DBUS glibc simple code problem

[flying match]

Dear Pidgin gurus,

I'm a newbie of Pidgin developer. And I'm trying to write a simple DBUS
glibc based application for Pidgin.

I know there are bunch of Python based eamples in Pidgin source code, such
as purple-notifications-example and purple-remote. What I want to achieve in
my first step is very simple, implement a glibc based
purple-notifications-example, and upload to the Pidgin web page to share
with everybody.

The code is complied, but just cannot get any received-im-msg notification
no matter how hard I try.  I wonder if anyone could spend some time helping
me find the reason (guess could be very stupid anyway)? If I managed to get
the code run as smoothly as that purple-notifications-example, I'll submit
to the web page to share with the community.

Your help is really appreciated!

Ok, now let's get to my stupid code, quite short anyway.

#include <stdio.h>
#include <stdlib.h>

#include <glib.h>
#include <glib-object.h>
#include <dbus/dbus.h>

/* access point of Pidgin dbus */
#define DBUS_SERVICE_PURPLE      "im.pidgin.purple.PurpleService"
#define DBUS_PATH_PURPLE         "/im/pidgin/purple/PurpleObject"
#define DBUS_INTERFACE_PURPLE    "im.pidgin.purple.PurpleInterface"

/* dbus globle instance */
DBusGConnection *bus;
DBusGProxy *purple_proxy;

 /* Main event loop */
GMainLoop *loop = NULL;

void received_im_msg_cb (DBusGProxy *purple_proxy, int account_id, const
char *name,
                                          const char *message, int conv_id,
unsigned int flags,
                                          gpointer user_data)
{
    g_print("%s says %s\n", name, message);
}

int main (int argc, char **argv)
{
    GError *error = NULL;

    g_type_init ();

    bus = dbus_g_bus_get (DBUS_BUS_SESSION, &error);
    if (bus == NULL) {
        g_printerr("Failed to open connection to bus: %s", error->message);
        g_error_free(error);
        return -1;
    }

    /* Create a proxy object for the bus driver */
    purple_proxy = dbus_g_proxy_new_for_name (bus,
                                              DBUS_SERVICE_PURPLE,
                                              DBUS_PATH_PURPLE,
                                              DBUS_INTERFACE_PURPLE);

    if (!purple_proxy) {
        g_printerr("Couldn't connect to the Purple Service: %s",
error->message);
        g_error_free(error);
        return -1;
    }

     loop = g_main_loop_new (NULL, FALSE);

     dbus_g_proxy_add_signal(purple_proxy, "ReceivedImMsg",
                            G_TYPE_NONE, G_TYPE_INT, G_TYPE_STRING,
G_TYPE_STRING,
                            G_TYPE_INT, G_TYPE_INT, G_TYPE_INVALID);

    dbus_g_proxy_connect_signal(purple_proxy, "ReceivedImMsg",
                                G_CALLBACK(received_im_msg_cb), bus, NULL);

    g_main_loop_run (loop);

   return 0;
}

I compiled the code above with following command:
$gcc -MMD -Wall -ggdb -O `pkg-config --cflags dbus-1 glib-2.0 dbus-glib-1`
`pkg-config --libs dbus-1 glib-2.0 dbus-glib-1` main.c -o dbus_test

And run it
$./dbus_test

But this dbus_test does not print any message no matter how many IM messages
I receive from my buddies on the Pidgin 2.3.1, which runs on my Ubuntu Linux
PC.

Couple of questions if you are still reading:
1. Unlike Pidgin dbus methods which can be viewed by dbus-viewer, dbus
signals don't have any definitions. As a result, I have no way to know the
parameters associated with each signal. I.e., I'm just guessing what
parameters associated with signal ReceviedImMsg above.

2. The dbus_g_proxy_add_signal() and dbus_g_proxy_connect_signal() do not
return any failure, so I don't know if my signal handler is added
successfully or not. I tried to change different parameters associated with
the ReceivedImMsg signal, given any parameter, the code can compile and run,
but just don't actually work.

Again, your help is appreciated!

Best,
Flying
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