fix invalid memory address or nil pointer dereference

net.go

@@ -234,9 +234,10 @@ func (m *Memberlist) streamListen() {
 
 // handleConn handles a single incoming stream connection from the transport.
 func (m *Memberlist) handleConn(conn net.Conn) {
-	defer func() {
+	defer func(conn net.Conn) {
 		_ = conn.Close()
-	}()
+	}(conn) // Capture the original conn, because the code before shadows it.
+
 	m.logger.Printf("[DEBUG] memberlist: Stream connection %s", LogConn(conn))
 
 	metrics.IncrCounterWithLabels([]string{"memberlist", "tcp", "accept"}, 1, m.metricLabels)

net_test.go

@@ -1016,3 +1016,54 @@ func TestHandleCommand(t *testing.T) {
 	m.handleCommand(nil, &net.TCPAddr{Port: 12345}, time.Now())
 	require.Contains(t, buf.String(), "missing message type byte")
 }
+
+func TestHandleConn_NilConnAfterRemoveLabelHeaderFromStream(t *testing.T) {
+	mockNet := &MockNetwork{}
+
+	t1 := mockNet.NewTransport("node1")
+
+	m := GetMemberlist(t, func(c *Config) {
+		c.Transport = t1
+	})
+	defer func() {
+		if err := m.Shutdown(); err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	errConn := &errorReadNetConn{
+		closed: make(chan struct{}),
+	}
+	if err := t1.IngestStream(errConn); err != nil {
+		t.Fatal(err)
+	}
+
+	// The connection must be successfully closed
+	<-errConn.closed
+}
+
+type errorReadNetConn struct {
+	net.Conn
+	closed chan struct{}
+}
+
+func (c *errorReadNetConn) LocalAddr() net.Addr {
+	return &MockAddress{"fake:0", "fake"}
+}
+
+func (c *errorReadNetConn) RemoteAddr() net.Addr {
+	return &MockAddress{"fake:0", "fake"}
+}
+
+func (c *errorReadNetConn) SetDeadline(t time.Time) error {
+	return nil
+}
+
+func (c *errorReadNetConn) Read(b []byte) (n int, err error) {
+	return 0, fmt.Errorf("test read error")
+}
+
+func (c *errorReadNetConn) Close() error {
+	close(c.closed)
+	return nil
+}