overrides: Try hard to make the query writable in the pad query function

Summary:
We know that the bindings will get an extra ref but we know that
it is not actually needed, so we are safe to decrease the refcount
by one in that particular context making sure we give PyGI its
ref back when we are done.

Reviewers: Mathieu_Du

Differential Revision: http://phabricator.freedesktop.org/D41

https://bugzilla.gnome.org/show_bug.cgi?id=746329

gi/overrides/Gst.py

@@ -25,6 +25,7 @@
 # any later version.
 
 import sys
+from inspect import signature
 from ..overrides import override
 from ..importer import modules
 
@@ -99,12 +100,27 @@ class Pad(Gst.Pad):
     def __init__(self):
         self._real_chain_func = None
         self._real_event_func = None
+        self._real_query_func = None
 
     def _chain_override(self, pad, parent, buf):
         return self._real_chain_func(pad, buf)
 
-    def _event_override(self, pad, parent, buf):
-        return self._real_event_func(pad, buf)
+    def _event_override(self, pad, parent, event):
+        return self._real_event_func(pad, event)
+
+    def _query_override(self, pad, parent, query):
+        query.mini_object.refcount -= 1
+        n_params = len(signature(self._real_query_func).parameters)
+        if n_params == 2:
+            res = self._real_query_func(pad, query)
+        elif n_params == 3:
+            res = self._real_query_func(pad, parent, query)
+        else:
+            raise TypeError("Invalid query method %s, 2 or 3 arguments requiered"
+                            % self._real_query_func)
+        query.mini_object.refcount += 1
+
+        return res
 
     def set_chain_function(self, func):
         self._real_chain_func = func
@@ -114,6 +130,14 @@ class Pad(Gst.Pad):
         self._real_event_func = func
         self.set_event_function_full(self._event_override, None)
 
+    def set_query_function(self, func):
+        self._real_query_func = func
+        self.set_query_function_full(self._chain_override, None)
+
+    def set_query_function_full(self, func, udata):
+        self._real_query_func = func
+        self._real_set_query_function_full(self._query_override, None)
+
     def query_caps(self, filter=None):
         return Gst.Pad.query_caps(self, filter)
 
@@ -123,6 +147,7 @@ class Pad(Gst.Pad):
             raise LinkError(ret)
         return ret
 
+Pad._real_set_query_function_full = Gst.Pad.set_query_function_full
 Pad = override(Pad)
 __all__.append('Pad')
 
@@ -199,6 +224,7 @@ __all__.append('Pipeline')
 class Structure(Gst.Structure):
     def __getitem__(self, key):
         return self.get_value(key)
+
     def __setitem__(self, key, value):
         return self.set_value(key, value)