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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: February 5, 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                                                          August 4, 2010
23
24
25                 HTTP/1.1, part 4: Conditional Requests
26                  draft-ietf-httpbis-p4-conditional-11
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.12.
48
49Status of This Memo
50
51   This Internet-Draft is submitted in full conformance with the
52
53
54
55Fielding, et al.        Expires February 5, 2011                [Page 1]
56
57Internet-Draft              HTTP/1.1, Part 4                 August 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 February 5, 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 February 5, 2011                [Page 2]
112
113Internet-Draft              HTTP/1.1, Part 4                 August 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  . . . . . . . . . . . . . . . . .  7
130   4.  Weak and Strong Validators . . . . . . . . . . . . . . . . . .  8
131   5.  Rules for When to Use Entity-tags and Last-Modified Dates  . . 10
132   6.  Header Field Definitions . . . . . . . . . . . . . . . . . . . 12
133     6.1.  ETag . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
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  . . . . . . . . . . . . . . . . . . . . . 18
140     7.1.  Status Code Registration . . . . . . . . . . . . . . . . . 19
141     7.2.  Header Field 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.  Changes from RFC 2616 . . . . . . . . . . . . . . . . 20
148   Appendix B.  Collected ABNF  . . . . . . . . . . . . . . . . . . . 21
149   Appendix C.  Change Log (to be removed by RFC Editor before
150                publication)  . . . . . . . . . . . . . . . . . . . . 21
151     C.1.  Since RFC2616  . . . . . . . . . . . . . . . . . . . . . . 21
152     C.2.  Since draft-ietf-httpbis-p4-conditional-00 . . . . . . . . 22
153     C.3.  Since draft-ietf-httpbis-p4-conditional-01 . . . . . . . . 22
154     C.4.  Since draft-ietf-httpbis-p4-conditional-02 . . . . . . . . 22
155     C.5.  Since draft-ietf-httpbis-p4-conditional-03 . . . . . . . . 22
156     C.6.  Since draft-ietf-httpbis-p4-conditional-04 . . . . . . . . 23
157     C.7.  Since draft-ietf-httpbis-p4-conditional-05 . . . . . . . . 23
158     C.8.  Since draft-ietf-httpbis-p4-conditional-06 . . . . . . . . 23
159     C.9.  Since draft-ietf-httpbis-p4-conditional-07 . . . . . . . . 23
160     C.10. Since draft-ietf-httpbis-p4-conditional-08 . . . . . . . . 23
161     C.11. Since draft-ietf-httpbis-p4-conditional-09 . . . . . . . . 23
162     C.12. Since draft-ietf-httpbis-p4-conditional-10 . . . . . . . . 24
163   Index  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
164
165
166
167Fielding, et al.        Expires February 5, 2011                [Page 3]
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169Internet-Draft              HTTP/1.1, Part 4                 August 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 representations of the
248   same resource.  HTTP/1.1 uses entity-tags in the ETag (Section 6.1),
249   If-Match (Section 6.2), If-None-Match (Section 6.4), and If-Range
250   (Section 5.3 of [Part5]) header fields.  The definition of how they
251   are used and compared as cache validators is in Section 4.  An
252   entity-tag consists of an opaque quoted string, possibly prefixed by
253   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 representations of a
260   resource 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 representations of a resource only if the representations are
264   equivalent and could be substituted for each other with no
265   significant change in semantics.  A weak entity-tag can only be used
266   for weak comparison.
267
268   An entity-tag MUST be unique across all versions of all
269   representations associated with a particular resource.  A given
270   entity-tag value MAY be used for representations obtained by requests
271   on different URIs.  The use of the same entity-tag value in
272   conjunction with representations obtained by requests on different
273   URIs does not imply the equivalence of those representations.
274
275
276
277
278
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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 5
287   of [Part3]), and where the representations returned upon a GET
288   request vary based on the Accept-Encoding request header field
289   (Section 6.3 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 might or might not use the gzip content
299   coding.  If it does not, the response might look like:
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   An alternative representation that does use gzip content coding would
317   be:
318
319   >> Response:
320
321     HTTP/1.1 200 OK
322     Date: Thu, 26 Mar 2010 00:05:00 GMT
323     ETag: "123-b"
324     Content-Length: 43
325     Vary: Accept-Encoding
326     Content-Type: text/plain
327     Content-Encoding: gzip
328
329     ...binary data...
330
331
332
333
334
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339
340      Note: Content codings are a property of the representation, so
341      therefore an entity-tag of an encoded representation must be
342      distinct from an unencoded representation to prevent conflicts
343      during cache updates and range requests.  In contrast, transfer
344      codings (Section 6.2 of [Part1]) apply only during message
345      transfer and do not require distinct entity-tags.
