René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"On Windows 11 when you initialize an mcp client it hangs indefinitely","articleBody":"**Describe the bug**\nOn Windows 11 when you initialize an mcp client it hangs indefinitely.\n\n**To Reproduce**\nCode to reproduce:\n```python\n# ruff: noqa\nimport asyncio\n\nfrom mcp import ClientSession, StdioServerParameters\nfrom mcp.client.sse import sse_client\nfrom mcp.client.stdio import stdio_client\n\n\nasync def run():\n    params = StdioServerParameters(\n        command='bunx', args=['@playwright/mcp@latest']\n    )\n    async with stdio_client(params) as (read, write):\n        print('inside client')\n        async with ClientSession(read, write) as c:\n            print('inside ClientSession')\n            await c.initialize()\n        print('exit ClientSession')\n    print('exit stdio_client')\n\n\nasync def run_sse():\n    async with sse_client('http://localhost:8931/sse') as (read, write):\n        async with ClientSession(read, write) as c:\n            await c.initialize()\n        print('exit ClientSession')\n    print('exit sse_client')\n\n\nif __name__ == '__main__':\n    asyncio.run(run_sse())  # works\n    asyncio.run(run())  # does not work\n\n```\n\n**Expected behavior**\nin both cases it should print both exit statements\n\n**Desktop (please complete the following information):**\n - OS: Windows 11\n - Python Version: Tested on both 3.13.1 and 3.12.7\n\n\n**Additional context**\ncounterintuitively commenting out the code meant to support windows fixes this issue:\n```python\nimport os\nimport sys\nfrom contextlib import asynccontextmanager\nfrom pathlib import Path\nfrom typing import Literal, TextIO\n\nimport anyio\nimport anyio.lowlevel\nfrom anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream\nfrom anyio.streams.text import TextReceiveStream\nfrom pydantic import BaseModel, Field\n\nimport mcp.types as types\n\n# from .win32 import (\n#     create_windows_process,\n#     get_windows_executable_command,\n#     terminate_windows_process,\n# )\n\n# Environment variables to inherit by default\nDEFAULT_INHERITED_ENV_VARS = (\n    [\n        \"APPDATA\",\n        \"HOMEDRIVE\",\n        \"HOMEPATH\",\n        \"LOCALAPPDATA\",\n        \"PATH\",\n        \"PROCESSOR_ARCHITECTURE\",\n        \"SYSTEMDRIVE\",\n        \"SYSTEMROOT\",\n        \"TEMP\",\n        \"USERNAME\",\n        \"USERPROFILE\",\n    ]\n    if sys.platform == \"win32\"\n    else [\"HOME\", \"LOGNAME\", \"PATH\", \"SHELL\", \"TERM\", \"USER\"]\n)\nprint( sys.platform)\n\ndef get_default_environment() -\u003e dict[str, str]:\n    \"\"\"\n    Returns a default environment object including only environment variables deemed\n    safe to inherit.\n    \"\"\"\n    env: dict[str, str] = {}\n\n    for key in DEFAULT_INHERITED_ENV_VARS:\n        value = os.environ.get(key)\n        if value is None:\n            continue\n\n        if value.startswith(\"()\"):\n            # Skip functions, which are a security risk\n            continue\n\n        env[key] = value\n\n    return env\n\n\nclass StdioServerParameters(BaseModel):\n    command: str\n    \"\"\"The executable to run to start the server.\"\"\"\n\n    args: list[str] = Field(default_factory=list)\n    \"\"\"Command line arguments to pass to the executable.\"\"\"\n\n    env: dict[str, str] | None = None\n    \"\"\"\n    The environment to use when spawning the process.\n\n    If not specified, the result of get_default_environment() will be used.\n    \"\"\"\n\n    cwd: str | Path | None = None\n    \"\"\"The working directory to use when spawning the process.\"\"\"\n\n    encoding: str = \"utf-8\"\n    \"\"\"\n    The text encoding used when sending/receiving messages to the server\n\n    defaults to utf-8\n    \"\"\"\n\n    encoding_error_handler: Literal[\"strict\", \"ignore\", \"replace\"] = \"strict\"\n    \"\"\"\n    The text encoding error handler.\n\n    See https://docs.python.org/3/library/codecs.html#codec-base-classes for\n    explanations of possible values\n    \"\"\"\n\n\n@asynccontextmanager\nasync def stdio_client(server: StdioServerParameters, errlog: TextIO = sys.stderr):\n    \"\"\"\n    Client transport for stdio: this will connect to a server by spawning a\n    process and communicating with it over stdin/stdout.