Handles message type Exception in lowlevel/server.py _handle_message function. Mentioned as TODO on line 528. (#786)

Co-authored-by: Felix Weinberger <fweinberger@anthropic.com>
Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com>

src/mcp/server/lowlevel/server.py

@@ -642,13 +642,21 @@ class Server(Generic[LifespanResultT, RequestT]):
         raise_exceptions: bool = False,
     ):
         with warnings.catch_warnings(record=True) as w:
-            # TODO(Marcelo): We should be checking if message is Exception here.
-            match message:  # type: ignore[reportMatchNotExhaustive]
+            match message:
                 case RequestResponder(request=types.ClientRequest(root=req)) as responder:
                     with responder:
                         await self._handle_request(message, req, session, lifespan_context, raise_exceptions)
                 case types.ClientNotification(root=notify):
                     await self._handle_notification(notify)
+                case Exception():
+                    logger.error(f"Received exception from stream: {message}")
+                    await session.send_log_message(
+                        level="error",
+                        data="Internal Server Error",
+                        logger="mcp.server.exception_handler",
+                    )
+                    if raise_exceptions:
+                        raise message
 
             for warning in w:
                 logger.info("Warning: %s: %s", warning.category.__name__, warning.message)