pkg/proxy/server.go
func (s *server) listenAndServe() {
	defer s.closeWg.Done()

	s.lg.Info("proxy is listening on", zap.String("from", s.From()))
	close(s.readyc)

	for {
		s.pauseAcceptMu.Lock()
		pausec := s.pauseAcceptc
		s.pauseAcceptMu.Unlock()
		select {
		case <-pausec:
		case <-s.donec:
			return
		}

		s.latencyAcceptMu.RLock()
		lat := s.latencyAccept
		s.latencyAcceptMu.RUnlock()
		if lat > 0 {
			select {
			case <-time.After(lat):
			case <-s.donec:
				return
			}
		}

		s.listenerMu.RLock()
		ln := s.listener
		s.listenerMu.RUnlock()

		in, err := ln.Accept()
		if err != nil {
			select {
			case s.errc <- err:
				select {
				case <-s.donec:
					return
				default:
				}
			case <-s.donec:
				return
			}
			s.lg.Debug("listener accept error", zap.Error(err))

			if strings.HasSuffix(err.Error(), "use of closed network connection") {
				select {
				case <-time.After(s.retryInterval):
				case <-s.donec:
					return
				}
				s.lg.Debug("listener is closed; retry listening on", zap.String("from", s.From()))

				if err = s.ResetListener(); err != nil {
					select {
					case s.errc <- err:
						select {
						case <-s.donec:
							return
						default:
						}
					case <-s.donec:
						return
					}
					s.lg.Warn("failed to reset listener", zap.Error(err))
				}
			}

			continue
		}

		var out net.Conn
		if !s.tlsInfo.Empty() {
			var tp *http.Transport
			tp, err = transport.NewTransport(s.tlsInfo, s.dialTimeout)
			if err != nil {
				select {
				case s.errc <- err:
					select {
					case <-s.donec:
						return
					default:
					}
				case <-s.donec:
					return
				}
				continue
			}
			out, err = tp.Dial(s.to.Scheme, s.to.Host)
		} else {
			out, err = net.Dial(s.to.Scheme, s.to.Host)
		}
		if err != nil {
			select {
			case s.errc <- err:
				select {
				case <-s.donec:
					return
				default:
				}
			case <-s.donec:
				return
			}
			s.lg.Debug("failed to dial", zap.Error(err))
			continue
		}

		go func() {
			// read incoming bytes from listener, dispatch to outgoing connection
			s.transmit(out, in)
			out.Close()
			in.Close()
		}()
		go func() {
			// read response from outgoing connection, write back to listener
			s.receive(in, out)
			in.Close()
			out.Close()
		}()
	}
}
func (s *server) listenAndServe() {
	defer s.closeWg.Done()

	s.lg.Info("proxy is listening on", zap.String("from", s.From()))
	close(s.readyc)

	for {
		s.pauseAcceptMu.Lock()
		pausec := s.pauseAcceptc
		s.pauseAcceptMu.Unlock()
		select {
		case <-pausec:
		case <-s.donec:
			return
		}

		s.latencyAcceptMu.RLock()
		lat := s.latencyAccept
		s.latencyAcceptMu.RUnlock()
		if lat > 0 {
			select {
			case <-time.After(lat):
			case <-s.donec:
				return
			}
		}

		s.listenerMu.RLock()
		ln := s.listener
		s.listenerMu.RUnlock()

		in, err := ln.Accept()
		if err != nil {
			select {
			case s.errc <- err:
				select {
				case <-s.donec:
					return
				default:
				}
			case <-s.donec:
				return
			}
			s.lg.Debug("listener accept error", zap.Error(err))

			if strings.HasSuffix(err.Error(), "use of closed network connection") {
				select {
				case <-time.After(s.retryInterval):
				case <-s.donec:
					return
				}
				s.lg.Debug("listener is closed; retry listening on", zap.String("from", s.From()))

				if err = s.ResetListener(); err != nil {
					select {
					case s.errc <- err:
						select {
						case <-s.donec:
							return
						default:
						}
					case <-s.donec:
						return
					}
					s.lg.Warn("failed to reset listener", zap.Error(err))
				}
			}

			continue
		}

		var out net.Conn
		if !s.tlsInfo.Empty() {
			var tp *http.Transport
			tp, err = transport.NewTransport(s.tlsInfo, s.dialTimeout)
			if err != nil {
				select {
				case s.errc <- err:
					select {
					case <-s.donec:
						return
					default:
					}
				case <-s.donec:
					return
				}
				continue
			}
			out, err = tp.Dial(s.to.Scheme, s.to.Host)
		} else {
			out, err = net.Dial(s.to.Scheme, s.to.Host)
		}
		if err != nil {
			select {
			case s.errc <- err:
				select {
				case <-s.donec:
					return
				default:
				}
			case <-s.donec:
				return
			}
			s.lg.Debug("failed to dial", zap.Error(err))
			continue
		}

		go func() {
			// read incoming bytes from listener, dispatch to outgoing connection
			s.transmit(out, in)
			out.Close()
			in.Close()
		}()
		go func() {
			// read response from outgoing connection, write back to listener
			s.receive(in, out)
			in.Close()
			out.Close()
		}()
	}
}
// TODO: implement packet reordering from multiple TCP connections
// buffer packets per connection for awhile, reorder before transmit
// - https://github.com/etcd-io/etcd/issues/5614
// - https://github.com/etcd-io/etcd/pull/6918#issuecomment-264093034