cannot get response from await session.call_tool()

Comienza con la reproducción mínima de run() del issue, centrándote en stdio_client, ClientSession y call_tool; compara la ruta exitosa de list_tools con la llamada a la herramienta que se queda bloqueada e inspecciona el registro del lado del cliente. Reproduce el bloqueo y determina por qué no se recibe el resultado de la herramienta; se considera terminado cuando call_tool devuelve el resultado.

hello, I'm sorry to bother you. I've recently encountered a blocking issue with the MCP client.
I've set up an MCP server, and it runs in Claude successfully. However, when I use the client I set up, the call to the tool result = await session.call_tool() gets stuck and doesn't return a response. But when I use tools = await session.list_tools(), I can retrieve the list of tools.

Through logging within the client file, I'm able to confirm that the tool call has been initiated and executed successfully, and the result is obtained, but the client side can't receive the result. It seems there's an issue with the transmission layer of the protocol. I've been struggling with this for two days and have looked for solutions without success, even after upgrading the system version.

I removed the other logic and only kept the tool invocation. The code is as follows.

Looking forward to your reply.

from mcp import ClientSession, StdioServerParameters, types
from mcp.client.stdio import stdio_client


server_params = StdioServerParameters(  # Create server parameters for stdio connection
    command="uvx",
    args=[
        "--from",
        "git+ssh://xxxx.xx.xxx",
        "server-name"
    ],
    env=None
)

# Optional: create a sampling callback
async def handle_sampling_message(message: types.CreateMessageRequestParams) -> types.CreateMessageResult:
    return types.CreateMessageResult(
        role="assistant",
        content=types.TextContent(
            type="text",
            text="Hello, world! from model",
        ),
        model="gpt-3.5-turbo",
        stopReason="endTurn",
    )

async def run():
    async with stdio_client(server_params) as (read, write):
        async with ClientSession(read, write, sampling_callback=handle_sampling_message) as session:
            # Initialize the connection
            await session.initialize()
            # List available tools
            tools = await session.list_tools()
            # Call a tool
            result = await session.call_tool("query-api-infos", arguments={"api_info_id": "8768555"})
            print(result)

if __name__ == "__main__":
    import asyncio
    asyncio.run(run())