udp: handle closed forwarding channel (#5470)

pkg/proto/udp/udp.go

@@ -63,9 +63,13 @@ func ForwardUserConn(udpConn *net.UDPConn, readCh <-chan *msg.UDPPacket, sendCh
 		// NewUDPPacket copies buf[:n], so the read buffer can be reused
 		udpMsg := NewUDPPacket(buf[:n], nil, remoteAddr)
 
-		select {
-		case sendCh <- udpMsg:
-		default:
+		if err = errors.PanicToError(func() {
+			select {
+			case sendCh <- udpMsg:
+			default:
+			}
+		}); err != nil {
+			return
 		}
 	}
 }

pkg/proto/udp/udp_test.go

@@ -1,9 +1,13 @@
 package udp
 
 import (
+	"net"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/require"
+
+	"github.com/fatedier/frp/pkg/msg"
 )
 
 func TestUdpPacket(t *testing.T) {
@@ -16,3 +20,33 @@ func TestUdpPacket(t *testing.T) {
 	require.NoError(err)
 	require.EqualValues(buf, newBuf)
 }
+
+func TestForwardUserConnReturnsWhenSendChannelIsClosed(t *testing.T) {
+	listener, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4(127, 0, 0, 1)})
+	require.NoError(t, err)
+	t.Cleanup(func() { _ = listener.Close() })
+
+	readCh := make(chan *msg.UDPPacket)
+	sendCh := make(chan *msg.UDPPacket)
+	close(sendCh)
+	t.Cleanup(func() { close(readCh) })
+
+	done := make(chan struct{})
+	go func() {
+		ForwardUserConn(listener, readCh, sendCh, 1500)
+		close(done)
+	}()
+
+	sender, err := net.DialUDP("udp4", nil, listener.LocalAddr().(*net.UDPAddr))
+	require.NoError(t, err)
+	t.Cleanup(func() { _ = sender.Close() })
+
+	_, err = sender.Write([]byte("trigger"))
+	require.NoError(t, err)
+
+	select {
+	case <-done:
+	case <-time.After(time.Second):
+		t.Fatal("ForwardUserConn did not return after sending to a closed channel")
+	}
+}