ETag-v
684     ETag-v = entity-tag
685
686   Examples:
687
688     ETag: "xyzzy"
689     ETag: W/"xyzzy"
690     ETag: ""
691
692   The ETag response-header field value, an entity tag, provides for an
693   "opaque" cache validator.  This might allow more reliable validation
694   in situations where it is inconvenient to store modification dates,
695   where the one-second resolution of HTTP date values is not
696   sufficient, or where the origin server wishes to avoid certain
697   paradoxes that might arise from the use of modification dates.
698
699   The principle behind entity tags is that only the service author
700   knows the semantics of a resource well enough to select an
701   appropriate cache validation mechanism, and the specification of any
702   validator comparison function more complex than byte-equality would
703   open up a can of worms.  Thus, comparisons of any other headers
704   (except Last-Modified, for compatibility with HTTP/1.0) are never
705   used for purposes of validating a cache entry.
706
7076.2.  If-Match
708
709   The "If-Match" request-header field is used to make a request method
710   conditional.  A client that has one or more entities previously
711   obtained from the resource can verify that one of those entities is
712   current by including a list of their associated entity tags in the
713   If-Match header field.
714
715   This allows efficient updates of cached information with a minimum
716   amount of transaction overhead.  It is also used when updating
717   resources, to prevent inadvertent modification of the wrong version
718   of a resource.  As a special case, the value "*" matches any current
719   entity of the resource.
720
721     If-Match   = "If-Match" ":" OWS If-Match-v
722     If-Match-v = "*" / 1#entity-tag
723
724
725
726
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731
732   If any of the entity tags match the entity tag of the entity that
733   would have been returned in the response to a similar GET request
734   (without the If-Match header) on that resource, or if "*" is given
735   and any current entity exists for that resource, then the server MAY
736   perform the requested method as if the If-Match header field did not
737   exist.
738
739   If none of the entity tags match, or if "*" is given and no current
740   entity exists, the server MUST NOT perform the requested method, and
741   MUST return a 412 (Precondition Failed) response.  This behavior is
742   most useful when the client wants to prevent an updating method, such
743   as PUT, from modifying a resource that has changed since the client
744   last retrieved it.
745
746   If the request would, without the If-Match header field, result in
747   anything other than a 2xx or 412 status, then the If-Match header
748   MUST be ignored.
749
750   The meaning of "If-Match: *" is that the method SHOULD be performed
751   if the representation selected by the origin server (or by a cache,
752   possibly using the Vary mechanism, see Section 3.5 of [Part6])
753   exists, and MUST NOT be performed if the representation does not
754   exist.
755
756   A request intended to update a resource (e.g., a PUT) MAY include an
757   If-Match header field to signal that the request method MUST NOT be
758   applied if the entity corresponding to the If-Match value (a single
759   entity tag) is no longer a representation of that resource.  This
760   allows the user to indicate that they do not wish the request to be
761   successful if the resource has been changed without their knowledge.
762   Examples:
763
764     If-Match: "xyzzy"
765     If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
766     If-Match: *
767
768   The result of a request having both an If-Match header field and
769   either an If-None-Match or an If-Modified-Since header fields is
770   undefined by this specification.
771
7726.3.  If-Modified-Since
773
774   The "If-Modified-Since" request-header field is used to make a
775   request method conditional: if the requested variant has not been
776   modified since the time specified in this field, the server will not
777   return an entity; instead, a 304 (Not Modified) response will be
778   returned.
779
780
781
782
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787
788     If-Modified-Since   = "If-Modified-Since" ":" OWS
789                           If-Modified-Since-v
790     If-Modified-Since-v = HTTP-date
791
792   An example of the field is:
793
794     If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
795
796   A GET method with an If-Modified-Since header and no Range header
797   requests that the identified entity be transferred only if it has
798   been modified since the date given by the If-Modified-Since header.
799   The algorithm for determining this includes the following cases:
800
801   1.  If the request would normally result in anything other than a 200
802       (OK) status, or if the passed If-Modified-Since date is invalid,
803       the response is exactly the same as for a normal GET.  A date
804       which is later than the server's current time is invalid.
