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| <manualpage metafile="modules.xml.meta"> |
| <parentdocument href="./">Developer Documentation</parentdocument> |
| |
| <title>Converting Modules from Apache 1.3 to Apache 2.0</title> |
| |
| <summary> |
| <p>This is a first attempt at writing the lessons I learned |
| when trying to convert the <code>mod_mmap_static</code> module to Apache |
| 2.0. It's by no means definitive and probably won't even be |
| correct in some ways, but it's a start.</p> |
| </summary> |
| |
| <section id="easy"><title>The easier changes ...</title> |
| |
| <section id="cleanup"><title>Cleanup Routines</title> |
| <p>These now need to be of type <code>apr_status_t</code> and return a |
| value of that type. Normally the return value will be |
| <code>APR_SUCCESS</code> unless there is some need to signal an error in |
| the cleanup. Be aware that even though you signal an error not all code |
| yet checks and acts upon the error.</p> |
| </section> |
| |
| <section id="init"><title>Initialisation Routines</title> |
| <p>These should now be renamed to better signify where they sit |
| in the overall process. So the name gets a small change from |
| <code>mmap_init</code> to <code>mmap_post_config</code>. The arguments |
| passed have undergone a radical change and now look like</p> |
| |
| <ul> |
| <li><code>apr_pool_t *p</code></li> |
| <li><code>apr_pool_t *plog</code></li> |
| <li><code>apr_pool_t *ptemp</code></li> |
| <li><code>server_rec *s</code></li> |
| </ul> |
| </section> |
| |
| <section id="datatypes"><title>Data Types</title> |
| <p>A lot of the data types have been moved into the <a |
| href="http://apr.apache.org/">APR</a>. This means that some have had |
| a name change, such as the one shown above. The following is a brief |
| list of some of the changes that you are likely to have to make.</p> |
| |
| <ul> |
| <li><code>pool</code> becomes <code>apr_pool_t</code></li> |
| <li><code>table</code> becomes <code>apr_table_t</code></li> |
| </ul> |
| </section> |
| </section> |
| |
| <section id="messy"><title>The messier changes...</title> |
| |
| <section id="register-hooks"><title>Register Hooks</title> |
| <p>The new architecture uses a series of hooks to provide for |
| calling your functions. These you'll need to add to your module |
| by way of a new function, <code>static void register_hooks(void)</code>. |
| The function is really reasonably straightforward once you |
| understand what needs to be done. Each function that needs |
| calling at some stage in the processing of a request needs to |
| be registered, handlers do not. There are a number of phases |
| where functions can be added, and for each you can specify with |
| a high degree of control the relative order that the function |
| will be called in.</p> |
| |
| <p>This is the code that was added to <code>mod_mmap_static</code>:</p> |
| <example><pre> |
| static void register_hooks(void) |
| { |
| static const char * const aszPre[]={ "http_core.c",NULL }; |
| ap_hook_post_config(mmap_post_config,NULL,NULL,HOOK_MIDDLE); |
| ap_hook_translate_name(mmap_static_xlat,aszPre,NULL,HOOK_LAST); |
| };</pre> |
| </example> |
| |
| <p>This registers 2 functions that need to be called, one in |
| the <code>post_config</code> stage (virtually every module will need this |
| one) and one for the <code>translate_name</code> phase. note that while |
| there are different function names the format of each is |
| identical. So what is the format?</p> |
| |
| <example> |
| ap_hook_<var>phase_name</var>(<var>function_name</var>, |
| <var>predecessors</var>, <var>successors</var>, <var>position</var>); |
| </example> |
| |
| <p>There are 3 hook positions defined...</p> |
| |
| <ul> |
| <li><code>HOOK_FIRST</code></li> |
| <li><code>HOOK_MIDDLE</code></li> |
| <li><code>HOOK_LAST</code></li> |
| </ul> |
| |
| <p>To define the position you use the position and then modify |
| it with the predecessors and successors. Each of the modifiers |
| can be a list of functions that should be called, either before |
| the function is run (predecessors) or after the function has |
| run (successors).</p> |
| |
| <p>In the <code>mod_mmap_static</code> case I didn't care about the |
| <code>post_config</code> stage, but the <code>mmap_static_xlat</code> |
| <strong>must</strong> be called after the core module had done its name |
| translation, hence the use of the aszPre to define a modifier to the |
| position <code>HOOK_LAST</code>.</p> |
| </section> |
| |
| <section id="moddef"><title>Module Definition</title> |
| <p>There are now a lot fewer stages to worry about when |
| creating your module definition. The old definition looked |
| like</p> |
| |
| <example><pre> |
