net/http: ensure that Listener.Close is called only once in Server.Serve

Fixes #24803

Change-Id: I8b1e7c5a74018a0c333f8c38a7ec5f5827ab1606
Reviewed-on: https://go-review.googlesource.com/106715Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

src/net/http/serve_test.go

@@ -5886,6 +5886,44 @@ func TestServerListenNotComparableListener(t *testing.T) {
 	s.Serve(make(eofListenerNotComparable, 1)) // used to panic
 }
 
+// countCloseListener is a Listener wrapper that counts the number of Close calls.
+type countCloseListener struct {
+	net.Listener
+	closes int32 // atomic
+}
+
+func (p *countCloseListener) Close() error {
+	atomic.AddInt32(&p.closes, 1)
+	return nil
+}
+
+// Issue 24803: don't call Listener.Close on Server.Shutdown.
+func TestServerCloseListenerOnce(t *testing.T) {
+	setParallel(t)
+	defer afterTest(t)
+
+	ln := newLocalListener(t)
+	defer ln.Close()
+
+	cl := &countCloseListener{Listener: ln}
+	server := &Server{}
+	sdone := make(chan bool, 1)
+
+	go func() {
+		server.Serve(cl)
+		sdone <- true
+	}()
+	time.Sleep(10 * time.Millisecond)
+	server.Shutdown(context.Background())
+	ln.Close()
+	<-sdone
+
+	nclose := atomic.LoadInt32(&cl.closes)
+	if nclose != 1 {
+		t.Errorf("Close calls = %v; want 1", nclose)
+	}
+}
+
 func BenchmarkResponseStatusLine(b *testing.B) {
 	b.ReportAllocs()
 	b.RunParallel(func(pb *testing.PB) {

src/net/http/server.go

@@ -2770,10 +2770,13 @@ var ErrServerClosed = errors.New("http: Server closed")
 // Serve always returns a non-nil error. After Shutdown or Close, the
 // returned error is ErrServerClosed.
 func (srv *Server) Serve(l net.Listener) error {
-	defer l.Close()
 	if fn := testHookServerServe; fn != nil {
-		fn(srv, l)
+		fn(srv, l) // call hook with unwrapped listener
 	}
+
+	l = &onceCloseListener{Listener: l}
+	defer l.Close()
+
 	var tempDelay time.Duration // how long to sleep on accept failure
 
 	if err := srv.setupHTTP2_Serve(); err != nil {
@@ -3249,6 +3252,21 @@ func (ln tcpKeepAliveListener) Accept() (net.Conn, error) {
 	return tc, nil
 }
 
+// onceCloseListener wraps a net.Listener, protecting it from
+// multiple Close calls.
+type onceCloseListener struct {
+	net.Listener
+	once     sync.Once
+	closeErr error
+}
+
+func (oc *onceCloseListener) Close() error {
+	oc.once.Do(oc.close)
+	return oc.closeErr
+}
+
+func (oc *onceCloseListener) close() { oc.closeErr = oc.Listener.Close() }
+
 // globalOptionsHandler responds to "OPTIONS *" requests.
 type globalOptionsHandler struct{}