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Changeset 205 for draft-ietf-httpbis/latest/p4-conditional.html
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- 06/02/08 19:15:29 (14 years ago)
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draft-ietf-httpbis/latest/p4-conditional.html (modified) (26 diffs)
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draft-ietf-httpbis/latest/p4-conditional.html
r204 r205 333 333 <link rel="Index" href="#rfc.index"> 334 334 <link rel="Chapter" title="1 Introduction" href="#rfc.section.1"> 335 <link rel="Chapter" title="2 Entity Tags" href="#rfc.section.2"> 336 <link rel="Chapter" title="3 Status Code Definitions" href="#rfc.section.3"> 337 <link rel="Chapter" title="4 Weak and Strong Validators" href="#rfc.section.4"> 338 <link rel="Chapter" title="5 Rules for When to Use Entity Tags and Last-Modified Dates" href="#rfc.section.5"> 339 <link rel="Chapter" title="6 Header Field Definitions" href="#rfc.section.6"> 340 <link rel="Chapter" title="7 IANA Considerations" href="#rfc.section.7"> 341 <link rel="Chapter" title="8 Security Considerations" href="#rfc.section.8"> 342 <link rel="Chapter" title="9 Acknowledgments" href="#rfc.section.9"> 343 <link rel="Chapter" href="#rfc.section.10" title="10 References"> 335 <link rel="Chapter" title="2 Notational Conventions and Generic Grammar" href="#rfc.section.2"> 336 <link rel="Chapter" title="3 Entity Tags" href="#rfc.section.3"> 337 <link rel="Chapter" title="4 Status Code Definitions" href="#rfc.section.4"> 338 <link rel="Chapter" title="5 Weak and Strong Validators" href="#rfc.section.5"> 339 <link rel="Chapter" title="6 Rules for When to Use Entity Tags and Last-Modified Dates" href="#rfc.section.6"> 340 <link rel="Chapter" title="7 Header Field Definitions" href="#rfc.section.7"> 341 <link rel="Chapter" title="8 IANA Considerations" href="#rfc.section.8"> 342 <link rel="Chapter" title="9 Security Considerations" href="#rfc.section.9"> 343 <link rel="Chapter" title="10 Acknowledgments" href="#rfc.section.10"> 344 <link rel="Chapter" href="#rfc.section.11" title="11 References"> 344 345 <link rel="Appendix" title="A Compatibility with Previous Versions" href="#rfc.section.A"> 345 346 <link rel="Appendix" title="B Change Log (to be removed by RFC Editor before publication)" href="#rfc.section.B"> … … 482 483 </ul> 483 484 </li> 484 <li class="tocline0">2. <a href="#entity.tags">Entity Tags</a></li> 485 <li class="tocline0">3. <a href="#rfc.section.3">Status Code Definitions</a><ul class="toc"> 486 <li class="tocline1">3.1 <a href="#status.304">304 Not Modified</a></li> 487 <li class="tocline1">3.2 <a href="#status.412">412 Precondition Failed</a></li> 485 <li class="tocline0">2. <a href="#notation">Notational Conventions and Generic Grammar</a></li> 486 <li class="tocline0">3. <a href="#entity.tags">Entity Tags</a></li> 487 <li class="tocline0">4. <a href="#rfc.section.4">Status Code Definitions</a><ul class="toc"> 488 <li class="tocline1">4.1 <a href="#status.304">304 Not Modified</a></li> 489 <li class="tocline1">4.2 <a href="#status.412">412 Precondition Failed</a></li> 488 490 </ul> 489 491 </li> 490 <li class="tocline0"> 4. <a href="#weak.and.strong.validators">Weak and Strong Validators</a></li>491 <li class="tocline0"> 5. <a href="#rules.for.when.to.use.entity.tags.and.last-modified.dates">Rules for When to Use Entity Tags and Last-Modified Dates</a></li>492 <li class="tocline0"> 6. <a href="#header.fields">Header Field Definitions</a><ul class="toc">493 <li class="tocline1"> 6.1 <a href="#header.etag">ETag</a></li>494 <li class="tocline1"> 6.2 <a href="#header.if-match">If-Match</a></li>495 <li class="tocline1"> 6.3 <a href="#header.if-modified-since">If-Modified-Since</a></li>496 <li class="tocline1"> 6.4 <a href="#header.if-none-match">If-None-Match</a></li>497 <li class="tocline1"> 6.5 <a href="#header.if-unmodified-since">If-Unmodified-Since</a></li>498 <li class="tocline1"> 6.6 <a href="#header.last-modified">Last-Modified</a></li>492 <li class="tocline0">5. <a href="#weak.and.strong.validators">Weak and Strong Validators</a></li> 493 <li class="tocline0">6. <a href="#rules.for.when.to.use.entity.tags.and.last-modified.dates">Rules for When to Use Entity Tags and Last-Modified Dates</a></li> 494 <li class="tocline0">7. <a href="#header.fields">Header Field Definitions</a><ul class="toc"> 495 <li class="tocline1">7.1 <a href="#header.etag">ETag</a></li> 496 <li class="tocline1">7.2 <a href="#header.if-match">If-Match</a></li> 497 <li class="tocline1">7.3 <a href="#header.if-modified-since">If-Modified-Since</a></li> 498 <li class="tocline1">7.4 <a href="#header.if-none-match">If-None-Match</a></li> 499 <li class="tocline1">7.5 <a href="#header.if-unmodified-since">If-Unmodified-Since</a></li> 500 <li class="tocline1">7.6 <a href="#header.last-modified">Last-Modified</a></li> 499 501 </ul> 500 502 </li> 501 <li class="tocline0"> 7. <a href="#IANA.considerations">IANA Considerations</a></li>502 <li class="tocline0"> 8. <a href="#security.considerations">Security Considerations</a></li>503 <li class="tocline0"> 9. <a href="#ack">Acknowledgments</a></li>504 <li class="tocline0">1 0. <a href="#rfc.references">References</a><ul class="toc">505 <li class="tocline1">1 0.1 <a href="#rfc.references.1">Normative References</a></li>506 <li class="tocline1">1 0.2 <a href="#rfc.references.2">Informative References</a></li>503 <li class="tocline0">8. <a href="#IANA.considerations">IANA Considerations</a></li> 504 <li class="tocline0">9. <a href="#security.considerations">Security Considerations</a></li> 505 <li class="tocline0">10. <a href="#ack">Acknowledgments</a></li> 506 <li class="tocline0">11. <a href="#rfc.references">References</a><ul class="toc"> 507 <li class="tocline1">11.1 <a href="#rfc.references.1">Normative References</a></li> 508 <li class="tocline1">11.2 <a href="#rfc.references.2">Informative References</a></li> 507 509 </ul> 508 510 </li> … … 541 543 <p id="rfc.section.1.1.p.2">An implementation is not compliant if it fails to satisfy one or more of the <em class="bcp14">MUST</em> or <em class="bcp14">REQUIRED</em> level requirements for the protocols it implements. An implementation that satisfies all the <em class="bcp14">MUST</em> or <em class="bcp14">REQUIRED</em> level and all the <em class="bcp14">SHOULD</em> level requirements for its protocols is said to be "unconditionally compliant"; one that satisfies all the <em class="bcp14">MUST</em> level requirements but not all the <em class="bcp14">SHOULD</em> level requirements for its protocols is said to be "conditionally compliant." 542 544 </p> 543 <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a> <a id="entity.tags" href="#entity.tags">Entity Tags</a></h1> 544 <p id="rfc.section.2.p.1">Entity tags are used for comparing two or more entities from the same requested resource. HTTP/1.1 uses entity tags in the 545 ETag (<a href="#header.etag" id="rfc.xref.header.etag.1" title="ETag">Section 6.1</a>), If-Match (<a href="#header.if-match" id="rfc.xref.header.if-match.1" title="If-Match">Section 6.2</a>), If-None-Match (<a href="#header.if-none-match" id="rfc.xref.header.if-none-match.1" title="If-None-Match">Section 6.4</a>), and If-Range (<a href="p5-range.html#header.if-range" title="If-Range">Section 5.3</a> of <a href="#Part5" id="rfc.xref.Part5.1"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>) header fields. The definition of how they are used and compared as cache validators is in <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section 4</a>. An entity tag consists of an opaque quoted string, possibly prefixed by a weakness indicator. 546 </p> 547 <div id="rfc.figure.u.1"></div><pre class="inline"><span id="rfc.iref.g.1"></span><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span> entity-tag = [ weak ] opaque-tag 545 <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a> <a id="notation" href="#notation">Notational Conventions and Generic Grammar</a></h1> 546 <p id="rfc.section.2.p.1">This specification uses the ABNF syntax defined in <a href="p1-messaging.html#notation.abnf" title="Augmented BNF">Section 2.1</a> of <a href="#Part1" id="rfc.xref.Part1.1"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> and the core rules defined in <a href="p1-messaging.html#basic.rules" title="Basic Rules">Section 2.2</a> of <a href="#Part1" id="rfc.xref.Part1.2"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>: <span class="comment">[abnf.dep: ABNF syntax and basic rules will be adopted from RFC 5234, see <<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/36">http://tools.ietf.org/wg/httpbis/trac/ticket/36</a>>.]