try sending pings before sending searches for an unresponsive session

src/yggdrasil/router.go

@@ -141,12 +141,27 @@ func (r *router) sendPacket(bs []byte) {
 		// No or unintiialized session, so we need to search first
 		doSearch(bs)
 	case time.Since(sinfo.time) > 6*time.Second:
-		// We haven't heard from the dest in a while; they may have changed coords
+		if sinfo.time.Before(sinfo.pingTime) && time.Since(sinfo.pingTime) > 6*time.Second {
-		// Maybe the connection is idle, or maybe one of us changed coords
+			// We haven't heard from the dest in a while
-		// Try searching to either ping them (a little overhead) or fix the coords
+			// We tried pinging but didn't get a response
+			// They may have changed coords
+			// Try searching to discover new coords
+			// Note that search spam is throttled internally
 			doSearch(nil)
-		fallthrough
+		} else {
-	//default: go func() { sinfo.send<-bs }()
+			// We haven't heard about the dest in a while
+			now := time.Now()
+			if !sinfo.time.Before(sinfo.pingTime) {
+				// Update pingTime to start the clock for searches (above)
+				sinfo.pingTime = now
+			}
+			if time.Since(sinfo.pingSend) > time.Second {
+				// Send at most 1 ping per second
+				sinfo.pingSend = now
+				r.core.sessions.sendPingPong(sinfo, false)
+			}
+		}
+		fallthrough // Also send the packet
 	default:
 		// Generate an ICMPv6 Packet Too Big for packets larger than session MTU
 		if len(bs) > int(sinfo.getMTU()) {

src/yggdrasil/session.go

@@ -30,6 +30,8 @@ type sessionInfo struct {
 	nonceMask    uint64
 	tstamp       int64     // tstamp from their last session ping, replay attack mitigation
 	mtuTime      time.Time // time myMTU was last changed
+	pingTime     time.Time // time the first ping was sent since the last received packet
+	pingSend     time.Time // time the last ping was sent
 }
 
 type sessionPing struct {
@@ -64,7 +66,8 @@ func (s *sessionInfo) update(p *sessionPing) bool {
 		s.theirMTU = p.mtu
 	}
 	s.coords = append([]byte{}, p.coords...)
-	s.time = time.Now()
+	now := time.Now()
+	s.time = now
 	s.tstamp = p.tstamp
 	s.init = true
 	return true
@@ -153,7 +156,11 @@ func (ss *sessions) createSession(theirPermKey *boxPubKey) *sessionInfo {
 	sinfo.myNonce = *newBoxNonce()
 	sinfo.theirMTU = 1280
 	sinfo.myMTU = uint16(ss.core.tun.mtu)
-	sinfo.mtuTime = time.Now()
+	now := time.Now()
+	sinfo.time = now
+	sinfo.mtuTime = now
+	sinfo.pingTime = now
+	sinfo.pingSend = now
 	higher := false
 	for idx := range ss.core.boxPub {
 		if ss.core.boxPub[idx] > sinfo.theirPermPub[idx] {
@@ -176,7 +183,6 @@ func (ss *sessions) createSession(theirPermKey *boxPubKey) *sessionInfo {
 	sinfo.send = make(chan []byte, 32)
 	sinfo.recv = make(chan *wire_trafficPacket, 32)
 	go sinfo.doWorker()
-	sinfo.time = time.Now()
 	// Do some cleanup
 	// Time thresholds almost certainly could use some adjusting
 	for _, s := range ss.sinfos {
@@ -255,6 +261,9 @@ func (ss *sessions) sendPingPong(sinfo *sessionInfo, isPong bool) {
 	}
 	packet := p.encode()
 	ss.core.router.out(packet)
+	if !isPong {
+		sinfo.pingSend = time.Now()
+	}
 }
 
 func (ss *sessions) handlePing(ping *sessionPing) {