simple http duplicator

http_duplicate.js

const forward = {host: 'duckduckgo.com', port: 80};
const duplicates = [{host: 'google.com', port: 80}];
const trace = console.trace.bind(console);

process.on('uncaughtException', console.trace.bind(console, 'uncaught exception:'));

const http = require('http');
const request = require('request');
const dns = require('dns');
const Promise = require('bluebird');

const memoizedDns = (function wrapper() {
  const cache = new Map();
  const lookup = Promise.promisify(dns.lookup, dns);
  const maxTs = 5000;

  return function memoizedDnsWrapped(url) {
    const isCached = cache.get(url);
    const isInFlight = isCached && !cache.get(url).ts;
    const isStale = isCached && Date.now() - cache.get(url).ts > maxTs;

    if (isInFlight) return cache.get(url);
    if (isCached && !isStale) return cache.get(url).val;

    console.log('looking up %s', url);
    const result = lookup(url).timeout(2000).then(([ip]) => {
      cache.set(url, { ts: Date.now(), val: Promise.resolve(ip) });
      console.log('%s resolved to %s', url, ip);
      return ip;
    }).catch(cache.delete(url));

    cache.set(url, result);
    return result;
  };
})();

const server = http.createServer((req, res) => {
  console.log('got %s request to %s', req.method, req.url);

  memoizedDns(forward.host)
  .then((ip) =>{
    req.pipe(request({
      method: req.method,
      url: `http://${ip}:${forward.port || 80}${req.url}`,
      headers: req.headers,
    }).on('error', () => trace.bind('socket hang up?'))).pipe(res)
    .on('error', trace.bind('got error'));
  }).catch(console.trace.bind(console, 'Error while forwarding'));

  function dupRequest(dup) {
    return (
      memoizedDns(dup.host)
      .then((ip) => {
        req.pipe(request({
          method: req.method,
          url: `http://${ip}:${dup.port || 80}${req.url}`,
          headers: req.headers,
        }).once('error', (err) => {
          console.error('error in dup request to :', dup.host, err);
          trace();
        }));
      })
    );
  }

  duplicates.map((dup) => {
    dupRequest(dup).catch(trace.bind('Error while duplicating to ' + dup.host));
  });
});

const port = 80;
server.listen(port, (err) => {
  if (err) {
    console.error('error while starting:', err);
    process.exit(1);
  }

  console.log(`started on port ${port}`);
});