# middlefiddle

**Repository Path**: mirrors_mdp/middlefiddle

## Basic Information

- **Project Name**: middlefiddle
- **Description**: Fiddle in the middle with HTTP/HTTPS traffic using Node.js
- **Primary Language**: Unknown
- **License**: MIT
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2020-09-25
- **Last Updated**: 2026-05-24

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

# MiddleFiddle

MiddleFiddle is an outbound local proxy which lets to modify your outbound request and responses
via [Connect](http://senchalabs.github.com/connect/) middleware. It support HTTP and HTTPS, the
latter through a hijacking of the request with locally generated SSL certs.

## Installtion

    $ npm install -g middlefiddle

## Installation via Github

    # Depends on Node 0.6.x
    $ git clone git://github.com/mdp/middlefiddle.git
    $ cd middlefiddle
    $ npm install
    $ npm link #If you want to use it globally

## Usage

### Basic usage

By default middlefiddle will start logging traffic and modifying
requests based on site specific middleware found in '.middlefiddle/sites'

You can find an example in 
[.middlefiddle/sites](https://github.com/mdp/middlefiddle/tree/master/.middlefiddle/sites)

    # Start middlefiddle with default options
    $ middlefiddle
    # Proxy will be at port 8080

### Using the logger

    $ middlefiddle logger
    # Now open http://localhost:8411

    # Only log for a certain URL
    $ middlefiddle logger --url google.com

    # Only log certain statuses
    $ middlefiddle logger --status 404

    # Only log responses containing text
    $ middlefiddle logger --grep "setTimeout"
    # Also work with regex
    $ middlefiddle logger -r --grep "Mark(Percival)?"
    # And case insensitive
    $ middlefiddle logger -ri --grep "m@mdp\.im"

## Site specific middleware

MiddleFiddle can alter requests based on the host name. You'll find some examples in
[.middlefiddle/sites](https://github.com/mdp/middlefiddle/tree/master/.middlefiddle/sites)

Simple add the middleware to your __~/.middlefiddle/sites__ directory, with
the appropriate hostname. For example, __~/.middlefiddle/sites/github.com.coffee'__
would get injected on any request to github.com 

MiddleFiddle middleware is connect compatible. Anything you can do with
Connect, you can do with middlefiddle middleware.

### Examples
----

### Saving any mp3's from a site

For example, lets say you want to save all the streamed mp3's from
Soundcloud.com

*Found in [soundcloud.com.coffee](https://github.com/mdp/middlefiddle/tree/master/.middlefiddle/sites/soundcloud.com.coffee)*

    fs = require 'fs'
    module.exports = (Mf) ->
      (req, res, next) ->
        res.on 'body', ->
          if res.headers["content-type"] == 'audio/mpeg'
            fileName = req.path.replace(/^[a-zA-Z]/, '').split('.')[0]
            path = "#{process.env["HOME"]}/Downloads/soundcloud#{fileName}.mp3"
            fs.writeFile path, res.body, ->
              console.log "Saved #{res.body.length} bytes to #{path}"
        next()

### Find and replace any text

In this case we used the MiddleFiddle helper 'replace'

*Found in [github.com.coffee](https://github.com/mdp/middlefiddle/tree/master/.middlefiddle/sites/github.com.coffee)*

    module.exports = (Mf) ->
      replacement = (string, req, res) ->
        contentType = res.headers['content-type'] || ''
        if contentType.search(/html/) >= 0
          string.replace(/repositories/ig, "suppositories")
        else
          false
      return  Mf.replace(replacement)

### Modify outbound request headers

Here we are going to change the user agent to GoogleBot

*Found in [ft.com.coffee](https://github.com/mdp/middlefiddle/tree/master/.middlefiddle/sites/ft.com.coffee)*

    module.exports = (Mf) ->
      # I'm the Google, let me in!
      (req, res, next) ->
        req.headers['user-agent'] = "GoogleBot"
        next()

## Web Logging

By default MiddleFiddle logs all outbound traffic to a web based logger on localhost:8411

![Request Logger](http://mdp.github.com/middlefiddle/images/RequestLogger.jpg)
![Request Logger](http://mdp.github.com/middlefiddle/images/RequestDetails.jpg)


## Configuration

MiddleFiddle looks for a .middlefiddle directory in the current working directory, or at ~/.middlefiddle.

Inside you'll find a config.coffee file, https certs, and a sites directory.

You'll need to add the https certs to you keychain if you want to avoid
the browser warning. The certs are generated on the first launch of
middlefiddle and are therefor unique to each machine.


## HTTPS Hijacking

When an HTTPS request is first seen, MiddleFiddle generates a certificate for that domain, signs
it with its 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 since it's streaming, so
middlefiddle emits events on the response along with writing to the stream.

    res.on 'data', (chunk) ->
      console.log chunk.toString()

    res.on 'end', (chunk) ->
      console.log chunk.toString()

    res.on 'close', (chunk) ->
      console.log "Closed response"

You've also got a couple helper properties:

- req.href #=> String: The full requested URL, including the scheme,
  host, path, and query params
- req.ssl #=> Boolean: Did it come via SSL?
- req.startTime #=> Datetime: When the request was started
- res.endTime #=> Datetime: I'll let you guess

## Modify responses

### Modifying the headers

Response headers can be modified before they are sent to the browser.
Just wait till they're available:

*Example in [add_csp.coffee](https://github.com/mdp/middlefiddle/tree/master/.middlefiddle/fiddles/add_csp.coffee)*

### Replace the response body

Modifying the a response body means buffering the stream,
waiting for it to finish, then making the replacement and sending it
back downstream. The 'replace' middleware provides this.

* Usage example in [github.com.coffee](https://github.com/mdp/middlefiddle/tree/master/.middlefiddle/sites/github.com.coffee)*

## Testing

Tests can be run from within the repo

    npm install
    npm test

## TODO

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

## Want to contribute

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 <m@mdp.im>