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From n.@apache.org
Subject cvs commit: httpd-2.0/docs/manual/developer hooks.html.en hooks.xml hooks.html
Date Sat, 05 Apr 2003 02:55:42 GMT
nd          2003/04/04 18:55:42

  Added:       docs/manual/developer hooks.html.en hooks.xml
  Removed:     docs/manual/developer hooks.html
  Log:
  new XML
  
  Revision  Changes    Path
  1.1                  httpd-2.0/docs/manual/developer/hooks.html.en
  
  Index: hooks.html.en
  ===================================================================
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          XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
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        -->
  <title>Apache 2.0 Hook Functions - Apache HTTP Server</title>
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  <p class="apache">Apache HTTP Server Version 2.1</p>
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  <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-project/">Documentation</a>
&gt; <a href="../">Version 2.1</a></div><div id="page-content"><div
id="preamble"><h1>Apache 2.0 Hook Functions</h1>
      <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This document is still in development and may be partially out of
        date.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 Apache 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"><ul id="toc"><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></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>
        <div class="example"><p><code>
          AP_DECLARE_HOOK(int, do_something, (request_rec *r, int n))
        </code></p></div>
  
        <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>
  
        <div class="example"><p><code>
          APR_HOOK_STRUCT(<br />
          <span class="indent">
            APR_HOOK_LINK(do_something)<br />
            ...<br />
          </span>
          )
        </code></p></div>
      
  
      <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>
  
          <div class="example"><p><code>
            AP_IMPLEMENT_HOOK_VOID(do_something, (request_rec *r, int n), (r, n))
          </code></p></div>
  
          <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>
  
          <div class="example"><p><code>
            void ap_run_do_something(request_rec *r, int n)<br />
            {<br />
            <span class="indent">
              ...<br />
              do_something(r, n);<br />
            </span>
            }
          </code></p></div>
        
  
        <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>
  
          <div class="example"><p><code>
            AP_IMPLEMENT_HOOK_RUN_FIRST(int, do_something, (request_rec *r, int n), (r, n),
DECLINED)
          </code></p></div>
  
          <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 tradition Apache
          hook return 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>
  
          <div class="example"><p><code>
            AP_IMPLEMENT_HOOK_RUN_ALL(int, do_something, (request_rec *r, int n), (r, n),
OK, DECLINED)
          </code></p></div>
  
          <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>
  
        <div class="example"><p><code>
          int n, ret;<br />
          request_rec *r;<br />
          <br />
          ret=ap_run_do_something(r, n);
        </code></p></div>
      
  </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>
  
        <div class="example"><p><code>
          static int my_something_doer(request_rec *r, int n)<br />
          {<br />
          <span class="indent">
            ...<br />
            return OK;<br />
          </span>
          }
        </code></p></div>
      
  
      <h3><a name="hooking-add" id="hooking-add">Add a hook registering function</a></h3>
        <p>During initialisation, Apache will call each modules hook
        registering function, which is included in the module
        structure:</p>
  
        <div class="example"><p><code>
          static void my_register_hooks()<br />
          {<br />
          <span class="indent">
            ap_hook_do_something(my_something_doer, NULL, NULL, HOOK_MIDDLE);<br />
          </span>
          }<br />
          <br />
          mode MODULE_VAR_EXPORT my_module =<br />
          {<br />
          <span class="indent">
            ...<br />
            my_register_hooks       /* register hooks */<br />
          </span>
          };
        </code></p></div>
      
  
      <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.
        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>HOOK_FIRST</code>,
        <code>HOOK_MIDDLE</code> and <code>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>HOOK_FIRST</code> will be run before <code>HOOK_MIDDLE</code>
        which are before <code>HOOK_LAST</code>. Modules that don't care
        when they are run should use <code>HOOK_MIDDLE</code>. <em>(I spaced
        these out so people could do stuff like <code>HOOK_FIRST-2</code>
        to get in slightly earlier, but is this wise? - Ben)</em></p>
  
        <p>Note that there are two more values,
        <code>HOOK_REALLY_FIRST</code> and <code>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>
  
        <div class="example"><p><code>
          static void register_hooks()<br />
          {<br />
          <span class="indent">
            static const char * const aszPre[] = { "mod_xyz.c", "mod_abc.c", NULL };<br
/>
            <br />
            ap_hook_do_something(my_something_doer, aszPre, NULL, HOOK_MIDDLE);<br />
          </span>
          }
        </code></p></div>
  
        <p>Note that the sort used to achieve this is stable, so
        ordering set by <code>HOOK_<var>ORDER</var></code> is preserved,
as far
        as is possible.</p>
  
        <p class="cite"><cite>Ben Laurie</cite>, 15th August 1999</p>
      
  </div></div>
  <div id="footer">
  <p class="apache">Maintained by the <a href="http://httpd.apache.org/docs-project/">Apache
HTTP Server Documentation Project</a></p>
  <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a>
| <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a>
| <a href="../sitemap.html">Sitemap</a></p></div>
  </body></html>
  
  
  1.1                  httpd-2.0/docs/manual/developer/hooks.xml
  
  Index: hooks.xml
  ===================================================================
  <?xml version="1.0" encoding="UTF-8" ?>
  <!DOCTYPE manualpage SYSTEM "../style/manualpage.dtd">
  <?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
  
