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| author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 06:33:50 +0000 |
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| committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 06:33:50 +0000 |
| commit | fe39ffb8b90ae4e002ed73fe98617cd590abb467 (patch) | |
| tree | b80e5956907d8aeaaffe4e4f0c068c0e6157ce8b /docs/manual/developer/hooks.html.en | |
| parent | Initial commit. (diff) | |
| download | apache2-upstream/2.4.56.tar.xz apache2-upstream/2.4.56.zip | |
Adding upstream version 2.4.56.upstream/2.4.56
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'docs/manual/developer/hooks.html.en')
| -rw-r--r-- | docs/manual/developer/hooks.html.en | 261 |
1 files changed, 261 insertions, 0 deletions
diff --git a/docs/manual/developer/hooks.html.en b/docs/manual/developer/hooks.html.en new file mode 100644 index 0000000..30aa6f9 --- /dev/null +++ b/docs/manual/developer/hooks.html.en @@ -0,0 +1,261 @@ +<?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>Hook Functions in the Apache HTTP Server 2.x - 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 Documentation</a></div><div id="page-content"><div id="preamble"><h1>Hook Functions in the Apache HTTP Server 2.x</h1> +<div class="toplang"> +<p><span>Available Languages: </span><a href="../en/developer/hooks.html" title="English"> en </a></p> +</div> + + <div class="warning"><h3>Warning</h3> + <p>This document is still in development and may be partially out of + date.</p> + </div> + + <p>In general, a hook function is one that the Apache HTTP Server + will call at some point during the processing of a request. + Modules can provide functions that are called, and specify when + they get called in comparison to other modules.</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="#corehooks">Core Hooks</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#create">Creating a hook function</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#hooking">Hooking the hook</a></li> +</ul><h3>See also</h3><ul class="seealso"><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="corehooks" id="corehooks">Core Hooks</a></h2> + <p>The httpd's core modules offer a predefinined list of hooks + used during the standard <a href="./request.html">request processing</a> + phase. Creating a new hook will expose a function that + implements it (see sections below) but it is essential to understand that you will not + extend the httpd's core hooks. Their presence and order in the request processing is in fact + a consequence of how they are called in <code>server/request.c</code> + (check <a href="./modguide.html#hooking">this section</a> + for an overview). The core hooks are listed in the + <a href="https://ci.apache.org/projects/httpd/trunk/doxygen/group__hooks.html">doxygen documentation</a>.</p> + + <p>Reading <a href="./modguide.html">guide for developing modules</a> and + <a href="./request.html">request processing</a> before proceeding is + highly recommended. + </p> +</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="section"> +<h2><a name="create" id="create">Creating a hook function</a></h2> + <p>In order to create a new hook, four things need to be + done:</p> + + <h3><a name="create-declare" id="create-declare">Declare the hook function</a></h3> + <p>Use the <code>AP_DECLARE_HOOK</code> macro, which needs to be given + the return type of the hook function, the name of the hook, and the + arguments. For example, if the hook returns an <code>int</code> and + takes a <code>request_rec *</code> and an <code>int</code> and is + called <code>do_something</code>, then declare it like this:</p> + <pre class="prettyprint lang-c">AP_DECLARE_HOOK(int, do_something, (request_rec *r, int n))</pre> + + + <p>This should go in a header which modules will include if + they want to use the hook.</p> + + + <h3><a name="create-create" id="create-create">Create the hook structure</a></h3> + <p>Each source file that exports a hook has a private structure + which is used to record the module functions that use the hook. + This is declared as follows:</p> + + <pre class="prettyprint lang-c">APR_HOOK_STRUCT( + APR_HOOK_LINK(do_something) + ... +)</pre> + + + + <h3><a name="create-implement" id="create-implement">Implement the hook caller</a></h3> + <p>The source file that exports the hook has to implement a + function that will call the hook. There are currently three + possible ways to do this. In all cases, the calling function is + called <code>ap_run_<var>hookname</var>()</code>.</p> + + <h4>Void hooks</h4> + <p>If the return value of a hook is <code>void</code>, then all the + hooks are called, and the caller is implemented like this:</p> + + <pre class="prettyprint lang-c">AP_IMPLEMENT_HOOK_VOID(do_something, (request_rec *r, int n), (r, n))</pre> + + + <p>The second and third arguments are the dummy argument + declaration and the dummy arguments as they will be used when + calling the hook. In other words, this macro expands to + something like this:</p> + + <pre class="prettyprint lang-c">void ap_run_do_something(request_rec *r, int n) +{ + ... + do_something(r, n); +}</pre> + + + + <h4>Hooks that return a value</h4> + <p>If the hook returns a value, then it can either be run until + the first hook that does something interesting, like so:</p> + + <pre class="prettyprint lang-c">AP_IMPLEMENT_HOOK_RUN_FIRST(int, do_something, (request_rec *r, int n), (r, n), DECLINED)</pre> + + + <p>The first hook that does <em>not</em> return <code>DECLINED</code> + stops the loop and its return value is returned from the hook + caller. Note that <code>DECLINED</code> is the traditional + hook return value meaning "I didn't do anything", but it can be + whatever suits you.