Changeset 183 for draft-ietf-httpbis/latest/p4-conditional.html

Timestamp:

Feb 1, 2008, 5:04:56 PM (12 years ago)

Author:

fielding@…

Message:

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).

File:

• draft-ietf-httpbis/latest/p4-conditional.html (modified) (2 diffs)

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

@@ -745 +745 @@
    ETag: W/"xyzzy"
    ETag: ""
-</pre><div id="rfc.iref.i.1"></div>
+</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
+         validation in situations where it is inconvenient to store modification dates, where the one-second resolution of HTTP date
+         values is not sufficient, or where the origin server wishes to avoid certain paradoxes that might arise from the use of modification
+         dates.
+      </p>
+      <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
+         appropriate cache validation mechanism, and the specification of any validator comparison function more complex than byte-equality
+         would open up a can of worms. Thus, comparisons of any other headers (except Last-Modified, for compatibility with HTTP/1.0)
+         are never used for purposes of validating a cache entry.
+      </p>
+      <div id="rfc.iref.i.1"></div>
       <div id="rfc.iref.h.2"></div>
       <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>
@@ -899 +909 @@
       </p>
       <p id="rfc.section.6.6.p.8">HTTP/1.1 servers <em class="bcp14">SHOULD</em> send Last-Modified whenever feasible.
+      </p>
+      <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
+         to be valid if the entity has not been modified since the Last-Modified value.
       </p>
       <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1>