source: draft-ietf-httpbis/latest/p4-conditional.xml @ 1426

Last change on this file since 1426 was 1426, checked in by julian.reschke@…, 8 years ago

bump up document dates; update to latest version of rfc2629.xslt, refresh appendices.

  • Property svn:eol-style set to native
File size: 72.2 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "September">
16  <!ENTITY ID-YEAR "2011">
17  <!ENTITY notation                   "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY notation-abnf              "<xref target='Part1' x:rel='#notation.abnf' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY acks                       "<xref target='Part1' x:rel='#acks' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY basic-rules                "<xref target='Part1' x:rel='#basic.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY field-rules                "<xref target='Part1' x:rel='#field.rules' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY header-date                "<xref target='Part1' x:rel='#header.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY caching                    "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY clockless                  "<xref target='Part1' x:rel='#clockless.origin.server.operation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY full-date                  "<xref target='Part1' x:rel='#date.time.formats.full.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY transfer-codings           "<xref target='Part1' x:rel='#transfer.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33]>
34<?rfc toc="yes" ?>
35<?rfc symrefs="yes" ?>
36<?rfc sortrefs="yes" ?>
37<?rfc compact="yes"?>
38<?rfc subcompact="no" ?>
39<?rfc linkmailto="no" ?>
40<?rfc editing="no" ?>
41<?rfc comments="yes"?>
42<?rfc inline="yes"?>
43<?rfc rfcedstyle="yes"?>
44<?rfc-ext allow-markup-in-artwork="yes" ?>
45<?rfc-ext include-references-in-index="yes" ?>
46<rfc obsoletes="2616" category="std" x:maturity-level="draft"
47     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"
48     xmlns:x='http://purl.org/net/xml2rfc/ext'>
49<front>
50
51  <title abbrev="HTTP/1.1, Part 4">HTTP/1.1, part 4: Conditional Requests</title>
52
53  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
54    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
55    <address>
56      <postal>
57        <street>345 Park Ave</street>
58        <city>San Jose</city>
59        <region>CA</region>
60        <code>95110</code>
61        <country>USA</country>
62      </postal>
63      <email>fielding@gbiv.com</email>
64      <uri>http://roy.gbiv.com/</uri>
65    </address>
66  </author>
67
68  <author initials="J." surname="Gettys" fullname="Jim Gettys">
69    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
70    <address>
71      <postal>
72        <street>21 Oak Knoll Road</street>
73        <city>Carlisle</city>
74        <region>MA</region>
75        <code>01741</code>
76        <country>USA</country>
77      </postal>
78      <email>jg@freedesktop.org</email>
79      <uri>http://gettys.wordpress.com/</uri>
80    </address>
81  </author>
82 
83  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
84    <organization abbrev="HP">Hewlett-Packard Company</organization>
85    <address>
86      <postal>
87        <street>HP Labs, Large Scale Systems Group</street>
88        <street>1501 Page Mill Road, MS 1177</street>
89        <city>Palo Alto</city>
90        <region>CA</region>
91        <code>94304</code>
92        <country>USA</country>
93      </postal>
94      <email>JeffMogul@acm.org</email>
95    </address>
96  </author>
97
98  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
99    <organization abbrev="Microsoft">Microsoft Corporation</organization>
100    <address>
101      <postal>
102        <street>1 Microsoft Way</street>
103        <city>Redmond</city>
104        <region>WA</region>
105        <code>98052</code>
106        <country>USA</country>
107      </postal>
108      <email>henrikn@microsoft.com</email>
109    </address>
110  </author>
111
112  <author initials="L." surname="Masinter" fullname="Larry Masinter">
113    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
114    <address>
115      <postal>
116        <street>345 Park Ave</street>
117        <city>San Jose</city>
118        <region>CA</region>
119        <code>95110</code>
120        <country>USA</country>
121      </postal>
122      <email>LMM@acm.org</email>
123      <uri>http://larry.masinter.net/</uri>
124    </address>
125  </author>
126 
127  <author initials="P." surname="Leach" fullname="Paul J. Leach">
128    <organization abbrev="Microsoft">Microsoft Corporation</organization>
129    <address>
130      <postal>
131        <street>1 Microsoft Way</street>
132        <city>Redmond</city>
133        <region>WA</region>
134        <code>98052</code>
135      </postal>
136      <email>paulle@microsoft.com</email>
137    </address>
138  </author>
139   
140  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
141    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
142    <address>
143      <postal>
144        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
145        <street>The Stata Center, Building 32</street>
146        <street>32 Vassar Street</street>
147        <city>Cambridge</city>
148        <region>MA</region>
149        <code>02139</code>
150        <country>USA</country>
151      </postal>
152      <email>timbl@w3.org</email>
153      <uri>http://www.w3.org/People/Berners-Lee/</uri>
154    </address>
155  </author>
156
157  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
158    <organization abbrev="W3C">World Wide Web Consortium</organization>
159    <address>
160      <postal>
161        <street>W3C / ERCIM</street>
162        <street>2004, rte des Lucioles</street>
163        <city>Sophia-Antipolis</city>
164        <region>AM</region>
165        <code>06902</code>
166        <country>France</country>
167      </postal>
168      <email>ylafon@w3.org</email>
169      <uri>http://www.raubacapeu.net/people/yves/</uri>
170    </address>
171  </author>
172
173  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
174    <organization abbrev="greenbytes">greenbytes GmbH</organization>
175    <address>
176      <postal>
177        <street>Hafenweg 16</street>
178        <city>Muenster</city><region>NW</region><code>48155</code>
179        <country>Germany</country>
180      </postal>
181      <phone>+49 251 2807760</phone>
182      <facsimile>+49 251 2807761</facsimile>
183      <email>julian.reschke@greenbytes.de</email>
184      <uri>http://greenbytes.de/tech/webdav/</uri>
185    </address>
186  </author>
187
188  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
189  <workgroup>HTTPbis Working Group</workgroup>
190
191<abstract>
192<t>
193   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
194   distributed, collaborative, hypertext information systems. HTTP has been in
195   use by the World Wide Web global information initiative since 1990. This
196   document is Part 4 of the seven-part specification that defines the protocol
197   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
198</t>
199<t>
200   Part 4 defines request header fields for indicating conditional requests and
201   the rules for constructing responses to those requests.
202</t>
203</abstract>
204
205<note title="Editorial Note (To be removed by RFC Editor)">
206  <t>
207    Discussion of this draft should take place on the HTTPBIS working group
208    mailing list (ietf-http-wg@w3.org), which is archived at
209    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
210  </t>
211  <t>
212    The current issues list is at
213    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
214    documents (including fancy diffs) can be found at
215    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
216  </t>
217  <t>
218    The changes in this draft are summarized in <xref target="changes.since.16"/>.
219  </t>
220</note>
221</front>
222<middle>
223<section title="Introduction" anchor="introduction">
224<t>
225   This document defines the HTTP/1.1 conditional request mechanisms,
226   including both metadata for indicating/observing changes in resource
227   representations and request header fields that specify preconditions
228   on that metadata be checked before performing the request method.
229   Conditional GET requests are the most efficient mechanism for HTTP
230   cache updates &caching;.  Conditionals can also be
231   applied to state-changing methods, such as PUT and DELETE, to prevent
232   the "lost update" problem: one client accidentally overwriting
233   the work of another client that has been acting in parallel.
234</t>
235<t>
236   Conditional request preconditions are based on the state of the target
237   resource as a whole (its current value set) or the state as observed
238   in a previously obtained representation (one value in that set).
239   A resource might have multiple current representations, each with its
240   own observable state.  The conditional request mechanisms assume that
241   the mapping of requests to corresponding representations will be
242   consistent over time if the server intends to take advantage of
243   conditionals.  Regardless, if the mapping is inconsistent and
244   the server is unable to select the appropriate representation, then
245   no harm will result when the precondition evaluates to false.