346
3473.  Status Code Definitions
348
3493.1.  304 Not Modified
350
351   If the client has performed a conditional GET request and access is
352   allowed, but the document has not been modified, the server SHOULD
353   respond with this status code.  The 304 response MUST NOT contain a
354   message-body, and thus is always terminated by the first empty line
355   after the header fields.
356
357   A 304 response MUST include a Date header field (Section 9.3 of
358   [Part1]) unless its omission is required by Section 9.3.1 of [Part1].
359   If a 200 response to the same request would have included any of the
360   header fields Cache-Control, Content-Location, ETag, Expires, Last-
361   Modified, or Vary, then those same header fields MUST be sent in a
362   304 response.
363
364   Since the goal of a 304 response is to minimize information transfer
365   when the recipient already has one or more cached representations,
366   the response SHOULD NOT include representation metadata other than
367   the above listed fields unless said metadata exists for the purpose
368   of guiding cache updates (e.g., future HTTP extensions).
369
370   If a 304 response includes an entity-tag that indicates a
371   representation not currently cached, then the recipient MUST NOT use
372   the 304 to update its own cache.  If that conditional request
373   originated with an outbound client, such as a user agent with its own
374   cache sending a conditional GET to a shared proxy, then the 304
375   response MAY be forwarded to the outbound client.  Otherwise,
376   disregard the response and repeat the request without the
377   conditional.
378
379   If a cache uses a received 304 response to update a cache entry, the
380   cache MUST update the entry to reflect any new field values given in
381   the response.
382
3833.2.  412 Precondition Failed
384
385   The precondition given in one or more of the request-header fields
386   evaluated to false when it was tested on the server.  This response
387   code allows the client to place preconditions on the current resource
388
389
390
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395
396   metadata (header field data) and thus prevent the requested method
397   from being applied to a resource other than the one intended.
398
3994.  Weak and Strong Validators
400
401   Since both origin servers and caches will compare two validators to
402   decide if they represent the same or different representations, one
403   normally would expect that if the representation (including both
404   representation header fields and representation body) changes in any
405   way, then the associated validator would change as well.  If this is
406   true, then we call this validator a "strong validator".
407
408   However, there might be cases when a server prefers to change the
409   validator only on semantically significant changes, and not when
410   insignificant aspects of the representation change.  A validator that
411   does not always change when the representation changes is a "weak
412   validator".
413
414   An entity-tag is normally a strong validator, but the protocol
415   provides a mechanism to tag an entity-tag as "weak".  One can think
416   of a strong validator as one that changes whenever the sequence of
417   bits in a representation changes, while a weak value changes whenever
418   the meaning of a representation changes.  Alternatively, one can
419   think of a strong validator as part of an identifier for a specific
420   representation, whereas a weak validator is part of an identifier for
421   a set of semantically equivalent representations.
422
423      Note: One example of a strong validator is an integer that is
424      incremented in stable storage every time a representation is
425      changed.
426
427      A representation's modification time, if defined with only one-
428      second resolution, could be a weak validator, since it is possible
429      that the representation might be modified twice during a single
430      second.
431
432      Support for weak validators is optional.  However, weak validators
433      allow for more efficient caching of equivalent objects; for
434      example, a hit counter on a site is probably good enough if it is
435      updated every few days or weeks, and any value during that period
436      is likely "good enough" to be equivalent.
437
438   A "use" of a validator is either when a client generates a request
439   and includes the validator in a validating header field, or when a
440   server compares two validators.
441
442   Strong validators are usable in any context.  Weak validators are
443   only usable in contexts that do not depend on exact equality of a
444
445
446
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451
452   representation.  For example, either kind is usable for a normal
453   conditional GET.  However, only a strong validator is usable for a
454   sub-range retrieval, since otherwise the client might end up with an
455   internally inconsistent representation.
456
457   Clients MUST NOT use weak validators in range requests ([Part5]).
458
459   The only function that HTTP/1.1 defines on validators is comparison.
460   There are two validator comparison functions, depending on whether
461   the comparison context allows the use of weak validators or not:
462
463   o  The strong comparison function: in order to be considered equal,
464      both opaque-tags MUST be identical character-by-character, and
465      both MUST NOT be weak.
466
467   o  The weak comparison function: in order to be considered equal,
468      both opaque-tags MUST be identical character-by-character, but
469      either or both of them MAY be tagged as "weak" without affecting
470      the result.
