node-http-proxy proxy chain with connect method implemented (+ bonus auth handling)

proxy-chain.js

"use strict";

const http = require('http');
const request = http.request;
const net = require('net');
const httpProxy = require('http-proxy');

let auth = "secret-string";
auth = new Buffer(auth).toString('base64');
auth = "Basic " + auth;

module.exports = function (proxyHost, proxyPort, listenPort) {

  const settings = {target: `http://${proxyHost}:${proxyPort}`, toProxy: true, prependPath: false};
  const proxy = httpProxy.createProxyServer(settings);
  const noProxyChain = !proxyHost && !proxyPort;

  proxy.on('error', function(err) {
    console.log('ERR:',err);
  });
  const server = http.createServer(function (req, res) {
    if (!req.headers['proxy-authorization'] || req.headers['proxy-authorization'] !== auth) {
      res.writeHead(401);
      res.end();
      return;
    }
    delete req.headers['proxy-authorization'];
    proxy.web(req, res, settings);
  });
  server.on('connect', function (req, socket) {
    if (!req.headers['proxy-authorization'] || req.headers['proxy-authorization'] !== auth) {
      socket.write("HTTP/1.1 401 UNAUTHORIZED\r\n\r\n");
      socket.end();
      socket.destroy();
      return;
    }
    delete req.headers['proxy-authorization'];
    if (noProxyChain) {
      const parts = req.url.split(':', 2);
      const conn = net.connect(parts[1], parts[0], function () {
        socket.write("HTTP/1.1 200 OK\r\n\r\n");
        socket.pipe(conn);
        conn.pipe(socket);
      });
      conn.on('error', function () {
        socket.write("HTTP/1.1 500 SERVER ERROR\r\n\r\n");
        socket.end();
        socket.destroy();
      });
      return;
    }
    const connectOptions = {
      "host": proxyHost,
      "port": proxyPort,
      "headers": req.headers,
      "method": "CONNECT",
      "path": req.url,
      "agent": false
    };
    // from TunnelingAgent.prototype.createSocket
    const connectReq = request(connectOptions);
    connectReq.useChunkedEncodingByDefault = false;
    connectReq.once('response', onResponse);
    connectReq.once('upgrade', onUpgrade);
    connectReq.once('connect', onConnect);
    connectReq.once('error', onError);
    connectReq.end();

    function onResponse(res) {
      res.upgrade = true;
    }

    function onUpgrade(res, proxySocket, head) {
      process.nextTick(function () {
        onConnect(res, proxySocket, head);
      });
    }

    function onConnect(res, proxySocket) {
      proxySocket.removeAllListeners();

      if (res.statusCode === 200) {
        socket.write("HTTP/1.1 200 OK\r\n\r\n");
        socket.pipe(proxySocket);
        proxySocket.pipe(socket);
      } else {
        socket.write("HTTP/1.1 500 SERVER ERROR\r\n\r\n");
        socket.end();
        socket.destroy();
      }
    }

    function onError() {
      socket.write("HTTP/1.1 500 SERVER ERROR\r\n\r\n");
      socket.end();
      socket.destroy();
    }

  });
  server.listen(listenPort);
};