Changeset 1381
- Timestamp:
- 06/08/11 01:32:35 (11 years ago)
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- 1 edited
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draft-ietf-httpbis/latest/p4-conditional.html
r1373 r1381 359 359 } 360 360 @bottom-center { 361 content: "Expires February 4, 2012";361 content: "Expires February 6, 2012"; 362 362 } 363 363 @bottom-right { … … 382 382 <link rel="Index" href="#rfc.index"> 383 383 <link rel="Chapter" title="1 Introduction" href="#rfc.section.1"> 384 <link rel="Chapter" title="2 Resource State Metadata (Validators)" href="#rfc.section.2">384 <link rel="Chapter" title="2 Validators" href="#rfc.section.2"> 385 385 <link rel="Chapter" title="3 Precondition Header Fields" href="#rfc.section.3"> 386 386 <link rel="Chapter" title="4 Status Code Definitions" href="#rfc.section.4"> … … 404 404 <meta name="dct.creator" content="Reschke, J. F."> 405 405 <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p4-conditional-latest"> 406 <meta name="dct.issued" scheme="ISO8601" content="2011-08-0 3">406 <meta name="dct.issued" scheme="ISO8601" content="2011-08-05"> 407 407 <meta name="dct.replaces" content="urn:ietf:rfc:2616"> 408 408 <meta name="dct.abstract" content="The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypertext information systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 4 of the seven-part specification that defines the protocol referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616. Part 4 defines request header fields for indicating conditional requests and the rules for constructing responses to those requests."> … … 430 430 </tr> 431 431 <tr> 432 <td class="left">Expires: February 4, 2012</td>432 <td class="left">Expires: February 6, 2012</td> 433 433 <td class="right">J. Mogul</td> 434 434 </tr> … … 487 487 <tr> 488 488 <td class="left"></td> 489 <td class="right">August 3, 2011</td>489 <td class="right">August 5, 2011</td> 490 490 </tr> 491 491 </tbody> … … 517 517 in progress”. 518 518 </p> 519 <p>This Internet-Draft will expire on February 4, 2012.</p>519 <p>This Internet-Draft will expire on February 6, 2012.</p> 520 520 <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1> 521 521 <p>Copyright © 2011 IETF Trust and the persons identified as the document authors. All rights reserved.</p> … … 540 540 </ul> 541 541 </li> 542 <li>2. <a href="#resource.metadata">Resource State Metadata (Validators)</a><ul> 543 <li>2.1 <a href="#header.last-modified">Last-Modified</a><ul> 544 <li>2.1.1 <a href="#lastmod.generation">Generation</a></li> 545 <li>2.1.2 <a href="#lastmod.comparison">Comparison</a></li> 542 <li>2. <a href="#validators">Validators</a><ul> 543 <li>2.1 <a href="#weak.and.strong.validators">Weak versus Strong</a></li> 544 <li>2.2 <a href="#header.last-modified">Last-Modified</a><ul> 545 <li>2.2.1 <a href="#lastmod.generation">Generation</a></li> 546 <li>2.2.2 <a href="#lastmod.comparison">Comparison</a></li> 546 547 </ul> 547 548 </li> 548 <li>2.2 <a href="#header.etag">ETag</a><ul> 549 <li>2.2.1 <a href="#entity.tag.generation">Generation</a></li> 550 <li>2.2.2 <a href="#weak.and.strong.validators">Weak versus Strong</a></li> 551 <li>2.2.3 <a href="#entity.tag.comparison">Comparison</a></li> 552 <li>2.2.4 <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> 553 <li>2.2.5 <a href="#example.entity.tag.vs.conneg">Example: Entity-tags varying on Content-Negotiated Resources</a></li> 549 <li>2.3 <a href="#header.etag">ETag</a><ul> 550 <li>2.3.1 <a href="#entity.tag.generation">Generation</a></li> 551 <li>2.3.2 <a href="#entity.tag.comparison">Comparison</a></li> 552 <li>2.3.3 <a href="#example.entity.tag.vs.conneg">Example: Entity-tags varying on Content-Negotiated Resources</a></li> 554 553 </ul> 555 554 </li> 555 <li>2.4 <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> 556 556 </ul> 557 557 </li> … … 607 607 </ul> 608 608 <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a> <a id="introduction" href="#introduction">Introduction</a></h1> 609 <p id="rfc.section.1.p.1">This document defines the HTTP/1.1 conditional request mechanisms, including both response metadata that can be used to indicate610 or observe changes to resource state and request header fields that specify preconditions tobe checked before performing611 the action given by therequest method. Conditional GET requests are the most efficient mechanism for HTTP cache updates <a href="#Part6" id="rfc.xref.Part6.1"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>. Conditionals can also be applied to state-changing methods, such as PUT and DELETE, to prevent the "lost update" problem:609 <p id="rfc.section.1.p.1">This document defines the HTTP/1.1 conditional request mechanisms, including both metadata for indicating/observing changes 610 in resource representations and request header fields that specify preconditions on that metadata be checked before performing 611 the request method. Conditional GET requests are the most efficient mechanism for HTTP cache updates <a href="#Part6" id="rfc.xref.Part6.1"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>. Conditionals can also be applied to state-changing methods, such as PUT and DELETE, to prevent the "lost update" problem: 612 612 one client accidentally overwriting the work of another client that has been acting in parallel. 613 613 </p> … … 646 646 </pre><div id="rfc.iref.m.1"></div> 647 647 <div id="rfc.iref.v.1"></div> 648 <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a> <a id=" resource.metadata" href="#resource.metadata">Resource State Metadata (Validators)</a></h1>648 <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a> <a id="validators" href="#validators">Validators</a></h1> 649 649 <p id="rfc.section.2.p.1">This specification defines two forms of metadata that are commonly used to observe resource state and test for preconditions: 650 650 modification dates and opaque entity tags. Additional metadata that reflects resource state has been defined by various extensions 651 651 of HTTP, such as WebDAV <a href="#RFC4918" id="rfc.xref.RFC4918.1"><cite title="HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)">[RFC4918]</cite></a>, that are beyond the scope of this specification. A resource metadata value is referred to as a "<dfn>validator</dfn>" when it is used within a precondition. 