<?xml version='1.0' encoding='UTF-8' ?>

<!DOCTYPE manualpage SYSTEM "/style/manualpage.dtd">

<?xml-stylesheet type="text/xsl" href="/style/manual.en.xsl"?>

<manualpage metafile="modguide.xml.meta">

<parentdocument href="./">Developer</parentdocument>

<title>Developing modules for the Apache HTTP Server 2.4</title>

<summary>

<p>This document explains how you can develop modules for the Apache HTTP

Server 2.4</p>

</summary>

<seealso><a href="request.html">Request Processing in Apache 2.4</a></seealso>

<seealso><a href="hooks.html">Apache 2.x Hook Functions</a></seealso>

<section id="introduction"><title>Introduction</title>

<section id="what"><title>What we will be discussing in this document</title>

<p>

This document will discuss how you can easily create modules for the Apache

HTTP Server 2.4 (&quot;Apache&quot;), by exploring an example module called

<code>mod_example</code>. In the first part of this document, the purpose

of this module will be to calculate and print out various digest values for

existing files on your web server, whenever we access the URL <code>

http://hostname/filename.sum</code>. For instance, if we want to know the

MD5 digest value of the file located at <code>

http://www.example.com/index.html</code>, we would visit <code>

http://www.example.com/index.html.sum</code>.

</p>

<p>

In the second part of this document, which deals with configuration

directive and context awareness, we will be looking at a module that simply

write out its own configuration to the client.

</p>

</section>

<section id="prerequisites"><title>Prerequisites</title>

<p>

First and foremost, you are expected to have a basic knowledge of how the C

programming language works. In most cases, we will try to be as pedagogical

as possible and link to documents describing the functions used in the

examples, but there are also many cases where it is necessary to either

just assume that "it works" or do some digging youself into what the hows

and whys of various function calls.

</p>

<p>

Lastly, you will need to have a basic understanding of how modules are

loaded and configured in Apache, as well as how to get the headers for

Apache if you do not have them already, as these are needed for compiling

new modules.

</p>

</section>

<section id="compiling"><title>Compiling your module</title>

<p>

To compile the source code we are building in this document, we will be

using <a href="/programs/apxs.html">APXS</a>. Assuming your source file

is called mod_example.c, compiling, installing and activating the module is

as simple as:

<example><pre>

apxs -i -a -c mod_example.c

</pre></example>

</p>

</section>

</section>

<section id="basics"><title>Defining a module</title>

<img src="/images/build_a_mod_3.png"/><br/>

<p>Every module starts with the same declaration, or name tag if you will,

that defines a module as <em>a separate entity within Apache</em>:

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

module AP_MODULE_DECLARE_DATA example_module <code style='color:#806030; '>=</code>

<code style='color:#806030; '>{</code>

STANDARD20_MODULE_STUFF<code style='color:#806030; '>,</code>

create_dir_conf<code style='color:#806030; '>,</code> <code style='color:#c34e00; '>/* Per-directory configuration handler */</code>

merge_dir_conf<code style='color:#806030; '>,</code> <code style='color:#c34e00; '>/* Merge handler for per-directory configurations */</code>

create_svr_conf<code style='color:#806030; '>,</code> <code style='color:#c34e00; '>/* Per-server configuration handler */</code>

merge_svr_conf<code style='color:#806030; '>,</code> <code style='color:#c34e00; '>/* Merge handler for per-server configurations */</code>

directives<code style='color:#806030; '>,</code> <code style='color:#c34e00; '>/* Any directives we may have for httpd */</code>

register_hooks <code style='color:#c34e00; '>/* Our hook registering function */</code>

<code style='color:#806030; '>}</code><code style='color:#806030; '>;</code>

</pre>

This bit of code lets Apache know that we have now registered a new module

in the system, and that its name is <code>example_module</code>. The name

of the module is used primarilly for two things:<br/>

<ul>

<li>Letting Apache know how to load the module using the LoadModule</li>

<li>Setting up a namespace for the module to use in configurations</li>

</ul>

For now, we're only concerned with the first purpose of the module name,

which comes into play when we need to load the module:<br/>

<example><pre><a href="/mod/mod_so.html#LoadModule">LoadModule</a> example_module modules/mod_example.so</pre></example>

In essence, this tells Apache to open up <code>mod_example.so</code> and look for a module

called <code>example_module</code>.

</p>

<p>

Within this name tag of ours is also a bunch of references to how we would

like to handle things: Which directives do we respond to in a configuration

file or .htaccess, how do we operate within specific contexts, and what

handlers are we interested in registering with the Apache service. We'll

return to all these elements later in this document.

</p>

</section>

<section id="hooking"><title>Getting started: Hooking into Apache</title>

<section id="hook_intro"><title>An introduction to hooks</title>

<p>

When handling requests in Apache, the first thing you will need to do is

create a hook into the request handling process. A hook is essentially a

message telling Apache that you are willing to either serve or at least

take a glance at certain requests given by clients. All handlers, whether

it's mod_rewrite, mod_authn_*, mod_proxy and so on, are hooked into

specific parts of the request process. As you are probably aware, modules

serve different purposes; Some are authentication/authorization handlers,

others are file or script handlers while some third modules rewrite URIs or

proxies content. Furthermore, in the end, it is up to the user of Apache

how and when each module will come into place. Thus, Apache itself does not

presume to know which module is responsible for handling a specific

request, and will ask each module whether they have an interest in a given

request or not. It is then up to each module to either gently decline

serving a request, accept serving it or flat out deny the request from

being served, as authentication/authorization modules do: <br/>

<img src="/images/build_a_mod_2.png" /><br/>

To make it a bit easier for handlers such as our mod_example to know

whether the client is requesting content we should handle or not, Apache

has directives for hinting to modules whether their assistance is needed or

not. Two of these are <directive module="mod_mime">AddHandler</directive>

and <directive module="core">SetHandler</directive>. Let's take a look at

an example using <directive module="mod_mime">AddHandler</directive>. In

our example case, we want every request ending with .sum to be served by

<code>mod_example</code>, so we'll add a configuration directive that tells

Apache to do just that:

<example><pre>

AddHandler example-handler .sum

</pre></example>

What this tells Apache is the following: <em>Whenever we receive a request

for a URI ending in .sum, we are to let all modules know that we are

looking for whoever goes by the name of &quot;example-handler&quot; </em>.

Thus, when a request is being served that ends in .sum, Apache will let all

modules know, that this request should be served by &quot;example-handler

&quot;. As you will see later, when we start building mod_example, we will

check for this handler tag relayed by <code>AddHandler</code> and reply to

Apache based on the value of this tag.

</p>

</section>

<section id="hook_declaration"><title>Hooking into httpd</title>

<p>

To begin with, we only want to create a simple handler, that replies to the

client browser when a specific URL is requested, so we won't bother setting

up configuration handlers and directives just yet. Our initial module

definition will look like this:<br/>

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

module AP_MODULE_DECLARE_DATA example_module =

{

STANDARD20_MODULE_STUFF,

<code style='color:#7f0055; font-weight:bold; '>NULL</code>,

<code style='color:#7f0055; font-weight:bold; '>NULL</code>,

<code style='color:#7f0055; font-weight:bold; '>NULL</code>,

<code style='color:#7f0055; font-weight:bold; '>NULL</code>,

<code style='color:#7f0055; font-weight:bold; '>NULL</code>,

<code style='color:#800040; '>register_hooks</code> <code style='color:#c34e00; '><code style='color:#c34e00; '>/* Our hook registering function */</code></code>

};

</pre>

This lets Apache know that we are not interesting in anything fancy, we

just want to hook onto the requests and possibly handle some of them. </p>

<p> The reference in our example declaration, <code>register_hooks</code>

is the name of a function we will create to manage how we hook onto the

request process. In this example module, the function has just one purpose;

To create a simple hook that gets called after all the rewrites, access

control etc has been handled. Thus, we will let Apache know, that we want

to hook into its process as one of the last modules:

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

<code style='color:#400000; font-weight:bold; '>static</code> <code style='color:#400000; font-weight:bold; '>void</code> register_hooks<code style='color:#806030; '>(</code>apr_pool_t <code style='color:#806030; '>*</code>pool<code style='color:#806030; '>)</code>

<code style='color:#806030; '>{</code>

<code style='color:#c34e00; '>/* Create a hook in the request handler, so we get called when a request arrives */</code>

<code style='color:#800040; '>ap_hook_handler</code><code style='color:#806030; '>(</code>example_handler<code style='color:#806030; '>,</code> <code style='color:#7f0055; font-weight:bold; '>NULL</code><code style='color:#806030; '>,</code> <code style='color:#7f0055; font-weight:bold; '>NULL</code><code style='color:#806030; '>,</code> APR_HOOK_LAST<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

</pre>

The <code>example_handler</code> reference is the function that will handle

the request. We will discuss how to create a handler in the next chapter.

</p>

</section>

<section id="hook_others"><title>Other useful hooks</title>

<p>

Hooking into the request handling phase is but one of many hooks that you

can create. Some other ways of hooking are:

<ul>

<li><code>ap_hook_child_init</code>: Place a hook that executes when a child process is spawned (commonly used for initializing modules after Apache has forked)</li>

<li><code>ap_hook_pre_config</code>: Place a hook that executes before any configuration data has been read (very early hook)</li>

<li><code>ap_hook_post_config</code>: Place a hook that executes after configuration has been parsed, but before Apache has forked</li>

<li><code>ap_hook_translate_name</code>: Place a hook that executes when a URI needs to be translated into a filename on the server (think <code>mod_rewrite</code>)</li>

</ul>

</p>

</section>

</section>

<section id="handling"><title>Building a handler</title>

<p>

A handler is essentially a function that receives a callback when a request

to Apache is made. It is passed a record of the current request (how it was

made, which headers and requests were passed along, who's giving the

request and so on), and is put in charge of either telling Apache that it's

not interested in the request or handle the request with the tools provided.