  <manualpage>
  <relativepath href=".."/>
  
  <title>Apache 2.0 Hook Functions</title>
  
  <summary>
      <note type="warning"><title>Warning</title>
        <p>This document is still in development and may be partially out of
        date.</p>
      </note>
  
      <p>In general, a hook function is one that Apache 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>
  </summary>
  
  <section id="create"><title>Creating a hook function</title>
      <p>In order to create a new hook, four things need to be
      done:</p>
  
      <section id="create-declare"><title>Declare the hook function</title>
        <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>
        <example>
          AP_DECLARE_HOOK(int, do_something, (request_rec *r, int n))
        </example>
  
        <p>This should go in a header which modules will include if
        they want to use the hook.</p>
      </section>
  
      <section id="create-create"><title>Create the hook structure</title>
        <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>
  
        <example>
          APR_HOOK_STRUCT(<br />
          <indent>
            APR_HOOK_LINK(do_something)<br />
            ...<br />
          </indent>
          )
        </example>
      </section>
  
      <section id="create-implement"><title>Implement the hook caller</title>
        <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>
  
        <section><title>Void hooks</title>
          <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>
  
          <example>
            AP_IMPLEMENT_HOOK_VOID(do_something, (request_rec *r, int n), (r, n))
          </example>
  
          <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>
  
          <example>
            void ap_run_do_something(request_rec *r, int n)<br />
            {<br />
            <indent>
              ...<br />
              do_something(r, n);<br />
            </indent>
            }
          </example>
        </section>
  
        <section><title>Hooks that return a value</title>
          <p>If the hook returns a value, then it can either be run until
          the first hook that does something interesting, like so:</p>
  
          <example>
            AP_IMPLEMENT_HOOK_RUN_FIRST(int, do_something, (request_rec *r, int n), (r, n),
DECLINED)
          </example>
  
          <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 tradition Apache
          hook return 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>
  
          <example>
            AP_IMPLEMENT_HOOK_RUN_ALL(int, do_something, (request_rec *r, int n), (r, n),
OK, DECLINED)
          </example>
  
          <p>Again, <code>OK</code> and <code>DECLINED</code>
are the traditional
          values. You can use what you want.</p>
        </section>
      </section>
  
      <section id="create-call"><title>Call the hook callers</title>
        <p>At appropriate moments in the code, call the hook caller,
        like so:</p>
  
        <example>
          int n, ret;<br />
          request_rec *r;<br />
          <br />
          ret=ap_run_do_something(r, n);
        </example>
      </section>
  </section>
  
  <section id="hooking"><title>Hooking the hook</title>
      <p>A module that wants a hook to be called needs to do two
      things.</p>
  
      <section id="hooking-implement"><title>Implement the hook function</title>
        <p>Include the appropriate header, and define a static function
        of the correct type:</p>
  
        <example>
          static int my_something_doer(request_rec *r, int n)<br />
          {<br />
          <indent>
            ...<br />
            return OK;<br />
          </indent>
          }
        </example>
      </section>
  
      <section id="hooking-add"><title>Add a hook registering function</title>
        <p>During initialisation, Apache will call each modules hook
        registering function, which is included in the module
        structure:</p>
  
        <example>
          static void my_register_hooks()<br />
          {<br />
          <indent>
            ap_hook_do_something(my_something_doer, NULL, NULL, HOOK_MIDDLE);<br />
          </indent>
          }<br />
          <br />
          mode MODULE_VAR_EXPORT my_module =<br />
          {<br />
          <indent>
            ...<br />
            my_register_hooks       /* register hooks */<br />
          </indent>
          };
        </example>
      </section>
  
      <section id="hooking-order"><title>Controlling hook calling order</title>
        <p>In the example above, we didn't use the three arguments in
        the hook registration function that control calling order.
        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>HOOK_FIRST</code>,
        <code>HOOK_MIDDLE</code> and <code>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>HOOK_FIRST</code> will be run before <code>HOOK_MIDDLE</code>
        which are before <code>HOOK_LAST</code>. Modules that don't care
        when they are run should use <code>HOOK_MIDDLE</code>. <em>(I spaced
        these out so people could do stuff like <code>HOOK_FIRST-2</code>
        to get in slightly earlier, but is this wise? - Ben)</em></p>
  
        <p>Note that there are two more values,
        <code>HOOK_REALLY_FIRST</code> and <code>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>
  
        <example>
          static void register_hooks()<br />
          {<br />
          <indent>
            static const char * const aszPre[] = { "mod_xyz.c", "mod_abc.c", NULL };<br
/>
            <br />
            ap_hook_do_something(my_something_doer, aszPre, NULL, HOOK_MIDDLE);<br />
          </indent>
          }
        </example>
  
        <p>Note that the sort used to achieve this is stable, so
        ordering set by <code>HOOK_<var>ORDER</var></code> is preserved,
as far
        as is possible.</p>
  
        <p class="cite"><cite>Ben Laurie</cite>, 15th August 1999</p>
      </section>
  </section>
  </manualpage>
  
  
  
  

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