streamtimeout.swift

import Foundation

struct TimeoutError: Error {
}

extension AsyncThrowingStream.Continuation where Failure == Error {
	func timeoutTask(with interval: TimeInterval) -> Task<Void, Error> {
		let sleepNS = UInt64(interval * 1_000_000_000)

		return Task {
			// this will throw on cancel
			try await Task.sleep(nanoseconds: sleepNS)

			self.finish(throwing: TimeoutError())
		}
	}
}

extension AsyncThrowingStream where Failure == Error, Element: Sendable {
	func timeout(_ interval: TimeInterval) -> Self {
		return Self { continuation in
			Task {
				do {
					var timeout = continuation.timeoutTask(with: interval)

					for try await value in self {
						timeout.cancel()
						continuation.yield(value)

						timeout = continuation.timeoutTask(with: interval)
					}

					continuation.finish()
				} catch {
					continuation.finish(throwing: error)
				}
			}
		}
	}
}

@jdanthinne yeah wasn't quite right. I've update it with Donny's approach, which I like more. It is still essential that Element conform to Sendable in this version.