</p>

<section id="simple_handler"><title>A simple &quot;Hello, world!&quot;

handler</title> Let's start off by making a very simple request handler

that does the following: <br/>

<ol>

<li>Check that this is a request that should be served by &quot;example-handler&quot;</li>

<li>Set the content type of our output to <code>text/html</code></li>

<li>Write &quot;Hello, world!&quot; back to the client browser</li>

<li>Let Apache know that we took care of this request and everything went fine</li>

</ol>

In C code, our example handler will now look like this:<br/>

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

<code style='color:#400000; font-weight:bold; '>static</code> <code style='color:#400000; font-weight:bold; '>int</code> example_handler<code style='color:#806030; '>(</code>request_rec <code style='color:#806030; '>*</code>r<code style='color:#806030; '>)</code>

<code style='color:#806030; '>{</code>

<code style='color:#c34e00; '>/* First off, we need to check if this is a call for the "example-handler" handler.</code>

<code style='color:#c34e00; '>&#xa0;&#xa0;&#xa0;&#xa0;&#xa0;* If it is, we accept it and do our things, if not, we simply return DECLINED,</code>

<code style='color:#c34e00; '>&#xa0;&#xa0;&#xa0;&#xa0;&#xa0;* and Apache will try somewhere else.</code>

<code style='color:#c34e00; '>&#xa0;&#xa0;&#xa0;&#xa0;&#xa0;*/</code>

<code style='color:#400000; font-weight:bold; '>if</code> <code style='color:#806030; '>(</code><code style='color:#806030; '>!</code>r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code><code style='color:#008833'>handler</code> <code style='color:#806030; '>|</code><code style='color:#806030; '>|</code> <code style='color:#800040; '>strcmp</code><code style='color:#806030; '>(</code>r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code><code style='color:#008833'>handler</code><code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>example-handler</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>)</code> <code style='color:#400000; font-weight:bold; '>return</code> <code style='color:#806030; '>(</code>DECLINED<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/* Now that we are handling this request, we'll write out "Hello, world!" to the client.</code>

<code style='color:#c34e00; '>&#xa0;&#xa0;&#xa0;&#xa0;&#xa0;* To do so, we must first set the appropriate content type, followed by our output.</code>

<code style='color:#c34e00; '>&#xa0;&#xa0;&#xa0;&#xa0;&#xa0;*/</code>

<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#gaa2f8412c400197338ec509f4a45e4579">ap_set_content_type</a><code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>text/html</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#ga5e91eb6ca777c9a427b2e82bf1eeb81d">ap_rprintf</a><code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>Hello, world!</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/* Lastly, we must tell Apache that we took care of this request and everything went fine.</code>

<code style='color:#c34e00; '>&#xa0;&#xa0;&#xa0;&#xa0;&#xa0;* We do so by simply returning the value OK to Apache.</code>

<code style='color:#c34e00; '>&#xa0;&#xa0;&#xa0;&#xa0;&#xa0;*/</code>

<code style='color:#400000; font-weight:bold; '>return</code> OK<code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

</pre>

Now, we put all we have learned together and end up with a program that

looks like

<a href="http://people.apache.org/~humbedooh/mods/examples/mod_example_1.c">mod_example_1.c</a>

. The functions used in this example will be explained later in the section

<a href= "#functions">&quot;Some useful functions you should know&quot;</a>

. </section> <section id="request_rec"><title>The request_rec structure

</title> <p>The most essential part of any request is the <em>request record

</em>. In a call to a handler function, this is represented by the <code>

request_req* </code> structure passed along with every call that is made.

This struct, typically just refered to as <code>r</code> in modules,

contains all the information you need for your module to fully process any

HTTP request and respond accordingly.</p> <p>Some key elements of the <code>

request_req </code> structure are:

<ul>

<li><code><code style='color:#008833'>r-&gt;handler</code> (char*)</code>: Contains the name of the handler Apache is currently asking to do the handling of this request</li>

<li><code><code style='color:#008833'>r-&gt;method</code> (char*)</code>: Contains the HTTP method being used, f.x. GET or POST</li>

<li><code><code style='color:#008833'>r-&gt;filename</code> (char*)</code>: Contains the translated filename the client is requesting</li>

<li><code><code style='color:#008833'>r-&gt;args</code> (char*)</code>: Contains the query string of the request, if any</li>

<li><code><code style='color:#008833'>r-&gt;headers_in</code> (apr_table_t*)</code>: Contains all the headers sent by the client</li>

<li><code><code style='color:#008833'>r-&gt;connection</code> (conn_rec*)</code>: A record containing information about the current connection</li>

<li><code><code style='color:#008833'>r-&gt;useragent_ip</code> (char*)</code>: The IP address of the client connecting to us</li>

<li><code><code style='color:#008833'>r-&gt;pool</code> (apr_pool_t*)</code>: The memory pool of this request. We'll discuss this in the &quot;

<a href="#memory">Memory management</a>&quot; chapter.</li>

</ul>

A complete list of all the values contained with in the <code>request_req</code> structure can be found in

the <a href="http://svn.apache.org/repos/asf/httpd/httpd/trunk/include/httpd.h"><code>httpd.h</code></a> header

file or at <a href="http://ci.apache.org/projects/httpd/trunk/doxygen/structrequest__rec.html">http://ci.apache.org/projects/httpd/trunk/doxygen/structrequest__rec.html</a>.

</p>

<p>

Let's try out some of these variables in another example handler:<br/>

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

<code style='color:#400000; font-weight:bold; '>static</code> <code style='color:#400000; font-weight:bold; '>int</code> example_handler<code style='color:#806030; '>(</code>request_rec <code style='color:#806030; '>*</code>r<code style='color:#806030; '>)</code>

<code style='color:#806030; '>{</code>

<code style='color:#c34e00; '>/* Set the appropriate content type */</code>

<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#gaa2f8412c400197338ec509f4a45e4579">ap_set_content_type</a><code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>text/html</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/* Print out the IP address of the client connecting to us: */</code>

<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#ga5e91eb6ca777c9a427b2e82bf1eeb81d">ap_rprintf</a><code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>&lt;h2>Hello, </code><code style='color:#0f6900; '>%s</code><code style='color:#e60000; '>!&lt;/h2></code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code><code style='color:#008833'>useragent_ip</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/* If we were reached through a GET or a POST request, be happy, else sad. */</code>

<code style='color:#400000; font-weight:bold; '>if</code> <code style='color:#806030; '>(</code> <code style='color:#806030; '>!</code><code style='color:#800040; '>strcmp</code><code style='color:#806030; '>(</code>r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code><code style='color:#008833'>method</code><code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>POST</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code> <code style='color:#806030; '>|</code><code style='color:#806030; '>|</code> <code style='color:#806030; '>!</code><code style='color:#800040; '>strcmp</code><code style='color:#806030; '>(</code>r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code><code style='color:#008833'>method</code><code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>GET</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code> <code style='color:#806030; '>)</code> <code style='color:#806030; '>{</code>

ap_rputs<code style='color:#806030; '>(</code><code style='color:#800000; '>"</code><code style='color:#e60000; '>You used a GET or a POST method, that makes us happy!&lt;br></code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> r<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

<code style='color:#400000; font-weight:bold; '>else</code> <code style='color:#806030; '>{</code>

ap_rputs<code style='color:#806030; '>(</code><code style='color:#800000; '>"</code><code style='color:#e60000; '>You did not use POST or GET, that makes us sad :(&lt;br></code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> r<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

<code style='color:#c34e00; '>/* Lastly, if there was a query string, let's print that too! */</code>

<code style='color:#400000; font-weight:bold; '>if</code> <code style='color:#806030; '>(</code>r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code><code style='color:#008833'>args</code><code style='color:#806030; '>)</code> <code style='color:#806030; '>{</code>

<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#ga5e91eb6ca777c9a427b2e82bf1eeb81d">ap_rprintf</a><code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>Your query string was: </code><code style='color:#0f6900; '>%s</code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code><code style='color:#008833'>args</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

<code style='color:#400000; font-weight:bold; '>return</code> OK<code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

</pre>

</p>

</section>

<section id="return_value"><title>Return values</title>

<p>

Apache relies on return values from handlers to signify whether a request

was handled or not, and if so, whether the request went well or not. If a

module is not interested in handling a specific request, it should always

return the value <code>DECLINED</code>. If it is handling a request, it

should either return the generic value <code>OK</code>, or a specific HTTP

status code, for example:

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

<code style='color:#400000; font-weight:bold; '>static</code> <code style='color:#400000; font-weight:bold; '>int</code> example_handler<code style='color:#806030; '>(</code>request_rec <code style='color:#806030; '>*</code>r<code style='color:#806030; '>)</code>

<code style='color:#806030; '>{</code>

<code style='color:#c34e00; '>/* Return 404: Not found */</code>

<code style='color:#400000; font-weight:bold; '>return</code> HTTP_NOT_FOUND<code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

</pre>

Returning <code>OK</code> or a HTTP status code does not necessarilly mean

that the request will end. Apache may still have other handlers that are

interested in this request, for instance the logging modules which, upon a

successful request, will write down a summary of what was requested and how

it went. To do a full stop and prevent any further processing after your

module is done, you can return the value <code>DONE</code> to let Apache

know that it should cease all activity on this request and carry on with

the next, without informing other handlers.

