Error is not triggering on url session using combine - ios

Question

enum FailureReason : Error {
case sessionFailed(error: URLError)
case decodingFailed
case other(Error)
}
the custom error enum
private func performOperation<T: Decodable>(requestUrl: URLRequest, responseType: T.Type)->AnyPublisher<T, FailureReason>
{
return URLSession.shared.dataTaskPublisher(for: requestUrl)
.map(\.data)
.decode(type: T.self, decoder: JSONDecoder())
.mapError({ error -> FailureReason in
switch error {
case is Swift.DecodingError:
return .decodingFailed
case let urlError as URLError:
return .sessionFailed(error: urlError)
default:
return .other(error)
}
})
.eraseToAnyPublisher()
}
this is how my urlsession publisher looks like
func validateLogin(username : String , password :String) {
let url = "\(Constants.baseUrl)api/v1/auth/login/"
let htppbodyRequest = EmailLogin(username: username, password: password)
let httpBody = try! JSONEncoder().encode(htppbodyRequest)
cancellable = webservice.apiRequest(url: URL(string: url)!, resultType: User.self, httpMethodType: .post, requestBody: httpBody)
.map{ $0 }
.receive(on: RunLoop.main)
.sink(receiveCompletion: {
print("Received completion: \($0).")
}, receiveValue: { (user) in
print("user name is :\(user)")
self.subject.send(user)
})
User is the decodable struct. Even if i enter invalid username and password the Received completion of sink prints finished error is never thrown.
Subject is a passthroughSubject.

Answer 1

It seems you have a misunderstanding regarding when a URLSession.DataTaskPublisher should fail with an error. A data task only fails with an error in case there is a network error (such as no internet connection, SSL error, etc).
Inputting an incorrect username or password is not a network error and hence will not result in the data task throwing an error. Depending on your backend implementation, it might result in an error status code (not in the 200..<300 range) and an error response in the body of the request.
To check the status code of the HTTPURLResponse and throw an error in case it's incorrect, you can use tryMap on the dataTaskPublisher.
Here's how you can define convenience methods on URLSession.DataTaskPublisher that handle the status code of the HTTPURLResponse and throw an error in case it's incorrect.
enum NetworkingError: Error {
case decoding(DecodingError)
case incorrectStatusCode(Int)
case network(URLError)
case nonHTTPResponse
case unknown(Error)
}
extension Publisher {
func mapErrorToNetworkingError() -> AnyPublisher<Output, NetworkingError> {
mapError { error -> NetworkingError in
switch error {
case let decodingError as DecodingError:
return .decoding(decodingError)
case let networkingError as NetworkingError:
return networkingError
case let urlError as URLError:
return .network(urlError)
default:
return .unknown(error)
}
}
.eraseToAnyPublisher()
}
}
extension URLSession.DataTaskPublisher {
func emptyBodyResponsePublisher() -> AnyPublisher<Void, NetworkingError> {
httpResponseValidator()
.map { _ in Void() }
.eraseToAnyPublisher()
}
}
extension URLSession.DataTaskPublisher {
func httpResponseValidator() -> AnyPublisher<Output, NetworkingError> {
tryMap { data, response in
guard let httpResponse = response as? HTTPURLResponse else { throw NetworkingError.nonHTTPResponse }
let statusCode = httpResponse.statusCode
guard (200..<300).contains(statusCode) else { throw NetworkingError.incorrectStatusCode(statusCode) }
return (data, httpResponse)
}
.mapErrorToNetworkingError()
}
func httpResponseValidatorDataPublisher() -> AnyPublisher<Data, NetworkingError> {
httpResponseValidator()
.map(\.data)
.eraseToAnyPublisher()
}
func jsonDecodingPublisher<T:Decodable>(type: T.Type) -> AnyPublisher<T, NetworkingError> {
httpResponseValidatorDataPublisher()
.decode(type: T.self, decoder: JSONDecoder())
.mapErrorToNetworkingError()
}
}
And then you can simplify your performOperation function as below and it will throw an error in case the status code of the response is not in the expected range.
private func performOperation<T: Decodable>(requestUrl: URLRequest, responseType: T.Type) -> AnyPublisher<T, NetworkingError> {
URLSession.shared.dataTaskPublisher(for: requestUrl)
.jsonDecodingPublisher(type: T.self)
}