How to resolve - Combine Error | Error Domain=NSURLErrorDomain Code=-999 "cancelled"

Question

I am attempting to parse JSON using the new Combine framework. However, every attempt I make comes back with a cancelled error. When I use the exact same url without combine it works fine.

The bottom function works fine, the top one gives me an error no matter what I do.

static func performNetworkRequestUsingCombine(url urlWithQuery:URL){
        //let decoder = JSONDecoder()
        let publisher = URLSession.shared.dataTaskPublisher(for: urlWithQuery)
            .map({$0.data})

        .eraseToAnyPublisher()
            .sink(receiveCompletion: { (status) in
                switch status {
                    case .failure(let incomingError):
                        print(incomingError.localizedDescription)
                    case .finished:
                    break
                }
            }) { (data) in
                let dataString = String(data: data, encoding: .utf8)
                print(dataString!)
        }
        publisher.cancel()
    }

static func performNetworkRequest(url urlWithQuery: URL, dataValue : @escaping (WeatherObject)->Void){

        let decoder = JSONDecoder()
        let task = URLSession.shared.dataTask(with: urlWithQuery) { (data, response, error) in

            if error != nil {
                print(error!.localizedDescription)
                return
            }
            if let data = data {
                do {
                    let weatherData = try decoder.decode(WeatherObject.self, from: data)
                    dataValue(weatherData)
                } catch let localError {
                    print(localError.localizedDescription)
                }
            }
        }
        task.resume()
    }

}

I expect to receive my JSON data printed in the terminal but instead I receive the following error:

2019-10-25 14:59:34.452071-0400 Clima[2127:98883] Task <663D6D3A-48B8-49E6-9103-AA1D89513D84>.<1> finished with error [-999] Error Domain=NSURLErrorDomain Code=-999 "cancelled" UserInfo={NSErrorFailingURLStringKey=https://api.openweathermap.org/data/2.5/weather?lon=-122.4&APPID=29ecd35ff6b9e63498cb8fb479ba6ca0&units=imperial&lat=37.8, NSLocalizedDescription=cancelled, NSErrorFailingURLKey=https://api.openweathermap.org/data/2.5/weather?lon=-122.4&APPID=29ecd35ff6b9e63498cb8fb479ba6ca0&units=imperial&lat=37.8}

Answer 1

Added .receive(on:) operator and this resolved the issue!

static func performNetworkRequestUsingCombine(url urlWithQuery:URL){
        //let decoder = JSONDecoder()

        let publisher = URLSession.shared.dataTaskPublisher(for: urlWithQuery)
            .map({$0.data})
            .receive(on: DispatchQueue.main)
            .sink(receiveCompletion: { (completionError) in
                switch completionError {
                    case .failure(let error):
                        print(error.localizedDescription)
                    case .finished:
                    break
                }
            }) { (data) in
                guard let stringData = String(data: data, encoding: .utf8) else {return}
                print(stringData)
        }
        publisher.cancel()
    }