</span> 547 </p> 548 <div id="rfc.figure.u.1"></div><pre class="inline"> quoted-string = <quoted-string, defined in <a href="#Part1" id="rfc.xref.Part1.3"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#basic.rules" title="Basic Rules">Section 2.2</a>> 549 </pre><p id="rfc.section.2.p.3">The ABNF rules below are defined in other parts:</p> 550 <div id="rfc.figure.u.2"></div><pre class="inline"> HTTP-date = <HTTP-date, defined in <a href="#Part1" id="rfc.xref.Part1.4"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#full.date" title="Full Date">Section 3.3.1</a>> 551 </pre><h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a> <a id="entity.tags" href="#entity.tags">Entity Tags</a></h1> 552 <p id="rfc.section.3.p.1">Entity tags are used for comparing two or more entities from the same requested resource. HTTP/1.1 uses entity tags in the 553 ETag (<a href="#header.etag" id="rfc.xref.header.etag.1" title="ETag">Section 7.1</a>), If-Match (<a href="#header.if-match" id="rfc.xref.header.if-match.1" title="If-Match">Section 7.2</a>), If-None-Match (<a href="#header.if-none-match" id="rfc.xref.header.if-none-match.1" title="If-None-Match">Section 7.4</a>), and If-Range (<a href="p5-range.html#header.if-range" title="If-Range">Section 6.3</a> of <a href="#Part5" id="rfc.xref.Part5.1"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>) header fields. The definition of how they are used and compared as cache validators is in <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section 5</a>. An entity tag consists of an opaque quoted string, possibly prefixed by a weakness indicator. 554 </p> 555 <div id="rfc.figure.u.3"></div><pre class="inline"><span id="rfc.iref.g.1"></span><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span> entity-tag = [ weak ] opaque-tag 548 556 weak = "W/" 549 557 opaque-tag = quoted-string 550 </pre><p id="rfc.section. 2.p.3">A "strong entity tag" <em class="bcp14">MAY</em> be shared by two entities of a resource only if they are equivalent by octet equality.551 </p> 552 <p id="rfc.section. 2.p.4">A "weak entity tag," indicated by the "W/" prefix, <em class="bcp14">MAY</em> be shared by two entities of a resource only if the entities are equivalent and could be substituted for each other with no558 </pre><p id="rfc.section.3.p.3">A "strong entity tag" <em class="bcp14">MAY</em> be shared by two entities of a resource only if they are equivalent by octet equality. 559 </p> 560 <p id="rfc.section.3.p.4">A "weak entity tag," indicated by the "W/" prefix, <em class="bcp14">MAY</em> be shared by two entities of a resource only if the entities are equivalent and could be substituted for each other with no 553 561 significant change in semantics. A weak entity tag can only be used for weak comparison. 554 562 </p> 555 <p id="rfc.section. 2.p.5">An entity tag <em class="bcp14">MUST</em> be unique across all versions of all entities associated with a particular resource. A given entity tag value <em class="bcp14">MAY</em> be used for entities obtained by requests on different URIs. The use of the same entity tag value in conjunction with entities563 <p id="rfc.section.3.p.5">An entity tag <em class="bcp14">MUST</em> be unique across all versions of all entities associated with a particular resource. A given entity tag value <em class="bcp14">MAY</em> be used for entities obtained by requests on different URIs. The use of the same entity tag value in conjunction with entities 556 564 obtained by requests on different URIs does not imply the equivalence of those entities. 557 565 </p> 558 <h1 id="rfc.section. 3"><a href="#rfc.section.3">3.</a> Status Code Definitions566 <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a> Status Code Definitions 559 567 </h1> 560 568 <div id="rfc.iref.3"></div> 561 569 <div id="rfc.iref.s.1"></div> 562 <h2 id="rfc.section. 3.1"><a href="#rfc.section.3.1">3.1</a> <a id="status.304" href="#status.304">304 Not Modified</a></h2>563 <p id="rfc.section. 3.1.p.1">If the client has performed a conditional GET request and access is allowed, but the document has not been modified, the server <em class="bcp14">SHOULD</em> respond with this status code. The 304 response <em class="bcp14">MUST NOT</em> contain a message-body, and thus is always terminated by the first empty line after the header fields.564 </p> 565 <p id="rfc.section. 3.1.p.2">The response <em class="bcp14">MUST</em> include the following header fields:570 <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a> <a id="status.304" href="#status.304">304 Not Modified</a></h2> 571 <p id="rfc.section.4.1.p.1">If the client has performed a conditional GET request and access is allowed, but the document has not been modified, the server <em class="bcp14">SHOULD</em> respond with this status code. The 304 response <em class="bcp14">MUST NOT</em> contain a message-body, and thus is always terminated by the first empty line after the header fields. 572 </p> 573 <p id="rfc.section.4.1.p.2">The response <em class="bcp14">MUST</em> include the following header fields: 566 574 </p> 567 575 <ul> 568 <li>Date, unless its omission is required by <a href="p1-messaging.html#clockless.origin.server.operation" title="Clockless Origin Server Operation">Section 8.3.1</a> of <a href="#Part1" id="rfc.xref.Part1. 1"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a></li>576 <li>Date, unless its omission is required by <a href="p1-messaging.html#clockless.origin.server.operation" title="Clockless Origin Server Operation">Section 8.3.1</a> of <a href="#Part1" id="rfc.xref.Part1.5"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a></li> 569 577 </ul> 570 <p id="rfc.section. 3.1.p.3">If a clockless origin server obeys these rules, and proxies and clients add their own Date to any response received without578 <p id="rfc.section.4.1.p.3">If a clockless origin server obeys these rules, and proxies and clients add their own Date to any response received without 571 579 one (as already specified by <a href="#RFC2068" id="rfc.xref.RFC2068.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, <a href="http://tools.ietf.org/html/rfc2068#section-14.19">Section 14.19</a>), caches will operate correctly. 572 580 </p> … … 577 585 </li> 578 586 </ul> 579 <p id="rfc.section. 3.1.p.4">If the conditional GET used a strong cache validator (see <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section 4</a>), the response <em class="bcp14">SHOULD NOT</em> include other entity-headers. Otherwise (i.e., the conditional GET used a weak validator), the response <em class="bcp14">MUST NOT</em> include other entity-headers; this prevents inconsistencies between cached entity-bodies and updated headers.580 </p> 581 <p id="rfc.section. 3.1.p.5">If a 304 response indicates an entity not currently cached, then the cache <em class="bcp14">MUST</em> disregard the response and repeat the request without the conditional.582 </p> 583 <p id="rfc.section. 3.1.p.6">If a cache uses a received 304 response to update a cache entry, the cache <em class="bcp14">MUST</em> update the entry to reflect any new field values given in the response.587 <p id="rfc.section.4.1.p.4">If the conditional GET used a strong cache validator (see <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section 5</a>), the response <em class="bcp14">SHOULD NOT</em> include other entity-headers. Otherwise (i.e., the conditional GET used a weak validator), the response <em class="bcp14">MUST NOT</em> include other entity-headers; this prevents inconsistencies between cached entity-bodies and updated headers. 588 </p> 589 <p id="rfc.section.4.1.p.5">If a 304 response indicates an entity not currently cached, then the cache <em class="bcp14">MUST</em> disregard the response and repeat the request without the conditional. 590 </p> 591 <p id="rfc.section.4.1.p.6">If a cache uses a received 304 response to update a cache entry, the cache <em class="bcp14">MUST</em> update the entry to reflect any new field values given in the response. 584 592 </p> 585 593 <div id="rfc.iref.4"></div> 586 594 <div id="rfc.iref.s.2"></div> 587 <h2 id="rfc.section. 3.2"><a href="#rfc.section.3.2">3.2</a> <a id="status.412" href="#status.412">412 Precondition Failed</a></h2>588 <p id="rfc.section. 3.2.p.1">The precondition given in one or more of the request-header fields evaluated to false when it was tested on the server. This595 <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a> <a id="status.412" href="#status.412">412 Precondition Failed</a></h2> 596 <p id="rfc.section.4.2.p.1">The precondition given in one or more of the request-header fields evaluated to false when it was tested on the server. This 589 597 response code allows the client to place preconditions on the current resource metainformation (header field data) and thus 590 598 prevent the requested method from being applied to a resource other than the one intended. 591 599 </p> 592 <h1 id="rfc.section. 4"><a href="#rfc.section.4">4.</a> <a id="weak.and.strong.validators" href="#weak.and.strong.validators">Weak and Strong Validators</a></h1>593 <p id="rfc.section. 