A best-guess upper bound on the number of bytes the client expects to send.
- iOS 11.0+
- macOS 10.13+
- UIKit for Mac 13.0+Beta
- tvOS 11.0+
- watchOS 4.0+
The value set for this property should account for the size of HTTP headers and body data or body stream. If no value is specified, the system uses
NSURLSession instead. This property is used by the system to optimize the scheduling of URL session tasks. Developers are strongly encouraged to provide an approximate upper bound, or an exact byte count, if possible, rather than accept the default.