Reject ambiguous registrations before polling (#110)

* Reject ambiguous Python handler registrations before polling

* Validate programmatic workflow handlers at every admission surface

---------

Co-authored-by: Durable Workflow <support@durable-workflow.com>

Author: rmcdaniel

docs/sdk-reference.md

@@ -411,6 +411,22 @@ entry points are rejected with `InvalidWorkflowDefinition` during definition or
 worker registration. Async activity handlers remain supported. Direct replay
 also rejects async entry points and awaitable results.
 
+Workers reject duplicate workflow or activity wire names with
+`DuplicateRegistrationError` before contacting Server or polling work. Each
+Worker and offline Replayer has its own registration scope. Distinct names
+remain supported, and separate workers may use different implementations of
+the same name. The error identifies the kind, wire name and both definitions.
+
+Within a workflow class, signal, query, update and validator names are checked
+independently. One name may be shared across these kinds. Python's normal
+method resolution applies to inheritance: overriding the same Python attribute
+is allowed, while two resolved attributes with the same handler kind and wire
+name are rejected at decoration time and at Worker, Replayer and test-environment
+admission, including programmatically defined classes. The test environment rejects a different
+workflow class replacing an existing name, while repeated registration of the
+same class remains idempotent for automatic execution. Explicit activity mock
+and canned-result setters continue to support replacement.
+
 ## Workflow signals, queries, and updates
 
 Signals mutate workflow state during replay:

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "durable-workflow"
-version = "2.5.3"
+version = "2.5.4"
 description = "Python client and worker SDK for Durable Workflow Cloud and self-hosted Server"
 readme = "README.md"
 requires-python = ">=3.10"
@@ -71,8 +71,8 @@ durable-workflow-replay-conformance = "durable_workflow.replay_conformance:main"
 durable-workflow-workflow-updates-conformance = "durable_workflow.workflow_updates_conformance:main"
 
 [tool.durable-workflow]
-product-train = "2.5.3"
-registry-version = "2.5.3"
+product-train = "2.5.4"
+registry-version = "2.5.4"
 supported-server-versions = "2.5.16"
 worker-protocol-version = "1.19"
 control-plane-version = "2"

src/durable_workflow/__init__.py

@@ -70,6 +70,7 @@
     ChildWorkflowCancelled,
     ChildWorkflowFailed,
     ChildWorkflowTerminated,
+    DuplicateRegistrationError,
     DurableOperationCancelled,
     DurableWorkflowError,
     ExternalPayloadError,
@@ -370,6 +371,7 @@
     "NexusOperationResult",
     "NexusServiceCall",
     "NonDeterministicReplayError",
+    "DuplicateRegistrationError",
     "InvalidWorkflowDefinition",
     "NoopMetrics",
     "QueryFailed",

src/durable_workflow/errors.py

@@ -31,6 +31,30 @@ class InvalidWorkflowDefinition(DurableWorkflowError, ValueError):
     """Workflow authoring uses an unsupported entry point or result."""
 
 
+class DuplicateRegistrationError(DurableWorkflowError, ValueError):
+    """One registration scope assigns a wire name to multiple definitions."""
+
+    def __init__(
+        self, registration_kind: str, wire_name: str,
+        first_definition: object, second_definition: object,
+    ) -> None:
+        def label(definition: object) -> str:
+            if isinstance(definition, str):
+                return definition
+            module = getattr(definition, "__module__", type(definition).__module__)
+            name = getattr(definition, "__qualname__", type(definition).__qualname__)
+            return f"{module}.{name}"
+
+        self.registration_kind = registration_kind
+        self.wire_name = wire_name
+        self.first_definition = label(first_definition)
+        self.second_definition = label(second_definition)
+        super().__init__(
+            f"duplicate {registration_kind} name {wire_name!r}: "
+            f"{self.first_definition} conflicts with {self.second_definition}"
+        )
+
+
 class DurableOperationCancelled(DurableWorkflowError):
     """A durable selection member was explicitly cancelled."""
 

