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283 lines
10 KiB
XML
283 lines
10 KiB
XML
<?xml version="1.0" encoding="UTF-8" ?>
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<!DOCTYPE manualpage SYSTEM "../style/manualpage.dtd">
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<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
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<!-- $LastChangedRevision$ -->
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<!--
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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this work for additional information regarding copyright ownership.
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The ASF licenses this file to You under the Apache License, Version 2.0
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(the "License"); you may not use this file except in compliance with
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the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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<manualpage metafile="modules.xml.meta">
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<parentdocument href="./">Developer Documentation</parentdocument>
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<title>Converting Modules from Apache 1.3 to Apache 2.0</title>
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<summary>
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<p>This is a first attempt at writing the lessons I learned
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when trying to convert the <code>mod_mmap_static</code> module to Apache
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2.0. It's by no means definitive and probably won't even be
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correct in some ways, but it's a start.</p>
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</summary>
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<section id="easy"><title>The easier changes ...</title>
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<section id="cleanup"><title>Cleanup Routines</title>
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<p>These now need to be of type <code>apr_status_t</code> and return a
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value of that type. Normally the return value will be
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<code>APR_SUCCESS</code> unless there is some need to signal an error in
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the cleanup. Be aware that even though you signal an error not all code
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yet checks and acts upon the error.</p>
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</section>
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<section id="init"><title>Initialisation Routines</title>
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<p>These should now be renamed to better signify where they sit
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in the overall process. So the name gets a small change from
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<code>mmap_init</code> to <code>mmap_post_config</code>. The arguments
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passed have undergone a radical change and now look like</p>
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<ul>
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<li><code>apr_pool_t *p</code></li>
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<li><code>apr_pool_t *plog</code></li>
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<li><code>apr_pool_t *ptemp</code></li>
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<li><code>server_rec *s</code></li>
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</ul>
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</section>
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<section id="datatypes"><title>Data Types</title>
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<p>A lot of the data types have been moved into the <a
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href="http://apr.apache.org/">APR</a>. This means that some have had
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a name change, such as the one shown above. The following is a brief
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list of some of the changes that you are likely to have to make.</p>
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<ul>
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<li><code>pool</code> becomes <code>apr_pool_t</code></li>
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<li><code>table</code> becomes <code>apr_table_t</code></li>
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</ul>
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</section>
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</section>
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<section id="messy"><title>The messier changes...</title>
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<section id="register-hooks"><title>Register Hooks</title>
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<p>The new architecture uses a series of hooks to provide for
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calling your functions. These you'll need to add to your module
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by way of a new function, <code>static void register_hooks(void)</code>.
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The function is really reasonably straightforward once you
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understand what needs to be done. Each function that needs
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calling at some stage in the processing of a request needs to
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be registered, handlers do not. There are a number of phases
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where functions can be added, and for each you can specify with
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a high degree of control the relative order that the function
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will be called in.</p>
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<p>This is the code that was added to <code>mod_mmap_static</code>:</p>
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<example><pre>
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static void register_hooks(void)
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{
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static const char * const aszPre[]={ "http_core.c",NULL };
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ap_hook_post_config(mmap_post_config,NULL,NULL,HOOK_MIDDLE);
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ap_hook_translate_name(mmap_static_xlat,aszPre,NULL,HOOK_LAST);
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};</pre>
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</example>
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<p>This registers 2 functions that need to be called, one in
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the <code>post_config</code> stage (virtually every module will need this
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one) and one for the <code>translate_name</code> phase. note that while
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there are different function names the format of each is
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identical. So what is the format?</p>
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<example>
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ap_hook_<var>phase_name</var>(<var>function_name</var>,
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<var>predecessors</var>, <var>successors</var>, <var>position</var>);
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</example>
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<p>There are 3 hook positions defined...</p>
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<ul>
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<li><code>HOOK_FIRST</code></li>
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<li><code>HOOK_MIDDLE</code></li>
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<li><code>HOOK_LAST</code></li>
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</ul>
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<p>To define the position you use the position and then modify
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it with the predecessors and successors. Each of the modifiers
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can be a list of functions that should be called, either before
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the function is run (predecessors) or after the function has
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run (successors).</p>
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<p>In the <code>mod_mmap_static</code> case I didn't care about the
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<code>post_config</code> stage, but the <code>mmap_static_xlat</code>
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<strong>must</strong> be called after the core module had done it's name
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translation, hence the use of the aszPre to define a modifier to the
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position <code>HOOK_LAST</code>.</p>
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</section>
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<section id="moddef"><title>Module Definition</title>
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<p>There are now a lot fewer stages to worry about when
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creating your module definition. The old defintion looked
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like</p>
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<example><pre>
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module MODULE_VAR_EXPORT <var>module_name</var>_module =
