proxy.js

http = require('http');
fs = require('fs');

FRONTEND_PORT = 8000;
BACKEND_PORT = 8001;

//CONTENT_LENGTH = 2147483648; // 2 GB
CONTENT_LENGTH = 2097152; // 2 MB

function log_events(prefix, obj) {
  var fun = obj.emit;
  obj.emit = function(what, b, c, d, e) {
    if (what !== 'newListener') {
      console.error(prefix, arguments);
    }
    return fun.call(obj, what, b, c, d, e);
  };
}
function log_events(prefix, obj) {}

function frontend(req, res) {
  res.writeHead(200, {
    'Content-Length': '' + CONTENT_LENGTH,
    'Content-Type': 'application/octet-stream',
    'Connection': 'close'
  });
  res._send(''); // force flush

  var options = {
    method: 'GET',
    host: '127.0.0.1',
    port: BACKEND_PORT,
    path: '/'
  };

  var client_req = http.request(options, function(stream) {
    stream.pipe(res);
  });

  log_events('frontend req', req);
  log_events('frontend res', res);
  log_events('frontend client req', client_req);

  client_req.end();
}

function backend(req, res) {
  res.writeHead(200, {
    'Content-Length': '' + CONTENT_LENGTH,
    'Content-Type': 'application/octet-stream',
    'Connection': 'close'
  });
  res._send(''); // force flush

  var stream = fs.createReadStream('/dev/zero', {
    start: 0,
    end: CONTENT_LENGTH 
  });

  log_events('backend req', req);
  log_events('backend res', res);
  log_events('backend stream', stream);

  stream.pipe(res);
}

http.createServer(frontend).listen(FRONTEND_PORT);
http.createServer(backend).listen(BACKEND_PORT);