246</t>
247<t><iref primary="true" item="selected representation"/>
248   We use the term "<x:dfn>selected representation</x:dfn>" to refer to
249   the current representation of the target resource that would have been
250   selected in a successful response if the same request had used the method
251   GET and had excluded all of the conditional request header fields.
252   The conditional request preconditions are evaluated by comparing the
253   values provided in the request header fields to the current metadata
254   for the selected representation.
255</t>
256
257<section title="Requirements" anchor="intro.requirements">
258<t>
259   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
260   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
261   document are to be interpreted as described in <xref target="RFC2119"/>.
262</t>
263<t>
264   An implementation is not compliant if it fails to satisfy one or more
265   of the "MUST" or "REQUIRED" level requirements for the protocols it
266   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
267   level and all the "SHOULD" level requirements for its protocols is said
268   to be "unconditionally compliant"; one that satisfies all the "MUST"
269   level requirements but not all the "SHOULD" level requirements for its
270   protocols is said to be "conditionally compliant".
271</t>
272</section>
273
274<section title="Syntax Notation" anchor="notation">
275  <x:anchor-alias value="ALPHA"/>
276  <x:anchor-alias value="CR"/>
277  <x:anchor-alias value="DIGIT"/>
278  <x:anchor-alias value="LF"/>
279  <x:anchor-alias value="OCTET"/>
280  <x:anchor-alias value="VCHAR"/>
281  <x:anchor-alias value="core.rules"/>
282  <x:anchor-alias value="quoted-string"/>
283  <x:anchor-alias value="OWS"/>
284  <x:anchor-alias value="HTTP-date"/>
285<t>
286  This specification uses the ABNF syntax defined in &notation; (which
287  extends the syntax defined in <xref target="RFC5234"/> with a list rule).
288  <xref target="collected.abnf"/> shows the collected ABNF, with the list
289  rule expanded.
290</t>
291<t>
292  The following core rules are included by
293  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
294  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
295  DIGIT (decimal 0-9), DQUOTE (double quote),
296  HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
297  OCTET (any 8-bit sequence of data), SP (space), and
298  VCHAR (any visible US-ASCII character).
299</t>
300<t>
301  The ABNF rules below are defined in <xref target="Part1"/>:
302</t>
303<figure><artwork type="abnf2616">
304  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &basic-rules;&gt;
305  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &field-rules;&gt;
306  <x:ref>HTTP-date</x:ref>     = &lt;HTTP-date, defined in &full-date;&gt;
307</artwork></figure>
308</section>
309</section>
310
311<section title="Validators" anchor="validators">
312   <iref primary="true" item="metadata"/>
313   <iref primary="true" item="validator"/>
314<t>
315   This specification defines two forms of metadata that are commonly used
316   to observe resource state and test for preconditions: modification dates
317   and opaque entity tags.  Additional metadata that reflects resource state
318   has been defined by various extensions of HTTP, such as WebDAV
319   <xref target="RFC4918"/>, that are beyond the scope of this specification.
320   A resource metadata value is referred to as a "<x:dfn>validator</x:dfn>"
321   when it is used within a precondition.
322</t>
323
324<section title="Weak versus Strong" anchor="weak.and.strong.validators">
325   <iref primary="true" item="validator" subitem="weak"/>
326   <iref primary="true" item="validator" subitem="strong"/>
327<t>
328   Validators come in two flavors: strong or weak.  Weak validators are easy
329   to generate but are far less useful for comparisons.  Strong validators
330   are ideal for comparisons but can be very difficult (and occasionally
331   impossible) to generate efficiently.  Rather than impose that all forms
332   of resource adhere to the same strength of validator, HTTP exposes the
333   type of validator in use and imposes restrictions on when weak validators
334   can be used as preconditions.
335</t>
336<t>
337   A "strong validator" is a representation metadata value that &MUST; be
338   changed to a new, previously unused or guaranteed unique, value whenever
339   a change occurs to the representation data such that a change would be
340   observable in the payload body of a 200 response to GET.  A strong
341   validator &MAY; be changed for other reasons, such as when a semantically
342   significant part of the representation metadata is changed (e.g.,
343   Content-Type), but it is in the best interests of the origin server to only
344   change the value when it is necessary to invalidate the stored responses
345   held by remote caches and authoring tools.  A strong validator &MUST; be
346   unique across all representations of a given resource, such that no two
347   representations of that resource share the same validator unless
348   their payload body would be identical.
349</t>
350<t>
351   Cache entries might persist for arbitrarily long periods, regardless
352   of expiration times.  Thus, a cache might attempt to validate an
353   entry using a validator that it obtained in the distant past.
354   A strong validator &MUST; be unique across all versions of all
355   representations associated with a particular resource over time.
356   However, there is no implication of uniqueness across representations
357   of different resources (i.e., the same strong validator might be
358   in use for representations of multiple resources at the same time
359   and does not imply that those representations are equivalent).
360</t>
361<t>
362   There are a variety of strong validators used in practice.  The best are
363   based on strict revision control, wherein each change to a representation
364   always results in a unique node name and revision identifier being assigned
365   before the representation is made accessible to GET.  A cryptographic hash
366   function applied to the representation data is also sufficient if the data
367   is available prior to the response header fields being sent and the digest
368   does not need to be recalculated every time a validation request is
369   received.  However, if a resource has distinct representations that differ
370   only in their metadata, such as might occur with content negotiation over
371   media types that happen to share the same data format, then a server
372   &SHOULD; incorporate additional information in the validator to
373   distinguish those representations and avoid confusing cache behavior.
374</t>
375<t>
376   In contrast, a "weak validator" is a representation metadata value that
377   might not be changed for every change to the representation data.  This
378   weakness might be due to limitations in how the value is calculated, such
379   as clock resolution or an inability to ensure uniqueness for all possible
380   representations of the resource, or due to a desire by the resource owner
381   to group representations by some self-determined set of equivalency
382   rather than unique sequences of data.  A weak entity-tag &SHOULD; change
383   whenever the origin server considers prior representations to be
384   unacceptable as a substitute for the current representation. In other
385   words, a weak entity-tag &SHOULD; change whenever the origin server wants
386   caches to invalidate old responses.
387</t>
388<t>
389   For example, the representation of a weather report that changes in
390   content every second, based on dynamic measurements, might be grouped
391   into sets of equivalent representations (from the origin server's
392   perspective) with the same weak validator in order to allow cached
393   representations to be valid for a reasonable period of time (perhaps
394   adjusted dynamically based on server load or weather quality).
395   Likewise, a representation's modification time, if defined with only
396   one-second resolution, might be a weak validator if it is possible
397   for the representation to be modified twice during a single second and
398   retrieved between those modifications.
399</t>
400<t>
401   A "use" of a validator occurs when either a client generates a request
402   and includes the validator in a precondition or when a server
403   compares two validators.
404   Weak validators are only usable in contexts that do not depend on exact
405   equality of a representation's payload body.
406   Strong validators are usable and preferred for all conditional requests,
407   including cache validation, partial content ranges, and "lost update"
408   avoidance.
409</t>
410</section>
411
412<section title="Last-Modified" anchor="header.last-modified">
413  <iref primary="true" item="Last-Modified header field" x:for-anchor=""/>
414  <iref primary="true" item="Header Fields" subitem="Last-Modified" x:for-anchor=""/>
415  <x:anchor-alias value="Last-Modified"/>
416<t>
417   The "Last-Modified" header field indicates the date and time at
418   which the origin server believes the selected representation was
419   last modified.
420</t>
421<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Last-Modified"/>
422  <x:ref>Last-Modified</x:ref> = <x:ref>HTTP-date</x:ref>
423</artwork></figure>
424<t>
425   An example of its use is
426</t>
427<figure><artwork type="example">
428  Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
429</artwork></figure>
430
431<section title="Generation" anchor="lastmod.generation">
432<t>
433   Origin servers &SHOULD; send Last-Modified for any selected
434   representation for which a last modification date can be reasonably
435   and consistently determined, since its use in conditional requests
436   and evaluating cache freshness (&caching;) results in a substantial
437   reduction of HTTP traffic on the Internet and can be a significant
438   factor in improving service scalability and reliability.
