Bug#509116: apache2: mod_deflate with mod_fastcgi gives wrong content-length header

[Simon Waters <simon@technocool.net>]

Package: apache2.2-common
Version: 2.2.9-10+lenny1
Severity: normal


On upgrading from Etch to Lenny I got exceeding slow response on some FastCGI servers.

It was identified that the line: 
AddOutputFilterByType DEFLATE text/html text/plain text/xml application/json application/x-javascript
which adds the "deflate" filter is the culprit.

On inspection with "curl":

curl -D h1  http://simon.example.com/ >b1
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 33180  100 33180    0     0   389k      0 --:--:-- --:--:-- --:--:--  826k

curl --compressed -D h2  http://simon.example.com/ >b2
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
 25 33180   25  8612    0     0    572      0  0:00:58  0:00:15  0:00:43     0
curl: (18) transfer closed with 24568 bytes remaining to read

b1 and b2 are identical.
The "content-length" header in h2 was still 33180, where as I'd expect this page to compress effectively.

So the slow response is the web browser timing out, but finding all the data it needs is already in memory.

Likely cause is bad interaction with mod_fastcgid, which we are using here to deploy a Catalyst application, as the content is dynamic in nature.

I'm not an expert in these things. 

This combination of mod_fastcgi and mod_deflate was broken in Sarge,
but it resulted in the content being sent without compression, where as here the result is simply broken HTTP response, because it is being compressed, but the content-length header is wrong.

I see old reports of similar problems in Google.
e.g. http://archives.devshed.com/forums/dsm-125/apache-2-mod-deflate-mod-fastcgi-1284864.html

Shall go try mod_fcgid.

-- Package-specific info:
List of /etc/apache2/mods-enabled/*.load:
  actions alias auth_basic auth_digest authn_file authz_default
  authz_groupfile authz_host authz_user autoindex cgi dav dav_fs
  dav_svn deflate dir env expires fastcgi fcgid include mime
  negotiation perl rewrite setenvif ssl status userdir zembperl

-- System Information:
Debian Release: lenny/sid
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: i386 (i686)

Kernel: Linux 2.6.26-1-686 (SMP w/2 CPU cores)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash

Versions of packages apache2 depends on:
ii  apache2-mpm-prefork      2.2.9-10+lenny1 Apache HTTP Server - traditional n

apache2 recommends no packages.

apache2 suggests no packages.

Versions of packages apache2.2-common depends on:
ii  apache2-utils          2.2.9-10+lenny1   utility programs for webservers
ii  libapr1                1.2.12-5          The Apache Portable Runtime Librar
ii  libaprutil1            1.2.12+dfsg-8     The Apache Portable Runtime Utilit
ii  libc6                  2.7-16            GNU C Library: Shared libraries
ii  libmagic1              4.26-1            File type determination library us
ii  libssl0.9.8            0.9.8g-14         SSL shared libraries
ii  lsb-base               3.2-20            Linux Standard Base 3.2 init scrip
ii  mime-support           3.44-1            MIME files 'mime.types' & 'mailcap
ii  net-tools              1.60-22           The NET-3 networking toolkit
ii  perl                   5.10.0-18         Larry Wall's Practical Extraction 
ii  procps                 1:3.2.7-8         /proc file system utilities
ii  zlib1g                 1:1.2.3.3.dfsg-12 compression library - runtime

-- no debconf information