Edit POST parameters prior to forwarding to a proxy target and sending response back to client

Question

I have a node/express proxy setup using http-proxy-middleware to route requests to a java-tomcat web service (proxy target).

I need to inject POST form data into the request rawbody with a context-type of "application/x-www-form-urlencoded" prior to forwarding the request to the proxy target. The proxy response will need to have the same post parameters removed prior to sending the response to the client.

I have used a number of different proxies include http-proxy, http-proxy-middleware, node-proxy, and express-proxy but none of these modules appear to have a solution available that allows for POST parameter manipulation

This question was originally posted on https://github.com/chimurai/http-proxy-middleware/issues/61#issuecomment-205494577

'use strict';

var express = require('express');
var router = express.Router();
//var request = require("request");

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

var proxy_options = {
    target: 'http://localhost:8080',
    logLevel: 'debug',
    //logProvider:
    onError(err, req, res) {
        res.writeHead(500, {
            'Content-Type': 'text/plain'
        });
        res.end('Something went wrong. And we are reporting a custom error message.' + err);
    },
    onProxyRes(proxyRes, req, res) {
        //proxyRes.headers['x-added'] = 'foobar';     // add new header to response
        //delete proxyRes.headers['x-removed'];       // remove header from response
    },
    onProxyReq(proxyReq, req, res) {
        if ( req.method == "POST" && req.body ) {
            proxyReq.write( encodeURIComponent( JSON.stringify(   req.body ) ) );
            proxyReq.end();
        }
    }
};

// Proxy configuration
var proxy = require( 'http-proxy-middleware' )( proxy_filter, proxy_options );

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

router.all('/report/*', function( req, res, next ) {

    //req.body.jdbc_sas = 'jdbc:postgresql://pg_dev:5432/sasdb';
    //req.body.jdbc_agency = 'jdbc:postgresql://pg_dev:5432/agency0329';
    //console.log('proxy body:',req.body);

    proxy( req, res, next );
} );

module.exports = router;

Any suggestions are greatly appreciated.

Respectfully,

Warren.

Answer 1

Ok Here's the final solution.

The following example allows you to inject POST parameters prior to forwarding to the proxy target. You don't have scrub any parameters from the proxy target response - as far as I can tell - because it maintains a copy of the original POST request.

On a side note this also allows the http-proxy-middleware to work with body-parser.

Example Node Express Route File:

'use strict';

var express = require('express');
var router = express.Router();

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

var proxy_options = {
    target: 'http://localhost:8080',
    pathRewrite: {
        '^/docs' : '/java/rep/server1' // Host path & target path conversion
    },
    onError(err, req, res) {
        res.writeHead(500, {
            'Content-Type': 'text/plain'
        });
        res.end('Something went wrong. And we are reporting a custom error message.' + err);
    },
    onProxyReq(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
var proxy = require( 'http-proxy-middleware' )( proxy_filter, proxy_options );

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

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

module.exports = router;