SW-957: by default, expire message after 5 days

LCS/Messaging/python/messaging/messages.py

@@ -59,7 +59,7 @@ class LofarMessage:
         self.content = content
         self.subject = subject
         self.priority = priority
-        self.ttl = ttl if ttl is not None else 5*24*60*60 # by default, expire message after 5 days. 
+        self.ttl = ttl if ttl is not None else 5*24*60*60 # by default, expire message after 5 days.
         self.id = uuid.uuid4() if id is None else uuid.UUID(id)
 
     def as_kombu_publish_kwargs(self):
@@ -75,7 +75,9 @@ class LofarMessage:
                           }
 
         if self.ttl:
-           publish_kwargs['expiration'] = self.ttl
+            # https://www.rabbitmq.com/ttl.html#per-message-ttl-in-publishers
+            # Since the expiration field must be a string, the broker will (only) accept the string representation of the number.
+            publish_kwargs['expiration'] = str(self.ttl)
 
         return publish_kwargs