clean up log.error (#1109)

CLAUDE.md

@@ -16,7 +16,7 @@ This document contains critical information about working with this codebase. Fo
    - Public APIs must have docstrings
    - Functions must be focused and small
    - Follow existing patterns exactly
-   - Line length: 88 chars maximum
+   - Line length: 120 chars maximum
 
 3. Testing Requirements
    - Framework: `uv run --frozen pytest`
@@ -116,3 +116,15 @@ This document contains critical information about working with this codebase. Fo
    - Follow existing patterns
    - Document public APIs
    - Test thoroughly
+
+## Exception Handling
+
+- **Always use `logger.exception()` instead of `logger.error()` when catching exceptions**
+  - Don't include the exception in the message: `logger.exception("Failed")` not `logger.exception(f"Failed: {e}")`
+- **Catch specific exceptions** where possible:
+  - File ops: `except (OSError, PermissionError):`
+  - JSON: `except json.JSONDecodeError:`
+  - Network: `except (ConnectionError, TimeoutError):`
+- **Only catch `Exception` for**:
+  - Top-level handlers that must not crash
+  - Cleanup blocks (log at debug level)

examples/servers/simple-auth/mcp_simple_auth/server.py

@@ -160,9 +160,8 @@ def main(port: int, auth_server: str, transport: Literal["sse", "streamable-http
         mcp_server.run(transport=transport)
         logger.info("Server stopped")
         return 0
-    except Exception as e:
+    except Exception:
-        logger.error(f"Server error: {e}")
+        logger.exception("Server error")
-        logger.exception("Exception details:")
         return 1
 
 

src/mcp/cli/claude.py

@@ -75,11 +75,10 @@ def update_claude_config(
     if not config_file.exists():
         try:
             config_file.write_text("{}")
-        except Exception as e:
+        except Exception:
-            logger.error(
+            logger.exception(
                 "Failed to create Claude config file",
                 extra={
-                    "error": str(e),
                     "config_file": str(config_file),
                 },
             )
@@ -139,11 +138,10 @@ def update_claude_config(
             extra={"config_file": str(config_file)},
         )
         return True
-    except Exception as e:
+    except Exception:
-        logger.error(
+        logger.exception(
             "Failed to update Claude config",
             extra={
-                "error": str(e),
                 "config_file": str(config_file),
             },
         )

src/mcp/cli/cli.py

@@ -349,12 +349,11 @@ def run(
 
         server.run(**kwargs)
 
-    except Exception as e:
+    except Exception:
-        logger.error(
+        logger.exception(
-            f"Failed to run server: {e}",
+            "Failed to run server",
             extra={
                 "file": str(file),
-                "error": str(e),
             },
         )
         sys.exit(1)
@@ -464,8 +463,8 @@ def install(
             if dotenv:
                 try:
                     env_dict |= {k: v for k, v in dotenv.dotenv_values(env_file).items() if v is not None}
-                except Exception as e:
+                except (OSError, ValueError):
-                    logger.error(f"Failed to load .env file: {e}")
+                    logger.exception("Failed to load .env file")
                     sys.exit(1)
             else:
                 logger.error("python-dotenv is not installed. Cannot load .env file.")

src/mcp/client/auth.py

@@ -464,8 +464,8 @@ class OAuthClientProvider(httpx.Auth):
             await self.context.storage.set_tokens(token_response)
 
             return True
-        except ValidationError as e:
+        except ValidationError:
-            logger.error(f"Invalid refresh response: {e}")
+            logger.exception("Invalid refresh response")
             self.context.clear_tokens()
             return False
 
@@ -522,8 +522,8 @@ class OAuthClientProvider(httpx.Auth):
                     token_request = await self._exchange_token(auth_code, code_verifier)
                     token_response = yield token_request
                     await self._handle_token_response(token_response)
-                except Exception as e:
+                except Exception:
-                    logger.error(f"OAuth flow error: {e}")
+                    logger.exception("OAuth flow error")
                     raise
 
             # Add authorization header and make request

src/mcp/client/sse.py

@@ -97,7 +97,7 @@ async def sse_client(
                                             )
                                             logger.debug(f"Received server message: {message}")
                                         except Exception as exc:
-                                            logger.error(f"Error parsing server message: {exc}")
+                                            logger.exception("Error parsing server message")
                                             await read_stream_writer.send(exc)
                                             continue
 
