Simple REST POST

Swift Rest POST

class func postJSON(urlString:String, params:[String: AnyObject], completion:(responseDataAsString:String?, response:NSHTTPURLResponse?, error:NSError?)->()) {
        
        let url = NSURL(string: urlString)!
        let session = NSURLSession.sharedSession()
        
        // Create request
        let request = NSMutableURLRequest(URL: url)
        request.HTTPMethod = "POST"
        request.setValue("application/json; charset=utf-8", forHTTPHeaderField: "Content-Type")
        
        do {
            
            request.HTTPBody = try NSJSONSerialization.dataWithJSONObject(params, options: NSJSONWritingOptions())
            
        } catch {
            
            let error = NSError(domain: "com.jalakoo.resthandler", code:404, userInfo: [NSLocalizedDescriptionKey:"Failed to convert params to a JSON payload.",
                NSLocalizedFailureReasonErrorKey:"JSON conversion failure.",
                NSLocalizedRecoverySuggestionErrorKey:"Make sure param payload is correct:\(params)"
                ])
            
            completion(responseDataAsString:nil, response: nil, error: error)
            
            return
            
        }
        
        // Make the POST
        session.dataTaskWithRequest(request, completionHandler: { ( data: NSData?, response: NSURLResponse?, error: NSError?) -> Void in
            
            
            // Session error
            if error != nil {
                
                completion(responseDataAsString:nil,response: nil, error: error)
                
                return
            }
            
            // Response not usable
            guard let responseActual = response as? NSHTTPURLResponse else {
                
                let error = NSError(domain: "com.jalakoo.resthandler", code:404, userInfo: [NSLocalizedDescriptionKey:"Response from \(urlString) not of type NSHTTPURLReponse.",
                    NSLocalizedFailureReasonErrorKey:"Unexpected Error.",
                    NSLocalizedRecoverySuggestionErrorKey:"Consult a dev."
                    ])
                
                completion(responseDataAsString:nil,response: nil, error: error)
                
                return
            }
            
            // Ok check
            if responseActual.statusCode != 200 {
                
                let error = NSError(domain: "com.jalakoo.resthandler", code:responseActual.statusCode, userInfo: [NSLocalizedDescriptionKey:"Non-200 response returned:\(String(responseActual.statusCode))",
                    NSLocalizedFailureReasonErrorKey:"Undesired response code returned.",
                    NSLocalizedRecoverySuggestionErrorKey:"Try again later or check server at:\(urlString)"
                    ])
                
                completion(responseDataAsString:nil,response: responseActual, error: error)
                
                return
            }
            
            // Read the JSON
            let dataString = NSString(data:data!, encoding: NSUTF8StringEncoding) as? String
            
            // Successful completion
            completion(responseDataAsString: dataString, response: responseActual, error: nil)
            
        }).resume()
    }