02/02/08 01:04:56 (14 years ago)

Reduce the description of cache validation to just those bits that
summarize what a cache SHOULD do, thus avoiding the need to respecify
what is defined in part 4. Move cache validator descriptions
to the associated header field definitions in part 4 (to be merged
at a later time).

1 edited


  • draft-ietf-httpbis/latest/p4-conditional.html

    r182 r183  
    745745   ETag: W/"xyzzy"
    746746   ETag: ""
    747 </pre><div id="rfc.iref.i.1"></div>
     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 reliable
     748         validation in situations where it is inconvenient to store modification dates, where the one-second resolution of HTTP date
     749         values is not sufficient, or where the origin server wishes to avoid certain paradoxes that might arise from the use of modification
     750         dates.
     751      </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 an
     753         appropriate cache validation mechanism, and the specification of any validator comparison function more complex than byte-equality
     754         would open up a can of worms. Thus, comparisons of any other headers (except Last-Modified, for compatibility with HTTP/1.0)
     755         are never used for purposes of validating a cache entry.
     756      </p>
     757      <div id="rfc.iref.i.1"></div>
    748758      <div id="rfc.iref.h.2"></div>
    749759      <h2 id="rfc.section.6.2"><a href="#rfc.section.6.2">6.2</a>&nbsp;<a id="header.if-match" href="#header.if-match">If-Match</a></h2>
    899909      </p>
    900910      <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 considered
     913         to be valid if the entity has not been modified since the Last-Modified value.
    901914      </p>
    902915      <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1>
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