805
806   2.  If the variant has been modified since the If-Modified-Since
807       date, the response is exactly the same as for a normal GET.
808
809   3.  If the variant has not been modified since a valid If-Modified-
810       Since date, the server SHOULD return a 304 (Not Modified)
811       response.
812
813   The purpose of this feature is to allow efficient updates of cached
814   information with a minimum amount of transaction overhead.
815
816      Note: The Range request-header field modifies the meaning of If-
817      Modified-Since; see Section 5.4 of [Part5] for full details.
818
819      Note: If-Modified-Since times are interpreted by the server, whose
820      clock might not be synchronized with the client.
821
822      Note: When handling an If-Modified-Since header field, some
823      servers will use an exact date comparison function, rather than a
824      less-than function, for deciding whether to send a 304 (Not
825      Modified) response.  To get best results when sending an If-
826      Modified-Since header field for cache validation, clients are
827      advised to use the exact date string received in a previous Last-
828      Modified header field whenever possible.
829
830      Note: If a client uses an arbitrary date in the If-Modified-Since
831      header instead of a date taken from the Last-Modified header for
832      the same request, the client should be aware of the fact that this
833      date is interpreted in the server's understanding of time.  The
834      client should consider unsynchronized clocks and rounding problems
835      due to the different encodings of time between the client and
836
837
838
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843
844      server.  This includes the possibility of race conditions if the
845      document has changed between the time it was first requested and
846      the If-Modified-Since date of a subsequent request, and the
847      possibility of clock-skew-related problems if the If-Modified-
848      Since date is derived from the client's clock without correction
849      to the server's clock.  Corrections for different time bases
850      between client and server are at best approximate due to network
851      latency.
852
853   The result of a request having both an If-Modified-Since header field
854   and either an If-Match or an If-Unmodified-Since header fields is
855   undefined by this specification.
856
8576.4.  If-None-Match
858
859   The "If-None-Match" request-header field is used to make a request
860   method conditional.  A client that has one or more entities
861   previously obtained from the resource can verify that none of those
862   entities is current by including a list of their associated entity
863   tags in the If-None-Match header field.
864
865   This allows efficient updates of cached information with a minimum
866   amount of transaction overhead.  It is also used to prevent a method
867   (e.g., PUT) from inadvertently modifying an existing resource when
868   the client believes that the resource does not exist.
869
870   As a special case, the value "*" matches any current entity of the
871   resource.
872
873     If-None-Match   = "If-None-Match" ":" OWS If-None-Match-v
874     If-None-Match-v = "*" / 1#entity-tag
875
876   If any of the entity tags match the entity tag of the entity that
877   would have been returned in the response to a similar GET request
878   (without the If-None-Match header) on that resource, or if "*" is
879   given and any current entity exists for that resource, then the
880   server MUST NOT perform the requested method, unless required to do
881   so because the resource's modification date fails to match that
882   supplied in an If-Modified-Since header field in the request.
883   Instead, if the request method was GET or HEAD, the server SHOULD
884   respond with a 304 (Not Modified) response, including the cache-
885   related header fields (particularly ETag) of one of the entities that
886   matched.  For all other request methods, the server MUST respond with
887   a status of 412 (Precondition Failed).
888
889   If none of the entity tags match, then the server MAY perform the
890   requested method as if the If-None-Match header field did not exist,
891   but MUST also ignore any If-Modified-Since header field(s) in the
892
893
894
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899
900   request.  That is, if no entity tags match, then the server MUST NOT
901   return a 304 (Not Modified) response.
902
903   If the request would, without the If-None-Match header field, result
904   in anything other than a 2xx or 304 status, then the If-None-Match
905   header MUST be ignored.  (See Section 5 for a discussion of server
906   behavior when both If-Modified-Since and If-None-Match appear in the
907   same request.)
908
909   The meaning of "If-None-Match: *" is that the method MUST NOT be
910   performed if the representation selected by the origin server (or by
911   a cache, possibly using the Vary mechanism, see Section 3.5 of
912   [Part6]) exists, and SHOULD be performed if the representation does
913   not exist.  This feature is intended to be useful in preventing races
914   between PUT operations.
