Introduce ClientAppException (#3191)

src/py/flwr/client/app.py

@@ -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
@@ -483,35 +484,49 @@ def _load_client_app() -> ClientApp:
                 # Create an error reply message that will never be used to prevent
                 # the used-before-assignment linting error
                 reply_message = message.create_error_reply(
-                    error=Error(code=0, reason="Unknown")
+                    error=Error(code=ErrorCode.UNKNOWN, reason="Unknown")
                 )
 
                 # Handle app loading and task message
                 try:
                     # Load ClientApp instance
                     client_app: ClientApp = load_client_app_fn()
 
+                    # Execute ClientApp
                     reply_message = client_app(message=message, context=context)
-                    # Update node state
-                    node_state.update_context(
-                        run_id=message.metadata.run_id,
-                        context=context,
-                    )
                 except Exception as ex:  # pylint: disable=broad-exception-caught
-                    log(ERROR, "ClientApp raised an exception", exc_info=ex)
 
                     # Legacy grpc-bidi
                     if transport in ["grpc-bidi", None]:
+                        log(ERROR, "Client raised an exception.", exc_info=ex)
                         # Raise exception, crash process
                         raise ex
 
                     # Don't update/change NodeState
 
-                    # Create error message
+                    e_code = ErrorCode.CLIENT_APP_RAISED_EXCEPTION
                     # Reason example: "<class 'ZeroDivisionError'>:<'division by zero'>"
                     reason = str(type(ex)) + ":<'" + str(ex) + "'>"
+                    exc_entity = "ClientApp"
+                    if isinstance(ex, LoadClientAppError):
+                        reason = (
+                            "An exception was raised when attempting to load "
+                            "`ClientApp`"
+                        )
+                        e_code = ErrorCode.LOAD_CLIENT_APP_EXCEPTION
+                        exc_entity = "SuperNode"
+
+                    log(ERROR, "%s raised an exception", exc_entity, exc_info=ex)
+
+                    # Create error message
                     reply_message = message.create_error_reply(
-                        error=Error(code=0, reason=reason)
+                        error=Error(code=e_code, reason=reason)
+                    )
+                else:
+                    # No exception, update node state
+                    node_state.update_context(
+                        run_id=message.metadata.run_id,
+                        context=context,
                     )
 
                 # Send

src/py/flwr/client/client_app.py

@@ -28,6 +28,15 @@
 from .typing import ClientAppCallable
 
 
+class ClientAppException(Exception):
+    """Exception raised when an exception is raised while executing a ClientApp."""
+
+    def __init__(self, message: str):
+        ex_name = self.__class__.__name__
+        self.message = f"\nException {ex_name} occurred. Message: " + message
+        super().__init__(self.message)
+
+
 class ClientApp:
     """Flower ClientApp.
 

src/py/flwr/common/constant.py

@@ -81,7 +81,8 @@ class ErrorCode:
     """Error codes for Message's Error."""
 
     UNKNOWN = 0
-    CLIENT_APP_RAISED_EXCEPTION = 1
+    LOAD_CLIENT_APP_EXCEPTION = 1
+    CLIENT_APP_RAISED_EXCEPTION = 2
 
     def __new__(cls) -> ErrorCode:
         """Prevent instantiation."""

src/py/flwr/server/superlink/fleet/vce/vce_api.py

@@ -22,9 +22,9 @@
 from logging import DEBUG, ERROR, INFO, WARN
 from typing import Callable, Dict, List, Optional
 
-from flwr.client.client_app import ClientApp, LoadClientAppError
+from flwr.client.client_app import ClientApp, ClientAppException, LoadClientAppError
 from flwr.client.node_state import NodeState
-from flwr.common.constant import PING_MAX_INTERVAL
+from flwr.common.constant import PING_MAX_INTERVAL, ErrorCode
 from flwr.common.logger import log
 from flwr.common.message import Error
 from flwr.common.object_ref import load_app
@@ -94,9 +94,18 @@ async def worker(
         except Exception as ex:  # pylint: disable=broad-exception-caught
             log(ERROR, ex)
             log(ERROR, traceback.format_exc())
+
+            if isinstance(ex, ClientAppException):
+                e_code = ErrorCode.CLIENT_APP_RAISED_EXCEPTION
+            elif isinstance(ex, LoadClientAppError):
+                e_code = ErrorCode.LOAD_CLIENT_APP_EXCEPTION
+            else:
+                e_code = ErrorCode.UNKNOWN
+
             reason = str(type(ex)) + ":<'" + str(ex) + "'>"
-            error = Error(code=0, reason=reason)
-            out_mssg = message.create_error_reply(error=error)
+            out_mssg = message.create_error_reply(
+                error=Error(code=e_code, reason=reason)
+            )
 
         finally:
             if out_mssg:

src/py/flwr/simulation/ray_transport/ray_actor.py

@@ -16,7 +16,6 @@
 
 import asyncio
 import threading
-import traceback
 from abc import ABC
 from logging import DEBUG, ERROR, WARNING
 from typing import Any, Callable, Dict, List, Optional, Set, Tuple, Type, Union
@@ -25,22 +24,13 @@
 from ray import ObjectRef
 from ray.util.actor_pool import ActorPool
 
-from flwr.client.client_app import ClientApp, LoadClientAppError
+from flwr.client.client_app import ClientApp, ClientAppException, LoadClientAppError
 from flwr.common import Context, Message
 from flwr.common.logger import log
 
 ClientAppFn = Callable[[], ClientApp]
 
 
-class ClientException(Exception):
-    """Raised when client side logic crashes with an exception."""
-
-    def __init__(self, message: str):
-        div = ">" * 7
-        self.message = "\n" + div + "A ClientException occurred." + message
-        super().__init__(self.message)
-
-
 class VirtualClientEngineActor(ABC):
     """Abstract base class for VirtualClientEngine Actors."""
 
@@ -71,17 +61,7 @@ def run(
             raise load_ex
 
         except Exception as ex:
-            client_trace = traceback.format_exc()
-            mssg = (
-                "\n\tSomething went wrong when running your client run."
-                "\n\tClient "
-                + cid
-                + " crashed when the "
-                + self.__class__.__name__
-                + " was running its run."
-                "\n\tException triggered on the client side: " + client_trace,
-            )
-            raise ClientException(str(mssg)) from ex
+            raise ClientAppException(str(ex)) from ex
 
         return cid, out_message, context