Reverse Proxy that passes through Postman's proxy to capture incoming HTTP traffic.

server.js

// A reverse proxy that captures incoming HTTP traffic and sends it
// through Postman's forward proxy, which forwards traffic to the 
// specified target in process.env.TARGET.

// request
// client -> this-proxy -> postman-proxy --|
//                                         |
//                                       target
// response                                |
// client <- this-proxy <- postman-proxy --|

const http = require('http');

const target = process.env.TARGET;
const proxy = new URL(
  process.env.http_proxy || process.env.HTTP_PROXY || 'http://localhost:5555');

const server = http.createServer((req, res) => {
  try {
    let forwardedFor = req.headers['x-forwarded-for'] || '';
    const ff = forwardedFor.split(',');
    ff.push(req.connection.remoteAddress);
    forwardedFor = ff.map(h => h.trim()).join(', ');

    const options = {
      headers: Object.assign({}, req.headers,
        {
          'host': target,
          'x-forwarded-proto': 'http',
          'x-forwarded-host': req.headers.host,
          'x-forwarded-for': forwardedFor
        }),
      host: proxy.hostname,
      port: proxy.port,
      method: req.method,
      path: `http://${target}${req.url}` // convert to forward proxy style
    };

    const client = http.request(options, (reply) => {
      res.statusCode = reply.statusCode;
      res.headers = reply.headers;
      reply.pipe(res);
    });

    log(`Forwarding request to ${options.path}`);

    req.pipe(client);
  } catch (ex) {
    console.error(ex);
  }
});

server.on('connect', (_req, clientSocket, _head) => {
  // HTTP tunneling not supported.
  log('Client attempted to use an HTTP tunnel, sending 502 Bad Gateway.')
  clientSocket.end('HTTP/1.1 502 Bad Gateway\r\n\rn');
});

server.on('listening', () => {
  log(`Proxy listening on ${JSON.stringify(server.address())}`);
});

server.listen(process.env.PORT || 3100);

const log = (msg) => {
  console.log(new Date(), `=> ${msg}`);
};