[gstreamermm] Gst::BaseTransform: fix copy_metadata_vfunc memory leak

[Marcin Kolny <mkolny src gnome org>]

commit 4d1efb14d2e99b7525f222a561bb1eb9f4576026
Author: Marcin Kolny <marcin kolny gmail com>
Date:   Sat Apr 14 16:22:47 2018 +0100

    Gst::BaseTransform: fix copy_metadata_vfunc memory leak
    
    default_copy_metadata() requires writable output buffer. However,
    gstreamermm increases refcount (Glib::wrap(outbuf, true)), so the
    buffer was not writable anymore. This commit fixes this issue.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=794249

 gstreamer/src/basetransform.ccg |   59 +++++++++++++++++++++++++++++++++++++++
 gstreamer/src/basetransform.hg  |    4 ++-
 2 files changed, 62 insertions(+), 1 deletions(-)
---
diff --git a/gstreamer/src/basetransform.ccg b/gstreamer/src/basetransform.ccg
index 14fc387..9ae7b68 100644
--- a/gstreamer/src/basetransform.ccg
+++ b/gstreamer/src/basetransform.ccg
@@ -208,6 +208,49 @@ GstFlowReturn BaseTransform_Class::generate_output_vfunc_callback(GstBaseTransfo
   return RType();
 }
 
+gboolean BaseTransform_Class::copy_metadata_vfunc_callback(GstBaseTransform* self, GstBuffer* input, 
GstBuffer* outbuf)
+{
+  const auto obj_base = static_cast<Glib::ObjectBase*>(
+      Glib::ObjectBase::_get_current_wrapper((GObject*)self));
+
+  // Non-gtkmmproc-generated custom classes implicitly call the default
+  // Glib::ObjectBase constructor, which sets is_derived_. But gtkmmproc-
+  // generated classes can use this optimisation, which avoids the unnecessary
+  // parameter conversions if there is no possibility of the virtual function
+  // being overridden:
+  if(obj_base && obj_base->is_derived_())
+  {
+    const auto obj = dynamic_cast<CppObjectType* const>(obj_base);
+    if(obj) // This can be NULL during destruction.
+    {
+      try // Trap C++ exceptions which would normally be lost because this is a C callback.
+      {
+        // Call the virtual member method, which derived classes might override.
+        // outbuf must be writable, so we can't increase a refcount:
+        Glib::RefPtr<Gst::Buffer> cpp_output = Glib::wrap(outbuf, false);
+        auto res = static_cast<int>(obj->copy_metadata_vfunc(Glib::wrap(input, true), cpp_output));
+        IGNORE_RESULT(cpp_output.release());
+        return res;
+      }
+      catch(...)
+      {
+        Glib::exception_handlers_invoke();
+      }
+    }
+  }
+
+  BaseClassType *const base = static_cast<BaseClassType*>(
+      g_type_class_peek_parent(G_OBJECT_GET_CLASS(self)) // Get the parent class of the object class (The 
original underlying C class).
+  );
+
+  // Call the original underlying C function:
+  if(base && base->copy_metadata)
+    return (*base->copy_metadata)(self, input, outbuf);
+
+  using RType = gboolean;
+  return RType();
+}
+
 FlowReturn Gst::BaseTransform::generate_output_vfunc(Glib::RefPtr<Gst::Buffer>& outbuf)
 {
   BaseClassType *const base = static_cast<BaseClassType*>(
@@ -227,6 +270,22 @@ FlowReturn Gst::BaseTransform::generate_output_vfunc(Glib::RefPtr<Gst::Buffer>&
   return RType();
 }
 
+bool Gst::BaseTransform::copy_metadata_vfunc(const Glib::RefPtr<Gst::Buffer>& input, const 
Glib::RefPtr<Gst::Buffer>& outbuf) 
+{
+  const auto base = static_cast<BaseClassType*>(
+      g_type_class_peek_parent(G_OBJECT_GET_CLASS(gobject_)) // Get the parent class of the object class 
(The original underlying C class).
+  );
+
+  if(base && base->copy_metadata)
+  {
+    bool retval((*base->copy_metadata)(gobj(),Glib::unwrap(input),Glib::unwrap(outbuf)));
+    return retval;
+  }
+
+  using RType = bool;
+  return RType();
+}
+
 gboolean BaseTransform_Class::query_vfunc_callback(GstBaseTransform* self, GstPadDirection direction, 
GstQuery* query)
 {
   const auto obj_base = static_cast<Glib::ObjectBase*>(
diff --git a/gstreamer/src/basetransform.hg b/gstreamer/src/basetransform.hg
index f845414..46a9b52 100644
--- a/gstreamer/src/basetransform.hg
+++ b/gstreamer/src/basetransform.hg
@@ -309,7 +309,7 @@ public:
   /** Optional. Copy the metadata from the input buffer to the output buffer.
    * The default implementation will copy the flags, timestamps and offsets of the buffer.
    */
-  _WRAP_VFUNC(bool copy_metadata(const Glib::RefPtr<Gst::Buffer>& input, const Glib::RefPtr<Gst::Buffer>& 
outbuf), "copy_metadata")
+  virtual bool copy_metadata_vfunc(const Glib::RefPtr<Gst::Buffer>& input, const Glib::RefPtr<Gst::Buffer>& 
outbuf);
 
   /** Optional. Handle a requested query. Subclasses that implement this should must chain up to
    * the parent if they didn't handle the query
@@ -321,6 +321,7 @@ protected:
   _PUSH(SECTION_PCC_CLASS_INIT_VFUNCS)
   klass->prepare_output_buffer = &prepare_output_buffer_vfunc_callback;
   klass->transform = &transform_vfunc_callback;
+  klass->copy_metadata = &copy_metadata_vfunc_callback;
   klass->generate_output = &generate_output_vfunc_callback;
   klass->query = &query_vfunc_callback;
   klass->propose_allocation = &propose_allocation_vfunc_callback;
@@ -328,6 +329,7 @@ protected:
   _SECTION(SECTION_PH_VFUNCS)
   static GstFlowReturn prepare_output_buffer_vfunc_callback(GstBaseTransform* self, GstBuffer* input, 
GstBuffer** buf);
   static GstFlowReturn transform_vfunc_callback(GstBaseTransform* self, GstBuffer* inbuf, GstBuffer* outbuf);
+  static gboolean copy_metadata_vfunc_callback(GstBaseTransform* self, GstBuffer* input, GstBuffer* outbuf);
   static GstFlowReturn generate_output_vfunc_callback(GstBaseTransform* self, GstBuffer** outbuf);
   static gboolean query_vfunc_callback(GstBaseTransform* self, GstPadDirection direction, GstQuery* query);
   static gboolean propose_allocation_vfunc_callback(GstBaseTransform* self, GstQuery* decide_query, 
GstQuery* query);