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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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+<title>Developing modules for the Apache HTTP Server 2.4 - Apache HTTP Server Version 2.4</title>
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+
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+<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="http://wiki.apache.org/httpd/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.png" /></div>
+<div class="up"><a href="./"><img title="&lt;-" alt="&lt;-" src="../images/left.gif" /></a></div>
+<div id="path">
+<a href="http://www.apache.org/">Apache</a> &gt; <a href="http://httpd.apache.org/">HTTP Server</a> &gt; <a href="http://httpd.apache.org/docs/">Documentation</a> &gt; <a href="../">Version 2.4</a> &gt; <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">&nbsp;en&nbsp;</a></p>
+</div>
+
+<p>This document explains how you can develop modules for the Apache HTTP
+Server 2.4</p>
+</div>
+<div id="quickview"><a href="https://www.apache.org/foundation/contributing.html" class="badge"><img src="https://www.apache.org/images/SupportApache-small.png" alt="Support Apache!" /></a><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 the server</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><li><a href="#comments_section">Comments</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 create modules for the Apache
+HTTP Server 2.4, 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
+writes 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 yourself 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 the Apache HTTP Server, 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:
+</p>
+<div class="example"><pre>apxs -i -a -c mod_example.c</pre></div>
+
+
+</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>
+<p>
+<img src="../images/build_a_mod_3.png" alt="Module name tags" /><br />
+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>:</p>
+
+
+
+<pre class="prettyprint lang-c">module AP_MODULE_DECLARE_DATA example_module =
+{
+ STANDARD20_MODULE_STUFF,
+ create_dir_conf, /* Per-directory configuration handler */
+ merge_dir_conf, /* Merge handler for per-directory configurations */
+ create_svr_conf, /* Per-server configuration handler */
+ merge_svr_conf, /* Merge handler for per-server configurations */
+ directives, /* Any directives we may have for httpd */
+ register_hooks /* Our hook registering function */
+};</pre>
+
+
+
+<p>
+This bit of code lets the server 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 primarily for two things:<br />
+</p>
+<ul>
+<li>Letting the server know how to load the module using the LoadModule</li>
+<li>Setting up a namespace for the module to use in configurations</li>
+</ul>
+<p>
+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:
+</p>
+<pre class="prettyprint lang-config">LoadModule example_module modules/mod_example.so</pre>
+
+<p>
+In essence, this tells the server 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 HTTP 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 the server</a></h2>
+<h3><a name="hook_intro" id="hook_intro">An introduction to hooks</a></h3>
+<p>
+When handling requests in Apache HTTP Server 2.4, the first thing you will need to do is
+create a hook into the request handling process. A hook is essentially a
+message telling the server 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 the server
+how and when each module will come into place. Thus, the server 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" alt="Hook handling in httpd" /><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, the server
+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
+the server to do just that:
+</p>
+<pre class="prettyprint lang-config">AddHandler example-handler .sum</pre>
+
+<p>
+What this tells the server 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, the server 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
+the server 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:</p>
+
+
+
+<pre class="prettyprint lang-c">module AP_MODULE_DECLARE_DATA example_module =
+{
+ STANDARD20_MODULE_STUFF,
+ NULL,
+ NULL,
+ NULL,
+ NULL,
+ NULL,
+ register_hooks /* Our hook registering function */
+};</pre>
+
+
+
+
+<p>This lets the server know that we are not interested 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 the server know that we want
+to hook into its process as one of the last modules:
+</p>
+
+
+<pre class="prettyprint lang-c">static void register_hooks(apr_pool_t *pool)
+{
+ /* Create a hook in the request handler, so we get called when a request arrives */
+ ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
+}</pre>
+
+
+
+<p>
+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:
+</p>
+<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 the server 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 the server has forked</li>
+<li><code>ap_hook_pre_translate_name</code>: Place a hook that executes when a URI needs to be translated into a filename on the server, before decoding</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>
+<li><code>ap_hook_quick_handler</code>: Similar to <code>ap_hook_handler</code>, except it is run before any other request hooks (translation, auth, fixups etc)</li>
+<li><code>ap_hook_log_transaction</code>: Place a hook that executes when the server is about to add a log entry of the current request</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="handling" id="handling">Building a handler</a></h2>
+<p>
+A handler is essentially a function that receives a callback when a request
+to the server 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 the server 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>
+<p>Let's start off by making a very simple request handler
+that does the following:
+</p>
+<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 the server know that we took care of this request and everything went fine</li>
+</ol>
+<p>
+In C code, our example handler will now look like this:
+</p>
+
+
+<pre class="prettyprint lang-c">static int example_handler(request_rec *r)
+{
+ /* First off, we need to check if this is a call for the "example-handler" handler.
+ * If it is, we accept it and do our things, if not, we simply return DECLINED,
+ * and the server will try somewhere else.
+ */
+ if (!r-&gt;handler || strcmp(r-&gt;handler, "example-handler")) return (DECLINED);
+
+ /* Now that we are handling this request, we'll write out "Hello, world!" to the client.
+ * To do so, we must first set the appropriate content type, followed by our output.
+ */
+ ap_set_content_type(r, "text/html");
+ ap_rprintf(r, "Hello, world!");
+
+ /* Lastly, we must tell the server that we took care of this request and everything went fine.
+ * We do so by simply returning the value OK to the server.
+ */
+ return OK;
+}</pre>
+
+
+
+<p>
+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>.
+</p>
+
+<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_rec* </code> structure passed along with every call that is made.