<br/>

<strong>General response codes:</strong>

<ul>

<li><code>DECLINED</code>: We are not handling this request</li>

<li><code>OK</code>: We handled this request and it went well</li>

<li><code>DONE</code>: We handled this request and Apache should just close this thread without further processing</li>

</ul><br/>

<strong>HTTP specific return codes (excerpt):</strong>

<ul>

<li><code>HTTP_OK (200)</code>: Request was okay</li>

<li><code>HTTP_MOVED_PERMANENTLY (301)</code>: The resource has moved to a new URL</li>

<li><code>HTTP_UNAUTHORIZED (401)</code>: Client is not authorized to visit this page</li>

<li><code>HTTP_FORBIDDEN (403)</code>: Permission denied</li>

<li><code>HTTP_NOT_FOUND (404)</code>: File not found</li>

<li><code>HTTP_INTERNAL_SERVER_ERROR (500)</code>: Internal server error (self explanatory)</li>

</ul>

</p>

</section>

<section id="functions"><title>Some useful functions you should know</title>

<ul>

<li>

<code>ap_rputs(const char *string, request_req *r)</code>: <br/>

Sends a string of text to the client. This is a shorthand version of <a

href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#gac827cd0537d2b6213a7c06d7c26cc36e">

ap_rwrite</a>.

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>ap_rputs<code style='color:#806030; '>(</code><code style='color:#800000; '>"</code><code style='color:#e60000; '>Hello, world!</code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> r<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code></pre>

</li>

<li>

<code>

<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#ga5e91eb6ca777c9a427b2e82bf1eeb81d">ap_rprintf</a></code>: <br/>

This function works just like <code>printf</code>, except it sends the result to the client.

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'><code style='color:#2e8800; '><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#ga5e91eb6ca777c9a427b2e82bf1eeb81d">ap_rprintf</a></code><code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>Hello, </code><code style='color:#0f6900; '>%s</code><code style='color:#e60000; '>!</code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code><code style='color:#008833'>useragent_ip</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code></pre>

</li>

<li>

<code>

<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#gaa2f8412c400197338ec509f4a45e4579">ap_set_content_type</a>(request_req *r, const char *type)</code>: <br/>

Sets the content type of the output you are sending.

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'><code style='color:#2e8800; '><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__PROTO.html#gaa2f8412c400197338ec509f4a45e4579">ap_set_content_type</a></code><code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>text/plain</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code> <code style='color:#c34e00; '>/* force a raw text output */</code></pre>

</li>

</ul>

</section>

<section id="memory"><title>Memory management</title>

<p>

Managing your resources in Apache is quite easy, thanks to the memory pool

system. In essence, each server, connection and request have their own

memory pool that gets cleaned up when its scope ends, e.g. when a request

is done or when a server process shuts down. All your module needs to do is

latch onto this memory pool, and you won't have to worry about having to

clean up after yourself - pretty neat, huh?

</p>

<p>

In our module, we will primarilly be allocating memory for each request, so

it's appropriate to use the <code style='color:#008833'>r-&gt;pool</code>

reference when creating new objects. A few of the functions for allocating

memory within a pool are:

<ul>

<li><code>void* <a href="http://apr.apache.org/docs/apr/1.4/group__apr__pools.html#ga85f1e193c31d109affda72f9a92c6915">apr_palloc</a>(

apr_pool_t *p, apr_size_t size)</code>: Allocates <code>size</code> number of bytes in the pool for you</li>

<li><code>void* <a href="http://apr.apache.org/docs/apr/1.4/group__apr__pools.html#gaf61c098ad258069d64cdf8c0a9369f9e">apr_pcalloc</a>(

apr_pool_t *p, apr_size_t size)</code>: Allocates <code>size</code> number of bytes in the pool for you and sets all bytes to 0</li>

<li><code>char* <a href="http://apr.apache.org/docs/apr/1.4/group__apr__strings.html#gabc79e99ff19abbd7cfd18308c5f85d47">apr_pstrdup</a>(

apr_pool_t *p, const char *s)</code>: Creates a duplicate of the string <code>s</code>. This is useful for copying constant values so you can edit them</li>

<li><code>char* <a href="http://apr.apache.org/docs/apr/1.4/group__apr__strings.html#ga3eca76b8d293c5c3f8021e45eda813d8">apr_psprintf</a>(

apr_pool_t *p, const char *fmt, ...)</code>: Similar to <code>sprintf</code>, except Apache supplies you with an appropriately allocated target variable</li>

</ul>

Let's put these functions into an example handler:<br/>

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

<code style='color:#400000; font-weight:bold; '>static</code> <code style='color:#400000; font-weight:bold; '>int</code> example_handler<code style='color:#806030; '>(</code>request_rec <code style='color:#806030; '>*</code>r<code style='color:#806030; '>)</code>

<code style='color:#806030; '>{</code>

<code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code><code style='color:#806030; '>*</code> original <code style='color:#806030; '>=</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>You can't edit this!</code><code style='color:#800000; '>"</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>char</code><code style='color:#806030; '>*</code> copy<code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>int</code><code style='color:#806030; '>*</code> integers<code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/* Allocate space for 10 integer values and set them all to zero. */</code>

integers <code style='color:#806030; '>=</code> apr_pcalloc<code style='color:#806030; '>(</code>r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code>pool<code style='color:#806030; '>,</code> <code style='color:#400000; font-weight:bold; '>sizeof</code><code style='color:#806030; '>(</code><code style='color:#400000; font-weight:bold; '>int</code><code style='color:#806030; '>)</code><code style='color:#806030; '>*</code><code style='color:#c00000; '>10</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/* Create a copy of the 'original' variable that we can edit. */</code>

copy <code style='color:#806030; '>=</code> apr_pstrdup<code style='color:#806030; '>(</code>r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code>pool<code style='color:#806030; '>,</code> original<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>return</code> OK<code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

</pre>

This is all well and good for our module, which won't need any

pre-initialized variables or structures. However, if we wanted to

initialize something early on, before the requests come rolling in, we

could simply add a call to a function in our <code>register_hooks</code>

function to sort it out:

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

<code style='color:#400000; font-weight:bold; '>static</code> <code style='color:#400000; font-weight:bold; '>void</code> register_hooks<code style='color:#806030; '>(</code>apr_pool_t <code style='color:#806030; '>*</code>pool<code style='color:#806030; '>)</code>

<code style='color:#806030; '>{</code>

<code style='color:#c34e00; '>/* Call a function that initializes some stuff */</code>

<code style='color:#800040; '>example_init_function</code><code style='color:#806030; '>(</code>pool<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/* Create a hook in the request handler, so we get called when a request arrives */</code>

<code style='color:#800040; '>ap_hook_handler</code><code style='color:#806030; '>(</code>example_handler<code style='color:#806030; '>,</code> <code style='color:#7f0055; font-weight:bold; '>NULL</code><code style='color:#806030; '>,</code> <code style='color:#7f0055; font-weight:bold; '>NULL</code><code style='color:#806030; '>,</code> APR_HOOK_LAST<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

</pre>

In this pre-request initialization function we would not be using the

same pool as we did when allocating resources for request-based functions.

Instead, we would use the pool given to us by Apache for allocating memory

on a per-process based level.

</p>

</section>

<section id="parsing"><title>Parsing request data</title>

<p>

In our example module, we would like to add a feature, that checks which

type of digest, MD5 or SHA1 the client would like to see. This could be

solved by adding a query string to the request. A query string is typically

comprised of several keys and values put together in a string, for instance

<code>valueA=yes&amp;valueB=no&amp;valueC=maybe</code>. It is up to the

module itself to parse these and get the data it requires. In our example,

we'll be looking for a key called <code>digest</code>, and if set to <code>

md5</code>, we'll produce an MD5 digest, otherwise we'll produce a SHA1

digest.

</p>

<p>

Since the introduction of Apache 2.4, parsing request data from GET and

POST requests have never been easier. All we require to parse both GET and

POST data is four simple lines:

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__apr__tables.html#gad7ea82d6608a4a633fc3775694ab71e4">apr_table_t</a> *GET;

<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/structapr__array__header__t.html">apr_array_header_t</a> *POST;

<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__SCRIPT.html#gaed25877b529623a4d8f99f819ba1b7bd">ap_args_to_table</a>(r, &amp;GET);

<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__DAEMON.html#ga9d426b6382b49754d4f87c55f65af202">ap_parse_form_data</a>(r, <code style='color:#7f0055; font-weight:bold; '>NULL</code>, &amp;POST, -1, 8192);

</pre>

In our specific example module, we're looking for the <code>digest</code>

value from the query string, which now resides inside a table called <code>

GET</code>. To extract this value, we need only perform a simple operation:

<br/>

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

<code style='color:#c34e00; '>/* Get the "digest" key from the query string, if any. */</code>

<code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code><code style='color:#806030; '> *</code>digestType <code style='color:#806030; '>=</code> <a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__apr__tables.html#ga4db13e3915c6b9a3142b175d4c15d915">apr_table_get</a><code style='color:#806030; '>(</code>GET<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>digest</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/* If no key was returned, we will set a default value instead. */</code>

<code style='color:#400000; font-weight:bold; '>if</code> <code style='color:#806030; '>(</code><code style='color:#806030; '>!</code>digestType<code style='color:#806030; '>)</code> digestType <code style='color:#806030; '>=</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>sha1</code><code style='color:#800000; '>"</code><code style='color:#806030; '>;</code>

</pre>

The structures used for the POST and GET data are not exactly the same, so

if we were to fetch a value from POST data instead of the query string, we

would have to resort to a few more lines, as outlined in <a href="#get_post"

>this example</a> in the last chapter of this document.