439</t>
440<t>
441   A representation is typically the sum of many parts behind the
442   resource interface.  The last-modified time would usually be
443   the most recent time that any of those parts were changed.
444   How that value is determined for any given resource is an
445   implementation detail beyond the scope of this specification.
446   What matters to HTTP is how recipients of the Last-Modified
447   header field can use its value to make conditional requests
448   and test the validity of locally cached responses.
449</t>
450<t>
451   An origin server &SHOULD; obtain the Last-Modified value of the
452   representation as close as possible to the time that it generates
453   the Date field-value for its response. This allows a recipient to
454   make an accurate assessment of the representation's modification time,
455   especially if the representation changes near the time that the
456   response is generated.
457</t>
458<t>
459   An origin server with a clock &MUST-NOT; send a Last-Modified date
460   that is later than the server's time of message origination (Date).
461   If the last modification time is derived from implementation-specific
462   metadata that evaluates to some time in the future, according to the
463   origin server's clock, then the origin server &MUST; replace that
464   value with the message origination date. This prevents a future
465   modification date from having an adverse impact on cache validation.
466</t>
467</section>
468
469<section title="Comparison" anchor="lastmod.comparison">
470<t>
471   A Last-Modified time, when used as a validator in a request, is
472   implicitly weak unless it is possible to deduce that it is strong,
473   using the following rules:
474  <list style="symbols">
475     <t>The validator is being compared by an origin server to the
476        actual current validator for the representation and,</t>
477     <t>That origin server reliably knows that the associated representation did
478        not change twice during the second covered by the presented
479        validator.</t>
480  </list>
481</t>
482<t>
483   or
484  <list style="symbols">
485     <t>The validator is about to be used by a client in an If-Modified-Since,
486        If-Unmodified-Since header field, because the client has a cache entry,
487        or If-Range for the associated representation, and</t>
488     <t>That cache entry includes a Date value, which gives the time
489        when the origin server sent the original response, and</t>
490     <t>The presented Last-Modified time is at least 60 seconds before
491        the Date value.</t>
492  </list>
493</t>
494<t>
495   or
496  <list style="symbols">
497     <t>The validator is being compared by an intermediate cache to the
498        validator stored in its cache entry for the representation, and</t>
499     <t>That cache entry includes a Date value, which gives the time
500        when the origin server sent the original response, and</t>
501     <t>The presented Last-Modified time is at least 60 seconds before
502        the Date value.</t>
503  </list>
504</t>
505<t>
506   This method relies on the fact that if two different responses were
507   sent by the origin server during the same second, but both had the
508   same Last-Modified time, then at least one of those responses would
509   have a Date value equal to its Last-Modified time. The arbitrary 60-second
510   limit guards against the possibility that the Date and Last-Modified
511   values are generated from different clocks, or at somewhat
512   different times during the preparation of the response. An
513   implementation &MAY; use a value larger than 60 seconds, if it is
514   believed that 60 seconds is too short.
515</t>
516</section>
517</section>
518
519<section title="ETag" anchor="header.etag">
520  <iref primary="true" item="ETag header field" x:for-anchor=""/>
521  <iref primary="true" item="Header Fields" subitem="ETag" x:for-anchor=""/>
522  <x:anchor-alias value="ETag"/>
523  <x:anchor-alias value="entity-tag"/>
524  <x:anchor-alias value="entity.tags"/>
525  <x:anchor-alias value="opaque-tag"/>
526  <x:anchor-alias value="weak"/>
527<t>
528   The ETag header field provides the current entity-tag for the
529   selected representation.
530   An entity-tag is an opaque validator for differentiating between
531   multiple representations of the same resource, regardless of whether
532   those multiple representations are due to resource state changes over
533   time, content negotiation resulting in multiple representations being
534   valid at the same time, or both. An entity-tag consists of an opaque
535   quoted string, possibly prefixed by a weakness indicator.
536</t>
537<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="ETag"/><iref primary="true" item="Grammar" subitem="entity-tag"/><iref primary="true" item="Grammar" subitem="weak"/><iref primary="true" item="Grammar" subitem="opaque-tag"/>
538  <x:ref>ETag</x:ref>       = <x:ref>entity-tag</x:ref>
539
540  <x:ref>entity-tag</x:ref> = [ <x:ref>weak</x:ref> ] <x:ref>opaque-tag</x:ref>
541  <x:ref>weak</x:ref>       = <x:abnf-char-sequence>"W/"</x:abnf-char-sequence> ; "W/", case-sensitive
542  <x:ref>opaque-tag</x:ref> = <x:ref>quoted-string</x:ref>
543</artwork></figure>
544<t>
545   An entity-tag can be more reliable for validation than a modification
546   date in situations where it is inconvenient to store modification
547   dates, where the one-second resolution of HTTP date values is not
548   sufficient, or where modification dates are not consistently maintained.
549</t>
550<figure><preamble>
551  Examples:
552</preamble>
553<artwork type="example">
554  ETag: "xyzzy"
555  ETag: W/"xyzzy"
556  ETag: ""
557</artwork></figure>
558<t>
559   An entity-tag can be either a weak or strong validator, with
560   strong being the default.  If an origin server provides an entity-tag
561   for a representation and the generation of that entity-tag does not satisfy
562   the requirements for a strong validator
563   (<xref target="weak.and.strong.validators"/>), then that
564   entity-tag &MUST; be marked as weak by prefixing its opaque value
565   with "W/" (case-sensitive).
566</t>
567
568<section title="Generation" anchor="entity.tag.generation">
569<t>
570   The principle behind entity-tags is that only the service author
571   knows the implementation of a resource well enough to select the
572   most accurate and efficient validation mechanism for that resource,
573   and that any such mechanism can be mapped to a simple sequence of
574   octets for easy comparison.  Since the value is opaque, there is no
575   need for the client to be aware of how each entity-tag is constructed.
576</t>
577<t>
578   For example, a resource that has implementation-specific versioning
579   applied to all changes might use an internal revision number, perhaps
580   combined with a variance identifier for content negotiation, to
581   accurately differentiate between representations.
582   Other implementations might use a stored hash of representation content,
583   a combination of various filesystem attributes, or a modification
584   timestamp that has sub-second resolution.
585</t>
586<t>
587   Origin servers &SHOULD; send ETag for any selected representation
588   for which detection of changes can be reasonably and consistently
589   determined, since the entity-tag's use in conditional requests and
590   evaluating cache freshness (&caching;) can result in a substantial
591   reduction of HTTP network traffic and can be a significant factor in
592   improving service scalability and reliability.
593</t>
594</section>
595
596<section title="Comparison" anchor="entity.tag.comparison">
597  <x:anchor-alias value="validator.comparison"/>
598<t>
599   There are two entity-tag comparison functions, depending
600   on whether the comparison context allows the use of weak validators
601   or not:
602  <list style="symbols">
603     <t>The strong comparison function: in order to be considered equal,
604        both opaque-tags &MUST; be identical character-by-character, and both
605        &MUST-NOT; be weak.</t>
606     <t>The weak comparison function: in order to be considered equal, both
607        opaque-tags &MUST; be identical character-by-character, but
608        either or both of them &MAY; be tagged as "weak" without affecting
609        the result.</t>
610  </list>
611</t>
612<t>
613   The example below shows the results for a set of entity-tag pairs,
614   and both the weak and strong comparison function results:
615</t>
616<texttable align="left">
617  <ttcol>ETag 1</ttcol>
618  <ttcol>ETag 2</ttcol>
619  <ttcol>Strong Comparison</ttcol>
620  <ttcol>Weak Comparison</ttcol>
621
622  <c>W/"1"</c>
623  <c>W/"1"</c>
624  <c>no match</c>
625  <c>match</c>
626 
627  <c>W/"1"</c>
628  <c>W/"2"</c>
629  <c>no match</c>
630  <c>no match</c>
631
632  <c>W/"1"</c>
633  <c>"1"</c>
634  <c>no match</c>
635  <c>match</c>
636
637  <c>"1"</c>
638  <c>"1"</c>
639  <c>match</c>
640  <c>match</c>
641</texttable>
642</section>
643
644<section title="Example: Entity-tags varying on Content-Negotiated Resources" anchor="example.entity.tag.vs.conneg">
645<t>
646   Consider a resource that is subject to content negotiation (&content-negotiation;),
647   and where the representations returned upon a GET request vary based on
648   the Accept-Encoding request header field (&header-accept-encoding;):
649</t>
650<figure><preamble>>> Request:</preamble><artwork type="message/http; msgtype=&#34;request&#34;"  x:indent-with="  ">
