[codec] Add ShortBytes type (#563)

* working on test

* add shortBytes implementation

* use const in const

* wrap with int

* add short bytes helpers

* add license header

codec/errors.go

@@ -10,4 +10,5 @@ var (
 	ErrDuplicateItem     = errors.New("duplicate item")
 	ErrFieldNotPopulated = errors.New("field is not populated")
 	ErrInvalidBitset     = errors.New("invalid bitset")
+	ErrTooLarge          = errors.New("too large")
 )

codec/packer.go

@@ -72,10 +72,29 @@ func (p *Packer) PackFixedBytes(b []byte) {
 	p.p.PackFixedBytes(b)
 }
 
+func (p *Packer) PackShortBytes(b ShortBytes) {
+	l := len(b)
+	if l > ShortBytesMaxSize {
+		p.addErr(fmt.Errorf("%w: ShortBytes is too large (found=%d)", ErrTooLarge, len(b)))
+		return
+	}
+	p.PackByte(uint8(l))
+	p.PackFixedBytes(b)
+}
+
 func (p *Packer) PackBytes(b []byte) {
 	p.p.PackBytes(b)
 }
 
+func (p *Packer) UnpackFixedBytes(size int, dest *[]byte) {
+	copy((*dest), p.p.UnpackFixedBytes(size))
+}
+
+func (p *Packer) UnpackShortBytes(dest *ShortBytes) {
+	l := int(p.p.UnpackByte())
+	*dest = p.p.UnpackFixedBytes(l)
+}
+
 // UnpackBytes unpacks [limit] bytes into [dest]. Otherwise
 // if [limit] >= 0, UnpackBytes unpacks a byte slice array into [dest]. If
 // [required] is set to true and the amount of bytes written to [dest] is 0,
@@ -91,10 +110,6 @@ func (p *Packer) UnpackBytes(limit int, required bool, dest *[]byte) {
 	}
 }
 
-func (p *Packer) UnpackFixedBytes(size int, dest *[]byte) {
-	copy((*dest), p.p.UnpackFixedBytes(size))
-}
-
 func (p *Packer) PackUint64(v uint64) {
 	p.p.PackLong(v)
 }

codec/packer_test.go

@@ -53,6 +53,7 @@ func TestPackerPublicKey(t *testing.T) {
 	copy(pubKey[:], TestPublicKey)
 	t.Run("Pack", func(t *testing.T) {
 		// Pack
+		require.Len(pubKey, ed25519.PublicKeyLen)
 		wp.PackPublicKey(pubKey)
 		require.Equal(TestPublicKey, wp.Bytes(), "PublicKey not packed correctly.")
 		require.NoError(wp.Err(), "Error packing PublicKey.")
@@ -153,6 +154,36 @@ func TestPackerWindow(t *testing.T) {
 	})
 }
 
+func TestPackerShortBytes(t *testing.T) {
+	require := require.New(t)
+	t.Run("Pack Too Large", func(t *testing.T) {
+		wp := NewWriter(1024, 1024)
+		wp.PackShortBytes(make([]byte, 1024))
+		require.ErrorIs(wp.Err(), ErrTooLarge)
+	})
+	wp := NewWriter(ed25519.PublicKeyLen+1, ed25519.PublicKeyLen+1)
+	pubKey := make(ShortBytes, ed25519.PublicKeyLen)
+	copy(pubKey[:], TestPublicKey)
+	t.Run("Pack", func(t *testing.T) {
+		// Pack
+		wp.PackShortBytes(pubKey)
+		b := wp.Bytes()
+		require.NoError(wp.Err(), "Error packing PublicKey.")
+		require.Len(b, ed25519.PublicKeyLen+1)
+		require.Equal(uint8(ed25519.PublicKeyLen), b[0], "PublicKeyLen not packed correctly.")
+		require.Equal(TestPublicKey, b[1:], "PublicKey not packed correctly.")
+	})
+	t.Run("Unpack", func(t *testing.T) {
+		// Unpack
+		rp := NewReader(wp.Bytes(), ed25519.PublicKeyLen+1)
+		require.Equal(wp.Bytes(), rp.Bytes(), "Reader not initialized correctly.")
+		var unpackedPubKey ShortBytes
+		rp.UnpackShortBytes(&unpackedPubKey)
+		require.Equal(pubKey, unpackedPubKey, "UnpackPublicKey unpacked incorrectly.")
+		require.NoError(rp.Err(), "UnpackPublicKey set an error.")
+	})
+}
+
 func TestNewReader(t *testing.T) {
 	require := require.New(t)
 	vInt := 900

codec/types.go

@@ -0,0 +1,10 @@
+// Copyright (C) 2023, Ava Labs, Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package codec
+
+import "github.com/ava-labs/hypersdk/consts"
+
+const ShortBytesMaxSize = int(consts.MaxUint8)
+
+type ShortBytes []byte

codec/utils.go

@@ -17,6 +17,14 @@ func CummSize[T SizeType](arr []T) int {
 	return size
 }
 
+func ShortBytesLen(msg []byte) int {
+	return consts.ByteLen + len(msg)
+}
+
+func ShortBytesLenSize(msgSize int) int {
+	return consts.ByteLen + msgSize
+}
+
 func BytesLen(msg []byte) int {
 	return consts.IntLen + len(msg)
 }