Segmentation fault in Apache2 Module

Question

I'm currently reading the book "The Apache Modules Book" to learn writing Apache2 modules. I tried some examples from the book and in one case I get a segmentation fault, even if I completely copy&paste the source file from the author's website.

The example is an output filter that works on a request for a *.txt file, adds a html header and footer with the html-escaped content of the requested txt file in between.

The sourcecode is available under: http://apache.webthing.com/mod_txt/

The error in apache's log file is the following:

[Thu Jan 12 20:38:01 2012] [notice] child pid 3500 exit signal Segmentation fault (11)

I installed the module using the following commands:

apxs2 -c mod_txt.c 
sudo apxs2 -i mod_txt.la 
sudo service apache2 restart

There are no compile-errors when using apxs2.

I added the Filter in the httpd.conf file as follows:

LoadModule txt_module /usr/lib/apache2/modules/mod_txt.so
AddOutputFilter text-filter .txt
AddType text/html .txt
TextHeader /home/robert/header.txt
TextFooter /home/robert/footer.txt

Is there anything wrong with the code or am I doing something wrong with comiling/installing/configuring the filter?

My System: Ubuntu Lucid Lynx 10.04.3 with Apache 2.2.14 installed from the default Ubuntu repository.

I'd really appreciate any hint on this!

Thanks in advance!

Best regards, Robert

[Edit] Some additional information:

I used gdb to get some more info on where the segfault happens. Is there any way I can get the exact line number?

This is the output:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0xab472b70 (LWP 4041)]
0xb7d3fb9b in txt_filter () from /usr/lib/apache2/modules/mod_txt.so
(gdb) bt
#0  0xb7d3fb9b in txt_filter () from /usr/lib/apache2/modules/mod_txt.so
#1  0x00154150 in ap_pass_brigade (next=0x2e3198, bb=0xb7f4fff4)
    at /build/buildd/apache2-2.2.14/server/util_filter.c:526
#2  0x00141147 in default_handler (r=0x2e4ea8)
    at /build/buildd/apache2-2.2.14/server/core.c:3757
#3  0x00148321 in ap_run_handler (r=0x2e4ea8)
    at /build/buildd/apache2-2.2.14/server/config.c:159
#4  0x0014c107 in ap_invoke_handler (r=0x2e4ea8)
    at /build/buildd/apache2-2.2.14/server/config.c:373
#5  0x0015b6b8 in ap_process_request (r=0x2e4ea8)
    at /build/buildd/apache2-2.2.14/modules/http/http_request.c:282
#6  0x001581e8 in ap_process_http_connection (c=0x2defd0)
    at /build/buildd/apache2-2.2.14/modules/http/http_core.c:190
#7  0x00150b91 in ap_run_process_connection (c=0x2defd0)
    at /build/buildd/apache2-2.2.14/server/connection.c:43
#8  0x0016249b in process_socket (thd=0x2a7958, dummy=0x2dda00)
    at /build/buildd/apache2-2.2.14/server/mpm/worker/worker.c:544
#9  worker_thread (thd=0x2a7958, dummy=0x2dda00)
    at /build/buildd/apache2-2.2.14/server/mpm/worker/worker.c:894
#10 0xb7f781e1 in ?? () from /usr/lib/libapr-1.so.0
#11 0xb7f3f96e in start_thread () from /lib/tls/i686/cmov/libpthread.so.0
#12 0xb7eada4e in clone () from /lib/tls/i686/cmov/libc.so.6

Answer 1

More specialized debugging tutorial for apache modules may be found in the book you're reading (Chapter 12).

Currently I'm running the same hardware/software configuration (apache 2.2.14) on Ubuntu Lucid Lynx and successfully compiled/run the module.

In the folder /var/www/ I've put an HTML document but only changed it's extension to .txt and access it through my browser (localhost/some-html.txt) and the output (depending on the tags you've put in header and footer files) was successfully represented (as preformated text because I've used <pre> and </pre> tags in my header and footer files respectively.)