From 74f1848d192d0f54c70d863690ee12d24eb71531 Mon Sep 17 00:00:00 2001
From: Anna Shaleva <shaleva.ann@nspcc.ru>
Date: Wed, 11 Aug 2021 14:29:03 +0300
Subject: [PATCH] core: adjust LastUpdatedBlock calculation for NEP17 balances

...wrt P2PStateExchange setting.
---
 docs/rpc.md              |  6 +++++-
 pkg/core/blockchain.go   | 15 ++++++++++++++-
 pkg/rpc/server/server.go | 11 ++++++++++-
 3 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/docs/rpc.md b/docs/rpc.md
index f12a7abca..1f8763f59 100644
--- a/docs/rpc.md
+++ b/docs/rpc.md
@@ -114,7 +114,11 @@ balance won't be shown in the list of NEP17 balances returned by the neo-go node
 (unlike the C# node behavior). However, transfer logs of such token are still
 available via `getnep17transfers` RPC call.
 
-The behaviour of the `LastUpdatedBlock` tracking matches the C# node's one.
+The behaviour of the `LastUpdatedBlock` tracking for archival nodes as far as for
+governing token balances matches the C# node's one. For non-archival nodes and
+other NEP17-compliant tokens if transfer's `LastUpdatedBlock` is lower than the
+latest state synchronization point P the node working against, then
+`LastUpdatedBlock` equals P.
 
 ### Unsupported methods
 
diff --git a/pkg/core/blockchain.go b/pkg/core/blockchain.go
index 18fdf786f..1b3a99370 100644
--- a/pkg/core/blockchain.go
+++ b/pkg/core/blockchain.go
@@ -1223,12 +1223,25 @@ func (bc *Blockchain) GetNEP17Contracts() []util.Uint160 {
 }
 
 // GetNEP17LastUpdated returns a set of contract ids with the corresponding last updated
-// block indexes.
+// block indexes. In case of an empty account, latest stored state synchronisation point
+// is returned under Math.MinInt32 key.
 func (bc *Blockchain) GetNEP17LastUpdated(acc util.Uint160) (map[int32]uint32, error) {
 	info, err := bc.dao.GetNEP17TransferInfo(acc)
 	if err != nil {
 		return nil, err
 	}
+	if bc.config.P2PStateExchangeExtensions && bc.config.RemoveUntraceableBlocks {
+		if _, ok := info.LastUpdated[bc.contracts.NEO.ID]; !ok {
+			nBalance, lub := bc.contracts.NEO.BalanceOf(bc.dao, acc)
+			if nBalance.Sign() != 0 {
+				info.LastUpdated[bc.contracts.NEO.ID] = lub
+			}
+		}
+	}
+	stateSyncPoint, err := bc.dao.GetStateSyncPoint()
+	if err == nil {
+		info.LastUpdated[math.MinInt32] = stateSyncPoint
+	}
 	return info.LastUpdated, nil
 }
 
diff --git a/pkg/rpc/server/server.go b/pkg/rpc/server/server.go
index 3fa82c659..8bd2e26a3 100644
--- a/pkg/rpc/server/server.go
+++ b/pkg/rpc/server/server.go
@@ -679,6 +679,7 @@ func (s *Server) getNEP17Balances(ps request.Params) (interface{}, *response.Err
 	if err != nil {
 		return nil, response.NewRPCError("Failed to get NEP17 last updated block", err.Error(), err)
 	}
+	stateSyncPoint := lastUpdated[math.MinInt32]
 	bw := io.NewBufBinWriter()
 	for _, h := range s.chain.GetNEP17Contracts() {
 		balance, err := s.getNEP17Balance(h, u, bw)
@@ -692,10 +693,18 @@ func (s *Server) getNEP17Balances(ps request.Params) (interface{}, *response.Err
 		if cs == nil {
 			continue
 		}
+		lub, ok := lastUpdated[cs.ID]
+		if !ok {
+			cfg := s.chain.GetConfig()
+			if !cfg.P2PStateExchangeExtensions && cfg.RemoveUntraceableBlocks {
+				return nil, response.NewInternalServerError(fmt.Sprintf("failed to get LastUpdatedBlock for balance of %s token", cs.Hash.StringLE()), nil)
+			}
+			lub = stateSyncPoint
+		}
 		bs.Balances = append(bs.Balances, result.NEP17Balance{
 			Asset:       h,
 			Amount:      balance.String(),
-			LastUpdated: lastUpdated[cs.ID],
+			LastUpdated: lub,
 		})
 	}
 	return bs, nil