</p>

</section>

<section id="advanced_handler"><title>Making an advanced handler</title>

Now that we have learned how to parse form data and manage our resources,

we can move on to creating an advanced version of our module, that spits

out the MD5 or SHA1 digest of files:<br/>

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

<code style='color:#400000; font-weight:bold; '>static</code> <code style='color:#400000; font-weight:bold; '>int</code> example_handler<code style='color:#806030; '>(</code>request_rec <code style='color:#806030; '>*</code>r<code style='color:#806030; '>)</code>

<code style='color:#806030; '>{</code>

<code style='color:#400000; font-weight:bold; '>int</code> rc<code style='color:#806030; '>,</code> exists<code style='color:#806030; '>;</code>

apr_finfo_t finfo<code style='color:#806030; '>;</code>

apr_file_t<code style='color:#806030; '> *</code>file<code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>char</code> <code style='color:#806030; '>*</code>filename<code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>char</code> buffer<code style='color:#806030; '>[</code><code style='color:#c00000; '>256</code><code style='color:#806030; '>]</code><code style='color:#806030; '>;</code>

apr_size_t readBytes<code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>int</code> n<code style='color:#806030; '>;</code>

apr_table_t<code style='color:#806030; '> *</code>GET<code style='color:#806030; '>;</code>

apr_array_header_t<code style='color:#806030; '> *</code>POST<code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code><code style='color:#806030; '> *</code>digestType<code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/* Check that the "example-handler" handler is being called. */</code>

<code style='color:#400000; font-weight:bold; '>if</code> <code style='color:#806030; '>(</code><code style='color:#806030; '>!</code>r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code><code style='color:#008833'>handler</code> <code style='color:#806030; '>|</code><code style='color:#806030; '>|</code> <code style='color:#800040; '>strcmp</code><code style='color:#806030; '>(</code>r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code><code style='color:#008833'>handler</code><code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>example-handler</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>)</code> <code style='color:#400000; font-weight:bold; '>return</code> <code style='color:#806030; '>(</code>DECLINED<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/* Figure out which file is being requested by removing the .sum from it */</code>

filename <code style='color:#806030; '>=</code> apr_pstrdup<code style='color:#806030; '>(</code>r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code><code style='color:#008833'>pool</code><code style='color:#806030; '>,</code> r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code><code style='color:#008833'>filename</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

filename<code style='color:#806030; '>[</code><code style='color:#800040; '>strlen</code><code style='color:#806030; '>(</code>filename<code style='color:#806030; '>)</code><code style='color:#806030; '>-</code><code style='color:#c00000; '>4</code><code style='color:#806030; '>]</code> <code style='color:#806030; '>=</code> <code style='color:#c00000; '>0</code><code style='color:#806030; '>;</code> <code style='color:#c34e00; '>/* Cut off the last 4 characters. */</code>

<code style='color:#c34e00; '>/* Figure out if the file we request a sum on exists and isn't a directory */</code>

rc <code style='color:#806030; '>=</code> apr_stat<code style='color:#806030; '>(</code><code style='color:#806030; '>&amp;</code>finfo<code style='color:#806030; '>,</code> filename<code style='color:#806030; '>,</code> APR_FINFO_MIN<code style='color:#806030; '>,</code> r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code><code style='color:#008833'>pool</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>if</code> <code style='color:#806030; '>(</code>rc <code style='color:#806030; '>=</code><code style='color:#806030; '>=</code> APR_SUCCESS<code style='color:#806030; '>)</code> <code style='color:#806030; '>{</code>

exists <code style='color:#806030; '>=</code>

<code style='color:#806030; '>(</code>

<code style='color:#806030; '>(</code>finfo<code style='color:#806030; '>.</code>filetype <code style='color:#806030; '>!</code><code style='color:#806030; '>=</code> APR_NOFILE<code style='color:#806030; '>)</code>

<code style='color:#806030; '>&amp;</code><code style='color:#806030; '>&amp;</code> <code style='color:#806030; '>!</code><code style='color:#806030; '>(</code>finfo<code style='color:#806030; '>.</code>filetype <code style='color:#806030; '>&amp;</code> APR_DIR<code style='color:#806030; '>)</code>

<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>if</code> <code style='color:#806030; '>(</code><code style='color:#806030; '>!</code>exists<code style='color:#806030; '>)</code> <code style='color:#400000; font-weight:bold; '>return</code> HTTP_NOT_FOUND<code style='color:#806030; '>;</code> <code style='color:#c34e00; '>/* Return a 404 if not found. */</code>

<code style='color:#806030; '>}</code>

<code style='color:#c34e00; '>/* If apr_stat failed, we're probably not allowed to check this file. */</code>

<code style='color:#400000; font-weight:bold; '>else</code> <code style='color:#400000; font-weight:bold; '>return</code> HTTP_FORBIDDEN<code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/* Parse the GET and, optionally, the POST data sent to us */</code>

ap_args_to_table<code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#806030; '>&amp;</code>GET<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

ap_parse_form_data<code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#007d45; '>NULL</code><code style='color:#806030; '>,</code> <code style='color:#806030; '>&amp;</code>POST<code style='color:#806030; '>,</code> <code style='color:#806030; '>-</code><code style='color:#c00000; '>1</code><code style='color:#806030; '>,</code> <code style='color:#c00000; '>8192</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/* Set the appropriate content type */</code>

ap_set_content_type<code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>text/html</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/* Print a title and some general information */</code>

ap_rprintf<code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>&lt;h2>Information on </code><code style='color:#0f6900; '>%s</code><code style='color:#e60000; '>:&lt;/h2></code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> filename<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

ap_rprintf<code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>&lt;b>Size:&lt;/b> </code><code style='color:#0f6900; '>%u</code><code style='color:#e60000; '> bytes&lt;br/></code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> finfo<code style='color:#806030; '>.</code>size<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/* Get the digest type the client wants to see */</code>

digestType <code style='color:#806030; '>=</code> apr_table_get<code style='color:#806030; '>(</code>GET<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>digest</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>if</code> <code style='color:#806030; '>(</code><code style='color:#806030; '>!</code>digestType<code style='color:#806030; '>)</code> digestType <code style='color:#806030; '>=</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>MD5</code><code style='color:#800000; '>"</code><code style='color:#806030; '>;</code>

rc <code style='color:#806030; '>=</code> apr_file_open<code style='color:#806030; '>(</code><code style='color:#806030; '>&amp;</code>file<code style='color:#806030; '>,</code> filename<code style='color:#806030; '>,</code> APR_READ<code style='color:#806030; '>,</code> APR_OS_DEFAULT<code style='color:#806030; '>,</code> r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code><code style='color:#008833'>pool</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>if</code> <code style='color:#806030; '>(</code>rc <code style='color:#806030; '>=</code><code style='color:#806030; '>=</code> APR_SUCCESS<code style='color:#806030; '>)</code> <code style='color:#806030; '>{</code>

<code style='color:#c34e00; '>/* Are we trying to calculate the MD5 or the SHA1 digest? */</code>

<code style='color:#400000; font-weight:bold; '>if</code> <code style='color:#806030; '>(</code><code style='color:#806030; '>!</code>strcasecmp<code style='color:#806030; '>(</code>digestType<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>md5</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>)</code> <code style='color:#806030; '>{</code>

<code style='color:#c34e00; '>/* Calculate the MD5 sum of the file */</code>

<code style='color:#400000; font-weight:bold; '>union</code> <code style='color:#806030; '>{</code>

<code style='color:#400000; font-weight:bold; '>char</code> chr<code style='color:#806030; '>[</code><code style='color:#c00000; '>16</code><code style='color:#806030; '>]</code><code style='color:#806030; '>;</code>

uint32_t num<code style='color:#806030; '>[</code><code style='color:#c00000; '>4</code><code style='color:#806030; '>]</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code> digest<code style='color:#806030; '>;</code>

apr_md5_ctx_t md5<code style='color:#806030; '>;</code>

apr_md5_init<code style='color:#806030; '>(</code><code style='color:#806030; '>&amp;</code>md5<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

readBytes <code style='color:#806030; '>=</code> <code style='color:#c00000; '>256</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>while</code> <code style='color:#806030; '>(</code> apr_file_read<code style='color:#806030; '>(</code>file<code style='color:#806030; '>,</code> buffer<code style='color:#806030; '>,</code> <code style='color:#806030; '>&amp;</code>readBytes<code style='color:#806030; '>)</code> <code style='color:#806030; '>=</code><code style='color:#806030; '>=</code> APR_SUCCESS <code style='color:#806030; '>)</code> <code style='color:#806030; '>{</code>

apr_md5_update<code style='color:#806030; '>(</code><code style='color:#806030; '>&amp;</code>md5<code style='color:#806030; '>,</code> buffer<code style='color:#806030; '>,</code> readBytes<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

apr_md5_final<code style='color:#806030; '>(</code>digest<code style='color:#806030; '>.</code>chr<code style='color:#806030; '>,</code> <code style='color:#806030; '>&amp;</code>md5<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/* Print out the MD5 digest */</code>

ap_rputs<code style='color:#806030; '>(</code><code style='color:#800000; '>"</code><code style='color:#e60000; '>&lt;b>MD5: &lt;/b>&lt;code></code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> r<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>for</code> <code style='color:#806030; '>(</code>n <code style='color:#806030; '>=</code> <code style='color:#c00000; '>0</code><code style='color:#806030; '>;</code> n <code style='color:#806030; '>&lt;</code> APR_MD5_DIGESTSIZE<code style='color:#806030; '>/</code><code style='color:#c00000; '>4</code><code style='color:#806030; '>;</code> n<code style='color:#806030; '>+</code><code style='color:#806030; '>+</code><code style='color:#806030; '>)</code> <code style='color:#806030; '>{</code>

ap_rprintf<code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#0f6900; '>%08x</code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> digest<code style='color:#806030; '>.</code>num<code style='color:#806030; '>[</code>n<code style='color:#806030; '>]</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

ap_rputs<code style='color:#806030; '>(</code><code style='color:#800000; '>"</code><code style='color:#e60000; '>&lt;/code></code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> r<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/* Print a link to the SHA1 version */</code>

ap_rputs<code style='color:#806030; '>(</code><code style='color:#800000; '>"</code><code style='color:#e60000; '>&lt;br/>&lt;a href='?digest=sha1'>View the SHA1 hash instead&lt;/a></code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> r<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

