wgengine/magicsock: add discoEndpoint heartbeat

Updates #483

wgengine/magicsock/magicsock.go

@@ -1522,10 +1522,11 @@ func (c *Conn) handleDiscoMessage(msg []byte, src netaddr.IPPort) bool {
 func (c *Conn) handlePingLocked(dm *disco.Ping, de *discoEndpoint, src netaddr.IPPort) {
 	c.logf("magicsock: disco: %v<-%v (%v, %v)  got ping tx=%x", c.discoShort, de.discoShort, de.publicKey.ShortString(), src, dm.TxID[:6])
 
-	// Remember this this route if not present.
+	// Remember this route if not present.
 	c.setAddrToDiscoLocked(src, de.discoKey, nil)
 
-	go de.sendDiscoMessage(src, &disco.Pong{
+	pongDst := src
+	go de.sendDiscoMessage(pongDst, &disco.Pong{
 		TxID: dm.TxID,
 		Src:  src,
 	})
@@ -2623,8 +2624,10 @@ type discoEndpoint struct {
 	// mu protects all following fields.
 	mu sync.Mutex // Lock ordering: Conn.mu, then discoEndpoint.mu
 
-	lastSend time.Time      // last time there was outgoing packets sent to this peer (from wireguard-go)
-	derpAddr netaddr.IPPort // fallback/bootstrap path, if non-zero (non-zero for well-behaved clients)
+	heartBeatTimer *time.Timer    // nil when idle
+	lastSend       time.Time      // last time there was outgoing packets sent to this peer (from wireguard-go)
+	lastFullPing   time.Time      // last time we pinged all endpoints
+	derpAddr       netaddr.IPPort // fallback/bootstrap path, if non-zero (non-zero for well-behaved clients)
 
 	bestAddr           netaddr.IPPort // best non-DERP path; zero if none
 	bestAddrLatency    time.Duration
@@ -2635,6 +2638,18 @@ type discoEndpoint struct {
 }
 
 const (
+	// sessionActiveTimeout is how long since the last activity we
+	// try to keep an established discoEndpoint peering alive.
+	sessionActiveTimeout = 2 * time.Minute
+
+	// upgradeInterval is how often we try to upgrade to a better path
+	// even if we have some non-DERP route that works.
+	upgradeInterval = 1 * time.Minute
+
+	// heartbeatInterval is how often pings to the best UDP address
+	// are sent.
+	heartbeatInterval = 2 * time.Second
+
 	// discoPingInterval is the minimum time between pings
 	// to an endpoint. (Except in the case of CallMeMaybe frames
 	// resetting the counter, as the first pings likely didn't through
@@ -2648,6 +2663,10 @@ const (
 	// trustUDPAddrDuration is how long we trust a UDP address as the exclusive
 	// path (without using DERP) without having heard a Pong reply.
 	trustUDPAddrDuration = 5 * time.Second
+
+	// goodEnoughLatency is the latency at or under which we don't
+	// try to upgrade to a better path.
+	goodEnoughLatency = 5 * time.Millisecond
 )
 
 // endpointState is some state and history for a specific endpoint of
@@ -2734,15 +2753,75 @@ func (de *discoEndpoint) addrForSendLocked(now time.Time) (udpAddr, derpAddr net
 	return
 }
 
+// heartbeat is called every heartbeatInterval to keep the best UDP path alive,
+// or kick off discovery of other paths.
+func (de *discoEndpoint) heartbeat() {
+	de.mu.Lock()
+	defer de.mu.Unlock()
+
+	de.heartBeatTimer = nil
+
+	if de.lastSend.IsZero() {
+		// Shouldn't happen.
+		return
+	}
+
+	if time.Since(de.lastSend) > sessionActiveTimeout {
+		// Session's idle. Stop heartbeating.
+		de.c.logf("magicsock: disco: ending heartbeats for idle session to %v (%v)", de.publicKey.ShortString(), de.discoShort)
+		return
+	}
+
+	now := time.Now()
+	udpAddr, _ := de.addrForSendLocked(now)
+	if !udpAddr.IsZero() {
+		// We have a preferred path. Ping that every 2 seconds.
+		de.startPingLocked(udpAddr, now)
+	}
+
+	if de.wantFullPingLocked(now) {
+		de.sendPingsLocked(now, true)
+	}
+
+	de.heartBeatTimer = time.AfterFunc(heartbeatInterval, de.heartbeat)
+}
+
+// wantFullPingLocked reports whether we should ping to all our peers looking for
+// a better path.
+//
+// de.mu must be held.
+func (de *discoEndpoint) wantFullPingLocked(now time.Time) bool {
+	if de.bestAddr.IsZero() || de.lastFullPing.IsZero() {
+		return true
+	}
+	if now.After(de.trustBestAddrUntil) {
+		return true
+	}
+	if de.bestAddrLatency <= goodEnoughLatency {
+		return false
+	}
+	if now.Sub(de.lastFullPing) >= upgradeInterval {
+		return true
+	}
+	return false
+}
+
+func (de *discoEndpoint) noteActiveLocked() {
+	de.lastSend = time.Now()
+	if de.heartBeatTimer == nil {
+		de.heartBeatTimer = time.AfterFunc(heartbeatInterval, de.heartbeat)
+	}
+}
+
 func (de *discoEndpoint) send(b []byte) error {
 	now := time.Now()
 
