Fehlerbehandlung und HTTP-Statuscodes

HTTP-Statuscodebereiche

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

Status in Swift prüfen

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)
}

Typisierte Netzwerkfehler

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

Statuscodes Fehlern zuordnen

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)
}

Fehlerantworten dekodieren

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")
}

Fehler in async weitergeben

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

Bestimmte Fehler abfangen

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

URLError-Codes

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

Result-Wrapper für Netzwerke

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)
  }
}

Fehlerprotokollierung

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

Benutzerfreundliche Fehlermeldungen

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."
    }
  }
}

Kurze Überprüfung

Zusammenfassung der Lektion