Make TCP candidates less preferrable to UDP

With exception of relay candidates (TCP host is more preferrable
than UDP relay).

candidate_base.go

@@ -355,7 +355,7 @@ func (c *candidateBase) Priority() uint32 {
 	// candidates for a particular component for a particular data stream
 	// that have the same type, the local preference MUST be unique for each
 	// one.
-	return (1<<24)*uint32(c.Type().Preference()) +
+	return (1<<24)*uint32(c.Type().Preference(c.networkType)) +
 		(1<<8)*uint32(c.LocalPreference()) +
 		uint32(256-c.Component())
 }

candidate_test.go

@@ -36,7 +36,7 @@ func TestCandidatePriority(t *testing.T) {
 					tcpType:       TCPTypeActive,
 				},
 			},
-			WantPriority: 2128609279,
+			WantPriority: 1675624447,
 		},
 		{
 			Candidate: &CandidateHost{
@@ -47,7 +47,7 @@ func TestCandidatePriority(t *testing.T) {
 					tcpType:       TCPTypePassive,
 				},
 			},
-			WantPriority: 2124414975,
+			WantPriority: 1671430143,
 		},
 		{
 			Candidate: &CandidateHost{
@@ -58,7 +58,7 @@ func TestCandidatePriority(t *testing.T) {
 					tcpType:       TCPTypeSimultaneousOpen,
 				},
 			},
-			WantPriority: 2120220671,
+			WantPriority: 1667235839,
 		},
 		{
 			Candidate: &CandidatePeerReflexive{
@@ -78,7 +78,7 @@ func TestCandidatePriority(t *testing.T) {
 					tcpType:       TCPTypeSimultaneousOpen,
 				},
 			},
-			WantPriority: 1860173823,
+			WantPriority: 1658847231,
 		},
 		{
 			Candidate: &CandidatePeerReflexive{
@@ -89,7 +89,7 @@ func TestCandidatePriority(t *testing.T) {
 					tcpType:       TCPTypeActive,
 				},
 			},
-			WantPriority: 1855979519,
+			WantPriority: 1654652927,
 		},
 		{
 			Candidate: &CandidatePeerReflexive{
@@ -100,7 +100,7 @@ func TestCandidatePriority(t *testing.T) {
 					tcpType:       TCPTypePassive,
 				},
 			},
-			WantPriority: 1851785215,
+			WantPriority: 1650458623,
 		},
 		{
 			Candidate: &CandidateServerReflexive{
@@ -285,7 +285,7 @@ func TestCandidateMarshal(t *testing.T) {
 				},
 				"",
 			},
-			"1052353102 1 tcp 2128609279 192.168.0.196 0 typ host tcptype active",
+			"1052353102 1 tcp 1675624447 192.168.0.196 0 typ host tcptype active",
 			false,
 		},
 		{

candidatetype.go

@@ -38,7 +38,21 @@ func (c CandidateType) String() string {
 // The RECOMMENDED values are 126 for host candidates, 100
 // for server reflexive candidates, 110 for peer reflexive candidates,
 // and 0 for relayed candidates.
-func (c CandidateType) Preference() uint16 {
+func (c CandidateType) Preference(networkType NetworkType) uint16 {
+	if networkType == NetworkTypeTCP4 || networkType == NetworkTypeTCP6 {
+		switch c {
+		case CandidateTypeHost:
+			return 99
+		case CandidateTypePeerReflexive:
+			return 98
+		case CandidateTypeServerReflexive:
+			return 97
+		case CandidateTypeRelay, CandidateTypeUnspecified:
+			return 0
+		}
+	}
+
+	// UDP candidates
 	switch c {
 	case CandidateTypeHost:
 		return 126

gather_test.go

@@ -751,7 +751,8 @@ func TestMultiTCPMuxUsage(t *testing.T) {
 
 	portFound := make(map[int]bool)
 	for c := range candidateCh {
-		if c.NetworkType().IsTCP() {
+		activeCandidate := c.Port() == 0
+		if c.NetworkType().IsTCP() && !activeCandidate {
 			portFound[c.Port()] = true
 		}
 	}