make connection heartbeating independent of periodic gossip

This was a convenient but rather suspect coupling. In particular, it
will break if the period gossip logic changes s.t. it no longer sends
gossip on all connections every interval.

router/connection.go

@@ -47,6 +47,7 @@ type LocalConnection struct {
 	stackFrag         bool
 	effectivePMTU     int
 	SessionKey        *[32]byte
+	heartbeatTCP      *time.Ticker
 	heartbeatTimeout  *time.Timer
 	heartbeatFrame    *ForwardedFrame
 	heartbeat         *time.Ticker
@@ -339,6 +340,7 @@ func (conn *LocalConnection) run(actionChan <-chan ConnectionAction, finished ch
 // goroutine, at least not without some synchronisation.
 
 func (conn *LocalConnection) initHeartbeats() error {
+	conn.heartbeatTCP = time.NewTicker(TCPHeartbeat)
 	conn.heartbeatTimeout = time.NewTimer(HeartbeatTimeout)
 	heartbeatFrameBytes := make([]byte, EthernetOverhead+8)
 	binary.BigEndian.PutUint64(heartbeatFrameBytes[EthernetOverhead:], conn.uid)
@@ -360,6 +362,8 @@ func (conn *LocalConnection) actorLoop(actionChan <-chan ConnectionAction) (err
 				break
 			}
 			err = action()
+		case <-conn.heartbeatTCP.C:
+			err = conn.sendSimpleProtocolMsg(ProtocolHeartbeat)
 		case <-conn.heartbeatTimeout.C:
 			err = fmt.Errorf("timed out waiting for UDP heartbeat")
 		case <-tickerChan(conn.heartbeat):
@@ -386,6 +390,7 @@ func (conn *LocalConnection) shutdown() {
 		conn.heartbeatTimeout.Stop()
 	}
 
+	stopTicker(conn.heartbeatTCP)
 	stopTicker(conn.heartbeat)
 	stopTicker(conn.fragTest)
 
@@ -439,6 +444,7 @@ func (conn *LocalConnection) receiveTCP(decoder *gob.Decoder) {
 
 func (conn *LocalConnection) handleProtocolMsg(tag ProtocolTag, payload []byte) error {
 	switch tag {
+	case ProtocolHeartbeat:
 	case ProtocolConnectionEstablished:
 		// We sent fast heartbeats to the remote peer, which has now
 		// received at least one of them and told us via this message.
@@ -469,7 +475,7 @@ func (conn *LocalConnection) handleProtocolMsg(tag ProtocolTag, payload []byte)
 }
 
 func (conn *LocalConnection) extendReadDeadline() {
-	conn.TCPConn.SetReadDeadline(time.Now().Add(ReadTimeout))
+	conn.TCPConn.SetReadDeadline(time.Now().Add(TCPHeartbeat * 2))
 }
 
 func (conn *LocalConnection) sendFastHeartbeats() error {

router/consts.go

@@ -16,10 +16,10 @@ const (
 	UDPNonceSendAt      = 8192
 	FragTestSize        = 60001
 	PMTUDiscoverySize   = 60000
+	TCPHeartbeat        = 30 * time.Second
 	FastHeartbeat       = 500 * time.Millisecond
 	SlowHeartbeat       = 10 * time.Second
 	FragTestInterval    = 5 * time.Minute
-	ReadTimeout         = 1 * time.Minute
 	PMTUVerifyAttempts  = 8
 	PMTUVerifyTimeout   = 10 * time.Millisecond // gets doubled with every attempt
 	MaxDuration         = time.Duration(math.MaxInt64)

router/protocol.go

@@ -8,7 +8,8 @@ const (
 type ProtocolTag byte
 
 const (
-	ProtocolConnectionEstablished ProtocolTag = iota
+	ProtocolHeartbeat ProtocolTag = iota
+	ProtocolConnectionEstablished
 	ProtocolFragmentationReceived
 	ProtocolStartFragmentationTest
 	ProtocolNonce