Chapter 1 — Introduction & course overview

What "networking" actually means in an app

• build a request — a URL, an HTTP method, headers (who you are, what format you send), and maybe a
• hand it to the operating system, which opens a connection, negotiates TLS (encryption), sends the
• receive a response — a status code, headers, and a body (usually JSON);
• decode that body into Swift types, or handle an error;
• and reflect the outcome in your UI — a spinner while waiting, content on success, a message on

Why not just use Alamofire (or another framework)?

The topics we'll cover — and why each matters

The app: Chirp for iOS

The stack and the ground rules

• Swift 6, iOS 17+, SwiftUI, @Observable, async/await. Modern, structured concurrency
• Plain URLSession, no HTTP framework. We add exactly two third-party SDKs, and only in Chapter
• Layered architecture. Views → view models → repositories → APIClient → URLSession. Each layer
• Testable by construction. Because the client is a seam we control, we test it against stubbed

What "done" looks like

• Describe every backend call as a typed Endpoint and run it through one APIClient.
• Drive every screen with a clean loading / loaded / error state.
• Log in, store JWT access + refresh tokens in the Keychain, and refresh them automatically
• Run requests through an interceptor chain that injects auth, retries transient failures,
• Paginate the feed with infinite scroll, upload avatars, download and cache images, and
• Report itself to Sentry and DataDog, collect URLSessionTaskMetrics, and pin its

Mental model to take away

• The URL Loading System (URLSession) can do everything a production app needs; the work is giving
• We build on raw URLSession, no framework, so nothing is hidden — you'll understand what any tool
• The app is Chirp for iOS, the client to the Chirp API; each screen carries one networking topic,
• The payoff is a networking layer that's reusable, testable, secure, and observable — the 95% past