@@ -106,7 +106,7 @@ async def sse_client(
                                     case _:
                                         logger.warning(f"Unknown SSE event: {sse.event}")
                         except Exception as exc:
-                            logger.error(f"Error in sse_reader: {exc}")
+                            logger.exception("Error in sse_reader")
                             await read_stream_writer.send(exc)
                         finally:
                             await read_stream_writer.aclose()
@@ -126,8 +126,8 @@ async def sse_client(
                                     )
                                     response.raise_for_status()
                                     logger.debug(f"Client message sent successfully: {response.status_code}")
-                        except Exception as exc:
+                        except Exception:
-                            logger.error(f"Error in post_writer: {exc}")
+                            logger.exception("Error in post_writer")
                         finally:
                             await write_stream.aclose()
 

src/mcp/client/streamable_http.py

@@ -308,7 +308,7 @@ class StreamableHTTPTransport:
             session_message = SessionMessage(message)
             await read_stream_writer.send(session_message)
         except Exception as exc:
-            logger.error(f"Error parsing JSON response: {exc}")
+            logger.exception("Error parsing JSON response")
             await read_stream_writer.send(exc)
 
     async def _handle_sse_response(
@@ -410,8 +410,8 @@ class StreamableHTTPTransport:
                     else:
                         await handle_request_async()
 
-        except Exception as exc:
+        except Exception:
-            logger.error(f"Error in post_writer: {exc}")
+            logger.exception("Error in post_writer")
         finally:
             await read_stream_writer.aclose()
             await write_stream.aclose()

src/mcp/os/posix/utilities.py

@@ -52,9 +52,9 @@ async def terminate_posix_process_tree(process: Process, timeout_seconds: float
             process.terminate()
             with anyio.fail_after(timeout_seconds):
                 await process.wait()
-        except Exception as term_error:
+        except Exception:
-            logger.warning(f"Process termination failed for PID {pid}: {term_error}, attempting force kill")
+            logger.warning(f"Process termination failed for PID {pid}, attempting force kill")
             try:
                 process.kill()
-            except Exception as kill_error:
+            except Exception:
-                logger.error(f"Failed to kill process {pid}: {kill_error}")
+                logger.exception(f"Failed to kill process {pid}")

src/mcp/server/fastmcp/server.py

@@ -311,7 +311,7 @@ class FastMCP:
             content = await resource.read()
             return [ReadResourceContents(content=content, mime_type=resource.mime_type)]
         except Exception as e:
-            logger.error(f"Error reading resource {uri}: {e}")
+            logger.exception(f"Error reading resource {uri}")
             raise ResourceError(str(e))
 
     def add_tool(
@@ -961,7 +961,7 @@ class FastMCP:
 
             return GetPromptResult(messages=pydantic_core.to_jsonable_python(messages))
         except Exception as e:
-            logger.error(f"Error getting prompt {name}: {e}")
+            logger.exception(f"Error getting prompt {name}")
             raise ValueError(str(e))
 
 

src/mcp/server/sse.py

@@ -105,8 +105,8 @@ class SseServerTransport:
         # Validate that endpoint is a relative path and not a full URL
         if "://" in endpoint or endpoint.startswith("//") or "?" in endpoint or "#" in endpoint:
             raise ValueError(
-                f"Given endpoint: {endpoint} is not a relative path (e.g., '/messages/'), \
+                f"Given endpoint: {endpoint} is not a relative path (e.g., '/messages/'), "
-                             expecting a relative path(e.g., '/messages/')."
+                "expecting a relative path (e.g., '/messages/')."
             )
 
         # Ensure endpoint starts with a forward slash
@@ -234,7 +234,7 @@ class SseServerTransport:
             message = types.JSONRPCMessage.model_validate_json(body)
             logger.debug(f"Validated client message: {message}")
         except ValidationError as err:
-            logger.error(f"Failed to parse message: {err}")
+            logger.exception("Failed to parse message")
             response = Response("Could not parse message", status_code=400)
             await response(scope, receive, send)
             await writer.send(err)