4.p.1">Since both origin servers and caches will compare two validators to decide if they represent the same or different entities,600 <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a> <a id="weak.and.strong.validators" href="#weak.and.strong.validators">Weak and Strong Validators</a></h1> 601 <p id="rfc.section.5.p.1">Since both origin servers and caches will compare two validators to decide if they represent the same or different entities, 594 602 one normally would expect that if the entity (the entity-body or any entity-headers) changes in any way, then the associated 595 603 validator would change as well. If this is true, then we call this validator a "strong validator." 596 604 </p> 597 <p id="rfc.section. 4.p.2">However, there might be cases when a server prefers to change the validator only on semantically significant changes, and605 <p id="rfc.section.5.p.2">However, there might be cases when a server prefers to change the validator only on semantically significant changes, and 598 606 not when insignificant aspects of the entity change. A validator that does not always change when the resource changes is 599 607 a "weak validator." 600 608 </p> 601 <p id="rfc.section. 4.p.3">Entity tags are normally "strong validators," but the protocol provides a mechanism to tag an entity tag as "weak." One can609 <p id="rfc.section.5.p.3">Entity tags are normally "strong validators," but the protocol provides a mechanism to tag an entity tag as "weak." One can 602 610 think of a strong validator as one that changes whenever the bits of an entity changes, while a weak value changes whenever 603 611 the meaning of an entity changes. Alternatively, one can think of a strong validator as part of an identifier for a specific … … 615 623 </dd> 616 624 </dl> 617 <p id="rfc.section. 4.p.4">A "use" of a validator is either when a client generates a request and includes the validator in a validating header field,625 <p id="rfc.section.5.p.4">A "use" of a validator is either when a client generates a request and includes the validator in a validating header field, 618 626 or when a server compares two validators. 619 627 </p> 620 <p id="rfc.section. 4.p.5">Strong validators are usable in any context. Weak validators are only usable in contexts that do not depend on exact equality628 <p id="rfc.section.5.p.5">Strong validators are usable in any context. Weak validators are only usable in contexts that do not depend on exact equality 621 629 of an entity. For example, either kind is usable for a conditional GET of a full entity. However, only a strong validator 622 630 is usable for a sub-range retrieval, since otherwise the client might end up with an internally inconsistent entity. 623 631 </p> 624 <p id="rfc.section. 4.p.6">Clients <em class="bcp14">MAY</em> issue simple (non-subrange) GET requests with either weak validators or strong validators. Clients <em class="bcp14">MUST NOT</em> use weak validators in other forms of request.625 </p> 626 <p id="rfc.section. 4.p.7">The only function that HTTP/1.1 defines on validators is comparison. There are two validator comparison functions, depending632 <p id="rfc.section.5.p.6">Clients <em class="bcp14">MAY</em> issue simple (non-subrange) GET requests with either weak validators or strong validators. Clients <em class="bcp14">MUST NOT</em> use weak validators in other forms of request. 633 </p> 634 <p id="rfc.section.5.p.7">The only function that HTTP/1.1 defines on validators is comparison. There are two validator comparison functions, depending 627 635 on whether the comparison context allows the use of weak validators or not: 628 636 </p> … … 633 641 </li> 634 642 </ul> 635 <p id="rfc.section. 4.p.8">An entity tag is strong unless it is explicitly tagged as weak. <a href="#entity.tags" title="Entity Tags">Section 2</a> gives the syntax for entity tags.636 </p> 637 <p id="rfc.section. 4.p.9">A Last-Modified time, when used as a validator in a request, is implicitly weak unless it is possible to deduce that it is643 <p id="rfc.section.5.p.8">An entity tag is strong unless it is explicitly tagged as weak. <a href="#entity.tags" title="Entity Tags">Section 3</a> gives the syntax for entity tags. 644 </p> 645 <p id="rfc.section.5.p.9">A Last-Modified time, when used as a validator in a request, is implicitly weak unless it is possible to deduce that it is 638 646 strong, using the following rules: 639 647 </p> … … 644 652 </li> 645 653 </ul> 646 <p id="rfc.section. 4.p.10">or </p>654 <p id="rfc.section.5.p.10">or </p> 647 655 <ul> 648 656 <li>The validator is about to be used by a client in an If-Modified-Since or If-Unmodified-Since header, because the client has … … 652 660 <li>The presented Last-Modified time is at least 60 seconds before the Date value.</li> 653 661 </ul> 654 <p id="rfc.section. 4.p.11">or </p>662 <p id="rfc.section.5.p.11">or </p> 655 663 <ul> 656 664 <li>The validator is being compared by an intermediate cache to the validator stored in its cache entry for the entity, and</li> … … 658 666 <li>The presented Last-Modified time is at least 60 seconds before the Date value.</li> 659 667 </ul> 660 <p id="rfc.section. 4.p.12">This method relies on the fact that if two different responses were sent by the origin server during the same second, but668 <p id="rfc.section.5.p.12">This method relies on the fact that if two different responses were sent by the origin server during the same second, but 661 669 both had the same Last-Modified time, then at least one of those responses would have a Date value equal to its Last-Modified 662 670 time. The arbitrary 60-second limit guards against the possibility that the Date and Last-Modified values are generated from 663 671 different clocks, or at somewhat different times during the preparation of the response. An implementation <em class="bcp14">MAY</em> use a value larger than 60 seconds, if it is believed that 60 seconds is too short. 664 672 </p> 665 <p id="rfc.section. 4.p.13">If a client wishes to perform a sub-range retrieval on a value for which it has only a Last-Modified time and no opaque validator,673 <p id="rfc.section.5.p.13">If a client wishes to perform a sub-range retrieval on a value for which it has only a Last-Modified time and no opaque validator, 666 674 it <em class="bcp14">MAY</em> do this only if the Last-Modified time is strong in the sense described here. 667 675 </p> 668 <p id="rfc.section. 4.p.14">A cache or origin server receiving a conditional request, other than a full-body GET request, <em class="bcp14">MUST</em> use the strong comparison function to evaluate the condition.669 </p> 670 <p id="rfc.section. 4.p.15">These rules allow HTTP/1.1 caches and clients to safely perform sub-range retrievals on values that have been obtained from676 <p id="rfc.section.5.p.14">A cache or origin server receiving a conditional request, other than a full-body GET request, <em class="bcp14">MUST</em> use the strong comparison function to evaluate the condition. 677 </p> 678 <p id="rfc.section.5.p.15">These rules allow HTTP/1.1 caches and clients to safely perform sub-range retrievals on values that have been obtained from 671 679 HTTP/1.0 servers. 672 680 </p> 673 <h1 id="rfc.section. 5"><a href="#rfc.section.5">5.</a> <a id="rules.for.when.to.use.entity.tags.and.last-modified.dates" href="#rules.for.when.to.use.entity.tags.and.last-modified.dates">Rules for When to Use Entity Tags and Last-Modified Dates</a></h1>674 <p id="rfc.section. 5.p.1">We adopt a set of rules and recommendations for origin servers, clients, and caches regarding when various validator types681 <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a> <a id="rules.for.when.to.use.entity.tags.and.last-modified.dates" href="#rules.for.when.to.use.entity.tags.and.last-modified.dates">Rules for When to Use Entity Tags and Last-Modified Dates</a></h1> 682 <p id="rfc.section.6.p.1">We adopt a set of rules and recommendations for origin servers, clients, and caches regarding when various validator types 675 683 ought to be used, and for what purposes. 676 684 </p> 677 <p id="rfc.section. 5.p.2">HTTP/1.1 origin servers: </p>685 <p id="rfc.section.6.p.2">HTTP/1.1 origin servers: </p> 678 686 <ul> 679 687 <li><em class="bcp14">SHOULD</em> send an entity tag validator unless it is not feasible to generate one. … … 686 694 </li> 687 695 </ul> 688 <p id="rfc.section. 5.p.3">In other words, the preferred behavior for an HTTP/1.1 origin server is to send both a strong entity tag and a Last-Modified696 <p id="rfc.section.6.p.3">In other words, the preferred behavior for an HTTP/1.1 origin server is to send both a strong entity tag and a Last-Modified 689 697 value. 690 698 </p> 691 <p id="rfc.section. 