From ff3107a412f7b9043fdba86630724af498080115 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jos=C3=A9=20M=C3=A9lan=C3=A7on?= <jmelancon@genetec.com>
Date: Wed, 22 Nov 2023 07:47:32 -0500
Subject: [PATCH] Match libwebrtc's TURN protocol priority

Today, all relay candidates from Pion have the same priority.
This PR attempts to reproduce libwebrtc's behavior, where the
TURN servers candidates priority is based on the underlying
relay protocol. UDP are preferred over TCP, which are preferred
over the TLS options.
---
 candidate_relay.go | 17 +++++++++++++++++
 gather.go          |  4 ++--
 ice.go             |  5 +++++
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/candidate_relay.go b/candidate_relay.go
index 449d077a..fa5297b2 100644
--- a/candidate_relay.go
+++ b/candidate_relay.go
@@ -70,6 +70,23 @@ func NewCandidateRelay(config *CandidateRelayConfig) (*CandidateRelay, error) {
 	}, nil
 }
 
+// LocalPreference returns the local preference for this candidate
+func (c *CandidateRelay) LocalPreference() uint16 {
+	// These preference values come from libwebrtc
+	// https://github.com/mozilla/libwebrtc/blob/1389c76d9c79839a2ca069df1db48aa3f2e6a1ac/p2p/base/turn_port.cc#L61
+	var relayPreference uint16
+	switch c.relayProtocol {
+	case relayProtocolTLS, relayProtocolDTLS:
+		relayPreference = 2
+	case tcp:
+		relayPreference = 1
+	default:
+		relayPreference = 0
+	}
+
+	return c.candidateBase.LocalPreference() + relayPreference
+}
+
 // RelayProtocol returns the protocol used between the endpoint and the relay server.
 func (c *CandidateRelay) RelayProtocol() string {
 	return c.relayProtocol
diff --git a/gather.go b/gather.go
index f93e6c16..024247d2 100644
--- a/gather.go
+++ b/gather.go
@@ -616,7 +616,7 @@ func (a *Agent) gatherCandidatesRelay(ctx context.Context, urls []*stun.URI) { /
 
 				relAddr = conn.LocalAddr().(*net.UDPAddr).IP.String() //nolint:forcetypeassert
 				relPort = conn.LocalAddr().(*net.UDPAddr).Port        //nolint:forcetypeassert
-				relayProtocol = "dtls"
+				relayProtocol = relayProtocolDTLS
 				locConn = &fakenet.PacketConn{Conn: conn}
 			case url.Proto == stun.ProtoTypeTCP && url.Scheme == stun.SchemeTypeTURNS:
 				tcpAddr, resolvErr := a.net.ResolveTCPAddr(NetworkTypeTCP4.String(), turnServerAddr)
@@ -646,7 +646,7 @@ func (a *Agent) gatherCandidatesRelay(ctx context.Context, urls []*stun.URI) { /
 
 				relAddr = conn.LocalAddr().(*net.TCPAddr).IP.String() //nolint:forcetypeassert
 				relPort = conn.LocalAddr().(*net.TCPAddr).Port        //nolint:forcetypeassert
-				relayProtocol = "tls"
+				relayProtocol = relayProtocolTLS
 				locConn = turn.NewSTUNConn(conn)
 			default:
 				a.log.Warnf("Unable to handle URL in gatherCandidatesRelay %v", url)
diff --git a/ice.go b/ice.go
index bd551206..73262dd3 100644
--- a/ice.go
+++ b/ice.go
@@ -83,3 +83,8 @@ func (t GatheringState) String() string {
 		return ErrUnknownType.Error()
 	}
 }
+
+const (
+	relayProtocolDTLS = "dtls"
+	relayProtocolTLS  = "tls"
+)