Waiting for a port with effection

wait-port.ts

import { fork, timeout, Sequence, Operation } from 'effection';
import { on } from '@effection/events';

import { createConnection } from 'net';

export function* waitConnect(host: string, port: number): Sequence {
  loop: {
    let socket = createConnection(port, host);

    let monitor = fork(function*() {
      let [error]: [Error] = yield on(socket, 'error');
      throw error;
    })

    try {
      yield on(socket, 'ready');
    } catch (error) {
      break loop;
    } finally {
      monitor.halt();
      socket.destroy();
    }
  }
}

export function* waitPort(host: string, port: number, maxtime: number): Sequence {
  yield timebox(maxtime, waitConnect(host, port));
}

// take any operation and timebox it to `duration`
export function* timebox(duration: number, operation: Operation): Sequence {

  // timebox process will throw an exception after `duration` milliseconds
  // thus aborting the parent operation (and all siblings).
  let timebomb = fork(function* () {
    yield timeout(duration);
    throw new Error(`timeout of ${duration}ms exceeded`);
  })

  try {
    return yield operation;
  } finally {
    timebomb.halt();
  }
}