public async override Task DrawPoints(IAsyncStreamReader <DrawPointRequest> requestStream, IServerStreamWriter <DrawPoint> responseStream, ServerCallContext context)
{
_broadcastService.AddReceiver(responseStream, requestStream.Current.Id);
while (await requestStream.MoveNext())
{
_broadcastService.AddPoint(requestStream.Current.DrawPoint, requestStream.Current.Id);
}
_broadcastService.RemoveReceiver(requestStream.Current.Id);
}