TUN-6617: Dont fallback to http2 if QUIC conn was successful.

cloudflared falls back aggressively to HTTP/2 protocol if a connection
attempt with QUIC failed. This was done to ensure that machines with UDP
egress disabled did not stop clients from connecting to the cloudlfare
edge. This PR improves on that experience by having cloudflared remember
if a QUIC connection was successful which implies UDP egress works. In
this case, cloudflared does not fallback to HTTP/2 and keeps trying to
connect to the edge with QUIC.

tunnelstate/conntracker.go

@@ -10,20 +10,26 @@ import (
 
 type ConnTracker struct {
 	sync.RWMutex
-	isConnected map[int]bool
-	log         *zerolog.Logger
+	// int is the connection Index
+	connectionInfo map[uint8]ConnectionInfo
+	log            *zerolog.Logger
+}
+
+type ConnectionInfo struct {
+	IsConnected bool
+	Protocol    connection.Protocol
 }
 
 func NewConnTracker(log *zerolog.Logger) *ConnTracker {
 	return &ConnTracker{
-		isConnected: make(map[int]bool, 0),
-		log:         log,
+		connectionInfo: make(map[uint8]ConnectionInfo, 0),
+		log:            log,
 	}
 }
 
-func MockedConnTracker(mocked map[int]bool) *ConnTracker {
+func MockedConnTracker(mocked map[uint8]ConnectionInfo) *ConnTracker {
 	return &ConnTracker{
-		isConnected: mocked,
+		connectionInfo: mocked,
 	}
 }
 
@@ -31,11 +37,17 @@ func (ct *ConnTracker) OnTunnelEvent(c connection.Event) {
 	switch c.EventType {
 	case connection.Connected:
 		ct.Lock()
-		ct.isConnected[int(c.Index)] = true
+		ci := ConnectionInfo{
+			IsConnected: true,
+			Protocol:    c.Protocol,
+		}
+		ct.connectionInfo[c.Index] = ci
 		ct.Unlock()
 	case connection.Disconnected, connection.Reconnecting, connection.RegisteringTunnel, connection.Unregistering:
 		ct.Lock()
-		ct.isConnected[int(c.Index)] = false
+		ci := ct.connectionInfo[c.Index]
+		ci.IsConnected = false
+		ct.connectionInfo[c.Index] = ci
 		ct.Unlock()
 	default:
 		ct.log.Error().Msgf("Unknown connection event case %v", c)
@@ -46,10 +58,23 @@ func (ct *ConnTracker) CountActiveConns() uint {
 	ct.RLock()
 	defer ct.RUnlock()
 	active := uint(0)
-	for _, connected := range ct.isConnected {
-		if connected {
+	for _, ci := range ct.connectionInfo {
+		if ci.IsConnected {
 			active++
 		}
 	}
 	return active
 }
+
+// HasConnectedWith checks if we've ever had a successful connection to the edge
+// with said protocol.
+func (ct *ConnTracker) HasConnectedWith(protocol connection.Protocol) bool {
+	ct.RLock()
+	defer ct.RUnlock()
+	for _, ci := range ct.connectionInfo {
+		if ci.Protocol == protocol {
+			return true
+		}
+	}
+	return false
+}