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+<?xml version="1.0" encoding="ISO-8859-1"?>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!--
+ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
+ This file is generated from xml source: DO NOT EDIT
+ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
+ -->
+<title>Developing modules for the Apache HTTP Server 2.4 - Apache HTTP Server</title>
+<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
+<link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
+<link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" />
+<link href="../images/favicon.ico" rel="shortcut icon" /></head>
+<body id="manual-page"><div id="page-header">
+<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
+<p class="apache">Apache HTTP Server Version 2.4</p>
+<img alt="" src="../images/feather.gif" /></div>
+<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
+<div id="path">
+<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.4</a> > <a href="./">Developer</a></div><div id="page-content"><div id="preamble"><h1>Developing modules for the Apache HTTP Server 2.4</h1>
+<div class="toplang">
+<p><span>Available Languages: </span><a href="../en/developer/modguide.html" title="English"> en </a></p>
+</div>
+
+<p>This document explains how you can develop modules for the Apache HTTP
+Server 2.4</p>
+</div>
+<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#introduction">Introduction</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#basics">Defining a module</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#hooking">Getting started: Hooking into Apache</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#handling">Building a handler</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#configuration">Adding configuration options</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#context">Context aware configurations</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#summary">Summing up</a></li>
+<li><img alt="" src="../images/down.gif" /> <a href="#snippets">Some useful snippets of code</a></li>
+</ul><h3>See also</h3><ul class="seealso"><li><a href="request.html">Request Processing in Apache 2.4</a></li><li><a href="hooks.html">Apache 2.x Hook Functions</a></li></ul></div>
+<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="introduction" id="introduction">Introduction</a></h2>
+<h3><a name="what" id="what">What we will be discussing in this document</a></h3>
+<p>
+This document will discuss how you can easily create modules for the Apache
+HTTP Server 2.4 ("Apache"), 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>
+
+<h3><a name="prerequisites" id="prerequisites">Prerequisites</a></h3>
+<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>
+
+<h3><a name="compiling" id="compiling">Compiling your module</a></h3>
+<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:
+<div class="example"><pre>
+apxs -i -a -c mod_example.c
+</pre></div>
+</p>
+
+</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="basics" id="basics">Defining a module</a></h2>
+<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 />
+<div class="example"><pre><a href="../mod/mod_so.html#LoadModule">LoadModule</a> example_module modules/mod_example.so</pre></div>
+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>
+</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="hooking" id="hooking">Getting started: Hooking into Apache</a></h2>
+<h3><a name="hook_intro" id="hook_intro">An introduction to hooks</a></h3>
+<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 <code class="directive"><a href="../mod/mod_mime.html#addhandler">AddHandler</a></code>
+and <code class="directive"><a href="../mod/core.html#sethandler">SetHandler</a></code>. Let's take a look at
+an example using <code class="directive"><a href="../mod/mod_mime.html#addhandler">AddHandler</a></code>. 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:
+<div class="example"><pre>
+AddHandler example-handler .sum
+</pre></div>
+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 "example-handler" </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 "example-handler
+". 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>
+
+<h3><a name="hook_declaration" id="hook_declaration">Hooking into httpd</a></h3>
+<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>
+
+<h3><a name="hook_others" id="hook_others">Other useful hooks</a></h3>
+<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>
+
+</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="handling" id="handling">Building a handler</a></h2>
+<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>
+<h3><a name="simple_handler" id="simple_handler">A simple "Hello, world!"