651GET /index HTTP/1.1
652Host: www.example.com
653Accept-Encoding: gzip
654
655</artwork></figure>
656<t>
657   In this case, the response might or might not use the gzip content coding.
658   If it does not, the response might look like:
659</t>
660<figure><preamble>>> Response:</preamble><artwork type="message/http; msgtype=&#34;response&#34;"  x:indent-with="  ">
661HTTP/1.1 200 OK
662Date: Thu, 26 Mar 2010 00:05:00 GMT
663ETag: "123-a"
664Content-Length: <x:length-of target="exbody"/>
665Vary: Accept-Encoding
666Content-Type: text/plain
667
668<x:span anchor="exbody">Hello World!
669Hello World!
670Hello World!
671Hello World!
672Hello World!
673</x:span></artwork></figure>
674<t>
675   An alternative representation that does use gzip content coding would be:
676</t>
677<figure><preamble>>> Response:</preamble><artwork type="message/http; msgtype=&#34;response&#34;"  x:indent-with="  ">
678HTTP/1.1 200 OK
679Date: Thu, 26 Mar 2010 00:05:00 GMT
680ETag: "123-b"
681Content-Length: 43
682Vary: Accept-Encoding
683Content-Type: text/plain
684Content-Encoding: gzip
685
686<spanx>...binary data...</spanx></artwork></figure>
687<x:note>
688  <t>
689    <x:h>Note:</x:h> Content codings are a property of the representation,
690    so therefore an entity-tag of an encoded representation must be distinct
691    from an unencoded representation to prevent conflicts during cache updates
692    and range requests.  In contrast, transfer codings (&transfer-codings;)
693    apply only during message transfer and do not require distinct entity-tags.
694  </t>
695</x:note>
696</section>
697</section>
698
699<section title="Rules for When to Use Entity-tags and Last-Modified Dates" anchor="rules.for.when.to.use.entity.tags.and.last-modified.dates">
700<t>
701   We adopt a set of rules and recommendations for origin servers,
702   clients, and caches regarding when various validator types ought to
703   be used, and for what purposes.
704</t>
705<t>
706   HTTP/1.1 origin servers:
707  <list style="symbols">
708     <t>&SHOULD; send an entity-tag validator unless it is not feasible to
709        generate one.</t>
710
711     <t>&MAY; send a weak entity-tag instead of a strong entity-tag, if
712        performance considerations support the use of weak entity-tags,
713        or if it is unfeasible to send a strong entity-tag.</t>
714
715     <t>&SHOULD; send a Last-Modified value if it is feasible to send one.</t>
716  </list>
717</t>
718<t>
719   In other words, the preferred behavior for an HTTP/1.1 origin server
720   is to send both a strong entity-tag and a Last-Modified value.
721</t>
722<t>
723   HTTP/1.1 clients:
724  <list style="symbols">
725     <t>&MUST; use that entity-tag in any cache-conditional request (using
726        If-Match or If-None-Match) if an entity-tag has been provided by the
727        origin server.</t>
728
729     <t>&SHOULD; use the Last-Modified value in non-subrange cache-conditional
730        requests (using If-Modified-Since) if only a Last-Modified value has
731        been provided by the origin server. </t>
732
733     <t>&MAY; use the Last-Modified value in subrange cache-conditional
734        requests (using If-Unmodified-Since) if only a Last-Modified value has
735        been provided by an HTTP/1.0 origin server. The user agent &SHOULD;
736        provide a way to disable this, in case of difficulty.</t>
737
738     <t>&SHOULD; use both validators in cache-conditional requests if both an
739        entity-tag and a Last-Modified value have been provided by the origin
740        server. This allows both HTTP/1.0 and HTTP/1.1 caches to respond
741        appropriately.</t>
742  </list>
743</t>
744<t>
745   An HTTP/1.1 origin server, upon receiving a conditional request that
746   includes both a Last-Modified date (e.g., in an If-Modified-Since or
747   If-Unmodified-Since header field) and one or more entity-tags (e.g.,
748   in an If-Match, If-None-Match, or If-Range header field) as cache
749   validators, &MUST-NOT; return a response status code of 304 (Not Modified)
750   unless doing so is consistent with all of the conditional header
751   fields in the request.
752</t>
753<t>
754   An HTTP/1.1 caching proxy, upon receiving a conditional request that
755   includes both a Last-Modified date and one or more entity-tags as
756   cache validators, &MUST-NOT; return a locally cached response to the
757   client unless that cached response is consistent with all of the
758   conditional header fields in the request.
759  <list><t>
760      <x:h>Note:</x:h> The general principle behind these rules is that HTTP/1.1
761      servers and clients ought to transmit as much non-redundant
762      information as is available in their responses and requests.
763      HTTP/1.1 systems receiving this information will make the most
764      conservative assumptions about the validators they receive.
765  </t><t>
766      HTTP/1.0 clients and caches might ignore entity-tags. Generally,
767      last-modified values received or used by these systems will
768      support transparent and efficient caching, and so HTTP/1.1 origin
769      servers should provide Last-Modified values. In those rare cases
770      where the use of a Last-Modified value as a validator by an
771      HTTP/1.0 system could result in a serious problem, then HTTP/1.1
772      origin servers should not provide one.
773  </t></list>
774</t>
775</section>
776</section>
777
778<section title="Precondition Header Fields" anchor="header.field.definitions">
779<t>
780   This section defines the syntax and semantics of HTTP/1.1 header fields
781   for applying preconditions on requests.
782</t>
783
784<section title="If-Match" anchor="header.if-match">
785  <iref primary="true" item="If-Match header field" x:for-anchor=""/>
786  <iref primary="true" item="Header Fields" subitem="If-Match" x:for-anchor=""/>
787  <x:anchor-alias value="If-Match"/>
788<t>
789   The "If-Match" header field &MAY; be used to make a request method
790   conditional on the current existence or value of an entity-tag for
791   one or more representations of the target resource.  If-Match is
792   generally useful for resource update requests, such as PUT requests,
793   as a means for protecting against accidental overwrites when multiple
794   clients are acting in parallel on the same resource (i.e., the
795   "lost update" problem).  An If-Match field-value of "*" places the
796   precondition on the existence of any current representation for the
797   target resource.
798</t>
799<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="If-Match"/>
800  <x:ref>If-Match</x:ref> = "*" / 1#<x:ref>entity-tag</x:ref>
801</artwork></figure>
802<t>
803   If any of the entity-tags listed in the If-Match field value match
804   (as per <xref target="entity.tag.comparison"/>) the entity-tag of the
805   selected representation for the target resource,
806   or if "*" is given and any current representation exists for the
807   target resource, then the server &MAY; perform the request method
808   as if the If-Match header field was not present.
809</t>
810<t>
811   If none of the entity-tags match, or if "*" is given and no current
812   representation exists, the server &MUST-NOT; perform the requested method.
813   Instead, the server &MUST; respond with the 412 (Precondition Failed)
814   status code.
815</t>
816<t>
817   If the request would, without the If-Match header field, result in
818   anything other than a 2xx or 412 status code, then the If-Match header field
819   &MUST; be ignored.
820</t>
821<t>
822   Examples:
823</t>
824<figure><artwork type="example">
825  If-Match: "xyzzy"
826  If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
827  If-Match: *
828</artwork></figure>
829<t>
830   The result of a request having both an If-Match header field and
831   either an If-None-Match or an If-Modified-Since header fields is
832   undefined by this specification.