+This struct, typically just referred 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_rec </code> structure are:
+</p>
+<ul>
+<li><code>r-&gt;handler (char*):</code> Contains the name of the handler the server is currently asking to do the handling of this request</li>
+<li><code>r-&gt;method (char*):</code> Contains the HTTP method being used, f.x. GET or POST</li>
+<li><code>r-&gt;filename (char*):</code> Contains the translated filename the client is requesting</li>
+<li><code>r-&gt;args (char*):</code> Contains the query string of the request, if any</li>
+<li><code>r-&gt;headers_in (apr_table_t*):</code> Contains all the headers sent by the client</li>
+<li><code>r-&gt;connection (conn_rec*):</code> A record containing information about the current connection</li>
+<li><code>r-&gt;user (char*):</code> If the URI requires authentication, this is set to the username provided</li>
+<li><code>r-&gt;useragent_ip (char*):</code> The IP address of the client connecting to us</li>
+<li><code>r-&gt;pool (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>
+<p>
+A complete list of all the values contained within the <code>request_rec</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 />
+</p>
+
+
+<pre class="prettyprint lang-c">static int example_handler(request_rec *r)
+{
+ /* Set the appropriate content type */
+ ap_set_content_type(r, "text/html");
+
+ /* Print out the IP address of the client connecting to us: */
+ ap_rprintf(r, "&lt;h2&gt;Hello, %s!&lt;/h2&gt;", r-&gt;useragent_ip);
+
+ /* If we were reached through a GET or a POST request, be happy, else sad. */
+ if ( !strcmp(r-&gt;method, "POST") || !strcmp(r-&gt;method, "GET") ) {
+ ap_rputs("You used a GET or a POST method, that makes us happy!&lt;br/&gt;", r);
+ }
+ else {
+ ap_rputs("You did not use POST or GET, that makes us sad :(&lt;br/&gt;", r);
+ }
+
+ /* Lastly, if there was a query string, let's print that too! */
+ if (r-&gt;args) {
+ ap_rprintf(r, "Your query string was: %s", r-&gt;args);
+ }
+ return OK;
+}</pre>
+
+
+
+
+
+<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:
+</p>
+
+
+<pre class="prettyprint lang-c">static int example_handler(request_rec *r)
+{
+ /* Return 404: Not found */
+ return HTTP_NOT_FOUND;
+}</pre>
+
+
+
+<p>
+Returning <code>OK</code> or a HTTP status code does not necessarily mean
+that the request will end. The server 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 the server
+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>
+</p>
+<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 the server should just close this thread without further processing</li>
+</ul>
+<p>
+<strong>HTTP specific return codes (excerpt):</strong>
+</p>
+<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>
+
+
+<h3><a name="functions" id="functions">Some useful functions you should know</a></h3>
+
+<ul>
+<li>
+ <code>ap_rputs(const char *string, request_rec *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 class="prettyprint lang-c">ap_rputs("Hello, world!", r);</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 class="prettyprint lang-c">ap_rprintf(r, "Hello, %s!", r-&gt;useragent_ip);</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_rec *r, const char *type)</code>: <br />
+ Sets the content type of the output you are sending.
+
+
+
+<pre class="prettyprint lang-c">ap_set_content_type(r, "text/plain"); /* force a raw text output */</pre>
+
+
+
+</li>
+
+
+</ul>
+
+
+<h3><a name="memory" id="memory">Memory management</a></h3>
+<p>
+Managing your resources in Apache HTTP Server 2.4 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 primarily be allocating memory for each request, so
+it's appropriate to use the <code>r-&gt;pool</code>
+reference when creating new objects. A few of the functions for allocating
+memory within a pool are:
+</p>
+<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 the server supplies you with an appropriately allocated target variable</li>
+</ul>
+
+<p>Let's put these functions into an example handler:</p>
+
+
+
+<pre class="prettyprint lang-c">static int example_handler(request_rec *r)
+{
+ const char *original = "You can't edit this!";
+ char *copy;
+ int *integers;
+
+ /* Allocate space for 10 integer values and set them all to zero. */
+ integers = apr_pcalloc(r-&gt;pool, sizeof(int)*10);
+
+ /* Create a copy of the 'original' variable that we can edit. */
+ copy = apr_pstrdup(r-&gt;pool, original);
+ return OK;
+}</pre>
+
+
+
+<p>
+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:
+</p>
+
+
+<pre class="prettyprint lang-c">static void register_hooks(apr_pool_t *pool)
+{
+ /* Call a function that initializes some stuff */
+ example_init_function(pool);
+ /* Create a hook in the request handler, so we get called when a request arrives */
+ ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
+}</pre>
+
+
+
+<p>
+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 the server 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&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 HTTP Server 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:
+</p>
+
+
+
+<pre class="prettyprint lang-c">
+<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__apr__tables.html#gad7ea82d6608a4a633fc3775694ab71e4">apr_table_t</a> *GET; <em>
+</em><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/structapr__array__header__t.html">apr_array_header_t</a>*POST;
+<em>
+</em>
+<a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__SCRIPT.html#gaed25877b529623a4d8f99f819ba1b7bd">
+ap_args_to_table</a>(r, &amp;GET); <em>
+</em><a href="http://ci.apache.org/projects/httpd/trunk/doxygen/group__APACHE__CORE__DAEMON.html#ga9d426b6382b49754d4f87c55f65af202">
+ap_parse_form_data</a>(r, NULL, &amp;POST, -1, 8192);</pre>
+
+
+
+<p>
+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:
+</p>
+
+
+
+<pre class="prettyprint lang-c">/* Get the "digest" key from the query string, if any. */
+const char *digestType = apr_table_get(GET, "digest");
+
+/* If no key was returned, we will set a default value instead. */
+if (!digestType) digestType = "sha1";</pre>
+
+
+
+<p>
+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>
+<p>
+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:
+</p>
+
+
+
+<pre class="prettyprint lang-c">static int example_handler(request_rec *r)
+{
+ int rc, exists;
+ apr_finfo_t finfo;
+ apr_file_t *file;
+ char *filename;
+ char buffer[256];
+ apr_size_t readBytes;
+ int n;
+ apr_table_t *GET;
+ apr_array_header_t *POST;
+ const char *digestType;
+
+
+ /* Check that the "example-handler" handler is being called. */
+ if (!r-&gt;handler || strcmp(r-&gt;handler, "example-handler")) return (DECLINED);
+
+ /* Figure out which file is being requested by removing the .sum from it */
+ filename = apr_pstrdup(r-&gt;pool, r-&gt;filename);
+ filename[strlen(filename)-4] = 0; /* Cut off the last 4 characters. */
+
+ /* Figure out if the file we request a sum on exists and isn't a directory */
+ rc = apr_stat(&amp;finfo, filename, APR_FINFO_MIN, r-&gt;pool);
+ if (rc == APR_SUCCESS) {
+ exists =
+ (
+ (finfo.filetype != APR_NOFILE)
+ &amp;&amp; !(finfo.filetype &amp; APR_DIR)
+ );
+ if (!exists) return HTTP_NOT_FOUND; /* Return a 404 if not found. */
+ }
+ /* If apr_stat failed, we're probably not allowed to check this file. */
+ else return HTTP_FORBIDDEN;
+
+ /* Parse the GET and, optionally, the POST data sent to us */
+
+ ap_args_to_table(r, &amp;GET);
+ ap_parse_form_data(r, NULL, &amp;POST, -1, 8192);
+
+ /* Set the appropriate content type */
+ ap_set_content_type(r, "text/html");
+
+ /* Print a title and some general information */
+ ap_rprintf(r, "&lt;h2&gt;Information on %s:&lt;/h2&gt;", filename);
+ ap_rprintf(r, "&lt;b&gt;Size:&lt;/b&gt; %u bytes&lt;br/&gt;", finfo.size);
+
+ /* Get the digest type the client wants to see */
+ digestType = apr_table_get(GET, "digest");
+ if (!digestType) digestType = "MD5";
+
+
+ rc = apr_file_open(&amp;file, filename, APR_READ, APR_OS_DEFAULT, r-&gt;pool);
+ if (rc == APR_SUCCESS) {
+
+ /* Are we trying to calculate the MD5 or the SHA1 digest? */
+ if (!strcasecmp(digestType, "md5")) {
+ /* Calculate the MD5 sum of the file */
+ union {
+ char chr[16];
+ uint32_t num[4];
+ } digest;
+ apr_md5_ctx_t md5;
+ apr_md5_init(&amp;md5);
+ readBytes = 256;
+ while ( apr_file_read(file, buffer, &amp;readBytes) == APR_SUCCESS ) {
+ apr_md5_update(&amp;md5, buffer, readBytes);
+ }
+ apr_md5_final(digest.chr, &amp;md5);
+
+ /* Print out the MD5 digest */
+ ap_rputs("&lt;b&gt;MD5: &lt;/b&gt;&lt;code&gt;", r);
+ for (n = 0; n &lt; APR_MD5_DIGESTSIZE/4; n++) {
+ ap_rprintf(r, "%08x", digest.num[n]);
+ }
+ ap_rputs("&lt;/code&gt;", r);
+ /* Print a link to the SHA1 version */
+ ap_rputs("&lt;br/&gt;&lt;a href='?digest=sha1'&gt;View the SHA1 hash instead&lt;/a&gt;", r);
+ }
+ else {
+ /* Calculate the SHA1 sum of the file */
+ union {
+ char chr[20];
+ uint32_t num[5];
+ } digest;
+ apr_sha1_ctx_t sha1;
+ apr_sha1_init(&amp;sha1);
+ readBytes = 256;
+ while ( apr_file_read(file, buffer, &amp;readBytes) == APR_SUCCESS ) {
+ apr_sha1_update(&amp;sha1, buffer, readBytes);
+ }
+ apr_sha1_final(digest.chr, &amp;sha1);
+
+ /* Print out the SHA1 digest */
+ ap_rputs("&lt;b&gt;SHA1: &lt;/b&gt;&lt;code&gt;", r);
+ for (n = 0; n &lt; APR_SHA1_DIGESTSIZE/4; n++) {
+ ap_rprintf(r, "%08x", digest.num[n]);
+ }
+ ap_rputs("&lt;/code&gt;", r);
+
+ /* Print a link to the MD5 version */
+ ap_rputs("&lt;br/&gt;&lt;a href='?digest=md5'&gt;View the MD5 hash instead&lt;/a&gt;", r);
+ }
+ apr_file_close(file);
+
+ }
+ /* Let the server know that we responded to this request. */
+ return OK;
+}</pre>
+
+
+
+<p>
+This version in its entirety can be found here:
+<a href="http://people.apache.org/~humbedooh/mods/examples/mod_example_2.c">mod_example_2.c</a>.
+</p>
+
+
+</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
+the server 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>
+<p>
+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:
+</p>
+<pre class="prettyprint lang-config">RewriteEngine On
+RewriteCond "%{REQUEST_URI}" "^/foo/bar"
+RewriteRule "^/foo/bar/(.*)$" "/foobar?page=$1"</pre>
+
+<p>
+Each of these configuration directives are handled by a separate function,
+that parses the parameters given and sets up a configuration accordingly.
+</p>
+
+<h3><a name="config_simple" id="config_simple">Making an example configuration</a></h3>
+<p>To begin with, we'll create a basic configuration in C-space:</p>
+
+
+
+<pre class="prettyprint lang-c">typedef struct {
+ int enabled; /* Enable or disable our module */
+ const char *path; /* Some path to...something */
+ int typeOfAction; /* 1 means action A, 2 means action B and so on */
+} example_config;</pre>
+
+
+
+<p>
+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:
+</p>
+
+
+<pre class="prettyprint lang-c">typedef struct {
+ int enabled; /* Enable or disable our module */
+ const char *path; /* Some path to...something */
+ int typeOfAction; /* 1 means action A, 2 means action B and so on */
+} example_config;
+
+static example_config config;
+
+static int example_handler(request_rec *r)
+{
+ if (!r-&gt;handler || strcmp(r-&gt;handler, "example-handler")) return(DECLINED);
+ ap_set_content_type(r, "text/plain");
+ ap_rprintf(r, "Enabled: %u\n", config.enabled);
+ ap_rprintf(r, "Path: %s\n", config.path);
+ ap_rprintf(r, "TypeOfAction: %x\n", config.typeOfAction);
+ return OK;
+}
+
+static void register_hooks(apr_pool_t *pool)
+{
+ config.enabled = 1;
+ config.path = "/foo/bar";
+ config.typeOfAction = 0x00;
+ ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
+}
+
+/* Define our module as an entity and assign a function for registering hooks */
+
+module AP_MODULE_DECLARE_DATA example_module =
+{
+ STANDARD20_MODULE_STUFF,
+ NULL, /* Per-directory configuration handler */
+ NULL, /* Merge handler for per-directory configurations */
+ NULL, /* Per-server configuration handler */
+ NULL, /* Merge handler for per-server configurations */
+ NULL, /* Any directives we may have for httpd */
+ register_hooks /* Our hook registering function */
+};</pre>
+
+
+
+<p>
+So far so good. To access our new handler, we could add the following to
+our configuration:
+</p>
+<pre class="prettyprint lang-config">&lt;Location "/example"&gt;
+ SetHandler example-handler
+&lt;/Location&gt;</pre>
+
+<p>
+When we visit, we'll see our current configuration being spit out by our
+module.