src/mcp/server/streamable_http.py

@@ -248,8 +248,9 @@ class StreamableHTTPServerTransport:
                 # Close the request stream
                 await self._request_streams[request_id][0].aclose()
                 await self._request_streams[request_id][1].aclose()
-            except Exception as e:
+            except Exception:
-                logger.debug(f"Error closing memory streams: {e}")
+                # During cleanup, we catch all exceptions since streams might be in various states
+                logger.debug("Error closing memory streams - may already be closed")
             finally:
                 # Remove the request stream from the mapping
                 self._request_streams.pop(request_id, None)
@@ -421,10 +422,10 @@ class StreamableHTTPServerTransport:
                             HTTPStatus.INTERNAL_SERVER_ERROR,
                         )
                         await response(scope, receive, send)
-                except Exception as e:
+                except Exception:
-                    logger.exception(f"Error processing JSON response: {e}")
+                    logger.exception("Error processing JSON response")
                     response = self._create_error_response(
-                        f"Error processing request: {str(e)}",
+                        "Error processing request",
                         HTTPStatus.INTERNAL_SERVER_ERROR,
                         INTERNAL_ERROR,
                     )
@@ -451,8 +452,8 @@ class StreamableHTTPServerTransport:
                                     JSONRPCResponse | JSONRPCError,
                                 ):
                                     break
-                    except Exception as e:
+                    except Exception:
-                        logger.exception(f"Error in SSE writer: {e}")
+                        logger.exception("Error in SSE writer")
                     finally:
                         logger.debug("Closing SSE writer")
                         await self._clean_up_memory_streams(request_id)
@@ -569,8 +570,8 @@ class StreamableHTTPServerTransport:
                         # Send the message via SSE
                         event_data = self._create_event_data(event_message)
                         await sse_stream_writer.send(event_data)
-            except Exception as e:
+            except Exception:
-                logger.exception(f"Error in standalone SSE writer: {e}")
+                logger.exception("Error in standalone SSE writer")
             finally:
                 logger.debug("Closing standalone SSE writer")
                 await self._clean_up_memory_streams(GET_STREAM_KEY)
@@ -585,8 +586,8 @@ class StreamableHTTPServerTransport:
         try:
             # This will send headers immediately and establish the SSE connection
             await response(request.scope, request.receive, send)
-        except Exception as e:
+        except Exception:
-            logger.exception(f"Error in standalone SSE response: {e}")
+            logger.exception("Error in standalone SSE response")
             await sse_stream_writer.aclose()
             await sse_stream_reader.aclose()
             await self._clean_up_memory_streams(GET_STREAM_KEY)
@@ -628,10 +629,7 @@ class StreamableHTTPServerTransport:
 
         # Close all request streams asynchronously
         for key in request_stream_keys:
-            try:
+            await self._clean_up_memory_streams(key)
-                await self._clean_up_memory_streams(key)
-            except Exception as e:
-                logger.debug(f"Error closing stream {key} during termination: {e}")
 
         # Clear the request streams dictionary immediately
         self._request_streams.clear()
@@ -645,6 +643,7 @@ class StreamableHTTPServerTransport:
             if self._write_stream is not None:
                 await self._write_stream.aclose()
         except Exception as e:
+            # During cleanup, we catch all exceptions since streams might be in various states
             logger.debug(f"Error closing streams: {e}")
 
     async def _handle_unsupported_request(self, request: Request, send: Send) -> None:
@@ -765,8 +764,8 @@ class StreamableHTTPServerTransport:
                                     event_data = self._create_event_data(event_message)
 
                                     await sse_stream_writer.send(event_data)
-                except Exception as e:
+                except Exception:
-                    logger.exception(f"Error in replay sender: {e}")
+                    logger.exception("Error in replay sender")
 
             # Create and start EventSourceResponse
             response = EventSourceResponse(
@@ -777,16 +776,16 @@ class StreamableHTTPServerTransport:
 
             try:
                 await response(request.scope, request.receive, send)
-            except Exception as e:
+            except Exception:
-                logger.exception(f"Error in replay response: {e}")
+                logger.exception("Error in replay response")
             finally:
                 await sse_stream_writer.aclose()
                 await sse_stream_reader.aclose()
 
-        except Exception as e:
+        except Exception:
-            logger.exception(f"Error replaying events: {e}")
+            logger.exception("Error replaying events")
             response = self._create_error_response(
-                f"Error replaying events: {str(e)}",
+                "Error replaying events",
                 HTTPStatus.INTERNAL_SERVER_ERROR,
                 INTERNAL_ERROR,
             )
@@ -874,8 +873,8 @@ class StreamableHTTPServerTransport:
                                 for message. Still processing message as the client
                                 might reconnect and replay."""
                             )
-                except Exception as e:
+                except Exception:
-                    logger.exception(f"Error in message router: {e}")
+                    logger.exception("Error in message router")
 
             # Start the message router
             tg.start_soon(message_router)
@@ -885,11 +884,7 @@ class StreamableHTTPServerTransport:
                 yield read_stream, write_stream
             finally:
                 for stream_id in list(self._request_streams.keys()):
-                    try:
+                    await self._clean_up_memory_streams(stream_id)
-                        await self._clean_up_memory_streams(stream_id)
-                    except Exception as e:
-                        logger.debug(f"Error closing request stream: {e}")
-                        pass
                 self._request_streams.clear()
 
                 # Clean up the read and write streams
@@ -899,4 +894,5 @@ class StreamableHTTPServerTransport:
                     await write_stream_reader.aclose()
                     await write_stream.aclose()
                 except Exception as e:
+                    # During cleanup, we catch all exceptions since streams might be in various states
                     logger.debug(f"Error closing streams: {e}")