Cannot get the data using Gio from gi.repository in the function read_async.
The C API describes the read_async as

void g_input_stream_read_async (GInputStream *stream,void *buffer,gsize count,int io_priority,GCancellable *cancellable,GAsyncReadyCallback callback,gpointer user_data);

but in python we call the function as

stream.read_async (buffer,self.block_size, GLib.PRIORITY_DEFAULT, self._cancel, self._read_cb, None)            

where buffer can't be a pointer, there is no way to get the data readed with the "introspected" function

How we can do this?