Function readClientHello

src/mcp/daemon.ts:763–815

* Read the optional client-hello line a proxy sends after the daemon hello. * Always resolves (never rejects) — fail-safe by design, since every connection * funnels through here. Resolves with the peer pids when the first line is a * client-hello; otherwise resolves with null pids and unshifts t

(
  socket: net.Socket,
)

 * straddling a chunk boundary in the unshifted tail is never corrupted.
 */
function readClientHello(
  socket: net.Socket,
): Promise<{ pid: number | null; hostPid: number | null }> {
  return new Promise((resolve) => {
    let chunks: Buffer[] = [];
    let total = 0;
    let settled = false;
    const finish = (
      peers: { pid: number | null; hostPid: number | null },
      putBack?: Buffer,
    ) => {
      if (settled) return;
      settled = true;
      socket.removeListener('data', onData);
      socket.removeListener('error', onEnd);
      socket.removeListener('close', onEnd);
      clearTimeout(timer);
      if (putBack && putBack.length > 0 && !socket.destroyed) {
        try { socket.unshift(putBack); } catch { /* stream already gone */ }
      }
      resolve(peers);
    };
    const onData = (chunk: Buffer | string) => {
      const buf = typeof chunk === 'string' ? Buffer.from(chunk, 'utf8') : chunk;
      chunks.push(buf);
      total += buf.length;
      const all = chunks.length === 1 ? buf : Buffer.concat(chunks, total);
      const nl = all.indexOf(0x0a); // '\n'
      if (nl === -1) {
        // No newline yet. If it's already too long to be a hello, it isn't one —
        // hand the bytes back as data; otherwise keep accumulating.
        if (total > MAX_HELLO_LINE_BYTES) finish({ pid: null, hostPid: null }, all);
        else chunks = [all];
        return;
      }
      const peers = parseClientHelloLine(all.subarray(0, nl).toString('utf8'));
      if (peers) {
        const tail = all.subarray(nl + 1);
        finish(peers, tail.length > 0 ? tail : undefined);
      } else {
        // First line is not a client-hello (legacy/direct client) — hand the
        // whole buffer back so the transport sees the message verbatim.
        finish({ pid: null, hostPid: null }, all);
      }
    };
    const onEnd = () => finish({ pid: null, hostPid: null });
    const timer = setTimeout(() => finish({ pid: null, hostPid: null }), CLIENT_HELLO_TIMEOUT_MS);
    timer.unref?.();
    socket.on('data', onData);
    socket.on('error', onEnd);
    socket.on('close', onEnd);
  });
}

/** Exported for test stubs that need to bound the hello-line read. */
export { MAX_HELLO_LINE_BYTES };