915
916   Examples:
917
918     If-None-Match: "xyzzy"
919     If-None-Match: W/"xyzzy"
920     If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
921     If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz"
922     If-None-Match: *
923
924   The result of a request having both an If-None-Match header field and
925   either an If-Match or an If-Unmodified-Since header fields is
926   undefined by this specification.
927
9286.5.  If-Unmodified-Since
929
930   The "If-Unmodified-Since" request-header field is used to make a
931   request method conditional.  If the requested resource has not been
932   modified since the time specified in this field, the server SHOULD
933   perform the requested operation as if the If-Unmodified-Since header
934   were not present.
935
936   If the requested variant has been modified since the specified time,
937   the server MUST NOT perform the requested operation, and MUST return
938   a 412 (Precondition Failed).
939
940     If-Unmodified-Since   = "If-Unmodified-Since" ":" OWS
941                             If-Unmodified-Since-v
942     If-Unmodified-Since-v = HTTP-date
943
944   An example of the field is:
945
946     If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
947
948
949
950
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954
955
956   If the request normally (i.e., without the If-Unmodified-Since
957   header) would result in anything other than a 2xx or 412 status, the
958   If-Unmodified-Since header SHOULD be ignored.
959
960   If the specified date is invalid, the header is ignored.
961
962   The result of a request having both an If-Unmodified-Since header
963   field and either an If-None-Match or an If-Modified-Since header
964   fields is undefined by this specification.
965
9666.6.  Last-Modified
967
968   The "Last-Modified" entity-header field indicates the date and time
969   at which the origin server believes the variant was last modified.
970
971     Last-Modified   = "Last-Modified" ":" OWS Last-Modified-v
972     Last-Modified-v = HTTP-date
973
974   An example of its use is
975
976     Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
977
978   The exact meaning of this header field depends on the implementation
979   of the origin server and the nature of the original resource.  For
980   files, it may be just the file system last-modified time.  For
981   entities with dynamically included parts, it may be the most recent
982   of the set of last-modify times for its component parts.  For
983   database gateways, it may be the last-update time stamp of the
984   record.  For virtual objects, it may be the last time the internal
985   state changed.
986
987   An origin server MUST NOT send a Last-Modified date which is later
988   than the server's time of message origination.  In such cases, where
989   the resource's last modification would indicate some time in the
990   future, the server MUST replace that date with the message
991   origination date.
992
993   An origin server SHOULD obtain the Last-Modified value of the entity
994   as close as possible to the time that it generates the Date value of
995   its response.  This allows a recipient to make an accurate assessment
996   of the entity's modification time, especially if the entity changes
997   near the time that the response is generated.
998
999   HTTP/1.1 servers SHOULD send Last-Modified whenever feasible.
1000
1001   The Last-Modified entity-header field value is often used as a cache
1002   validator.  In simple terms, a cache entry is considered to be valid
1003   if the entity has not been modified since the Last-Modified value.
1004
1005
1006
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1010
1011
10127.  IANA Considerations
1013
10147.1.  Status Code Registration
1015
1016   The HTTP Status Code Registry located at
1017   <http://www.iana.org/assignments/http-status-codes> should be updated
1018   with the registrations below:
1019
1020   +-------+---------------------+-------------+
1021   | Value | Description         | Reference   |
1022   +-------+---------------------+-------------+
1023   | 304   | Not Modified        | Section 3.1 |
1024   | 412   | Precondition Failed | Section 3.2 |
1025   +-------+---------------------+-------------+
1026
10277.2.  Message Header Registration
1028
1029   The Message Header Registry located at <http://www.iana.org/
1030   assignments/message-headers/message-header-index.html> should be
1031   updated with the permanent registrations below (see [RFC3864]):
1032
1033   +---------------------+----------+----------+-------------+
1034   | Header Field Name   | Protocol | Status   | Reference   |
1035   +---------------------+----------+----------+-------------+
1036   | ETag                | http     | standard | Section 6.1 |
1037   | If-Match            | http     | standard | Section 6.2 |
1038   | If-Modified-Since   | http     | standard | Section 6.3 |
1039   | If-None-Match       | http     | standard | Section 6.4 |
1040   | If-Unmodified-Since | http     | standard | Section 6.5 |
1041   | Last-Modified       | http     | standard | Section 6.6 |
1042   +---------------------+----------+----------+-------------+
1043
1044   The change controller is: "IETF (iesg@ietf.org) - Internet
1045   Engineering Task Force".
1046
10478.  Security Considerations
1048
1049   No additional security considerations have been identified beyond
1050   those applicable to HTTP in general [Part1].
