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Posted to users@httpd.apache.org by Neil Skrypuch <ne...@tembosocial.com> on 2015/09/01 23:55:12 UTC
[users@httpd] mod_cache + worker mpm + php-fpm mangling response headers on cache misses
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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Re: [users@httpd] mod_cache + worker mpm + php-fpm mangling response headers on cache misses
Posted by Neil Skrypuch <ne...@tembosocial.com>.
On Wednesday 16 September 2015 08:50:29 Edward Lu wrote:
> In any case, here is the updated patch. It may be worth opening this as a
> bug report so we can keep track of it easier.
I reworked the patch to apply to httpd 2.4.6 (as shipped with CentOS 7) and
can confirm that it fixes the issue for me.
I went to file a bug report, but found someone who had already filed it:
https://bz.apache.org/bugzilla/show_bug.cgi?id=56898
I've added the reworked patch and a comment to the above bug report.
- Neil
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Re: [users@httpd] mod_cache + worker mpm + php-fpm mangling response
headers on cache misses
Posted by Edward Lu <ch...@gmail.com>.
Yes, looks like you're right. It seems odd that we have some paths that
assign r->headers_out and some that don't.
In any case, here is the updated patch. It may be worth opening this as a
bug report so we can keep track of it easier.
On Wed, Sep 16, 2015 at 3:47 AM, Yann Ylavic <yl...@gmail.com> wrote:
> Hi Ed,
>
> On Tue, Sep 15, 2015 at 10:10 PM, Edward Lu <ch...@gmail.com> wrote:
> > 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?
>
> I think the patch would also need this hunk:
>
> Index: modules/cache/mod_cache.c
> ===================================================================
> --- modules/cache/mod_cache.c (revision 1703149)
> +++ modules/cache/mod_cache.c (working copy)
> @@ -1462,6 +1462,7 @@ static apr_status_t cache_save_filter(ap_filter_t
> * forward all of them to the client, including non-cacheable
> ones).
> */
> r->headers_out = cache_merge_headers_out(r);
> + apr_table_clear(r->err_headers_out);
>
> /* Merge in our cached headers. However, keep any updated
> values. */
> /* take output, overlay on top of cached */
> --
>
> Otherwise we might leave this path with some headers both in
> headers_out and err_headers_out.
>
> Regards,
> Yann.
>
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> To unsubscribe, e-mail: users-unsubscribe@httpd.apache.org
> For additional commands, e-mail: users-help@httpd.apache.org
>
>
Re: [users@httpd] mod_cache + worker mpm + php-fpm mangling response
headers on cache misses
Posted by Yann Ylavic <yl...@gmail.com>.
Hi Ed,
On Tue, Sep 15, 2015 at 10:10 PM, Edward Lu <ch...@gmail.com> wrote:
> 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?
I think the patch would also need this hunk:
Index: modules/cache/mod_cache.c
===================================================================
--- modules/cache/mod_cache.c (revision 1703149)
+++ modules/cache/mod_cache.c (working copy)
@@ -1462,6 +1462,7 @@ static apr_status_t cache_save_filter(ap_filter_t
* forward all of them to the client, including non-cacheable ones).
*/
r->headers_out = cache_merge_headers_out(r);
+ apr_table_clear(r->err_headers_out);
/* Merge in our cached headers. However, keep any updated values. */
/* take output, overlay on top of cached */
--
Otherwise we might leave this path with some headers both in
headers_out and err_headers_out.
Regards,
Yann.
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Re: [users@httpd] mod_cache + worker mpm + php-fpm mangling response
headers on cache misses
Posted by Edward Lu <ch...@gmail.com>.
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 <ne...@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
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: users-unsubscribe@httpd.apache.org
> For additional commands, e-mail: users-help@httpd.apache.org
>
>