C Plugin Tutorial

Introduction

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.

Getting Started

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.

An Example

I know every tutorial has a hello world, so why should libpurple be any different?

#include <purple.h>

static GPluginPluginInfo *
hello_world_query(GError **error)
{
    const gchar * const authors[] = {
        "Author Name <e@mail>",
        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
hello_world_load(GPluginPlugin *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
hello_world_unload(GPluginPlugin *plugin, GError **error)
{
    return TRUE;
}

GPLUGIN_NATIVE_PLUGIN_DECLARE(hello_world)

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

hello_world_query, hello_world_load and hello_world_unload are functions that must be implemented in every plugin. These functions are named according to the value passed to GPLUGIN_NATIVE_PLUGIN_DECLARE which is described below.

hello_world_query is called when the plugin is queried by the plugin system, and returns various information about the plugin in form of a newly created instance of GPluginPluginInfo or a subclass. For a list of all available properties, see purple_plugin_info_new().

If anything should go wrong during the query you can return an error by using g_set_error() on the error argument.

hello_world_load is called when the plugin is loaded. That is the user has enabled the plugin or libpurple is loading a plugin that was previously loaded. You can initialize any variables, register dynamic types, and so on in this function. 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. Just like hello_world_query if there are any errors that arise, you can call g_set_error() on the error argument and return FALSE.

hello_world_unload is called when the plugin is unloaded. That is, when the user has manually unloaded the plugin or the program is shutting down. We can use it to wrap up everything, and free our variables. Again, if there are any errors, you can call g_set_error() on the error argument and return FALSE.

Finally we have GPLUGIN_NATIVE_PLUGIN_DECLARE(). It is a helper macro that makes creating plugins easier. It has a single argument which is the prefix used for the _query, _load, and _unload functions.