iOS Networking

Use URLSession with async/await and structured concurrency for ordinary HTTP, REST, uploads, downloads, and streaming. Use Network.framework for lower-level protocols and delegate/task APIs for durable background transfers.

Contents

• Core URLSession async/await
• API Client Architecture
• Error Handling
• Pagination
• Network Reachability
• Configuring URLSession
• App Transport Security (ATS)
• Common Mistakes
• Review Checklist
• References

Core URLSession async/await

URLSession gained native async/await overloads in iOS 15. Prefer these for foreground data, upload, download, and streaming work. Background URLSession transfers are the main exception: they still use task/delegate APIs so the system can deliver events after suspension or relaunch.

Validate networking policy locally with URLProtocol fixtures for valid 2xx, malformed 2xx, one-time 401 refresh, bounded 429/5xx retry, timeout/offline, cancellation, and nonretryable 4xx. Inspect headers, status, and error classification; fix the policy and rerun. Retry only safe/idempotent or explicitly replayable requests, and never loop token refresh.

Data Requests

// Basic GET
let (data, response) = try await URLSession.shared.data(from: url)

// With a configured URLRequest
var request = URLRequest(url: url)
request.httpMethod = "POST"
request.setValue("application/json", forHTTPHeaderField: "Content-Type")
request.httpBody = try JSONEncoder().encode(payload)
request.timeoutInterval = 30
request.cachePolicy = .reloadIgnoringLocalCacheData

let (data, response) = try await URLSession.shared.data(for: request)

Response Validation