ASF: fix empty exception member serialization when required (#13186)

bentsku · web-flow · commit f7ffe66ecc6c · 2025-09-24T12:37:51.000+02:00
diff --git a/localstack-core/localstack/aws/protocol/serializer.py b/localstack-core/localstack/aws/protocol/serializer.py
@@ -1338,7 +1338,13 @@ def _serialize_error(
                 else:
                     continue
 
-                if value:
+                if value is None:
+                    # do not serialize a value that is set to `None`
+                    continue
+
+                # if the value is falsy (empty string, empty list) and not in the Shape required members, AWS will
+                # not serialize it, and it will not be part of the response body.
+                if value or member in shape.required_members:
                     remaining_params[member] = value
 
             self._serialize(body, remaining_params, shape, None, mime_type)
@@ -1845,7 +1851,13 @@ def _serialize_error_structure(
             else:
                 continue
 
-            if value:
+            if value is None:
+                # do not serialize a value that is set to `None`
+                continue
+
+            # if the value is falsy (empty string, empty list) and not in the Shape required members, AWS will
+            # not serialize it, and it will not be part of the response body.
+            if value or member in shape.required_members:
                 params[member] = value
 
         self._serialize_type_structure(body, params, shape, None, shape_members=shape_members)
diff --git a/tests/unit/aws/protocol/test_serializer.py b/tests/unit/aws/protocol/test_serializer.py
@@ -764,6 +764,96 @@ def test_json_protocol_error_serialization_with_shaped_default_members_on_root()
     assert "message" not in parsed_body
 
 
+def test_json_protocol_error_serialization_empty_message():
+    # if the exception message is not passed when instantiating the exception, the message attribute will be set to
+    # an empty string "". This is not serialized if the message field is not a required member
+    exception = TransactionCanceledException()
+
+    response = _botocore_error_serializer_integration_test(
+        "dynamodb",
+        "ExecuteTransaction",
+        exception,
+        "TransactionCanceledException",
+        400,
+        "",
+    )
+    assert "message" not in response
+
+
+@pytest.mark.parametrize("empty_value", ("", None))
+def test_json_protocol_error_serialization_with_empty_non_required_members(empty_value):
+    class _ResourceNotFoundException(ServiceException):
+        code: str = "ResourceNotFoundException"
+        sender_fault: bool = True
+        status_code: int = 404
+        ResourceType: str | None
+        ResourceId: str | None
+
+    exception = _ResourceNotFoundException("Not Found", ResourceType="")
+
+    response = _botocore_error_serializer_integration_test(
+        "arc-region-switch",
+        "ApprovePlanExecutionStep",
+        exception,
+        "ResourceNotFoundException",
+        404,
+        "Not Found",
+        protocol="json",
+    )
+    assert "ResourceType" not in response
+
+
+def test_json_protocol_error_serialization_falsy_non_required_members():
+    # if the exception message is not passed, an empty message will be passed as an empty string `""`
+    exception = TransactionCanceledException("Exception message!", CancellationReasons=[])
+
+    response = _botocore_error_serializer_integration_test(
+        "dynamodb",
+        "ExecuteTransaction",
+        exception,
+        "TransactionCanceledException",
+        400,
+        "Exception message!",
+        Message="Exception message!",
+    )
+    assert "CancellationReasons" not in response
+
+
+@pytest.mark.parametrize("empty_value", ("", None))
+def test_json_protocol_error_serialization_with_empty_required_members(empty_value):
+    class _ResourceNotFoundException(ServiceException):
+        code: str = "ResourceNotFoundException"
+        sender_fault: bool = False
+        status_code: int = 404
+        resourceId: str
+        resourceType: str
+
+    resource_type = "test"
+    exception = _ResourceNotFoundException(
+        "Exception message!",
+        resourceType=resource_type,
+        resourceId=empty_value,
+    )
+    expected_exception_values = {
+        "resourceType": resource_type,
+    }
+    # if the value is None, it is not serialized, even if required
+    # but if it is an empty string, it will be
+    if empty_value is not None:
+        expected_exception_values["resourceId"] = ""
+
+    response = _botocore_error_serializer_integration_test(
+        "verifiedpermissions",
+        "IsAuthorizedWithToken",
+        exception,
+        "ResourceNotFoundException",
+        404,
+        "Exception message!",
+        **expected_exception_values,
+    )
+    assert "" not in response
+
+
 def test_rest_json_protocol_error_serialization_with_additional_members():
     class NotFoundException(ServiceException):
         code: str = "NotFoundException"
@@ -929,6 +1019,48 @@ class _ResourceNotFoundException(ServiceException):
     assert serialized_response.headers["Smithy-Protocol"] == "rpc-v2-cbor"
 
 
+@pytest.mark.parametrize("empty_value", ("", None))
+def test_rpc_v2_cbor_protocol_error_serialization_with_empty_required_members(empty_value):
+    class AccessDeniedException(ServiceException):
+        code: str = "AccessDeniedException"
+        sender_fault: bool = True
+        status_code: int = 403
+
+    exception = AccessDeniedException("")
+
+    _botocore_error_serializer_integration_test(
+        "arc-region-switch",
+        "ApprovePlanExecutionStep",
+        exception,
+        "AccessDeniedException",
+        403,
+        "",
+    )
+
+
+@pytest.mark.parametrize("empty_value", ("", None))
+def test_rpc_v2_cbor_protocol_error_serialization_with_empty_non_required_members(empty_value):
+    class _ResourceNotFoundException(ServiceException):
+        code: str = "ResourceNotFoundException"
+        sender_fault: bool = True
+        status_code: int = 404
+        ResourceType: str | None
+        ResourceId: str | None
+
+    exception = _ResourceNotFoundException("Not Found", ResourceType="")
+
+    response = _botocore_error_serializer_integration_test(
+        "arc-region-switch",
+        "ApprovePlanExecutionStep",
+        exception,
+        "ResourceNotFoundException",
+        404,
+        "Not Found",
+        protocol="smithy-rpc-v2-cbor",
+    )
+    assert "ResourceType" not in response
+
+
 def test_json_protocol_content_type_1_0():
     """AppRunner defines the jsonVersion 1.0, therefore the Content-Type needs to be application/x-amz-json-1.0."""
     service = load_service("apprunner")