652 652 </p> 653 <div id="rfc.iref.v.2"></div> 654 <div id="rfc.iref.v.3"></div> 655 <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a> <a id="weak.and.strong.validators" href="#weak.and.strong.validators">Weak versus Strong</a></h2> 656 <p id="rfc.section.2.1.p.1">Validators come in two flavors: strong or weak. Weak validators are easy to generate but are far less useful for comparisons. 657 Strong validators are ideal for comparisons but can be very difficult (and occasionally impossible) to generate efficiently. 658 Rather than impose that all forms of resource adhere to the same strength of validator, HTTP exposes the type of validator 659 in use and imposes restrictions on when weak validators can be used as preconditions. 660 </p> 661 <p id="rfc.section.2.1.p.2">A "strong validator" is a representation metadata value that <em class="bcp14">MUST</em> be changed to a new, previously unused or guaranteed unique, value whenever a change occurs to the representation data such 662 that a change would be observable in the payload body of a 200 response to GET. A strong validator <em class="bcp14">MAY</em> be changed for other reasons, such as when a semantically significant part of the representation metadata is changed (e.g., 663 Content-Type), but it is in the best interests of the origin server to only change the value when it is necessary to invalidate 664 the stored responses held by remote caches and authoring tools. A strong validator <em class="bcp14">MUST</em> be unique across all representations of a given resource, such that no two representations of that resource share the same 665 validator unless their payload body would be identical. 666 </p> 667 <p id="rfc.section.2.1.p.3">Cache entries might persist for arbitrarily long periods, regardless of expiration times. Thus, a cache might attempt to validate 668 an entry using a validator that it obtained in the distant past. A strong validator <em class="bcp14">MUST</em> be unique across all versions of all representations associated with a particular resource over time. However, there is no 669 implication of uniqueness across representations of different resources (i.e., the same strong validator might be in use for 670 representations of multiple resources at the same time and does not imply that those representations are equivalent). 671 </p> 672 <p id="rfc.section.2.1.p.4">There are a variety of strong validators used in practice. The best are based on strict revision control, wherein each change 673 to a representation always results in a unique node name and revision identifier being assigned before the representation 674 is made accessible to GET. A cryptographic hash function applied to the representation data is also sufficient if the data 675 is available prior to the response header fields being sent and the digest does not need to be recalculated every time a validation 676 request is received. However, if a resource has distinct representations that differ only in their metadata, such as might 677 occur with content negotiation over media types that happen to share the same data format, then a server <em class="bcp14">SHOULD</em> incorporate additional information in the validator to distinguish those representations and avoid confusing cache behavior. 678 </p> 679 <p id="rfc.section.2.1.p.5">In contrast, a "weak validator" is a representation metadata value that might not be changed for every change to the representation 680 data. This weakness might be due to limitations in how the value is calculated, such as clock resolution or an inability to 681 ensure uniqueness for all possible representations of the resource, or due to a desire by the resource owner to group representations 682 by some self-determined set of equivalency rather than unique sequences of data. A weak entity-tag <em class="bcp14">SHOULD</em> change whenever the origin server considers prior representations to be unacceptable as a substitute for the current representation. 683 In other words, a weak entity-tag <em class="bcp14">SHOULD</em> change whenever the origin server wants caches to invalidate old responses. 684 </p> 685 <p id="rfc.section.2.1.p.6">For example, the representation of a weather report that changes in content every second, based on dynamic measurements, might 686 be grouped into sets of equivalent representations (from the origin server's perspective) with the same weak validator in 687 order to allow cached representations to be valid for a reasonable period of time (perhaps adjusted dynamically based on server 688 load or weather quality). Likewise, a representation's modification time, if defined with only one-second resolution, might 689 be a weak validator if it is possible for the representation to be modified twice during a single second and retrieved between 690 those modifications. 691 </p> 692 <p id="rfc.section.2.1.p.7">A "use" of a validator occurs when either a client generates a request and includes the validator in a precondition or when 693 a server compares two validators. Weak validators are only usable in contexts that do not depend on exact equality of a representation's 694 payload body. Strong validators are usable and preferred for all conditional requests, including cache validation, partial 695 content ranges, and "lost update" avoidance. 696 </p> 653 697 <div id="rfc.iref.l.1"></div> 654 698 <div id="rfc.iref.h.1"></div> 655 <h2 id="rfc.section.2. 1"><a href="#rfc.section.2.1">2.1</a> <a id="header.last-modified" href="#header.last-modified">Last-Modified</a></h2>656 <p id="rfc.section.2. 1.p.1">The "Last-Modified" header field indicates the date and time at which the origin server believes the selected representation699 <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a> <a id="header.last-modified" href="#header.last-modified">Last-Modified</a></h2> 700 <p id="rfc.section.2.2.p.1">The "Last-Modified" header field indicates the date and time at which the origin server believes the selected representation 657 701 was last modified. 658 702 </p> 659 703 <div id="rfc.figure.u.2"></div><pre class="inline"><span id="rfc.iref.g.1"></span> <a href="#header.last-modified" class="smpl">Last-Modified</a> = <a href="#notation" class="smpl">HTTP-date</a> 660 </pre><p id="rfc.section.2. 