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| author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-08 19:09:22 +0000 |
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| committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-08 19:09:22 +0000 |
| commit | 2faa747e2303ee774a4b4aace961188e950e185a (patch) | |
| tree | 604e79c7481956ce48f458e3546eaf1090b3ffff /docs/manual/developer/modguide.html.en | |
| parent | Initial commit. (diff) | |
| download | apache2-2faa747e2303ee774a4b4aace961188e950e185a.tar.xz apache2-2faa747e2303ee774a4b4aace961188e950e185a.zip | |
Adding upstream version 2.4.58.upstream/2.4.58
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'docs/manual/developer/modguide.html.en')
| -rw-r--r-- | docs/manual/developer/modguide.html.en | 1739 |
1 files changed, 1739 insertions, 0 deletions
diff --git a/docs/manual/developer/modguide.html.en b/docs/manual/developer/modguide.html.en new file mode 100644 index 0000000..3ac127e --- /dev/null +++ b/docs/manual/developer/modguide.html.en @@ -0,0 +1,1739 @@ +<?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"> +<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head> +<meta content="text/html; charset=UTF-8" http-equiv="Content-Type" /> +<!-- + 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 Version 2.4</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 rel="stylesheet" type="text/css" href="../style/css/prettify.css" /> +<script src="../style/scripts/prettify.min.js" type="text/javascript"> +</script> + +<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="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="<-" 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"><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->handler || strcmp(r->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->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->method (char*):</code> Contains the HTTP method being used, f.x. GET or POST</li> +<li><code>r->filename (char*):</code> Contains the translated filename the client is requesting</li> +<li><code>r->args (char*):</code> Contains the query string of the request, if any</li> +<li><code>r->headers_in (apr_table_t*):</code> Contains all the headers sent by the client</li> +<li><code>r->connection (conn_rec*):</code> A record containing information about the current connection</li> +<li><code>r->user (char*):</code> If the URI requires authentication, this is set to the username provided</li> +<li><code>r->useragent_ip (char*):</code> The IP address of the client connecting to us</li> +<li><code>r->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, "<h2>Hello, %s!</h2>", r->useragent_ip); + + /* If we were reached through a GET or a POST request, be happy, else sad. */ + if ( !strcmp(r->method, "POST") || !strcmp(r->method, "GET") ) { + ap_rputs("You used a GET or a POST method, that makes us happy!<br/>", r); + } + else { + ap_rputs("You did not use POST or GET, that makes us sad :(<br/>", r); + } + + /* Lastly, if there was a query string, let's print that too! */ + if (r->args) { + ap_rprintf(r, "Your query string was: %s", r->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->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->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->pool, sizeof(int)*10); + + /* Create a copy of the 'original' variable that we can edit. */ + copy = apr_pstrdup(r->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&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 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, &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, &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->handler || strcmp(r->handler, "example-handler")) return (DECLINED); + + /* Figure out which file is being requested by removing the .sum from it */ + filename = apr_pstrdup(r->pool, r->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(&finfo, filename, APR_FINFO_MIN, r->pool); + if (rc == APR_SUCCESS) { + exists = + ( + (finfo.filetype != APR_NOFILE) + && !(finfo.filetype & 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, &GET); + ap_parse_form_data(r, NULL, &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, "<h2>Information on %s:</h2>", filename); + ap_rprintf(r, "<b>Size:</b> %u bytes<br/>", 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(&file, filename, APR_READ, APR_OS_DEFAULT, r->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(&md5); + readBytes = 256; + while ( apr_file_read(file, buffer, &readBytes) == APR_SUCCESS ) { + apr_md5_update(&md5, buffer, readBytes); + } + apr_md5_final(digest.chr, &md5); + + /* Print out the MD5 digest */ + ap_rputs("<b>MD5: </b><code>", r); + for (n = 0; n < APR_MD5_DIGESTSIZE/4; n++) { + ap_rprintf(r, "%08x", digest.num[n]); + } + ap_rputs("</code>", r); + /* Print a link to the SHA1 version */ + ap_rputs("<br/><a href='?digest=sha1'>View the SHA1 hash instead</a>", 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(&sha1); + readBytes = 256; + while ( apr_file_read(file, buffer, &readBytes) == APR_SUCCESS ) { + apr_sha1_update(&sha1, buffer, readBytes); + } + apr_sha1_final(digest.chr, &sha1); + + /* Print out the SHA1 digest */ + ap_rputs("<b>SHA1: </b><code>", r); + for (n = 0; n < APR_SHA1_DIGESTSIZE/4; n++) { + ap_rprintf(r, "%08x", digest.num[n]); + } + ap_rputs("</code>", r); + + /* Print a link to the MD5 version */ + ap_rputs("<br/><a href='?digest=md5'>View the MD5 hash instead</a>", 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->handler || strcmp(r->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"><Location "/example"> + SetHandler example-handler +</Location></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 <stdio.h> +#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->handler || strcmp(r->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"><Directory "/var/www"> + RewriteCond "%{HTTP_HOST}" "^example.com$" + RewriteRule "(.