Apache: The Definitive Guide, 3rd Edition

Overview

Perhaps the most important part of an Apache module is the module structure. This is defined in http_config.h, so all modules should start (apart from copyright notices, etc.) with the following lines:

#include "httpd.h"
#include "http_config.h"

Note that httpd.h is required for all Apache source code.

What is the module structure for? Simple: it provides the glue between the Apache core and the module’s code. It contains pointers (to functions, lists, and so on) that are used by components of the core at the correct moments. The core knows about the various module structures because they are listed in modules.c, which is generated by the Configure script from the Configuration file.^[2]

Traditionally, each module ends with its module structure. Here is a particularly trivial example, from mod_asis.c (1.3):

module asis_module = {
   STANDARD_MODULE_STUFF,
   NULL,                          /* initializer */
   NULL,                          /* create per-directory config structure */
   NULL,                          /* merge per-directory config structures */
   NULL,                          /* create per-server config structure */
   NULL,                          /* merge per-server config structures */
   NULL,                          /* command table */
   asis_handlers,                 /* handlers */
   NULL,                          /* translate_handler */
   NULL,                          /* check_user_id */
   NULL,                          /* check auth */
   NULL,                          /* check access */
   NULL,                          /* type_checker */
   NULL,                          /* prerun fixups */
   NULL                           /* logger */
   NULL,                          /* header parser */
   NULL,                          /* child_init */
   NULL,                          /* child_exit */
   NULL                           /* post read request */
};

The first entry, STANDARD_MODULE_STUFF, must appear in all module structures. It ...