Hi all,
I think I found a problem with mod_cache of the httpd trunk (revision 171201).
First off all I added the following configuration directives to the default
httpd.conf:
CacheRoot /home/ruediger/apache_head/apache_trunk/cache
CacheEnable disk /test
CacheMaxFilesize 100000000
CacheDirLevels 5
CacheDirLength 3
CacheMaxExpire 60
CacheIgnoreNoLastMod On
CacheDefaultExpire 60
CacheIgnoreHeaders BLAH set-cookie
/test is a subdirectory below the htdocs document root and contains a single
static file
called check.html. If I request the file for the first time everything is fine:
[EMAIL PROTECTED]:~> telnet 192.168.2.4 80
Trying 192.168.2.4...
Connected to 192.168.2.4.
Escape character is '^]'.
GET /test/check.html HTTP/1.1
Host: 192.168.2.4
HTTP/1.1 200 OK
Date: Sat, 21 May 2005 18:54:52 GMT
Server: Apache/2.1.5-dev (Unix) mod_ssl/2.1.5-dev OpenSSL/0.9.6g DAV/2
Last-Modified: Sat, 21 May 2005 18:54:43 GMT
ETag: "125f-29-5f22a2c0"
Accept-Ranges: bytes
Content-Length: 41
Expires: Sat, 21 May 2005 18:54:54 GMT
Content-Type: text/html
<html><body><h1>Check</h1></body></html>
Connection closed by foreign host.
But if I request it for a second time after 60 seconds (thus the cache entry is
expired,
see CacheDefaultExpire) in the same way I get a 304:
[EMAIL PROTECTED]:~> telnet 192.168.2.4 80
Trying 192.168.2.4...
Connected to 192.168.2.4.
Escape character is '^]'.
GET /test/check.html HTTP/1.1
Host: 192.168.2.4
HTTP/1.1 304 Not Modified
Date: Sat, 21 May 2005 18:55:16 GMT
Server: Apache/2.1.5-dev (Unix) mod_ssl/2.1.5-dev OpenSSL/0.9.6g DAV/2
ETag: "125f-29-5f22a2c0"
Connection closed by foreign host.
Using two different browsers that would access /test/check.html with a time
difference
of one minute this leads to an empty page in the second browser, since the
browser does not
know how to handle a 304 for a first time request of a resource.
I found out that during the second request which returns a 304 the CACHE_SAVE
filter,
which would be able to deal with such things (-> (not so) stale cache entries)
is never
used.
The change of the conditionals in cache_storage.c starting at line 269 leads to
the creation
of a 304 code in the default handler and the default handler does not pass 304
responses down
the filter chain.
So the 304 response is delivered instead of the (not so) stale cache entry. So
I created the following
patch to cache_storage.c which prevents the modification or better creation of
any conditionals
if the original request did not contain any:
--- cache_storage.c.orig 2005-05-21 10:28:28.000000000 +0200
+++ cache_storage.c 2005-05-21 21:56:27.000000000 +0200
@@ -254,6 +254,7 @@ int cache_select_url(request_rec *r, cha
fresh = ap_cache_check_freshness(h, r);
if (!fresh) {
const char *etag, *lastmod;
+ const char *ma_req, *mo_req, *nm_req, *ra_req, *us_req;
ap_log_error(APLOG_MARK, APLOG_DEBUG, APR_SUCCESS, r->server,
"Cached response for %s isn't fresh. Adding/replacing "
@@ -263,6 +264,18 @@ int cache_select_url(request_rec *r, cha
cache->stale_headers = apr_table_copy(r->pool,
r->headers_in);
+ /* Check if revalidation is ok. Revalidation is not ok if
+ the original request did not contain any conditionals */
+ ma_req = apr_table_get(r->headers_in, "If-Match");
+ mo_req = apr_table_get(r->headers_in, "If-Modified-Since");
+ nm_req = apr_table_get(r->headers_in, "If-None-Match");
+ ra_req = apr_table_get(r->headers_in, "If-Range");
+ us_req = apr_table_get(r->headers_in, "If-Unmodified-Since");
+
+ if (!(ma_req || mo_req || nm_req || ra_req || us_req)) {
+ return DECLINED;
+ }
+
/* We can only revalidate with our own conditionals: remove the
* conditions from the original request.
*/
I am aware that this forces a full request to the backend for requests without
conditionals
to expired resources. So I am not very happy with this solution. Maybe it is
better to let
the default handler pass 304 responses down the filter chain.
Some might also say that my configuration seems stupid (do disk caching for
static resources,
which was actually born during some tests for another problem I am currently
hunting), but
this problem also applies to other providers than mod_disk_cache and the
document root might
be on a non local disk.
Comments/Thoughts/Flames?
Regards
Rüdiger