1.p.3">An example of its use is</p>704 </pre><p id="rfc.section.2.2.p.3">An example of its use is</p> 661 705 <div id="rfc.figure.u.3"></div><pre class="text"> Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT 662 </pre><h3 id="rfc.section.2. 1.1"><a href="#rfc.section.2.1.1">2.1.1</a> <a id="lastmod.generation" href="#lastmod.generation">Generation</a></h3>663 <p id="rfc.section.2. 1.1.p.1">Origin servers <em class="bcp14">SHOULD</em> send Last-Modified for any selected representation for which a last modification date can be reasonably and consistently determined,706 </pre><h3 id="rfc.section.2.2.1"><a href="#rfc.section.2.2.1">2.2.1</a> <a id="lastmod.generation" href="#lastmod.generation">Generation</a></h3> 707 <p id="rfc.section.2.2.1.p.1">Origin servers <em class="bcp14">SHOULD</em> send Last-Modified for any selected representation for which a last modification date can be reasonably and consistently determined, 664 708 since its use in conditional requests and evaluating cache freshness (<a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) results in a substantial reduction of HTTP traffic on the Internet and can be a significant factor in improving service 665 709 scalability and reliability. 666 710 </p> 667 <p id="rfc.section.2. 1.1.p.2">A representation is typically the sum of many parts behind the resource interface. The last-modified time would usually be711 <p id="rfc.section.2.2.1.p.2">A representation is typically the sum of many parts behind the resource interface. The last-modified time would usually be 668 712 the most recent time that any of those parts were changed. How that value is determined for any given resource is an implementation 669 713 detail beyond the scope of this specification. What matters to HTTP is how recipients of the Last-Modified header field can 670 714 use its value to make conditional requests and test the validity of locally cached responses. 671 715 </p> 672 <p id="rfc.section.2. 1.1.p.3">An origin server <em class="bcp14">SHOULD</em> obtain the Last-Modified value of the representation as close as possible to the time that it generates the Date field-value716 <p id="rfc.section.2.2.1.p.3">An origin server <em class="bcp14">SHOULD</em> obtain the Last-Modified value of the representation as close as possible to the time that it generates the Date field-value 673 717 for its response. This allows a recipient to make an accurate assessment of the representation's modification time, especially 674 718 if the representation changes near the time that the response is generated. 675 719 </p> 676 <p id="rfc.section.2. 1.1.p.4">An origin server with a clock <em class="bcp14">MUST NOT</em> send a Last-Modified date that is later than the server's time of message origination (Date). If the last modification time720 <p id="rfc.section.2.2.1.p.4">An origin server with a clock <em class="bcp14">MUST NOT</em> send a Last-Modified date that is later than the server's time of message origination (Date). If the last modification time 677 721 is derived from implementation-specific metadata that evaluates to some time in the future, according to the origin server's 678 722 clock, then the origin server <em class="bcp14">MUST</em> replace that value with the message origination date. This prevents a future modification date from having an adverse impact 679 723 on cache validation. 680 724 </p> 681 <h3 id="rfc.section.2. 1.2"><a href="#rfc.section.2.1.2">2.1.2</a> <a id="lastmod.comparison" href="#lastmod.comparison">Comparison</a></h3>682 <p id="rfc.section.2. 1.2.p.1">A Last-Modified time, when used as a validator in a request, is implicitly weak unless it is possible to deduce that it is725 <h3 id="rfc.section.2.2.2"><a href="#rfc.section.2.2.2">2.2.2</a> <a id="lastmod.comparison" href="#lastmod.comparison">Comparison</a></h3> 726 <p id="rfc.section.2.2.2.p.1">A Last-Modified time, when used as a validator in a request, is implicitly weak unless it is possible to deduce that it is 683 727 strong, using the following rules: 684 728 </p> … … 689 733 </li> 690 734 </ul> 691 <p id="rfc.section.2. 1.2.p.2">or </p>735 <p id="rfc.section.2.2.2.p.2">or </p> 692 736 <ul> 693 737 <li>The validator is about to be used by a client in an If-Modified-Since, If-Unmodified-Since header field, because the client … … 697 741 <li>The presented Last-Modified time is at least 60 seconds before the Date value.</li> 698 742 </ul> 699 <p id="rfc.section.2. 1.2.p.3">or </p>743 <p id="rfc.section.2.2.2.p.3">or </p> 700 744 <ul> 701 745 <li>The validator is being compared by an intermediate cache to the validator stored in its cache entry for the representation, … … 705 749 <li>The presented Last-Modified time is at least 60 seconds before the Date value.</li> 706 750 </ul> 707 <p id="rfc.section.2. 1.2.p.4">This method relies on the fact that if two different responses were sent by the origin server during the same second, but751 <p id="rfc.section.2.2.2.p.4">This method relies on the fact that if two different responses were sent by the origin server during the same second, but 708 752 both had the same Last-Modified time, then at least one of those responses would have a Date value equal to its Last-Modified 709 753 time. The arbitrary 60-second limit guards against the possibility that the Date and Last-Modified values are generated from … … 712 756 <div id="rfc.iref.e.1"></div> 713 757 <div id="rfc.iref.h.2"></div> 714 <h2 id="rfc.section.2. 2"><a href="#rfc.section.2.2">2.2</a> <a id="header.etag" href="#header.etag">ETag</a></h2>715 <p id="rfc.section.2. 2.p.1">The ETag header field provides the current entity-tag for the selected representation. An entity-tag is an opaque validator758 <h2 id="rfc.section.2.3"><a href="#rfc.section.2.3">2.3</a> <a id="header.etag" href="#header.etag">ETag</a></h2> 759 <p id="rfc.section.2.3.p.1">The ETag header field provides the current entity-tag for the selected representation. An entity-tag is an opaque validator 716 760 for differentiating between multiple representations of the same resource, regardless of whether those multiple representations 717 761 are due to resource state changes over time, content negotiation resulting in multiple representations being valid at the … … 723 767 <a href="#header.etag" class="smpl">weak</a> = %x57.2F ; "W/", case-sensitive 724 768 <a href="#header.etag" class="smpl">opaque-tag</a> = <a href="#notation" class="smpl">quoted-string</a> 725 </pre><p id="rfc.section.2. 