Fix durable client 500 when host sends config fields as null

The Durable Functions host client-config JSON can send fields explicitly as null (observed with maxGrpcMessageSizeInBytes on newer extension bundles) rather than omitting them. dict.get(key, default) only substitutes the default for absent keys, so a present-but-null value returned None -- crashing the 'maxGrpcMessageSizeInBytes > 0' guard in __init__ (TypeError: '>' not supported between NoneType and int) and failing every durable-client binding decode with a 500. Parse every field with 'client.get(key) or default' so an explicit null (like a missing key) collapses to its falsy default. Diagnosed from the e2e func host log; add regression tests for a single null field and for all fields sent as null.

Author: andystaples

azure-functions-durable/azure/durable_functions/client.py

@@ -133,17 +133,26 @@ def _parse_client_configuration(self, client_as_string: str) -> None:
         """
         client = json.loads(client_as_string)
 
-        self.taskHubName = client.get("taskHubName", "")
-        self.connectionName = client.get("connectionName", "")
-        self.creationUrls = client.get("creationUrls", {})
-        self.managementUrls = client.get("managementUrls", {})
-        self.baseUrl = client.get("baseUrl", "")
-        self.requiredQueryStringParameters = client.get("requiredQueryStringParameters", "")
-        self.rpcBaseUrl = client.get("rpcBaseUrl", "")
-        self.httpBaseUrl = client.get("httpBaseUrl", "")
-        self.maxGrpcMessageSizeInBytes = client.get("maxGrpcMessageSizeInBytes", 0)
+        # Depending on the extension-bundle version, the host may send a field
+        # explicitly as ``null`` rather than omitting it. ``dict.get(key,
+        # default)`` only substitutes the default for *absent* keys, so a
+        # present-but-``null`` value slips through as ``None`` (this crashed the
+        # ``maxGrpcMessageSizeInBytes > 0`` guard in __init__ on newer bundles).
+        # Use ``... or default`` so an explicit ``null`` -- like a missing key --
+        # always collapses to the intended default. Every default here is falsy
+        # and no field carries a meaningful falsy value, so this never discards a
+        # real value.
+        self.taskHubName = client.get("taskHubName") or ""
+        self.connectionName = client.get("connectionName") or ""
+        self.creationUrls = client.get("creationUrls") or {}
+        self.managementUrls = client.get("managementUrls") or {}
+        self.baseUrl = client.get("baseUrl") or ""
+        self.requiredQueryStringParameters = client.get("requiredQueryStringParameters") or ""
+        self.rpcBaseUrl = client.get("rpcBaseUrl") or ""
+        self.httpBaseUrl = client.get("httpBaseUrl") or ""
+        self.maxGrpcMessageSizeInBytes = client.get("maxGrpcMessageSizeInBytes") or 0
         # TODO: convert the string value back to timedelta - annoying regex?
-        self.grpcHttpClientTimeout = client.get("grpcHttpClientTimeout", timedelta(seconds=30))
+        self.grpcHttpClientTimeout = client.get("grpcHttpClientTimeout") or timedelta(seconds=30)
 
     def create_check_status_response(self, request: func.HttpRequest, instance_id: str) -> func.HttpResponse:
         """Creates an HTTP response for checking the status of a Durable Function instance.

tests/azure-functions-durable/test_client_compat.py

@@ -34,6 +34,51 @@ def _make_client() -> df.DurableFunctionsClient:
     return df.DurableFunctionsClient(_CLIENT_CONFIG)
 
 
+def test_client_handles_null_max_grpc_message_size():
+    # The Durable Functions host may send ``maxGrpcMessageSizeInBytes``
+    # explicitly as ``null`` (not just omit it). ``dict.get(key, 0)`` returns
+    # ``None`` in that case, which previously blew up the ``> 0`` guard in
+    # ``__init__`` (``TypeError: '>' not supported between 'NoneType' and
+    # 'int'``) and made every durable-client binding decode fail with a 500.
+    config = json.dumps({
+        "taskHubName": "TestHub",
+        "rpcBaseUrl": "http://localhost:8080/",
+        "maxGrpcMessageSizeInBytes": None,
+    })
+    client = df.DurableFunctionsClient(config)
+    assert client.maxGrpcMessageSizeInBytes == 0
+
+
+def test_client_handles_all_config_fields_sent_as_null():
+    # Newer host extension bundles serialize the full client configuration and
+    # can send any field explicitly as ``null``. Every field must collapse to
+    # its (falsy) default rather than ``None`` so construction never crashes and
+    # downstream code sees well-typed values.
+    config = json.dumps({
+        "taskHubName": None,
+        "connectionName": None,
+        "creationUrls": None,
+        "managementUrls": None,
+        "baseUrl": None,
+        "requiredQueryStringParameters": None,
+        "rpcBaseUrl": None,
+        "httpBaseUrl": None,
+        "maxGrpcMessageSizeInBytes": None,
+        "grpcHttpClientTimeout": None,
+    })
+    client = df.DurableFunctionsClient(config)
+    assert client.taskHubName == ""
+    assert client.connectionName == ""
+    assert client.creationUrls == {}
+    assert client.managementUrls == {}
+    assert client.baseUrl == ""
+    assert client.requiredQueryStringParameters == ""
+    assert client.rpcBaseUrl == ""
+    assert client.httpBaseUrl == ""
+    assert client.maxGrpcMessageSizeInBytes == 0
+    assert client.grpcHttpClientTimeout == timedelta(seconds=30)
+
+
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 # RetryOptions shim
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