CODEWITHSUNDEEP
iosjsonswiftstrongloop
Nathan McKaskle
Nathan McKaskle

Reputation: 3083

Why do I get an error Code=3840 Parsing JSON?

I'm new to Swift and iOS development in general. I'm testing and learning how to use remote server api's. I'm getting JSON from a Strongloop (Loopback) api while attempting authentication and the parsing I'm trying to use gets an error:

Error Domain=NSCocoaErrorDomain Code=3840 "The operation couldn’t be completed. (Cocoa error 3840.)" (No value.) UserInfo=0x7fd623e38870 {NSDebugDescription=No value.}

Here is the return value in a string, I'm obviously getting a proper JSON response from Loopback, an authentication token, ttl, date and userId:

{"id":"BHzKnjrbUPn9KSC1GegQTNHJFNwfuifNXPfZuKkYxC5IwRDEHuerurvSdBMzzrVi","ttl":1209600,"created":"2015-07-03T13:04:39.791Z","userId":2}

I think the actual problem is NOT occurring in the parseJSON method but rather the performLoginRequestWithURL method. It's returning an empty string. Something to do with the asynchronous request. I noticed that the json string variable does not get set until after it's returned from the method, so it gets returned blank. If I put two println(json) methods, one inside the asynchronous request and one after it, the one after prints first. Which makes sense in a way but I don't know how to solve this. I need to get the json returned from the post but I don't know how to capture that. Something tells me I need to use a synchronous request instead but I don't know how to do that in this context of getting json from a POST request.

Here is my code:

//Login button pressed
@IBAction func login() {
    //Gets url string
    let url = getLogin()
    //Posts url with UITextField data.
    if let jsonString = performLoginRequestWithURL(url) {
        //Error occurs in the parseJSON method
        if let dictionary = parseJSON(jsonString) {
            /*
            if let at = dictionary["id"] as? String {
                accesstoken = at
            }
            if let id = dictionary["userId"] as? Int {
                println(id)
            }
            */
        }
    }

}

func getLogin() -> NSURL {
    let toEscape = "http://localhost:3000/api/Users/login"
    let urlString = toEscape.stringByAddingPercentEscapesUsingEncoding(NSUTF8StringEncoding)!
    let url = NSURL(string: urlString)
    return url!
}

func performLoginRequestWithURL(url: NSURL) -> String? {
    let bodyData = "username=\(textEmail.text)&password=\(textPW.text)"
    var request: NSMutableURLRequest = NSMutableURLRequest(URL: url)
    var json = ""
    request.HTTPMethod = "POST"
    request.HTTPBody = bodyData.dataUsingEncoding(NSUTF8StringEncoding)
    NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue()){
        response, data, error in

        if data != nil {
            json = NSString(data: data, encoding: NSUTF8StringEncoding) as! String
        }
        println(json)
    }
    return json
}

func parseJSON(jsonString: String) -> [String: AnyObject]? {
    if let data = jsonString.dataUsingEncoding(NSUTF8StringEncoding) {
        var error: NSError?
        if let json = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions(0), error: &error) as? [String: AnyObject] {
            return json
        } else if let error = error {
            //Here's where the error comes back.
            println("JSON Error: \(error)")
        } else {
            println("Unknown JSON Error")
        }
    }
    return nil
}

Upvotes: 5

Views: 16682

Answers (3)

Roman Solodyashkin
Roman Solodyashkin

Reputation: 829

NSArray *jsonObj = [NSJSONSerialization JSONObjectWithData:data
                                                   options:kNilOptions
                                                     error:&err];

if ( err )
{
    // code 3840, data.length = 1 byte, so empty and no error
    if ( NSPropertyListErrorMinimum == err.code )
    {
        return [NSArray array];
    }

    *error = err;
    return nil;
}

Upvotes: 0

zaph
zaph

Reputation: 112875

The parseJSON method must be called from the NSURLConnection.sendAsynchronousRequest completion block, not just after the asynchronous request is made, there generally is no response by that point.

if data != nil {
    json = NSString(data: data, encoding: NSUTF8StringEncoding) as! String
    println("json: \(json)")

    if let dictionary = parseJSON(jsonString) {
        println("dictionary: \(dictionary)")
   }
}

Upvotes: 2

zaph
zaph

Reputation: 112875

I tested parseJSON with the string from the question and it succeeded so the error must be that the string is not being sent to the parseJSON method correctly.

let jsonString = "{\"id\":\"BHzKnjrbUPn9KSC1GegQTNHJFNwfuifNXPfZuKkYxC5IwRDEHuerurvSdBMzzrVi\",\"ttl\":1209600,\"created\":\"2015-07-03T13:04:39.791Z\",\"userId\":2}"
println("jsonString:\n\(jsonString)")

func parseJSON(jsonString: String) -> [String: AnyObject]? {
    if let data = jsonString.dataUsingEncoding(NSUTF8StringEncoding) {
        var error: NSError?
        if let json = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions(0), error: &error) as? [String: AnyObject] {
            return json
        } else if let error = error {
            println("JSON Error: \(error)")
        } else {
            println("Unknown JSON Error")
        }
    }
    return nil
}

let obj = parseJSON(jsonString)
println("obj:\n\(obj!)")

Output:

jsonString: {"id":"BHzKnjrbUPn9KSC1GegQTNHJFNwfuifNXPfZuKkYxC5IwRDEHuerurvSdBMzzrVi","ttl":1209600,"created":"2015-07-03T13:04:39.791Z","userId":2}

obj: [created: 2015-07-03T13:04:39.791Z, userId: 2, ttl: 1209600, id: BHzKnjrbUPn9KSC1GegQTNHJFNwfuifNXPfZuKkYxC5IwRDEHuerurvSdBMzzrVi]

Some what the lesson is to create a small self-contained test—or write Unit Tests.

Upvotes: 4

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