| module MODULE_VAR_EXPORT <var>module_name</var>_module = |
| { |
| STANDARD_MODULE_STUFF, |
| /* initializer */ |
| /* dir config creater */ |
| /* dir merger --- default is to override */ |
| /* server config */ |
| /* merge server config */ |
| /* command handlers */ |
| /* handlers */ |
| /* filename translation */ |
| /* check_user_id */ |
| /* check auth */ |
| /* check access */ |
| /* type_checker */ |
| /* fixups */ |
| /* logger */ |
| /* header parser */ |
| /* child_init */ |
| /* child_exit */ |
| /* post read-request */ |
| };</pre> |
| </example> |
| |
| <p>The new structure is a great deal simpler...</p> |
| <example><pre> |
| module MODULE_VAR_EXPORT <var>module_name</var>_module = |
| { |
| STANDARD20_MODULE_STUFF, |
| /* create per-directory config structures */ |
| /* merge per-directory config structures */ |
| /* create per-server config structures */ |
| /* merge per-server config structures */ |
| /* command handlers */ |
| /* handlers */ |
| /* register hooks */ |
| };</pre> |
| </example> |
| |
| <p>Some of these read directly across, some don't. I'll try to |
| summarise what should be done below.</p> |
| |
| <p>The stages that read directly across :</p> |
| |
| <dl> |
| <dt><code>/* dir config creater */</code></dt> |
| <dd><code>/* create per-directory config structures */</code></dd> |
| |
| <dt><code>/* server config */</code></dt> |
| <dd><code>/* create per-server config structures */</code></dd> |
| |
| <dt><code>/* dir merger */</code></dt> |
| <dd><code>/* merge per-directory config structures */</code></dd> |
| |
| <dt><code>/* merge server config */</code></dt> |
| <dd><code>/* merge per-server config structures */</code></dd> |
| |
| <dt><code>/* command table */</code></dt> |
| <dd><code>/* command apr_table_t */</code></dd> |
| |
| <dt><code>/* handlers */</code></dt> |
| <dd><code>/* handlers */</code></dd> |
| </dl> |
| |
| <p>The remainder of the old functions should be registered as |
| hooks. There are the following hook stages defined so |
| far...</p> |
| |
| <dl> |
| <dt><code>ap_hook_pre_config</code></dt> |
| <dd>do any setup required prior to processing configuration |
| directives</dd> |
| |
| <dt><code>ap_hook_check_config</code></dt> |
| <dd>review configuration directive interdependencies</dd> |
| |
| <dt><code>ap_hook_test_config</code></dt> |
| <dd>executes only with <code>-t</code> option</dd> |
| |
| <dt><code>ap_hook_open_logs</code></dt> |
| <dd>open any specified logs</dd> |
| |
| <dt><code>ap_hook_post_config</code></dt> |
| <dd>this is where the old <code>_init</code> routines get |
| registered</dd> |
| |
| <dt><code>ap_hook_http_method</code></dt> |
| <dd>retrieve the http method from a request. (legacy)</dd> |
| |
| <dt><code>ap_hook_auth_checker</code></dt> |
| <dd>check if the resource requires authorization</dd> |
| |
| <dt><code>ap_hook_access_checker</code></dt> |
| <dd>check for module-specific restrictions</dd> |
| |
| <dt><code>ap_hook_check_user_id</code></dt> |
| <dd>check the user-id and password</dd> |
| |
| <dt><code>ap_hook_default_port</code></dt> |
| <dd>retrieve the default port for the server</dd> |
| |
| <dt><code>ap_hook_pre_connection</code></dt> |
| <dd>do any setup required just before processing, but after |
| accepting</dd> |
| |
| <dt><code>ap_hook_process_connection</code></dt> |
| <dd>run the correct protocol</dd> |
| |
| <dt><code>ap_hook_child_init</code></dt> |
| <dd>call as soon as the child is started</dd> |
| |
| <dt><code>ap_hook_create_request</code></dt> |
| <dd>??</dd> |
| |
| <dt><code>ap_hook_fixups</code></dt> |
| <dd>last chance to modify things before generating content</dd> |
| |
| <dt><code>ap_hook_handler</code></dt> |
| <dd>generate the content</dd> |
| |
| <dt><code>ap_hook_header_parser</code></dt> |
| <dd>lets modules look at the headers, not used by most modules, because |
| they use <code>post_read_request</code> for this</dd> |
| |
| <dt><code>ap_hook_insert_filter</code></dt> |
| <dd>to insert filters into the filter chain</dd> |
| |
| <dt><code>ap_hook_log_transaction</code></dt> |
| <dd>log information about the request</dd> |
| |
| <dt><code>ap_hook_optional_fn_retrieve</code></dt> |
| <dd>retrieve any functions registered as optional</dd> |
| |
| <dt><code>ap_hook_post_read_request</code></dt> |
| <dd>called after reading the request, before any other phase</dd> |
| |
| <dt><code>ap_hook_quick_handler</code></dt> |
| <dd>called before any request processing, used by cache modules.</dd> |
| |
| <dt><code>ap_hook_translate_name</code></dt> |
| <dd>translate the URI into a filename</dd> |
| |
| <dt><code>ap_hook_type_checker</code></dt> |
| <dd>determine and/or set the doc type</dd> |
| </dl> |
| </section> |
| </section> |
| </manualpage> |
| |