network: request blocks when there is a ping with bigger than ours height

Turns out, C# node no longer broadcasts an Inv when it's creating a block,
instead it sends a ping and if we're not paying attention to the height
specified there we're technically missing a new block. Of course we'll get it
later after ping timer expiration and regular ping/pong sequence, but that's
delaying it for no good reason.

pkg/network/helper_test.go

@@ -286,6 +286,11 @@ func (p *localPeer) SendPing(m *Message) error {
 	_ = p.EnqueueMessage(m)
 	return nil
 }
+func (p *localPeer) HandlePing(ping *payload.Ping) error {
+	p.lastBlockIndex = ping.LastBlockIndex
+	return nil
+}
+
 func (p *localPeer) HandlePong(pong *payload.Ping) error {
 	p.lastBlockIndex = pong.LastBlockIndex
 	p.pingSent--

pkg/network/peer.go

@@ -67,6 +67,9 @@ type Peer interface {
 	HandleVersion(*payload.Version) error
 	HandleVersionAck() error
 
+	// HandlePing checks ping contents against Peer's state and updates it.
+	HandlePing(ping *payload.Ping) error
+
 	// HandlePong checks pong contents against Peer's state and updates it.
 	HandlePong(pong *payload.Ping) error
 }

pkg/network/server.go

@@ -453,6 +453,16 @@ func (s *Server) handleBlockCmd(p Peer, block *block.Block) error {
 
 // handlePing processes ping request.
 func (s *Server) handlePing(p Peer, ping *payload.Ping) error {
+	err := p.HandlePing(ping)
+	if err != nil {
+		return err
+	}
+	if s.chain.BlockHeight() < ping.LastBlockIndex {
+		err = s.requestBlocks(p)
+		if err != nil {
+			return err
+		}
+	}
 	return p.EnqueueP2PMessage(NewMessage(CMDPong, payload.NewPing(s.chain.BlockHeight(), s.id)))
 }
 

pkg/network/tcp_peer.go

@@ -431,6 +431,14 @@ func (p *TCPPeer) SendPing(msg *Message) error {
 	return p.EnqueueMessage(msg)
 }
 
+// HandlePing handles a ping message received from the peer.
+func (p *TCPPeer) HandlePing(ping *payload.Ping) error {
+	p.lock.Lock()
+	defer p.lock.Unlock()
+	p.lastBlockIndex = ping.LastBlockIndex
+	return nil
+}
+
 // 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 {