5.p.4">In order to be legal, a strong entity tag <em class="bcp14">MUST</em> change whenever the associated entity value changes in any way. A weak entity tag <em class="bcp14">SHOULD</em> change whenever the associated entity changes in a semantically significant way.699 <p id="rfc.section.6.p.4">In order to be legal, a strong entity tag <em class="bcp14">MUST</em> change whenever the associated entity value changes in any way. A weak entity tag <em class="bcp14">SHOULD</em> change whenever the associated entity changes in a semantically significant way. 692 700 </p> 693 701 <dl class="empty"> … … 698 706 </dd> 699 707 </dl> 700 <p id="rfc.section. 5.p.5">HTTP/1.1 clients: </p>708 <p id="rfc.section.6.p.5">HTTP/1.1 clients: </p> 701 709 <ul> 702 710 <li>If an entity tag has been provided by the origin server, <em class="bcp14">MUST</em> use that entity tag in any cache-conditional request (using If-Match or If-None-Match). … … 709 717 </li> 710 718 </ul> 711 <p id="rfc.section. 5.p.6">An HTTP/1.1 origin server, upon receiving a conditional request that includes both a Last-Modified date (e.g., in an If-Modified-Since719 <p id="rfc.section.6.p.6">An HTTP/1.1 origin server, upon receiving a conditional request that includes both a Last-Modified date (e.g., in an If-Modified-Since 712 720 or If-Unmodified-Since header field) and one or more entity tags (e.g., in an If-Match, If-None-Match, or If-Range header 713 721 field) as cache validators, <em class="bcp14">MUST NOT</em> return a response status of 304 (Not Modified) unless doing so is consistent with all of the conditional header fields in 714 722 the request. 715 723 </p> 716 <p id="rfc.section. 5.p.7">An HTTP/1.1 caching proxy, upon receiving a conditional request that includes both a Last-Modified date and one or more entity724 <p id="rfc.section.6.p.7">An HTTP/1.1 caching proxy, upon receiving a conditional request that includes both a Last-Modified date and one or more entity 717 725 tags as cache validators, <em class="bcp14">MUST NOT</em> return a locally cached response to the client unless that cached response is consistent with all of the conditional header 718 726 fields in the request. … … 729 737 </dd> 730 738 </dl> 731 <h1 id="rfc.section. 6"><a href="#rfc.section.6">6.</a> <a id="header.fields" href="#header.fields">Header Field Definitions</a></h1>732 <p id="rfc.section. 6.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to conditional requests.</p>733 <p id="rfc.section. 6.p.2">For entity-header fields, both sender and recipient refer to either the client or the server, depending on who sends and who739 <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a> <a id="header.fields" href="#header.fields">Header Field Definitions</a></h1> 740 <p id="rfc.section.7.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to conditional requests.</p> 741 <p id="rfc.section.7.p.2">For entity-header fields, both sender and recipient refer to either the client or the server, depending on who sends and who 734 742 receives the entity. 735 743 </p> 736 744 <div id="rfc.iref.e.1"></div> 737 745 <div id="rfc.iref.h.1"></div> 738 <h2 id="rfc.section. 6.1"><a href="#rfc.section.6.1">6.1</a> <a id="header.etag" href="#header.etag">ETag</a></h2>739 <p id="rfc.section. 6.1.p.1">The ETag response-header field provides the current value of the entity tag for the requested variant. The headers used with740 entity tags are described in Sections <a href="#header.if-match" id="rfc.xref.header.if-match.2" title="If-Match"> 6.2</a> and <a href="#header.if-none-match" id="rfc.xref.header.if-none-match.2" title="If-None-Match">6.4</a> of this document, and in <a href="p5-range.html#header.if-range" title="If-Range">Section 5.3</a> of <a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>. The entity tag <em class="bcp14">MAY</em> be used for comparison with other entities from the same resource (see <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section 4</a>).741 </p> 742 <div id="rfc.figure.u. 2"></div><pre class="inline"><span id="rfc.iref.g.4"></span> ETag = "ETag" ":" entity-tag743 </pre><div id="rfc.figure.u. 3"></div>746 <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a> <a id="header.etag" href="#header.etag">ETag</a></h2> 747 <p id="rfc.section.7.1.p.1">The ETag response-header field provides the current value of the entity tag for the requested variant. The headers used with 748 entity tags are described in Sections <a href="#header.if-match" id="rfc.xref.header.if-match.2" title="If-Match">7.2</a> and <a href="#header.if-none-match" id="rfc.xref.header.if-none-match.2" title="If-None-Match">7.4</a> of this document, and in <a href="p5-range.html#header.if-range" title="If-Range">Section 6.3</a> of <a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>. The entity tag <em class="bcp14">MAY</em> be used for comparison with other entities from the same resource (see <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section 5</a>). 749 </p> 750 <div id="rfc.figure.u.4"></div><pre class="inline"><span id="rfc.iref.g.4"></span> ETag = "ETag" ":" entity-tag 751 </pre><div id="rfc.figure.u.5"></div> 744 752 <p>Examples:</p> <pre class="text"> ETag: "xyzzy" 745 753 ETag: W/"xyzzy" 746 754 ETag: "" 747 </pre><p id="rfc.section. 6.1.p.4">The ETag response-header field value, an entity tag, provides for an "opaque" cache validator. This might allow more reliable755 </pre><p id="rfc.section.7.1.p.4">The ETag response-header field value, an entity tag, provides for an "opaque" cache validator. This might allow more reliable 748 756 validation in situations where it is inconvenient to store modification dates, where the one-second resolution of HTTP date 749 757 values is not sufficient, or where the origin server wishes to avoid certain paradoxes that might arise from the use of modification 750 758 dates. 751 759 </p> 752 <p id="rfc.section. 6.1.p.5">The principle behind entity tags is that only the service author knows the semantics of a resource well enough to select an760 <p id="rfc.section.7.1.p.5">The principle behind entity tags is that only the service author knows the semantics of a resource well enough to select an 753 761 appropriate cache validation mechanism, and the specification of any validator comparison function more complex than byte-equality 754 762 would open up a can of worms. Thus, comparisons of any other headers (except Last-Modified, for compatibility with HTTP/1.0) … … 757 765 <div id="rfc.iref.i.1"></div> 758 766 <div id="rfc.iref.h.2"></div> 759 <h2 id="rfc.section. 6.2"><a href="#rfc.section.6.2">6.2</a> <a id="header.if-match" href="#header.if-match">If-Match</a></h2>760 <p id="rfc.section. 6.2.p.1">The If-Match request-header field is used with a method to make it conditional. A client that has one or more entities previously767 <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a> <a id="header.if-match" href="#header.if-match">If-Match</a></h2> 768 <p id="rfc.section.7.2.p.1">The If-Match request-header field is used with a method to make it conditional. A client that has one or more entities previously 761 769 obtained from the resource can verify that one of those entities is current by including a list of their associated entity 762 tags in the If-Match header field. Entity tags are defined in <a href="#entity.tags" title="Entity Tags">Section 2</a>. The purpose of this feature is to allow efficient updates of cached information with a minimum amount of transaction overhead.770 tags in the If-Match header field. Entity tags are defined in <a href="#entity.tags" title="Entity Tags">Section 3</a>. The purpose of this feature is to allow efficient updates of cached information with a minimum amount of transaction overhead. 763 771 It is also used, on updating requests, to prevent inadvertent modification of the wrong version of a resource. As a special 764 772 case, the value "*" matches any current entity of the resource. 765 773 </p> 766 <div id="rfc.figure.u. 4"></div><pre class="inline"><span id="rfc.iref.g.5"></span> If-Match = "If-Match" ":" ( "*" | 1#entity-tag )767 </pre><p id="rfc.section. 6.2.p.3">If any of the entity tags match the entity tag of the entity that would have been returned in the response to a similar GET774 <div id="rfc.figure.u.6"></div><pre class="inline"><span id="rfc.iref.g.5"></span> If-Match = "If-Match" ":" ( "*" | 1#entity-tag ) 775 </pre><p id="rfc.section.7.2.p.3">If any of the entity tags match the entity tag of the entity that would have been returned in the response to a similar GET 768 776 request (without the If-Match header) on that resource, or if "*" is given and any current entity exists for that resource, 769 777 then the server <em class="bcp14">MAY</em> perform the requested method as if the If-Match header field did not exist. 770 778 </p> 771 <p id="rfc.section. 6.2.p.4">A server <em class="bcp14">MUST</em> use the strong comparison function (see <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section 4</a>) to compare the entity tags in If-Match.772 </p> 773 <p id="rfc.section. 