<code style='color:#400000; font-weight:bold; '>else</code> <code style='color:#806030; '>{</code>

<code style='color:#c34e00; '>/* Calculate the SHA1 sum of the file */</code>

<code style='color:#400000; font-weight:bold; '>union</code> <code style='color:#806030; '>{</code>

<code style='color:#400000; font-weight:bold; '>char</code> chr<code style='color:#806030; '>[</code><code style='color:#c00000; '>20</code><code style='color:#806030; '>]</code><code style='color:#806030; '>;</code>

uint32_t num<code style='color:#806030; '>[</code><code style='color:#c00000; '>5</code><code style='color:#806030; '>]</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code> digest<code style='color:#806030; '>;</code>

apr_sha1_ctx_t sha1<code style='color:#806030; '>;</code>

apr_sha1_init<code style='color:#806030; '>(</code><code style='color:#806030; '>&amp;</code>sha1<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

readBytes <code style='color:#806030; '>=</code> <code style='color:#c00000; '>256</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>while</code> <code style='color:#806030; '>(</code> apr_file_read<code style='color:#806030; '>(</code>file<code style='color:#806030; '>,</code> buffer<code style='color:#806030; '>,</code> <code style='color:#806030; '>&amp;</code>readBytes<code style='color:#806030; '>)</code> <code style='color:#806030; '>=</code><code style='color:#806030; '>=</code> APR_SUCCESS <code style='color:#806030; '>)</code> <code style='color:#806030; '>{</code>

apr_sha1_update<code style='color:#806030; '>(</code><code style='color:#806030; '>&amp;</code>sha1<code style='color:#806030; '>,</code> buffer<code style='color:#806030; '>,</code> readBytes<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

apr_sha1_final<code style='color:#806030; '>(</code>digest<code style='color:#806030; '>.</code>chr<code style='color:#806030; '>,</code> <code style='color:#806030; '>&amp;</code>sha1<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/* Print out the SHA1 digest */</code>

ap_rputs<code style='color:#806030; '>(</code><code style='color:#800000; '>"</code><code style='color:#e60000; '>&lt;b>SHA1: &lt;/b>&lt;code></code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> r<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>for</code> <code style='color:#806030; '>(</code>n <code style='color:#806030; '>=</code> <code style='color:#c00000; '>0</code><code style='color:#806030; '>;</code> n <code style='color:#806030; '>&lt;</code> APR_SHA1_DIGESTSIZE<code style='color:#806030; '>/</code><code style='color:#c00000; '>4</code><code style='color:#806030; '>;</code> n<code style='color:#806030; '>+</code><code style='color:#806030; '>+</code><code style='color:#806030; '>)</code> <code style='color:#806030; '>{</code>

ap_rprintf<code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#0f6900; '>%08x</code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> digest<code style='color:#806030; '>.</code>num<code style='color:#806030; '>[</code>n<code style='color:#806030; '>]</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

ap_rputs<code style='color:#806030; '>(</code><code style='color:#800000; '>"</code><code style='color:#e60000; '>&lt;/code></code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> r<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/* Print a link to the MD5 version */</code>

ap_rputs<code style='color:#806030; '>(</code><code style='color:#800000; '>"</code><code style='color:#e60000; '>&lt;br/>&lt;a href='?digest=md5'>View the MD5 hash instead&lt;/a></code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> r<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

apr_file_close<code style='color:#806030; '>(</code>file<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

<code style='color:#c34e00; '>/* Let Apache know that we responded to this request. */</code>

<code style='color:#400000; font-weight:bold; '>return</code> OK<code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

</pre>

This version in its entirity can be found here:

<a href="http://people.apache.org/~humbedooh/mods/examples/mod_example_2.c">mod_example_2.c</a>.

</section>

</section>

<section id="configuration"><title>Adding configuration options</title>

<p>

In this next segment of this document, we will turn our eyes away from the

digest module and create a new example module, whose only function is to

write out its own configuration. The purpose of this is to examine how

Apache works with configuration, and what happens when you start writing

advanced configurations

for your modules.

</p>

<section id="config_intro"><title>An introduction to configuration

directives</title> If you are reading this, then you probably already know

what a configuration directive is. Simply put, a directive is a way of

telling an individual module (or a set of modules) how to behave, such as

these directives control how <code>mod_rewrite</code> works:

<example><pre>

RewriteEngine On

RewriteCond %{REQUEST_URI} ^/foo/bar

RewriteRule ^/foo/bar/(.*)$ /foobar?page=$1

</pre></example>

Each of these configuration directives are handled by a separate function,

that parses the parameters given and sets up a configuration accordingly.

</section>

<section id="config_simple"><title>Making an example configuration</title>

To begin with, we'll create a basic configuration in C-space:

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

<code style='color:#400000; font-weight:bold; '>typedef</code> <code style='color:#400000; font-weight:bold; '>struct</code> <code style='color:#806030; '>{</code>

<code style='color:#400000; font-weight:bold; '>int</code> enabled<code style='color:#806030; '>;</code> <code style='color:#c34e00; '>/* Enable or disable our module */</code>

<code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code> <code style='color:#806030; '>*</code>path<code style='color:#806030; '>;</code> <code style='color:#c34e00; '>/* Some path to...something */</code>

<code style='color:#400000; font-weight:bold; '>int</code> typeOfAction<code style='color:#806030; '>;</code> <code style='color:#c34e00; '>/* 1 means action A, 2 means action B and so on */</code>

<code style='color:#806030; '>}</code> example_config<code style='color:#806030; '>;</code>

</pre>

Now, let's put this into perspective by creating a very small module that

just prints out a hard-coded configuration. You'll notice that we use the

<code>register_hooks</code> function for initializing the configuration

values to their defaults:

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

<code style='color:#400000; font-weight:bold; '>typedef</code> <code style='color:#400000; font-weight:bold; '>struct</code> <code style='color:#806030; '>{</code>

<code style='color:#400000; font-weight:bold; '>int</code> enabled<code style='color:#806030; '>;</code> <code style='color:#c34e00; '>/* Enable or disable our module */</code>

<code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code> <code style='color:#806030; '>*</code>path<code style='color:#806030; '>;</code> <code style='color:#c34e00; '>/* Some path to...something */</code>

<code style='color:#400000; font-weight:bold; '>int</code> typeOfAction<code style='color:#806030; '>;</code> <code style='color:#c34e00; '>/* 1 means action A, 2 means action B and so on */</code>

<code style='color:#806030; '>}</code> example_config<code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>static</code> example_config config<code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>static</code> <code style='color:#400000; font-weight:bold; '>int</code> example_handler<code style='color:#806030; '>(</code>request_rec <code style='color:#806030; '>*</code>r<code style='color:#806030; '>)</code>

<code style='color:#806030; '>{</code>

<code style='color:#400000; font-weight:bold; '>if</code> <code style='color:#806030; '>(</code><code style='color:#806030; '>!</code>r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code><code style='color:#008833'>handler</code> <code style='color:#806030; '>|</code><code style='color:#806030; '>|</code> <code style='color:#800040; '>strcmp</code><code style='color:#806030; '>(</code>r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code><code style='color:#008833'>handler</code><code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>example-handler</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>)</code> <code style='color:#400000; font-weight:bold; '>return</code><code style='color:#806030; '>(</code>DECLINED<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

ap_set_content_type<code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>text/plain</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

ap_rprintf<code style='color:#806030; '>(r, </code><code style='color:#800000; '>"</code><code style='color:#e60000; '>Enabled: </code><code style='color:#0f6900; '>%u</code><code style='color:#0f6900; '>\n</code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> config<code style='color:#806030; '>.</code>enabled<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

ap_rprintf<code style='color:#806030; '>(r, </code><code style='color:#800000; '>"</code><code style='color:#e60000; '>Path: </code><code style='color:#0f6900; '>%s</code><code style='color:#0f6900; '>\n</code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> config<code style='color:#806030; '>.</code>path<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

ap_rprintf<code style='color:#806030; '>(r, </code><code style='color:#800000; '>"</code><code style='color:#e60000; '>TypeOfAction: </code><code style='color:#0f6900; '>%x</code><code style='color:#0f6900; '>\n</code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> config<code style='color:#806030; '>.</code>typeOfAction<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>return</code> OK<code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

<code style='color:#400000; font-weight:bold; '>static</code> <code style='color:#400000; font-weight:bold; '>void</code> register_hooks<code style='color:#806030; '>(</code>apr_pool_t <code style='color:#806030; '>*</code>pool<code style='color:#806030; '>)</code>

