fix: redirect the stderr of mcp servers to local

Author: calmini

src/mcpm/router/client_connection.py

@@ -1,6 +1,6 @@
 import asyncio
 import logging
-from typing import Optional, cast
+from typing import Optional, TextIO, cast
 
 from mcp import ClientSession, InitializeResult, StdioServerParameters, stdio_client
 from mcp.client.sse import sse_client
@@ -10,10 +10,10 @@
 logger = logging.getLogger(__name__)
 
 
-def _stdio_transport_context(server_config: ServerConfig):
+def _stdio_transport_context(server_config: ServerConfig, errlog: TextIO):
     server_config = cast(STDIOServerConfig, server_config)
     server_params = StdioServerParameters(command=server_config.command, args=server_config.args, env=server_config.env)
-    return stdio_client(server_params)
+    return stdio_client(server_params, errlog=errlog)
 
 
 def _sse_transport_context(server_config: ServerConfig):
@@ -22,16 +22,19 @@ def _sse_transport_context(server_config: ServerConfig):
 
 
 class ServerConnection:
-    def __init__(self, server_config: ServerConfig) -> None:
+    def __init__(self, server_config: ServerConfig, errlog: TextIO) -> None:
         self.session: Optional[ClientSession] = None
         self.session_initialized_response: Optional[InitializeResult] = None
         self._initialized = False
         self.server_config = server_config
         self._initialized_event = asyncio.Event()
         self._shutdown_event = asyncio.Event()
+        self._errlog = errlog
 
         self._transport_context_factory = (
-            _stdio_transport_context if isinstance(server_config, STDIOServerConfig) else _sse_transport_context
+            lambda config: _stdio_transport_context(config, errlog=self._errlog)
+            if isinstance(config, STDIOServerConfig)
+            else _sse_transport_context(config)
         )
 
         self._server_task = asyncio.create_task(self._server_lifespan_cycle())

src/mcpm/router/router.py

@@ -6,7 +6,7 @@
 import typing as t
 from collections import defaultdict
 from contextlib import asynccontextmanager
-from typing import Literal, Optional
+from typing import Literal, Optional, TextIO
 
 import uvicorn
 from mcp import server, types
@@ -24,6 +24,7 @@
 from mcpm.profile.profile_config import ProfileConfigManager
 from mcpm.schemas.server_config import ServerConfig
 from mcpm.utils.config import PROMPT_SPLITOR, RESOURCE_SPLITOR, RESOURCE_TEMPLATE_SPLITOR, TOOL_SPLITOR
+from mcpm.utils.errlog_manager import ServerErrorLogManager
 
 from .client_connection import ServerConnection
 from .transport import RouterSseTransport
@@ -60,6 +61,7 @@ def __init__(self, reload_server: bool = False, profile_path: str | None = None,
         if reload_server:
             self.watcher = ConfigWatcher(self.profile_manager.profile_path)
         self.strict: bool = strict
+        self.error_log_manager = ServerErrorLogManager()
 
     def get_unique_servers(self) -> list[ServerConfig]:
         profiles = self.profile_manager.list_profiles()
@@ -110,11 +112,13 @@ async def add_server(self, server_id: str, server_config: ServerConfig) -> None:
             raise ValueError(f"Server with ID {server_id} already exists")
 
         # Create client based on connection type
-        client = ServerConnection(server_config)
+        errlog: TextIO = self.error_log_manager.open_errlog_file(server_id)
+        client = ServerConnection(server_config, errlog=errlog)
 
         # Connect to the server
         await client.wait_for_initialization()
         if not client.healthy():
+            self.error_log_manager.close_errlog_file(server_id)
             raise ValueError(f"Failed to connect to server {server_id}")
 
         response = client.session_initialized_response
@@ -218,6 +222,7 @@ async def remove_server(self, server_id: str) -> None:
         # Remove the server from all collections
         del self.server_sessions[server_id]
         del self.capabilities_mapping[server_id]
+        self.error_log_manager.close_errlog_file(server_id)
 
         # Delete registered tools, resources and prompts
         for key in list(self.tools_mapping.keys()):
@@ -574,4 +579,7 @@ async def shutdown(self):
             if client.healthy():
                 await client.request_for_shutdown()
 
+        # close all errlog files
+        self.error_log_manager.close_all()
+
         logger.info("all alive client sessions have been shut down")

src/mcpm/utils/errlog_manager.py

@@ -0,0 +1,34 @@
+import os
+from pathlib import Path
+from typing import Optional, TextIO
+
+from .platform import get_log_directory
+
+DEFAULT_ROOT_STDERR_LOG_DIR = get_log_directory("mcpm") / "errlogs"
+
+class ServerErrorLogManager:
+    """
+    A manager for server error logs.
+    """
+
+    def __init__(self, root_dir: Optional[Path] = None) -> None:
+        self.root_log_dir = root_dir if root_dir else DEFAULT_ROOT_STDERR_LOG_DIR
+        os.makedirs(self.root_log_dir, exist_ok=True)
+        self._log_files: dict[str, TextIO] = {}
+
+    def open_errlog_file(self, server_id: str) -> TextIO:
+        if server_id not in self._log_files or self._log_files[server_id].closed:
+            log_file = self.root_log_dir / f"{server_id}.log"
+            # use line buffering, flush to disk when meeting a newline
+            self._log_files[server_id] = log_file.open("a", encoding="utf-8", buffering=1)
+        return self._log_files[server_id]
+
+    def close_errlog_file(self, server_id: str) -> None:
+        if server_id in self._log_files and not self._log_files[server_id].closed:
+            self._log_files[server_id].flush()
+            self._log_files[server_id].close()
+            del self._log_files[server_id]
+
+    def close_all(self) -> None:
+        for server_id in self._log_files:
+            self.close_errlog_file(server_id)