6.2.p.5">If none of the entity tags match, or if "*" is given and no current entity exists, the server <em class="bcp14">MUST NOT</em> perform the requested method, and <em class="bcp14">MUST</em> return a 412 (Precondition Failed) response. This behavior is most useful when the client wants to prevent an updating method,779 <p id="rfc.section.7.2.p.4">A server <em class="bcp14">MUST</em> use the strong comparison function (see <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section 5</a>) to compare the entity tags in If-Match. 780 </p> 781 <p id="rfc.section.7.2.p.5">If none of the entity tags match, or if "*" is given and no current entity exists, the server <em class="bcp14">MUST NOT</em> perform the requested method, and <em class="bcp14">MUST</em> return a 412 (Precondition Failed) response. This behavior is most useful when the client wants to prevent an updating method, 774 782 such as PUT, from modifying a resource that has changed since the client last retrieved it. 775 783 </p> 776 <p id="rfc.section. 6.2.p.6">If the request would, without the If-Match header field, result in anything other than a 2xx or 412 status, then the If-Match784 <p id="rfc.section.7.2.p.6">If the request would, without the If-Match header field, result in anything other than a 2xx or 412 status, then the If-Match 777 785 header <em class="bcp14">MUST</em> be ignored. 778 786 </p> 779 <p id="rfc.section. 6.2.p.7">The meaning of "If-Match: *" is that the method <em class="bcp14">SHOULD</em> be performed if the representation selected by the origin server (or by a cache, possibly using the Vary mechanism, see <a href="p6-cache.html#header.vary" title="Vary">Section 15.5</a> of <a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) exists, and <em class="bcp14">MUST NOT</em> be performed if the representation does not exist.780 </p> 781 <p id="rfc.section. 6.2.p.8">A request intended to update a resource (e.g., a PUT) <em class="bcp14">MAY</em> include an If-Match header field to signal that the request method <em class="bcp14">MUST NOT</em> be applied if the entity corresponding to the If-Match value (a single entity tag) is no longer a representation of that resource.787 <p id="rfc.section.7.2.p.7">The meaning of "If-Match: *" is that the method <em class="bcp14">SHOULD</em> be performed if the representation selected by the origin server (or by a cache, possibly using the Vary mechanism, see <a href="p6-cache.html#header.vary" title="Vary">Section 16.5</a> of <a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) exists, and <em class="bcp14">MUST NOT</em> be performed if the representation does not exist. 788 </p> 789 <p id="rfc.section.7.2.p.8">A request intended to update a resource (e.g., a PUT) <em class="bcp14">MAY</em> include an If-Match header field to signal that the request method <em class="bcp14">MUST NOT</em> be applied if the entity corresponding to the If-Match value (a single entity tag) is no longer a representation of that resource. 782 790 This allows the user to indicate that they do not wish the request to be successful if the resource has been changed without 783 791 their knowledge. Examples: 784 792 </p> 785 <div id="rfc.figure.u. 5"></div><pre class="text"> If-Match: "xyzzy"793 <div id="rfc.figure.u.7"></div><pre class="text"> If-Match: "xyzzy" 786 794 If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz" 787 795 If-Match: * 788 </pre><p id="rfc.section. 6.2.p.10">The result of a request having both an If-Match header field and either an If-None-Match or an If-Modified-Since header fields796 </pre><p id="rfc.section.7.2.p.10">The result of a request having both an If-Match header field and either an If-None-Match or an If-Modified-Since header fields 789 797 is undefined by this specification. 790 798 </p> 791 799 <div id="rfc.iref.i.2"></div> 792 800 <div id="rfc.iref.h.3"></div> 793 <h2 id="rfc.section. 6.3"><a href="#rfc.section.6.3">6.3</a> <a id="header.if-modified-since" href="#header.if-modified-since">If-Modified-Since</a></h2>794 <p id="rfc.section. 6.3.p.1">The If-Modified-Since request-header field is used with a method to make it conditional: if the requested variant has not801 <h2 id="rfc.section.7.3"><a href="#rfc.section.7.3">7.3</a> <a id="header.if-modified-since" href="#header.if-modified-since">If-Modified-Since</a></h2> 802 <p id="rfc.section.7.3.p.1">The If-Modified-Since request-header field is used with a method to make it conditional: if the requested variant has not 795 803 been modified since the time specified in this field, an entity will not be returned from the server; instead, a 304 (Not 796 804 Modified) response will be returned without any message-body. 797 805 </p> 798 <div id="rfc.figure.u. 6"></div><pre class="inline"><span id="rfc.iref.g.6"></span> If-Modified-Since = "If-Modified-Since" ":" HTTP-date799 </pre><p id="rfc.section. 6.3.p.3">An example of the field is:</p>800 <div id="rfc.figure.u. 7"></div><pre class="text"> If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT801 </pre><p id="rfc.section. 6.3.p.5">A GET method with an If-Modified-Since header and no Range header requests that the identified entity be transferred only806 <div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.6"></span> If-Modified-Since = "If-Modified-Since" ":" HTTP-date 807 </pre><p id="rfc.section.7.3.p.3">An example of the field is:</p> 808 <div id="rfc.figure.u.9"></div><pre class="text"> If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT 809 </pre><p id="rfc.section.7.3.p.5">A GET method with an If-Modified-Since header and no Range header requests that the identified entity be transferred only 802 810 if it has been modified since the date given by the If-Modified-Since header. The algorithm for determining this includes 803 811 the following cases: … … 811 819 </li> 812 820 </ol> 813 <p id="rfc.section. 6.3.p.6">The purpose of this feature is to allow efficient updates of cached information with a minimum amount of transaction overhead. </p>821 <p id="rfc.section.7.3.p.6">The purpose of this feature is to allow efficient updates of cached information with a minimum amount of transaction overhead. </p> 814 822 <dl class="empty"> 815 <dd> <b>Note:</b> The Range request-header field modifies the meaning of If-Modified-Since; see <a href="p5-range.html#header.range" title="Range">Section 5.4</a> of <a href="#Part5" id="rfc.xref.Part5.3"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a> for full details.823 <dd> <b>Note:</b> The Range request-header field modifies the meaning of If-Modified-Since; see <a href="p5-range.html#header.range" title="Range">Section 6.4</a> of <a href="#Part5" id="rfc.xref.Part5.3"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a> for full details. 816 824 </dd> 817 825 <dd> <b>Note:</b> If-Modified-Since times are interpreted by the server, whose clock might not be synchronized with the client. … … 831 839 </dd> 832 840 </dl> 833 <p id="rfc.section. 6.3.p.7">The result of a request having both an If-Modified-Since header field and either an If-Match or an If-Unmodified-Since header841 <p id="rfc.section.7.3.p.7">The result of a request having both an If-Modified-Since header field and either an If-Match or an If-Unmodified-Since header 834 842 fields is undefined by this specification. 835 843 </p> 836 844 <div id="rfc.iref.i.3"></div> 837 845 <div id="rfc.iref.h.4"></div> 838 <h2 id="rfc.section. 6.4"><a href="#rfc.section.6.4">6.4</a> <a id="header.if-none-match" href="#header.if-none-match">If-None-Match</a></h2>839 <p id="rfc.section. 6.4.p.1">The If-None-Match request-header field is used with a method to make it conditional. A client that has one or more entities846 <h2 id="rfc.section.7.4"><a href="#rfc.section.7.4">7.4</a> <a id="header.if-none-match" href="#header.if-none-match">If-None-Match</a></h2> 847 <p id="rfc.section.7.4.p.1">The If-None-Match request-header field is used with a method to make it conditional. A client that has one or more entities 840 848 previously obtained from the resource can verify that none of those entities is current by including a list of their associated 841 849 entity tags in the If-None-Match header field. The purpose of this feature is to allow efficient updates of cached information … … 843 851 an existing resource when the client believes that the resource does not exist. 844 852 </p> 845 <p id="rfc.section. 6.4.p.2">As a special case, the value "*" matches any current entity of the resource.</p>846 <div id="rfc.figure.u. 8"></div><pre class="inline"><span id="rfc.iref.g.7"></span> If-None-Match = "If-None-Match" ":" ( "*" | 1#entity-tag )847 </pre><p id="rfc.section. 6.4.p.4">If any of the entity tags match the entity tag of the entity that would have been returned in the response to a similar GET853 <p id="rfc.section.7.4.p.2">As a special case, the value "*" matches any current entity of the resource.