<code style='color:#806030; '>{</code>

config<code style='color:#806030; '>.</code>enabled <code style='color:#806030; '>=</code> <code style='color:#c00000; '>1</code><code style='color:#806030; '>;</code>

config<code style='color:#806030; '>.</code>path <code style='color:#806030; '>=</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>/foo/bar</code><code style='color:#800000; '>"</code><code style='color:#806030; '>;</code>

config<code style='color:#806030; '>.</code>typeOfAction <code style='color:#806030; '>=</code> <code style='color:#c00000; '>0x00</code><code style='color:#806030; '>;</code>

ap_hook_handler<code style='color:#806030; '>(</code>example_handler<code style='color:#806030; '>,</code> <code style='color:#007d45; '>NULL</code><code style='color:#806030; '>,</code> <code style='color:#007d45; '>NULL</code><code style='color:#806030; '>,</code> APR_HOOK_LAST<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

<code style='color:#c34e00; '>/* Define our module as an entity and assign a function for registering hooks */</code>

module AP_MODULE_DECLARE_DATA example_module <code style='color:#806030; '>=</code>

<code style='color:#806030; '>{</code>

STANDARD20_MODULE_STUFF<code style='color:#806030; '>,</code>

<code style='color:#007d45; '>NULL</code><code style='color:#806030; '>,</code> <code style='color:#c34e00; '>/* Per-directory configuration handler */</code>

<code style='color:#007d45; '>NULL</code><code style='color:#806030; '>,</code> <code style='color:#c34e00; '>/* Merge handler for per-directory configurations */</code>

<code style='color:#007d45; '>NULL</code><code style='color:#806030; '>,</code> <code style='color:#c34e00; '>/* Per-server configuration handler */</code>

<code style='color:#007d45; '>NULL</code><code style='color:#806030; '>,</code> <code style='color:#c34e00; '>/* Merge handler for per-server configurations */</code>

<code style='color:#007d45; '>NULL</code><code style='color:#806030; '>,</code> <code style='color:#c34e00; '>/* Any directives we may have for httpd */</code>

register_hooks <code style='color:#c34e00; '>/* Our hook registering function */</code>

<code style='color:#806030; '>}</code><code style='color:#806030; '>;</code>

</pre>

So far so good. To access our new handler, we could add the following to

our configuration:

<example><pre>

&lt;Location /example&gt;

SetHandler example-handler

&lt;/Location&gt;

</pre></example>

When we visit, we'll see our current configuration being spit out by our

module.

</section>

<section id="register_directive"><title>Registering directives with Apache</title>

What if we want to change our configuration, not by hard-coding new values

into the module, but by using either the httpd.conf file or possibly a

.htaccess file? It's time to let Apache know that we want this to be

possible. To do so, we must first change our <em>name tag</em> to include a

reference to the configuration directives we want to register with Apache:

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

module AP_MODULE_DECLARE_DATA example_module =

{

STANDARD20_MODULE_STUFF,

<code style='color:#7f0055; font-weight:bold; '>NULL</code>, <code style='color:#c34e00; '>/* Per-directory configuration handler */</code>

<code style='color:#7f0055; font-weight:bold; '>NULL</code>, <code style='color:#c34e00; '>/* Merge handler for per-directory configurations */</code>

<code style='color:#7f0055; font-weight:bold; '>NULL</code>, <code style='color:#c34e00; '>/* Per-server configuration handler */</code>

<code style='color:#7f0055; font-weight:bold; '>NULL</code>, <code style='color:#c34e00; '>/* Merge handler for per-server configurations */</code>

example_directives, <code style='color:#c34e00; '>/* Any directives we may have for httpd */</code>

register_hooks <code style='color:#c34e00; '>/* Our hook registering function */</code>

};

</pre>

This will tell Apache that we are now accepting directives from the

configuration files, and that the structure called <code>example_directives

</code> holds information on what our directives are and how they work.

Since we have three different variables in our module configuration, we

will add a structure with three directives and a NULL at the end:

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

static const command_rec example_directives[] =

{

<code style='color:#2e8800; '><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__CONFIG.html#ga07c7d22ae17805e61204463326cf9c34">AP_INIT_TAKE1</a></code>("exampleEnabled", example_set_enabled, <code style='color:#7f0055; font-weight:bold; '>NULL</code>, RSRC_CONF, "Enable or disable mod_example"),

<code style='color:#2e8800; '><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__CONFIG.html#ga07c7d22ae17805e61204463326cf9c34">AP_INIT_TAKE1</a></code>("examplePath", example_set_path, <code style='color:#7f0055; font-weight:bold; '>NULL</code>, RSRC_CONF, "The path to whatever"),

<code style='color:#2e8800; '><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__CONFIG.html#gafaec43534fcf200f37d9fecbf9247c21">AP_INIT_TAKE2</a></code>("exampleAction", example_set_action, <code style='color:#7f0055; font-weight:bold; '>NULL</code>, RSRC_CONF, "Special action value!"),

{ <code style='color:#7f0055; font-weight:bold; '>NULL</code> }

};

</pre>

<img src="/images/build_a_mod_4.png" border="1"/><br/>

<p>

As you can see, each directive needs at least 5 parameters set:

<ol>

<li><code><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__CONFIG.html#ga07c7d22ae17805e61204463326cf9c34">AP_INIT_TAKE1</a></code>: This is a macro that tells Apache that this directive takes one and only one argument.

If we required two arguments, we could use the macro <code><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__CONFIG.html#gafaec43534fcf200f37d9fecbf9247c21">AP_INIT_TAKE2</a></code> and so on (refer to httpd_conf.h

for more macros).</li>

<li><code>exampleEnabled</code>: This is the name of our directive. More precisely, it is what the user must put in his/her

configuration in order to invoke a configuration change in our module.</li>

<li><code>example_set_enabled</code>: This is a reference to a C function that parses the directive and sets the configuration

accordingly. We will discuss how to make this in the following paragraph.</li>

<li><code>RSRC_CONF</code>: This tells Apache where the directive is permissable. We'll go into details on this value in the

later chapters, but for now, <code>RSRC_CONF</code> means that Apache will only accept these directives in a server context.</li>

<li><code>"Enable or disable...."</code>: This is simply a brief description of what the directive does.</li>

</ol>

(<em>The "missing" parameter in our definition, which is usually set to

<code>NULL</code>, is an optional function that can be run after the

initial function to parse the arguments have been run. This is usually

omitted, as the function for verifying arguments might as well be used to

set them.</em>)

</p>

</section>

<section id="directive_handler"><title>The directive handler function</title>

<p>

Now that we've told Apache to expect some directives for our module, it's

time to make a few functions for handling these. What Apache reads in the

configuration file(s) is text, and so naturally, what it passes along to

our directive handler is one or more strings, that we ourselves need to

recognize and act upon. You'll notice, that since we set our <code>

exampleAction</code> directive to accept two arguments, its C function also

has an additional parameter defined:<br/>

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

<code style='color:#c34e00; '>/* Handler for the "exambleEnabled" directive */</code>

<code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code><code style='color:#806030; '> *</code>example_set_enabled<code style='color:#806030; '>(</code>cmd_parms <code style='color:#806030; '>*</code>cmd<code style='color:#806030; '>,</code> <code style='color:#400000; font-weight:bold; '>void</code> <code style='color:#806030; '>*</code>cfg<code style='color:#806030; '>,</code> <code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code> <code style='color:#806030; '>*</code>arg<code style='color:#806030; '>)</code>

<code style='color:#806030; '>{</code>

<code style='color:#400000; font-weight:bold; '>if</code><code style='color:#806030; '>(</code><code style='color:#806030; '>!</code>strcasecmp<code style='color:#806030; '>(</code>arg<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>on</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>)</code> config<code style='color:#806030; '>.</code>enabled <code style='color:#806030; '>=</code> <code style='color:#c00000; '>1</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>else</code> config<code style='color:#806030; '>.</code>enabled <code style='color:#806030; '>=</code> <code style='color:#c00000; '>0</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>return</code> <code style='color:#007d45; '>NULL</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

<code style='color:#c34e00; '>/* Handler for the "examplePath" directive */</code>

<code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code><code style='color:#806030; '> *</code>example_set_path<code style='color:#806030; '>(</code>cmd_parms <code style='color:#806030; '>*</code>cmd<code style='color:#806030; '>,</code> <code style='color:#400000; font-weight:bold; '>void</code> <code style='color:#806030; '>*</code>cfg<code style='color:#806030; '>,</code> <code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code> <code style='color:#806030; '>*</code>arg<code style='color:#806030; '>)</code>

<code style='color:#806030; '>{</code>

config<code style='color:#806030; '>.</code>path <code style='color:#806030; '>=</code> arg<code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>return</code> <code style='color:#007d45; '>NULL</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

<code style='color:#c34e00; '>/* Handler for the "exampleAction" directive */</code>

<code style='color:#c34e00; '>/* Let's pretend this one takes one argument (file or db), and a second (deny or allow), */</code>

<code style='color:#c34e00; '>/* and we store it in a bit-wise manner. */</code>

<code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code><code style='color:#806030; '> *</code>example_set_action<code style='color:#806030; '>(</code>cmd_parms <code style='color:#806030; '>*</code>cmd<code style='color:#806030; '>,</code> <code style='color:#400000; font-weight:bold; '>void</code> <code style='color:#806030; '>*</code>cfg<code style='color:#806030; '>,</code> <code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code> <code style='color:#806030; '>*</code>arg1<code style='color:#806030; '>,</code> <code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code><code style='color:#806030; '>*</code> arg2<code style='color:#806030; '>)</code>

