# write(_:timeout:completionHandler:) Asynchronously writes the specified data to the stream, and calls a handler upon completion. ``` func write(_ data: Data, timeout: TimeInterval, completionHandler: @escaping @Sendable ((any Error)?) -> Void) ``` ## Parameters `data` The data to be written. `timeout` A timeout for writing bytes. If the write is not completed within the specified interval, the write is canceled and the `completionHandler` is called with an error. Pass `0` to prevent a write from timing out. `completionHandler` The completion handler to call when all bytes are written, or an error occurs. This handler is executed on the delegate queue. This completion handler takes the following parameter: - `error`: An error object that indicates why the write failed, or `nil` if the write was successful. ## Discussion There is no guarantee that the remote side of the stream has received all of the written bytes at the time that `completionHandler` is called, only that all of the data has been written to the kernel. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)