From 686f983ccf54630f1c74989a34f701d96bac78b5 Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Fri, 5 Feb 2021 14:54:43 +0300
Subject: [PATCH] network: prevent disconnects during initial sync

Node receiving extensible payload from the future is confused and drops
connection. Note that this can still happen if the node is to loose its
synchrony.

Calling `IsInSync()` is quite expensive, so we stop doing that once synchrony
is reached (hence bool flag).
---
 pkg/network/server.go | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/pkg/network/server.go b/pkg/network/server.go
index e2be7b021..c915f45f0 100644
--- a/pkg/network/server.go
+++ b/pkg/network/server.go
@@ -86,6 +86,7 @@ type (
 		transactions chan *transaction.Transaction
 
 		consensusStarted *atomic.Bool
+		canHandleExtens  *atomic.Bool
 
 		oracle *oracle.Oracle
 
@@ -131,6 +132,7 @@ func newServerFromConstructors(config ServerConfig, chain blockchainer.Blockchai
 		unregister:        make(chan peerDrop),
 		peers:             make(map[Peer]bool),
 		consensusStarted:  atomic.NewBool(false),
+		canHandleExtens:   atomic.NewBool(false),
 		extensiblePool:    extpool.New(chain),
 		log:               log,
 		transactions:      make(chan *transaction.Transaction, 64),
@@ -786,6 +788,12 @@ func (s *Server) handleGetHeadersCmd(p Peer, gh *payload.GetBlockByIndex) error
 
 // handleExtensibleCmd processes received extensible payload.
 func (s *Server) handleExtensibleCmd(e *payload.Extensible) error {
+	if !s.canHandleExtens.Load() {
+		if !s.IsInSync() {
+			return nil
+		}
+		s.canHandleExtens.Store(true)
+	}
 	ok, err := s.extensiblePool.Add(e)
 	if err != nil {
 		return err