# write(contents:to:at:replyHandler:) Writes contents to the given file item. ``` func write(contents: Data, to item: FSItem, at offset: off_t, replyHandler reply: @escaping @Sendable (Int, (any Error)?) -> Void) ``` ## Parameters `contents` A buffer containing the data to write to the file. `item` The item to which to write. FSKit guarantees this item will be of type [`FSItem.ItemType.file`](/documentation/FSKit/FSItem/ItemType/file). `offset` The offset in the file from which to start writing. `reply` A block or closure to indicate success or failure. If writing succeeds, pass the number of bytes written and a `nil` error. If writing fails, pass the number of bytes written prior to the error along with the relevant error. For an `async` Swift implementation, there’s no reply handler; simply return the byte count or throw an error. ## Discussion FSKit expects this routine to allocate space in the file system to extend the file as necessary. If the volume experiences an out-of-space condition, reply with an error of domain and code `ENOSPC`. --- 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)