Obsługa błędów i kody statusu HTTP

Przedziały kodów statusu HTTP

// 200 OK, 201 Created
// 400 Bad Request, 401 Unauthorized, 404 Not Found
// 500 Internal Server Error

Sprawdzanie statusu w Swift

let (data, response) = try await URLSession.shared.data(from: url)
guard let http = response as? HTTPURLResponse else {
  throw NetworkError.invalidResponse
}
guard (200..<300).contains(http.statusCode) else {
  throw NetworkError.httpError(http.statusCode)
}

Typowane błędy sieciowe

enum NetworkError: Error {
  case invalidURL
  case invalidResponse
  case httpError(Int)
  case decodingError(Error)
  case noData
}

Mapowanie kodów statusu na błędy

switch http.statusCode {
case 200..<300: break // success
case 401: throw NetworkError.unauthorized
case 404: throw NetworkError.notFound
case 500..<600: throw NetworkError.serverError(http.statusCode)
default: throw NetworkError.httpError(http.statusCode)
}

Dekodowanie odpowiedzi z błędem

if http.statusCode != 200 {
  struct APIError: Decodable { var message: String }
  let apiError = try? JSONDecoder().decode(APIError.self, from: data)
  throw NetworkError.serverMessage(apiError?.message ?? "Unknown error")
}

Propagowanie błędów w async

async let users = fetchUsers()
async let posts = fetchPosts()
let (u, p) = try await (users, posts) // if either throws, both cancel

Przechwytywanie konkretnych błędów

do {
  let items = try await fetchItems()
} catch NetworkError.unauthorized {
  showLoginScreen()
} catch NetworkError.httpError(let code) {
  print("HTTP Error: \(code)")
} catch {
  print("Unexpected: \(error)")
}

Kody URLError

do {
  let (data, _) = try await URLSession.shared.data(from: url)
} catch let urlError as URLError where urlError.code == .notConnectedToInternet {
  print("No internet connection")
}

Opakowanie Result dla operacji sieciowych

func fetchUser() async -> Result<User, NetworkError> {
  do {
    let user = try await performFetch()
    return .success(user)
  } catch let e as NetworkError {
    return .failure(e)
  } catch {
    return .failure(.unknown)
  }
}

Rejestrowanie błędów

func log(_ error: NetworkError, url: URL) {
  print("[Network] \(url.absoluteString) → \(error)")
}

Komunikaty o błędach dla użytkownika

extension NetworkError: LocalizedError {
  var errorDescription: String? {
    switch self {
    case .unauthorized: return "Please log in again."
    case .notFound: return "The requested item was not found."
    case .serverError: return "Server error. Please try again later."
    default: return "Something went wrong."
    }
  }
}

Szybkie sprawdzenie

Podsumowanie lekcji