DBusMessageFilterFunction

Signature for function used in add_filter.

A filter function is passed a DBusMessage and expected to return a DBusMessage too. Passive filter functions that don't modify the message can simply return the message object:

static GDBusMessage *
passive_filter (GDBusConnection *connection
								GDBusMessage		*message,
								gboolean				 incoming,
								gpointer				 user_data)
{
	// inspect @message
	return message;
}

Filter functions that wants to drop a message can simply return null:

static GDBusMessage *
drop_filter (GDBusConnection *connection
						 GDBusMessage		*message,
						 gboolean				 incoming,
						 gpointer				 user_data)
{
	if (should_drop_message)
		{
			g_object_unref (message);
			message = NULL;
		}
	return message;
}

Finally, a filter function may modify a message by copying it:

static GDBusMessage *
modifying_filter (GDBusConnection *connection
									GDBusMessage		*message,
									gboolean				 incoming,
									gpointer				 user_data)
{
	GDBusMessage *copy;
	GError *error;

	error = NULL;
	copy = g_dbus_message_copy (message, &error);
	// handle @error being set
	g_object_unref (message);

	// modify @copy

	return copy;
}

If the returned DBusMessage is different from message and cannot be sent on connection (it could use features, such as file descriptors, not compatible with connection), then a warning is logged to standard error. Applications can check this ahead of time using to_blob passing a DBusCapabilityFlags value obtained from connection .

Parameters:

connection	A DBusConnection.
message	A locked DBusMessage that the filter function takes ownership of.
incoming	true if it is a message received from the other peer, false if it is a message to be sent to the other peer.
user_data	User data passed when adding the filter.

Returns:

A DBusMessage that will be freed with unref or null to drop the message. Passive filter functions can simply return the passed message object.