src/durable_workflow/testing.py

@@ -39,7 +39,7 @@ def test_my_workflow():
 from typing import Any
 
 from . import serializer
-from .errors import WorkflowCancelled, WorkflowFailed, WorkflowTerminated
+from .errors import DuplicateRegistrationError, WorkflowCancelled, WorkflowFailed, WorkflowTerminated
 from .workflow import (
     CompleteWorkflow,
     ContinueAsNew,
@@ -52,6 +52,7 @@ def test_my_workflow():
     StartTimer,
     UpsertSearchAttributes,
     _validate_workflow_entrypoint,
+    _workflow_handler_registries,
     registry,
     replay,
 )
@@ -136,6 +137,9 @@ def register_workflow(self, workflow_cls: type) -> None:
                 "decorate it with @workflow.defn(name=...) first."
             )
         _validate_workflow_entrypoint(workflow_cls)
+        _workflow_handler_registries(workflow_cls)
+        if name in self._registered_workflows and self._registered_workflows[name] is not workflow_cls:
+            raise DuplicateRegistrationError("workflow", name, self._registered_workflows[name], workflow_cls)
         self._registered_workflows[name] = workflow_cls
 
     def signal(

src/durable_workflow/worker.py

@@ -66,6 +66,7 @@
     ActivityCancelled,
     ActivityFailed,
     AvroNotInstalledError,
+    DuplicateRegistrationError,
     DurableWorkflowError,
     ExternalPayloadError,
     InvalidArgument,
@@ -106,6 +107,7 @@
     StartChildWorkflow,
     UpsertMemo,
     _validate_workflow_entrypoint,
+    _workflow_handler_registries,
     apply_update,
     commands_to_server_commands,
     query_state,
@@ -1028,7 +1030,11 @@ def __init__(
         self.workflows: dict[str, type] = {}
         for definition in workflows:
             _validate_workflow_entrypoint(definition)
-            self.workflows[_workflow_name(definition)] = definition
+            _workflow_handler_registries(definition)
+            name = _workflow_name(definition)
+            if name in self.workflows:
+                raise DuplicateRegistrationError("workflow", name, self.workflows[name], definition)
+            self.workflows[name] = definition
         self.workflow_definition_fingerprints = {
             workflow_type: _workflow_definition_fingerprint(workflow_cls)
             for workflow_type, workflow_cls in self.workflows.items()
@@ -1037,7 +1043,12 @@ def __init__(
             workflow_type: _workflow_command_contract(workflow_cls)
             for workflow_type, workflow_cls in self.workflows.items()
         }
-        self.activities = {_activity_name(a): a for a in activities}
+        self.activities: dict[str, Callable[..., Any]] = {}
+        for activity_definition in activities:
+            name = _activity_name(activity_definition)
+            if name in self.activities:
+                raise DuplicateRegistrationError("activity", name, self.activities[name], activity_definition)
+            self.activities[name] = activity_definition
         self.capabilities = tuple(dict.fromkeys(capability.strip() for capability in capabilities))
         self._sticky_cache = StickyWorkflowCache(
             sticky_cache_capacity, sticky_cache_max_bytes, sticky_cache_ttl_seconds,

src/durable_workflow/workflow.py

@@ -58,6 +58,7 @@
     ChildWorkflowCancelled,
     ChildWorkflowFailed,
     ChildWorkflowTerminated,
+    DuplicateRegistrationError,
     DurableOperationCancelled,
     InvalidWorkflowDefinition,
     NexusOperationFailed,
@@ -124,6 +125,29 @@ def _validate_workflow_result(value: Any, cls: type) -> None:
         )
 
 
+def _workflow_handler_registries(
+    cls: type,
+) -> tuple[dict[str, str], dict[str, str], dict[str, str], dict[str, str]]:
+    handlers: dict[str, dict[str, str]] = {kind: {} for kind in ("signal", "query", "update", "update_validator")}
+    for attr in dir(cls):
+        if attr.startswith("_"):
+            continue
+        member = getattr(cls, attr, None)
+        for kind, registry in handlers.items():
+            wire_name = getattr(member, f"__{kind}_name__", None)
+            if not isinstance(wire_name, str) or not wire_name:
+                continue
+            if kind == "signal" and wire_name == MESSAGE_STREAM_SIGNAL:
+                raise ValueError(f"signal name {wire_name!r} is reserved by the workflow runtime")
+            if wire_name in registry:
+                owner = f"{cls.__module__}.{cls.__qualname__}"
+                raise DuplicateRegistrationError(
+                    kind, wire_name, f"{owner}.{registry[wire_name]}", f"{owner}.{attr}",
+                )
+            registry[wire_name] = attr
+    return handlers["signal"], handlers["query"], handlers["update"], handlers["update_validator"]
+
+
 def defn(*, name: str) -> Callable[[type[_WorkflowT]], type[_WorkflowT]]:
     """Register a class as a workflow type under a language-neutral name.
 
