the correct way of handling callback in socket.io

Question

Disclaimer: I'm totally new to Node.js and Socket.io and this is more like a Javascript/general programming question than a Node.js specific question but since it's written in Node.js I had to post it here.

I have a function like this

configs.socket.on('device_pair_authorization', function(device, callback) {
    var pair_token = device.pair_token;
    var server_signature = device.server_signature;
    if(pair_token && server_signature) {
        var decipher = crypto.createDecipher('aes-256-cbc', 'SOME_KEY');
        var decryptedSignature = decipher.update(server_signature, 'base64', 'utf8');
        decryptedSignature = decryptedSignature  + decipher.final('utf8');
        deSigJSON = JSON.parse(decryptedSignature);
        if(deSigJSON.user_id && deSigJSON.pair_token) {
            if(deSigJSON.pair_token === pair_token) {
                var server_handshake_token = deSigJSON.server_token;
                if(server_handshake_token) {
                    //VALIDATED
                    var one_time_access_token = crypto.createHash('sha512').update([Math.random(), server_handshake_token, new Date()].join()).digest('base64');
                    var expires = new Date().getTime() + 60;
                    callback({ 
                        is_authorized: true, 
                        one_time_access_token: one_time_access_token
                    });
                }
                callback({ 
                    is_authorized: false,
                    error: "Server Token Is Missing"
                });
            }
            callback({ 
                is_authorized: false,
                error: "Pair Token is Incorrect"
            });
        }
        callback({ 
            is_authorized: false,
            error: "Signature is corrupted"
        });
    }
    callback({ 
        is_authorized: false,
        error: "Pair_Token or Server_Signature is missing"
    });
});

The whole idea is that the function is a authorization function and to prevent fraud, each step is checked separately and if something goes wrong in the middle of the checks, the callback is executed with a specific error message and is_authorized=false. If everything goes well, the callback is executed with is_authorized=true and a token is sent back.

My problem is, the code does not look neat to me and I'm sure there is a way to modify this code so that callback is not written multiple times but I don't know why.

I want to re-write the code in a more professional way. Any suggestions?

Answer 1

You don't need any special async flow helpers here, just format you code properly. But you could take a look on Q promises helpers , Async.js and PubSubJS

configs.socket.on('device_pair_authorization', function(device, callback) {
    var pair_token = device.pair_token;
    var server_signature = device.server_signature;
    var errorCallback = function(error) {
        callback({ 
            is_authorized: false,
            error: error
        });
    }

    if(!pair_token || !server_signature) {
        return errorCallback("Pair_Token or Server_Signature is missing")
    }

    var decipher = crypto.createDecipher('aes-256-cbc', 'SOME_KEY');
    var decryptedSignature = decipher.update(server_signature, 'base64', 'utf8');

    decryptedSignature = decryptedSignature  + decipher.final('utf8');
    deSigJSON = JSON.parse(decryptedSignature);

    if(!deSigJSON.user_id || !deSigJSON.pair_token) {
        return errorCallback("Signature is corrupted");
    }

    if(deSigJSON.pair_token !== pair_token) {
        return errorCallback("Pair Token is Incorrect");
    }

    if(!deSigJSON.server_token) {
        return errorCallback("Server Token Is Missing");
    }

    //VALIDATED
    var server_handshake_token = deSigJSON.server_token;
    var one_time_access_token = crypto.createHash('sha512').update([
        Math.random(), server_handshake_token, new Date()
        ].join()).digest('base64');

    var expires = new Date().getTime() + 60;

    callback({ 
        is_authorized: true, 
        one_time_access_token: one_time_access_token
    });
});