Adds Encode and Decode logic for "arbitrary" objects for Durable Python

azure/functions/__init__.py

@@ -9,7 +9,6 @@
 from ._servicebus import ServiceBusMessage  # NoQA
 from ._durable_functions import OrchestrationContext  # NoQA
 from .meta import get_binding_registry  # NoQA
-
 # Import binding implementations to register them
 from . import blob  # NoQA
 from . import cosmosdb  # NoQA
@@ -44,7 +43,7 @@
     'TimerRequest',
 
     # Middlewares
-    'WsgiMiddleware',
+    'WsgiMiddleware'
 )
 
 __version__ = '1.2.0'

azure/functions/_durable_functions.py

@@ -1,5 +1,84 @@
 from typing import Union
 from . import _abc
+from importlib import import_module
+
+
+# Utilities
+def _serialize_custom_object(obj):
+    """Serialize a user-defined object to JSON.
+
+    This function gets called when `json.dumps` cannot serialize
+    an object and returns a serializable dictionary containing enough
+    metadata to recontrust the original object.
+
+    Parameters
+    ----------
+    obj: Object
+        The object to serialize
+
+    Returns
+    -------
+    dict_obj: A serializable dictionary with enough metadata to reconstruct
+              `obj`
+
+    Exceptions
+    ----------
+    TypeError:
+        Raise if `obj` does not contain a `to_json` attribute
+    """
+    # 'safety' guard: raise error if object does not
+    # support serialization
+    if not hasattr(obj, "to_json"):
+        raise TypeError(f"class {type(obj)} does not expose a `to_json` "
+                        "function")
+    # Encode to json using the object's `to_json`
+    obj_type = type(obj)
+    dict_obj = {
+        "__class__": obj.__class__.__name__,
+        "__module__": obj.__module__,
+        "__data__": obj_type.to_json(obj)
+    }
+    return dict_obj
+
+
+def _deserialize_custom_object(obj: dict) -> object:
+    """Deserialize a user-defined object from JSON.
+
+    Deserializes a dictionary encoding a custom object,
+    if it contains class metadata suggesting that it should be
+    decoded further.
+
+    Parameters:
+    ----------
+    obj: dict
+        Dictionary object that potentially encodes a custom class
+
+    Returns:
+    --------
+    object
+        Either the original `obj` dictionary or the custom object it encoded
+
+    Exceptions
+    ----------
+    TypeError
+        If the decoded object does not contain a `from_json` function
+    """
+    if ("__class__" in obj) and ("__module__" in obj) and ("__data__" in obj):
+        class_name = obj.pop("__class__")
+        module_name = obj.pop("__module__")
+        obj_data = obj.pop("__data__")
+
+        # Importing the clas
+        module = import_module(module_name)
+        class_ = getattr(module, class_name)
+
+        if not hasattr(class_, "from_json"):
+            raise TypeError(f"class {type(obj)} does not expose a `from_json` "
+                            "function")
+
+        # Initialize the object using its `from_json` deserializer
+        obj = class_.from_json(obj_data)
+    return obj
 
 
 class OrchestrationContext(_abc.OrchestrationContext):

azure/functions/durable_functions.py

@@ -2,7 +2,6 @@
 import json
 
 from azure.functions import _durable_functions
-
 from . import meta
 
 
@@ -62,7 +61,8 @@ def decode(cls,
         # See durable functions library's call_activity_task docs
         if data_type == 'string' or data_type == 'json':
             try:
-                result = json.loads(data.value)
+                callback = _durable_functions._deserialize_custom_object
+                result = json.loads(data.value, object_hook=callback)
             except json.JSONDecodeError:
                 # String failover if the content is not json serializable
                 result = data.value
@@ -80,7 +80,8 @@ def decode(cls,
     def encode(cls, obj: typing.Any, *,
                expected_type: typing.Optional[type]) -> meta.Datum:
         try:
-            result = json.dumps(obj)
+            callback = _durable_functions._serialize_custom_object
+            result = json.dumps(obj, default=callback)
         except TypeError:
             raise ValueError(
                 f'activity trigger output must be json serializable ({obj})')