URLSession Delegate Callback Order After Cancellation or Timeout

Uncertain Callback Sequencing

When a URLSession data task is cancelled via task.cancel() or by cancelling the surrounding Task in Swift 5.5’s async/await API, the underlying CFNetwork stack may still invoke delegate methods with partial data. The documentation does not specify whether urlSession(_:task:didCompleteWithError:) is guaranteed to fire after all urlSession(_:task:didReceive:) callbacks, or whether the order can vary.

Specific Unresolved Questions

• Does urlSession(_:task:didCompleteWithError:) always occur after the last didReceive callback when a task is cancelled?
• Can the completion callback be invoked before any final data callbacks in a cancellation scenario?
• In async/await, if a task is cancelled while data is being streamed, does the data(for:) call return any data before throwing URLError.cancelled?