833</t>
834</section>
835
836<section title="If-None-Match" anchor="header.if-none-match">
837  <iref primary="true" item="If-None-Match header field" x:for-anchor=""/>
838  <iref primary="true" item="Header Fields" subitem="If-None-Match" x:for-anchor=""/>
839  <x:anchor-alias value="If-None-Match"/>
840<t>
841   The "If-None-Match" header field &MAY; be used to make a request method
842   conditional on not matching any of the current entity-tag values for
843   representations of the target resource.  If-None-Match is primarily
844   used in conditional GET requests to enable efficient updates of cached
845   information with a minimum amount of transaction overhead.  A client
846   that has one or more representations previously obtained from the
847   target resource can send If-None-Match with a list of the associated
848   entity-tags in the hope of receiving a 304 response if at least one
849   of those representations matches the selected representation.
850</t>
851<t>
852   If-None-Match MAY also be used with a value of "*" to prevent an unsafe
853   request method (e.g., PUT) from inadvertently modifying an existing
854   representation of the target resource when the client believes that
855   the resource does not have a current representation.  This is a variation
856   on the "lost update" problem that might arise if more than one client
857   attempts to create an initial representation for the target resource.
858</t>
859<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="If-None-Match"/>
860  <x:ref>If-None-Match</x:ref> = "*" / 1#<x:ref>entity-tag</x:ref>
861</artwork></figure>
862<t>
863   If any of the entity-tags listed in the If-None-Match field-value match
864   (as per <xref target="entity.tag.comparison"/>) the entity-tag of the
865   selected representation, or if "*" is
866   given and any current representation exists for that resource, then the
867   server &MUST-NOT; perform the requested method.
868   Instead, if the request method was GET or HEAD, the server &SHOULD;
869   respond with a 304 (Not Modified) status code, including the cache-related
870   header fields (particularly ETag) of the selected representation that has
871   a matching entity-tag.  For all other request methods, the server &MUST;
872   respond with a 412 (Precondition Failed) status code.
873</t>
874<t>
875   If none of the entity-tags match, then the server &MAY; perform the
876   requested method as if the If-None-Match header field did not exist,
877   but &MUST; also ignore any If-Modified-Since header field(s) in the
878   request. That is, if no entity-tags match, then the server &MUST-NOT;
879   return a 304 (Not Modified) response.
880</t>
881<t>
882   If the request would, without the If-None-Match header field, result
883   in anything other than a 2xx or 304 status code, then the If-None-Match
884   header field &MUST; be ignored. (See <xref
885   target="rules.for.when.to.use.entity.tags.and.last-modified.dates"/> for
886   a discussion of server behavior when both If-Modified-Since and
887   If-None-Match appear in the same request.)
888</t>
889<t>
890   Examples:
891</t>
892<figure><artwork type="example">
893  If-None-Match: "xyzzy"
894  If-None-Match: W/"xyzzy"
895  If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
896  If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz"
897  If-None-Match: *
898</artwork></figure>
899<t>
900   The result of a request having both an If-None-Match header field and
901   either an If-Match or an If-Unmodified-Since header fields is
902   undefined by this specification.
903</t>
904</section>
905
906<section title="If-Modified-Since" anchor="header.if-modified-since">
907  <iref primary="true" item="If-Modified-Since header field" x:for-anchor=""/>
908  <iref primary="true" item="Header Fields" subitem="If-Modified-Since" x:for-anchor=""/>
909  <x:anchor-alias value="If-Modified-Since"/>
910<t>
911   The "If-Modified-Since" header field &MAY; be used to make a request
912   method conditional by modification date: if the selected representation
913   has not been modified since the time specified in this field, then
914   do not perform the request method; instead, respond as detailed below.
915</t>
916<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="If-Modified-Since"/>
917  <x:ref>If-Modified-Since</x:ref> = <x:ref>HTTP-date</x:ref>
918</artwork></figure>
919<t>
920   An example of the field is:
921</t>
922<figure><artwork type="example">
923  If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
924</artwork></figure>
925<t>
926   A GET method with an If-Modified-Since header field and no Range header
927   field requests that the selected representation be transferred only if
928   it has been modified since the date given by the If-Modified-Since
929   header field.
930   The algorithm for determining this includes the following cases:
931  <list style="numbers">
932      <t>If the request would normally result in anything other than a
933         200 (OK) status code, or if the passed If-Modified-Since date is
934         invalid, the response is exactly the same as for a normal GET.
935         A date which is later than the server's current time is
936         invalid.</t>
937
938      <t>If the selected representation has been modified since the
939         If-Modified-Since date, the response is exactly the same as for
940         a normal GET.</t>
941
942      <t>If the selected representation has not been modified since a valid
943         If-Modified-Since date, the server &SHOULD; return a
944         304 (Not Modified) response.</t>
945  </list>
946</t>
947<t>
948   The purpose of this feature is to allow efficient updates of cached
949   information with a minimum amount of transaction overhead.
950  <list><t>
951      <x:h>Note:</x:h> The Range header field modifies the meaning of If-Modified-Since;
952      see &header-range; for full details.
953    </t><t>
954      <x:h>Note:</x:h> If-Modified-Since times are interpreted by the server, whose
955      clock might not be synchronized with the client.
956    </t><t>
957      <x:h>Note:</x:h> When handling an If-Modified-Since header field, some
958      servers will use an exact date comparison function, rather than a
959      less-than function, for deciding whether to send a 304 (Not
960      Modified) response. To get best results when sending an If-Modified-Since
961      header field for cache validation, clients are
962      advised to use the exact date string received in a previous Last-Modified
963      header field whenever possible.
964    </t><t>
965      <x:h>Note:</x:h> If a client uses an arbitrary date in the If-Modified-Since
966      header field instead of a date taken from the Last-Modified header field for
967      the same request, the client needs to be aware that this
968      date is interpreted in the server's understanding of time.
969      Unsynchronized clocks and rounding problems, due to the different
970      encodings of time between the client and server, are concerns.
971      This includes the possibility of race conditions if the
972      document has changed between the time it was first requested and
973      the If-Modified-Since date of a subsequent request, and the
974      possibility of clock-skew-related problems if the If-Modified-Since
975      date is derived from the client's clock without correction
976      to the server's clock. Corrections for different time bases
977      between client and server are at best approximate due to network
978      latency.
979    </t>
980  </list>
981</t>
982<t>
983   The result of a request having both an If-Modified-Since header field
984   and either an If-Match or an If-Unmodified-Since header fields is
985   undefined by this specification.
986</t>
987</section>
988
989<section title="If-Unmodified-Since" anchor="header.if-unmodified-since">
990  <iref primary="true" item="If-Unmodified-Since header field" x:for-anchor=""/>
991  <iref primary="true" item="Header Fields" subitem="If-Unmodified-Since" x:for-anchor=""/>
992  <x:anchor-alias value="If-Unmodified-Since"/>
993<t>
994   The "If-Unmodified-Since" header field &MAY; be used to make a request
995   method conditional by modification date: if the selected representation
996   has been modified since the time specified in this field, then the
997   server &MUST-NOT; perform the requested operation and &MUST; instead
998   respond with the 412 (Precondition Failed) status code.
999   If the selected representation has not been modified since the time
1000   specified in this field, the server &SHOULD; perform the request
1001   method as if the If-Unmodified-Since header field were not present.
1002</t>
1003<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="If-Unmodified-Since"/>
1004  <x:ref>If-Unmodified-Since</x:ref> = <x:ref>HTTP-date</x:ref>
1005</artwork></figure>
1006<t>
1007   An example of the field is:
1008</t>
1009<figure><artwork type="example">
1010  If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
1011</artwork></figure>
1012<t>
1013   If the request normally (i.e., without the If-Unmodified-Since
1014   header field) would result in anything other than a 2xx or 412 status code,
1015   the If-Unmodified-Since header field &SHOULD; be ignored.
