Respect IncludeLoopback in UDPMuxDefault

Currently, when using UDPMuxDefault with unspecified address,
the loopback address is included by default, but
agentConfig.IncludeLoopback is not respected when gathering
local candidates.

The same holds true when UDPMuxDefault is configured with a loopback
address, but agentConfig.IncludeLoopback is not explicitly set to
true.

This commit adds an extra check to gatherCandidatesLocalUDPMux()
for respecting that setting in both cases.

agent_udpmux_test.go

@@ -49,6 +49,7 @@ func TestMuxAgent(t *testing.T) {
 				NetworkTypes: []NetworkType{
 					NetworkTypeUDP4,
 				},
+				IncludeLoopback: addr.IP.IsLoopback(),
 			})
 			require.NoError(t, err)
 

gather.go

@@ -266,6 +266,13 @@ func (a *Agent) gatherCandidatesLocalUDPMux(ctx context.Context) error { //nolin
 			return errInvalidAddress
 		}
 		candidateIP := udpAddr.IP
+
+		if _, ok := a.udpMux.(*UDPMuxDefault); ok && !a.includeLoopback && candidateIP.IsLoopback() {
+			// Unlike MultiUDPMux Default, UDPMuxDefault doesn't have
+			// a separate param to include loopback, so we respect agent config
+			continue
+		}
+
 		if a.mDNSMode != MulticastDNSModeQueryAndGather &&
 			a.extIPMapper != nil &&
 			a.extIPMapper.candidateType == CandidateTypeHost {

gather_test.go

@@ -133,6 +133,16 @@ func TestLoopbackCandidate(t *testing.T) {
 	assert.NoError(t, err)
 	muxWithLo, errlo := NewMultiUDPMuxFromPort(12501, UDPMuxFromPortWithLoopback())
 	assert.NoError(t, errlo)
+
+	unspecConn, errconn := net.ListenPacket("udp", ":0")
+	assert.NoError(t, errconn)
+	defer func() {
+		_ = unspecConn.Close()
+	}()
+	muxUnspecDefault := NewUDPMuxDefault(UDPMuxParams{
+		UDPConn: unspecConn,
+	})
+
 	testCases := []testCase{
 		{
 			name: "mux should not have loopback candidate",
@@ -150,6 +160,23 @@ func TestLoopbackCandidate(t *testing.T) {
 			},
 			loExpected: true,
 		},
+		{
+			name: "UDPMuxDefault with unspecified IP should not have loopback candidate",
+			agentConfig: &AgentConfig{
+				NetworkTypes: []NetworkType{NetworkTypeUDP4, NetworkTypeUDP6},
+				UDPMux:       muxUnspecDefault,
+			},
+			loExpected: false,
+		},
+		{
+			name: "UDPMuxDefault with unspecified IP should respect agent includeloopback",
+			agentConfig: &AgentConfig{
+				NetworkTypes:    []NetworkType{NetworkTypeUDP4, NetworkTypeUDP6},
+				UDPMux:          muxUnspecDefault,
+				IncludeLoopback: true,
+			},
+			loExpected: true,
+		},
 		{
 			name: "includeloopback enabled",
 			agentConfig: &AgentConfig{
@@ -198,6 +225,7 @@ func TestLoopbackCandidate(t *testing.T) {
 
 	assert.NoError(t, mux.Close())
 	assert.NoError(t, muxWithLo.Close())
+	assert.NoError(t, muxUnspecDefault.Close())
 }
 
 // Assert that STUN gathering is done concurrently