1051
10529.  Acknowledgments
1053
105410.  References
1055
105610.1.  Normative References
1057
1058   [Part1]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
1059              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
1060
1061
1062
1063Fielding, et al.        Expires January 13, 2011               [Page 19]
1064
1065Internet-Draft              HTTP/1.1, Part 4                   July 2010
1066
1067
1068              and J. Reschke, Ed., "HTTP/1.1, part 1: URIs, Connections,
1069              and Message Parsing", draft-ietf-httpbis-p1-messaging-10
1070              (work in progress), July 2010.
1071
1072   [Part3]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
1073              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
1074              and J. Reschke, Ed., "HTTP/1.1, part 3: Message Payload
1075              and Content Negotiation", draft-ietf-httpbis-p3-payload-10
1076              (work in progress), July 2010.
1077
1078   [Part5]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
1079              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
1080              and J. Reschke, Ed., "HTTP/1.1, part 5: Range Requests and
1081              Partial Responses", draft-ietf-httpbis-p5-range-10 (work
1082              in progress), July 2010.
1083
1084   [Part6]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
1085              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
1086              Nottingham, M., Ed., and J. Reschke, Ed., "HTTP/1.1, part
1087              6: Caching", draft-ietf-httpbis-p6-cache-10 (work in
1088              progress), July 2010.
1089
1090   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
1091              Requirement Levels", BCP 14, RFC 2119, March 1997.
1092
1093   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
1094              Specifications: ABNF", STD 68, RFC 5234, January 2008.
1095
109610.2.  Informative References
1097
1098   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
1099              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
1100              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
1101
1102   [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
1103              Procedures for Message Header Fields", BCP 90, RFC 3864,
1104              September 2004.
1105
1106Appendix A.  Compatibility with Previous Versions
1107
1108A.1.  Changes from RFC 2616
1109
1110   Allow weak entity tags in all requests except range requests
1111   (Sections 4 and 6.4).
1112
1113
1114
1115
1116
1117
1118
1119Fielding, et al.        Expires January 13, 2011               [Page 20]
1120
1121Internet-Draft              HTTP/1.1, Part 4                   July 2010
1122
1123
1124Appendix B.  Collected ABNF
1125
1126   ETag = "ETag:" OWS ETag-v
1127   ETag-v = entity-tag
1128
1129   HTTP-date = <HTTP-date, defined in [Part1], Section 6.1>
1130
1131   If-Match = "If-Match:" OWS If-Match-v
1132   If-Match-v = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS
1133    entity-tag ] ) )
1134   If-Modified-Since = "If-Modified-Since:" OWS If-Modified-Since-v
1135   If-Modified-Since-v = HTTP-date
1136   If-None-Match = "If-None-Match:" OWS If-None-Match-v
1137   If-None-Match-v = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS
1138    entity-tag ] ) )
1139   If-Unmodified-Since = "If-Unmodified-Since:" OWS
1140    If-Unmodified-Since-v
1141   If-Unmodified-Since-v = HTTP-date
1142
1143   Last-Modified = "Last-Modified:" OWS Last-Modified-v
1144   Last-Modified-v = HTTP-date
1145
1146   OWS = <OWS, defined in [Part1], Section 1.2.2>
1147
1148   entity-tag = [ weak ] opaque-tag
1149
1150   opaque-tag = quoted-string
1151
1152   quoted-string = <quoted-string, defined in [Part1], Section 1.2.2>
1153
1154   weak = %x57.2F ; W/
1155
1156   ABNF diagnostics:
1157
1158   ; ETag defined but not used
1159   ; If-Match defined but not used
1160   ; If-Modified-Since defined but not used
1161   ; If-None-Match defined but not used
1162   ; If-Unmodified-Since defined but not used
1163   ; Last-Modified defined but not used
1164
1165Appendix C.  Change Log (to be removed by RFC Editor before publication)
