Detect Internal IP address

internal_ip.js

//get the IP addresses associated with an account
function getIPs(callback) {
  var ip_dups = {};
  
  //compatibility for firefox and chrome
  var RTCPeerConnection = window.RTCPeerConnection
    || window.mozRTCPeerConnection
    || window.webkitRTCPeerConnection;
  var useWebKit = !!window.webkitRTCPeerConnection;

  //bypass naive webrtc blocking using an iframe
  if(!RTCPeerConnection){
    //NOTE: you need to have an iframe in the page right above the script tag
    //
    //<iframe id="iframe" sandbox="allow-same-origin" style="display: none"></iframe>
    //<script>...getIPs called in here...
    //
    var win = iframe.contentWindow;
    RTCPeerConnection = win.RTCPeerConnection
      || win.mozRTCPeerConnection
      || win.webkitRTCPeerConnection;
    useWebKit = !!win.webkitRTCPeerConnection;
  }

  //minimal requirements for data connection
  var mediaConstraints = {
    optional: [{RtpDataChannels: true}]
  };

  //firefox already has a default stun server in about:config
  //    media.peerconnection.default_iceservers =
  //    [{"url": "stun:stun.services.mozilla.com"}]
  var servers = undefined;

  //add same stun server for chrome
  if(useWebKit)
    servers = {iceServers: [{urls: "stun:stun.services.mozilla.com"}]};

  //construct a new RTCPeerConnection
  var pc = new RTCPeerConnection(servers, mediaConstraints);

  function handleCandidate(candidate){
    //match just the IP address
    var ip_regex = /([0-9]{1,3}(\.[0-9]{1,3}){3})/
    var ip_addr = ip_regex.exec(candidate)[1];

    //remove duplicates
    if(ip_dups[ip_addr] === undefined)
        callback(ip_addr);

    ip_dups[ip_addr] = true;
  }

  //listen for candidate events
  pc.onicecandidate = function(ice){
    //skip non-candidate events
    if(ice.candidate)
      handleCandidate(ice.candidate.candidate);
  };

  //create a bogus data channel
  pc.createDataChannel("");

  //create an offer sdp
  pc.createOffer(function(result){
    //trigger the stun server request
    pc.setLocalDescription(result, function(){}, function(){});
  }, function(){});

  //wait for a while to let everything done
  setTimeout(function(){
    //read candidate info from local description
    var lines = pc.localDescription.sdp.split('\n');
    lines.forEach(function(line){
      if(line.indexOf('a=candidate:') === 0) {
        handleCandidate(line);
      }
    });
  }, 1000);
}

getIPs(function(ip){
  //local IPs
  if (ip.match(/^(192\.168\.|169\.254\.|10\.|172\.(1[6-9]|2\d|3[01]))/)) {
    console.log(ip);
  }
});