# CFMessagePortCallBack Callback invoked to process a message received on a CFMessagePort object. ``` typealias CFMessagePortCallBack = (CFMessagePort?, Int32, CFData?, UnsafeMutableRawPointer?) -> Unmanaged? ``` ## Parameters `local` The local message port that received the message. `msgid` An arbitrary integer value assigned to the message by the sender. `data` The message data. `info` The `info` member of the [`CFMessagePortContext`](/documentation/CoreFoundation/CFMessagePortContext) structure that was used when creating `local`. ## Return Value Data to send back to the sender of the message. The system releases the returned CFData object. Return `NULL` if you want an empty reply returned to the sender. ## Discussion If you want the message data to persist beyond this callback, you must explicitly create a copy of `data` rather than merely retain it; the contents of `data` will be deallocated after the callback exits. --- 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)