https://issues.apache.org/bugzilla/show_bug.cgi?id=47580
Summary: mod_cache sends 200 response instead of 304
Product: Apache httpd-2
Version: 2.2.11
Platform: All
OS/Version: All
Status: NEW
Severity: normal
Priority: P2
Component: mod_cache
AssignedTo: [email protected]
ReportedBy: [email protected]
Created an attachment (id=24037)
--> (https://issues.apache.org/bugzilla/attachment.cgi?id=24037)
PHP script to demonstrate the problem
If you make a conditional request for a cached document, but the document is
expired in the cache, mod_cache correctly passes on the conditional request to
the backend. If the backend responds with a "304 Not Modified" response that
indicates that the cached copy is still up to date, mod_cache serves the
contents of the cache to the client with a 200 code. This is a
standards-conforming valid way of responding.
But couldn't it just send a "304 Not Modified" code instead? RFC2616 14.26 says
"instead, if the request method was GET or HEAD, the server SHOULD respond with
a 304 (Not Modified) response, including the cache- related header fields
(particularly ETag) of one of the entities that matched." The current behaviour
unnecessarily sends a response body to the client. This ends up wasting
bandwidth in the case where you press refresh on an unmodified object (at least
in Firefox,) which sends these request headers:
If-None-Match="My ETag"
Cache-Control=max-age=0
I do not want the behaviour given by the "CacheIgnoreCacheControl yes"
directive. I still want mod_cache to validate the request against the backend,
but I don't want it to waste bandwidth by sending a 200 response code.
To test it, I have these cache-related lines in my virtual host definition:
CacheRoot C:/temp
CacheEnable disk /
My index.php is the attached file.
My web browser with an empty cache requests index.php, the (trimmed) response
is:
Status=OK - 200
Date=Mon, 20 Jul 2009 07:16:05 GMT
Expires=Wed, 19 Aug 2009 07:16:05 GMT
Etag="ComputedETag"
The log performed by index.php indicates:
Mon, 20 Jul 2009 19:16:05 +1200 - Response: 200. Generated document.
So far so good. But now I press refresh in my web browser. This makes a
conditional request for the document:
If-None-Match="ComputedETag"
Cache-Control=max-age=0
With the max-age of 0, the cache will be bypassed, which is the desired
behaviour. The cache passes this conditional request onto the backend, and the
backend logs it:
Mon, 20 Jul 2009 19:16:12 +1200 - Response: 304 Not Modified
So the backend is trying to tell the client that it already has an up-to-date
body. But the response sent to the client by mod_cache is:
Status=OK - 200
Date=Mon, 20 Jul 2009 07:16:12 GMT
Etag="ComputedETag"
Expires=Wed, 19 Aug 2009 07:16:12 GMT
My Apache configuratiion is:
Apache/2.2.11 (Win32) DAV/2 mod_ssl/2.2.11 OpenSSL/0.9.8i SVN/1.6.3 PHP/5.3.0
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