gststructure: Add gst_structure_get_flags method

We don't prevent setting G_TYPE_FLAGS on GstStructure
but no helper method for getting the value.
Add a method similar to gst_structure_get_enum()

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2770>

subprojects/gstreamer/gst/gststructure.c

@@ -3476,3 +3476,43 @@ gst_structure_set_list (GstStructure * structure, const gchar * fieldname,
 {
   _gst_structure_set_any_list (structure, GST_TYPE_LIST, fieldname, array);
 }
+
+/**
+ * gst_structure_get_flags:
+ * @structure: a #GstStructure
+ * @fieldname: the name of a field
+ * @flags_type: the flags type of a field
+ * @value: (out): a pointer to an unsigned int to set
+ *
+ * Sets the unsigned int pointed to by @value corresponding to the value of the
+ * given field. Caller is responsible for making sure the field exists,
+ * has the correct type and that the flagstype is correct.
+ *
+ * Returns: %TRUE if the value could be set correctly. If there was no field
+ * with @fieldname or the existing field did not contain flags or
+ * did not contain flags of the given type, this function returns %FALSE.
+ *
+ * Since: 1.22
+ */
+gboolean
+gst_structure_get_flags (const GstStructure * structure,
+    const gchar * fieldname, GType flags_type, guint * value)
+{
+  GstStructureField *field;
+
+  g_return_val_if_fail (structure != NULL, FALSE);
+  g_return_val_if_fail (fieldname != NULL, FALSE);
+  g_return_val_if_fail (flags_type != G_TYPE_INVALID, FALSE);
+  g_return_val_if_fail (value != NULL, FALSE);
+
+  field = gst_structure_get_field (structure, fieldname);
+
+  if (field == NULL)
+    return FALSE;
+  if (!G_TYPE_CHECK_VALUE_TYPE (&field->value, flags_type))
+    return FALSE;
+
+  *value = g_value_get_flags (&field->value);
+
+  return TRUE;
+}

subprojects/gstreamer/gst/gststructure.h

@@ -342,6 +342,13 @@ GST_API
 gboolean              gst_structure_get_list             (GstStructure        * structure,
                                                           const gchar         * fieldname,
                                                           GValueArray        ** array);
+
+GST_API
+gboolean              gst_structure_get_flags            (const GstStructure  * structure,
+                                                          const gchar         * fieldname,
+                                                          GType                 flags_type,
+                                                          guint               * value);
+
 GST_API
 gchar *               gst_structure_to_string            (const GstStructure * structure) G_GNUC_MALLOC;
 GST_API

subprojects/gstreamer/tests/check/gst/gststructure.c

@@ -1018,6 +1018,22 @@ GST_START_TEST (test_flagset)
 
 GST_END_TEST;
 
+GST_START_TEST (test_flags)
+{
+  GstStructure *s;
+  GstSeekFlags flags = GST_SEEK_FLAG_FLUSH | GST_SEEK_FLAG_KEY_UNIT;
+  guint parsed_flags = 0;
+
+  s = gst_structure_new ("test-struct", "test-seek-flags",
+      GST_TYPE_SEEK_FLAGS, flags, NULL);
+  fail_unless (gst_structure_get_flags (s, "test-seek-flags",
+          GST_TYPE_SEEK_FLAGS, &parsed_flags));
+  fail_unless (flags == (GstSeekFlags) parsed_flags);
+  gst_structure_free (s);
+}
+
+GST_END_TEST;
+
 static Suite *
 gst_structure_suite (void)
 {
@@ -1050,6 +1066,7 @@ gst_structure_suite (void)
   tcase_add_test (tc_chain, test_map_in_place);
   tcase_add_test (tc_chain, test_filter_and_map_in_place);
   tcase_add_test (tc_chain, test_flagset);
+  tcase_add_test (tc_chain, test_flags);
   return s;
 }