// If srv.Addr is blank, ":http" is used.
//
// ListenAndServe always returns a non-nil error. After [Server.Shutdown] or [Server.Close],
// the returned error is [ErrServerClosed].
func (srv *Server) ListenAndServe() error {
	if srv.shuttingDown() {
		return ErrServerClosed
	}
	addr := srv.Addr
	if addr == "" {
		addr = ":http"
	}
	ln, err := net.Listen("tcp", addr)
	if err != nil {
		return err
	}

func TestServerShutdownThenServe(t *testing.T) {
	var srv Server
	cl := &countCloseListener{Listener: nil}
	srv.Shutdown(context.Background())
	got := srv.Serve(cl)
	if got != ErrServerClosed {
		t.Errorf("Serve err = %v; want ErrServerClosed", got)
	}
	nclose := atomic.LoadInt32(&cl.closes)
	if nclose != 1 {
		t.Errorf("Close calls = %v; want 1", nclose)
	}
}