Using NSURLSession from a Swift command line program

Question

I\'m trying to test a little proof-of-concept command line app prior to integrating it into a larger app. What I\'m trying to do is download some data using NSURLSession usi

Answer 1

For proof of concept(s) or tryouts/testing purposes, you can simplify asynchronous complexity by hard coding some timeout period until your stuff finishes. (see notes below)

SWIFT 5

    //...your magic here
    // add a little                                                                     

                                                        
            

Answer 2

Try this

let sema = DispatchSemaphore( value: 0)

let url = URL(string: "https://upload.wikimedia.org/wikipedia/commons/4/4d/Cat_November_2010-1a.jpg")!;

let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
  print("after image is downloaded");
  sema.signal(); // signals the process to continue
};

task.resume();
sema.wait(); // sets the process to wait

Answer 3

You can use a semaphore to block the current thread and wait for your URL session to finish.

Create the semaphore, kick off your URL session, then wait on the semaphore. From your URL session completion callback, signal the semaphore.

You could use a global flag (declare a volatile boolean variable) and poll that from a while loop, but that is less optimal. For one thing, you're burning CPU cycles unnecessarily.

Here's a quick example I did using a playground:

import Foundation

var sema = DispatchSemaphore( value: 0 )

class Delegate : NSObject, URLSessionDataDelegate
{
    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data)
    {
        print("got data \(String(data: data, encoding: .utf8 ) ?? "<empty>")");
        sema.signal()
    }
}

let config = URLSessionConfiguration.default
let session = URLSession(configuration: config, delegate: Delegate(), delegateQueue: nil )

guard let url = URL( string:"http://apple.com" ) else { fatalError("Could not create URL object") }

session.dataTask( with: url ).resume()    

sema.wait()