# readData(ofMinLength:maxLength:timeout:completionHandler:) Asynchronously reads a number of bytes from the stream, and calls a handler upon completion. ``` func readData(ofMinLength minBytes: Int, maxLength maxBytes: Int, timeout: TimeInterval, completionHandler: @escaping @Sendable (Data?, Bool, (any Error)?) -> Void) ``` ## Parameters `minBytes` The minimum number of bytes to read. `maxBytes` The maximum number of bytes to read. `timeout` A timeout for reading bytes. If the read is not completed within the specified interval, the read is canceled and the `completionHandler` is called with an error. Pass `0` to prevent a read from timing out. `completionHandler` The completion handler to call when all bytes are read, or an error occurs. This handler is executed on the delegate queue. This completion handler takes the following parameters: - `data`: The data read from the stream. - `atEOF`: Whether or not the stream reached end-of-file (EOF), such that no more data can be read. - `error`: An error object that indicates why the read failed, or `nil` if the read was successful. --- 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)