doc/reference/libpurple/tut_c_plugins.xml

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<chapter id="chapter-tut-c-plugins">
  <title>C Plugins tutorial</title>

  <sect2 id="tut-c-plugins-introduction">
  <title>Introduction</title>
  <para>
  C plugins are native plugins.  They have complete access to all of the API,
  and can do basically whatever they want.  All of the protocol plugins are
  also written in C.
  </para>
  </sect2>

  <sect2 id="tut-c-plugins-getting-started">
  <title>Getting Started</title>
  <para>
  To develop a plugin you need to have the libpurple and (for UI plugins) the
  Pidgin/Finch source code or development headers.  It is generally a good idea
  to compile against the same version of Pidgin that you are running.  You may
  also want to develop against the code in our Mercurial repository if you need
  to use a new feature.  Please do not abuse our Mercurial repository, however.
  </para>
  </sect2>

  <sect2 id="tut-c-plugins-hello-world">
  <title>An Example</title>
  <para>
  I know every tutorial has a hello world, so why should libpurple be any
  different?

<example>
<title>Hello World!</title>
<programlisting>
#include &lt;purple.h&gt;

static PurplePluginInfo *
plugin_query(GError **error)
{
	const gchar * const authors[] = {
		"Author Name &lt;e@mail&gt;",
		NULL
	};

	/* For specific notes on the meanings of each of these members, consult the
	   C Plugin Howto on the website. */
	return purple_plugin_info_new (
		"name",         "Hello World!",
		"version",      VERSION,
		"category",     "Example",
		"summary",      "Hello World Plugin",
		"description",  "Hello World Plugin",
		"authors",      authors,
		"website",      "http://helloworld.tld",
		"abi-version",  PURPLE_ABI_VERSION,
		NULL
	);
}

static gboolean
plugin_load(PurplePlugin *plugin, GError **error)
{
	purple_notify_message(plugin, PURPLE_NOTIFY_MSG_INFO, "Hello World!",
						"This is the Hello World! plugin :)",
						NULL, NULL, NULL, NULL);

	return TRUE;
}

static gboolean
plugin_unload(PurplePlugin *plugin, GError **error)
{
	return TRUE;
}

PURPLE_PLUGIN_INIT(hello_world, plugin_query, plugin_load, plugin_unload);
</programlisting>
</example>
  </para>

  <para>
  Okay, so what does all this mean?  We start off by including purple.h.  This
  file includes all the libpurple header files.
  </para>

  <para>
  <literal>plugin_query</literal>, <literal>plugin_load</literal> and
  <literal>plugin_unload</literal> must be implemented in every plugin.  Each of
  these functions can return an error on failure by using
  <function>g_set_error()</function> on the <literal>error</literal> argument.
  </para>

  <para>
  <literal>plugin_query</literal> is called when the plugin is probed by the
  plugin system, and returns various information about the plugin in form of a
  newly created <literal>PurplePluginInfo</literal> instance.  For a list of all
  available properties, see
  <link linkend="purple-plugin-info-new"><function>purple_plugin_info_new()</function></link>.
  </para>

  <para>
  <literal>plugin_load</literal> is called when the plugin is loaded so that you
  can initialize any variables, register dynamic types, and so on.  Plugins may
  also want to add their preferences to the pref tree--more about that later.
  In this plugin we'll just use it to display a message.
  </para>

  <para>
  <literal>plugin_unload</literal> is called when the plugin is unloaded, and we
  can use it to wrap up everything, and free our variables.
  </para>

  <para>
  Finally we have
  <link linkend="PURPLE-PLUGIN-INIT:CAPS"><function>PURPLE_PLUGIN_INIT()</function></link>.
  It is a macro that every plugin MUST have. It tells libpurple some basic
  things about your plugin, like what name to use if the plugin is compiled
  statically, along with the <literal>plugin_query</literal>,
  <literal>plugin_load</literal>, and <literal>plugin_unload</literal>
  functions.
  </para>
 </sect2>
</chapter>