1016</t>
1017<t>
1018   If the specified date is invalid, the header field &MUST; be ignored.
1019</t>
1020<t>
1021   The result of a request having both an If-Unmodified-Since header
1022   field and either an If-None-Match or an If-Modified-Since header
1023   fields is undefined by this specification.
1024</t>
1025</section>
1026
1027<section title="If-Range" anchor="header.if-range">
1028<t>
1029   The If-Range header field provides a special conditional request
1030   mechanism that is similar to If-Match and If-Unmodified-Since but
1031   specific to HTTP range requests. If-Range is defined in &header-if-range;.
1032</t>
1033</section>
1034
1035</section>
1036
1037<section title="Status Code Definitions" anchor="status.code.definitions">
1038<section title="304 Not Modified" anchor="status.304">
1039  <iref primary="true" item="304 Not Modified (status code)" x:for-anchor=""/>
1040  <iref primary="true" item="Status Codes" subitem="304 Not Modified" x:for-anchor=""/>
1041<t>
1042   The 304 status code indicates that a conditional GET request has been
1043   received and would have resulted in a 200 (OK) response if it were not
1044   for the fact that the condition has evaluated to false.  In other words,
1045   there is no need for the server to transfer a representation of the
1046   target resource because the client's request indicates that it already
1047   has a valid representation, as indicated by the 304 response header
1048   fields, and is therefore redirecting the client to make use of that
1049   stored representation as if it were the payload of a 200 response.
1050   The 304 response &MUST-NOT; contain a message-body, and thus is always
1051   terminated by the first empty line after the header fields.
1052</t>
1053<t>
1054   A 304 response &MUST; include a Date header field (&header-date;)
1055   unless its omission is required by &clockless;.  If a 200 response
1056   to the same request would have included any of the header fields
1057   Cache-Control, Content-Location, ETag, Expires, Last-Modified, or
1058   Vary, then those same header fields &MUST; be sent in a 304 response.
1059</t>
1060<t>
1061   Since the goal of a 304 response is to minimize information transfer
1062   when the recipient already has one or more cached representations,
1063   the response &SHOULD-NOT; include representation metadata other
1064   than the above listed fields unless said metadata exists for the
1065   purpose of guiding cache updates (e.g., future HTTP extensions).
1066</t>
1067<t>
1068   If the recipient of a 304 response does not have a cached representation
1069   corresponding to the entity-tag indicated by the 304 response, then the
1070   recipient &MUST-NOT; use the 304 to update its own cache.  If this
1071   conditional request originated with an outbound client, such as a
1072   user agent with its own cache sending a conditional GET to a shared
1073   proxy, then the 304 response &MAY; be forwarded to the outbound client.
1074   Otherwise, the recipient &MUST; disregard the 304 response and repeat
1075   the request without any preconditions.
1076</t>
1077<t>
1078   If a cache uses a received 304 response to update a cache entry, the
1079   cache &MUST; update the entry to reflect any new field values given in
1080   the response.
1081</t>
1082</section>
1083
1084<section title="412 Precondition Failed" anchor="status.412">
1085  <iref primary="true" item="412 Precondition Failed (status code)" x:for-anchor=""/>
1086  <iref primary="true" item="Status Codes" subitem="412 Precondition Failed" x:for-anchor=""/>
1087<t>
1088   The 412 status code indicates that one or more preconditions given in
1089   the request header fields evaluated to false when tested on the server.
1090   This response code allows the client to place preconditions on the
1091   current resource state (its current representations and metadata)
1092   and thus prevent the request method from being applied if the target
1093   resource is in an unexpected state.
1094</t>
1095</section>
1096</section>
1097
1098<section title="IANA Considerations" anchor="IANA.considerations">
1099
1100<section title="Status Code Registration" anchor="status.code.registration">
1101<t>
1102   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
1103   shall be updated with the registrations below:
1104</t>
1105<?BEGININC p4-conditional.iana-status-codes ?>
1106<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
1107<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
1108   <ttcol>Value</ttcol>
1109   <ttcol>Description</ttcol>
1110   <ttcol>Reference</ttcol>
1111   <c>304</c>
1112   <c>Not Modified</c>
1113   <c>
1114      <xref target="status.304"/>
1115   </c>
1116   <c>412</c>
1117   <c>Precondition Failed</c>
1118   <c>
1119      <xref target="status.412"/>
1120   </c>
1121</texttable>
1122<!--(END)-->
1123<?ENDINC p4-conditional.iana-status-codes ?>
1124</section>
1125
1126<section title="Header Field Registration" anchor="header.field.registration">
1127<t>
1128   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
1129   with the permanent registrations below (see <xref target="RFC3864"/>):
1130</t>
1131<?BEGININC p4-conditional.iana-headers ?>
1132<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
1133<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
1134   <ttcol>Header Field Name</ttcol>
1135   <ttcol>Protocol</ttcol>
1136   <ttcol>Status</ttcol>
1137   <ttcol>Reference</ttcol>
1138
1139   <c>ETag</c>
1140   <c>http</c>
1141   <c>standard</c>
1142   <c>
1143      <xref target="header.etag"/>
1144   </c>
1145   <c>If-Match</c>
1146   <c>http</c>
1147   <c>standard</c>
1148   <c>
1149      <xref target="header.if-match"/>
1150   </c>
1151   <c>If-Modified-Since</c>
1152   <c>http</c>
1153   <c>standard</c>
1154   <c>
1155      <xref target="header.if-modified-since"/>
1156   </c>
1157   <c>If-None-Match</c>
1158   <c>http</c>
1159   <c>standard</c>
1160   <c>
1161      <xref target="header.if-none-match"/>
1162   </c>
1163   <c>If-Unmodified-Since</c>
1164   <c>http</c>
1165   <c>standard</c>
1166   <c>
1167      <xref target="header.if-unmodified-since"/>
1168   </c>
1169   <c>Last-Modified</c>
1170   <c>http</c>
1171   <c>standard</c>
1172   <c>
1173      <xref target="header.last-modified"/>
1174   </c>
1175</texttable>
1176<!--(END)-->
1177<?ENDINC p4-conditional.iana-headers ?>
1178<t>
1179   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
1180</t>
1181</section>
1182</section>
1183
1184<section title="Security Considerations" anchor="security.considerations">
1185<t>
1186   No additional security considerations have been identified beyond
1187   those applicable to HTTP in general &messaging;.
