# readData(ofLength:) Reads data synchronously up to the specified number of bytes. ``` func readData(ofLength length: Int) -> Data ``` ## Parameters `length` The number of bytes to read from the file handle. ## Return Value The data available through the receiver up to a maximum of `length` bytes, or the maximum size that can be represented by an [`NSData`](/documentation/Foundation/NSData) object, whichever is the smaller. ## Discussion If the handle represents a file, this method returns the data obtained by reading `length` bytes starting at the current file pointer. If `length` bytes aren’t available, this method returns the data from the current file pointer to the end of the file. If the handle represents a communications channel, the method reads up to `length` bytes from the channel. Returns an empty `NSData` object if the handle is at the file’s end or if the communications channel returns an end-of-file indicator. > Important: > This method raises ``doc://com.apple.foundation/documentation/Foundation/NSExceptionName/fileHandleOperationException`` if attempts to determine the file-handle type fail or if attempts to read from the file or channel fail. ## See Also [`availableData`](/documentation/Foundation/FileHandle/availableData) The data currently available in the receiver. --- 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)