dreid 00/01/04 09:14:00
Added: htdocs modules.html
Log:
HTML doc outlining how to convert a module from 1.3 to 2.0.
Not complete but at least it's a start.
Revision Changes Path
1.1 apache-2.0/htdocs/modules.html
Index: modules.html
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<TITLE>Converting Modules from Apache 1.3 to Apache 2.0</TITLE>
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<H1 ALIGN="CENTER">From Apache 1.3 to Apache 2.0<br>Modules</H1>
<p>
This is a first attempt at writing the lessons I learned when trying to
convert the mod_mmap_static 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>
<hr>
<h2>The easier changes...
</h2>
<h3>Cleanup Routines</h3>
<p>
These now need to be of type ap_status_t and return a value of that type.
Normally the return value will be APR_SUCCESS 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>
<h3>Initialisation Routines</h3>
<p>
These should now be renamed to better signify where they sit in the overall
process. So the name gets a small change from mmap_init to mmap_post_config.
The arguments passed have undergone a radical change and now look like
</p>
<ul style="list-style:none">
<li>ap_context_t *p,</li>
<li>ap_context_t *plog,</li>
<li>ap_context_t *ptemp,</li>
<li>server_rec *s</li>
</ul>
<p>
Throughout Apache the old pools have been replced by the ap_context_t, though
their use remains remarkably similar.
</p>
<h3>Data Types</h3>
<p>
A lot of the data types have been moved into the APR. 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.
<ul style="list-style:none">
<li>pool becomes ap_context_t</li>
<li>table becomes ap_table_t</li>
</ul>
<hr>
<h2>
The <em>messier</em> changes...
</h2>
<h3>Register Hooks</h3>
<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,
static void register_hooks(void). 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 mod_mmap_static
</p>
<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>
<p>
This registers 2 functions that need to be called, one in the post_config
stage (virtually every module will need this one) and one for the
translate_name phase. note that while there are different function names the
format of each is identical. So what is the format?
</p>
<p><strong>
ap_hook_[phase_name](function_name, predecessors, successors, position);
</strong></p>
<p>
There are 3 hook positions defined...
</p>
<ul style="list-style:none">
<li>HOOK_FIRST</li>
<li>HOOK_MIDDLE</li>
<li>HOOK_LAST</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 mod_mmap_static case I didn't care about the post_config stage, but
the mmap_static_xlat MUST be called after the core module had done it's name
translation, hence the use of the aszPre to define a modifier to the position
HOOK_LAST.
</p>
<h3>Module Definition</h3>
<p>
There are now a lot fewer stages to worry about when creating your module
definition. The old defintion looked like
</p>
<pre>
module MODULE_VAR_EXPORT [module_name]_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>
<p>
The new structure is a great deal simpler...
</p>
<pre>
module MODULE_VAR_EXPORT [module_name]_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>
<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>
<ul style="list-style:none">
<li>
/* dir config creater */ ==> /* create per-directory config structures */
</li>
<li>
/* server config */ ==> /* create per-server config structures */
</li>
<li>
/* dir merger */ ==> /* merge per-directory config structures */
</li>
<li>
/* merge server config */ ==> /* merge per-server config structures */
</li>
<li>
/* command table */ ==> /* command ap_table_t */
</li>
<li>
/* handlers */ ==> /* handlers */
</li>
</ul>
<P>
The remainder of the old functions should be registered as hooks. There are
the following hook stages defined so far...
</P>
<ul style="list-style:none">
<li>
ap_hook_post_config <em>(this is where the old _init routines get
registered)</em>
</li>
<li>
ap_hook_http_method
</li>
<li>
ap_hook_open_logs
</li>
<li>
ap_hook_auth_checker
</li>
<li>
ap_hook_default_port
</li>
<li>
ap_hook_access_checker
</li>
<li>
ap_hook_process_connection
</li>
<li>
ap_hook_child_init_hook
</li>
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