Ignore:
Timestamp:
May 19, 2011, 7:28:25 PM (9 years ago)
Author:
mnot@…
Message:

Rewrite Pragma section; addresses #292

File:
1 edited

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Unmodified
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Removed
  • draft-ietf-httpbis/latest/p6-cache.xml

    r1281 r1284  
    15021502   <x:anchor-alias value="pragma-directive"/>
    15031503<t>
    1504    The "Pragma" header field is used to include
    1505    implementation-specific directives that might apply to any recipient along
    1506    the request/response chain. All pragma directives specify optional behavior
    1507    from the viewpoint of the protocol; however, some systems &MAY; require
    1508    that behavior be consistent with the directives.
     1504         The "Pragma" header field allows backwards compatibility with HTTP/1.0
     1505   caches, so that clients can specify a "no-cache" request that they will
     1506   understand (as Cache-Control was not defined until HTTP/1.1). When the
     1507   Cache-Control header is also present and understood in a request, Pragma is
     1508   ignored.
     1509</t>
     1510<t>
     1511         In HTTP/1.0, Pragma was defined as an extensible field for
     1512   implementation-specified directives for recipients. This specification
     1513   deprecates such extensions to improve interoperability.
    15091514</t>
    15101515<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Pragma"/><iref primary="true" item="Grammar" subitem="pragma-directive"/><iref primary="true" item="Grammar" subitem="extension-pragma"/>
     
    15141519</artwork></figure>
    15151520<t>
    1516    When the no-cache directive is present in a request message, a cache
    1517    &SHOULD; forward the request toward the origin server even if it has a
    1518    stored copy of what is being requested. This pragma directive has the same
    1519    semantics as the no-cache request directive (see <xref
    1520    target="cache-request-directive" />) and is defined here for backward
    1521    compatibility with HTTP/1.0. A client &SHOULD; include both header fields
    1522    when a no-cache request is sent to a server not known to be HTTP/1.1
    1523    compliant. A cache &SHOULD; treat "Pragma: no-cache" as if the
    1524    client had sent "Cache-Control: no-cache".
     1521         When the Cache-Control header is not present in a request, the no-cache
     1522   request pragma-directive &MUST; have the same effect on caches as if
     1523   "Cache-Control: no-cache" were present (see <xref
     1524   target="cache-request-directive" />).
     1525</t>
     1526<t>
     1527   When sending a no-cache request, a client &SHOULD; include both pragma and
     1528   cache-control directives unless Cache-Control: no-cache is purposefully
     1529   omitted to target other Cache-Control response directives at HTTP/1.1
     1530   caches. For example:
     1531</t>
     1532<figure>
     1533<artwork type="code">
     1534GET / HTTP/1.1
     1535Host: www.example.com
     1536Cache-Control: max-age=30
     1537Pragma: no-cache
     1538</artwork>
     1539</figure>
     1540<t>
     1541   will constrain HTTP/1.1 caches to serve a response no older than 30
     1542   seconds, while precluding implementations that do not understand
     1543   Cache-Control from serving a cached response.
    15251544</t>
    15261545<x:note>
    15271546   <t>
    1528       <x:h>Note:</x:h> Because the meaning of "Pragma: no-cache" as a
    1529       header field is not actually specified, it does not provide a
    1530       reliable replacement for "Cache-Control: no-cache" in a response.
    1531   </t>
     1547      Note: Because the meaning of "Pragma: no-cache" in responses is not
     1548      specified, it does not provide a reliable replacement for
     1549      "Cache-Control: no-cache" in them.
     1550        </t>
    15321551</x:note>
    1533 <t>
    1534    This mechanism is deprecated; no new Pragma directives will be defined in
    1535    HTTP.
    1536 </t>
    15371552</section>
    15381553
     
    26842699<section title="Since draft-ietf-httpbis-p6-cache-14" anchor="changes.since.14">
    26852700<t>
    2686   None yet.
     2701  Closed issues:
     2702        <list style="symbols">
     2703                <t>
     2704                        <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/292"/>:
     2705                        "Pragma"
     2706                </t>
     2707        </list>
    26872708</t>
    26882709</section>
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