 	de.mu.Lock()
-	de.lastSend = now
 	udpAddr, derpAddr := de.addrForSendLocked(now)
 	if udpAddr.IsZero() || now.After(de.trustBestAddrUntil) {
 		de.sendPingsLocked(now, true)
 	}
+	de.noteActiveLocked()
 	de.mu.Unlock()
 
 	if udpAddr.IsZero() && derpAddr.IsZero() {
@@ -2778,34 +2857,47 @@ func (de *discoEndpoint) removeSentPingLocked(txid stun.TxID, sp sentPing) {
 	delete(de.sentPing, txid)
 }
 
-// sendPing sends a ping with the provided txid to ep.
-// The caller should've already been recorded the ping in sentPing
-// and set up the timer.
-func (de *discoEndpoint) sendPing(ep netaddr.IPPort, txid stun.TxID) {
+// sendDiscoPing sends a ping with the provided txid to ep.
+//
+// The caller (startPingLocked) should've already been recorded the ping in
+// sentPing and set up the timer.
+func (de *discoEndpoint) sendDiscoPing(ep netaddr.IPPort, txid stun.TxID) {
 	sent, _ := de.sendDiscoMessage(ep, &disco.Ping{TxID: [12]byte(txid)})
 	if !sent {
 		de.forgetPing(txid)
 	}
 }
 
+func (de *discoEndpoint) startPingLocked(ep netaddr.IPPort, now time.Time) {
+	st, ok := de.endpointState[ep]
+	if !ok {
+		// Shouldn't happen. But don't ping an endpoint that's
+		// not active for us.
+		de.c.logf("magicsock: disco: [unexpected] attempt to ping no longer live endpoint %v", ep)
+		return
+	}
+	st.lastPing = now
+
+	txid := stun.NewTxID()
+	de.sentPing[txid] = sentPing{
+		to: ep,
+		at: now,
+		timer: time.AfterFunc(pingTimeoutDuration, func() {
+			de.c.logf("magicsock: disco: timeout waiting for pong %x from %v (%v, %v)", txid[:6], ep, de.publicKey.ShortString(), de.discoShort)
+			de.forgetPing(txid)
+		}),
+	}
+	go de.sendDiscoPing(ep, txid)
+}
+
 func (de *discoEndpoint) sendPingsLocked(now time.Time, sendCallMeMaybe bool) {
+	de.lastFullPing = now
 	var sentAny bool
 	for ep, st := range de.endpointState {
 		ep := ep
 		if !st.lastPing.IsZero() && now.Sub(st.lastPing) < discoPingInterval {
 			continue
 		}
-		st.lastPing = now
-
-		txid := stun.NewTxID()
-		de.sentPing[txid] = sentPing{
-			to: ep,
-			at: now,
-			timer: time.AfterFunc(pingTimeoutDuration, func() {
-				de.c.logf("magicsock: disco: timeout waiting for pong %x from %v (%v, %v)", txid[:6], ep, de.publicKey.ShortString(), de.discoShort)
-				de.forgetPing(txid)
-			}),
-		}
 
 		firstPing := !sentAny
 		sentAny = true
@@ -2814,7 +2906,7 @@ func (de *discoEndpoint) sendPingsLocked(now time.Time, sendCallMeMaybe bool) {
 			de.c.logf("magicsock: disco: send, starting discovery for %v (%v)", de.publicKey.ShortString(), de.discoShort)
 		}
 
-		go de.sendPing(ep, txid)
+		de.startPingLocked(ep, now)
 	}
 	derpAddr := de.derpAddr
 	if sentAny && sendCallMeMaybe && !derpAddr.IsZero() {
@@ -3003,6 +3095,10 @@ func (de *discoEndpoint) cleanup() {
 	for txid, sp := range de.sentPing {
 		de.removeSentPingLocked(txid, sp)
 	}
+	if de.heartBeatTimer != nil {
+		de.heartBeatTimer.Stop()
+		de.heartBeatTimer = nil
+	}
 }
 
 // ippCache is a cache of *net.UDPAddr => netaddr.IPPort mappings.