<code style='color:#806030; '>{</code>

<code style='color:#400000; font-weight:bold; '>if</code><code style='color:#806030; '>(</code><code style='color:#806030; '>!</code>strcasecmp<code style='color:#806030; '>(</code>arg1<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>file</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>)</code> config<code style='color:#806030; '>.</code>typeOfAction <code style='color:#806030; '>=</code> <code style='color:#c00000; '>0x01</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>else</code> config<code style='color:#806030; '>.</code>typeOfAction <code style='color:#806030; '>=</code> <code style='color:#c00000; '>0x02</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>if</code><code style='color:#806030; '>(</code><code style='color:#806030; '>!</code>strcasecmp<code style='color:#806030; '>(</code>arg2<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>deny</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>)</code> config<code style='color:#806030; '>.</code>typeOfAction <code style='color:#806030; '>+</code><code style='color:#806030; '>=</code> <code style='color:#c00000; '>0x10</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>else</code> config<code style='color:#806030; '>.</code>typeOfAction <code style='color:#806030; '>+</code><code style='color:#806030; '>=</code> <code style='color:#c00000; '>0x20</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>return</code> <code style='color:#007d45; '>NULL</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

</pre>

</p>

</section>

<section id="directive_complete"><title>Putting it all together</title>

<p>

Now that we have our directives set up, and handlers configured for them,

we can assemble our module into one big file:

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

<code style='color:#c34e00; '>/* mod_example_config_simple.c: */</code>

<code style='color:#004a43; '>#</code><code style='color:#004a43; '>include </code><code style='color:#800000; '>&lt;</code><code style='color:#40015a; '>stdio.h</code><code style='color:#800000; '>></code>

<code style='color:#004a43; '>#</code><code style='color:#004a43; '>include </code><code style='color:#800000; '>"</code><code style='color:#40015a; '>apr_hash.h</code><code style='color:#800000; '>"</code>

<code style='color:#004a43; '>#</code><code style='color:#004a43; '>include </code><code style='color:#800000; '>"</code><code style='color:#40015a; '>ap_config.h</code><code style='color:#800000; '>"</code>

<code style='color:#004a43; '>#</code><code style='color:#004a43; '>include </code><code style='color:#800000; '>"</code><code style='color:#40015a; '>ap_provider.h</code><code style='color:#800000; '>"</code>

<code style='color:#004a43; '>#</code><code style='color:#004a43; '>include </code><code style='color:#800000; '>"</code><code style='color:#40015a; '>httpd.h</code><code style='color:#800000; '>"</code>

<code style='color:#004a43; '>#</code><code style='color:#004a43; '>include </code><code style='color:#800000; '>"</code><code style='color:#40015a; '>http_core.h</code><code style='color:#800000; '>"</code>

<code style='color:#004a43; '>#</code><code style='color:#004a43; '>include </code><code style='color:#800000; '>"</code><code style='color:#40015a; '>http_config.h</code><code style='color:#800000; '>"</code>

<code style='color:#004a43; '>#</code><code style='color:#004a43; '>include </code><code style='color:#800000; '>"</code><code style='color:#40015a; '>http_log.h</code><code style='color:#800000; '>"</code>

<code style='color:#004a43; '>#</code><code style='color:#004a43; '>include </code><code style='color:#800000; '>"</code><code style='color:#40015a; '>http_protocol.h</code><code style='color:#800000; '>"</code>

<code style='color:#004a43; '>#</code><code style='color:#004a43; '>include </code><code style='color:#800000; '>"</code><code style='color:#40015a; '>http_request.h</code><code style='color:#800000; '>"</code>

<code style='color:#c34e00; '>/*</code>

<code style='color:#c34e00; '>&#xa0;==============================================================================</code>

<code style='color:#c34e00; '>&#xa0;Our configuration prototype and declaration:</code>

<code style='color:#c34e00; '>&#xa0;==============================================================================</code>

<code style='color:#c34e00; '>&#xa0;*/</code>

<code style='color:#400000; font-weight:bold; '>typedef</code> <code style='color:#400000; font-weight:bold; '>struct</code> <code style='color:#806030; '>{</code>

<code style='color:#400000; font-weight:bold; '>int</code> enabled<code style='color:#806030; '>;</code> <code style='color:#c34e00; '>/* Enable or disable our module */</code>

<code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code> <code style='color:#806030; '>*</code>path<code style='color:#806030; '>;</code> <code style='color:#c34e00; '>/* Some path to...something */</code>

<code style='color:#400000; font-weight:bold; '>int</code> typeOfAction<code style='color:#806030; '>;</code> <code style='color:#c34e00; '>/* 1 means action A, 2 means action B and so on */</code>

<code style='color:#806030; '>}</code> example_config<code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>static</code> example_config config<code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/*</code>

<code style='color:#c34e00; '>&#xa0;==============================================================================</code>

<code style='color:#c34e00; '>&#xa0;Our directive handlers:</code>

<code style='color:#c34e00; '>&#xa0;==============================================================================</code>

<code style='color:#c34e00; '>&#xa0;*/</code>

<code style='color:#c34e00; '>/* Handler for the "exambleEnabled" directive */</code>

<code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code><code style='color:#806030; '> *</code>example_set_enabled<code style='color:#806030; '>(</code>cmd_parms <code style='color:#806030; '>*</code>cmd<code style='color:#806030; '>,</code> <code style='color:#400000; font-weight:bold; '>void</code> <code style='color:#806030; '>*</code>cfg<code style='color:#806030; '>,</code> <code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code> <code style='color:#806030; '>*</code>arg<code style='color:#806030; '>)</code>

<code style='color:#806030; '>{</code>

<code style='color:#400000; font-weight:bold; '>if</code><code style='color:#806030; '>(</code><code style='color:#806030; '>!</code>strcasecmp<code style='color:#806030; '>(</code>arg<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>on</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>)</code> config<code style='color:#806030; '>.</code>enabled <code style='color:#806030; '>=</code> <code style='color:#c00000; '>1</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>else</code> config<code style='color:#806030; '>.</code>enabled <code style='color:#806030; '>=</code> <code style='color:#c00000; '>0</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>return</code> <code style='color:#007d45; '>NULL</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

<code style='color:#c34e00; '>/* Handler for the "examplePath" directive */</code>

<code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code><code style='color:#806030; '> *</code>example_set_path<code style='color:#806030; '>(</code>cmd_parms <code style='color:#806030; '>*</code>cmd<code style='color:#806030; '>,</code> <code style='color:#400000; font-weight:bold; '>void</code> <code style='color:#806030; '>*</code>cfg<code style='color:#806030; '>,</code> <code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code> <code style='color:#806030; '>*</code>arg<code style='color:#806030; '>)</code>

<code style='color:#806030; '>{</code>

config<code style='color:#806030; '>.</code>path <code style='color:#806030; '>=</code> arg<code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>return</code> <code style='color:#007d45; '>NULL</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

<code style='color:#c34e00; '>/* Handler for the "exampleAction" directive */</code>

<code style='color:#c34e00; '>/* Let's pretend this one takes one argument (file or db), and a second (deny or allow), */</code>

<code style='color:#c34e00; '>/* and we store it in a bit-wise manner. */</code>

<code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code><code style='color:#806030; '> *</code>example_set_action<code style='color:#806030; '>(</code>cmd_parms <code style='color:#806030; '>*</code>cmd<code style='color:#806030; '>,</code> <code style='color:#400000; font-weight:bold; '>void</code> <code style='color:#806030; '>*</code>cfg<code style='color:#806030; '>,</code> <code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code> <code style='color:#806030; '>*</code>arg1<code style='color:#806030; '>,</code> <code style='color:#400000; font-weight:bold; '>const</code> <code style='color:#400000; font-weight:bold; '>char</code><code style='color:#806030; '>*</code> arg2<code style='color:#806030; '>)</code>

<code style='color:#806030; '>{</code>

<code style='color:#400000; font-weight:bold; '>if</code><code style='color:#806030; '>(</code><code style='color:#806030; '>!</code>strcasecmp<code style='color:#806030; '>(</code>arg1<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>file</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>)</code> config<code style='color:#806030; '>.</code>typeOfAction <code style='color:#806030; '>=</code> <code style='color:#c00000; '>0x01</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>else</code> config<code style='color:#806030; '>.</code>typeOfAction <code style='color:#806030; '>=</code> <code style='color:#c00000; '>0x02</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>if</code><code style='color:#806030; '>(</code><code style='color:#806030; '>!</code>strcasecmp<code style='color:#806030; '>(</code>arg2<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>deny</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>)</code> config<code style='color:#806030; '>.</code>typeOfAction <code style='color:#806030; '>+</code><code style='color:#806030; '>=</code> <code style='color:#c00000; '>0x10</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>else</code> config<code style='color:#806030; '>.</code>typeOfAction <code style='color:#806030; '>+</code><code style='color:#806030; '>=</code> <code style='color:#c00000; '>0x20</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>return</code> <code style='color:#007d45; '>NULL</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

<code style='color:#c34e00; '>/*</code>

<code style='color:#c34e00; '>&#xa0;==============================================================================</code>

<code style='color:#c34e00; '>&#xa0;The directive structure for our name tag:</code>

<code style='color:#c34e00; '>&#xa0;==============================================================================</code>

<code style='color:#c34e00; '>&#xa0;*/</code>

<code style='color:#400000; font-weight:bold; '>static</code> <code style='color:#400000; font-weight:bold; '>const</code> command_rec example_directives<code style='color:#806030; '>[</code><code style='color:#806030; '>]</code> <code style='color:#806030; '>=</code>

<code style='color:#806030; '>{</code>

<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__CONFIG.html#ga07c7d22ae17805e61204463326cf9c34">AP_INIT_TAKE1</a><code style='color:#806030; '>(</code><code style='color:#800000; '>"</code><code style='color:#e60000; '>exampleEnabled</code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> example_set_enabled<code style='color:#806030; '>,</code> <code style='color:#007d45; '>NULL</code><code style='color:#806030; '>,</code> RSRC_CONF<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>Enable or disable mod_example</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>,</code>