471
472   The example below shows the results for a set of entity-tag pairs,
473   and both the weak and strong comparison function results:
474
475   +--------+--------+-------------------+-----------------+
476   | ETag 1 | ETag 2 | Strong Comparison | Weak Comparison |
477   +--------+--------+-------------------+-----------------+
478   | W/"1"  | W/"1"  | no match          | match           |
479   | W/"1"  | W/"2"  | no match          | no match        |
480   | W/"1"  | "1"    | no match          | match           |
481   | "1"    | "1"    | match             | match           |
482   +--------+--------+-------------------+-----------------+
483
484   An entity-tag is strong unless it is explicitly tagged as weak.
485   Section 2 gives the syntax for entity-tags.
486
487   A Last-Modified time, when used as a validator in a request, is
488   implicitly weak unless it is possible to deduce that it is strong,
489   using the following rules:
490
491   o  The validator is being compared by an origin server to the actual
492      current validator for the representation and,
493
494   o  That origin server reliably knows that the associated
495      representation did not change twice during the second covered by
496      the presented validator.
497
498   or
499
500
501
502
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507
508   o  The validator is about to be used by a client in an If-Modified-
509      Since or If-Unmodified-Since header, because the client has a
510      cache entry for the associated representation, and
511
512   o  That cache entry includes a Date value, which gives the time when
513      the origin server sent the original response, and
514
515   o  The presented Last-Modified time is at least 60 seconds before the
516      Date value.
517
518   or
519
520   o  The validator is being compared by an intermediate cache to the
521      validator stored in its cache entry for the representation, and
522
523   o  That cache entry includes a Date value, which gives the time when
524      the origin server sent the original response, and
525
526   o  The presented Last-Modified time is at least 60 seconds before the
527      Date value.
528
529   This method relies on the fact that if two different responses were
530   sent by the origin server during the same second, but both had the
531   same Last-Modified time, then at least one of those responses would
532   have a Date value equal to its Last-Modified time.  The arbitrary 60-
533   second limit guards against the possibility that the Date and Last-
534   Modified values are generated from different clocks, or at somewhat
535   different times during the preparation of the response.  An
536   implementation MAY use a value larger than 60 seconds, if it is
537   believed that 60 seconds is too short.
538
539   If a client wishes to perform a sub-range retrieval on a value for
540   which it has only a Last-Modified time and no opaque validator, it
541   MAY do this only if the Last-Modified time is strong in the sense
542   described here.
543
544   A cache or origin server receiving a conditional range request
545   ([Part5]) MUST use the strong comparison function to evaluate the
546   condition.
547
548   These rules allow HTTP/1.1 caches and clients to safely perform sub-
549   range retrievals on values that have been obtained from HTTP/1.0
550   servers.
551
5525.  Rules for When to Use Entity-tags and Last-Modified Dates
553
554   We adopt a set of rules and recommendations for origin servers,
555   clients, and caches regarding when various validator types ought to
556
557
558
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563
564   be used, and for what purposes.
565
566   HTTP/1.1 origin servers:
567
568   o  SHOULD send an entity-tag validator unless it is not feasible to
569      generate one.
570
571   o  MAY send a weak entity-tag instead of a strong entity-tag, if
572      performance considerations support the use of weak entity-tags, or
573      if it is unfeasible to send a strong entity-tag.
574
575   o  SHOULD send a Last-Modified value if it is feasible to send one,
576      unless the risk of a breakdown in semantic transparency that could
577      result from using this date in an If-Modified-Since header would
578      lead to serious problems.
579
580   In other words, the preferred behavior for an HTTP/1.1 origin server
581   is to send both a strong entity-tag and a Last-Modified value.
582
583   In order to be legal, a strong entity-tag MUST change whenever the
584   associated representation changes in any way.  A weak entity-tag
585   SHOULD change whenever the associated representation changes in a
586   semantically significant way.
587
588      Note: In order to provide semantically transparent caching, an
589      origin server must avoid reusing a specific strong entity-tag
590      value for two different representations, or reusing a specific
591      weak entity-tag value for two semantically different
592      representations.  Cache entries might persist for arbitrarily long
593      periods, regardless of expiration times, so it might be
594      inappropriate to expect that a cache will never again attempt to
595      validate an entry using a validator that it obtained at some point
596      in the past.
597
598   HTTP/1.1 clients:
599
600   o  MUST use that entity-tag in any cache-conditional request (using
601      If-Match or If-None-Match) if an entity-tag has been provided by
602      the origin server.
