Improve OG Discovery Protocol (OGDP)

[mkahn-optv]

OGDP can falsely identify other mobile devices sending inquiry packets as OG devices. This is because the received JSON is not checked for a "signature" to indicate it is a "real OG". :)

So, the received packet must be checked for:

1. That it is valid JSON
2. That the JSON has the following keys: "name", "randomFactoid". Both of these are sent in response to inbound OGDP Discovery packets.

In addition, the OGDP discovery packet sent by the mobile device should have the following structure:
{ "ip":"192.168.1.23", "action": "discover", "time": 142364758 }

Where the IP address is the mobile device's IP address and the time is the Unix timestamp of when the packet is being sent. NodeJS example below.

function sendPingFrom(ipAddress){

    var pingMsg = JSON.stringify( { ip: ipAddress, action: "discover", time: Date.now() } );
    server.send( pingMsg, 0, pingMsg.length, 9091, '255.255.255.255', function ( err ) {
        if (err){
            console.log("Error sending UDP ping!");
        }
    });
}