From 62092c703d20874eb93711b33482cd68843a775f Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Mon, 20 Jan 2020 17:39:59 +0300
Subject: [PATCH] network: use local timestamp to decide when to ping

We don't and we won't have synchronized clocks in the network so the only
timestamp that we can compare our local time with is the one made
ourselves. What this ping mechanism is used for is to recover from missing the
block broadcast, thus it's appropriate for it to trigger after X seconds of
the local time since the last block received.

Relates to #430.
---
 pkg/network/server.go   | 10 ++++++++++
 pkg/network/tcp_peer.go | 13 ++++---------
 2 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/pkg/network/server.go b/pkg/network/server.go
index cf11d1df6..6c98ed665 100644
--- a/pkg/network/server.go
+++ b/pkg/network/server.go
@@ -68,6 +68,8 @@ type (
 		quit       chan struct{}
 
 		connected *atomic.Bool
+		// Time of the last block receival.
+		lastBlockTS *atomic.Int64
 
 		log *zap.Logger
 	}
@@ -101,6 +103,7 @@ func NewServer(config ServerConfig, chain core.Blockchainer, log *zap.Logger) *S
 		unregister:   make(chan peerDrop),
 		peers:        make(map[Peer]bool),
 		connected:    atomic.NewBool(false),
+		lastBlockTS:  atomic.NewInt64(0),
 		log:          log,
 	}
 
@@ -359,6 +362,7 @@ func (s *Server) handleHeadersCmd(p Peer, headers *payload.Headers) {
 
 // handleBlockCmd processes the received block received from its peer.
 func (s *Server) handleBlockCmd(p Peer, block *block.Block) error {
+	s.lastBlockTS.Store(time.Now().UTC().Unix())
 	return s.bQueue.putBlock(block)
 }
 
@@ -658,6 +662,12 @@ func (s *Server) handleNewPayload(p *consensus.Payload) {
 	s.relayInventoryCmd(CMDInv, payload.ConsensusType, p.Hash())
 }
 
+// getLastBlockTime returns unix timestamp for the moment when the last block
+// was received.
+func (s *Server) getLastBlockTime() int64 {
+	return s.lastBlockTS.Load()
+}
+
 func (s *Server) requestTx(hashes ...util.Uint256) {
 	if len(hashes) == 0 {
 		return
diff --git a/pkg/network/tcp_peer.go b/pkg/network/tcp_peer.go
index 2c408b22d..329a51130 100644
--- a/pkg/network/tcp_peer.go
+++ b/pkg/network/tcp_peer.go
@@ -208,15 +208,10 @@ func (p *TCPPeer) StartProtocol() {
 			if p.LastBlockIndex() > p.server.chain.BlockHeight() {
 				err = p.server.requestBlocks(p)
 			} else {
-				block, errGetBlock := p.server.chain.GetBlock(p.server.chain.CurrentBlockHash())
-				if errGetBlock != nil {
-					err = errGetBlock
-				} else {
-					diff := uint32(time.Now().UTC().Unix()) - block.Timestamp
-					if diff > uint32(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())))
-					}
+				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())))
 				}
 			}
 			if err == nil {