603
604   o  SHOULD use the Last-Modified value in non-subrange cache-
605      conditional requests (using If-Modified-Since) if only a Last-
606      Modified value has been provided by the origin server.
607
608   o  MAY use the Last-Modified value in subrange cache-conditional
609      requests (using If-Unmodified-Since) if only a Last-Modified value
610      has been provided by an HTTP/1.0 origin server.  The user agent
611      SHOULD provide a way to disable this, in case of difficulty.
612
613
614
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619
620   o  SHOULD use both validators in cache-conditional requests if both
621      an entity-tag and a Last-Modified value have been provided by the
622      origin server.  This allows both HTTP/1.0 and HTTP/1.1 caches to
623      respond appropriately.
624
625   An HTTP/1.1 origin server, upon receiving a conditional request that
626   includes both a Last-Modified date (e.g., in an If-Modified-Since or
627   If-Unmodified-Since header field) and one or more entity-tags (e.g.,
628   in an If-Match, If-None-Match, or If-Range header field) as cache
629   validators, MUST NOT return a response status code of 304 (Not
630   Modified) unless doing so is consistent with all of the conditional
631   header fields in the request.
632
633   An HTTP/1.1 caching proxy, upon receiving a conditional request that
634   includes both a Last-Modified date and one or more entity-tags as
635   cache validators, MUST NOT return a locally cached response to the
636   client unless that cached response is consistent with all of the
637   conditional header fields in the request.
638
639      Note: The general principle behind these rules is that HTTP/1.1
640      servers and clients ought to transmit as much non-redundant
641      information as is available in their responses and requests.
642      HTTP/1.1 systems receiving this information will make the most
643      conservative assumptions about the validators they receive.
644
645      HTTP/1.0 clients and caches will ignore entity-tags.  Generally,
646      last-modified values received or used by these systems will
647      support transparent and efficient caching, and so HTTP/1.1 origin
648      servers should provide Last-Modified values.  In those rare cases
649      where the use of a Last-Modified value as a validator by an
650      HTTP/1.0 system could result in a serious problem, then HTTP/1.1
651      origin servers should not provide one.
652
6536.  Header Field Definitions
654
655   This section defines the syntax and semantics of HTTP/1.1 header
656   fields related to conditional requests.
657
6586.1.  ETag
659
660   The "ETag" response-header field provides the current value of the
661   entity-tag (see Section 2) for one representation of the target
662   resource.  An entity-tag is intended for use as a resource-local
663   identifier for differentiating between representations of the same
664   resource that vary over time or via content negotiation (see
665   Section 4).
666
667     ETag   = "ETag" ":" OWS ETag-v
668
669
670
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675
676     ETag-v = entity-tag
677
678   Examples:
679
680     ETag: "xyzzy"
681     ETag: W/"xyzzy"
682     ETag: ""
683
684   An entity-tag provides an "opaque" cache validator that allows for
685   more reliable validation than modification dates in situations where
686   it is inconvenient to store modification dates, where the one-second
687   resolution of HTTP date values is not sufficient, or where the origin
688   server wishes to avoid certain paradoxes that might arise from the
689   use of modification dates.
690
691   The principle behind entity-tags is that only the service author
692   knows the semantics of a resource well enough to select an
693   appropriate cache validation mechanism, and the specification of any
694   validator comparison function more complex than byte-equality would
695   open up a can of worms.  Thus, comparisons of any other headers
696   (except Last-Modified, for compatibility with HTTP/1.0) are never
697   used for purposes of validating a cache entry.
698
6996.2.  If-Match
700
701   The "If-Match" request-header field is used to make a request method
702   conditional.  A client that has one or more representations
703   previously obtained from the resource can verify that one of those
704   representations is current by including a list of their associated
705   entity-tags in the If-Match header field.
706
707   This allows efficient updates of cached information with a minimum
708   amount of transaction overhead.  It is also used when updating
709   resources, to prevent inadvertent modification of the wrong version
710   of a resource.  As a special case, the value "*" matches any current
711   representation of the resource.
712
713     If-Match   = "If-Match" ":" OWS If-Match-v
714     If-Match-v = "*" / 1#entity-tag
715
716   If any of the entity-tags match the entity-tag of the representation
717   that would have been returned in the response to a similar GET
718   request (without the If-Match header) on that resource, or if "*" is
719   given and any current representation exists for that resource, then
720   the server MAY perform the requested method as if the If-Match header
721   field did not exist.
722
723   If none of the entity-tags match, or if "*" is given and no current
724
725
726
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731
732   representation exists, the server MUST NOT perform the requested
733   method, and MUST return a 412 (Precondition Failed) response.  This
734   behavior is most useful when the client wants to prevent an updating
735   method, such as PUT, from modifying a resource that has changed since
736   the client last retrieved it.
