From 806b89db76659fdd542d73196e9fa79e9aadff81 Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Mon, 21 Sep 2020 21:46:40 +0300
Subject: [PATCH] state: store the length of NEP5TransferLog in the first byte

We lose `size` field after serialization/deserialization which can lead to
adding more than NEP5TransferBatchSize elements into the NEP5TransferLog.
---
 pkg/core/dao/cacheddao.go |  2 +-
 pkg/core/dao/dao.go       |  4 +---
 pkg/core/state/nep5.go    | 20 +++++++++++++++-----
 3 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/pkg/core/dao/cacheddao.go b/pkg/core/dao/cacheddao.go
index 8c8bf1aa6..9cfa8992e 100644
--- a/pkg/core/dao/cacheddao.go
+++ b/pkg/core/dao/cacheddao.go
@@ -95,7 +95,7 @@ func (cd *Cached) AppendNEP5Transfer(acc util.Uint160, index uint32, tr *state.N
 	if err := lg.Append(tr); err != nil {
 		return false, err
 	}
-	return lg.Size() >= nep5TransferBatchSize, cd.PutNEP5TransferLog(acc, index, lg)
+	return lg.Size() >= state.NEP5TransferBatchSize, cd.PutNEP5TransferLog(acc, index, lg)
 }
 
 // Persist flushes all the changes made into the (supposedly) persistent
diff --git a/pkg/core/dao/dao.go b/pkg/core/dao/dao.go
index af746cef4..f4fa5050d 100644
--- a/pkg/core/dao/dao.go
+++ b/pkg/core/dao/dao.go
@@ -208,8 +208,6 @@ func (dao *Simple) putNEP5Balances(acc util.Uint160, bs *state.NEP5Balances, buf
 
 // -- start transfer log.
 
-const nep5TransferBatchSize = 128
-
 func getNEP5TransferLogKey(acc util.Uint160, index uint32) []byte {
 	key := make([]byte, 1+util.Uint160Size+4)
 	key[0] = byte(storage.STNEP5Transfers)
@@ -250,7 +248,7 @@ func (dao *Simple) AppendNEP5Transfer(acc util.Uint160, index uint32, tr *state.
 	if err := lg.Append(tr); err != nil {
 		return false, err
 	}
-	return lg.Size() >= nep5TransferBatchSize, dao.PutNEP5TransferLog(acc, index, lg)
+	return lg.Size() >= state.NEP5TransferBatchSize, dao.PutNEP5TransferLog(acc, index, lg)
 }
 
 // -- end transfer log.
diff --git a/pkg/core/state/nep5.go b/pkg/core/state/nep5.go
index b3dc38715..9679ab57e 100644
--- a/pkg/core/state/nep5.go
+++ b/pkg/core/state/nep5.go
@@ -8,6 +8,9 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/util"
 )
 
+// NEP5TransferBatchSize is the maximum number of entries for NEP5TransferLog.
+const NEP5TransferBatchSize = 128
+
 // NEP5Tracker contains info about a single account in a NEP5 contract.
 type NEP5Tracker struct {
 	// Balance is the current balance of the account.
@@ -20,8 +23,6 @@ type NEP5Tracker struct {
 // NEP5TransferLog is a log of NEP5 token transfers for the specific command.
 type NEP5TransferLog struct {
 	Raw []byte
-	// size is the number of NEP5Transfers written into Raw
-	size int
 }
 
 // NEP5Transfer represents a single NEP5 Transfer event.
@@ -85,12 +86,18 @@ func (bs *NEP5Balances) EncodeBinary(w *io.BinWriter) {
 // Append appends single transfer to a log.
 func (lg *NEP5TransferLog) Append(tr *NEP5Transfer) error {
 	w := io.NewBufBinWriter()
+	// The first entry, set up counter.
+	if len(lg.Raw) == 0 {
+		w.WriteB(1)
+	}
 	tr.EncodeBinary(w.BinWriter)
 	if w.Err != nil {
 		return w.Err
 	}
+	if len(lg.Raw) != 0 {
+		lg.Raw[0]++
+	}
 	lg.Raw = append(lg.Raw, w.Bytes()...)
-	lg.size++
 	return nil
 }
 
@@ -101,7 +108,7 @@ func (lg *NEP5TransferLog) ForEach(f func(*NEP5Transfer) error) error {
 	}
 	tr := new(NEP5Transfer)
 	var bytesRead int
-	for i := 0; i < len(lg.Raw); i += bytesRead {
+	for i := 1; i < len(lg.Raw); i += bytesRead {
 		r := io.NewBinReaderFromBuf(lg.Raw[i:])
 		bytesRead = tr.DecodeBinaryReturnCount(r)
 		if r.Err != nil {
@@ -115,7 +122,10 @@ func (lg *NEP5TransferLog) ForEach(f func(*NEP5Transfer) error) error {
 
 // Size returns an amount of transfer written in log.
 func (lg *NEP5TransferLog) Size() int {
-	return lg.size
+	if len(lg.Raw) == 0 {
+		return 0
+	}
+	return int(lg.Raw[0])
 }
 
 // EncodeBinary implements io.Serializable interface.