</p> 854 <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.7"></span> If-None-Match = "If-None-Match" ":" ( "*" | 1#entity-tag ) 855 </pre><p id="rfc.section.7.4.p.4">If any of the entity tags match the entity tag of the entity that would have been returned in the response to a similar GET 848 856 request (without the If-None-Match header) on that resource, or if "*" is given and any current entity exists for that resource, 849 857 then the server <em class="bcp14">MUST NOT</em> perform the requested method, unless required to do so because the resource's modification date fails to match that supplied … … 851 859 that matched. For all other request methods, the server <em class="bcp14">MUST</em> respond with a status of 412 (Precondition Failed). 852 860 </p> 853 <p id="rfc.section. 6.4.p.5">See <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section 4</a> for rules on how to determine if two entities tags match. The weak comparison function can only be used with GET or HEAD requests.854 </p> 855 <p id="rfc.section. 6.4.p.6">If none of the entity tags match, then the server <em class="bcp14">MAY</em> perform the requested method as if the If-None-Match header field did not exist, but <em class="bcp14">MUST</em> also ignore any If-Modified-Since header field(s) in the request. That is, if no entity tags match, then the server <em class="bcp14">MUST NOT</em> return a 304 (Not Modified) response.856 </p> 857 <p id="rfc.section. 6.4.p.7">If the request would, without the If-None-Match header field, result in anything other than a 2xx or 304 status, then the858 If-None-Match header <em class="bcp14">MUST</em> be ignored. (See <a href="#rules.for.when.to.use.entity.tags.and.last-modified.dates" title="Rules for When to Use Entity Tags and Last-Modified Dates">Section 5</a> for a discussion of server behavior when both If-Modified-Since and If-None-Match appear in the same request.)859 </p> 860 <p id="rfc.section. 6.4.p.8">The meaning of "If-None-Match: *" is that the method <em class="bcp14">MUST NOT</em> be performed if the representation selected by the origin server (or by a cache, possibly using the Vary mechanism, see <a href="p6-cache.html#header.vary" title="Vary">Section 15.5</a> of <a href="#Part6" id="rfc.xref.Part6.3"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) exists, and <em class="bcp14">SHOULD</em> be performed if the representation does not exist. This feature is intended to be useful in preventing races between PUT operations.861 </p> 862 <p id="rfc.section. 6.4.p.9">Examples:</p>863 <div id="rfc.figure.u. 9"></div><pre class="text"> If-None-Match: "xyzzy"861 <p id="rfc.section.7.4.p.5">See <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section 5</a> for rules on how to determine if two entities tags match. The weak comparison function can only be used with GET or HEAD requests. 862 </p> 863 <p id="rfc.section.7.4.p.6">If none of the entity tags match, then the server <em class="bcp14">MAY</em> perform the requested method as if the If-None-Match header field did not exist, but <em class="bcp14">MUST</em> also ignore any If-Modified-Since header field(s) in the request. That is, if no entity tags match, then the server <em class="bcp14">MUST NOT</em> return a 304 (Not Modified) response. 864 </p> 865 <p id="rfc.section.7.4.p.7">If the request would, without the If-None-Match header field, result in anything other than a 2xx or 304 status, then the 866 If-None-Match header <em class="bcp14">MUST</em> be ignored. (See <a href="#rules.for.when.to.use.entity.tags.and.last-modified.dates" title="Rules for When to Use Entity Tags and Last-Modified Dates">Section 6</a> for a discussion of server behavior when both If-Modified-Since and If-None-Match appear in the same request.) 867 </p> 868 <p id="rfc.section.7.4.p.8">The meaning of "If-None-Match: *" is that the method <em class="bcp14">MUST NOT</em> be performed if the representation selected by the origin server (or by a cache, possibly using the Vary mechanism, see <a href="p6-cache.html#header.vary" title="Vary">Section 16.5</a> of <a href="#Part6" id="rfc.xref.Part6.3"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) exists, and <em class="bcp14">SHOULD</em> be performed if the representation does not exist. This feature is intended to be useful in preventing races between PUT operations. 869 </p> 870 <p id="rfc.section.7.4.p.9">Examples:</p> 871 <div id="rfc.figure.u.11"></div><pre class="text"> If-None-Match: "xyzzy" 864 872 If-None-Match: W/"xyzzy" 865 873 If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz" 866 874 If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz" 867 875 If-None-Match: * 868 </pre><p id="rfc.section. 6.4.p.11">The result of a request having both an If-None-Match header field and either an If-Match or an If-Unmodified-Since header876 </pre><p id="rfc.section.7.4.p.11">The result of a request having both an If-None-Match header field and either an If-Match or an If-Unmodified-Since header 869 877 fields is undefined by this specification. 870 878 </p> 871 879 <div id="rfc.iref.i.4"></div> 872 880 <div id="rfc.iref.h.5"></div> 873 <h2 id="rfc.section. 6.5"><a href="#rfc.section.6.5">6.5</a> <a id="header.if-unmodified-since" href="#header.if-unmodified-since">If-Unmodified-Since</a></h2>874 <p id="rfc.section. 6.5.p.1">The If-Unmodified-Since request-header field is used with a method to make it conditional. If the requested resource has not881 <h2 id="rfc.section.7.5"><a href="#rfc.section.7.5">7.5</a> <a id="header.if-unmodified-since" href="#header.if-unmodified-since">If-Unmodified-Since</a></h2> 882 <p id="rfc.section.7.5.p.1">The If-Unmodified-Since request-header field is used with a method to make it conditional. If the requested resource has not 875 883 been modified since the time specified in this field, the server <em class="bcp14">SHOULD</em> perform the requested operation as if the If-Unmodified-Since header were not present. 876 884 </p> 877 <p id="rfc.section. 6.5.p.2">If the requested variant has been modified since the specified time, the server <em class="bcp14">MUST NOT</em> perform the requested operation, and <em class="bcp14">MUST</em> return a 412 (Precondition Failed).878 </p> 879 <div id="rfc.figure.u.1 0"></div><pre class="inline"><span id="rfc.iref.g.8"></span> If-Unmodified-Since = "If-Unmodified-Since" ":" HTTP-date880 </pre><p id="rfc.section. 6.5.p.4">An example of the field is:</p>881 <div id="rfc.figure.u.1 1"></div><pre class="text"> If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT882 </pre><p id="rfc.section. 6.5.p.6">If the request normally (i.e., without the If-Unmodified-Since header) would result in anything other than a 2xx or 412 status,885 <p id="rfc.section.7.5.p.2">If the requested variant has been modified since the specified time, the server <em class="bcp14">MUST NOT</em> perform the requested operation, and <em class="bcp14">MUST</em> return a 412 (Precondition Failed). 886 </p> 887 <div id="rfc.figure.u.12"></div><pre class="inline"><span id="rfc.iref.g.8"></span> If-Unmodified-Since = "If-Unmodified-Since" ":" HTTP-date 888 </pre><p id="rfc.section.7.5.p.4">An example of the field is:</p> 889 <div id="rfc.figure.u.13"></div><pre class="text"> If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT 890 </pre><p id="rfc.section.7.5.p.6">If the request normally (i.e., without the If-Unmodified-Since header) would result in anything other than a 2xx or 412 status, 883 891 the If-Unmodified-Since header <em class="bcp14">SHOULD</em> be ignored. 884 892 </p> 885 <p id="rfc.section. 6.5.p.7">If the specified date is invalid, the header is ignored.</p>886 <p id="rfc.section. 6.5.p.8">The result of a request having both an If-Unmodified-Since header field and either an If-None-Match or an If-Modified-Since893 <p id="rfc.section.7.5.p.7">If the specified date is invalid, the header is ignored.</p> 894 <p id="rfc.section.7.5.p.8">The result of a request having both an If-Unmodified-Since header field and either an If-None-Match or an If-Modified-Since 887 895 header fields is undefined by this specification. 888 896 </p> 889 897 <div id="rfc.iref.l.1"></div> 890 898 <div id="rfc.iref.h.6"></div> 891 <h2 id="rfc.section. 6.6"><a href="#rfc.section.6.6">6.6</a> <a id="header.last-modified" href="#header.last-modified">Last-Modified</a></h2>892 <p id="rfc.section. 6.6.p.1">The Last-Modified entity-header field indicates the date and time at which the origin server believes the variant was last899 <h2 id="rfc.section.7.6"><a href="#rfc.section.7.6">7.6</a> <a id="header.last-modified" href="#header.last-modified">Last-Modified</a></h2> 900 <p id="rfc.section.7.6.p.1">The Last-Modified entity-header field indicates the date and time at which the origin server believes the variant was last 893 901 modified. 894 902 </p> 895 <div id="rfc.figure.u.1 2"></div><pre class="inline"><span id="rfc.iref.g.9"></span> Last-Modified = "Last-Modified" ":" HTTP-date896 </pre><p id="rfc.section. 