2.p.3">An entity-tag can be more reliable for validation than a modification date in situations where it is inconvenient to store769 </pre><p id="rfc.section.2.3.p.3">An entity-tag can be more reliable for validation than a modification date in situations where it is inconvenient to store 726 770 modification dates, where the one-second resolution of HTTP date values is not sufficient, or where modification dates are 727 771 not consistently maintained. … … 731 775 ETag: W/"xyzzy" 732 776 ETag: "" 733 </pre><h3 id="rfc.section.2.2.1"><a href="#rfc.section.2.2.1">2.2.1</a> <a id="entity.tag.generation" href="#entity.tag.generation">Generation</a></h3> 734 <p id="rfc.section.2.2.1.p.1">The principle behind entity-tags is that only the service author knows the implementation of a resource well enough to select 777 </pre><p id="rfc.section.2.3.p.5">An entity-tag can be either a weak or strong validator, with strong being the default. If an origin server provides an entity-tag 778 for a representation and the generation of that entity-tag does not satisfy the requirements for a strong validator (<a href="#weak.and.strong.validators" title="Weak versus Strong">Section 2.1</a>), then that entity-tag <em class="bcp14">MUST</em> be marked as weak by prefixing its opaque value with "W/" (case-sensitive). 779 </p> 780 <h3 id="rfc.section.2.3.1"><a href="#rfc.section.2.3.1">2.3.1</a> <a id="entity.tag.generation" href="#entity.tag.generation">Generation</a></h3> 781 <p id="rfc.section.2.3.1.p.1">The principle behind entity-tags is that only the service author knows the implementation of a resource well enough to select 735 782 the most accurate and efficient validation mechanism for that resource, and that any such mechanism can be mapped to a simple 736 783 sequence of octets for easy comparison. Since the value is opaque, there is no need for the client to be aware of how each 737 784 entity-tag is constructed. 738 785 </p> 739 <p id="rfc.section.2. 2.1.p.2">For example, a resource that has implementation-specific versioning applied to all changes might use an internal revision786 <p id="rfc.section.2.3.1.p.2">For example, a resource that has implementation-specific versioning applied to all changes might use an internal revision 740 787 number, perhaps combined with a variance identifier for content negotiation, to accurately differentiate between representations. 741 788 Other implementations might use a stored hash of representation content, a combination of various filesystem attributes, or 742 789 a modification timestamp that has sub-second resolution. 743 790 </p> 744 <p id="rfc.section.2. 2.1.p.3">Origin servers <em class="bcp14">SHOULD</em> send ETag for any selected representation for which detection of changes can be reasonably and consistently determined, since791 <p id="rfc.section.2.3.1.p.3">Origin servers <em class="bcp14">SHOULD</em> send ETag for any selected representation for which detection of changes can be reasonably and consistently determined, since 745 792 the entity-tag's use in conditional requests and evaluating cache freshness (<a href="#Part6" id="rfc.xref.Part6.3"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) can result in a substantial reduction of HTTP network traffic and can be a significant factor in improving service scalability 746 793 and reliability. 747 794 </p> 748 <h3 id="rfc.section.2.2.2"><a href="#rfc.section.2.2.2">2.2.2</a> <a id="weak.and.strong.validators" href="#weak.and.strong.validators">Weak versus Strong</a></h3> 749 <p id="rfc.section.2.2.2.p.1">Since both origin servers and caches will compare two validators to decide if they indicate the same or different representations, 750 one normally would expect that if the representation (including both representation header fields and representation body) 751 changes in any way, then the associated validator would change as well. If this is true, then we call that validator a "strong 752 validator". One example of a strong validator is an integer that is incremented in stable storage every time a representation 753 is changed. 754 </p> 755 <p id="rfc.section.2.2.2.p.2">However, there might be cases when a server prefers to change the validator only when it desires cached representations to 756 be invalidated. For example, the representation of a weather report that changes in content every second, based on dynamic 757 measurements, might be grouped into sets of equivalent representations (from the origin server's perspective) in order to 758 allow cached representations to be valid for a reasonable period of time (perhaps adjusted dynamically based on server load 759 or weather quality). A validator that does not always change when the representation changes is a "weak validator". 760 </p> 761 <p id="rfc.section.2.2.2.p.3">One can think of a strong validator as part of an identifier for a specific representation, whereas a weak validator is part 762 of an identifier for a set of equivalent representations (where this notion of equivalence is entirely governed by the origin 763 server and beyond the scope of this specification). 764 </p> 765 <p id="rfc.section.2.2.2.p.4">An entity-tag is normally a strong validator, but the protocol provides a mechanism to tag an entity-tag as "weak". </p> 766 <ul class="empty"> 767 <li>A representation's modification time, if defined with only one-second resolution, could be a weak validator, since it is possible 768 that the representation might be modified twice during a single second. 769 </li> 770 <li>Support for weak validators is optional. However, weak validators allow for more efficient caching of equivalent objects; 771 for example, a hit counter on a site is probably good enough if it is updated every few days or weeks, and any value during 772 that period is likely "good enough" to be equivalent. 773 </li> 774 </ul> 775 <p id="rfc.section.2.2.2.p.5">A strong entity-tag <em class="bcp14">MUST</em> change whenever the associated representation changes in any way. A weak entity-tag <em class="bcp14">SHOULD</em> change whenever the origin server considers prior representations to be unacceptable as a substitute for the current representation. 