+</p>
+
+
+<h3><a name="register_directive" id="register_directive">Registering directives with the server</a></h3>
+<p>
+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 the server 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 the server:
+</p>
+
+
+<pre class="prettyprint lang-c">module AP_MODULE_DECLARE_DATA example_module =
+{
+ STANDARD20_MODULE_STUFF,
+ NULL, /* Per-directory configuration handler */
+ NULL, /* Merge handler for per-directory configurations */
+ NULL, /* Per-server configuration handler */
+ NULL, /* Merge handler for per-server configurations */
+ example_directives, /* Any directives we may have for httpd */
+ register_hooks /* Our hook registering function */
+};</pre>
+
+
+
+<p>
+This will tell the server 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:
+</p>
+
+
+<pre class="prettyprint lang-c">static const command_rec example_directives[] =
+{
+ AP_INIT_TAKE1("exampleEnabled", example_set_enabled, NULL, RSRC_CONF, "Enable or disable mod_example"),
+ AP_INIT_TAKE1("examplePath", example_set_path, NULL, RSRC_CONF, "The path to whatever"),
+ AP_INIT_TAKE2("exampleAction", example_set_action, NULL, RSRC_CONF, "Special action value!"),
+ { NULL }
+};</pre>
+
+
+
+<p>
+<img src="../images/build_a_mod_4.png" alt="Directives structure" /><br />
+As you can see, each directive needs at least 5 parameters set:
+</p>
+<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 the server 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 the server where the directive is permitted. We'll go into details on this value in the
+later chapters, but for now, <code>RSRC_CONF</code> means that the server 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>
+<p>
+(<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 have told the server to expect some directives for our module, it's
+time to make a few functions for handling these. What the server 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:</p>
+
+
+<pre class="prettyprint lang-c">/* Handler for the "exampleEnabled" directive */
+const char *example_set_enabled(cmd_parms *cmd, void *cfg, const char *arg)
+{
+ if(!strcasecmp(arg, "on")) config.enabled = 1;
+ else config.enabled = 0;
+ return NULL;
+}
+
+/* Handler for the "examplePath" directive */
+const char *example_set_path(cmd_parms *cmd, void *cfg, const char *arg)
+{
+ config.path = arg;
+ return NULL;
+}
+
+/* Handler for the "exampleAction" directive */
+/* Let's pretend this one takes one argument (file or db), and a second (deny or allow), */
+/* and we store it in a bit-wise manner. */
+const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char *arg2)
+{
+ if(!strcasecmp(arg1, "file")) config.typeOfAction = 0x01;
+ else config.typeOfAction = 0x02;
+
+ if(!strcasecmp(arg2, "deny")) config.typeOfAction += 0x10;
+ else config.typeOfAction += 0x20;
+ return NULL;
+}</pre>
+
+
+
+
+
+<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:
+</p>
+
+
+<pre class="prettyprint lang-c">/* mod_example_config_simple.c: */
+#include &lt;stdio.h&gt;
+#include "apr_hash.h"
+#include "ap_config.h"
+#include "ap_provider.h"
+#include "httpd.h"
+#include "http_core.h"
+#include "http_config.h"
+#include "http_log.h"
+#include "http_protocol.h"
+#include "http_request.h"
+
+/*
+ ==============================================================================
+ Our configuration prototype and declaration:
+ ==============================================================================
+ */
+typedef struct {
+ int enabled; /* Enable or disable our module */
+ const char *path; /* Some path to...something */
+ int typeOfAction; /* 1 means action A, 2 means action B and so on */
+} example_config;
+
+static example_config config;
+
+/*
+ ==============================================================================
+ Our directive handlers:
+ ==============================================================================
+ */
+/* Handler for the "exampleEnabled" directive */
+const char *example_set_enabled(cmd_parms *cmd, void *cfg, const char *arg)
+{
+ if(!strcasecmp(arg, "on")) config.enabled = 1;
+ else config.enabled = 0;
+ return NULL;
+}
+
+/* Handler for the "examplePath" directive */
+const char *example_set_path(cmd_parms *cmd, void *cfg, const char *arg)
+{
+ config.path = arg;
+ return NULL;
+}
+
+/* Handler for the "exampleAction" directive */
+/* Let's pretend this one takes one argument (file or db), and a second (deny or allow), */
+/* and we store it in a bit-wise manner. */
+const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char *arg2)
+{
+ if(!strcasecmp(arg1, "file")) config.typeOfAction = 0x01;
+ else config.typeOfAction = 0x02;
+
+ if(!strcasecmp(arg2, "deny")) config.typeOfAction += 0x10;
+ else config.typeOfAction += 0x20;
+ return NULL;
+}
+
+/*
+ ==============================================================================
+ The directive structure for our name tag:
+ ==============================================================================
+ */
+static const command_rec example_directives[] =
+{
+ AP_INIT_TAKE1("exampleEnabled", example_set_enabled, NULL, RSRC_CONF, "Enable or disable mod_example"),
+ AP_INIT_TAKE1("examplePath", example_set_path, NULL, RSRC_CONF, "The path to whatever"),
+ AP_INIT_TAKE2("exampleAction", example_set_action, NULL, RSRC_CONF, "Special action value!"),
+ { NULL }
+};
+/*
+ ==============================================================================
+ Our module handler:
+ ==============================================================================
+ */
+static int example_handler(request_rec *r)
+{
+ if(!r-&gt;handler || strcmp(r-&gt;handler, "example-handler")) return(DECLINED);
+ ap_set_content_type(r, "text/plain");
+ ap_rprintf(r, "Enabled: %u\n", config.enabled);
+ ap_rprintf(r, "Path: %s\n", config.path);
+ ap_rprintf(r, "TypeOfAction: %x\n", config.typeOfAction);
+ return OK;
+}
+
+/*
+ ==============================================================================
+ The hook registration function (also initializes the default config values):
+ ==============================================================================
+ */