<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__CONFIG.html#ga07c7d22ae17805e61204463326cf9c34">AP_INIT_TAKE1</a><code style='color:#806030; '>(</code><code style='color:#800000; '>"</code><code style='color:#e60000; '>examplePath</code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> example_set_path<code style='color:#806030; '>,</code> <code style='color:#007d45; '>NULL</code><code style='color:#806030; '>,</code> RSRC_CONF<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>The path to whatever</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>,</code>

<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__CONFIG.html#gafaec43534fcf200f37d9fecbf9247c21">AP_INIT_TAKE2</a><code style='color:#806030; '>(</code><code style='color:#800000; '>"</code><code style='color:#e60000; '>exampleAction</code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> example_set_action<code style='color:#806030; '>,</code> <code style='color:#007d45; '>NULL</code><code style='color:#806030; '>,</code> RSRC_CONF<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>Special action value!</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>,</code>

<code style='color:#806030; '>{</code> <code style='color:#007d45; '>NULL</code> <code style='color:#806030; '>}</code>

<code style='color:#806030; '>}</code><code style='color:#806030; '>;</code>

<code style='color:#c34e00; '>/*</code>

<code style='color:#c34e00; '>&#xa0;==============================================================================</code>

<code style='color:#c34e00; '>&#xa0;Our module handler:</code>

<code style='color:#c34e00; '>&#xa0;==============================================================================</code>

<code style='color:#c34e00; '>&#xa0;*/</code>

<code style='color:#400000; font-weight:bold; '>static</code> <code style='color:#400000; font-weight:bold; '>int</code> example_handler<code style='color:#806030; '>(</code>request_rec <code style='color:#806030; '>*</code>r<code style='color:#806030; '>)</code>

<code style='color:#806030; '>{</code>

<code style='color:#400000; font-weight:bold; '>if</code><code style='color:#806030; '>(</code><code style='color:#806030; '>!</code>r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code><code style='color:#008833'>handler</code> <code style='color:#806030; '>|</code><code style='color:#806030; '>|</code> <code style='color:#800040; '>strcmp</code><code style='color:#806030; '>(</code>r<code style='color:#806030; '>-</code><code style='color:#806030; '>></code><code style='color:#008833'>handler</code><code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>example-handler</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>)</code> <code style='color:#400000; font-weight:bold; '>return</code><code style='color:#806030; '>(</code>DECLINED<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

ap_set_content_type<code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>text/plain</code><code style='color:#800000; '>"</code><code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

ap_rprintf<code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>Enabled: </code><code style='color:#0f6900; '>%u</code><code style='color:#0f6900; '>\n</code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> config<code style='color:#806030; '>.</code>enabled<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

ap_rprintf<code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>Path: </code><code style='color:#0f6900; '>%s</code><code style='color:#0f6900; '>\n</code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> config<code style='color:#806030; '>.</code>path<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

ap_rprintf<code style='color:#806030; '>(</code>r<code style='color:#806030; '>,</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>TypeOfAction: </code><code style='color:#0f6900; '>%x</code><code style='color:#0f6900; '>\n</code><code style='color:#800000; '>"</code><code style='color:#806030; '>,</code> config<code style='color:#806030; '>.</code>typeOfAction<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>return</code> OK<code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

<code style='color:#c34e00; '>/*</code>

<code style='color:#c34e00; '>&#xa0;==============================================================================</code>

<code style='color:#c34e00; '>&#xa0;The hook registration function (also initializes the default config values):</code>

<code style='color:#c34e00; '>&#xa0;==============================================================================</code>

<code style='color:#c34e00; '>&#xa0;*/</code>

<code style='color:#400000; font-weight:bold; '>static</code> <code style='color:#400000; font-weight:bold; '>void</code> register_hooks<code style='color:#806030; '>(</code>apr_pool_t <code style='color:#806030; '>*</code>pool<code style='color:#806030; '>)</code>

<code style='color:#806030; '>{</code>

config<code style='color:#806030; '>.</code>enabled <code style='color:#806030; '>=</code> <code style='color:#c00000; '>1</code><code style='color:#806030; '>;</code>

config<code style='color:#806030; '>.</code>path <code style='color:#806030; '>=</code> <code style='color:#800000; '>"</code><code style='color:#e60000; '>/foo/bar</code><code style='color:#800000; '>"</code><code style='color:#806030; '>;</code>

config<code style='color:#806030; '>.</code>typeOfAction <code style='color:#806030; '>=</code> <code style='color:#c00000; '>3</code><code style='color:#806030; '>;</code>

ap_hook_handler<code style='color:#806030; '>(</code>example_handler<code style='color:#806030; '>,</code> <code style='color:#007d45; '>NULL</code><code style='color:#806030; '>,</code> <code style='color:#007d45; '>NULL</code><code style='color:#806030; '>,</code> APR_HOOK_LAST<code style='color:#806030; '>)</code><code style='color:#806030; '>;</code>

<code style='color:#806030; '>}</code>

<code style='color:#c34e00; '>/*</code>

<code style='color:#c34e00; '>&#xa0;==============================================================================</code>

<code style='color:#c34e00; '>&#xa0;Our module name tag:</code>

<code style='color:#c34e00; '>&#xa0;==============================================================================</code>

<code style='color:#c34e00; '>&#xa0;*/</code>

module AP_MODULE_DECLARE_DATA example_module <code style='color:#806030; '>=</code>

<code style='color:#806030; '>{</code>

STANDARD20_MODULE_STUFF<code style='color:#806030; '>,</code>

<code style='color:#007d45; '>NULL</code><code style='color:#806030; '>,</code> <code style='color:#c34e00; '>/* Per-directory configuration handler */</code>

<code style='color:#007d45; '>NULL</code><code style='color:#806030; '>,</code> <code style='color:#c34e00; '>/* Merge handler for per-directory configurations */</code>

<code style='color:#007d45; '>NULL</code><code style='color:#806030; '>,</code> <code style='color:#c34e00; '>/* Per-server configuration handler */</code>

<code style='color:#007d45; '>NULL</code><code style='color:#806030; '>,</code> <code style='color:#c34e00; '>/* Merge handler for per-server configurations */</code>

example_directives<code style='color:#806030; '>,</code> <code style='color:#c34e00; '>/* Any directives we may have for httpd */</code>

register_hooks <code style='color:#c34e00; '>/* Our hook registering function */</code>

<code style='color:#806030; '>}</code><code style='color:#806030; '>;</code>

</pre>

</p>

<p>

In our httpd.conf file, we can now change the hard-coded configuration by

adding a few lines:

<example><pre>

ExampleEnabled On

ExamplePath "/usr/bin/foo"

ExampleAction file allow

</pre></example>

And thus we apply the configuration, visit <code>/example</code> on our

web site, and we see the configuration has adapted to what we wrote in our

configuration file.

</p>

</section>

</section>

<section id="context"><title>Context aware configurations</title>

<section id="context_intro"><title>Introduction to context aware configurations</title>

<p>

In Apache, different URLs, virtual hosts, directories etc can have very

different meanings to the user of Apache, and thus different contexts

within which modules must operate. For example, let's assume you have this

configuration set up for mod_rewrite:

<example><pre>

&lt;Directory &quot;/var/www&quot;&gt;

RewriteCond %{HTTP_HOST} ^example.com$

RewriteRule (.*) http://www.example.com/$1

&lt;/Directory&gt;

&lt;Directory &quot;/var/www/sub&quot;&gt;

RewriteRule ^foobar$ index.php?foobar=true

&lt;/Directory&gt;

</pre></example>

In this example, you will have set up two different contexts for

mod_rewrite:

<ol>

<li>Inside <code>/var/www</code>, all requests for <code>http://example.com</code> must go to <code>http://www.example.com</code></li>

<li>Inside <code>/var/www/sub</code>, all requests for <code>foobar</code> must go to <code>index.php?foobar=true</code></li>

</ol>

If mod_rewrite (or Apache for that matter) wasn't context aware, then

these rewrite rules would just apply to every and any request made,

regardless of where and how they were made, but since the module can pull

the context specific configuration straight from Apache, it does not need

to know itself, which of the directives are valid in this context, since

Apache takes care of this.</p>

<p>

So how does a module get the specific configuration for the server,

directory or location in question? It does so by making one simple call:

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

example_config *config = (example_config*) <a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__CONFIG.html#ga1093a5908a384eacc929b028c79f2a02">ap_get_module_config</a>(<code style='color:#008833'>r-&gt;per_dir_config</code>, &amp;example_module);

</pre>

That's it! Of course, a whole lot goes on behind the scenes, which we will

discuss in this chapter, starting with how Apache came to know what our

configuration looks like, and how it came to be set up as it is in the

specific context.

</p>

</section>

<section id="context_base"><title>Our basic configuration setup</title>

<p>In this chapter, we will be working with a slightly modified version of

our previous context structure. We will set a <code>context</code>

variable that we can use to track which context configuration is being

used by Apache in various places:

<pre style='color:#000000;background:#ffffef;border: 1px dashed #333; padding: 0.5em; margin: 1em 2em 1em 1em;'>

<code style='color:#400000; font-weight:bold; '>typedef</code> <code style='color:#400000; font-weight:bold; '>struct</code> <code style='color:#806030; '>{</code>

<code style='color:#400000; font-weight:bold; '>char</code> context<code style='color:#806030; '>[</code><code style='color:#c00000; '>256</code><code style='color:#806030; '>]</code><code style='color:#806030; '>;</code>

<code style='color:#400000; font-weight:bold; '>char</code> path<code style='color:#806030; '>[</code><code style='color:#c00000; '>256</code><code style='color:#806030; '>]</code><code style='color:#806030; '>;</code>