SIGINT and SIGTERM handled for graceful shutdown

MCP servers running as child processes receive SIGINT when the user presses Ctrl+C and SIGTERM when the parent process shuts down. Without signal handlers, the Node.js process exits immediately (SIGINT default), potentially mid-write on an in-progress JSON-RPC response. The client receives a truncated or empty message and marks the server as crashed. CWE-404 (improper resource shutdown) covers this: open database connections, file handles, and HTTP keep-alives are abandoned rather than closed, which can leave the remote systems in inconsistent state.

Register SIGINT and SIGTERM handlers that call server.close() before exiting. The SDK's close() drains in-flight messages and closes the transport cleanly.

// src/index.ts
async function shutdown() {
  console.error('Shutting down...')
  await server.close()  // closes transport, drains in-flight messages
  process.exit(0)
}

process.on('SIGINT', shutdown)
process.on('SIGTERM', shutdown)

const transport = new StdioServerTransport()
await server.connect(transport)

If your server holds database connections or open file handles, close them inside shutdown() before calling process.exit(0).

• ID: mcp-server.error-resilience.graceful-shutdown

• Severity: medium

• What to look for: Count all signal handlers (SIGINT, SIGTERM) and cleanup routines. Enumerate whether the server completes in-flight requests before shutting down. Check for signal handlers (process.on('SIGINT'), process.on('SIGTERM'), signal.signal() in Python). When the server receives a shutdown signal, it should close the transport cleanly, finish any in-progress tool calls if possible, and release resources (database connections, file handles). Check that the server doesn't just call process.exit() immediately (which could corrupt in-progress responses).

• Pass criteria: The server handles SIGINT and SIGTERM, closes the transport cleanly, and exits. In-progress operations are either completed or cancelled gracefully. At least 1 signal handler must be registered for graceful shutdown.

• Fail criteria: No signal handlers (abrupt termination may corrupt in-progress responses), or signal handlers that call process.exit(0) immediately without cleanup.

• Skip (N/A) when: All checks skip when no MCP server is detected.

• Cross-reference: For timeout handling during shutdown, see timeout-handling.

• Detail on fail: "No SIGINT/SIGTERM handlers — server will be killed abruptly, potentially corrupting in-progress responses or leaving resources open" or "Signal handler calls process.exit(0) immediately without closing the transport or cleaning up database connections"

• Remediation: Handle shutdown signals gracefully:

  // src/index.ts — graceful shutdown
  process.on('SIGINT', async () => { await server.close(); process.exit(0) })
  

  const server = new McpServer({ name: 'my-server', version: '1.0.0' })
  const transport = new StdioServerTransport()
  
  async function shutdown() {
    console.error('Shutting down...')
    await server.close()  // closes transport and cleans up
    process.exit(0)
  }
  
  process.on('SIGINT', shutdown)
  process.on('SIGTERM', shutdown)
  
  await server.connect(transport)
  

  import signal
  import asyncio
  
  async def shutdown(server):
      await server.close()
  
  loop = asyncio.get_event_loop()
  loop.add_signal_handler(signal.SIGINT, lambda: asyncio.create_task(shutdown(server)))
  loop.add_signal_handler(signal.SIGTERM, lambda: asyncio.create_task(shutdown(server)))