1166
1167C.1.  Since RFC2616
1168
1169   Extracted relevant partitions from [RFC2616].
1170
1171
1172
1173
1174
1175Fielding, et al.        Expires January 13, 2011               [Page 21]
1176
1177Internet-Draft              HTTP/1.1, Part 4                   July 2010
1178
1179
1180C.2.  Since draft-ietf-httpbis-p4-conditional-00
1181
1182   Closed issues:
1183
1184   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/35>: "Normative and
1185      Informative references"
1186
1187   Other changes:
1188
1189   o  Move definitions of 304 and 412 condition codes from Part2.
1190
1191C.3.  Since draft-ietf-httpbis-p4-conditional-01
1192
1193   Ongoing work on ABNF conversion
1194   (<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):
1195
1196   o  Add explicit references to BNF syntax and rules imported from
1197      other parts of the specification.
1198
1199C.4.  Since draft-ietf-httpbis-p4-conditional-02
1200
1201   Closed issues:
1202
1203   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/116>: "Weak ETags on
1204      non-GET requests"
1205
1206   Ongoing work on IANA Message Header Registration
1207   (<http://tools.ietf.org/wg/httpbis/trac/ticket/40>):
1208
1209   o  Reference RFC 3984, and update header registrations for headers
1210      defined in this document.
1211
1212C.5.  Since draft-ietf-httpbis-p4-conditional-03
1213
1214   Closed issues:
1215
1216   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/71>: "Examples for
1217      ETag matching"
1218
1219   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/124>: "'entity
1220      value' undefined"
1221
1222   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/126>: "bogus 2068
1223      Date header reference"
1224
1225
1226
1227
1228
1229
1230
1231Fielding, et al.        Expires January 13, 2011               [Page 22]
1232
1233Internet-Draft              HTTP/1.1, Part 4                   July 2010
1234
1235
1236C.6.  Since draft-ietf-httpbis-p4-conditional-04
1237
1238   Ongoing work on ABNF conversion
1239   (<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):
1240
1241   o  Use "/" instead of "|" for alternatives.
1242
1243   o  Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
1244      whitespace ("OWS") and required whitespace ("RWS").
1245
1246   o  Rewrite ABNFs to spell out whitespace rules, factor out header
1247      value format definitions.
1248
1249C.7.  Since draft-ietf-httpbis-p4-conditional-05
1250
1251   Final work on ABNF conversion
1252   (<http://tools.ietf.org/wg/httpbis/trac/ticket/36>):
1253
1254   o  Add appendix containing collected and expanded ABNF, reorganize
1255      ABNF introduction.
1256
1257C.8.  Since draft-ietf-httpbis-p4-conditional-06
1258
1259   Closed issues:
1260
1261   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/153>: "case-
1262      sensitivity of etag weakness indicator"
1263
1264C.9.  Since draft-ietf-httpbis-p4-conditional-07
1265
1266   Closed issues:
1267
1268   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/116>: "Weak ETags on
1269      non-GET requests" (If-Match still was defined to require strong
1270      matching)
1271
1272   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/198>: "move IANA
1273      registrations for optional status codes"
