From 373c669c6a7e8e7d03abff3c78903560706da113 Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Tue, 8 Sep 2020 12:57:45 +0300
Subject: [PATCH] core/state: reverse the order of ForEachTransfer

When using limits we're usually concerned about the most recent
transfers. Returning 3 transfers from the middle of the chain isn't very
helpful.
---
 pkg/core/blockchain.go      |  4 ++--
 pkg/core/state/nep5.go      | 22 ++++++++++++----------
 pkg/core/state/nep5_test.go |  4 ++--
 3 files changed, 16 insertions(+), 14 deletions(-)

diff --git a/pkg/core/blockchain.go b/pkg/core/blockchain.go
index b6582c6a4..a8c9f0e6d 100644
--- a/pkg/core/blockchain.go
+++ b/pkg/core/blockchain.go
@@ -789,8 +789,8 @@ func (bc *Blockchain) ForEachNEP5Transfer(acc util.Uint160, f func(*state.NEP5Tr
 	if err != nil {
 		return nil
 	}
-	for i := uint32(0); i <= balances.NextTransferBatch; i++ {
-		lg, err := bc.dao.GetNEP5TransferLog(acc, i)
+	for i := int(balances.NextTransferBatch); i >= 0; i-- {
+		lg, err := bc.dao.GetNEP5TransferLog(acc, uint32(i))
 		if err != nil {
 			return nil
 		}
diff --git a/pkg/core/state/nep5.go b/pkg/core/state/nep5.go
index a19f571ad..dce048e0b 100644
--- a/pkg/core/state/nep5.go
+++ b/pkg/core/state/nep5.go
@@ -103,18 +103,20 @@ func (lg *NEP5TransferLog) Append(tr *NEP5Transfer) error {
 
 // ForEach iterates over transfer log returning on first error.
 func (lg *NEP5TransferLog) ForEach(f func(*NEP5Transfer) error) error {
-	if lg == nil {
+	if lg == nil || len(lg.Raw) == 0 {
 		return nil
 	}
-	tr := new(NEP5Transfer)
-	var bytesRead int
-	for i := 1; i < len(lg.Raw); i += bytesRead {
-		r := io.NewBinReaderFromBuf(lg.Raw[i:])
-		bytesRead = tr.DecodeBinaryReturnCount(r)
-		if r.Err != nil {
-			return r.Err
-		} else if err := f(tr); err != nil {
-			return nil
+	transfers := make([]NEP5Transfer, lg.Size())
+	r := io.NewBinReaderFromBuf(lg.Raw[1:])
+	for i := 0; i < lg.Size(); i++ {
+		transfers[i].DecodeBinary(r)
+	}
+	if r.Err != nil {
+		return r.Err
+	}
+	for i := len(transfers) - 1; i >= 0; i-- {
+		if err := f(&transfers[i]); err != nil {
+			return err
 		}
 	}
 	return nil
diff --git a/pkg/core/state/nep5_test.go b/pkg/core/state/nep5_test.go
index 507e848c0..06012c31d 100644
--- a/pkg/core/state/nep5_test.go
+++ b/pkg/core/state/nep5_test.go
@@ -29,10 +29,10 @@ func TestNEP5TransferLog_Append(t *testing.T) {
 
 	require.Equal(t, len(expected), lg.Size())
 
-	i := 0
+	i := len(expected) - 1
 	err := lg.ForEach(func(tr *NEP5Transfer) error {
 		require.Equal(t, expected[i], tr)
-		i++
+		i--
 		return nil
 	})
 	require.NoError(t, err)