completeClosed method
void
completeClosed()
Marks the session as closed.
Incoming stream sources are closed rather than failed: once the session
is gone there are no more streams to deliver, which is what the browser
does with the corresponding ReadableStreams.
Implementation
void completeClosed() {
if (!_closed.isCompleted) _closed.complete();
if (!_incomingBi.isClosed) _incomingBi.close();
if (!_incomingUni.isClosed) _incomingUni.close();
_datagrams?.dispose();
}