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259 lines
8.1 KiB
HTML
259 lines
8.1 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta name="generator" content="HTML Tidy, see www.w3.org" />
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<title>Converting Modules from Apache 1.3 to Apache 2.0</title>
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</head>
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<!-- Background white, links blue (unvisited), navy (visited), red (active) -->
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<body bgcolor="#FFFFFF" text="#000000" link="#0000FF"
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vlink="#000080" alink="#FF0000">
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<!--#include virtual="header.html" -->
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<h1 align="CENTER">From Apache 1.3 to Apache 2.0<br />
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Modules</h1>
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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 mod_mmap_static 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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<hr />
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<h2>The easier changes...</h2>
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<h3>Cleanup Routines</h3>
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<p>These now need to be of type apr_status_t and return a value
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of that type. Normally the return value will be APR_SUCCESS
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unless there is some need to signal an error in the cleanup. Be
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aware that even though you signal an error not all code yet
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checks and acts upon the error.</p>
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<h3>Initialisation Routines</h3>
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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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mmap_init to mmap_post_config. The arguments passed have
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undergone a radical change and now look like</p>
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<ul style="list-style:none">
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<li>apr_pool_t *p,</li>
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<li>apr_pool_t *plog,</li>
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<li>apr_pool_t *ptemp,</li>
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<li>server_rec *s</li>
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</ul>
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<h3>Data Types</h3>
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<p>A lot of the data types have been moved into the APR. This
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means that some have had a name change, such as the one shown
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above. The following is a brief list of some of the changes
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that you are likely to have to make.</p>
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<ul style="list-style:none">
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<li>pool becomes apr_pool_t</li>
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<li>table becomes apr_table_t</li>
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</ul>
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<hr />
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<h2>The <em>messier</em> changes...</h2>
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<h3>Register Hooks</h3>
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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, static void register_hooks(void). The
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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 mod_mmap_static:</p>
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<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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};
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</pre>
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<p>This registers 2 functions that need to be called, one in
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the post_config stage (virtually every module will need this
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one) and one for the translate_name 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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<p><strong>ap_hook_[phase_name](function_name, predecessors,
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successors, position);</strong></p>
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<p>There are 3 hook positions defined...</p>
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<ul style="list-style:none">
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<li>HOOK_FIRST</li>
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<li>HOOK_MIDDLE</li>
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<li>HOOK_LAST</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 mod_mmap_static case I didn't care about the
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post_config stage, but the mmap_static_xlat MUST be called
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after the core module had done it's name translation, hence the
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use of the aszPre to define a modifier to the position
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HOOK_LAST.</p>
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<h3>Module Definition</h3>
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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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<pre>
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module MODULE_VAR_EXPORT [module_name]_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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};
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</pre>
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<p>The new structure is a great deal simpler...</p>
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<pre>
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module MODULE_VAR_EXPORT [module_name]_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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};
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</pre>
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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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<ul style="list-style:none">
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<li>/* dir config creater */ ==> /* create per-directory
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config structures */</li>
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<li>/* server config */ ==> /* create per-server config
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structures */</li>
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<li>/* dir merger */ ==> /* merge per-directory config
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structures */</li>
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<li>/* merge server config */ ==> /* merge per-server
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config structures */</li>
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<li>/* command table */ ==> /* command apr_table_t */</li>
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<li>/* handlers */ ==> /* handlers */</li>
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</ul>
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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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<ul style="list-style:none">
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<li>ap_hook_post_config <em>(this is where the old _init
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routines get registered)</em></li>
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<li>ap_hook_http_method <em>(retrieve the http method from a
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request. (legacy))</em></li>
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<li>ap_hook_open_logs <em>(open any specified logs)</em></li>
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<li>ap_hook_auth_checker <em>(check if the resource requires
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authorization)</em></li>
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<li>ap_hook_access_checker <em>(check for module-specific
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restrictions)</em></li>
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<li>ap_hook_check_user_id <em>(check the user-id and
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password)</em></li>
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<li>ap_hook_default_port <em>(retrieve the default port for
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the server)</em></li>
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<li>ap_hook_pre_connection <em>(do any setup required just
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before processing, but after accepting)</em></li>
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<li>ap_hook_process_connection <em>(run the correct
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protocol)</em></li>
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<li>ap_hook_child_init <em>(call as soon as the child is
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started)</em></li>
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<li>ap_hook_create_request <em>(??)</em></li>
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<li>ap_hook_fixups <em>(last chance to modify things before
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generating content)</em></li>
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<li>ap_hook_handler <em>(generate the content)</em></li>
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<li>ap_hook_header_parser <em>(let's modules look at the
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headers, not used by most modules, because they use
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post_read_request for this.)</em></li>
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<li>ap_hook_insert_filter <em>(to insert filters into the
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filter chain)</em></li>
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<li>ap_hook_log_transaction <em>(log information about the
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request)</em></li>
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<li>ap_hook_optional_fn_retrieve <em>(retrieve any functions
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registered as optional)</em></li>
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<li>ap_hook_post_read_request <em>(called after reading the
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request, before any other phase)</em></li>
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<li>ap_hook_quick_handler <em>(??)</em></li>
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<li>ap_hook_translate_name <em>(translate the URI into a
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filename)</em></li>
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<li>ap_hook_type_checker <em>(determine and/or set the doc
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type)</em> <!--#include virtual="footer.html" -->
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</li>
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</ul>
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</body>
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</html>
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