20200418 Swift URLSession HTTP GET CommandLine Application

I have implemented a command line application to test my understanding of how to use an URLSession object in Swift to perform a HTTP GET request is correct.

My code works, but what I missed when reading the documentation of URLSession was, it was asynchron, means you have to wait for the request to finish.

I did not handle this in my first try and my application terminated without performing the request. Luckily … better than thinking it works because you see the request being performed but then this only works sometimes … that would be bad.

I have found the solution here : Steven G. Harms : Learning to work with command-line Swift on Linux

There I learned, that you need to wait for asynchron tasks to finish.

I guess when doing this in an IOS APP it is a little bit more obvious, because you would connect it with a delegate to handle it.

Anyroad, I learned you need to use a DispatchGroup or DispatchSemaphore to wait for tasks to finish.

This is my code :

    import Foundation

    var components = URLComponents()
    components.scheme = "http"
    components.host = "localhost"
    components.port = 4567
    components.path = "/hello"
    let parameter1 = URLQueryItem(name:"x700", value:"macos")
    let parameter2 = URLQueryItem(name:"x800", value:"right")
    components.queryItems = [URLQueryItem]()
    components.queryItems!.append(parameter1)
    components.queryItems!.append(parameter2)

    print("url :")
    print(components.url!)

    var request = URLRequest(url: components.url!)
    request.httpMethod = "GET"
    request.setValue("application/json", forHTTPHeaderField: "Accept")

    let sessionConfiguration = URLSessionConfiguration.default
    let session = URLSession(configuration: sessionConfiguration)
    let group = DispatchGroup()

    print("starting sync")
    group.enter()
    session.dataTask(with: request, completionHandler: {
        (data, response, error) in
        print("Task ran!")
        group.leave()
    }).resume()

    print("ending sync")
    group.wait()