Getting the error code and description from a session.dataTask call

Question

I am calling some APIs from my app. I'd like to get and process the error code. There seems to be a lot of information on how to retrieve and process the response codes, but very little on the error code. I'd like to access the error code in case, say the user has no internet connection so the call to the API fails. I am using this code:

session.dataTask(with: request, completionHandler: { (data: Data?, response: URLResponse?, error: Error?) in

        if let error = error {
            print("Tide Station API call failed with error \(error)")
            return
        }

        if let response = response as? HTTPURLResponse {
            print("Tide Station API call response is \(response.statusCode)")
        }

        if let data = data
        {
            do {
                let result = try JSONDecoder().decode(TideStations.self, from: data)
                self.tideStations = result.stations
                print("\(result.stations.count) Tide Stations successfully loaded")
                self.showTideStationsOnMap()
            } catch {
                print("Error while stations parsing: \(error)")
            }
        }
    }).resume()

Which generates the following output in the debug area when my device is is airplane mode, i.e. I am forcing one sure way of the API call failing: (note I have bolded the area from my error handling print statement)

2020-02-26 17:57:58.235368+0000 APITest[5464:2590011] Task <006E7876-214F-41E3-8BDE-26960AF1F554>.<1> finished with error [-1009] Error Domain=NSURLErrorDomain Code=-1009 "The Internet connection appears to be offline." UserInfo={NSUnderlyingError=0x283a918f0 {Error Domain=kCFErrorDomainCFNetwork Code=-1009 "(null)" UserInfo={_kCFStreamErrorCodeKey=50, _kCFStreamErrorDomainKey=1}}, NSErrorFailingURLStringKey=https://api.sunrise-sunset.org/json?lat=57.5081&lng=-1.7841&date=2020-06-21&formatted=0, NSErrorFailingURLKey=https://api.sunrise-sunset.org/json?lat=57.5081&lng=-1.7841&date=2020-06-21&formatted=0, _kCFStreamErrorDomainKey=1, _kCFStreamErrorCodeKey=50, NSLocalizedDescription=The Internet connection appears to be offline.} Astronomical Times API call failed with error Error Domain=NSURLErrorDomain Code=-1009 "The Internet connection appears to be offline." UserInfo={NSUnderlyingError=0x283a918f0 {Error Domain=kCFErrorDomainCFNetwork Code=-1009 "(null)" UserInfo={_kCFStreamErrorCodeKey=50, _kCFStreamErrorDomainKey=1}}, NSErrorFailingURLStringKey=https://api.sunrise-sunset.org/json?lat=57.5081&lng=-1.7841&date=2020-06-21&formatted=0, NSErrorFailingURLKey=https://api.sunrise-sunset.org/json?lat=57.5081&lng=-1.7841&date=2020-06-21&formatted=0, _kCFStreamErrorDomainKey=1, _kCFStreamErrorCodeKey=50, NSLocalizedDescription=The Internet connection appears to be offline.}

In this example, I want to extract from this the fact that the internet connection appears down and advise the user. I would have thought that there would be similar support for error code extraction as there is for result code extraction. Would it be more normal to just say an error occurred (easy to detect) and handle elsewhere (e.g. detect no internet before calling the API)? If so, what shout I be guarding for?

Vlad Rusu Vlad Rusu · Accepted Answer · 2020-02-26T19:33:52

The Error class in swift does not contain the error code and the error domain in it. However, if you print the error you can definitely see the error code and domain in the logs.

You can access those by simply casting the Swift's Error to the old Objective-C NSError. This classes are toll-free bridgeable, so there is no need to check if the cast fails or forcefully perform the cast with as!. Simply do:

    let nsError = error as NSError
    print("Error code is: \(nsError.code)")

Getting the error code and description from a session.dataTask call

1 Answers