Plugins
=======
Plugins in Dovecot are really simple. They basically have two functions:
* <plugin_name>_init(module) is called when 'module_dir_init()' is called.
* <plugin_name>_deinit() is called when 'module_dir_deinit()' or
'module_dir_unload()' is called.
The <plugin_name> is the short version of the plugin name, based on the
filename. For example if the filename is 'lib11_imap_quota_plugin.so', the
<plugin_name> is "imap_quota" and the init function to be called is
imap_quota_plugin_init().
Versioning
----------
Since different Dovecot versions can have different APIs, your plugin should
usually also define<plugin_name>_version, like:
---%<-------------------------------------------------------------------------
const char *imap_quota_plugin_version = DOVECOT_VERSION;
---%<-------------------------------------------------------------------------
If the version string in plugin doesn't match the version of the running
binary, the plugin loading fails. The DOVECOT_VERSION is defined in Dovecot's
'config.h', which you're typically including.
Dependencies
------------
Some plugins depend on another one. In some systems (but not all) it's possible
to handle this by giving a nicer error message than "symbol xyz not found".
There are two steps for this:
First create <plugin_name>_dependencies array listing plugin names that the
plugin depends on, like:
---%<-------------------------------------------------------------------------
const char *imap_quota_plugin_dependencies[] = { "quota", NULL };
---%<-------------------------------------------------------------------------
Then you'll also have to make the plugin .so binary link to the other plugins:
---%<-------------------------------------------------------------------------
if PLUGIN_DEPS
lib11_imap_quota_plugin_la_LIBADD = \
../quota/lib10_quota_plugin.la
endif
---%<-------------------------------------------------------------------------
PLUGIN_DEPS is set only if plugin dependencies are actually supported.
Otherwise the build might fail or plugin loading might fail.
Once all this is done, trying to load imap_quota plugin without quota plugin
gives a nice error message:
---%<-------------------------------------------------------------------------
Error: Can't load plugin imap_quota_plugin: Plugin quota must be loaded also
---%<-------------------------------------------------------------------------
(This file was created from the wiki on 2011-01-13 04:52)
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