+handler</a></h3> 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 "example-handler"</li>
+<li>Set the content type of our output to <code>text/html</code></li>
+<li>Write "Hello, world!" 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; "> * If it is, we accept it and do our things, if not, we simply return DECLINED,</code>
+<code style="color:#c34e00; "> * and Apache will try somewhere else.</code>
+<code style="color:#c34e00; "> */</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; "> * To do so, we must first set the appropriate content type, followed by our output.</code>
+<code style="color:#c34e00; "> */</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; "> * We do so by simply returning the value OK to Apache.</code>
+<code style="color:#c34e00; "> */</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">"Some useful functions you should know"</a>
+. <h3><a name="request_rec" id="request_rec">The request_rec structure
+</a></h3> <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->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->method</code> (char*)</code>: Contains the HTTP method being used, f.x. GET or POST</li>
+<li><code><code style="color:#008833">r->filename</code> (char*)</code>: Contains the translated filename the client is requesting</li>
+<li><code><code style="color:#008833">r->args</code> (char*)</code>: Contains the query string of the request, if any</li>
+<li><code><code style="color:#008833">r->headers_in</code> (apr_table_t*)</code>: Contains all the headers sent by the client</li>
+<li><code><code style="color:#008833">r->connection</code> (conn_rec*)</code>: A record containing information about the current connection</li>
+<li><code><code style="color:#008833">r->useragent_ip</code> (char*)</code>: The IP address of the client connecting to us</li>
+<li><code><code style="color:#008833">r->pool</code> (apr_pool_t*)</code>: The memory pool of this request. We'll discuss this in the "
+<a href="#memory">Memory management</a>" 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; "><h2>Hello, </code><code style="color:#0f6900; ">%s</code><code style="color:#e60000; ">!</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!<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 :(<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>
+
+
+<h3><a name="return_value" id="return_value">Return values</a></h3>
+<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>
+
+
+<h3><a name="functions" id="functions">Some useful functions you should know</a></h3>
+
+<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>
+
+
+<h3><a name="memory" id="memory">Memory management</a></h3>
+<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->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>
+
+
+<h3><a name="parsing" id="parsing">Parsing request data</a></h3>
+<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&valueB=no&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, &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>, &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>
+
+
+<h3><a name="advanced_handler" id="advanced_handler">Making an advanced handler</a></h3>
+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; ">&</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; ">&</code><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> 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; ">&</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; ">&</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; "><h2>Information on </code><code style="color:#0f6900; ">%s</code><code style="color:#e60000; ">:</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; "><b>Size:</b> </code><code style="color:#0f6900; ">%u</code><code style="color:#e60000; "> bytes<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; ">&</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; ">&</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; ">&</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; ">&</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; ">&</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; "><b>MD5: </b><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; "><</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; "></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; "><br/><a href='?digest=sha1'>View the SHA1 hash instead</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; ">&</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; ">&</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; ">&</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; ">&</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; "><b>SHA1: </b><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; "><</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; "></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; "><br/><a href='?digest=md5'>View the MD5 hash instead</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>.
+
+
+</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="configuration" id="configuration">Adding configuration options</a></h2>
+<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>
+<h3><a name="config_intro" id="config_intro">An introduction to configuration
+directives</a></h3> 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:
+<div class="example"><pre>
+RewriteEngine On
+RewriteCond %{REQUEST_URI} ^/foo/bar
+RewriteRule ^/foo/bar/(.*)$ /foobar?page=$1
+</pre></div>
+Each of these configuration directives are handled by a separate function,
+that parses the parameters given and sets up a configuration accordingly.
+
+<h3><a name="config_simple" id="config_simple">Making an example configuration</a></h3>
+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:
+<div class="example"><pre>
+<Location /example>
+ SetHandler example-handler
+</Location>
+</pre></div>
+When we visit, we'll see our current configuration being spit out by our
+module.
+
+
+<h3><a name="register_directive" id="register_directive">Registering directives with Apache</a></h3>
+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>
+
+<h3><a name="directive_handler" id="directive_handler">The directive handler function</a></h3>
+<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>
+
+<h3><a name="directive_complete" id="directive_complete">Putting it all together</a></h3>
+<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; "><</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; "> ==============================================================================</code>
+<code style="color:#c34e00; "> Our configuration prototype and declaration:</code>
+<code style="color:#c34e00; "> ==============================================================================</code>
+<code style="color:#c34e00; "> */</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>
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