+static void register_hooks(apr_pool_t *pool)
+{
+ config.enabled = 1;
+ config.path = "/foo/bar";
+ config.typeOfAction = 3;
+ ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
+}
+/*
+ ==============================================================================
+ Our module name tag:
+ ==============================================================================
+ */
+module AP_MODULE_DECLARE_DATA example_module =
+{
+ STANDARD20_MODULE_STUFF,
+ NULL, /* Per-directory configuration handler */
+ NULL, /* Merge handler for per-directory configurations */
+ NULL, /* Per-server configuration handler */
+ NULL, /* Merge handler for per-server configurations */
+ example_directives, /* Any directives we may have for httpd */
+ register_hooks /* Our hook registering function */
+};</pre>
+
+
+
+
+<p>
+In our httpd.conf file, we can now change the hard-coded configuration by
+adding a few lines:
+</p>
+<pre class="prettyprint lang-config">ExampleEnabled On
+ExamplePath "/usr/bin/foo"
+ExampleAction file allow</pre>
+
+<p>
+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>
+
+
+
+</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="context" id="context">Context aware configurations</a></h2>
+<h3><a name="context_intro" id="context_intro">Introduction to context aware configurations</a></h3>
+<p>
+In Apache HTTP Server 2.4, different URLs, virtual hosts, directories etc can have very
+different meanings to the user of the server, and thus different contexts
+within which modules must operate. For example, let's assume you have this
+configuration set up for mod_rewrite:
+</p>
+<pre class="prettyprint lang-config">&lt;Directory "/var/www"&gt;
+ RewriteCond "%{HTTP_HOST}" "^example.com$"
+ RewriteRule "(.*)" "http://www.example.com/$1"
+&lt;/Directory&gt;
+&lt;Directory "/var/www/sub"&gt;
+ RewriteRule "^foobar$" "index.php?foobar=true"
+&lt;/Directory&gt;</pre>
+
+<p>
+In this example, you will have set up two different contexts for
+mod_rewrite:</p>
+<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>
+<p>
+If mod_rewrite (or the entire server 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 the server, it does not need
+to know itself, which of the directives are valid in this context, since
+the server 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:
+</p>
+
+
+<pre class="prettyprint lang-c">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>(r-&gt;per_dir_config, &amp;example_module);</pre>
+
+
+
+<p>
+That's it! Of course, a whole lot goes on behind the scenes, which we will
+discuss in this chapter, starting with how the server came to know what our
+configuration looks like, and how it came to be set up as it is in the
+specific context.
+</p>
+
+
+<h3><a name="context_base" id="context_base">Our basic configuration setup</a></h3>
+<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 the server in various places:
+</p>
+
+<pre class="prettyprint lang-c">typedef struct {
+ char context[256];
+ char path[256];
+ int typeOfAction;
+ int enabled;
+} example_config;</pre>
+
+
+
+<p>Our handler for requests will also be modified, yet still very simple:</p>
+
+
+
+<pre class="prettyprint lang-c">static int example_handler(request_rec *r)
+{
+ if(!r-&gt;handler || strcmp(r-&gt;handler, "example-handler")) return(DECLINED);
+ example_config *config = (example_config*) ap_get_module_config(r-&gt;per_dir_config, &amp;example_module);
+ ap_set_content_type(r, "text/plain");
+ ap_rprintf("Enabled: %u\n", config-&gt;enabled);
+ ap_rprintf("Path: %s\n", config-&gt;path);
+ ap_rprintf("TypeOfAction: %x\n", config-&gt;typeOfAction);
+ ap_rprintf("Context: %s\n", config-&gt;context);
+ return OK;
+}</pre>
+
+
+
+
+
+<h3><a name="context_which" id="context_which">Choosing a context</a></h3>
+<p>
+Before we can start making our module context aware, we must first define,
+which contexts we will accept. As we saw in the previous chapter, defining
+a directive required five elements be set:</p>
+
+
+
+<pre class="prettyprint lang-c">AP_INIT_TAKE1("exampleEnabled", example_set_enabled, NULL, RSRC_CONF, "Enable or disable mod_example"),</pre>
+
+
+
+
+<p>The <code>RSRC_CONF</code> definition told the server that we would only allow
+this directive in a global server context, but since we are now trying out
+a context aware version of our module, we should set this to something
+more lenient, namely the value <code>ACCESS_CONF</code>, which lets us use
+the directive inside &lt;Directory&gt; and &lt;Location&gt; blocks. For more
+control over the placement of your directives, you can combine the following
+restrictions together to form a specific rule:
+</p>
+<ul>
+<li><code>RSRC_CONF</code>: Allow in .conf files (not .htaccess) outside &lt;Directory&gt; or &lt;Location&gt;</li>
+<li><code>ACCESS_CONF</code>: Allow in .conf files (not .htaccess) inside &lt;Directory&gt; or &lt;Location&gt;</li>
+<li><code>OR_OPTIONS</code>: Allow in .conf files and .htaccess when <code>AllowOverride Options</code> is set</li>
+<li><code>OR_FILEINFO</code>: Allow in .conf files and .htaccess when <code>AllowOverride FileInfo</code> is set</li>
+<li><code>OR_AUTHCFG</code>: Allow in .conf files and .htaccess when <code>AllowOverride AuthConfig</code> is set</li>
+<li><code>OR_INDEXES</code>: Allow in .conf files and .htaccess when <code>AllowOverride Indexes</code> is set</li>
+<li><code>OR_ALL</code>: Allow anywhere in .conf files and .htaccess</li>
+</ul>
+
+
+<h3><a name="context_pool" id="context_pool">Using the server to allocate configuration slots</a></h3>
+<p> A much smarter way to manage your configurations is by letting the server
+help you create them. To do so, we must first start off by changing our
+<em>name tag</em> to let the server know, that it should assist us in creating
+and managing our configurations. Since we have chosen the per-directory
+(or per-location) context for our module configurations, we'll add a
+per-directory creator and merger function reference in our tag:</p>
+
+
+<pre class="prettyprint lang-c">module AP_MODULE_DECLARE_DATA example_module =
+{
+ STANDARD20_MODULE_STUFF,
+ create_dir_conf, /* Per-directory configuration handler */
