Log or modify the request body in the node-http-proxy before to pass it to the express.js application

proxy.js

/*******************************************************************************
 * Copyright (c) 2017 Nicola Del Gobbo
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the license at http://www.apache.org/licenses/LICENSE-2.0
 *
 * THIS CODE IS PROVIDED ON AN *AS IS* BASIS, WITHOUT WARRANTIES OR CONDITIONS
 * OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION ANY
 * IMPLIED WARRANTIES OR CONDITIONS OF TITLE, FITNESS FOR A PARTICULAR PURPOSE,
 * MERCHANTABLITY OR NON-INFRINGEMENT.
 *
 * See the Apache Version 2.0 License for specific language governing
 * permissions and limitations under the License.
 *
 * Contributors - initial API implementation:
 * Nicola Del Gobbo <[email protected]>
 ******************************************************************************/
'use strict';

const http = require('http');
const express = require('express');
const bodyParser = require('body-parser');
const httpProxy = require('http-proxy');
const morgan = require('morgan');

/////////////////////////////////// PROXY SERVER ///////////////////////////////

const proxy = httpProxy.createProxyServer({});

// Restream parsed body before proxying
proxy.on('proxyReq', function(proxyReq, req, res, options) {
  if(req.body) {
    let bodyData = JSON.stringify(req.body);
    // In case if content-type is application/x-www-form-urlencoded -> we need to change to application/json
    proxyReq.setHeader('Content-Type','application/json');
    proxyReq.setHeader('Content-Length', Buffer.byteLength(bodyData));
    // Stream the content
    proxyReq.write(bodyData);
  }
});

const proxyApp = express();
proxyApp.use(bodyParser.json());
proxyApp.use(bodyParser.urlencoded({extended: true}));
proxyApp.use(function(req, res){
    // ... do some stuff
    // ... log your body and something else
    console.log('proxy body:',req.body)
    proxy.web(req, res, {
      target: 'http://127.0.0.1:5000'
    })
  });

http.createServer(proxyApp).listen(8080, '0.0.0.0', () => {
  console.log('Proxy server linsten on 8080');
});

/////////////////////////////////// PROXY SERVER ///////////////////////////////

////////////////////////// YOUR APP BEHIND PROXY ///////////////////////////////

const app = express();
app.use(morgan('dev'));
app.use(bodyParser.json());
//app.use(bodyParser.urlencoded({extended: true}));
app.post('/post', (req, res) => { 
  console.log("App body => ", req.body);
  res.send('POST REQUEST');
});
app.get('/get', (req, res) => { 
  res.send('GET REQUEST');
});
http.createServer(app).listen(5000, '127.0.0.1', () => {
  console.log('Applicaton server linsten on 5000');
});

////////////////////////////////////////////////////////////////////////////////

You have literally saved me.
Thanks, men!

A little addition.
As far as I understood that "proxy.on proxyReq" handler should be the last. In another case, you will see an error like "cant modify request because it was sent" while modifying request.