csanz/middlefiddle

Fiddle in the middle with HTTP/HTTPS traffic using Node.js

MiddleFiddle

MiddleFiddle is an outbound local proxy which lets to modify your outbound request and responses via Connect middleware. It support HTTP and HTTPS, the latter through a hijacking of the request with locally generated SSL certs.

Installation

npm install middlefiddle

Examples

Change your user agent

Changes your outbound user-agent depending on the URL

var Mf = require('middlefiddle');
var iPhoneUA = "Mozilla/5.0 (iPhone; U; CPU like Mac OS X; en) AppleWebKit/420+ (KHTML, like Gecko) Version/3.0 Mobile/1A543a Safari/419.3"
Mf.createProxy(Mf.logger(), Mf.user_agent(iPhoneUA, /google\.com/)).listen(8088).listenHTTPS(8089);

Add headers to a response

var Mf = require('middlefiddle');

var addCSP = function(urlRegex) {
  return function(req, res, next){
    if (req.fullUrl.match(urlRegex)) {
      var writeHead = res.writeHead;
      res.writeHead = function(){
        var headers = arguments[arguments.length-1];
        var statusCode = arguments[0];
        headers['x-content-security-policy'] = "allow 'self'";
        writeHead.call(res, statusCode, headers);
      };
    }
    next();
  };
};

Mf.createProxy(addCSP(/google.com/)).listen(8088).listenHTTPS(8089);

Streaming MP3 recorder

Grab any mp3 downloaded or streamed to your browser:

var Mf = require('middlefiddle');
var url = require('url');
var fs = require('fs');


var mp3Grab = function() {
  return function(req, res, next){
    var path = url.parse(req.url).pathname;
    var filename;
    if (path) {filename = path.split('/').pop()}
    if (filename && filename.match(/\.mp3$/)){
      console.log("Beginning capture of " + filename);
      var file = fs.createWriteStream(filename);
      res.addListener('data', function (chunk) {
        file.write(chunk);
      });
      res.addListener("end", function(chunk) {
        if (chunk) {
          file.write(chunk);
        }
        file = undefined;
        console.log("Downloaded - " + filename);
      });
    }
    next();
  };
};

Mf.createProxy(mp3Grab()).listen(8088).listenHTTPS(8089);

HTTPS Hijacking

When an HTTPS request is first seen, MiddleFiddle generates a certificate for that domain, signs it with it's own generated root cert, and stores the cert for future use in ~/.middlefiddle/certs

In order to make this look legit to your browser, you'll need to add the generated root cert in ~/.middlefiddle/ca.crt to your keychain. This cert is auto generated just for your machine, so you won't be compromising your browser security.

Things to note

Connect typically doesn't have a simple way to hijack downstream responses, so middlefiddle emits events on the response along with writing to the stream.

You've also got a couple helper properties:

• req.fullUrl #=> The full requested URL, including the schema
• req.isSecure #=> Did it come via SSL?

TODO

• Clean up cert generation
• Expand logging
• Add more middleware

Want to contribute

This is my first node project, criticism is gladly accepted as long as it's in the form of a pull request.

Development

MiddleFiddle is written in CoffeeScript. It's set up with a Cakefile for building files in src/ to lib/ and running tests with nodeunit. There's also a docs task that generates Docco documentation from the source in src/.

Released under the MIT license.

Mark Percival [email protected]