defined ClientAppException

src/py/flwr/client/app.py

@@ -24,7 +24,7 @@
 from grpc import RpcError
 
 from flwr.client.client import Client
-from flwr.client.client_app import ClientApp, LoadClientAppError
+from flwr.client.client_app import ClientApp, ClientAppException, LoadClientAppError
 from flwr.client.typing import ClientFn
 from flwr.common import GRPC_MAX_MESSAGE_LENGTH, EventType, Message, event
 from flwr.common.address import parse_address
@@ -34,6 +34,7 @@
     TRANSPORT_TYPE_GRPC_RERE,
     TRANSPORT_TYPE_REST,
     TRANSPORT_TYPES,
+    ErrorCode,
 )
 from flwr.common.exit_handlers import register_exit_handlers
 from flwr.common.logger import log, warn_deprecated_feature
@@ -507,11 +508,15 @@ def _load_client_app() -> ClientApp:
 
                     # Don't update/change NodeState
 
+                    e_code = ErrorCode.UNKNOWN
+                    if isinstance(ex, ClientAppException):
+                        e_code = ErrorCode.CLIENT_APP_RAISED_EXCEPTION
+
                     # Create error message
                     # Reason example: "<class 'ZeroDivisionError'>:<'division by zero'>"
                     reason = str(type(ex)) + ":<'" + str(ex) + "'>"
                     reply_message = message.create_error_reply(
-                        error=Error(code=0, reason=reason)
+                        error=Error(code=e_code, reason=reason)
                     )
 
                 # Send

src/py/flwr/client/client_app.py

@@ -28,6 +28,15 @@
 from .typing import ClientAppCallable
 
 
+class ClientAppException(Exception):
+    """Exepction raised when an exception is raised while executing a ClientApp."""
+
+    def __init__(self, message: str):
+        ex_name = self.__class__.__name__
+        self.message = f"\nA {ex_name} occurred." + message
+        super().__init__(self.message)
+
+
 class ClientApp:
     """Flower ClientApp.
 
@@ -84,26 +93,29 @@ def ffn(
 
     def __call__(self, message: Message, context: Context) -> Message:
         """Execute `ClientApp`."""
-        # Execute message using `client_fn`
-        if self._call:
-            return self._call(message, context)
-
-        # Execute message using a new
-        if message.metadata.message_type == MessageType.TRAIN:
-            if self._train:
-                return self._train(message, context)
-            raise ValueError("No `train` function registered")
-        if message.metadata.message_type == MessageType.EVALUATE:
-            if self._evaluate:
-                return self._evaluate(message, context)
-            raise ValueError("No `evaluate` function registered")
-        if message.metadata.message_type == MessageType.QUERY:
-            if self._query:
-                return self._query(message, context)
-            raise ValueError("No `query` function registered")
-
-        # Message type did not match one of the known message types abvoe
-        raise ValueError(f"Unknown message_type: {message.metadata.message_type}")
+        try:
+            # Execute message using `client_fn`
+            if self._call:
+                return self._call(message, context)
+
+            # Execute message using a new
+            if message.metadata.message_type == MessageType.TRAIN:
+                if self._train:
+                    return self._train(message, context)
+                raise ValueError("No `train` function registered")
+            if message.metadata.message_type == MessageType.EVALUATE:
+                if self._evaluate:
+                    return self._evaluate(message, context)
+                raise ValueError("No `evaluate` function registered")
+            if message.metadata.message_type == MessageType.QUERY:
+                if self._query:
+                    return self._query(message, context)
+                raise ValueError("No `query` function registered")
+
+            # Message type did not match one of the known message types abvoe
+            raise ValueError(f"Unknown message_type: {message.metadata.message_type}")
+        except Exception as ex:
+            raise ClientAppException(str(ex)) from ex
 
     def train(self) -> Callable[[ClientAppCallable], ClientAppCallable]:
         """Return a decorator that registers the train fn with the client app.