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Timestamp:
Jan 10, 2013, 10:27:20 PM (7 years ago)
Author:
fielding@…
Message:

(editorial) Vary applies to any response content, not just the selected representation

File:
1 edited

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  • draft-ietf-httpbis/latest/p2-semantics.html

    r2107 r2108  
    30173017      <div id="rfc.figure.u.58"></div>
    30183018      <p>For example, a response that contains</p><pre class="text">  Vary: accept-encoding, accept-language
    3019 </pre><p>indicates that the origin server might have used the request's <a href="#header.accept-encoding" class="smpl">Accept-Encoding</a> and <a href="#header.accept-language" class="smpl">Accept-Language</a> fields (or lack thereof) as determining factors while choosing this <a href="#selected.representation" class="smpl">selected representation</a>.
     3019</pre><p>indicates that the origin server might have used the request's <a href="#header.accept-encoding" class="smpl">Accept-Encoding</a> and <a href="#header.accept-language" class="smpl">Accept-Language</a> fields (or lack thereof) as determining factors while choosing the content for this response.
    30203020      </p>
    30213021      <p id="rfc.section.7.1.4.p.6">An origin server might send Vary with a list of fields for two purposes: </p>
     
    30343034      <p id="rfc.section.7.1.4.p.7">An origin server <em class="bcp14">SHOULD</em> send a Vary header field when its algorithm for selecting a representation varies based on aspects of the request message
    30353035         other than the method and request target, unless the variance cannot be crossed or the origin server has been deliberately
    3036          configured to prevent cache transparency. For example, there is no need to send the Authorization field name (<a href="p7-auth.html#header.authorization" title="Authorization">Section 4.1</a> of <a href="#Part7" id="rfc.xref.Part7.7"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[Part7]</cite></a>) in Vary because reuse across users is constrained by the field definition. Likewise, Cache-Control directives (<a href="p6-cache.html#header.cache-control" title="Cache-Control">Section 7.2</a> of <a href="#Part6" id="rfc.xref.Part6.20"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[Part6]</cite></a>) might be used to supplant the need for Vary, particularly when the variance is considered less significant than the performance
    3037          cost of Vary's impact on caching.
     3036         configured to prevent cache transparency. For example, there is no need to send the Authorization field name in Vary because
     3037         reuse across users is constrained by the field definition (<a href="p7-auth.html#header.authorization" title="Authorization">Section 4.1</a> of <a href="#Part7" id="rfc.xref.Part7.7"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Authentication">[Part7]</cite></a>). Likewise, an origin server might use Cache-Control directives (<a href="p6-cache.html#header.cache-control" title="Cache-Control">Section 7.2</a> of <a href="#Part6" id="rfc.xref.Part6.20"><cite title="Hypertext Transfer Protocol (HTTP/1.1): Caching">[Part6]</cite></a>) to supplant Vary if it considers the variance less significant than the performance cost of Vary's impact on caching.
    30383038      </p>
    30393039      <div id="rfc.iref.s.7"></div>
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