+ merge_dir_conf, /* Merge handler for per-directory configurations */
+ NULL, /* Per-server configuration handler */
+ NULL, /* Merge handler for per-server configurations */
+ directives, /* Any directives we may have for httpd */
+ register_hooks /* Our hook registering function */
+};</pre>
+
+
+
+
+
+
+
+<h3><a name="context_new" id="context_new">Creating new context configurations</a></h3>
+<p>
+Now that we have told the server to help us create and manage configurations,
+our first step is to make a function for creating new, blank
+configurations. We do so by creating the function we just referenced in
+our name tag as the Per-directory configuration handler:</p>
+
+<pre class="prettyprint lang-c">void *create_dir_conf(apr_pool_t *pool, char *context) {
+ context = context ? context : "(undefined context)";
+ example_config *cfg = apr_pcalloc(pool, sizeof(example_config));
+ if(cfg) {
+ /* Set some default values */
+ strcpy(cfg-&gt;context, context);
+ cfg-&gt;enabled = 0;
+ cfg-&gt;path = "/foo/bar";
+ cfg-&gt;typeOfAction = 0x11;
+ }
+ return cfg;
+}</pre>
+
+
+
+
+
+
+<h3><a name="context_merge" id="context_merge">Merging configurations</a></h3>
+<p>
+Our next step in creating a context aware configuration is merging
+configurations. This part of the process particularly applies to scenarios
+where you have a parent configuration and a child, such as the following:
+</p>
+<pre class="prettyprint lang-config">&lt;Directory "/var/www"&gt;
+ ExampleEnabled On
+ ExamplePath "/foo/bar"
+ ExampleAction file allow
+&lt;/Directory&gt;
+&lt;Directory "/var/www/subdir"&gt;
+ ExampleAction file deny
+&lt;/Directory&gt;</pre>
+
+<p>
+In this example, it is natural to assume that the directory <code>
+/var/www/subdir</code> should inherit the values set for the <code>/var/www
+</code> directory, as we did not specify an <code>ExampleEnabled</code> nor
+an <code>ExamplePath</code> for this directory. The server does not presume to
+know if this is true, but cleverly does the following:
+</p>
+<ol>
+<li>Creates a new configuration for <code>/var/www</code></li>
+<li>Sets the configuration values according to the directives given for <code>/var/www</code></li>
+<li>Creates a new configuration for <code>/var/www/subdir</code></li>
+<li>Sets the configuration values according to the directives given for <code>/var/www/subdir</code></li>
+<li><strong>Proposes a merge</strong> of the two configurations into a new configuration for <code>/var/www/subdir</code></li>
+</ol>
+<p>
+This proposal is handled by the <code>merge_dir_conf</code> function we
+referenced in our name tag. The purpose of this function is to assess the
+two configurations and decide how they are to be merged:</p>
+
+
+
+<pre class="prettyprint lang-c">void *merge_dir_conf(apr_pool_t *pool, void *BASE, void *ADD) {
+ example_config *base = (example_config *) BASE ; /* This is what was set in the parent context */
+ example_config *add = (example_config *) ADD ; /* This is what is set in the new context */
+ example_config *conf = (example_config *) create_dir_conf(pool, "Merged configuration"); /* This will be the merged configuration */
+
+ /* Merge configurations */
+ conf-&gt;enabled = ( add-&gt;enabled == 0 ) ? base-&gt;enabled : add-&gt;enabled ;
+ conf-&gt;typeOfAction = add-&gt;typeOfAction ? add-&gt;typeOfAction : base-&gt;typeOfAction;
+ strcpy(conf-&gt;path, strlen(add-&gt;path) ? add-&gt;path : base-&gt;path);
+
+ return conf ;
+}</pre>
+
+
+
+
+
+
+<h3><a name="context_example" id="context_example">Trying out our new context aware configurations</a></h3>
+<p>
+Now, let's try putting it all together to create a new module that is
+context aware. First off, we'll create a configuration that lets us test
+how the module works:
+</p>
+<pre class="prettyprint lang-config">&lt;Location "/a"&gt;
+ SetHandler example-handler
+ ExampleEnabled on
+ ExamplePath "/foo/bar"
+ ExampleAction file allow
+&lt;/Location&gt;
+
+&lt;Location "/a/b"&gt;
+ ExampleAction file deny
+ ExampleEnabled off
+&lt;/Location&gt;
+
+&lt;Location "/a/b/c"&gt;
+ ExampleAction db deny
+ ExamplePath "/foo/bar/baz"
+ ExampleEnabled on
+&lt;/Location&gt;</pre>
+
+<p>
+Then we'll assemble our module code. Note, that since we are now using our
+name tag as reference when fetching configurations in our handler, I have
+added some prototypes to keep the compiler happy:
+</p>
+
+
+<pre class="prettyprint lang-c">/*$6
+ +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ * mod_example_config.c
+ +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ */
+
+
+#include &lt;stdio.h&gt;
+#include "apr_hash.h"
+#include "ap_config.h"
+#include "ap_provider.h"
+#include "httpd.h"
+#include "http_core.h"
+#include "http_config.h"
+#include "http_log.h"
+#include "http_protocol.h"
+#include "http_request.h"
+
+/*$1
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ Configuration structure
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ */
+
+typedef struct
+{
+ char context[256];
+ char path[256];
+ int typeOfAction;
+ int enabled;
+} example_config;
+
+/*$1
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ Prototypes
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ */
+
+static int example_handler(request_rec *r);
+const char *example_set_enabled(cmd_parms *cmd, void *cfg, const char *arg);
+const char *example_set_path(cmd_parms *cmd, void *cfg, const char *arg);
+const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char *arg2);
+void *create_dir_conf(apr_pool_t *pool, char *context);
+void *merge_dir_conf(apr_pool_t *pool, void *BASE, void *ADD);
+static void register_hooks(apr_pool_t *pool);
+
+/*$1
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ Configuration directives
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ */
+
+static const command_rec directives[] =
+{
+ AP_INIT_TAKE1("exampleEnabled", example_set_enabled, NULL, ACCESS_CONF, "Enable or disable mod_example"),
+ AP_INIT_TAKE1("examplePath", example_set_path, NULL, ACCESS_CONF, "The path to whatever"),
+ AP_INIT_TAKE2("exampleAction", example_set_action, NULL, ACCESS_CONF, "Special action value!"),
+ { NULL }
+};
+
+/*$1
