how to correctly make cloud code request with parse?

Question

I am attempting to make all my user sessions with Parse exclusive, meaning if a user is already logged in on a certain device in a certain location, if another device logs in with the same credentials, I want the previous session(s) to be terminated, with a message of an alert view of course. Sort of like the old AOL Instant Messaging format. I figured the code for this action should be written in the login logic, so I wrote this within my login "succession" code :

 PFUser.logInWithUsernameInBackground(userName, password: passWord) {
        (user, error: NSError?) -> Void in
        if user != nil || error == nil {
            dispatch_async(dispatch_get_main_queue()) {
                self.performSegueWithIdentifier("loginSuccess", sender: self)

                 PFCloud.callFunctionInBackground("currentUser", withParameters: ["PFUser":"currentUser"])
                    //..... Get other currentUser session tokens and destroy them

            }

        } else {

Thats probably not the correct cloud code call, but you get the point. When the user logs in once again on another device, I want to grab the other sessions and terminate them. Does anyone know the correct way to go about making this request in swift?

Answer 1

I speak swift with a stutter, but I think I can answer adequately in almost-swift. The key idea is to start the success segue only after the cloud says it's okay. Here's what I think you want:

PFUser.logInWithUsernameInBackground(userName, password: passWord) {
    (user, error: NSError?) -> Void in
    if (user != nil) {
        // don't do the segue until we know it's unique login
        // pass no params to the cloud in swift (not sure if [] is the way to say that)
        PFCloud.callFunctionInBackground("isLoginRedundant", withParameters: []) {
            (response: AnyObject?, error: NSError?) -> Void in
            let dictionary = response as! [String:Bool]
            var isRedundant : Bool
            isRedundant = dictionary["isRedundant"]!
            if (isRedundant) {
                // I think you can adequately undo everything about the login by logging out
                PFUser.logOutInBackgroundWithBlock() { (error: NSError?) -> Void in
                    // update the UI to say, login rejected because you're logged in elsewhere
                    // maybe do a segue here?
                }
            } else {
                // good login and non-redundant, do the segue
                self.performSegueWithIdentifier("loginSuccess", sender: self)
            }
        }
    } else {
        // login failed for typical reasons, update the UI
    }
} 

Please don't take me too seriously on swift syntax. The idea is to nest the segue in the completion handlers to know that you need to do it before starting it. Also, please note that the explicit placement on the main_queue within the completion handler is unnecessary. The SDK runs those blocks on the main.

A simple check to determine if a user's session is redundant (not unique) looks like this...

Parse.Cloud.define("isLoginRedundant", function(request, response) {
    var sessionQuery = new Parse.Query(Parse.Session);
    sessionQuery.equalTo("user", request.user);
    sessionQuery.find().then(function(sessions) {
        response.success( { isRedundant: sessions.length>1 } );
    }, function(error) {
        response.error(error);
    });
});