iOS Networking Skill

Build robust network layers for iOS applications

Learning Objectives

By completing this skill, you will:

• Master URLSession with async/await
• Implement type-safe API clients
• Handle authentication flows (OAuth, JWT)
• Build offline-first applications

Prerequisites

Curriculum

Module 1: URLSession Fundamentals (4 hours)

Topics:

• URLSession configuration
• URLRequest building
• Response handling
• Error management

Code Example:

func fetch<T: Decodable>(_ type: T.Type, from url: URL) async throws -> T {
    let (data, response) = try await URLSession.shared.data(from: url)

    guard let httpResponse = response as? HTTPURLResponse,
          (200...299).contains(httpResponse.statusCode) else {
        throw NetworkError.invalidResponse
    }

    return try JSONDecoder().decode(T.self, from: data)
}

Module 2: API Client Architecture (5 hours)

Topics:

• Endpoint abstraction
• Request/response interceptors
• Retry logic with exponential backoff
• Request deduplication

Module 3: Codable & JSON (3 hours)

Topics:

• Custom encoding/decoding
• Date format handling
• Nested JSON parsing
• Error handling

Module 4: Authentication (5 hours)

Topics:

• OAuth 2.0 flow
• JWT handling
• Token refresh logic
• Secure token storage

Module 5: Offline Support (4 hours)

Topics:

• Response caching
• Request queuing
• Sync strategies
• Conflict resolution

Module 6: Testing Network Code (3 hours)

Topics:

• Mock URLProtocol
• Stub responses
• Network condition testing

Assessment Criteria

Common Mistakes

1. Force unwrapping responses → Use proper error handling
2. Ignoring cancellation → Respect Task cancellation
3. Hardcoded URLs → Use configuration
4. Missing retry logic → Implement exponential backoff

Skill Validation

1. REST Client: Type-safe API client with Codable
2. Auth Flow: OAuth 2.0 with token refresh
3. Offline App: Cached data with sync
4. Test Suite: 80% network code coverage