101 lines
3.1 KiB
Python
101 lines
3.1 KiB
Python
#!/usr/bin/env python3
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"""
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MCP server (NDJSON JSON-RPC over stdio) that spawns a long-lived grandchild which inherits
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this process's stdin/stdout/stderr and keeps them open.
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This reproduces the reader-teardown deadlock: killing the direct MCP child (SIGKILL, which is
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all subprocess_terminate() does) does NOT close the stdout/stderr pipe write ends, because the
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grandchild still holds them. A server that reads those pipes with a blocking read would then
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wait forever for an EOF that never arrives, hanging teardown (both warmup shutdown at startup
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and process shutdown). The polled, running-aware reader must exit regardless.
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"""
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import json
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import os
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import subprocess
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import sys
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# Spawn a grandchild that inherits our std handles (fds 0/1/2 = the MCP pipes) and lives well
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# past any teardown in the tests. We do NOT redirect its stdio, so it keeps the pipe write ends
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# open even after this process is killed.
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subprocess.Popen([sys.executable, "-c", "import time; time.sleep(30)"])
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TOOLS = [
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{
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"name": "echo",
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"description": "Echo back the input message",
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"inputSchema": {
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"type": "object",
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"properties": {"message": {"type": "string", "description": "Message to echo"}},
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"required": ["message"],
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},
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}
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]
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def handle_initialize(params, req_id):
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return {
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"jsonrpc": "2.0",
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"id": req_id,
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"result": {
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"protocolVersion": "2024-11-05",
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"capabilities": {"tools": {}},
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"serverInfo": {"name": "grandchild-test", "version": "1.0"},
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},
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}
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def handle_tools_list(params, req_id):
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return {"jsonrpc": "2.0", "id": req_id, "result": {"tools": TOOLS}}
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def handle_tools_call(params, req_id):
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if params.get("name") == "echo":
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message = params.get("arguments", {}).get("message", "")
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return {
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"jsonrpc": "2.0",
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"id": req_id,
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"result": {"content": [{"type": "text", "text": f"echo: {message}"}]},
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}
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return {"jsonrpc": "2.0", "id": req_id, "error": {"code": -32602, "message": "Unknown tool"}}
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HANDLERS = {
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"initialize": handle_initialize,
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"tools/list": handle_tools_list,
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"tools/call": handle_tools_call,
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}
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def main():
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sys.stdout = os.fdopen(sys.stdout.fileno(), "w", buffering=1)
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sys.stderr = os.fdopen(sys.stderr.fileno(), "w", buffering=1)
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for line in sys.stdin:
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line = line.strip()
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if not line:
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continue
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try:
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request = json.loads(line)
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except json.JSONDecodeError:
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continue
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method = request.get("method")
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req_id = request.get("id")
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params = request.get("params", {})
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if req_id is None:
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continue # notification, no response
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handler = HANDLERS.get(method)
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if handler:
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response = handler(params, req_id)
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else:
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response = {"jsonrpc": "2.0", "id": req_id, "error": {"code": -32601, "message": f"Method not found: {method}"}}
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sys.stdout.write(json.dumps(response) + "\n")
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sys.stdout.flush()
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if __name__ == "__main__":
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main()
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