6.6.p.3">An example of its use is</p>897 <div id="rfc.figure.u.1 3"></div><pre class="text"> Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT898 </pre><p id="rfc.section. 6.6.p.5">The exact meaning of this header field depends on the implementation of the origin server and the nature of the original resource.903 <div id="rfc.figure.u.14"></div><pre class="inline"><span id="rfc.iref.g.9"></span> Last-Modified = "Last-Modified" ":" HTTP-date 904 </pre><p id="rfc.section.7.6.p.3">An example of its use is</p> 905 <div id="rfc.figure.u.15"></div><pre class="text"> Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT 906 </pre><p id="rfc.section.7.6.p.5">The exact meaning of this header field depends on the implementation of the origin server and the nature of the original resource. 899 907 For files, it may be just the file system last-modified time. For entities with dynamically included parts, it may be the 900 908 most recent of the set of last-modify times for its component parts. For database gateways, it may be the last-update time 901 909 stamp of the record. For virtual objects, it may be the last time the internal state changed. 902 910 </p> 903 <p id="rfc.section. 6.6.p.6">An origin server <em class="bcp14">MUST NOT</em> send a Last-Modified date which is later than the server's time of message origination. In such cases, where the resource's911 <p id="rfc.section.7.6.p.6">An origin server <em class="bcp14">MUST NOT</em> send a Last-Modified date which is later than the server's time of message origination. In such cases, where the resource's 904 912 last modification would indicate some time in the future, the server <em class="bcp14">MUST</em> replace that date with the message origination date. 905 913 </p> 906 <p id="rfc.section. 6.6.p.7">An origin server <em class="bcp14">SHOULD</em> obtain the Last-Modified value of the entity as close as possible to the time that it generates the Date value of its response.914 <p id="rfc.section.7.6.p.7">An origin server <em class="bcp14">SHOULD</em> obtain the Last-Modified value of the entity as close as possible to the time that it generates the Date value of its response. 907 915 This allows a recipient to make an accurate assessment of the entity's modification time, especially if the entity changes 908 916 near the time that the response is generated. 909 917 </p> 910 <p id="rfc.section. 6.6.p.8">HTTP/1.1 servers <em class="bcp14">SHOULD</em> send Last-Modified whenever feasible.911 </p> 912 <p id="rfc.section. 6.6.p.9">The Last-Modified entity-header field value is often used as a cache validator. In simple terms, a cache entry is considered918 <p id="rfc.section.7.6.p.8">HTTP/1.1 servers <em class="bcp14">SHOULD</em> send Last-Modified whenever feasible. 919 </p> 920 <p id="rfc.section.7.6.p.9">The Last-Modified entity-header field value is often used as a cache validator. In simple terms, a cache entry is considered 913 921 to be valid if the entity has not been modified since the Last-Modified value. 914 922 </p> 915 <h1 id="rfc.section. 7"><a href="#rfc.section.7">7.</a> <a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1>916 <p id="rfc.section. 7.p.1"> <span class="comment">[rfc.comment.1: TBD.]</span>917 </p> 918 <h1 id="rfc.section. 8"><a href="#rfc.section.8">8.</a> <a id="security.considerations" href="#security.considerations">Security Considerations</a></h1>919 <p id="rfc.section. 8.p.1">No additional security considerations have been identified beyond those applicable to HTTP in general <a href="#Part1" id="rfc.xref.Part1.2"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>.920 </p> 921 <h1 id="rfc.section. 9"><a href="#rfc.section.9">9.</a> <a id="ack" href="#ack">Acknowledgments</a></h1>922 <h1 id="rfc.references"><a id="rfc.section.1 0" href="#rfc.section.10">10.</a> References923 <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a> <a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1> 924 <p id="rfc.section.8.p.1"> <span class="comment">[rfc.comment.1: TBD.]</span> 925 </p> 926 <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a> <a id="security.considerations" href="#security.considerations">Security Considerations</a></h1> 927 <p id="rfc.section.9.p.1">No additional security considerations have been identified beyond those applicable to HTTP in general <a href="#Part1" id="rfc.xref.Part1.6"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. 928 </p> 929 <h1 id="rfc.section.10"><a href="#rfc.section.10">10.</a> <a id="ack" href="#ack">Acknowledgments</a></h1> 930 <h1 id="rfc.references"><a id="rfc.section.11" href="#rfc.section.11">11.</a> References 923 931 </h1> 924 <h2 id="rfc.references.1"><a href="#rfc.section.1 0.1" id="rfc.section.10.1">10.1</a> Normative References932 <h2 id="rfc.references.1"><a href="#rfc.section.11.1" id="rfc.section.11.1">11.1</a> Normative References 925 933 </h2> 926 934 <table summary="Normative References"> … … 946 954 </tr> 947 955 </table> 948 <h2 id="rfc.references.2"><a href="#rfc.section.1 0.2" id="rfc.section.10.2">10.2</a> Informative References956 <h2 id="rfc.references.2"><a href="#rfc.section.11.2" id="rfc.section.11.2">11.2</a> Informative References 949 957 </h2> 950 958 <table summary="Informative References"> … … 997 1005 <h2 id="rfc.section.B.3"><a href="#rfc.section.B.3">B.3</a> Since draft-ietf-httpbis-p4-conditional-01 998 1006 </h2> 1007 <p id="rfc.section.B.3.p.1">Ongoing work on ABNF conversion (<<a href="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36">http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36</a>>): 1008 </p> 1009 <ul> 1010 <li>Add explicit references to BNF syntax and rules imported from other parts of the specification.</li> 1011 </ul> 999 1012 <h1><a id="rfc.copyright" href="#rfc.copyright">Full Copyright Statement</a></h1> 1000 1013 <p>Copyright © The IETF Trust (2008).</p> … … 1030 1043 <ul class="ind"> 1031 1044 <li class="indline0"><a id="rfc.index.3" href="#rfc.index.3"><b>3</b></a><ul class="ind"> 1032 <li class="indline1">304 Not Modified (status code) <a class="iref" href="#rfc.iref.3"><b> 3.1</b></a></li>1045 <li class="indline1">304 Not Modified (status code) <a class="iref" href="#rfc.iref.3"><b>4.1</b></a></li> 1033 1046 </ul> 1034 1047 </li> 1035 1048 <li class="indline0"><a id="rfc.index.4" href="#rfc.index.4"><b>4</b></a><ul class="ind"> 1036 <li class="indline1">412 Precondition Failed (status code) <a class="iref" href="#rfc.iref.4"><b> 3.2</b></a></li>1049 <li class="indline1">412 Precondition Failed (status code) <a class="iref" href="#rfc.iref.4"><b>4.2</b></a></li> 1037 1050 </ul> 1038 1051 </li> 1039 1052 <li class="indline0"><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul class="ind"> 1040 <li class="indline1">ETag header <a class="iref" href="#rfc.xref.header.etag.1"> 2</a>, <a class="iref" href="#rfc.iref.e.1"><b>6.1</b></a></li>1053 <li class="indline1">ETag header <a class="iref" href="#rfc.xref.header.etag.1">3</a>, <a class="iref" href="#rfc.iref.e.1"><b>7.1</b></a></li> 1041 1054 </ul> 1042 1055 </li> … … 1044 1057 <li class="indline1"><tt>Grammar</tt> 1045 1058 <ul class="ind"> 1046 <li class="indline1"><tt>entity-tag</tt> <a class="iref" href="#rfc.iref.g.1"><b> 2</b></a></li>1047 <li class="indline1"><tt>ETag</tt> <a class="iref" href="#rfc.iref.g.4"><b> 6.1</b></a></li>1048 <li class="indline1"><tt>If-Match</tt> <a class="iref" href="#rfc.iref.g.5"><b> 6.2</b></a></li>1049 <li class="indline1"><tt>If-Modified-Since</tt> <a class="iref" href="#rfc.iref.g.6"><b> 6.3</b></a></li>1050 <li class="indline1"><tt>If-None-Match</tt> <a class="iref" href="#rfc.iref.g.7"><b> 6.4</b></a></li>1051 <li class="indline1"><tt>If-Unmodified-Since</tt> <a class="iref" href="#rfc.iref.g.8"><b> 6.5</b></a></li>1052 <li class="indline1"><tt>Last-Modified</tt> <a class="iref" href="#rfc.iref.g.9"><b> 6.6</b></a></li>1053 <li class="indline1"><tt>opaque-tag</tt> <a class="iref" href="#rfc.iref.g.3"><b> 2</b></a></li>1054 <li class="indline1"><tt>weak</tt> <a class="iref" href="#rfc.iref.g.2"><b> 2</b></a></li>1059 <li class="indline1"><tt>entity-tag</tt> <a class="iref" href="#rfc.iref.g.1"><b>3</b></a></li> 1060 <li class="indline1"><tt>ETag</tt> <a class="iref" href="#rfc.iref.g.4"><b>7.1</b></a></li> 1061 <li class="indline1"><tt>If-Match</tt> <a class="iref" href="#rfc.iref.g.5"><b>7.2</b></a></li> 1062 <li class="indline1"><tt>If-Modified-Since</tt> <a class="iref" href="#rfc.iref.g.6"><b>7.3</b></a></li> 1063 <li class="indline1"><tt>If-None-Match</tt> <a class="iref" href="#rfc.iref.g.7"><b>7.4</b></a></li> 1064 <li class="indline1"><tt>If-Unmodified-Since</tt> <a class="iref" href="#rfc.iref.g.8"><b>7.5</b></a></li> 1065 <li class="indline1"><tt>Last-Modified</tt> <a class="iref" href="#rfc.iref.g.9"><b>7.6</b></a></li> 1066 <li class="indline1"><tt>opaque-tag</tt> <a class="iref" href="#rfc.iref.g.3"><b>3</b></a></li> 1067 <li