1274
1275C.10.  Since draft-ietf-httpbis-p4-conditional-08
1276
1277   No significant changes.
1278
1279C.11.  Since draft-ietf-httpbis-p4-conditional-09
1280
1281   No significant changes.
1282
1283
1284
1285
1286
1287Fielding, et al.        Expires January 13, 2011               [Page 23]
1288
1289Internet-Draft              HTTP/1.1, Part 4                   July 2010
1290
1291
1292Index
1293
1294   3
1295      304 Not Modified (status code)  7
1296
1297   4
1298      412 Precondition Failed (status code)  8
1299
1300   E
1301      ETag header  13
1302
1303   G
1304      Grammar
1305         entity-tag  5
1306         ETag  13
1307         ETag-v  13
1308         If-Match  13
1309         If-Match-v  13
1310         If-Modified-Since  15
1311         If-Modified-Since-v  15
1312         If-None-Match  16
1313         If-None-Match-v  16
1314         If-Unmodified-Since  17
1315         If-Unmodified-Since-v  17
1316         Last-Modified  18
1317         Last-Modified-v  18
1318         opaque-tag  5
1319         weak  5
1320
1321   H
1322      Headers
1323         ETag  13
1324         If-Match  13
1325         If-Modified-Since  14
1326         If-None-Match  16
1327         If-Unmodified-Since  17
1328         Last-Modified  18
1329
1330   I
1331      If-Match header  13
1332      If-Modified-Since header  14
1333      If-None-Match header  16
1334      If-Unmodified-Since header  17
1335
1336   L
1337      Last-Modified header  18
1338
1339   S
1340
1341
1342
1343Fielding, et al.        Expires January 13, 2011               [Page 24]
1344
1345Internet-Draft              HTTP/1.1, Part 4                   July 2010
1346
1347
1348      Status Codes
1349         304 Not Modified  7
1350         412 Precondition Failed  8
1351
1352Authors' Addresses
1353
1354   Roy T. Fielding (editor)
1355   Day Software
1356   23 Corporate Plaza DR, Suite 280
1357   Newport Beach, CA  92660
1358   USA
1359
1360   Phone: +1-949-706-5300
1361   Fax:   +1-949-706-5305
1362   EMail: fielding@gbiv.com
1363   URI:   http://roy.gbiv.com/
1364
1365
1366   Jim Gettys
1367   Alcatel-Lucent Bell Labs
1368   21 Oak Knoll Road
1369   Carlisle, MA  01741
1370   USA
1371
1372   EMail: jg@freedesktop.org
1373   URI:   http://gettys.wordpress.com/
1374
1375
1376   Jeffrey C. Mogul
1377   Hewlett-Packard Company
1378   HP Labs, Large Scale Systems Group
1379   1501 Page Mill Road, MS 1177
1380   Palo Alto, CA  94304
1381   USA
1382
1383   EMail: JeffMogul@acm.org
1384
1385
1386   Henrik Frystyk Nielsen
1387   Microsoft Corporation
1388   1 Microsoft Way
1389   Redmond, WA  98052
1390   USA
1391
1392   EMail: henrikn@microsoft.com
1393
1394
1395
1396
1397
1398
1399Fielding, et al.        Expires January 13, 2011               [Page 25]
1400
1401Internet-Draft              HTTP/1.1, Part 4                   July 2010
1402
1403
1404   Larry Masinter
1405   Adobe Systems, Incorporated
1406   345 Park Ave
1407   San Jose, CA  95110
1408   USA
1409
1410   EMail: LMM@acm.org
1411   URI:   http://larry.masinter.net/
1412
1413
1414   Paul J. Leach
1415   Microsoft Corporation
1416   1 Microsoft Way
1417   Redmond, WA  98052
1418
1419   EMail: paulle@microsoft.com
1420
1421
1422   Tim Berners-Lee
1423   World Wide Web Consortium
1424   MIT Computer Science and Artificial Intelligence Laboratory
1425   The Stata Center, Building 32
1426   32 Vassar Street
1427   Cambridge, MA  02139
1428   USA
1429
1430   EMail: timbl@w3.org
1431   URI:   http://www.w3.org/People/Berners-Lee/
1432
1433
1434   Yves Lafon (editor)
1435   World Wide Web Consortium
1436   W3C / ERCIM
1437   2004, rte des Lucioles
1438   Sophia-Antipolis, AM  06902
1439   France
1440
1441   EMail: ylafon@w3.org
1442   URI:   http://www.raubacapeu.net/people/yves/
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455Fielding, et al.        Expires January 13, 2011               [Page 26]
1456
1457Internet-Draft              HTTP/1.1, Part 4                   July 2010
1458
1459
1460   Julian F. Reschke (editor)
1461   greenbytes GmbH
1462   Hafenweg 16
1463   Muenster, NW  48155
1464   Germany
1465
1466   Phone: +49 251 2807760
1467   Fax:   +49 251 2807761
1468   EMail: julian.reschke@greenbytes.de
1469   URI:   http://greenbytes.de/tech/webdav/
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511Fielding, et al.        Expires January 13, 2011               [Page 27]
1512
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