737
738   If the request would, without the If-Match header field, result in
739   anything other than a 2xx or 412 status code, then the If-Match
740   header MUST be ignored.
741
742   The meaning of "If-Match: *" is that the method SHOULD be performed
743   if the representation selected by the origin server (or by a cache,
744   possibly using the Vary mechanism, see Section 3.5 of [Part6])
745   exists, and MUST NOT be performed if the representation does not
746   exist.
747
748   A request intended to update a resource (e.g., a PUT) MAY include an
749   If-Match header field to signal that the request method MUST NOT be
750   applied if the representation corresponding to the If-Match value (a
751   single entity-tag) is no longer a representation of that resource.
752   This allows the user to indicate that they do not wish the request to
753   be successful if the resource has been changed without their
754   knowledge.  Examples:
755
756     If-Match: "xyzzy"
757     If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
758     If-Match: *
759
760   The result of a request having both an If-Match header field and
761   either an If-None-Match or an If-Modified-Since header fields is
762   undefined by this specification.
763
7646.3.  If-Modified-Since
765
766   The "If-Modified-Since" request-header field is used to make a
767   request method conditional by date: if the representation that would
768   have been transferred in a 200 response to a GET request has not been
769   modified since the time specified in this field, then do not perform
770   the method; instead, respond as detailed below.
771
772     If-Modified-Since   = "If-Modified-Since" ":" OWS
773                           If-Modified-Since-v
774     If-Modified-Since-v = HTTP-date
775
776   An example of the field is:
777
778     If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
779
780
781
782
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787
788   A GET method with an If-Modified-Since header and no Range header
789   requests that the representation be transferred only if it has been
790   modified since the date given by the If-Modified-Since header.  The
791   algorithm for determining this includes the following cases:
792
793   1.  If the request would normally result in anything other than a 200
794       (OK) status code, or if the passed If-Modified-Since date is
795       invalid, the response is exactly the same as for a normal GET.  A
796       date which is later than the server's current time is invalid.
797
798   2.  If the representation has been modified since the If-Modified-
799       Since date, the response is exactly the same as for a normal GET.
800
801   3.  If the representation has not been modified since a valid If-
802       Modified-Since date, the server SHOULD return a 304 (Not
803       Modified) response.
804
805   The purpose of this feature is to allow efficient updates of cached
806   information with a minimum amount of transaction overhead.
807
808      Note: The Range request-header field modifies the meaning of If-
809      Modified-Since; see Section 5.4 of [Part5] for full details.
810
811      Note: If-Modified-Since times are interpreted by the server, whose
812      clock might not be synchronized with the client.
813
814      Note: When handling an If-Modified-Since header field, some
815      servers will use an exact date comparison function, rather than a
816      less-than function, for deciding whether to send a 304 (Not
817      Modified) response.  To get best results when sending an If-
818      Modified-Since header field for cache validation, clients are
819      advised to use the exact date string received in a previous Last-
820      Modified header field whenever possible.
821
822      Note: If a client uses an arbitrary date in the If-Modified-Since
823      header instead of a date taken from the Last-Modified header for
824      the same request, the client needs to be aware that this date is
825      interpreted in the server's understanding of time.  Unsynchronized
826      clocks and rounding problems, due to the different encodings of
827      time between the client and server, are concerns.  This includes
828      the possibility of race conditions if the document has changed
829      between the time it was first requested and the If-Modified-Since
830      date of a subsequent request, and the possibility of clock-skew-
831      related problems if the If-Modified-Since date is derived from the
832      client's clock without correction to the server's clock.
833      Corrections for different time bases between client and server are
834      at best approximate due to network latency.
835
836
837
838
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843
844   The result of a request having both an If-Modified-Since header field
845   and either an If-Match or an If-Unmodified-Since header fields is
846   undefined by this specification.
847
8486.4.  If-None-Match
849
850   The "If-None-Match" request-header field is used to make a request
851   method conditional.  A client that has one or more representations
852   previously obtained from the resource can verify that none of those
853   representations is current by including a list of their associated
854   entity-tags in the If-None-Match header field.
855
856   This allows efficient updates of cached information with a minimum
857   amount of transaction overhead.  It is also used to prevent a method
858   (e.g., PUT) from inadvertently modifying an existing resource when
859   the client believes that the resource does not exist.
860
861   As a special case, the value "*" matches any current representation
862   of the resource.