class="indline1"><tt>weak</tt> <a class="iref" href="#rfc.iref.g.2"><b>3</b></a></li> 1055 1068 </ul> 1056 1069 </li> … … 1060 1073 <li class="indline1">Headers 1061 1074 <ul class="ind"> 1062 <li class="indline1">ETag <a class="iref" href="#rfc.xref.header.etag.1"> 2</a>, <a class="iref" href="#rfc.iref.h.1"><b>6.1</b></a></li>1063 <li class="indline1">If-Match <a class="iref" href="#rfc.xref.header.if-match.1"> 2</a>, <a class="iref" href="#rfc.xref.header.if-match.2">6.1</a>, <a class="iref" href="#rfc.iref.h.2"><b>6.2</b></a></li>1064 <li class="indline1">If-Modified-Since <a class="iref" href="#rfc.iref.h.3"><b> 6.3</b></a></li>1065 <li class="indline1">If-None-Match <a class="iref" href="#rfc.xref.header.if-none-match.1"> 2</a>, <a class="iref" href="#rfc.xref.header.if-none-match.2">6.1</a>, <a class="iref" href="#rfc.iref.h.4"><b>6.4</b></a></li>1066 <li class="indline1">If-Unmodified-Since <a class="iref" href="#rfc.iref.h.5"><b> 6.5</b></a></li>1067 <li class="indline1">Last-Modified <a class="iref" href="#rfc.iref.h.6"><b> 6.6</b></a></li>1075 <li class="indline1">ETag <a class="iref" href="#rfc.xref.header.etag.1">3</a>, <a class="iref" href="#rfc.iref.h.1"><b>7.1</b></a></li> 1076 <li class="indline1">If-Match <a class="iref" href="#rfc.xref.header.if-match.1">3</a>, <a class="iref" href="#rfc.xref.header.if-match.2">7.1</a>, <a class="iref" href="#rfc.iref.h.2"><b>7.2</b></a></li> 1077 <li class="indline1">If-Modified-Since <a class="iref" href="#rfc.iref.h.3"><b>7.3</b></a></li> 1078 <li class="indline1">If-None-Match <a class="iref" href="#rfc.xref.header.if-none-match.1">3</a>, <a class="iref" href="#rfc.xref.header.if-none-match.2">7.1</a>, <a class="iref" href="#rfc.iref.h.4"><b>7.4</b></a></li> 1079 <li class="indline1">If-Unmodified-Since <a class="iref" href="#rfc.iref.h.5"><b>7.5</b></a></li> 1080 <li class="indline1">Last-Modified <a class="iref" href="#rfc.iref.h.6"><b>7.6</b></a></li> 1068 1081 </ul> 1069 1082 </li> … … 1071 1084 </li> 1072 1085 <li class="indline0"><a id="rfc.index.I" href="#rfc.index.I"><b>I</b></a><ul class="ind"> 1073 <li class="indline1">If-Match header <a class="iref" href="#rfc.xref.header.if-match.1"> 2</a>, <a class="iref" href="#rfc.xref.header.if-match.2">6.1</a>, <a class="iref" href="#rfc.iref.i.1"><b>6.2</b></a></li>1074 <li class="indline1">If-Modified-Since header <a class="iref" href="#rfc.iref.i.2"><b> 6.3</b></a></li>1075 <li class="indline1">If-None-Match header <a class="iref" href="#rfc.xref.header.if-none-match.1"> 2</a>, <a class="iref" href="#rfc.xref.header.if-none-match.2">6.1</a>, <a class="iref" href="#rfc.iref.i.3"><b>6.4</b></a></li>1076 <li class="indline1">If-Unmodified-Since header <a class="iref" href="#rfc.iref.i.4"><b> 6.5</b></a></li>1086 <li class="indline1">If-Match header <a class="iref" href="#rfc.xref.header.if-match.1">3</a>, <a class="iref" href="#rfc.xref.header.if-match.2">7.1</a>, <a class="iref" href="#rfc.iref.i.1"><b>7.2</b></a></li> 1087 <li class="indline1">If-Modified-Since header <a class="iref" href="#rfc.iref.i.2"><b>7.3</b></a></li> 1088 <li class="indline1">If-None-Match header <a class="iref" href="#rfc.xref.header.if-none-match.1">3</a>, <a class="iref" href="#rfc.xref.header.if-none-match.2">7.1</a>, <a class="iref" href="#rfc.iref.i.3"><b>7.4</b></a></li> 1089 <li class="indline1">If-Unmodified-Since header <a class="iref" href="#rfc.iref.i.4"><b>7.5</b></a></li> 1077 1090 </ul> 1078 1091 </li> 1079 1092 <li class="indline0"><a id="rfc.index.L" href="#rfc.index.L"><b>L</b></a><ul class="ind"> 1080 <li class="indline1">Last-Modified header <a class="iref" href="#rfc.iref.l.1"><b> 6.6</b></a></li>1093 <li class="indline1">Last-Modified header <a class="iref" href="#rfc.iref.l.1"><b>7.6</b></a></li> 1081 1094 </ul> 1082 1095 </li> 1083 1096 <li class="indline0"><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul class="ind"> 1084 <li class="indline1"><em>Part1</em> <a class="iref" href="#rfc.xref.Part1.1">3.1</a>, <a class="iref" href="#rfc.xref.Part1.2">8</a>, <a class="iref" href="#Part1"><b>10.1</b></a><ul class="ind"> 1085 <li class="indline1"><em>Section 8.3.1</em> <a class="iref" href="#rfc.xref.Part1.1">3.1</a></li> 1097 <li class="indline1"><em>Part1</em> <a class="iref" href="#rfc.xref.Part1.1">2</a>, <a class="iref" href="#rfc.xref.Part1.2">2</a>, <a class="iref" href="#rfc.xref.Part1.3">2</a>, <a class="iref" href="#rfc.xref.Part1.4">2</a>, <a class="iref" href="#rfc.xref.Part1.5">4.1</a>, <a class="iref" href="#rfc.xref.Part1.6">9</a>, <a class="iref" href="#Part1"><b>11.1</b></a><ul class="ind"> 1098 <li class="indline1"><em>Section 2.1</em> <a class="iref" href="#rfc.xref.Part1.1">2</a></li> 1099 <li class="indline1"><em>Section 2.2</em> <a class="iref" href="#rfc.xref.Part1.2">2</a>, <a class="iref" href="#rfc.xref.Part1.3">2</a></li> 1100 <li class="indline1"><em>Section 3.3.1</em> <a class="iref" href="#rfc.xref.Part1.4">2</a></li> 1101 <li class="indline1"><em>Section 8.3.1</em> <a class="iref" href="#rfc.xref.Part1.5">4.1</a></li> 1086 1102 </ul> 1087 1103 </li> 1088 <li class="indline1"><em>Part5</em> <a class="iref" href="#rfc.xref.Part5.1"> 2</a>, <a class="iref" href="#rfc.xref.Part5.2">6.1</a>, <a class="iref" href="#rfc.xref.Part5.3">6.3</a>, <a class="iref" href="#Part5"><b>10.1</b></a><ul class="ind">1089 <li class="indline1"><em>Section 5.3</em> <a class="iref" href="#rfc.xref.Part5.1">2</a>, <a class="iref" href="#rfc.xref.Part5.2">6.1</a></li>1090 <li class="indline1"><em>Section 5.4</em> <a class="iref" href="#rfc.xref.Part5.3">6.3</a></li>1104 <li class="indline1"><em>Part5</em> <a class="iref" href="#rfc.xref.Part5.1">3</a>, <a class="iref" href="#rfc.xref.Part5.2">7.1</a>, <a class="iref" href="#rfc.xref.Part5.3">7.3</a>, <a class="iref" href="#Part5"><b>11.1</b></a><ul class="ind"> 1105 <li class="indline1"><em>Section 6.3</em> <a class="iref" href="#rfc.xref.Part5.1">3</a>, <a class="iref" href="#rfc.xref.Part5.2">7.1</a></li> 1106 <li class="indline1"><em>Section 6.4</em> <a class="iref" href="#rfc.xref.Part5.3">7.3</a></li> 1091 1107 </ul> 1092 1108 </li> 1093 <li class="indline1"><em>Part6</em> <a class="iref" href="#rfc.xref.Part6.1">1</a>, <a class="iref" href="#rfc.xref.Part6.2"> 6.2</a>, <a class="iref" href="#rfc.xref.Part6.3">6.4</a>, <a class="iref" href="#Part6"><b>10.1</b></a><ul class="ind">1094 <li class="indline1"><em>Section 1 5.5</em> <a class="iref" href="#rfc.xref.Part6.2">6.2</a>, <a class="iref" href="#rfc.xref.Part6.3">6.4</a></li>1109 <li class="indline1"><em>Part6</em> <a class="iref" href="#rfc.xref.Part6.1">1</a>, <a class="iref" href="#rfc.xref.Part6.2">7.2</a>, <a class="iref" href="#rfc.xref.Part6.3">7.4</a>, <a class="iref" href="#Part6"><b>11.1</b></a><ul class="ind"> 1110 <li class="indline1"><em>Section 16.5</em> <a class="iref" href="#rfc.xref.Part6.2">7.2</a>, <a class="iref" href="#rfc.xref.Part6.3">7.4</a></li> 1095 1111 </ul> 1096 1112 </li> … … 1098 1114 </li> 1099 1115 <li class="indline0"><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul class="ind"> 1100 <li class="indline1"><em>RFC2068</em> <a class="iref" href="#rfc.xref.RFC2068.1"> 3.1</a>, <a class="iref" href="#RFC2068"><b>10.2</b></a><ul class="ind">1101 <li class="indline1"><em>Section 14.19</em> <a class="iref" href="#rfc.xref.RFC2068.1"> 3.1</a></li>1116 <li class="indline1"><em>RFC2068</em> <a class="iref" href="#rfc.xref.RFC2068.1">4.1</a>, <a class="iref" href="#RFC2068"><b>11.2</b></a><ul class="ind"> 1117 <li class="indline1"><em>Section 14.19</em> <a class="iref" href="#rfc.xref.RFC2068.1">4.1</a></li> 1102 1118 </ul> 1103 1119 </li> 1104 <li class="indline1"><em>RFC2119</em> <a class="iref" href="#rfc.xref.RFC2119.1">1.1</a>, <a class="iref" href="#RFC2119"><b>1 0.1</b></a></li>1105 <li class="indline1"><em>RFC2616</em> <a class="iref" href="#rfc.xref.RFC2616.1">1</a>, <a class="iref" href="#RFC2616"><b>1 0.2</b></a>, <a class="iref" href="#rfc.xref.RFC2616.2">B.1</a></li>1120 <li class="indline1"><em>RFC2119</em> <a class="iref" href="#rfc.xref.RFC2119.1">1.1</a>, <a class="iref" href="#RFC2119"><b>11.1</b></a></li> 1121 <li class="indline1"><em>RFC2616</em> <a class="iref" href="#rfc.xref.RFC2616.1">1</a>, <a class="iref" href="#RFC2616"><b>11.2</b></a>, <a class="iref" href="#rfc.xref.RFC2616.2">B.1</a></li> 1106 1122 </ul> 1107 1123 </li> … … 1109 1125 <li class="indline1">Status Codes 1110 1126 <ul class="ind"> 1111 <li class="indline1">304 Not Modified <a class="iref" href="#rfc.iref.s.1"><b> 3.1</b></a></li>1112 <li class="indline1">412 Precondition Failed <a class="iref" href="#rfc.iref.s.2"><b> 3.2</b></a></li>1127 <li class="indline1">304 Not Modified <a class="iref" href="#rfc.iref.s.1"><b>4.1</b></a></li> 1128 <li class="indline1">412 Precondition Failed <a class="iref" href="#rfc.iref.s.2"><b>4.2</b></a></li> 1113 1129 </ul> 1114 1130 </li>
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