Urlsession Code Review

Reviews URLSession networking code for iOS/macOS. Covers async/await patterns, request building, error handling, caching, and background sessions. Use when reviewing code that uses URLSession, URLRequest, URLCache, or URLError, or any iOS networking path.

Quick Reference

Topic	Reference
Async/Await	async-networking.md
Requests	request-building.md
Errors	error-handling.md
Caching	caching.md

Review Checklist

Response Validation

• HTTP status codes validated - URLSession does NOT throw on 404/500
• Response cast to HTTPURLResponse before checking status
• Both transport errors (URLError) and HTTP errors handled

Memory & Resources

• Downloaded files moved/deleted (async API doesn't auto-delete)
• Sessions with delegates call finishTasksAndInvalidate()
• Long-running tasks use [weak self]
• Stored Task references cancelled when appropriate

Configuration

• timeoutIntervalForResource set (default is 7 days!)
• URLCache sized adequately (default 512KB too small)
• Sessions reused for connection pooling

Background Sessions

• Unique identifier (especially with app extensions)
• File-based uploads (not data-based)
• Delegate methods used (not completion handlers)

Security

• No hardcoded secrets (use Keychain)
• Header values sanitized for CRLF injection
• Query params via URLComponents (not string concat)

Hard gates (before reporting findings)

Complete in order. Do not advance while a prior gate is open.

1. Scope — Pass: You name at least one file under review where URLSession, URLRequest, HTTPURLResponse / URLResponse, URLCache, or URLError appears on a networking path. If none apply, stop with “out of scope.”
2. HTTP vs transport — Pass: Before claiming missing HTTP status handling or “404 treated as success,” you cite file:line for the completion/async/for await path that receives response and state whether HTTPURLResponse is cast and statusCode is checked (or cite the helper that does). If you cannot see the handler, say unknown and ask for it—do not assume.
3. Session lifecycle — Pass: For a custom URLSession with a delegate, you cite finishTasksAndInvalidate() or the documented long-lived/singleton pattern you rely on; for .shared, say so if the finding depends on configuration. Skip if only ad hoc URLSession.shared one-shots with no delegate issues.
4. Background or file transfer (if applicable) — Pass: If URLSessionConfiguration.background, downloadTask, or app-extension–scoped sessions appear, findings cite identifier uniqueness, delegate vs completion-handler usage, or file URLs as required. If none of those APIs appear, mark N/A and continue.
5. Severity and checklist — Pass: Every Critical item includes file:line and names which Review Checklist subsection it violates (e.g. Response Validation, Background Sessions). Lower-severity items still name the file(s) they are drawn from.

Output Format

markdown

### Critical
1. [FILE:LINE] Missing HTTP status validation
   - Issue: 404/500 responses not treated as errors
   - Fix: Check `httpResponse.statusCode` is 200-299