Function connectWithHello

src/mcp/proxy.ts:131–166

(
  socketPath: string,
  expectedVersion: string = CodeGraphPackageVersion,
)

 * owns the socket. Used by the local-handshake proxy's background connect.
 */
export async function connectWithHello(
  socketPath: string,
  expectedVersion: string = CodeGraphPackageVersion,
): Promise<net.Socket | 'version-mismatch' | null> {
  if (process.platform !== 'win32' && !fs.existsSync(socketPath)) return null;
  const socket = net.createConnection(socketPath);
  socket.setEncoding('utf8');
  // Keep an 'error' listener attached for the socket's ENTIRE life. readHelloLine
  // attaches its own and then REMOVES it on success (its cleanup()), which left a
  // window — from here until the caller attaches its onDaemonLost handler — where
  // a socket 'error' had NO listener. In Node an unhandled socket 'error' is
  // re-thrown as an uncaughtException, which the global fatal handler turns into
  // process.exit(1); to an MCP client that surfaces as a bare "Transport closed"
  // (#974). The window is rarely hit on a healthy FS but is common on flaky
  // AF_UNIX-over-DrvFs (WSL2 /mnt drives). A no-op guard makes the error
  // recoverable: the follow-up 'close' drives the caller's normal fallback.
  socket.on('error', () => { /* absorbed — see #974; 'close' drives the fallback */ });
  const hello = await readHelloLine(socket).catch(() => null);
  if (!hello) {
    socket.destroy();
    return null; // no daemon yet — caller should keep polling
  }
  if (hello.codegraph !== expectedVersion) {
    // A daemon IS up but it's the wrong version — definitive, not a "not yet".
    // Don't poll; the caller serves in-process so we never run stale-vs-new.
    process.stderr.write(
      `[CodeGraph MCP] Found a daemon on ${socketPath} but version (${hello.codegraph}) ` +
      `differs from ours (${expectedVersion}); serving this session in-process.\n`
    );
    socket.destroy();
    return 'version-mismatch';
  }
  logAttachedDaemon(socketPath, hello);
  sendClientHello(socket);
  return socket;
}

/**
 * Tell the daemon our pids right after we verify its hello, so its liveness