863
864     If-None-Match   = "If-None-Match" ":" OWS If-None-Match-v
865     If-None-Match-v = "*" / 1#entity-tag
866
867   If any of the entity-tags match the entity-tag of the representation
868   that would have been returned in the response to a similar GET
869   request (without the If-None-Match header) on that resource, or if
870   "*" is given and any current representation exists for that resource,
871   then the server MUST NOT perform the requested method, unless
872   required to do so because the resource's modification date fails to
873   match that supplied in an If-Modified-Since header field in the
874   request.  Instead, if the request method was GET or HEAD, the server
875   SHOULD respond with a 304 (Not Modified) response, including the
876   cache-related header fields (particularly ETag) of one of the
877   representations that matched.  For all other request methods, the
878   server MUST respond with a 412 (Precondition Failed) status code.
879
880   If none of the entity-tags match, then the server MAY perform the
881   requested method as if the If-None-Match header field did not exist,
882   but MUST also ignore any If-Modified-Since header field(s) in the
883   request.  That is, if no entity-tags match, then the server MUST NOT
884   return a 304 (Not Modified) response.
885
886   If the request would, without the If-None-Match header field, result
887   in anything other than a 2xx or 304 status code, then the If-None-
888   Match header MUST be ignored.  (See Section 5 for a discussion of
889   server behavior when both If-Modified-Since and If-None-Match appear
890   in the same request.)
891
892
893
894
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899
900   The meaning of "If-None-Match: *" is that the method MUST NOT be
901   performed if the representation selected by the origin server (or by
902   a cache, possibly using the Vary mechanism, see Section 3.5 of
903   [Part6]) exists, and SHOULD be performed if the representation does
904   not exist.  This feature is intended to be useful in preventing races
905   between PUT operations.
906
907   Examples:
908
909     If-None-Match: "xyzzy"
910     If-None-Match: W/"xyzzy"
911     If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
912     If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz"
913     If-None-Match: *
914
915   The result of a request having both an If-None-Match header field and
916   either an If-Match or an If-Unmodified-Since header fields is
917   undefined by this specification.
918
9196.5.  If-Unmodified-Since
920
921   The "If-Unmodified-Since" request-header field is used to make a
922   request method conditional.  If the representation that would have
923   been transferred in a 200 response to a GET request on the same
924   resource has not been modified since the time specified in this
925   field, the server SHOULD perform the requested operation as if the
926   If-Unmodified-Since header were not present.
927
928   If the representation has been modified since the specified time, the
929   server MUST NOT perform the requested operation, and MUST return a
930   412 (Precondition Failed).
931
932     If-Unmodified-Since   = "If-Unmodified-Since" ":" OWS
933                             If-Unmodified-Since-v
934     If-Unmodified-Since-v = HTTP-date
935
936   An example of the field is:
937
938     If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
939
940   If the request normally (i.e., without the If-Unmodified-Since
941   header) would result in anything other than a 2xx or 412 status code,
942   the If-Unmodified-Since header SHOULD be ignored.
943
944   If the specified date is invalid, the header is ignored.
945
946   The result of a request having both an If-Unmodified-Since header
947   field and either an If-None-Match or an If-Modified-Since header
948
949
950
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955
956   fields is undefined by this specification.
957
9586.6.  Last-Modified
959
960   The "Last-Modified" header field indicates the date and time at which
961   the origin server believes the representation was last modified.
962
963     Last-Modified   = "Last-Modified" ":" OWS Last-Modified-v
964     Last-Modified-v = HTTP-date
965
966   An example of its use is
967
968     Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
969
970   The exact meaning of this header field depends on the implementation
971   of the origin server and the nature of the original resource.  For
972   files, it might be just the file system last-modified time.  For
973   representations with dynamically included parts, it might be the most
974   recent of the set of last-modify times for its component parts.  For
975   database gateways, it might be the last-update time stamp of the
976   record.  For virtual objects, it might be the last time the internal
977   state changed.
978
979   An origin server MUST NOT send a Last-Modified date which is later
980   than the server's time of message origination.  In such cases, where
981   the resource's last modification would indicate some time in the
982   future, the server MUST replace that date with the message
983   origination date.
984
985   An origin server SHOULD obtain the Last-Modified value of the
986   representation as close as possible to the time that it generates the
987   Date value of its response.  This allows a recipient to make an
988   accurate assessment of the representation's modification time,
989   especially if the representation changes near the time that the
990   response is generated.
991
992   HTTP/1.1 servers SHOULD send Last-Modified whenever feasible.
993
994   The Last-Modified header field value is often used as a cache
995   validator.  In simple terms, a cache entry is considered to be valid
996   if the representation has not been modified since the Last-Modified
997   value.