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ Our name tag
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ */
+
+module AP_MODULE_DECLARE_DATA example_module =
+{
+ STANDARD20_MODULE_STUFF,
+ create_dir_conf, /* Per-directory configuration handler */
+ merge_dir_conf, /* Merge handler for per-directory configurations */
+ NULL, /* Per-server configuration handler */
+ NULL, /* Merge handler for per-server configurations */
+ directives, /* Any directives we may have for httpd */
+ register_hooks /* Our hook registering function */
+};
+
+/*
+ =======================================================================================================================
+ Hook registration function
+ =======================================================================================================================
+ */
+static void register_hooks(apr_pool_t *pool)
+{
+ ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
+}
+
+/*
+ =======================================================================================================================
+ Our example web service handler
+ =======================================================================================================================
+ */
+static int example_handler(request_rec *r)
+{
+ if(!r-&gt;handler || strcmp(r-&gt;handler, "example-handler")) return(DECLINED);
+
+ /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
+ example_config *config = (example_config *) ap_get_module_config(r-&gt;per_dir_config, &amp;example_module);
+ /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
+
+ ap_set_content_type(r, "text/plain");
+ ap_rprintf(r, "Enabled: %u\n", config-&gt;enabled);
+ ap_rprintf(r, "Path: %s\n", config-&gt;path);
+ ap_rprintf(r, "TypeOfAction: %x\n", config-&gt;typeOfAction);
+ ap_rprintf(r, "Context: %s\n", config-&gt;context);
+ return OK;
+}
+
+/*
+ =======================================================================================================================
+ Handler for the "exampleEnabled" directive
+ =======================================================================================================================
+ */
+const char *example_set_enabled(cmd_parms *cmd, void *cfg, const char *arg)
+{
+ /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
+ example_config *conf = (example_config *) cfg;
+ /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
+
+ if(conf)
+ {
+ if(!strcasecmp(arg, "on"))
+ conf-&gt;enabled = 1;
+ else
+ conf-&gt;enabled = 0;
+ }
+
+ return NULL;
+}
+
+/*
+ =======================================================================================================================
+ Handler for the "examplePath" directive
+ =======================================================================================================================
+ */
+const char *example_set_path(cmd_parms *cmd, void *cfg, const char *arg)
+{
+ /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
+ example_config *conf = (example_config *) cfg;
+ /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
+
+ if(conf)
+ {
+ strcpy(conf-&gt;path, arg);
+ }
+
+ return NULL;
+}
+
+/*
+ =======================================================================================================================
+ Handler for the "exampleAction" directive ;
+ Let's pretend this one takes one argument (file or db), and a second (deny or allow), ;
+ and we store it in a bit-wise manner.
+ =======================================================================================================================
+ */
+const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char *arg2)
+{
+ /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
+ example_config *conf = (example_config *) cfg;
+ /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
+
+ if(conf)
+ {
+ {
+ if(!strcasecmp(arg1, "file"))
+ conf-&gt;typeOfAction = 0x01;
+ else
+ conf-&gt;typeOfAction = 0x02;
+ if(!strcasecmp(arg2, "deny"))
+ conf-&gt;typeOfAction += 0x10;
+ else
+ conf-&gt;typeOfAction += 0x20;
+ }
+ }
+
+ return NULL;
+}
+
+/*
+ =======================================================================================================================
+ Function for creating new configurations for per-directory contexts
+ =======================================================================================================================
+ */
+void *create_dir_conf(apr_pool_t *pool, char *context)
+{
+ context = context ? context : "Newly created configuration";
+
+ /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
+ example_config *cfg = apr_pcalloc(pool, sizeof(example_config));
+ /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
+
+ if(cfg)
+ {
+ {
+ /* Set some default values */
+ strcpy(cfg-&gt;context, context);
+ cfg-&gt;enabled = 0;
+ memset(cfg-&gt;path, 0, 256);
+ cfg-&gt;typeOfAction = 0x00;
+ }
+ }
+
+ return cfg;
+}
+
+/*
+ =======================================================================================================================
+ Merging function for configurations
+ =======================================================================================================================
+ */
+void *merge_dir_conf(apr_pool_t *pool, void *BASE, void *ADD)
+{
+ /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
+ example_config *base = (example_config *) BASE;
+ example_config *add = (example_config *) ADD;
+ example_config *conf = (example_config *) create_dir_conf(pool, "Merged configuration");
+ /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
+
+ conf-&gt;enabled = (add-&gt;enabled == 0) ? base-&gt;enabled : add-&gt;enabled;
+ conf-&gt;typeOfAction = add-&gt;typeOfAction ? add-&gt;typeOfAction : base-&gt;typeOfAction;
+ strcpy(conf-&gt;path, strlen(add-&gt;path) ? add-&gt;path : base-&gt;path);
+ return conf;
+}</pre>
+
+
+
+
+
+
+
+</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="summary" id="summary">Summing up</a></h2>
+<p>
+We have now looked at how to create simple modules for Apache HTTP Server 2.4 and
+configuring them. What you do next is entirely up to you, but it is my
+hope that something valuable has come out of reading this documentation.
