Error while contacting my gdbus server without the bus daemon

Question

I am trying to create a peer-to-peer gdbus communication on a linux system. I used gdbus-codegen tool to generate the code which I can use to create the server. My server program instantiates an object using the generated skeleton functions and exports it via the g_dbus_interface_skeleton_export function. Here is an overview of the server function which gets invoked when the server receives a new connection:

static gboolean on_new_connection(GDBusServer *server, GDBusConnection *connection, gpointer user_data)
{
    GError *error = NULL;
    printf("Got a new connection!\n");

    my_object = org_some_object_skeleton_new();
    g_signal_connect(my_object, "handle-get-magic-number", G_CALLBACK(my_callback_function), NULL);
    if(!g_dbus_interface_skeleton_export(G_DBUS_INTERFACE_SKELETON(my_object), connection,  "/some/path", &error))

    return TRUE;
}

After compiling and starting the server, I try to contact it using the gdbus tool:

gdbus call --address=unix:path=/home/my_user_name/MySockets/some_socket --object-path=/some/path --method=org.some.object.get_magic_number

However, I get the following response:

Error connecting: GDBus.Error:org.freedesktop.DBus.Error.UnknownMethod: No such interface “org.freedesktop.DBus” on object at path /org/freedesktop/DBus

What is going on here? Is it actually possible to use the generated skeleton functions when creating a peer-to-peer server, or do I have to use the lower-level API calls such as g_dbus_connection_register_object?

Answer 1

From what I gather from your question and your comment, it seems like you're trying to do D-Bus IPC on a raw socket, without any D-Bus daemon running on that path. It unfortunately doesn't work like that, since D-Bus really needs some kind of broker running. You have a few options here:

• Rather than use a raw socket, you can connect to the session or system bus (both should be available in a normal Linux session)
• You start a D-Bus daemon that listens to the socket at the provided path before starting your application. See also dbus-daemon or D-Bus Broker for implementations.
• You keep on using a raw socket, at which point you use an application-specific protocol (which can be based on any kind of RPC).