in cpp/acs_agent_client_reactor.cc [242:254]
void AcsAgentClientReactor::NextWrite() {
if (msg_request_ == nullptr && ack_buffer_.empty()) {
return;
}
writing_ = true;
if (!ack_buffer_.empty()) {
// Prioritize the send of ack over message.
request_ = ack_buffer_.front().get();
} else {
request_ = msg_request_.get();
}
StartWrite(request_);
}