network/config: redesign ping timeout handling a bit

1) Make timeout a timeout, don't do magic ping counts.
2) Drop additional timer from the main peer's protocol loop, create it
   dynamically and make it disconnect the peer.
3) Don't expose the ping counter to the outside, handle more logic inside the
   Peer.

Relates to #430.

pkg/network/tcp_peer.go

@@ -25,7 +25,9 @@ const (
 )
 
 var (
-	errStateMismatch = errors.New("tried to send protocol message before handshake completed")
+	errStateMismatch  = errors.New("tried to send protocol message before handshake completed")
+	errPingPong       = errors.New("ping/pong timeout")
+	errUnexpectedPong = errors.New("pong message wasn't expected")
 )
 
 // TCPPeer represents a connected remote node in the
@@ -51,7 +53,8 @@ type TCPPeer struct {
 	wg sync.WaitGroup
 
 	// number of sent pings.
-	pingSent int
+	pingSent  int
+	pingTimer *time.Timer
 }
 
 // NewTCPPeer returns a TCPPeer structure based on the given connection.
@@ -191,7 +194,6 @@ func (p *TCPPeer) StartProtocol() {
 	}
 
 	timer := time.NewTimer(p.server.ProtoTickInterval)
-	pingTimer := time.NewTimer(p.server.PingTimeout)
 	for {
 		select {
 		case <-p.done:
@@ -210,20 +212,12 @@ func (p *TCPPeer) StartProtocol() {
 			} else {
 				diff := time.Now().UTC().Unix() - p.server.getLastBlockTime()
 				if diff > int64(p.server.PingInterval/time.Second) {
-					p.UpdatePingSent(p.GetPingSent() + 1)
-					err = p.EnqueueMessage(NewMessage(p.server.Net, CMDPing, payload.NewPing(p.server.id, p.server.chain.HeaderHeight())))
+					err = p.SendPing()
 				}
 			}
 			if err == nil {
 				timer.Reset(p.server.ProtoTickInterval)
 			}
-		case <-pingTimer.C:
-			if p.GetPingSent() > defaultPingLimit {
-				err = errors.New("ping/pong timeout")
-			} else {
-				pingTimer.Reset(p.server.PingTimeout)
-				p.UpdatePingSent(0)
-			}
 		}
 		if err != nil {
 			timer.Stop()
@@ -350,23 +344,33 @@ func (p *TCPPeer) LastBlockIndex() uint32 {
 	return p.lastBlockIndex
 }
 
-// UpdateLastBlockIndex updates last block index.
-func (p *TCPPeer) UpdateLastBlockIndex(newIndex uint32) {
+// SendPing sends a ping message to the peer and does appropriate accounting of
+// outstanding pings and timeouts.
+func (p *TCPPeer) SendPing() error {
 	p.lock.Lock()
-	defer p.lock.Unlock()
-	p.lastBlockIndex = newIndex
+	p.pingSent++
+	if p.pingTimer == nil {
+		p.pingTimer = time.AfterFunc(p.server.PingTimeout, func() {
+			p.Disconnect(errPingPong)
+		})
+	}
+	p.lock.Unlock()
+	return p.EnqueueMessage(NewMessage(p.server.Net, CMDPing, payload.NewPing(p.server.id, p.server.chain.HeaderHeight())))
 }
 
-// GetPingSent returns flag whether ping was sent or not.
-func (p *TCPPeer) GetPingSent() int {
-	p.lock.RLock()
-	defer p.lock.RUnlock()
-	return p.pingSent
-}
-
-// UpdatePingSent updates pingSent value.
-func (p *TCPPeer) UpdatePingSent(newValue int) {
+// HandlePong handles a pong message received from the peer and does appropriate
+// accounting of outstanding pings and timeouts.
+func (p *TCPPeer) HandlePong(pong *payload.Ping) error {
 	p.lock.Lock()
 	defer p.lock.Unlock()
-	p.pingSent = newValue
+	if p.pingTimer != nil && !p.pingTimer.Stop() {
+		return errPingPong
+	}
+	p.pingTimer = nil
+	p.pingSent--
+	if p.pingSent < 0 {
+		return errUnexpectedPong
+	}
+	p.lastBlockIndex = pong.LastBlockIndex
+	return nil
 }