From 43b28ffa06205406cc5f416f94a0fe653215b248 Mon Sep 17 00:00:00 2001
From: Anna Shaleva <shaleva.ann@nspcc.ru>
Date: Thu, 9 Jul 2020 10:41:53 +0300
Subject: [PATCH] core: get rid of NEP5TransferSize

Part of #1133

It will help us to use big.Int to store amount of NEP5 tokens. As far as
big.Int doesn't have constant size, we shouldn't use `NEP5TransferSize`
constant anymore.
---
 pkg/core/state/nep5.go      | 22 ++++++++++++++--------
 pkg/core/state/nep5_test.go |  8 +++++++-
 2 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/pkg/core/state/nep5.go b/pkg/core/state/nep5.go
index a0631dd09..ee552af7e 100644
--- a/pkg/core/state/nep5.go
+++ b/pkg/core/state/nep5.go
@@ -17,11 +17,10 @@ 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
 }
 
-// NEP5TransferSize is a size of a marshaled NEP5Transfer struct in bytes.
-const NEP5TransferSize = util.Uint160Size*3 + 8 + 4 + 8 + util.Uint256Size
-
 // NEP5Transfer represents a single NEP5 Transfer event.
 type NEP5Transfer struct {
 	// Asset is a NEP5 contract hash.
@@ -89,6 +88,7 @@ func (lg *NEP5TransferLog) Append(tr *NEP5Transfer) error {
 		return w.Err
 	}
 	lg.Raw = append(lg.Raw, w.Bytes()...)
+	lg.size++
 	return nil
 }
 
@@ -98,9 +98,10 @@ func (lg *NEP5TransferLog) ForEach(f func(*NEP5Transfer) error) error {
 		return nil
 	}
 	tr := new(NEP5Transfer)
-	for i := 0; i < len(lg.Raw); i += NEP5TransferSize {
-		r := io.NewBinReaderFromBuf(lg.Raw[i : i+NEP5TransferSize])
-		tr.DecodeBinary(r)
+	var bytesRead int
+	for i := 0; 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 {
@@ -112,7 +113,7 @@ func (lg *NEP5TransferLog) ForEach(f func(*NEP5Transfer) error) error {
 
 // Size returns an amount of transfer written in log.
 func (lg *NEP5TransferLog) Size() int {
-	return len(lg.Raw) / NEP5TransferSize
+	return lg.size
 }
 
 // EncodeBinary implements io.Serializable interface.
@@ -128,7 +129,6 @@ func (t *NEP5Tracker) DecodeBinary(r *io.BinReader) {
 }
 
 // EncodeBinary implements io.Serializable interface.
-// Note: change NEP5TransferSize constant when changing this function.
 func (t *NEP5Transfer) EncodeBinary(w *io.BinWriter) {
 	w.WriteBytes(t.Asset[:])
 	w.WriteBytes(t.Tx[:])
@@ -141,6 +141,11 @@ func (t *NEP5Transfer) EncodeBinary(w *io.BinWriter) {
 
 // DecodeBinary implements io.Serializable interface.
 func (t *NEP5Transfer) DecodeBinary(r *io.BinReader) {
+	_ = t.DecodeBinaryReturnCount(r)
+}
+
+// DecodeBinaryReturnCount decodes NEP5Transfer and returns the number of bytes read.
+func (t *NEP5Transfer) DecodeBinaryReturnCount(r *io.BinReader) int {
 	r.ReadBytes(t.Asset[:])
 	r.ReadBytes(t.Tx[:])
 	r.ReadBytes(t.From[:])
@@ -148,4 +153,5 @@ func (t *NEP5Transfer) DecodeBinary(r *io.BinReader) {
 	t.Block = r.ReadU32LE()
 	t.Timestamp = r.ReadU64LE()
 	t.Amount = int64(r.ReadU64LE())
+	return util.Uint160Size*3 + 8 + 4 + 8 + util.Uint256Size
 }
diff --git a/pkg/core/state/nep5_test.go b/pkg/core/state/nep5_test.go
index 543d05819..d95dbc3ff 100644
--- a/pkg/core/state/nep5_test.go
+++ b/pkg/core/state/nep5_test.go
@@ -64,7 +64,13 @@ func TestNEP5Transfer_DecodeBinary(t *testing.T) {
 func TestNEP5TransferSize(t *testing.T) {
 	tr := randomTransfer(rand.New(rand.NewSource(0)))
 	size := io.GetVarSize(tr)
-	require.EqualValues(t, NEP5TransferSize, size)
+	w := io.NewBufBinWriter()
+	tr.EncodeBinary(w.BinWriter)
+	require.NoError(t, w.Err)
+	r := io.NewBinReaderFromBuf(w.Bytes())
+	actualTr := &NEP5Transfer{}
+	actual := actualTr.DecodeBinaryReturnCount(r)
+	require.EqualValues(t, actual, size)
 }
 
 func randomTransfer(r *rand.Rand) *NEP5Transfer {