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{
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STANDARD_MODULE_STUFF,
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/* initializer */
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/* dir config creater */
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/* dir merger --- default is to override */
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/* server config */
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/* merge server config */
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/* command handlers */
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/* handlers */
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/* filename translation */
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/* check_user_id */
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/* check auth */
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/* check access */
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/* type_checker */
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/* fixups */
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/* logger */
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/* header parser */
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/* child_init */
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/* child_exit */
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/* post read-request */
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};</pre>
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</example>
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<p>The new structure is a great deal simpler...</p>
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<example><pre>
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module MODULE_VAR_EXPORT <var>module_name</var>_module =
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{
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STANDARD20_MODULE_STUFF,
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/* create per-directory config structures */
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/* merge per-directory config structures */
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/* create per-server config structures */
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/* merge per-server config structures */
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/* command handlers */
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/* handlers */
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/* register hooks */
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};</pre>
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</example>
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<p>Some of these read directly across, some don't. I'll try to
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summarise what should be done below.</p>
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<p>The stages that read directly across :</p>
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<dl>
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<dt><code>/* dir config creater */</code></dt>
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<dd><code>/* create per-directory config structures */</code></dd>
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<dt><code>/* server config */</code></dt>
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<dd><code>/* create per-server config structures */</code></dd>
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<dt><code>/* dir merger */</code></dt>
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<dd><code>/* merge per-directory config structures */</code></dd>
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<dt><code>/* merge server config */</code></dt>
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<dd><code>/* merge per-server config structures */</code></dd>
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<dt><code>/* command table */</code></dt>
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<dd><code>/* command apr_table_t */</code></dd>
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<dt><code>/* handlers */</code></dt>
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<dd><code>/* handlers */</code></dd>
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</dl>
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<p>The remainder of the old functions should be registered as
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hooks. There are the following hook stages defined so
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far...</p>
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<dl>
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<dt><code>ap_hook_pre_config</code></dt>
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<dd>do any setup required prior to processing configuration
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directives</dd>
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<dt><code>ap_hook_check_config</code></dt>
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<dd>review configuration directive interdependencies</dd>
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<dt><code>ap_hook_test_config</code></dt>
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<dd>executes only with <code>-t</code> option</dd>
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<dt><code>ap_hook_open_logs</code></dt>
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<dd>open any specified logs</dd>
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<dt><code>ap_hook_post_config</code></dt>
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<dd>this is where the old <code>_init</code> routines get
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registered</dd>
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<dt><code>ap_hook_http_method</code></dt>
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<dd>retrieve the http method from a request. (legacy)</dd>
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<dt><code>ap_hook_auth_checker</code></dt>
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<dd>check if the resource requires authorization</dd>
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<dt><code>ap_hook_access_checker</code></dt>
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<dd>check for module-specific restrictions</dd>
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<dt><code>ap_hook_check_user_id</code></dt>
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<dd>check the user-id and password</dd>
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<dt><code>ap_hook_default_port</code></dt>
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<dd>retrieve the default port for the server</dd>
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<dt><code>ap_hook_pre_connection</code></dt>
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<dd>do any setup required just before processing, but after
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accepting</dd>
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<dt><code>ap_hook_process_connection</code></dt>
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<dd>run the correct protocol</dd>
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<dt><code>ap_hook_child_init</code></dt>
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<dd>call as soon as the child is started</dd>
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<dt><code>ap_hook_create_request</code></dt>
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<dd>??</dd>
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<dt><code>ap_hook_fixups</code></dt>
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<dd>last chance to modify things before generating content</dd>
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<dt><code>ap_hook_handler</code></dt>
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<dd>generate the content</dd>
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<dt><code>ap_hook_header_parser</code></dt>
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<dd>lets modules look at the headers, not used by most modules, because
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they use <code>post_read_request</code> for this</dd>
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<dt><code>ap_hook_insert_filter</code></dt>
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<dd>to insert filters into the filter chain</dd>
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<dt><code>ap_hook_log_transaction</code></dt>
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<dd>log information about the request</dd>
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<dt><code>ap_hook_optional_fn_retrieve</code></dt>
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<dd>retrieve any functions registered as optional</dd>
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<dt><code>ap_hook_post_read_request</code></dt>
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<dd>called after reading the request, before any other phase</dd>
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<dt><code>ap_hook_quick_handler</code></dt>
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<dd>called before any request processing, used by cache modules.</dd>
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<dt><code>ap_hook_translate_name</code></dt>
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<dd>translate the URI into a filename</dd>
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<dt><code>ap_hook_type_checker</code></dt>
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<dd>determine and/or set the doc type</dd>
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</dl>
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</section>
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</section>
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</manualpage>
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