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From Edward Lu <chaos...@gmail.com>
Subject Re: [users@httpd] mod_cache + worker mpm + php-fpm mangling response headers on cache misses
Date Tue, 15 Sep 2015 20:10:41 GMT
This looks like a bug. I believe I've tracked down the cause to a single
errant line in the cache module; can you apply the attached patch to 2.4.x
and see if it fixes the problem?

 - Thanks, Ed

On Tue, Sep 1, 2015 at 5:55 PM, Neil Skrypuch <neil@tembosocial.com> wrote:

> We're trying to introduce mod_cache usage into our application, and it's
> working well, except that on a cache miss most response headers are either
> overridden or simply discarded by Apache before they make it to the client.
> This is particularly problematic for gzipped content, which is not decoded
> correctly in this case. Let me show you:
>
> $ curl -sS -D /proc/self/fd/2 --compressed
> http://neil2-dev-vote.polldev.com:8080/admin.php >/dev/null
> HTTP/1.1 200 OK
> Date: Tue, 01 Sep 2015 18:59:01 GMT
> Server: Apache
> Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
> Etag: 1
> X-Cache: MISS from neil2-dev-vote.polldev.com
> X-Cache-Detail: "cache miss: attempting entity save" from neil2-dev-
> vote.polldev.com
> Transfer-Encoding: chunked
> Content-Type: text/plain
>
> $ curl -sS -D /proc/self/fd/2 --compressed
> http://neil2-dev-vote.polldev.com:8080/admin.php >/dev/null
> HTTP/1.1 200 OK
> Date: Tue, 01 Sep 2015 18:59:02 GMT
> Server: AwesomeServer/1.0
> Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
> Etag: 1
> Content-Encoding: gzip
> X-Custom: foo
> Vary: Accept-Encoding
> Age: 0
> X-Cache: HIT from neil2-dev-vote.polldev.com
> X-Cache-Detail: "cache hit" from neil2-dev-vote.polldev.com
> Content-Length: 3
> Content-Type: text/plain
>
> Here is the php script in the requests above:
> <?
> header("Content-Encoding: gzip");
> header("Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT");
> header("Etag: 1");
> header("X-Custom: foo");
> header("Content-Type: text/plain");
> header("Server: AwesomeServer/1.0");
> header("Vary: Accept-Encoding");
> print "11\n";
> ?>
>
> The script in question is strictly for testing this problem, aside from a
> very
> short response body, all it does is set a variety of headers. From the curl
> responses, we can see that one of three things is happening to the headers
> in
> the cache miss situation. More specifically...
>
> These headers are completely missing:
> - Content-Encoding
> - X-Custom
> - Vary
>
> These headers are overwritten:
> - Server
>
> These headers are passed through verbatim:
> - Last-Modified
> - Etag
> - Content-Type
>
> It's worth noting that on the initial cache miss, I've confirmed that the
> actual on disk cache file is populated with the expected headers, and that
> on
> cache hits, php-fpm is never contacted, so the actual caching portion of
> mod_cache is working correctly.
>
> Now, one thing that's particularly interesting is that if I switch back to
> mod_php with prefork mpm, all of the headers set in the php script are
> passed
> through verbatim (ie, the expected behaviour). I'm not keen on this
> approach
> as my understanding is that mod_php is deprecated these days.
>
> Here's the mod_cache config that I'm currently working with:
>
> CacheRoot /tmp/httpd_cacheroot
> CacheEnable disk /admin.php
> CacheLock on
> CacheHeader on
> CacheDetailHeader on
> CacheQuickHandler off
>
> I have tried toggling all of the boolean mod_cache directives above, but
> that
> didn't help.
>
> The software versions involved are a fully updated CentOS 7, which for
> httpd
> means:
>
> Server version: Apache/2.4.6 (CentOS)
> Server built:   Aug 24 2015 18:11:25
>
> I'm running out of ideas on how to solve this issue, but I'm not sure if
> it's
> a configuration issue or an actual bug. Any ideas?
>
> - Neil
>
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