1188</t>
1189</section>
1190
1191<section title="Acknowledgments" anchor="acks">
1192<t>
1193  See &acks;.
1194</t>
1195</section>
1196</middle>
1197<back>
1198
1199<references title="Normative References">
1200
1201<reference anchor="Part1">
1202  <front>
1203    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
1204    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1205      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1206      <address><email>fielding@gbiv.com</email></address>
1207    </author>
1208    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1209      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1210      <address><email>jg@freedesktop.org</email></address>
1211    </author>
1212    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1213      <organization abbrev="HP">Hewlett-Packard Company</organization>
1214      <address><email>JeffMogul@acm.org</email></address>
1215    </author>
1216    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1217      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1218      <address><email>henrikn@microsoft.com</email></address>
1219    </author>
1220    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1221      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1222      <address><email>LMM@acm.org</email></address>
1223    </author>
1224    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1225      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1226      <address><email>paulle@microsoft.com</email></address>
1227    </author>
1228    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1229      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1230      <address><email>timbl@w3.org</email></address>
1231    </author>
1232    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1233      <organization abbrev="W3C">World Wide Web Consortium</organization>
1234      <address><email>ylafon@w3.org</email></address>
1235    </author>
1236    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1237      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1238      <address><email>julian.reschke@greenbytes.de</email></address>
1239    </author>
1240    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1241  </front>
1242  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
1243  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
1244</reference>
1245
1246<reference anchor="Part3">
1247  <front>
1248    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
1249    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1250      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1251      <address><email>fielding@gbiv.com</email></address>
1252    </author>
1253    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1254      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1255      <address><email>jg@freedesktop.org</email></address>
1256    </author>
1257    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1258      <organization abbrev="HP">Hewlett-Packard Company</organization>
1259      <address><email>JeffMogul@acm.org</email></address>
1260    </author>
1261    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1262      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1263      <address><email>henrikn@microsoft.com</email></address>
1264    </author>
1265    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1266      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1267      <address><email>LMM@acm.org</email></address>
1268    </author>
1269    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1270      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1271      <address><email>paulle@microsoft.com</email></address>
1272    </author>
1273    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1274      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1275      <address><email>timbl@w3.org</email></address>
1276    </author>
1277    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1278      <organization abbrev="W3C">World Wide Web Consortium</organization>
1279      <address><email>ylafon@w3.org</email></address>
1280    </author>
1281    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1282      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1283      <address><email>julian.reschke@greenbytes.de</email></address>
1284    </author>
1285    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1286  </front>
1287  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
1288  <x:source href="p3-payload.xml" basename="p3-payload"/>
1289</reference>
1290
1291<reference anchor="Part5">
1292  <front>
1293    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
1294    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1295      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1296      <address><email>fielding@gbiv.com</email></address>
1297    </author>
1298    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1299      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1300      <address><email>jg@freedesktop.org</email></address>
1301    </author>
1302    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1303      <organization abbrev="HP">Hewlett-Packard Company</organization>
1304      <address><email>JeffMogul@acm.org</email></address>
1305    </author>
1306    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1307      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1308      <address><email>henrikn@microsoft.com</email></address>
1309    </author>
1310    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1311      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1312      <address><email>LMM@acm.org</email></address>
1313    </author>
1314    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1315      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1316      <address><email>paulle@microsoft.com</email></address>
1317    </author>
1318    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1319      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1320      <address><email>timbl@w3.org</email></address>
1321    </author>
1322    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1323      <organization abbrev="W3C">World Wide Web Consortium</organization>
1324      <address><email>ylafon@w3.org</email></address>
1325    </author>
1326    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1327      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1328      <address><email>julian.reschke@greenbytes.de</email></address>
1329    </author>
1330    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1331  </front>
1332  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
1333  <x:source href="p5-range.xml" basename="p5-range"/>
1334</reference>
1335
1336<reference anchor="Part6">
1337  <front>
1338    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
1339    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
1340      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1341      <address><email>fielding@gbiv.com</email></address>
1342    </author>
1343    <author initials="J." surname="Gettys" fullname="Jim Gettys">
1344      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
1345      <address><email>jg@freedesktop.org</email></address>
1346    </author>
1347    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
1348      <organization abbrev="HP">Hewlett-Packard Company</organization>
1349      <address><email>JeffMogul@acm.org</email></address>
1350    </author>
1351    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
1352      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1353      <address><email>henrikn@microsoft.com</email></address>
1354    </author>
1355    <author initials="L." surname="Masinter" fullname="Larry Masinter">
1356      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
1357      <address><email>LMM@acm.org</email></address>
1358    </author>
1359    <author initials="P." surname="Leach" fullname="Paul J. Leach">
1360      <organization abbrev="Microsoft">Microsoft Corporation</organization>
1361      <address><email>paulle@microsoft.com</email></address>
1362    </author>
1363    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
1364      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
1365      <address><email>timbl@w3.org</email></address>
1366    </author>
1367    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
1368      <organization abbrev="W3C">World Wide Web Consortium</organization>
1369      <address><email>ylafon@w3.org</email></address>
1370    </author>
1371    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
1372      <address><email>mnot@mnot.net</email></address>
1373    </author>
1374    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
1375      <organization abbrev="greenbytes">greenbytes GmbH</organization>
1376      <address><email>julian.reschke@greenbytes.de</email></address>
1377    </author>
1378    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
1379  </front>
1380  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
1381  <x:source href="p6-cache.xml" basename="p6-cache"/>
1382</reference>
1383
1384<reference anchor="RFC2119">
1385  <front>
1386    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
1387    <author initials="S." surname="Bradner" fullname="Scott Bradner">
1388      <organization>Harvard University</organization>
1389      <address><email>sob@harvard.edu</email></address>
1390    </author>
1391    <date month="March" year="1997"/>
1392  </front>
1393  <seriesInfo name="BCP" value="14"/>
1394  <seriesInfo name="RFC" value="2119"/>
1395</reference>
1396
1397<reference anchor="RFC5234">
1398  <front>
1399    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
1400    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
1401      <organization>Brandenburg InternetWorking</organization>
1402      <address>
1403        <email>dcrocker@bbiw.net</email>
1404      </address> 
1405    </author>
1406    <author initials="P." surname="Overell" fullname="Paul Overell">
1407      <organization>THUS plc.</organization>
1408      <address>
1409        <email>paul.overell@thus.net</email>
1410      </address>
1411    </author>
1412    <date month="January" year="2008"/>
1413  </front>
1414  <seriesInfo name="STD" value="68"/>
1415  <seriesInfo name="RFC" value="5234"/>
1416</reference>
1417
1418</references>
1419
1420<references title="Informative References">
1421
1422<reference anchor="RFC2616">
1423  <front>
1424    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
1425    <author initials="R." surname="Fielding" fullname="R. Fielding">
1426      <organization>University of California, Irvine</organization>
1427      <address><email>fielding@ics.uci.edu</email></address>
1428    </author>
1429    <author initials="J." surname="Gettys" fullname="J. Gettys">
1430      <organization>W3C</organization>
1431      <address><email>jg@w3.org</email></address>
1432    </author>
1433    <author initials="J." surname="Mogul" fullname="J. Mogul">
1434      <organization>Compaq Computer Corporation</organization>
1435      <address><email>mogul@wrl.dec.com</email></address>
1436    </author>
1437    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
1438      <organization>MIT Laboratory for Computer Science</organization>
1439      <address><email>frystyk@w3.org</email></address>
1440    </author>
1441    <author initials="L." surname="Masinter" fullname="L. Masinter">
1442      <organization>Xerox Corporation</organization>
1443      <address><email>masinter@parc.xerox.com</email></address>
1444    </author>
1445    <author initials="P." surname="Leach" fullname="P. Leach">
1446      <organization>Microsoft Corporation</organization>
1447      <address><email>paulle@microsoft.com</email></address>
1448    </author>
1449    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
1450      <organization>W3C</organization>
1451      <address><email>timbl@w3.org</email></address>
1452    </author>
1453    <date month="June" year="1999"/>
1454  </front>
1455  <seriesInfo name="RFC" value="2616"/>
1456</reference>
1457
1458<reference anchor='RFC3864'>
1459  <front>
1460    <title>Registration Procedures for Message Header Fields</title>
1461    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
1462      <organization>Nine by Nine</organization>
1463      <address><email>GK-IETF@ninebynine.org</email></address>
1464    </author>
1465    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
1466      <organization>BEA Systems</organization>
1467      <address><email>mnot@pobox.com</email></address>
1468    </author>
1469    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
1470      <organization>HP Labs</organization>
1471      <address><email>JeffMogul@acm.org</email></address>
1472    </author>
1473    <date year='2004' month='September' />
1474  </front>
1475  <seriesInfo name='BCP' value='90' />
1476  <seriesInfo name='RFC' value='3864' />
1477</reference>
1478
1479<reference anchor='RFC4918'>
1480  <front>
1481    <title>HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)</title>
1482    <author initials="L.M." surname="Dusseault" fullname="Lisa Dusseault" role="editor" >
1483      <organization abbrev="CommerceNet">CommerceNet</organization>
1484      <address><email>ldusseault@commerce.net</email></address>
1485    </author>
1486    <date month="June" year="2007" />
1487  </front>
1488  <seriesInfo name='RFC' value='4918' />
1489</reference>
1490</references>
1491
1492<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
1493<t>
1494  Allow weak entity-tags in all requests except range requests (Sections
1495  <xref target="weak.and.strong.validators" format="counter"/> and
1496  <xref target="header.if-none-match" format="counter"/>).