+If you have questions on how to further develop modules, you are welcome
+to join our <a href="http://httpd.apache.org/lists.html">mailing lists</a>
+or check out the rest of our documentation for further tips.
+</p>
+</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="section">
+<h2><a name="snippets" id="snippets">Some useful snippets of code</a></h2>
+
+<h3><a name="get_post" id="get_post">Retrieve variables from POST form data</a></h3>
+
+
+
+<pre class="prettyprint lang-c">typedef struct {
+ const char *key;
+ const char *value;
+} keyValuePair;
+
+keyValuePair *readPost(request_rec *r) {
+ apr_array_header_t *pairs = NULL;
+ apr_off_t len;
+ apr_size_t size;
+ int res;
+ int i = 0;
+ char *buffer;
+ keyValuePair *kvp;
+
+ res = ap_parse_form_data(r, NULL, &amp;pairs, -1, HUGE_STRING_LEN);
+ if (res != OK || !pairs) return NULL; /* Return NULL if we failed or if there are is no POST data */
+ kvp = apr_pcalloc(r-&gt;pool, sizeof(keyValuePair) * (pairs-&gt;nelts + 1));
+ while (pairs &amp;&amp; !apr_is_empty_array(pairs)) {
+ ap_form_pair_t *pair = (ap_form_pair_t *) apr_array_pop(pairs);
+ apr_brigade_length(pair-&gt;value, 1, &amp;len);
+ size = (apr_size_t) len;
+ buffer = apr_palloc(r-&gt;pool, size + 1);
+ apr_brigade_flatten(pair-&gt;value, buffer, &amp;size);
+ buffer[len] = 0;
+ kvp[i].key = apr_pstrdup(r-&gt;pool, pair-&gt;name);
+ kvp[i].value = buffer;
+ i++;
+ }
+ return kvp;
+}
+
+static int example_handler(request_rec *r)
+{
+ /*~~~~~~~~~~~~~~~~~~~~~~*/
+ keyValuePair *formData;
+ /*~~~~~~~~~~~~~~~~~~~~~~*/
+
+ formData = readPost(r);
+ if (formData) {
+ int i;
+ for (i = 0; &amp;formData[i]; i++) {
+ if (formData[i].key &amp;&amp; formData[i].value) {
+ ap_rprintf(r, "%s = %s\n", formData[i].key, formData[i].value);
+ } else if (formData[i].key) {
+ ap_rprintf(r, "%s\n", formData[i].key);
+ } else if (formData[i].value) {
+ ap_rprintf(r, "= %s\n", formData[i].value);
+ } else {
+ break;
+ }
+ }
+ }
+ return OK;
+}</pre>
+
+
+
+
+
+
+ <h3><a name="headers_out" id="headers_out">Printing out every HTTP header received</a></h3>
+
+
+
+<pre class="prettyprint lang-c">static int example_handler(request_rec *r)
+{
+ /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
+ const apr_array_header_t *fields;
+ int i;
+ apr_table_entry_t *e = 0;
+ /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
+
+ fields = apr_table_elts(r-&gt;headers_in);
+ e = (apr_table_entry_t *) fields-&gt;elts;
+ for(i = 0; i &lt; fields-&gt;nelts; i++) {
+ ap_rprintf(r, "%s: %s\n", e[i].key, e[i].val);
+ }
+ return OK;
+}</pre>
+
+
+
+
+
+
+ <h3><a name="request_body" id="request_body">Reading the request body into memory</a></h3>
+
+
+
+<pre class="prettyprint lang-c">static int util_read(request_rec *r, const char **rbuf, apr_off_t *size)
+{
+ /*~~~~~~~~*/
+ int rc = OK;
+ /*~~~~~~~~*/
+
+ if((rc = ap_setup_client_block(r, REQUEST_CHUNKED_ERROR))) {
+ return(rc);
+ }
+
+ if(ap_should_client_block(r)) {
+
+ /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
+ char argsbuffer[HUGE_STRING_LEN];
+ apr_off_t rsize, len_read, rpos = 0;
+ apr_off_t length = r-&gt;remaining;
+ /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
+
+ *rbuf = (const char *) apr_pcalloc(r-&gt;pool, (apr_size_t) (length + 1));
+ *size = length;
+ while((len_read = ap_get_client_block(r, argsbuffer, sizeof(argsbuffer))) &gt; 0) {
+ if((rpos + len_read) &gt; length) {
+ rsize = length - rpos;
+ }
+ else {
+ rsize = len_read;
+ }
+
+ memcpy((char *) *rbuf + rpos, argsbuffer, (size_t) rsize);
+ rpos += rsize;
+ }
+ }
+ return(rc);
+}
+
+static int example_handler(request_rec *r)
+{
+ /*~~~~~~~~~~~~~~~~*/
+ apr_off_t size;
+ const char *buffer;
+ /*~~~~~~~~~~~~~~~~*/
+
+ if(util_read(r, &amp;buffer, &amp;size) == OK) {
+ ap_rprintf(r, "We read a request body that was %" APR_OFF_T_FMT " bytes long", size);
+ }
+ return OK;
+}</pre>
+
+
+
+
+
+
+
+</div></div>
+<div class="bottomlang">
+<p><span>Available Languages: </span><a href="../en/developer/modguide.html" title="English">&nbsp;en&nbsp;</a></p>
+</div><div class="top"><a href="#page-header"><img src="../images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&amp;A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Libera.chat, or sent to our <a href="https://httpd.apache.org/lists.html">mailing lists</a>.</div>
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