Sent when a download object has received sufficient load data to construct the NSURLResponse object for the download.
- macOS 10.2+
The URL download object sending the message.
The URL response object received as part of the download.
responseis immutable and will not be modified after this method is called.
In some rare cases, multiple responses may be received for a single download. In this case, the client should assume that each new response resets the download progress to 0 and should check the new response for the expected content length.