Fix Windows compatibility for STDIO with async DummyProcess

Author: theailanguage

src/mcp/client/stdio/__init__.py

@@ -108,7 +108,8 @@ async def stdio_client(server: StdioServerParameters, errlog: TextIO = sys.stder
     read_stream_writer, read_stream = anyio.create_memory_object_stream(0)
     write_stream, write_stream_reader = anyio.create_memory_object_stream(0)
 
-    command = _get_executable_command(server.command)
+    try:
+        command = _get_executable_command(server.command)
 
         # Open process with stderr piped for capture
         process = await _create_platform_compatible_process(

src/mcp/client/stdio/win32.py

@@ -62,12 +62,8 @@ def __init__(self, popen_obj: subprocess.Popen[bytes]):
         self.stdout_raw = popen_obj.stdout  # type: ignore[assignment]
         self.stderr = popen_obj.stderr  # type: ignore[assignment]
 
-        self.stdin = (
-            FileWriteStream(cast(BinaryIO, self.stdin_raw)) if self.stdin_raw else None
-        )
-        self.stdout = (
-            FileReadStream(cast(BinaryIO, self.stdout_raw)) if self.stdout_raw else None
-        )
+        self.stdin = FileWriteStream(cast(BinaryIO, self.stdin_raw)) if self.stdin_raw else None
+        self.stdout = FileReadStream(cast(BinaryIO, self.stdout_raw)) if self.stdout_raw else None
 
     async def __aenter__(self):
         """Support async context manager entry."""
@@ -91,6 +87,10 @@ def terminate(self):
         """Terminate the subprocess immediately."""
         return self.popen.terminate()
 
+    def kill(self) -> None:
+        """Kill the subprocess immediately (alias for terminate)."""
+        self.terminate()
+
 
 # ------------------------
 # Updated function
@@ -131,7 +131,7 @@ async def create_windows_process(
             env=env,
             cwd=cwd,
             bufsize=0,  # Unbuffered output
-            creationflags = getattr(subprocess, "CREATE_NO_WINDOW", 0),
+            creationflags=getattr(subprocess, "CREATE_NO_WINDOW", 0),
         )
         return DummyProcess(popen_obj)
 
@@ -148,7 +148,8 @@ async def create_windows_process(
         )
         return DummyProcess(popen_obj)
 
-async def terminate_windows_process(process: Process):
+
+async def terminate_windows_process(process: Process | DummyProcess):
     """
     Terminate a Windows process.
 

tests/client/test_stdio.py

@@ -2,11 +2,17 @@
 
 import pytest
 
-from mcp.client.stdio import StdioServerParameters, stdio_client
+from mcp.client.session import ClientSession
+from mcp.client.stdio import (
+    StdioServerParameters,
+    stdio_client,
+)
+from mcp.shared.exceptions import McpError
 from mcp.shared.message import SessionMessage
-from mcp.types import JSONRPCMessage, JSONRPCRequest, JSONRPCResponse
+from mcp.types import CONNECTION_CLOSED, JSONRPCMessage, JSONRPCRequest, JSONRPCResponse
 
 tee: str = shutil.which("tee")  # type: ignore
+python: str = shutil.which("python")  # type: ignore
 
 
 @pytest.mark.anyio