modify-post.md

Modify Post Parameters:

The code example below illustrates how to modify POST body data prior to forwarding to the proxy target. Key to this example is the "OnProxyReq" event handler that creates a new POST body that can be manipulated to format the POST data as required. For example: inject new POST parameters that should only be visible server side.

This example uses the "body-parser" module in the main app to create a req.body object with the decoded POST parameters. Side note - the code below will allow "http-proxy-middleware" to work with "body-parser".

Since this only modifies the request body stream the original POST body parameters remain in tact, so any POST data changes will not be sent back in the response to the client.

Example:

'use strict';

const express = require('express');
const { createProxyMiddleware } = require('http-proxy-middleware');
const router = express.Router();

const proxy_filter = function (path, req) {
  return path.match('^/docs') && (req.method === 'GET' || req.method === 'POST');
};

const proxy_options = {
  target: 'http://localhost:8080',
  pathRewrite: {
    '^/docs': '/java/rep/server1', // Host path & target path conversion
  },
  on: {
    error(err, req, res) {
      res.writeHead(500, {
        'Content-Type': 'text/plain',
      });
      res.end('Something went wrong. And we are reporting a custom error message.' + err);
    },
    proxyReq(proxyReq, req, res) {
      if (req.method == 'POST' && req.body) {
        // Add req.body logic here if needed....

        // ....

        // Remove body-parser body object from the request
        if (req.body) delete req.body;

        // Make any needed POST parameter changes
        let body = new Object();

        body.filename = 'reports/statistics/summary_2016.pdf';
        body.routeId = 's003b012d002';
        body.authId = 'bac02c1d-258a-4177-9da6-862580154960';

        // URI encode JSON object
        body = Object.keys(body)
          .map(function (key) {
            return encodeURIComponent(key) + '=' + encodeURIComponent(body[key]);
          })
          .join('&');

        // Update header
        proxyReq.setHeader('content-type', 'application/x-www-form-urlencoded');
        proxyReq.setHeader('content-length', body.length);

        // Write out body changes to the proxyReq stream
        proxyReq.write(body);
        proxyReq.end();
      }
    },
  },
};

// Proxy configuration
const proxy = createProxyMiddleware(proxy_filter, proxy_options);

/* GET home page. */
router.get('/', function (req, res, next) {
  res.render('index', { title: 'Node.js Express Proxy Test' });
});

router.all('/docs', proxy);

module.exports = router;