776 In other words, a weak entity tag <em class="bcp14">SHOULD</em> change whenever the origin server wants caches to invalidate old responses. 777 </p> 778 <p id="rfc.section.2.2.2.p.6">A "strong entity-tag" <em class="bcp14">MAY</em> be shared by two representations of a resource only if they are equivalent by octet equality. 779 </p> 780 <p id="rfc.section.2.2.2.p.7">A "weak entity-tag", indicated by the "W/" prefix, <em class="bcp14">MAY</em> be shared by two representations of a resource. A weak entity-tag can only be used for weak comparison. 781 </p> 782 <p id="rfc.section.2.2.2.p.8">Cache entries might persist for arbitrarily long periods, regardless of expiration times. Thus, a cache might attempt to validate 783 an entry using a validator that it obtained in the distant past. A strong entity-tag <em class="bcp14">MUST</em> be unique across all versions of all representations associated with a particular resource over time. However, there is no 784 implication of uniqueness across entity-tags of different resources (i.e., the same entity-tag value might be in use for representations 785 of multiple resources at the same time and does not imply that those representations are equivalent). 786 </p> 787 <h3 id="rfc.section.2.2.3"><a href="#rfc.section.2.2.3">2.2.3</a> <a id="entity.tag.comparison" href="#entity.tag.comparison">Comparison</a></h3> 788 <p id="rfc.section.2.2.3.p.1">There are two entity-tag comparison functions, depending on whether the comparison context allows the use of weak validators 795 <h3 id="rfc.section.2.3.2"><a href="#rfc.section.2.3.2">2.3.2</a> <a id="entity.tag.comparison" href="#entity.tag.comparison">Comparison</a></h3> 796 <p id="rfc.section.2.3.2.p.1">There are two entity-tag comparison functions, depending on whether the comparison context allows the use of weak validators 789 797 or not: 790 798 </p> … … 795 803 </li> 796 804 </ul> 797 <p id="rfc.section.2.2.3.p.2">A "use" of a validator is either when a client generates a request and includes the validator in a precondition, or when a 798 server compares two validators. 799 </p> 800 <p id="rfc.section.2.2.3.p.3">Strong validators are usable in any context. Weak validators are only usable in contexts that do not depend on exact equality 801 of a representation. For example, either kind is usable for a normal conditional GET. 802 </p> 803 <p id="rfc.section.2.2.3.p.4">The example below shows the results for a set of entity-tag pairs, and both the weak and strong comparison function results:</p> 805 <p id="rfc.section.2.3.2.p.2">The example below shows the results for a set of entity-tag pairs, and both the weak and strong comparison function results:</p> 804 806 <div id="rfc.table.u.1"> 805 807 <table class="tt full left" cellpadding="3" cellspacing="0"> … … 840 842 </table> 841 843 </div> 842 <p id="rfc.section.2.2.3.p.5">An entity-tag is strong unless it is explicitly tagged as weak.</p> 843 <h3 id="rfc.section.2.2.4"><a href="#rfc.section.2.2.4">2.2.4</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></h3> 844 <p id="rfc.section.2.2.4.p.1">We adopt a set of rules and recommendations for origin servers, clients, and caches regarding when various validator types 845 ought to be used, and for what purposes. 846 </p> 847 <p id="rfc.section.2.2.4.p.2">HTTP/1.1 origin servers: </p> 848 <ul> 849 <li><em class="bcp14">SHOULD</em> send an entity-tag validator unless it is not feasible to generate one. 850 </li> 851 <li><em class="bcp14">MAY</em> send a weak entity-tag instead of a strong entity-tag, if performance considerations support the use of weak entity-tags, 852 or if it is unfeasible to send a strong entity-tag. 853 </li> 854 <li><em class="bcp14">SHOULD</em> send a Last-Modified value if it is feasible to send one. 855 </li> 856 </ul> 857 <p id="rfc.section.2.2.4.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 858 value. 859 </p> 860 <p id="rfc.section.2.2.4.p.4">HTTP/1.1 clients: </p> 861 <ul> 862 <li><em class="bcp14">MUST</em> use that entity-tag in any cache-conditional request (using If-Match or If-None-Match) if an entity-tag has been provided 863 by the origin server. 864 </li> 865 <li><em class="bcp14">SHOULD</em> use the Last-Modified value in non-subrange cache-conditional requests (using If-Modified-Since) if only a Last-Modified value 866 has been provided by the origin server. 867 </li> 868 <li><em class="bcp14">MAY</em> use the Last-Modified value in subrange cache-conditional requests (using If-Unmodified-Since) if only a Last-Modified value 869 has been provided by an HTTP/1.0 origin server. The user agent <em class="bcp14">SHOULD</em> provide a way to disable this, in case of difficulty. 870 </li> 871 <li><em class="bcp14">SHOULD</em> use both validators in cache-conditional requests if both an entity-tag and a Last-Modified value have been provided by the 872 origin server. This allows both HTTP/1.0 and HTTP/1.1 caches to respond appropriately. 873 </li> 874 </ul> 875 <p id="rfc.section.2.2.4.p.5">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 876 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 877 field) as cache validators, <em class="bcp14">MUST NOT</em> return a response status code of 304 (Not Modified) unless doing so is consistent with all of the conditional header fields 878 in the request. 879 </p> 880 <p id="rfc.section.2.2.4.p.6">An HTTP/1.1 caching proxy, upon receiving a conditional request that includes both a Last-Modified date and one or more entity-tags 881 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 882 fields in the request. 883 </p> 884 <ul class="empty"> 885 <li> <b>Note:</b> The general principle behind these rules is that HTTP/1.1 servers and clients ought to transmit as much non-redundant information 886 as is available in their responses and requests. HTTP/1.1 systems receiving this information will make the most conservative 887 assumptions about the validators they receive. 