*)" "http://www.example.com/$1" +</Directory> +<Directory "/var/www/sub"> + RewriteRule "^foobar$" "index.php?foobar=true" +</Directory></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->per_dir_config, &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->handler || strcmp(r->handler, "example-handler")) return(DECLINED); + example_config *config = (example_config*) ap_get_module_config(r->per_dir_config, &example_module); + ap_set_content_type(r, "text/plain"); + ap_rprintf("Enabled: %u\n", config->enabled); + ap_rprintf("Path: %s\n", config->path); + ap_rprintf("TypeOfAction: %x\n", config->typeOfAction); + ap_rprintf("Context: %s\n", config->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 <Directory> and <Location> 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 <Directory> or <Location></li> +<li><code>ACCESS_CONF</code>: Allow in .conf files (not .htaccess) inside <Directory> or <Location></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->context, context); + cfg->enabled = 0; + cfg->path = "/foo/bar"; + cfg->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"><Directory "/var/www"> + ExampleEnabled On + ExamplePath "/foo/bar" + ExampleAction file allow +</Directory> +<Directory "/var/www/subdir"> + ExampleAction file deny +</Directory></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->enabled = ( add->enabled == 0 ) ? base->enabled : add->enabled ; + conf->typeOfAction = add->typeOfAction ? add->typeOfAction : base->typeOfAction; + strcpy(conf->path, strlen(add->path) ? add->path : base->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"><Location "/a"> + SetHandler example-handler + ExampleEnabled on + ExamplePath "/foo/bar" + ExampleAction file allow +</Location> + +<Location "/a/b"> + ExampleAction file deny + ExampleEnabled off +</Location> + +<Location "/a/b/c"> + ExampleAction db deny + ExamplePath "/foo/bar/baz" + ExampleEnabled on +</Location></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 <stdio.h> +#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->handler || strcmp(r->handler, "example-handler")) return(DECLINED); + + /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/ + example_config *config = (example_config *) ap_get_module_config(r->per_dir_config, &example_module); + /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/ + + 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); + ap_rprintf(r, "Context: %s\n", config->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->enabled = 1; + else + conf->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->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->typeOfAction = 0x01; + else + conf->typeOfAction = 0x02; + if(!strcasecmp(arg2, "deny")) + conf->typeOfAction += 0x10; + else + conf->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->context, context); + cfg->enabled = 0; + memset(cfg->path, 0, 256); + cfg->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->enabled = (add->enabled == 0) ? base->enabled : add->enabled; + conf->typeOfAction = add->typeOfAction ? add->typeOfAction : base->typeOfAction; + strcpy(conf->path, strlen(add->path) ? add->path : base->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, &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->pool, sizeof(keyValuePair) * (pairs->nelts + 1)); + while (pairs && !apr_is_empty_array(pairs)) { + ap_form_pair_t *pair = (ap_form_pair_t *) apr_array_pop(pairs); + apr_brigade_length(pair->value, 1, &len); + size = (apr_size_t) len; + buffer = apr_palloc(r->pool, size + 1); + apr_brigade_flatten(pair->value, buffer, &size); + buffer[len] = 0; + kvp[i].key = apr_pstrdup(r->pool, pair->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; &formData[i]; i++) { + if (formData[i].key && 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->headers_in); + e = (apr_table_entry_t *) fields->elts; + for(i = 0; i < fields->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->remaining; + /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/ + + *rbuf = (const char *) apr_pcalloc(r->pool, (apr_size_t) (length + 1)); + *size = length; + while((len_read = ap_get_client_block(r, argsbuffer, sizeof(argsbuffer))) > 0) { + if((rpos + len_read) > 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, &buffer, &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"> en </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&A section. 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