Function makeCallback

test/pummel/test-net-write-callbacks.js:43–56

(c)

let lastCalled = -1;
function makeCallback(c) {
  let called = false;
  return function() {
    if (called)
      throw new Error(`called callback #${c} more than once`);
    called = true;
    if (c < lastCalled) {
      throw new Error(
        `callbacks out of order. last=${lastCalled} current=${c}`);
    }
    lastCalled = c;
    cbcount++;
  };
}

server.listen(0, function() {
  const client = net.createConnection(server.address().port);