Fix building argument-less messages

Building an argument-less message such as eos yields an assertion failure due to the inner structure being null. The short term solution consists in checking that the inner `structure` is not `null` before attempting to insert `other_fields`. The consequence is that `others_fields` defined for argument-less messages will be ignored. A correction will be applied when GStreamer 1.14 is released thank to the introduction of `gst_message_writable_structure` (see https://bugzilla.gnome.org/show_bug.cgi?id=792928). Due to the dependency on GStreamer 1.14, the correction will be only available under the activation of a feature "v1_14".

Events are not affected as the build method the availability of `gst_event_writable_structure` and this function "will never return NULL". However, we can avoid a `structure` allocation for argument-less messages without `other_fields`.

gstreamer/src/event.rs

@@ -895,7 +895,7 @@ macro_rules! event_builder_generic_impl {
                     ffi::gst_event_set_running_time_offset(event, running_time_offset);
                 }
 
-                {
+                if !self.other_fields.is_empty() {
                     let s = StructureRef::from_glib_borrow_mut(
                         ffi::gst_event_writable_structure(event)
                     );
@@ -1667,3 +1667,49 @@ impl<'a> CustomBothOobBuilder<'a> {
         ev
     });
 }
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_simple() {
+        ::init().unwrap();
+
+        // Event without arguments
+        let flush_start_evt = Event::new_flush_start().build();
+        match flush_start_evt.view() {
+            EventView::FlushStart(flush_start_evt) => {
+                assert!(flush_start_evt.0.get_structure().is_none());
+            },
+            _ => panic!("flush_start_evt.view() is not an EventView::FlushStart(_)"),
+        }
+
+        let flush_start_evt = Event::new_flush_start()
+            .other_fields(&[("extra-field", &true)])
+            .build();
+        match flush_start_evt.view() {
+            EventView::FlushStart(flush_start_evt) => {
+                assert!(flush_start_evt.0.get_structure().is_some());
+                if let Some(other_fields) = flush_start_evt.0.get_structure() {
+                    assert!(other_fields.has_field("extra-field"));
+                }
+            },
+            _ => panic!("flush_start_evt.view() is not an EventView::FlushStart(_)"),
+        }
+
+        // Event with arguments
+        let flush_stop_evt = Event::new_flush_stop(true)
+            .other_fields(&[("extra-field", &true)])
+            .build();
+        match flush_stop_evt.view() {
+            EventView::FlushStop(flush_stop_evt) => {
+                assert_eq!(flush_stop_evt.get_reset_time(), true);
+                assert!(flush_stop_evt.0.get_structure().is_some());
+                if let Some(other_fields) = flush_stop_evt.0.get_structure() {
+                    assert!(other_fields.has_field("extra-field"));
+                }
+            }
+            _ => panic!("flush_stop_evt.view() is not an EventView::FlushStop(_)"),
+        }
+    }
+}

gstreamer/src/message.rs

@@ -1165,6 +1165,8 @@ macro_rules! message_builder_generic_impl {
             }
         }
 
+        // Warning: other_fields are ignored with argument-less messages
+        // until GStreamer 1.14 is released
         pub fn other_fields(self, other_fields: &[(&'a str, &'a ToSendValue)]) -> Self {
             Self {
                 other_fields: self.other_fields.iter().cloned()
@@ -1183,13 +1185,19 @@ macro_rules! message_builder_generic_impl {
                     ffi::gst_message_set_seqnum(msg, seqnum.to_glib());
                 }
 
-                {
-                    let s = StructureRef::from_glib_borrow_mut(
-                        ffi::gst_message_get_structure(msg) as *mut _
-                    );
+                if !self.other_fields.is_empty() {
+                    // issue with argument-less messages. We need the function
+                    // ffi::gst_message_writable_structure to sort this out
+                    // and this function will be available in GStreamer 1.14
+                    // See https://github.com/sdroege/gstreamer-rs/pull/75
+                    // and https://bugzilla.gnome.org/show_bug.cgi?id=792928
+                    let structure = ffi::gst_message_get_structure(msg);
+                    if !structure.is_null() {
+                        let structure = StructureRef::from_glib_borrow_mut(structure as *mut _);
 
                         for (k, v) in self.other_fields {
-                        s.set_value(k, v.to_send_value());
+                            structure.set_value(k, v.to_send_value());
+                        }
                     }
                 }
 
@@ -2442,3 +2450,37 @@ impl<'a> RedirectBuilder<'a> {
         msg
     });
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_simple() {
+        ::init().unwrap();
+
+        // Message without arguments
+        let eos_msg = Message::new_eos().build();
+        match eos_msg.view() {
+            MessageView::Eos(eos_msg) => {
+                assert!(eos_msg.0.get_structure().is_none());
+            },
+            _ => panic!("eos_msg.view() is not a MessageView::Eos(_)"),
+        }
+
+        // Note: can't define other_fields for argument-less messages before GStreamer 1.14
+
+        // Message with arguments
+        let buffering_msg = Message::new_buffering(42)
+            .other_fields(&[("extra-field", &true)])
+            .build();
+        match buffering_msg.view() {
+            MessageView::Buffering(buffering_msg) => {
+                assert_eq!(buffering_msg.get_percent(), 42);
+                assert!(buffering_msg.0.get_structure().is_some());
+                assert!(buffering_msg.0.get_structure().unwrap().has_field("extra-field"));
+            }
+            _ => panic!("buffering_msg.view() is not a MessageView::Buffering(_)"),
+        }
+    }
+}