server.go
func (s *Server) ListenAndServe(addr string) error {
	ln, err := net.Listen("tcp4", addr)
	if err != nil {
		return err
	}
	if s.TCPKeepalive {
		if tcpln, ok := ln.(*net.TCPListener); ok {
			return s.Serve(tcpKeepaliveListener{
				TCPListener:     tcpln,
				keepalivePeriod: s.TCPKeepalivePeriod,
			})
		}
	}
	return s.Serve(ln)
}
func (s *Server) ListenAndServe(addr string) error {
	ln, err := net.Listen("tcp4", addr)
	if err != nil {
		return err
	}
	if s.TCPKeepalive {
		if tcpln, ok := ln.(*net.TCPListener); ok {
			return s.Serve(tcpKeepaliveListener{
				TCPListener:     tcpln,
				keepalivePeriod: s.TCPKeepalivePeriod,
			})
		}
	}
	return s.Serve(ln)
}
// ListenAndServe serves HTTP requests from the given TCP4 addr.
//
// Pass custom listener to Serve if you need listening on non-TCP4 media
// such as IPv6.
//
// Accepted connections are configured to enable TCP keep-alives.