How does `URLSession` work?

Answer: URLSession is Apple's networking API for HTTP requests. It manages connection pooling, caching, cookies, and authentication. You create tasks from it to perform requests.

Code Example:

// Modern async/await approach
func fetchUser(id: Int) async throws -> User {
    let url = URL(string: "https://api.example.com/users/\(id)")!
    let (data, response) = try await URLSession.shared.data(from: url)

    guard let httpResponse = response as? HTTPURLResponse,
          httpResponse.statusCode == 200 else {
        throw NetworkError.badResponse
    }

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

// POST request
func createUser(_ user: User) async throws {
    var request = URLRequest(url: URL(string: "https://api.example.com/users")!)
    request.httpMethod = "POST"
    request.setValue("application/json", forHTTPHeaderField: "Content-Type")
    request.httpBody = try JSONEncoder().encode(user)

    let (_, response) = try await URLSession.shared.data(for: request)
    // handle response
}