DevServer.js

'use strict';

const _ = require('lodash');
const cp = require('child_process');
const util = require('gulp-util');

class DevServer {

  constructor(options) {
    process.env.PORT = process.env.PORT || 3000;
    options = options || {};
    this.script = options.script;
    this.browser = !!options.browser;
    this.browserSync = _.defaults((options.browserSync || {}), {
      port: process.env.PORT,
      notify: false,
      ghostMode: false,
      logPrefix: this.script,
      logConnections: true
    });
    this.server = false;
    this.client = false;
    this.info = {};
  }

  restart() {
    return Promise.resolve()
      .then(() => this.stop())
      .then(() => this.start())
      .then(() => this.proxy());
  }

  start() {
    return new Promise((resolve, reject) => {
      this.server = cp.fork(this.script, {env: _.extend({}, process.env, {PORT: this.info.port || ''})});
      this.server.on('close', () => {
        this.server = null;
        reject(util.PluginError(this.script, 'Fail to startup server.'));
      });
      this.server.on('message', res => {
        if (res.message && res.message === 'online') {
          this.server.removeAllListeners();
          this.info = res;
          util.log(`${this.script} listening on '${util.colors.green(`${this.info.address}:${this.info.port}`)}'`);
          resolve();
        }
      });
    });
  }

  stop() {
    return new Promise(resolve => {
      if (this.server) {
        this.server.removeAllListeners();
        this.server.once('close', () => resolve());
        this.server.kill();
      } else {
        resolve();
      }
    });
  }

  proxy() {
    return new Promise(resolve => {
      if (this.browser) {
        if (this.client) {
          this.client.reload();
          resolve();
        } else {
          this.client = require('browser-sync');
          this.client(_.extend(this.browserSync, {proxy: `${this.info.address}:${this.info.port}`}), () => resolve());
        }
      } else {
        resolve();
      }
    });
  }
}

module.exports = DevServer;

Gulpfile.js

'use strict';

const DevServer = require('./DevServer');
const server = new DevServer({script: './server.js', browser: true});

gulp.task('server:restart', function() {
  return server.restart();
});

gulp.task('default', function() {
  gulp.watch('./**/*.js', ['server:restart']);
});

server.js

#!/usr/bin/env node

'use strict';

const app = require('./app.js');
const server = app.listen(process.env.PORT, process.env.HOST, ~~process.env.BACKLOG, function() {
  process.send && process.send({message: 'online', address: server.address().address, port: server.address().port});
});

server.timeout = ~~process.env.TIMEOUT;