888 </li> 889 <li>HTTP/1.0 clients and caches might ignore entity-tags. Generally, last-modified values received or used by these systems will 890 support transparent and efficient caching, and so HTTP/1.1 origin servers should provide Last-Modified values. In those rare 891 cases where the use of a Last-Modified value as a validator by an HTTP/1.0 system could result in a serious problem, then 892 HTTP/1.1 origin servers should not provide one. 893 </li> 894 </ul> 895 <h3 id="rfc.section.2.2.5"><a href="#rfc.section.2.2.5">2.2.5</a> <a id="example.entity.tag.vs.conneg" href="#example.entity.tag.vs.conneg">Example: Entity-tags varying on Content-Negotiated Resources</a></h3> 896 <p id="rfc.section.2.2.5.p.1">Consider a resource that is subject to content negotiation (<a href="p3-payload.html#content.negotiation" title="Content Negotiation">Section 5</a> of <a href="#Part3" id="rfc.xref.Part3.1"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>), and where the representations returned upon a GET request vary based on the Accept-Encoding request header field (<a href="p3-payload.html#header.accept-encoding" title="Accept-Encoding">Section 6.3</a> of <a href="#Part3" id="rfc.xref.Part3.2"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>): 844 <h3 id="rfc.section.2.3.3"><a href="#rfc.section.2.3.3">2.3.3</a> <a id="example.entity.tag.vs.conneg" href="#example.entity.tag.vs.conneg">Example: Entity-tags varying on Content-Negotiated Resources</a></h3> 845 <p id="rfc.section.2.3.3.p.1">Consider a resource that is subject to content negotiation (<a href="p3-payload.html#content.negotiation" title="Content Negotiation">Section 5</a> of <a href="#Part3" id="rfc.xref.Part3.1"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>), and where the representations returned upon a GET request vary based on the Accept-Encoding request header field (<a href="p3-payload.html#header.accept-encoding" title="Accept-Encoding">Section 6.3</a> of <a href="#Part3" id="rfc.xref.Part3.2"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>): 897 846 </p> 898 847 <div id="rfc.figure.u.6"></div> … … 901 850 Accept-Encoding: gzip 902 851 903 </pre><p id="rfc.section.2. 2.5.p.3">In this case, the response might or might not use the gzip content coding. If it does not, the response might look like:</p>852 </pre><p id="rfc.section.2.3.3.p.3">In this case, the response might or might not use the gzip content coding. If it does not, the response might look like:</p> 904 853 <div id="rfc.figure.u.7"></div> 905 854 <p>>> Response:</p><pre class="text">HTTP/1.1 200 OK … … 915 864 Hello World! 916 865 Hello World! 917 </span></pre><p id="rfc.section.2. 2.5.p.5">An alternative representation that does use gzip content coding would be:</p>866 </span></pre><p id="rfc.section.2.3.3.p.5">An alternative representation that does use gzip content coding would be:</p> 918 867 <div id="rfc.figure.u.8"></div> 919 868 <p>>> Response:</p><pre class="text">HTTP/1.1 200 OK … … 925 874 Content-Encoding: gzip 926 875 927 <em>...binary data...</em></pre><div class="note" id="rfc.section.2. 2.5.p.7">876 <em>...binary data...</em></pre><div class="note" id="rfc.section.2.3.3.p.7"> 928 877 <p> <b>Note:</b> Content codings are a property of the representation, so therefore an entity-tag of an encoded representation must be distinct 929 878 from an unencoded representation to prevent conflicts during cache updates and range requests. In contrast, transfer codings … … 931 880 </p> 932 881 </div> 882 <h2 id="rfc.section.2.4"><a href="#rfc.section.2.4">2.4</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></h2> 883 <p id="rfc.section.2.4.p.1">We adopt a set of rules and recommendations for origin servers, clients, and caches regarding when various validator types 884 ought to be used, and for what purposes. 885 </p> 886 <p id="rfc.section.2.4.p.2">HTTP/1.1 origin servers: </p> 887 <ul> 888 <li><em class="bcp14">SHOULD</em> send an entity-tag validator unless it is not feasible to generate one. 889 </li> 890 <li><em class="bcp14">MAY</em> send a weak entity-tag instead of a strong entity-tag, if performance considerations support the use of weak entity-tags, 891 or if it is unfeasible to send a strong entity-tag. 892 </li> 893 <li><em class="bcp14">SHOULD</em> send a Last-Modified value if it is feasible to send one. 894 </li> 895 </ul> 896 <p id="rfc.section.2.4.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 897 value. 898 </p> 899 <p id="rfc.section.2.4.p.4">HTTP/1.1 clients: </p> 900 <ul> 901 <li><em class="bcp14">MUST</em> use that entity-tag in any cache-conditional request (using If-Match or If-None-Match) if an entity-tag has been provided 902 by the origin server. 903 </li> 904 <li><em class="bcp14">SHOULD</em> use the Last-Modified value in non-subrange cache-conditional requests (using If-Modified-Since) if only a Last-Modified value 905 has been provided by the origin server. 906 </li> 907 <li><em class="bcp14">MAY</em> use the Last-Modified value in subrange cache-conditional requests (using If-Unmodified-Since) if only a Last-Modified value 908 has been provided by an HTTP/1.0 origin server. The user agent <em class="bcp14">SHOULD</em> provide a way to disable this, in case of difficulty. 909 </li> 910 <li><em class="bcp14">SHOULD</em> use both validators in cache-conditional requests if both an entity-tag and a Last-Modified value have been provided by the 911 origin server. This allows both HTTP/1.0 and HTTP/1.1 caches to respond appropriately. 912 </li> 913 </ul> 914 <p id="rfc.section.2.4.p.5">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 915 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 916 field) as cache validators, <em class="bcp14">MUST NOT</em> return a response status code of 304 (Not Modified) unless doing so is consistent with all of the conditional header fields 917 in the request. 918 </p> 919 <p id="rfc.section.2.4.p.6">An HTTP/1.1 caching proxy, upon receiving a conditional request that includes both a Last-Modified date and one or more entity-tags 920 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 921 fields in the request. 922 </p> 923 <ul class="empty"> 924 <li> <b>Note:</b> The general principle behind these rules is that HTTP/1.1 servers and clients ought to transmit as much non-redundant information 925 as is available in their responses and requests. HTTP/1.1 systems receiving this information will make the most conservative 926 assumptions about the validators they receive. 