Add support for arbitrary deserializers

rele/subscription.py

@@ -8,6 +8,8 @@
 
 logger = logging.getLogger(__name__)
 
+def json_deserializer(message):
+    return json.loads(message.data.decode("utf-8"))
 
 class Subscription:
     """The Subscription class
@@ -35,14 +37,22 @@ def callback_func(self, data, **kwargs):
     """
 
     def __init__(
-        self, func, topic, prefix="", suffix="", filter_by=None, backend_filter_by=None
+        self,
+        func,
+        topic,
+        prefix="",
+        suffix="",
+        filter_by=None,
+        backend_filter_by=None,
+        deserializer=json_deserializer,
     ):
         self._func = func
         self.topic = topic
         self._prefix = prefix
         self._suffix = suffix
         self._filters = self._init_filters(filter_by)
         self.backend_filter_by = backend_filter_by
+        self._deserializer = self._init_deserializer(deserializer)
 
     def _init_filters(self, filter_by):
         if filter_by and not (
@@ -61,6 +71,11 @@ def _init_filters(self, filter_by):
 
         return None
 
+    def _init_deserializer(self, deserializer):
+        if not callable(deserializer):
+            raise ValueError("deserializer must be a callable or None.")
+        return deserializer
+
     @property
     def name(self):
         name_parts = [self._prefix, self.topic, self._suffix]
@@ -109,8 +124,8 @@ def __call__(self, message):
         start_time = time.time()
 
         try:
-            data = json.loads(message.data.decode("utf-8"))
-        except json.JSONDecodeError as e:
+            data = self._subscription._deserializer(message)
+        except Exception as e:
             message.ack()
             run_middleware_hook(
                 "post_process_message_failure",
@@ -145,7 +160,14 @@ def __call__(self, message):
             run_middleware_hook("post_process_message")
 
 
-def sub(topic, prefix=None, suffix=None, filter_by=None, backend_filter_by=None):
+def sub(
+    topic,
+    prefix=None,
+    suffix=None,
+    filter_by=None,
+    backend_filter_by=None,
+    deserializer=json_deserializer,
+):
     """Decorator function that makes declaring a PubSub Subscription simple.
 
     The Subscriber returned will automatically create and name
@@ -181,6 +203,11 @@ def purpose_2(data, **kwargs):
         def sub_process_landscape_photos(data, **kwargs):
             pass
 
+        @sub(topic='string-messages', deserializer=lambda x: x.data.decode('utf-8'))
+        def sub_process_non_json(data, **kwargs):
+            pass
+
+
     :param topic: string The topic that is being subscribed to.
     :param prefix: string An optional prefix to the subscription name.
                    Useful to namespace your subscription with your project name
@@ -190,6 +217,8 @@ def sub_process_landscape_photos(data, **kwargs):
     :param filter_by: Union[function, list] An optional function or tuple of
                       functions that filters the messages to be processed by
                       the sub regarding their attributes.
+    :param deserializer: function An optional deserialization function that
+                        replaces the default json deserialization.
     :return: :class:`~rele.subscription.Subscription`
     """
 
@@ -214,6 +243,7 @@ def decorator(func):
             suffix=suffix,
             filter_by=filter_by,
             backend_filter_by=backend_filter_by,
+            deserializer=deserializer,
         )
 
     return decorator

tests/test_subscription.py

@@ -51,6 +51,15 @@ def sub_process_landscape_gif_photos(data, **kwargs):
     return f'Received a {kwargs.get("format")} photo of type {kwargs.get("type")}'
 
 
+def deserializer_handler(message):
+    return message.data.decode("utf-8")
+
+
+@sub(topic="string-data", deserializer=deserializer_handler)
+def sub_string_deserializer(data, **kwargs):
+    return data
+
+
 class TestSubscription:
     def test_subs_return_subscription_objects(self):
         assert isinstance(sub_stub, Subscription)
@@ -294,6 +303,12 @@ def crashy_sub_stub(data, **kwargs):
         }
         assert failed_log.subscription_message == str(message_wrapper)
 
+    def test_deserializer_handler(self, message_wrapper_invalid_json):
+        callback = Callback(sub_string_deserializer)
+        res = callback(message_wrapper_invalid_json)
+
+        assert res == "foobar"
+
     def test_log_acks_called_message_when_not_json_serializable(
         self, caplog, message_wrapper_invalid_json, published_at
     ):