When debugging problems with web applications, it is often useful to display the HTTP request and response headers along with the HTTP entity bodies. There are numerous ways to do this, and I covered several client centric solutions in my SysAdmin article Debugging Web Applications. Client side tools are extremely useful for pinpointing problems, but periodically it is helpful to see the raw requests from the client, and the responses from the server. If you happen to be running Apache, you can use the dumpio module to dump the request and response data to the Apache error log.
Setting up dumpio is super easy. To enable the dumpio module during the Apache build process, you can pass the “–enable-dumpio=shared” option to the configure script:
$ ./configure --enable-mods-shared=most --enable-dumpio-shared --with-mpm=worker \ --enable-deflate=shared --prefix=/opt/apache-2.2.3
To enable the module, you will first need to load the module with “LoadModule” directive. Once the module is configured to load, you can add the “DumpIOInput On” directive to to dump incoming data, and “DumpIOOutput On” to dump data sent by Apache. This will result in messages similar to the following appearing in the Apache error logfile:
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(103): mod_dumpio: dumpio_in [getline-blocking] 0 readbytes
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(51): mod_dumpio: dumpio_in (data-HEAP): 16 bytes
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(67): mod_dumpio: dumpio_in (data-HEAP): GET / HTTP/1.1rn
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(103): mod_dumpio: dumpio_in [getline-blocking] 0 readbytes
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(51): mod_dumpio: dumpio_in (data-HEAP): 13 bytes
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(67): mod_dumpio: dumpio_in (data-HEAP): Accept: */*rn
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(103): mod_dumpio: dumpio_in [getline-blocking] 0 readbytes
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(51): mod_dumpio: dumpio_in (data-HEAP): 21 bytes
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(67): mod_dumpio: dumpio_in (data-HEAP): Accept-Language: enrn
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(103): mod_dumpio: dumpio_in [getline-blocking] 0 readbytes
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(51): mod_dumpio: dumpio_in (data-HEAP): 32 bytes
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(67): mod_dumpio: dumpio_in (data-HEAP): Accept-Encoding: gzip, deflatern
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(103): mod_dumpio: dumpio_in [getline-blocking] 0 readbytes
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(103): mod_dumpio: dumpio_in [getline-blocking] 0 readbytes
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(51): mod_dumpio: dumpio_in (data-HEAP): 24 bytes
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(67): mod_dumpio: dumpio_in (data-HEAP): Connection: keep-alivern
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(103): mod_dumpio: dumpio_in [getline-blocking] 0 readbytes
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(51): mod_dumpio: dumpio_in (data-HEAP): 20 bytes
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(67): mod_dumpio: dumpio_in (data-HEAP): Host: 192.168.9.24rn
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(103): mod_dumpio: dumpio_in [getline-blocking] 0 readbytes
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(51): mod_dumpio: dumpio_in (data-HEAP): 2 bytes
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(67): mod_dumpio: dumpio_in (data-HEAP): rn
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(129): mod_dumpio: dumpio_out
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(51): mod_dumpio: dumpio_out (data-HEAP): 281 bytes
[Sat Oct 28 10:52:31 2006] [debug] mod_dumpio.c(67): mod_dumpio: dumpio_out (data-HEAP): HTTP/1.1 200 OKrnDate: Sat, 28 Oct 2006 14:52:31 GMTrnServer: Apache/2.2.3 (Unix)rnLast-Modified: Sat, 20 Nov 2004 20:16:24 GMTrnETag: "45b81-2c-4c23b600"rnAccept-Ranges: bytesrnContent-Length: 44rnKeep-Alive: timeout=5, max=100rnConnection: Keep-AlivernContent-Type:Ttext/htmlrnrn:00-04:00
Dumpio is an extremely useful module, and is an invaluable tool for debugging web application.