swift - Refresh Token Mechanism with Combine framework iOS

Question

Followed refresh token strategy from this gist - https://gist.github.com/saroar/ca78de9dc798cdbaaa47791380062596

but couldn't get it working.

Ideal flow - run function from NetworkAgent will make a call using the tokenSubject from Authenticator. If that call fails with authentication error, refreshToken function from Authenticator will be called. Now, when this refresh token call gets completed, the tokenSubject will send a value (check the receiveCompletion block of sink operator in Authenticator) which NetworkAgent has already subscribed in run function. Once the NetworkAgent receives this value from tokenSubject it will again execute that request in the run function.

Bug - Once the 401 error is received, the refresh token request is made but after that completes successfully, failed request doesn't get retried. Seems like the value sent by the tokenSubject is not received by the subscriber may be due to some reference issue.

Please find my implementation below: -

This is the Network Agent that makes all the api calls -

class NetworkAgent {
struct Response {
let value: T
let response: URLResponse
}
let authenticator = Authenticator()

func run<T: Decodable>(_ request: URLRequest) -> AnyPublisher<Response<T>, Error> {
    let tokenSubject = authenticator.tokenSubject()
    // a better way to handle refresh token logic would be to use tryCatch operator suceeded by retry operator
    // should be done in one of the upcoming releases
    
    return tokenSubject
        .flatMap({ token -> AnyPublisher<Response<T>, Error> in
            return URLSession.shared
                .dataTaskPublisher(for: request)
                .tryMap { [weak self] result -> Response<T> in
                    self?.logResponse(result.response, request: request, data: result.data)
                    
                    // check for the response status
                    if let httpURLResponse = result.response as? HTTPURLResponse {
                        let networkResponse = APIClient.status(httpURLResponse)
                        switch networkResponse {
                        case .success: break
                            
                        case .failure(let error):
                            if error == HTTPURLResponseError.authenticationError {
                                // refresh token logic
                                if request.url?.absoluteString.contains("/auth/token/refresh") == false {
                                    self?.authenticator.refreshToken(using: tokenSubject)
                                }
                            } else {
                                throw error
                            }
                        }
                    }
                    
                    // map response and return in case of a successful request
                    let value = try JSONDecoder().decode(T.self, from: result.data)
                    return Response(value: value, response: result.response)
                }
                .retry(3)
                .receive(on: DispatchQueue.main)
                .eraseToAnyPublisher()
        })
        .handleEvents(receiveOutput: { _ in
            tokenSubject.send(completion: .finished)
        })
        .eraseToAnyPublisher()
}
}

And this is the Authenticator class implementation -

class Authenticator {
//MARK:- Properties
private var disposables = Set()
private let queue = DispatchQueue(label: "Autenticator.(UUID().uuidString)")

//MARK:- Functions
func refreshToken<S: Subject>(using subject: S) where S.Output == Bool {
    queue.sync {
        URLSession.shared
            .dataTaskPublisher(for: APIRouter.refreshToken.request()!)
            .retry(3)
            .sink { com in
                print(com)
                subject.send(true)
            } receiveValue: { data in
                print(#line, data)
                
                do {
                    let jsonDecoder2 = JSONDecoder()
                    let user = try jsonDecoder2.decode(User.self, from: data.data)
                    
                    LocalData.loggedInUser = user
                    LocalData.token = user.token
                    
                } catch  {
                    print(#line, error)
                }
                
            }
            .store(in: &disposables)
    }
}

func tokenSubject() -> CurrentValueSubject<Bool, Never> {
    return CurrentValueSubject(true)
}
}

Any input would be greatly appreciated.

Answer 1

Waitting for answers