sendStdin method
Writes data to standard input (client → node).
When onFlushed is supplied it is invoked as the credit window lets each
chunk of this write onto the wire, with the cumulative number of bytes of
data flushed so far — a faithful, socket-paced signal for upload progress.
Implementation
void sendStdin(List<int> data, {void Function(int sentSoFar)? onFlushed}) =>
_sendData(DataOpcode.stdin, data, onFlushed: onFlushed);