998
9997.  IANA Considerations
1000
1001
1002
1003
1004
1005
1006
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1011
10127.1.  Status Code Registration
1013
1014   The HTTP Status Code Registry located at
1015   <http://www.iana.org/assignments/http-status-codes> shall be updated
1016   with the registrations below:
1017
1018   +-------+---------------------+-------------+
1019   | Value | Description         | Reference   |
1020   +-------+---------------------+-------------+
1021   | 304   | Not Modified        | Section 3.1 |
1022   | 412   | Precondition Failed | Section 3.2 |
1023   +-------+---------------------+-------------+
1024
10257.2.  Header Field Registration
1026
1027   The Message Header Field Registry located at <http://www.iana.org/
1028   assignments/message-headers/message-header-index.html> shall be
1029   updated with the permanent registrations below (see [RFC3864]):
1030
1031   +---------------------+----------+----------+-------------+
1032   | Header Field Name   | Protocol | Status   | Reference   |
1033   +---------------------+----------+----------+-------------+
1034   | ETag                | http     | standard | Section 6.1 |
1035   | If-Match            | http     | standard | Section 6.2 |
1036   | If-Modified-Since   | http     | standard | Section 6.3 |
1037   | If-None-Match       | http     | standard | Section 6.4 |
1038   | If-Unmodified-Since | http     | standard | Section 6.5 |
1039   | Last-Modified       | http     | standard | Section 6.6 |
1040   +---------------------+----------+----------+-------------+
1041
1042   The change controller is: "IETF (iesg@ietf.org) - Internet
1043   Engineering Task Force".
1044
10458.  Security Considerations
1046
1047   No additional security considerations have been identified beyond
1048   those applicable to HTTP in general [Part1].
1049
10509.  Acknowledgments
1051
105210.  References
1053
105410.1.  Normative References
1055
1056   [Part1]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
1057              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
1058              and J. Reschke, Ed., "HTTP/1.1, part 1: URIs, Connections,
1059              and Message Parsing", draft-ietf-httpbis-p1-messaging-11
1060
1061
1062
1063Fielding, et al.        Expires February 5, 2011               [Page 19]
1064
1065Internet-Draft              HTTP/1.1, Part 4                 August 2010
1066
1067
1068              (work in progress), August 2010.
1069
1070   [Part3]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
1071              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
1072              and J. Reschke, Ed., "HTTP/1.1, part 3: Message Payload
1073              and Content Negotiation", draft-ietf-httpbis-p3-payload-11
1074              (work in progress), August 2010.
1075
1076   [Part5]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
1077              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
1078              and J. Reschke, Ed., "HTTP/1.1, part 5: Range Requests and
1079              Partial Responses", draft-ietf-httpbis-p5-range-11 (work
1080              in progress), August 2010.
1081
1082   [Part6]    Fielding, R., Ed., Gettys, J., Mogul, J., Frystyk, H.,
1083              Masinter, L., Leach, P., Berners-Lee, T., Lafon, Y., Ed.,
1084              Nottingham, M., Ed., and J. Reschke, Ed., "HTTP/1.1, part
1085              6: Caching", draft-ietf-httpbis-p6-cache-11 (work in
1086              progress), August 2010.
1087
1088   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
1089              Requirement Levels", BCP 14, RFC 2119, March 1997.
1090
1091   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
1092              Specifications: ABNF", STD 68, RFC 5234, January 2008.
1093
109410.2.  Informative References
1095
1096   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
1097              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
1098              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
1099
1100   [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
1101              Procedures for Message Header Fields", BCP 90, RFC 3864,
1102              September 2004.
1103
1104Appendix A.  Changes from RFC 2616
1105
1106   Allow weak entity-tags in all requests except range requests
1107   (Sections 4 and 6.4).
