Question 1
Designing a networking layer
How would you design a scalable and maintainable networking layer for an iOS app?
Answer outline
Build the networking layer around clear separation of responsibilities. Three layers cover most apps:
- 1.Transport: makes requests and returns responses, nothing more. This is the only code that talks to
URLSession. - 2.Endpoint definitions: describe paths, methods, headers, query parameters, and bodies in one consistent shape.
- 3.Decoding and error mapping: convert raw responses into typed models and app-level failures, so feature code never sees a raw response.
Keep it protocol-driven, with a protocol at each boundary so features depend on abstractions. That lets you swap in a stub transport in tests.
Handle cross-cutting concerns such as authentication, retries, and logging in one shared layer so they don't drift between features. As the app grows, a team should be able to add an endpoint without rethinking the stack.
Principles
- Give each layer one job, and treat a feature that calls
URLSessiondirectly as a sign the boundaries have leaked. - Put a protocol at each boundary so every layer can be tested against a stub.
- Map network errors into typed app-level categories at the boundary, so feature code never inspects raw status codes.
- Keep cross-cutting concerns such as authentication in one shared layer, so a change to retries or logging lands once.
- A new endpoint should need only an endpoint definition and a response model, never a change to transport or decoding.
