Fix panic for empty sequences

Signed-off-by: Luca Della Vedova <[email protected]>

Author: luca-della-vedova

rclrs/src/dynamic_message/field_access/dynamic_sequence.rs

@@ -196,6 +196,9 @@ impl TypeErasedSequence {
         T: Proxy<'msg>,
     {
         let element_size = T::size_in_memory(metadata);
+        if self.data.is_null() {
+            return Vec::new();
+        };
         let sequence_data =
             std::slice::from_raw_parts(self.data as *const u8, self.size * element_size);
         check::<T>(sequence_data);
@@ -210,6 +213,9 @@ impl TypeErasedSequence {
         T: ProxyMut<'msg>,
     {
         let element_size = T::size_in_memory(metadata);
+        if self.data.is_null() {
+            return Vec::new();
+        };
         let sequence_data =
             std::slice::from_raw_parts_mut(self.data as *mut u8, self.size * element_size);
         check::<T>(sequence_data);

rclrs/src/dynamic_message/message_structure.rs

@@ -1141,4 +1141,16 @@ mod tests {
         let _dyn_msg =
             DynamicMessage::new("test_msgs/msg/BoundedSequences".try_into().unwrap()).unwrap();
     }
+
+    #[test]
+    fn empty_sequence_issue_492() {
+        let message_type = MessageTypeName {
+            package_name: "test_msgs".to_owned(),
+            type_name: "UnboundedSequences".to_owned(),
+        };
+        let mut msg = DynamicMessage::new(message_type).unwrap();
+
+        let _ = msg.get("basic_types_values");
+        let _ = msg.get_mut("basic_types_values");
+    }
 }