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119Fielding, et al.        Expires February 5, 2011               [Page 20]
1120
1121Internet-Draft              HTTP/1.1, Part 4                 August 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 February 5, 2011               [Page 21]
1176
1177Internet-Draft              HTTP/1.1, Part 4                 August 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 February 5, 2011               [Page 22]
1232
1233Internet-Draft              HTTP/1.1, Part 4                 August 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 February 5, 2011               [Page 23]
1288
1289Internet-Draft              HTTP/1.1, Part 4                 August 2010
1290
1291
1292C.12.  Since draft-ietf-httpbis-p4-conditional-10
1293
1294   Closed issues:
1295
1296   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/69>: "Clarify
1297      'Requested Variant'"
1298
1299   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/109>: "Clarify
1300      entity / representation / variant terminology"
1301
1302   o  <http://tools.ietf.org/wg/httpbis/trac/ticket/220>: "consider
1303      removing the 'changes from 2068' sections"
1304
1305Index
1306
1307   3
1308      304 Not Modified (status code)  7
1309
1310   4
1311      412 Precondition Failed (status code)  7
1312
1313   E
1314      ETag header  12
1315
1316   G
1317      Grammar
1318         entity-tag  5
1319         ETag  12
1320         ETag-v  12
1321         If-Match  13
1322         If-Match-v  13
1323         If-Modified-Since  14
1324         If-Modified-Since-v  14
1325         If-None-Match  16
1326         If-None-Match-v  16
1327         If-Unmodified-Since  17
1328         If-Unmodified-Since-v  17
1329         Last-Modified  18
1330         Last-Modified-v  18
1331         opaque-tag  5
1332         weak  5
1333
1334   H
1335      Headers
1336         ETag  12
1337         If-Match  13
1338         If-Modified-Since  14
1339         If-None-Match  16
1340
1341
1342
1343Fielding, et al.        Expires February 5, 2011               [Page 24]
1344
1345Internet-Draft              HTTP/1.1, Part 4                 August 2010
1346
1347
1348         If-Unmodified-Since  17
1349         Last-Modified  18
1350
1351   I
1352      If-Match header  13
1353      If-Modified-Since header  14
1354      If-None-Match header  16
1355      If-Unmodified-Since header  17
1356
1357   L
1358      Last-Modified header  18
1359
1360   S
1361      Status Codes
1362         304 Not Modified  7
1363         412 Precondition Failed  7
1364
1365Authors' Addresses
1366
1367   Roy T. Fielding (editor)
1368   Day Software
1369   23 Corporate Plaza DR, Suite 280
1370   Newport Beach, CA  92660
1371   USA
1372
1373   Phone: +1-949-706-5300
1374   Fax:   +1-949-706-5305
1375   EMail: fielding@gbiv.com
1376   URI:   http://roy.gbiv.com/
1377
1378
1379   Jim Gettys
1380   Alcatel-Lucent Bell Labs
1381   21 Oak Knoll Road
1382   Carlisle, MA  01741
1383   USA
1384
1385   EMail: jg@freedesktop.org
1386   URI:   http://gettys.wordpress.com/
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399Fielding, et al.        Expires February 5, 2011               [Page 25]
1400
1401Internet-Draft              HTTP/1.1, Part 4                 August 2010
1402
1403
1404   Jeffrey C. Mogul
1405   Hewlett-Packard Company
1406   HP Labs, Large Scale Systems Group
1407   1501 Page Mill Road, MS 1177
1408   Palo Alto, CA  94304
1409   USA
1410
1411   EMail: JeffMogul@acm.org
1412
1413
1414   Henrik Frystyk Nielsen
1415   Microsoft Corporation
1416   1 Microsoft Way
1417   Redmond, WA  98052
1418   USA
1419
1420   EMail: henrikn@microsoft.com
1421
1422
1423   Larry Masinter
1424   Adobe Systems, Incorporated
1425   345 Park Ave
1426   San Jose, CA  95110
1427   USA
1428
1429   EMail: LMM@acm.org
1430   URI:   http://larry.masinter.net/
1431
1432
1433   Paul J. Leach
1434   Microsoft Corporation
1435   1 Microsoft Way
1436   Redmond, WA  98052
1437
1438   EMail: paulle@microsoft.com
1439
1440
1441   Tim Berners-Lee
1442   World Wide Web Consortium
1443   MIT Computer Science and Artificial Intelligence Laboratory
1444   The Stata Center, Building 32
1445   32 Vassar Street
1446   Cambridge, MA  02139
1447   USA
1448
1449   EMail: timbl@w3.org
1450   URI:   http://www.w3.org/People/Berners-Lee/
1451
1452
1453
1454
1455Fielding, et al.        Expires February 5, 2011               [Page 26]
1456
1457Internet-Draft              HTTP/1.1, Part 4                 August 2010
1458
1459
1460   Yves Lafon (editor)
1461   World Wide Web Consortium
1462   W3C / ERCIM
1463   2004, rte des Lucioles
1464   Sophia-Antipolis, AM  06902
1465   France
1466
1467   EMail: ylafon@w3.org
1468   URI:   http://www.raubacapeu.net/people/yves/
1469
1470
1471   Julian F. Reschke (editor)
1472   greenbytes GmbH
1473   Hafenweg 16
1474   Muenster, NW  48155
1475   Germany
1476
1477   Phone: +49 251 2807760
1478   Fax:   +49 251 2807761
1479   EMail: julian.reschke@greenbytes.de
1480   URI:   http://greenbytes.de/tech/webdav/
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 February 5, 2011               [Page 27]
1512
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