1497</t>
1498<t>
1499  Change ABNF productions for header fields to only define the field value.
1500  (<xref target="header.field.definitions"/>)
1501</t>
1502</section>
1503
1504<?BEGININC p4-conditional.abnf-appendix ?>
1505<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
1506<figure>
1507<artwork type="abnf" name="p4-conditional.parsed-abnf">
1508<x:ref>ETag</x:ref> = entity-tag
1509
1510<x:ref>HTTP-date</x:ref> = &lt;HTTP-date, defined in [Part1], Section 6.1&gt;
1511
1512<x:ref>If-Match</x:ref> = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS
1513 entity-tag ] ) )
1514<x:ref>If-Modified-Since</x:ref> = HTTP-date
1515<x:ref>If-None-Match</x:ref> = "*" / ( *( "," OWS ) entity-tag *( OWS "," [ OWS
1516 entity-tag ] ) )
1517<x:ref>If-Unmodified-Since</x:ref> = HTTP-date
1518
1519<x:ref>Last-Modified</x:ref> = HTTP-date
1520
1521<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
1522
1523<x:ref>entity-tag</x:ref> = [ weak ] opaque-tag
1524
1525<x:ref>opaque-tag</x:ref> = quoted-string
1526
1527<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.3&gt;
1528
1529<x:ref>weak</x:ref> = %x57.2F ; W/
1530</artwork>
1531</figure>
1532<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
1533; ETag defined but not used
1534; If-Match defined but not used
1535; If-Modified-Since defined but not used
1536; If-None-Match defined but not used
1537; If-Unmodified-Since defined but not used
1538; Last-Modified defined but not used
1539</artwork></figure></section>
1540<?ENDINC p4-conditional.abnf-appendix ?>
1541
1542<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
1543
1544<section title="Since RFC 2616">
1545<t>
1546  Extracted relevant partitions from <xref target="RFC2616"/>.
1547</t>
1548</section>
1549
1550<section title="Since draft-ietf-httpbis-p4-conditional-00">
1551<t>
1552  Closed issues:
1553  <list style="symbols"> 
1554    <t>
1555      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
1556      "Normative and Informative references"
1557    </t>
1558  </list>
1559</t>
1560<t>
1561  Other changes:
1562  <list style="symbols"> 
1563    <t>
1564      Move definitions of 304 and 412 condition codes from Part2.
1565    </t>
1566  </list>
1567</t>
1568</section>
1569
1570<section title="Since draft-ietf-httpbis-p4-conditional-01">
1571<t>
1572  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
1573  <list style="symbols"> 
1574    <t>
1575      Add explicit references to BNF syntax and rules imported from other parts of the specification.
1576    </t>
1577  </list>
1578</t>
1579</section>
1580
1581<section title="Since draft-ietf-httpbis-p4-conditional-02" anchor="changes.since.02">
1582<t>
1583  Closed issues:
1584  <list style="symbols"> 
1585    <t>
1586      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/116"/>:
1587      "Weak ETags on non-GET requests"
1588    </t>
1589  </list>
1590</t>
1591<t>
1592  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
1593  <list style="symbols"> 
1594    <t>
1595      Reference RFC 3984, and update header field registrations for header fields defined
1596      in this document.
1597    </t>
1598  </list>
1599</t>
1600</section>
1601
1602<section title="Since draft-ietf-httpbis-p4-conditional-03" anchor="changes.since.03">
1603<t>
1604  Closed issues:
1605  <list style="symbols"> 
1606    <t>
1607      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/71"/>:
1608      "Examples for ETag matching"
1609    </t>
1610    <t>
1611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/124"/>:
1612      "'entity value' undefined"
1613    </t>
1614    <t>
1615      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/126"/>:
1616      "bogus 2068 Date header reference"
1617    </t>
1618  </list>
1619</t>
1620</section>
1621
1622<section title="Since draft-ietf-httpbis-p4-conditional-04" anchor="changes.since.04">
1623<t>
1624  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
1625  <list style="symbols"> 
1626    <t>
1627      Use "/" instead of "|" for alternatives.
1628    </t>
1629    <t>
1630      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
1631      whitespace ("OWS") and required whitespace ("RWS").
1632    </t>
1633    <t>
1634      Rewrite ABNFs to spell out whitespace rules, factor out
1635      header field value format definitions.
1636    </t>
1637  </list>
1638</t>
1639</section>
1640
1641<section title="Since draft-ietf-httpbis-p4-conditional-05" anchor="changes.since.05">
1642<t>
1643  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
1644  <list style="symbols"> 
1645    <t>
1646      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
1647    </t>
1648  </list>
1649</t>
1650</section>
1651
1652<section title="Since draft-ietf-httpbis-p4-conditional-06" anchor="changes.since.06">
1653<t>
1654  Closed issues:
1655  <list style="symbols"> 
1656    <t>
1657      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/153"/>:
1658      "case-sensitivity of etag weakness indicator"
1659    </t>
1660  </list>
1661</t>
1662</section>
1663
1664<section title="Since draft-ietf-httpbis-p4-conditional-07" anchor="changes.since.07">
1665<t>
1666  Closed issues:
1667  <list style="symbols"> 
1668    <t>
1669      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/116"/>:
1670      "Weak ETags on non-GET requests" (If-Match still was defined to require
1671      strong matching)
1672    </t>
1673    <t>
1674      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
1675      "move IANA registrations for optional status codes"
1676    </t>
1677  </list>
1678</t>
1679</section>
1680
1681<section title="Since draft-ietf-httpbis-p4-conditional-08" anchor="changes.since.08">
1682<t>
1683  No significant changes.
1684</t>
1685</section>
1686
1687<section title="Since draft-ietf-httpbis-p4-conditional-09" anchor="changes.since.09">
1688<t>
1689  No significant changes.
1690</t>
1691</section>
1692
1693<section title="Since draft-ietf-httpbis-p4-conditional-10" anchor="changes.since.10">
1694<t>
1695  Closed issues:
1696  <list style="symbols"> 
1697    <t>
1698      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
1699      "Clarify 'Requested Variant'"
1700    </t>
1701    <t>
1702      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
1703      "Clarify entity / representation / variant terminology"
1704    </t>
1705    <t>
1706      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
1707      "consider removing the 'changes from 2068' sections"
1708    </t>
1709  </list>
1710</t>
1711</section>
1712
1713<section title="Since draft-ietf-httpbis-p4-conditional-11" anchor="changes.since.11">
1714<t>
1715  None.
1716</t>
1717</section>
1718
1719<section title="Since draft-ietf-httpbis-p4-conditional-12" anchor="changes.since.12">
1720<t>
1721  Closed issues:
1722  <list style="symbols"> 
1723    <t>
1724      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
1725      "Header Classification"
1726    </t>
1727  </list>
1728</t>
1729</section>
1730
1731<section title="Since draft-ietf-httpbis-p4-conditional-13" anchor="changes.since.13">
1732<t>
1733  Closed issues:
1734  <list style="symbols"> 
1735    <t>
1736      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/89"/>:
1737      "If-* and entities"
1738    </t>
1739    <t>
1740      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/101"/>:
1741      "Definition of validator weakness"
1742    </t>
1743    <t>
1744      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
1745      "untangle ABNFs for header fields"
1746    </t>
1747    <t>
1748      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/269"/>:
1749      "ETags and Quotes"
1750    </t>
1751  </list>
1752</t>
1753</section>
1754
1755<section title="Since draft-ietf-httpbis-p4-conditional-14" anchor="changes.since.14">
1756<t>
1757  None.
1758</t>
1759</section>
1760
1761<section title="Since draft-ietf-httpbis-p4-conditional-15" anchor="changes.since.15">
1762<t>
1763  Closed issues:
1764  <list style="symbols"> 
1765    <t>
1766      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/304"/>:
1767      "If-Range should be listed when dicussing contexts where L-M can be considered strong"
1768    </t>
1769  </list>
1770</t>
1771</section>
1772
1773<section title="Since draft-ietf-httpbis-p4-conditional-16" anchor="changes.since.16">
1774<t>
1775  None yet.
1776</t>
1777</section>
1778
1779</section>
1780
1781</back>
1782</rfc>
Note: See TracBrowser for help on using the repository browser.