prevent use after frees with structures that are transfer:none

gst/gst_message.go

@@ -95,9 +95,7 @@ func (m *Message) GetStructure() *Structure {
 		return nil
 	}
 
-	// The returned structure must not be freed. Applies to all methods.
-	// https://gstreamer.freedesktop.org/documentation/gstreamer/gstmessage.html#gst_message_parse_error_details
-	return wrapStructure(st)
+	return structureFromGlibNone(st)
 }
 
 // parseToError returns a new GError from this message instance. There are multiple

gst/gst_structure.go

@@ -17,6 +17,7 @@ import (
 	"fmt"
 	"os"
 	"reflect"
+	"runtime"
 	"sync"
 	"unsafe"
 
@@ -35,7 +36,7 @@ func NewStructure(name string) *Structure {
 	cName := C.CString(name)
 	defer C.free(unsafe.Pointer(cName))
 	structure := C.gst_structure_new_empty(cName)
-	return wrapStructure(structure)
+	return structureFromGlibFull(structure)
 }
 
 // NewStructureFromString builds a new GstStructure from the given string.
@@ -46,7 +47,7 @@ func NewStructureFromString(stStr string) *Structure {
 	if structure == nil {
 		return nil
 	}
-	return wrapStructure(structure)
+	return structureFromGlibFull(structure)
 }
 
 // MarshalStructure will convert the given go struct into a GstStructure. Currently nested
@@ -190,22 +191,54 @@ var TypeStructure = glib.Type(C.gst_structure_get_type())
 
 var _ glib.ValueTransformer = &Structure{}
 
+func (s *Structure) copy() *C.GstStructure {
+	return C.gst_structure_copy(s.Instance())
+}
+
 // ToGValue implements a glib.ValueTransformer
 func (s *Structure) ToGValue() (*glib.Value, error) {
 	val, err := glib.ValueInit(TypeStructure)
 	if err != nil {
 		return nil, err
 	}
+
 	C.gst_value_set_structure(
 		(*C.GValue)(unsafe.Pointer(val.GValue)),
-		s.Instance(),
+		s.copy(),
 	)
 	return val, nil
 }
 
+// marshalStructure is used to extract the GstStructure from a GValue.
+func marshalStructure(p unsafe.Pointer) (interface{}, error) {
+	c := C.gst_value_get_structure(toGValue(p))
+	obj := (*C.GstStructure)(unsafe.Pointer(c))
+	return structureFromGlibNone(obj), nil
+}
+
 func wrapStructure(st *C.GstStructure) *Structure {
 	return &Structure{
 		ptr:   unsafe.Pointer(st),
 		gType: glib.Type(st._type),
 	}
 }
+
+// structureFromGlibNone wraps a *C.GstStructure in a Structure after copying it.
+// this is needed when the structure is returned from a function that does not transfer ownership.
+func structureFromGlibNone(st *C.GstStructure) *Structure {
+	copy := C.gst_structure_copy(st)
+
+	return structureFromGlibFull(copy)
+}
+
+// structureFromGlibFull wraps a *C.GstStructure in a Structure. This is used when the structure
+// is returned by a function that transfers ownership to the caller.
+func structureFromGlibFull(st *C.GstStructure) *Structure {
+	s := wrapStructure(st)
+
+	runtime.SetFinalizer(s, func(s *Structure) {
+		s.Free()
+	})
+
+	return s
+}

gst/gst_values.go

@@ -161,16 +161,6 @@ func ValueGetCapsFeatures(value *glib.Value) *CapsFeatures {
 	return &CapsFeatures{native: feats}
 }
 
-// ValueGetStructure extracts the GstStructure from a glib.Value, or nil
-// if one does not exist.
-func ValueGetStructure(gval *glib.Value) *Structure {
-	st := C.gst_value_get_structure((*C.GValue)(unsafe.Pointer(gval.GValue)))
-	if st == nil {
-		return nil
-	}
-	return wrapStructure(st)
-}
-
 // ValueIntersect calculates the intersection of two values. If the values have a non-empty intersection,
 // the value representing the intersection isreturned. Otherwise this function returns false. This function
 // can also return false for any allocation errors.

gst/gst_wrappers.go

@@ -461,12 +461,6 @@ func marshalCapsFeatures(p unsafe.Pointer) (interface{}, error) {
 	return wrapCapsFeatures(obj), nil
 }
 
-func marshalStructure(p unsafe.Pointer) (interface{}, error) {
-	c := C.gst_value_get_structure(toGValue(p))
-	obj := (*C.GstStructure)(unsafe.Pointer(c))
-	return wrapStructure(obj), nil
-}
-
 func marshalContext(p unsafe.Pointer) (interface{}, error) {
 	c := C.g_value_get_object(toGValue(p))
 	obj := (*C.GstContext)(unsafe.Pointer(c))