\n    \"\"\"\n    read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception]\n    read_stream_writer: MemoryObjectSendStream[types.JSONRPCMessage | Exception]\n\n    write_stream: MemoryObjectSendStream[types.JSONRPCMessage]\n    write_stream_reader: MemoryObjectReceiveStream[types.JSONRPCMessage]\n\n    read_stream_writer, read_stream = anyio.create_memory_object_stream(0)\n    write_stream, write_stream_reader = anyio.create_memory_object_stream(0)\n\n    command = _get_executable_command(server.command)\n\n    # Open process with stderr piped for capture\n    process = await _create_platform_compatible_process(\n        command=command,\n        args=server.args,\n        env=(\n            {**get_default_environment(), **server.env}\n            if server.env is not None\n            else get_default_environment()\n        ),\n        errlog=errlog,\n        cwd=server.cwd,\n    )\n\n    async def stdout_reader():\n        assert process.stdout, \"Opened process is missing stdout\"\n\n        try:\n            async with read_stream_writer:\n                buffer = \"\"\n                async for chunk in TextReceiveStream(\n                    process.stdout,\n                    encoding=server.encoding,\n                    errors=server.encoding_error_handler,\n                ):\n                    lines = (buffer + chunk).split(\"\\n\")\n                    buffer = lines.pop()\n\n                    for line in lines:\n                        try:\n                            message = types.JSONRPCMessage.model_validate_json(line)\n                        except Exception as exc:\n                            await read_stream_writer.send(exc)\n                            continue\n\n                        await read_stream_writer.send(message)\n        except anyio.ClosedResourceError:\n            await anyio.lowlevel.checkpoint()\n\n    async def stdin_writer():\n        assert process.stdin, \"Opened process is missing stdin\"\n\n        try:\n            async with write_stream_reader:\n                async for message in write_stream_reader:\n                    json = message.model_dump_json(by_alias=True, exclude_none=True)\n                    await process.stdin.send(\n                        (json + \"\\n\").encode(\n                            encoding=server.encoding,\n                            errors=server.encoding_error_handler,\n                        )\n                    )\n        except anyio.ClosedResourceError:\n            await anyio.lowlevel.checkpoint()\n\n    async with (\n        anyio.create_task_group() as tg,\n        process,\n    ):\n        tg.start_soon(stdout_reader)\n        tg.start_soon(stdin_writer)\n        try:\n            yield read_stream, write_stream\n        finally:\n            # Clean up process to prevent any dangling orphaned processes\n            # if sys.platform == \"win32\":\n            #     await terminate_windows_process(process)\n            # else:\n            process.terminate()\n\n\ndef _get_executable_command(command: str) -\u003e str:\n    \"\"\"\n    Get the correct executable command normalized for the current platform.\n\n    Args:\n        command: Base command (e.g., 'uvx', 'npx')\n\n    Returns:\n        str: Platform-appropriate command\n    \"\"\"\n      # if sys.platform == \"win32\":\n      #     return get_windows_executable_command(command)\n      # else:\n    return command\n\n\nasync def _create_platform_compatible_process(\n    command: str,\n    args: list[str],\n    env: dict[str, str] | None = None,\n    errlog: TextIO = sys.stderr,\n    cwd: Path | str | None = None,\n):\n    \"\"\"\n    Creates a subprocess in a platform-compatible way.\n    Returns a process handle.\n    \"\"\"\n    # if sys.platform == \"win32\":\n    #     print('attempting create windows process')\n    #     process = await create_windows_process(command, args, env, errlog, cwd)\n    #     print('created windows process')\n    # else:\n    process = await anyio.open_process(\n        [command, *args], env=env, stderr=errlog, cwd=cwd\n    )\n\n    return process\n\n```","author":{"url":"https://github.com/BenMawnMahlauNBTC","@type":"Person","name":"BenMawnMahlauNBTC"},"datePublished":"2025-04-21T16:03:05.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":15},"url":"https://github.com/552/python-sdk/issues/552"}