An attempt to detect NAT type with javascript and WebRTC.

NatDetector.js

// Doesn't work.
// Some NAT servers reset the port binding at new 'connections'.

let NatDetector = new (function() {

    this.settings = {
        server1p1: 'stun:stun1.l.google.com:19302',
        server1p2: 'stun:stun1.l.google.com:19302', // TODO: change port only
        server2p1: 'stun:stun2.l.google.com:19302'
        // 'stun:stun.l.google.com:19302',
        // 'stun:stun3.l.google.com:19302',
        // 'stun:stun4.l.google.com:19302',
        // 'stun:stun.services.mozilla.com:3478',
    };

    this.NatType = Object.freeze({
        undetermined:   0,
        noNat:          1,
        fullCone:       2,
        ipRestricted:   3,
        portRestricted: 4,
        symmetric:      5
    });

    this.candidate = undefined;

    this.getNatType = function() {
        let self = this;
        console.log('1p1', self.candidate1p1);
        console.log('1p2', self.candidate1p2);
        console.log('2p1', self.candidate2p1);
    };

    this.getCandidate = function(server) {
        let self = this;
        let connection = new RTCPeerConnection({iceServers: [{urls: server}]});
        connection.onicecandidate = function(ice) {
            let ic = ice.candidate;
            self.candidate = ic ? ic.candidate : undefined;
            console.log(ic);
        };
        connection.createDataChannel('temp');
        connection.createOffer().then(offer => connection.setLocalDescription(offer));
        return new Promise(function(resolve, reject) {
            setTimeout(function() {
                connection.close();
                resolve();
            }, 500);
        });
    };

    this.main = function() {
        let self = this;
        return self.getCandidate(self.settings.server1p1).then(a => {
            return self.getCandidate(self.settings.server1p2);
        }).then(a => {
            return self.getCandidate(self.settings.server2p1);
        }).then(a => {
            console.log('done');
        });
    };

})();

NatDetector.main();