Apache Server for Windows Little Black Book:The Apache API
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Other parts of the request_rec structure contain information about the request (the_request), information about the server itself (server), and any internal redirect information (main/next/prev).
How Modules Use Resources
Modules use resource pools to deal with resource allocation. Pools allow a module (and Apache) to easily keep track of the memory and files it is using and clean the files up as necessary.
Memory is allocated by calling the ap_palloc or ap_pcalloc functions, which take as arguments a pointer to a pool structure and the amount of memory to be allocated.
Files are opened by calling the ap_pfopen function, which takes a pointer to a pool structure, a string with the path to the file, and a string containing access permissions to the file.
All resources are freed when their parent pool is cleared.
Immediate Solutions
Viewing Module Structure
The best way to structure a module for Apache is to follow the structure of one of the modules that is compiled into Apache by default. To view the structure, you need to download the source code. You can do that by following these steps:


1.  Go to the Apache download area at www.apache.org/dist.
2.  Click on the link for a Gzip version of the current release and download the file to your computer.
3.  Open the file you just downloaded with WinZip or a similar application.


TIP:  You’ll need to rename the source file you downloaded in order to open it with WinZip. Change the name so that it has a double file extension (for example, apache_1_3_3_tar.tar.gz) instead of just a .tar extension (for example, apache_1_3_3_tar.tar).


4.  Extract any files you want to view. This example examines the mod_alias.c, the source code for the mod_alias module.
5.  Open the mod_alias.c or other file in a text editor such as Note-pad and view the contents.
6.  Scroll past the licensing and copyright information and view the module code. The Apache module structure is defined in http_config and, therefore, all modules should start with the following lines:


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


These lines establish a link between the apache core and the module’s core.
7.  The convention is to conclude each module by declaring the module structure. Scroll to the end of the source code and you’ll see the structure as follows:


module MODULE_VAR_EXPORT alias_module =
{
STANDARD_MODULE_STUFF,
NULL, /* initializer */
create_alias_dir_config, /* dir config creater */
merge_alias_dir_config, /* dir merger — default
is to override */
create_alias_config, /* server config */
merge_alias_config, /* merge server configs */
alias_cmds, /* command table */
NULL, /* handlers */
translate_alias_redir, /* filename translation */
NULL, /* check_user_id */
NULL, /* check auth */
NULL, /* check access */
NULL, /* type_checker */
fixup_redir, /* fixups */
NULL, /* logger */
NULL, /* header parser */
NULL, /* child_init */
NULL, /* child_exit */
NULL /* post read-request */
};



The STANDARD_MODULE_STUFF line must appear in all module structures. It initializes important structural elements that the core uses to implement modules.
Using Common API Functions
All of the public functions and variables included as part of the Apache API are preceded by the prefix ap_. If you write your own modules, it’s important to use this prefix. The naming system was devised to prevent conflicts between function names in Apache and functions in third-party libraries linked via modules.
Many of the most commonly used functions are presented in Table 15.1.
Table 15.1 Common Apache API Functions.

Function
Purpose

ap_call_exec
Signifies a shell to an external program

ap_clear_pool
Clears a pool without destroying the pool itself

ap_clear_table
Clears a table

ap_copy_table
Returns a copy of a table

ap_destroy_pool
Destroys a pool and all of its subpools, releasing their memory

ap_internal_redirect
Forces Apache to redirect to a specified URL

ap_log_error
Writes to the error log

ap_make_array
Allocates an array of arbitrarily sized elements

ap_make_table
Creates a table in a resource pool

ap_make_sub_pool
Returns a pool that is the child of the pool passed to it

ap_no2slash
Removes // from a path

ap_palloc
Allocates memory for a resource pool

ap_pcalloc
Allocates memory for a resource pool, clearing it first

ap_pfclose
Closes an open file in a resource pool

ap_pfopen
Opens a file within a resource pool

ap_rprintf
Prints a formatted string

ap_rputs
Prints a string

ap_rputc
Prints a character

ap_run_cleanup
Executes the Apache cleanup routine

ap_send_http_header
Sends response header to the client

ap_start_restart
Restarts the Apache server, forcing the configuration files to be reread

ap_start_shutdown
Performs a “clean” shutdown of the server

ap_table_add
Places a new key/value pair in a table

ap_table_get
Determines the value in a table

ap_table_set
Replaces or creates a new table entry

ap_pstrcat
Concatenates the NULL-terminated list of strings in a new block of memory

ap_uudecode
Decodes an UUEncoded string





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