proxy.js

const http = require('http')
const fs = require('fs')
const express = require('express')
const app = express()

app.use('/proxy', (req, res) => {
  const headers = req.headers
  delete headers['host']

  const options = {
    host: 'www.mocky.io',
    port: 80,
    path: '/v2/5899dc3e0f0000890a1f4c56',
    method: 'POST',
    headers: headers
  }

  const fixture = fs.createWriteStream('./fixture', 'utf-8');

  const proxy = req.pipe(http.request(options, r => {
    res.status(r.statusCode).header('Content-Type', 'application/json')

    r.on('data', (chunk) => {
      res.write(chunk)
      fixture.write(chunk)
    })
    r.on('end', () => {
      res.end()
      fixture.end()
      console.log('end')
    })
  }));
})

app.listen(4000, () => {
  console.log('started')
})