net/http: don't crash if Server.Server is called with non-comparable Listener

Fixes #24812

Change-Id: If8d496d61b1120233e44c72d854e80cb06bab970
Reviewed-on: https://go-review.googlesource.com/106657
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/http/serve_test.go

@@ -5843,6 +5843,19 @@ func TestServerValidatesMethod(t *testing.T) {
 	}
 }
 
+// Listener for TestServerListenNotComparableListener.
+type eofListenerNotComparable []int
+
+func (eofListenerNotComparable) Accept() (net.Conn, error) { return nil, io.EOF }
+func (eofListenerNotComparable) Addr() net.Addr            { return nil }
+func (eofListenerNotComparable) Close() error              { return nil }
+
+// Issue 24812: don't crash on non-comparable Listener
+func TestServerListenNotComparableListener(t *testing.T) {
+	var s Server
+	s.Serve(make(eofListenerNotComparable, 1)) // used to panic
+}
+
 func BenchmarkResponseStatusLine(b *testing.B) {
 	b.ReportAllocs()
 	b.RunParallel(func(pb *testing.PB) {

src/net/http/server.go

@@ -2485,7 +2485,7 @@ type Server struct {
 	nextProtoErr      error     // result of http2.ConfigureServer if used
 
 	mu         sync.Mutex
-	listeners  map[net.Listener]struct{}
+	listeners  map[*net.Listener]struct{}
 	activeConn map[*conn]struct{}
 	doneChan   chan struct{}
 	onShutdown []func()
@@ -2621,7 +2621,7 @@ func (s *Server) closeIdleConns() bool {
 func (s *Server) closeListenersLocked() error {
 	var err error
 	for ln := range s.listeners {
-		if cerr := ln.Close(); cerr != nil && err == nil {
+		if cerr := (*ln).Close(); cerr != nil && err == nil {
 			err = cerr
 		}
 		delete(s.listeners, ln)
@@ -2765,8 +2765,8 @@ func (srv *Server) Serve(l net.Listener) error {
 		return err
 	}
 
-	srv.trackListener(l, true)
-	defer srv.trackListener(l, false)
+	srv.trackListener(&l, true)
+	defer srv.trackListener(&l, false)
 
 	baseCtx := context.Background() // base is always background, per Issue 16220
 	ctx := context.WithValue(baseCtx, ServerContextKey, srv)
@@ -2843,11 +2843,19 @@ func (srv *Server) ServeTLS(l net.Listener, certFile, keyFile string) error {
 	return srv.Serve(tlsListener)
 }
 
-func (s *Server) trackListener(ln net.Listener, add bool) {
+// trackListener adds or removes a net.Listener to the set of tracked
+// listeners.
+//
+// We store a pointer to interface in the map set, in case the
+// net.Listener is not comparable. This is safe because we only call
+// trackListener via Serve and can track+defer untrack the same
+// pointer to local variable there. We never need to compare a
+// Listener from another caller.
+func (s *Server) trackListener(ln *net.Listener, add bool) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	if s.listeners == nil {
-		s.listeners = make(map[net.Listener]struct{})
+		s.listeners = make(map[*net.Listener]struct{})
 	}
 	if add {
 		// If the *Server is being reused after a previous