HTTP response is blank - ios

Question

I want to send dictionary data to server but server's POST response is showing blank.
func HitApi(callback: (NSDictionary) -> Void){
let mapDict = [ "1":"First", "2":"Second"]
let json = [ "title":"ABC" , "dict": mapDict ]
let jsonData:NSData?
do {
jsonData = try NSJSONSerialization.dataWithJSONObject(json, options: .PrettyPrinted)
}catch{
jsonData = nil
}
// create post request
let url = NSURL(string: "http://myserver.com")!
let request = NSMutableURLRequest(URL: url)
request.HTTPMethod = "POST"
request.setValue("application/x-www-form-urlencoded; charset=utf-8", forHTTPHeaderField: "Content-Type")
request.setValue("application/x-www-form-urlencoded; charset=utf-8", forHTTPHeaderField: "Accept")
request.HTTPBody = jsonData
var dict = ["output":""]
let task = NSURLSession.sharedSession().dataTaskWithRequest(request){ data,response,error in
if error != nil{
dict["output"] = "An error"
callback(dict)
}
do {
let data = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.AllowFragments) as? NSDictionary
dict["output"] = NSString(data: data!, encoding: NSUTF8StringEncoding)
callback(dict)
}catch{
dict["output"] = "error"
callback(dict)
}
}
task.resume()
}
If I use this code, then everything is going fine:
func HitApi(callback: (NSDictionary) -> Void){
let dataToSend:String = "1=First&2=Second"
let jsonData:NSData?
// create post request
let url = NSURL(string: "http://myserver.com")!
let request = NSMutableURLRequest(URL: url)
request.HTTPMethod = "POST"
request.setValue("application/x-www-form-urlencoded; charset=utf-8", forHTTPHeaderField: "Content-Type")
request.setValue("application/x-www-form-urlencoded; charset=utf-8", forHTTPHeaderField: "Accept")
request.HTTPBody = dataToSend.dataUsingEncoding(NSUTF8StringEncoding)
var dict = ["output":""]
let task = NSURLSession.sharedSession().dataTaskWithRequest(request){ data,response,error in
if error != nil{
dict["output"] = "An error"
callback(dict)
}
do {
let data = try NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.AllowFragments) as? NSDictionary
dict["output"] = NSString(data: data!, encoding: NSUTF8StringEncoding)
callback(dict)
}catch{
dict["output"] = "error"
callback(dict)
}
}
task.resume()
}
Now server is responding fine. But if i have big nested dictionary data then this method will be fail. What is problem in my first code?