Sent as the body (message data) of a request is transmitted (such as in an http POST request).
- iOS 3.0+
- macOS 10.8+
- tvOS 9.0+
- watchOS 2.0+
The connection sending the message.
The number of bytes written in the latest write.
The total number of bytes written for this connection.
Bytes Expected To Write
The number of bytes the connection expects to write.
This method provides an estimate of the progress of a URL upload.
The value of
total may change during the upload if the request needs to be retransmitted due to a lost connection or an authentication challenge from the server.