Example of using connect session cookies with socket.io

gistfile1.js

socket.on('connection', function(client){
    // helper function that goes inside your socket connection
    client.connectSession = function(fn) {
        if (!client.request || !client.request.headers || !client.request.headers.cookie) {
            disconnectAndRedirectClient(client,function() {
               console.log('Null request/header/cookie!');
            });
            return;
        }

        console.log('Cookie is' + client.request.headers.cookie);

        var match = client.request.headers.cookie.match(/connect\.sid=([^;]+)/);
        if (!match || match.length < 2) {
            disconnectAndRedirectClient(client,function() {
                console.log('Failed to find connect.sid in cookie')
            });
            return;
        }

        var sid = unescape(match[1]);

        rc.get(sid, function(err, data) {
            fn(err, JSON.parse(data));
        });
    };

    client.connectSession(function(err, data) {
        if(err) {
            console.log('Error on connectionSession: ' + err);
            return;
        }

        var connectedUser = getConnectedUser(data, client);
        if(connectedUser) {
            client.on('message', function(msg){message(client, socket, msg)});

            sendInitialDataToClient(client);
        }
        else 
            console.log("Failed to connect user");
    });
});

rc.get(sid, function(err, data) { what is rc ?