927 </li> 928 <li>HTTP/1.0 clients and caches might ignore entity-tags. Generally, last-modified values received or used by these systems will 929 support transparent and efficient caching, and so HTTP/1.1 origin servers should provide Last-Modified values. In those rare 930 cases where the use of a Last-Modified value as a validator by an HTTP/1.0 system could result in a serious problem, then 931 HTTP/1.1 origin servers should not provide one. 932 </li> 933 </ul> 933 934 <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a> <a id="header.fields" href="#header.fields">Precondition Header Fields</a></h1> 934 935 <p id="rfc.section.3.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields for applying preconditions on requests.</p> … … 942 943 </p> 943 944 <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.6"></span> <a href="#header.if-match" class="smpl">If-Match</a> = "*" / 1#<a href="#header.etag" class="smpl">entity-tag</a> 944 </pre><p id="rfc.section.3.1.p.3">If any of the entity-tags listed in the If-Match field value match (as per <a href="#entity.tag.comparison" title="Comparison">Section 2. 2.3</a>) the entity-tag of the selected representation for the target resource, or if "*" is given and any current representation945 </pre><p id="rfc.section.3.1.p.3">If any of the entity-tags listed in the If-Match field value match (as per <a href="#entity.tag.comparison" title="Comparison">Section 2.3.2</a>) the entity-tag of the selected representation for the target resource, or if "*" is given and any current representation 945 946 exists for the target resource, then the server <em class="bcp14">MAY</em> perform the request method as if the If-Match header field was not present. 946 947 </p> … … 972 973 </p> 973 974 <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.7"></span> <a href="#header.if-none-match" class="smpl">If-None-Match</a> = "*" / 1#<a href="#header.etag" class="smpl">entity-tag</a> 974 </pre><p id="rfc.section.3.2.p.4">If any of the entity-tags listed in the If-None-Match field-value match (as per <a href="#entity.tag.comparison" title="Comparison">Section 2. 2.3</a>) the entity-tag of the selected representation, or if "*" is given and any current representation exists for that resource,975 </pre><p id="rfc.section.3.2.p.4">If any of the entity-tags listed in the If-None-Match field-value match (as per <a href="#entity.tag.comparison" title="Comparison">Section 2.3.2</a>) the entity-tag of the selected representation, or if "*" is given and any current representation exists for that resource, 975 976 then the server <em class="bcp14">MUST NOT</em> perform the requested method. Instead, if the request method was GET or HEAD, the server <em class="bcp14">SHOULD</em> respond with a 304 (Not Modified) status code, including the cache-related header fields (particularly ETag) of the selected 976 977 representation that has a matching entity-tag. For all other request methods, the server <em class="bcp14">MUST</em> respond with a 412 (Precondition Failed) status code. … … 979 980 </p> 980 981 <p id="rfc.section.3.2.p.6">If the request would, without the If-None-Match header field, result in anything other than a 2xx or 304 status code, then 981 the If-None-Match header field <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 2. 2.4</a> for a discussion of server behavior when both If-Modified-Since and If-None-Match appear in the same request.)982 the If-None-Match header field <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 2.4</a> for a discussion of server behavior when both If-Modified-Since and If-None-Match appear in the same request.) 982 983 </p> 983 984 <p id="rfc.section.3.2.p.7">Examples:</p> … … 1060 1061 </p> 1061 1062 <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a> <a id="status.code.definitions" href="#status.code.definitions">Status Code Definitions</a></h1> 1062 <div id="rfc.iref.2 4"></div>1063 <div id="rfc.iref.26"></div> 1063 1064 <div id="rfc.iref.s.2"></div> 1064 1065 <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> … … 1082 1083 <p id="rfc.section.4.1.p.5">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. 1083 1084 </p> 1084 <div id="rfc.iref.2 5"></div>1085 <div id="rfc.iref.27"></div> 1085 1086 <div id="rfc.iref.s.3"></div> 1086 1087 <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> … … 1138 1139 <td class="left">http</td> 1139 1140 <td class="left">standard</td> 1140 <td class="left"> <a href="#header.etag" id="rfc.xref.header.etag.1" title="ETag">Section 2. 2</a>1141 <td class="left"> <a href="#header.etag" id="rfc.xref.header.etag.1" title="ETag">Section 2.3</a> 1141 1142 </td> 1142 1143 </tr> … … 1173 1174 <td class="left">http</td> 1174 1175 <td class="left">standard</td> 1175 <td class="left"> <a href="#header.last-modified" id="rfc.xref.header.last-modified.1" title="Last-Modified">Section 2. 1</a>1176 <td class="left"> <a href="#header.last-modified" id="rfc.xref.header.last-modified.1" title="Last-Modified">Section 2.2</a> 1176 1177 </td> 1177 1178 </tr> … … 1260 1261 </div> 1261 1262 <h1 id="rfc.section.A" class="np"><a href="#rfc.section.A">A.</a> <a id="changes.from.rfc.2616" href="#changes.from.rfc.2616">Changes from RFC 2616</a></h1> 1262 <p id="rfc.section.A.p.1">Allow weak entity-tags in all requests except range requests (Sections <a href="#weak.and.strong.validators" title="Weak versus Strong">2. 2.2</a> and <a href="#header.if-none-match" id="rfc.xref.header.if-none-match.2" title="If-None-Match">3.2</a>).1263 <p id="rfc.section.A.p.1">Allow weak entity-tags in all requests except range requests (Sections <a href="#weak.and.strong.validators" title="Weak versus Strong">2.1</a> and <a href="#header.if-none-match" id="rfc.xref.header.if-none-match.2" title="If-None-Match">3.2</a>). 