</p> + + <p>Alternatively, all hooks can be run until an error occurs. + This boils down to permitting <em>two</em> return values, one of + which means "I did something, and it was OK" and the other + meaning "I did nothing". The first function that returns a + value other than one of those two stops the loop, and its + return is the return value. Declare these like so:</p> + + <pre class="prettyprint lang-c">AP_IMPLEMENT_HOOK_RUN_ALL(int, do_something, (request_rec *r, int n), (r, n), OK, DECLINED)</pre> + + + <p>Again, <code>OK</code> and <code>DECLINED</code> are the traditional + values. You can use what you want.</p> + + + + <h3><a name="create-call" id="create-call">Call the hook callers</a></h3> + <p>At appropriate moments in the code, call the hook caller, + like so:</p> + + <pre class="prettyprint lang-c">int n, ret; +request_rec *r; + +ret=ap_run_do_something(r, n);</pre> + + +</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">Hooking the hook</a></h2> + <p>A module that wants a hook to be called needs to do two + things.</p> + + <h3><a name="hooking-implement" id="hooking-implement">Implement the hook function</a></h3> + <p>Include the appropriate header, and define a static function + of the correct type:</p> + + <pre class="prettyprint lang-c">static int my_something_doer(request_rec *r, int n) +{ + ... + return OK; +}</pre> + + + + <h3><a name="hooking-add" id="hooking-add">Add a hook registering function</a></h3> + <p>During initialisation, the server will call each modules hook + registering function, which is included in the module + structure:</p> + + <pre class="prettyprint lang-c">static void my_register_hooks() +{ + ap_hook_do_something(my_something_doer, NULL, NULL, APR_HOOK_MIDDLE); +} + +mode MODULE_VAR_EXPORT my_module = +{ + ... + my_register_hooks /* register hooks */ +};</pre> + + + + <h3><a name="hooking-order" id="hooking-order">Controlling hook calling order</a></h3> + <p>In the example above, we didn't use the three arguments in + the hook registration function that control calling order of + all the functions registered within the hook. + There are two mechanisms for doing this. The first, rather + crude, method, allows us to specify roughly where the hook is + run relative to other modules. The final argument control this. + There are three possible values: <code>APR_HOOK_FIRST</code>, + <code>APR_HOOK_MIDDLE</code> and <code>APR_HOOK_LAST</code>.</p> + + <p>All modules using any particular value may be run in any + order relative to each other, but, of course, all modules using + <code>APR_HOOK_FIRST</code> will be run before <code>APR_HOOK_MIDDLE</code> + which are before <code>APR_HOOK_LAST</code>. Modules that don't care + when they are run should use <code>APR_HOOK_MIDDLE</code>. <em>These + values are spaced out, so that positions like <code>APR_HOOK_FIRST-2</code> + are possible to hook slightly earlier than other functions.</em></p> + + <p>Note that there are two more values, + <code>APR_HOOK_REALLY_FIRST</code> and <code>APR_HOOK_REALLY_LAST</code>. These + should only be used by the hook exporter.</p> + + <p>The other method allows finer control. When a module knows + that it must be run before (or after) some other modules, it + can specify them by name. The second (third) argument is a + NULL-terminated array of strings consisting of the names of + modules that must be run before (after) the current module. For + example, suppose we want "mod_xyz.c" and "mod_abc.c" to run + before we do, then we'd hook as follows:</p> + + <pre class="prettyprint lang-c">static void register_hooks() +{ + static const char * const aszPre[] = { "mod_xyz.c", "mod_abc.c", NULL }; + + ap_hook_do_something(my_something_doer, aszPre, NULL, APR_HOOK_MIDDLE); +}</pre> + + + <p>Note that the sort used to achieve this is stable, so + ordering set by <code>APR_HOOK_<var>ORDER</var></code> is preserved, as far + as is possible.</p> + + +</div></div> +<div class="bottomlang"> +<p><span>Available Languages: </span><a href="../en/developer/hooks.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. 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> +<script type="text/javascript"><!--//--><![CDATA[//><!-- +var comments_shortname = 'httpd'; +var comments_identifier = 'http://httpd.apache.org/docs/2.4/developer/hooks.html'; +(function(w, d) { + if (w.location.hostname.toLowerCase() == "httpd.apache.org") { + d.write('<div id="comments_thread"><\/div>'); + var s = d.createElement('script'); + s.type = 'text/javascript'; + s.async = true; + s.src = 'https://comments.apache.org/show_comments.lua?site=' + comments_shortname + '&page=' + comments_identifier; + (d.getElementsByTagName('head')[0] || d.getElementsByTagName('body')[0]).appendChild(s); + } + else { + d.write('<div id="comments_thread">Comments are disabled for this page at the moment.<\/div>'); + } +})(window, document); +//--><!]]></script></div><div id="footer"> +<p class="apache">Copyright 2023 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p> +<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></div><script type="text/javascript"><!--//--><![CDATA[//><!-- +if (typeof(prettyPrint) !== 'undefined') { + prettyPrint(); +} +//--><!]]></script> +</body></html>
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