transaction: avoid reencoding and reading what can't be read

name               old time/op    new time/op    delta
DecodeFromBytes-8    1.79µs ± 2%    1.46µs ± 4%  -18.44%  (p=0.000 n=10+10)

name               old alloc/op   new alloc/op   delta
DecodeFromBytes-8      800B ± 0%      624B ± 0%  -22.00%  (p=0.000 n=10+10)

name               old allocs/op  new allocs/op  delta
DecodeFromBytes-8      10.0 ± 0%       8.0 ± 0%  -20.00%  (p=0.000 n=10+10)

pkg/core/transaction/transaction.go

@@ -130,7 +130,12 @@ func (t *Transaction) GetAttributes(typ AttrType) []Attribute {
 
 // decodeHashableFields decodes the fields that are used for signing the
 // transaction, which are all fields except the scripts.
-func (t *Transaction) decodeHashableFields(br *io.BinReader) {
+func (t *Transaction) decodeHashableFields(br *io.BinReader, buf []byte) {
+	var start, end int
+
+	if buf != nil {
+		start = len(buf) - br.Len()
+	}
 	t.Version = uint8(br.ReadB())
 	t.Nonce = br.ReadU32LE()
 	t.SystemFee = int64(br.ReadU64LE())
@@ -164,10 +169,14 @@ func (t *Transaction) decodeHashableFields(br *io.BinReader) {
 	if br.Err == nil {
 		br.Err = t.isValid()
 	}
+	if buf != nil {
+		end = len(buf) - br.Len()
+		t.hash = hash.Sha256(buf[start:end])
+	}
 }
 
-func (t *Transaction) decodeBinaryNoSize(br *io.BinReader) {
-	t.decodeHashableFields(br)
+func (t *Transaction) decodeBinaryNoSize(br *io.BinReader, buf []byte) {
+	t.decodeHashableFields(br, buf)
 	if br.Err != nil {
 		return
 	}
@@ -186,14 +195,14 @@ func (t *Transaction) decodeBinaryNoSize(br *io.BinReader) {
 
 	// Create the hash of the transaction at decode, so we dont need
 	// to do it anymore.
-	if br.Err == nil {
+	if br.Err == nil && buf == nil {
 		br.Err = t.createHash()
 	}
 }
 
 // DecodeBinary implements Serializable interface.
 func (t *Transaction) DecodeBinary(br *io.BinReader) {
-	t.decodeBinaryNoSize(br)
+	t.decodeBinaryNoSize(br, nil)
 
 	if br.Err == nil {
 		_ = t.Size()
@@ -258,18 +267,15 @@ func (t *Transaction) createHash() error {
 // DecodeHashableFields decodes a part of transaction which should be hashed.
 func (t *Transaction) DecodeHashableFields(buf []byte) error {
 	r := io.NewBinReaderFromBuf(buf)
-	t.decodeHashableFields(r)
+	t.decodeHashableFields(r, buf)
 	if r.Err != nil {
 		return r.Err
 	}
 	// Ensure all the data was read.
-	_ = r.ReadB()
-	if r.Err == nil {
+	if r.Len() != 0 {
 		return errors.New("additional data after the signed part")
 	}
 	t.Scripts = make([]Witness, 0)
-
-	t.hash = hash.Sha256(buf)
 	return nil
 }
 
@@ -287,12 +293,11 @@ func (t *Transaction) Bytes() []byte {
 func NewTransactionFromBytes(b []byte) (*Transaction, error) {
 	tx := &Transaction{}
 	r := io.NewBinReaderFromBuf(b)
-	tx.decodeBinaryNoSize(r)
+	tx.decodeBinaryNoSize(r, b)
 	if r.Err != nil {
 		return nil, r.Err
 	}
-	_ = r.ReadB()
-	if r.Err == nil {
+	if r.Len() != 0 {
 		return nil, errors.New("additional data after the transaction")
 	}
 	tx.size = len(b)

pkg/core/transaction/transaction_test.go

@@ -97,6 +97,11 @@ func TestNewTransactionFromBytes(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, tx, tx1)
 
+	tx2 := new(Transaction)
+	err = testserdes.DecodeBinary(data, tx2)
+	require.NoError(t, err)
+	require.Equal(t, tx1, tx2)
+
 	data = append(data, 42)
 	_, err = NewTransactionFromBytes(data)
 	require.Error(t, err)

pkg/io/binaryReader.go

@@ -31,6 +31,17 @@ func NewBinReaderFromBuf(b []byte) *BinReader {
 	return NewBinReaderFromIO(r)
 }
 
+// Len returns the number of bytes of the unread portion of the buffer if
+// reading from bytes.Reader or -1 otherwise.
+func (r *BinReader) Len() int {
+	var res = -1
+	byteReader, ok := r.r.(*bytes.Reader)
+	if ok {
+		res = byteReader.Len()
+	}
+	return res
+}
+
 // ReadU64LE reads a little-endian encoded uint64 value from the underlying
 // io.Reader. On read failures it returns zero.
 func (r *BinReader) ReadU64LE() uint64 {

pkg/network/payload/notary_request.go

@@ -29,8 +29,7 @@ func NewP2PNotaryRequestFromBytes(b []byte) (*P2PNotaryRequest, error) {
 	if br.Err != nil {
 		return nil, br.Err
 	}
-	_ = br.ReadB()
-	if br.Err == nil {
+	if br.Len() != 0 {
 		return nil, errors.New("additional data after the payload")
 	}
 	return req, nil