1263 1264 </p> 1264 1265 <p id="rfc.section.A.p.2">Change ABNF productions for header fields to only define the field value. (<a href="#header.fields" title="Precondition Header Fields">Section 3</a>) … … 1414 1415 <ul class="ind"> 1415 1416 <li><a id="rfc.index.3" href="#rfc.index.3"><b>3</b></a><ul> 1416 <li>304 Not Modified (status code) <a href="#rfc.iref.2 4"><b>4.1</b></a>, <a href="#rfc.xref.status.304.1">5.1</a></li>1417 <li>304 Not Modified (status code) <a href="#rfc.iref.26"><b>4.1</b></a>, <a href="#rfc.xref.status.304.1">5.1</a></li> 1417 1418 </ul> 1418 1419 </li> 1419 1420 <li><a id="rfc.index.4" href="#rfc.index.4"><b>4</b></a><ul> 1420 <li>412 Precondition Failed (status code) <a href="#rfc.iref.2 5"><b>4.2</b></a>, <a href="#rfc.xref.status.412.1">5.1</a></li>1421 <li>412 Precondition Failed (status code) <a href="#rfc.iref.27"><b>4.2</b></a>, <a href="#rfc.xref.status.412.1">5.1</a></li> 1421 1422 </ul> 1422 1423 </li> 1423 1424 <li><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul> 1424 <li>ETag header field <a href="#rfc.iref.e.1"><b>2. 2</b></a>, <a href="#rfc.xref.header.etag.1">5.2</a></li>1425 <li>ETag header field <a href="#rfc.iref.e.1"><b>2.3</b></a>, <a href="#rfc.xref.header.etag.1">5.2</a></li> 1425 1426 </ul> 1426 1427 </li> … … 1428 1429 <li><tt>Grammar</tt> 1429 1430 <ul> 1430 <li><tt>entity-tag</tt> <a href="#rfc.iref.g.3"><b>2. 2</b></a></li>1431 <li><tt>ETag</tt> <a href="#rfc.iref.g.2"><b>2. 2</b></a></li>1431 <li><tt>entity-tag</tt> <a href="#rfc.iref.g.3"><b>2.3</b></a></li> 1432 <li><tt>ETag</tt> <a href="#rfc.iref.g.2"><b>2.3</b></a></li> 1432 1433 <li><tt>If-Match</tt> <a href="#rfc.iref.g.6"><b>3.1</b></a></li> 1433 1434 <li><tt>If-Modified-Since</tt> <a href="#rfc.iref.g.8"><b>3.3</b></a></li> 1434 1435 <li><tt>If-None-Match</tt> <a href="#rfc.iref.g.7"><b>3.2</b></a></li> 1435 1436 <li><tt>If-Unmodified-Since</tt> <a href="#rfc.iref.g.9"><b>3.4</b></a></li> 1436 <li><tt>Last-Modified</tt> <a href="#rfc.iref.g.1"><b>2. 1</b></a></li>1437 <li><tt>opaque-tag</tt> <a href="#rfc.iref.g.5"><b>2. 2</b></a></li>1438 <li><tt>weak</tt> <a href="#rfc.iref.g.4"><b>2. 2</b></a></li>1437 <li><tt>Last-Modified</tt> <a href="#rfc.iref.g.1"><b>2.2</b></a></li> 1438 <li><tt>opaque-tag</tt> <a href="#rfc.iref.g.5"><b>2.3</b></a></li> 1439 <li><tt>weak</tt> <a href="#rfc.iref.g.4"><b>2.3</b></a></li> 1439 1440 </ul> 1440 1441 </li> … … 1444 1445 <li>Header Fields 1445 1446 <ul> 1446 <li>ETag <a href="#rfc.iref.h.2"><b>2. 2</b></a>, <a href="#rfc.xref.header.etag.1">5.2</a></li>1447 <li>ETag <a href="#rfc.iref.h.2"><b>2.3</b></a>, <a href="#rfc.xref.header.etag.1">5.2</a></li> 1447 1448 <li>If-Match <a href="#rfc.iref.h.3"><b>3.1</b></a>, <a href="#rfc.xref.header.if-match.1">5.2</a></li> 1448 1449 <li>If-Modified-Since <a href="#rfc.iref.h.5"><b>3.3</b></a>, <a href="#rfc.xref.header.if-modified-since.1">5.2</a></li> 1449 1450 <li>If-None-Match <a href="#rfc.iref.h.4"><b>3.2</b></a>, <a href="#rfc.xref.header.if-none-match.1">5.2</a>, <a href="#rfc.xref.header.if-none-match.2">A</a></li> 1450 1451 <li>If-Unmodified-Since <a href="#rfc.iref.h.6"><b>3.4</b></a>, <a href="#rfc.xref.header.if-unmodified-since.1">5.2</a></li> 1451 <li>Last-Modified <a href="#rfc.iref.h.1"><b>2. 1</b></a>, <a href="#rfc.xref.header.last-modified.1">5.2</a></li>1452 <li>Last-Modified <a href="#rfc.iref.h.1"><b>2.2</b></a>, <a href="#rfc.xref.header.last-modified.1">5.2</a></li> 1452 1453 </ul> 1453 1454 </li> … … 1462 1463 </li> 1463 1464 <li><a id="rfc.index.L" href="#rfc.index.L"><b>L</b></a><ul> 1464 <li>Last-Modified header field <a href="#rfc.iref.l.1"><b>2. 1</b></a>, <a href="#rfc.xref.header.last-modified.1">5.2</a></li>1465 <li>Last-Modified header field <a href="#rfc.iref.l.1"><b>2.2</b></a>, <a href="#rfc.xref.header.last-modified.1">5.2</a></li> 1465 1466 </ul> 1466 1467 </li> … … 1470 1471 </li> 1471 1472 <li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul> 1472 <li><em>Part1</em> <a href="#rfc.xref.Part1.1">1.2</a>, <a href="#rfc.xref.Part1.2">1.2</a>, <a href="#rfc.xref.Part1.3">1.2</a>, <a href="#rfc.xref.Part1.4">1.2</a>, <a href="#rfc.xref.Part1.5">2. 2.5</a>, <a href="#rfc.xref.Part1.6">4.1</a>, <a href="#rfc.xref.Part1.7">4.1</a>, <a href="#rfc.xref.Part1.8">6</a>, <a href="#rfc.xref.Part1.9">7</a>, <a href="#Part1"><b>8.1</b></a><ul>1473 <li><em>Part1</em> <a href="#rfc.xref.Part1.1">1.2</a>, <a href="#rfc.xref.Part1.2">1.2</a>, <a href="#rfc.xref.Part1.3">1.2</a>, <a href="#rfc.xref.Part1.4">1.2</a>, <a href="#rfc.xref.Part1.5">2.3.3</a>, <a href="#rfc.xref.Part1.6">4.1</a>, <a href="#rfc.xref.Part1.7">4.1</a>, <a href="#rfc.xref.Part1.8">6</a>, <a href="#rfc.xref.Part1.9">7</a>, <a href="#Part1"><b>8.1</b></a><ul> 1473 1474 <li><em>Section 1.2</em> <a href="#rfc.xref.Part1.1">1.2</a></li> 1474 1475 <li><em>Section 1.2.2</em> <a href="#rfc.xref.Part1.2">1.2</a>, <a href="#rfc.xref.Part1.3">1.2</a></li> 1475 1476 <li><em>Section 6.1</em> <a href="#rfc.xref.Part1.4">1.2</a></li> 1476 <li><em>Section 6.2</em> <a href="#rfc.xref.Part1.5">2. 2.5</a></li>1477 <li><em>Section 6.2</em> <a href="#rfc.xref.Part1.5">2.3.3</a></li> 1477 1478 <li><em>Section 9.3</em> <a href="#rfc.xref.Part1.6">4.1</a></li> 1478 1479 <li><em>Section 9.3.1</em> <a href="#rfc.xref.Part1.7">4.1</a></li> … … 1480 1481 </ul> 1481 1482 </li> 1482 <li><em>Part3</em> <a href="#rfc.xref.Part3.1">2. 2.5</a>, <a href="#rfc.xref.Part3.2">2.2.5</a>, <a href="#Part3"><b>8.1</b></a><ul>1483 <li><em>Section 5</em> <a href="#rfc.xref.Part3.1">2. 2.5</a></li>1484 <li><em>Section 6.3</em> <a href="#rfc.xref.Part3.2">2. 2.5</a></li>1483 <li><em>Part3</em> <a href="#rfc.xref.Part3.1">2.3.3</a>, <a href="#rfc.xref.Part3.2">2.3.3</a>, <a href="#Part3"><b>8.1</b></a><ul> 1484 <li><em>Section 5</em> <a href="#rfc.xref.Part3.1">2.3.3</a></li> 1485 <li><em>Section 6.3</em> <a href="#rfc.xref.Part3.2">2.3.3</a></li> 1485 1486 </ul> 1486 1487 </li> … … 1490 1491 </ul> 1491 1492 </li> 1492 <li><em>Part6</em> <a href="#rfc.xref.Part6.1">1</a>, <a href="#rfc.xref.Part6.2">2. 1.1</a>, <a href="#rfc.xref.Part6.3">2.2.1</a>, <a href="#Part6"><b>8.1</b></a></li>1493 <li><em>Part6</em> <a href="#rfc.xref.Part6.1">1</a>, <a href="#rfc.xref.Part6.2">2.2.1</a>, <a href="#rfc.xref.Part6.3">2.3.1</a>, <a href="#Part6"><b>8.1</b></a></li> 1493 1494 </ul> 1494 1495 </li> … … 1515 1516 </li> 1516 1517 <li><a id="rfc.index.V" href="#rfc.index.V"><b>V</b></a><ul> 1517 <li>validator <a href="#rfc.iref.v.1"><b>2</b></a></li> 1518 <li>validator <a href="#rfc.iref.v.1"><b>2</b></a><ul> 1519 <li>strong <a href="#rfc.iref.v.3"><b>2.1</b></a></li> 1520 <li>weak <a href="#rfc.iref.v.2"><b>2.1</b></a></li> 1521 </ul> 1522 </li> 1518 1523 </ul> 1519 1524 </li>
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