@@ -136,28 +160,7 @@ def defn(*, name: str) -> Callable[[type[_WorkflowT]], type[_WorkflowT]]:
     def wrap(cls: type[_WorkflowT]) -> type[_WorkflowT]:
         cls.__workflow_name__ = name  # type: ignore[attr-defined]
         _validate_workflow_entrypoint(cls)
-        signals: dict[str, str] = {}
-        queries: dict[str, str] = {}
-        updates: dict[str, str] = {}
-        update_validators: dict[str, str] = {}
-        for attr in dir(cls):
-            if attr.startswith("_"):
-                continue
-            member = getattr(cls, attr, None)
-            signal_name = getattr(member, "__signal_name__", None)
-            if isinstance(signal_name, str) and signal_name:
-                if signal_name == MESSAGE_STREAM_SIGNAL:
-                    raise ValueError(f"signal name {signal_name!r} is reserved by the workflow runtime")
-                signals[signal_name] = attr
-            query_name = getattr(member, "__query_name__", None)
-            if isinstance(query_name, str) and query_name:
-                queries[query_name] = attr
-            update_name = getattr(member, "__update_name__", None)
-            if isinstance(update_name, str) and update_name:
-                updates[update_name] = attr
-            update_validator_name = getattr(member, "__update_validator_name__", None)
-            if isinstance(update_validator_name, str) and update_validator_name:
-                update_validators[update_validator_name] = attr
+        signals, queries, updates, update_validators = _workflow_handler_registries(cls)
         cls.__workflow_signals__ = signals  # type: ignore[attr-defined]
         cls.__workflow_queries__ = queries  # type: ignore[attr-defined]
         cls.__workflow_updates__ = updates  # type: ignore[attr-defined]
@@ -2578,9 +2581,12 @@ class Replayer:
     def __init__(self, *, workflows: Iterable[type]) -> None:
         self._workflows: dict[str, type] = {}
         for workflow_cls in workflows:
+            _workflow_handler_registries(workflow_cls)
             workflow_type = str(getattr(workflow_cls, "__workflow_name__", workflow_cls.__name__))
             if workflow_type in self._workflows:
-                raise ValueError(f"duplicate workflow type registered with Replayer: {workflow_type!r}")
+                raise DuplicateRegistrationError(
+                    "workflow", workflow_type, self._workflows[workflow_type], workflow_cls,
+                )
             self._workflows[workflow_type] = workflow_cls
         if not self._workflows:
             raise ValueError("Replayer requires at least one workflow class")

tests/fixtures/replay_regressions/ambiguous-worker-registration-rejected.json

@@ -0,0 +1,20 @@
+{
+  "$schema": "https://raw.githubusercontent.com/durable-workflow/.github/main/regression-corpus/evidence-schema.json",
+  "fixture_schema": "durable-workflow.replay-regression/v1",
+  "id": "python-ambiguous-worker-registration-rejected",
+  "protocol_version": "1.19",
+  "bindings": ["python"],
+  "consumers": ["workflow-executor"],
+  "workflow": {
+    "type": "golden.single-activity",
+    "input": ["Ada"],
+    "payload_codec": "avro",
+    "worker_registrations": ["golden.single-activity", "golden.single-activity"]
+  },
+  "history": [
+    {"event_type": "WorkflowStarted", "payload": {"payload_codec": "avro"}},
+    {"event_type": "ActivityScheduled", "payload": {"sequence": 1, "activity_type": "golden.greet"}},
+    {"event_type": "ActivityCompleted", "payload": {"sequence": 1, "result": "wwHioz3/VYAiNwoSaGVsbG8gQWRh"}}
+  ],
+  "expected": {"error": "duplicate workflow name 'golden.single-activity'"}
+}