Why is my Combine httpMethod post request not working?

Question

I am trying to use Combine to perform a POST request. When doing my http request that I used before, my Credentials object comes back with status code 200, so all good. But when I am trying to use the Combine framework, it just returns an error.

finished with error [-999] Error Domain=NSURLErrorDomain Code=-999 "cancelled"

How to solve this issue to make my Combine POST request works as expected?

My Combine request that doesn't work and need to be fixed:

func demoLogin() -> AnyPublisher {
  let url = URL(string: "https://web-api/auth/create-demo-account")!

  var urlRequest = URLRequest(url: url)
  urlRequest.httpMethod = "POST"

  return URLSession.shared
    .dataTaskPublisher(for: urlRequest)
    .receive(on: DispatchQueue.main)
    .map(\.data)
    .decode(
      type: Credentials.self,
      decoder: JSONDecoder())
    .eraseToAnyPublisher()
}

So this is where I sink the value:

final class OnboardingViewModel: ObservableObject {

  private var subscriptions = Set()

  func demoLogin() {
    AuthRequest.shared.demoLogin()
      .sink(
        receiveCompletion: { print($0) },
        receiveValue: {
          print("Receive value:\nLogin: \($0.login)\nToken: \($0.token)") })
      .store(in: &subscriptions)
  }
}

This is the SwiftUI view where the button asks for the call:

struct CredentialsButtons: View {

  @ObservedObject var viewModel = OnboardingViewModel()

  var body: some View {
    VStack {
      Button(action: { self.viewModel.demoLogin() }) {
        Text("Try demo")
          .font(.subheadline)
          .fontWeight(.medium)
          .foregroundColor(.blue)
      }
    }
  }
}

My request that works normally:

  func demoLogin(completion: @escaping (NetworkResult) -> Void) {
    let url = URL(string: "https://web-api/auth/create-demo-account")!

    var urlRequest = URLRequest(url: url)
    urlRequest.httpMethod = "POST"

    let dataTask = authSession.dataTask(with: urlRequest) { data, response, error in
      guard let httpResponse = response as? HTTPURLResponse,
        httpResponse.statusCode == 200,
        let jsonData = data else {
          completion(.failure)
          return
      }
      do {
        let credentials = try JSONDecoder().decode(Credentials.self, from: jsonData)
        completion(.success(credentials))
      }
      catch {
        completion(.failure)
      }
    }
    dataTask.resume()
  }

user_5012441 · Answer

That is not a valid URL. insert a print into your publisher as follows so you can see the errors:

func demoLogin() -> AnyPublisher {
  let url = URL(string: "https://web-api/auth/create-demo-account")!

  var urlRequest = URLRequest(url: url)
  urlRequest.httpMethod = "POST"

  return URLSession.shared
    .dataTaskPublisher(for: urlRequest)
    .receive(on: DispatchQueue.main)
    .map(\.data)
    .print()
    .decode(
      type: Credentials.self,
      decoder: JSONDecoder())
    .eraseToAnyPublisher()
}

Once you get it to return valid data you can move the print after the decode to report and decoding errors.

user_10408494 · Answer

The network call is working as expected. The code that was making this error was found in the button where I called the demoLogin() ViewModel method. The thing is that I could not call @State variables at the same time as the ViewModel network call.

The button with an error send:

Button(action: {
  withAnimation {
    self.viewModel.demoLogin()
    self.isLoggedIn.toggle()
    self.enterDemoMode.toggle() }
}) {
  Text("Try demo")
    .font(.subheadline)
    .fontWeight(.medium)
    .foregroundColor(.blue)
}

The error is fixed by replacing the @State variables of the SwiftUI view to @Published ones in my ViewModel and calling them in demoLogin() instead of inside the SwiftUI view button.

Button(action: {
  withAnimation {
    self.viewModel.demoLogin() } // Fixed
}) {
  Text("Try demo")
    .font(.subheadline)
    .fontWeight(.medium)
    .foregroundColor(.blue)
}

Why is my Combine httpMethod post request not working?

2 Answers