Add predicate packing helper

Author: aaronbuchwald

utils/bytes.go

@@ -3,8 +3,6 @@
 
 package utils
 
-import "github.com/ethereum/go-ethereum/common"
-
 // IncrOne increments bytes value by one
 func IncrOne(bytes []byte) {
 	index := len(bytes) - 1
@@ -18,27 +16,3 @@ func IncrOne(bytes []byte) {
 		}
 	}
 }
-
-// HashSliceToBytes serializes a []common.Hash into a tightly packed byte array.
-func HashSliceToBytes(hashes []common.Hash) []byte {
-	bytes := make([]byte, common.HashLength*len(hashes))
-	for i, hash := range hashes {
-		copy(bytes[i*common.HashLength:], hash[:])
-	}
-	return bytes
-}
-
-// BytesToHashSlice packs [b] into a slice of hash values with zero padding
-// to the right if the length of b is not a multiple of 32.
-func BytesToHashSlice(b []byte) []common.Hash {
-	var (
-		numHashes = (len(b) + 31) / 32
-		hashes    = make([]common.Hash, numHashes)
-	)
-
-	for i := range hashes {
-		start := i * common.HashLength
-		copy(hashes[i][:], b[start:])
-	}
-	return hashes
-}

utils/bytes_test.go

@@ -4,13 +4,10 @@
 package utils
 
 import (
-	"bytes"
 	"testing"
 
-	"github.com/ava-labs/avalanchego/utils"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
 )
 
 func TestIncrOne(t *testing.T) {
@@ -39,28 +36,3 @@ func TestIncrOne(t *testing.T) {
 		})
 	}
 }
-
-func testBytesToHashSlice(t testing.TB, b []byte) {
-	hashSlice := BytesToHashSlice(b)
-
-	copiedBytes := HashSliceToBytes(hashSlice)
-
-	if len(b)%32 == 0 {
-		require.Equal(t, b, copiedBytes)
-	} else {
-		require.Equal(t, b, copiedBytes[:len(b)])
-		// Require that any additional padding is all zeroes
-		padding := copiedBytes[len(b):]
-		require.Equal(t, bytes.Repeat([]byte{0x00}, len(padding)), padding)
-	}
-}
-
-func FuzzHashSliceToBytes(f *testing.F) {
-	for i := 0; i < 100; i++ {
-		f.Add(utils.RandomBytes(i))
-	}
-
-	f.Fuzz(func(t *testing.T, a []byte) {
-		testBytesToHashSlice(t, a)
-	})
-}

utils/predicate_bytes.go

@@ -0,0 +1,68 @@
+// (c) 2023, Ava Labs, Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package utils
+
+import (
+	"fmt"
+
+	"github.com/ethereum/go-ethereum/common"
+)
+
+// PredicateEndByte is used as a delimiter for the bytes packed into a precompile predicate.
+// Precompile predicates are encoded in the Access List of transactions in the access tuples
+// which means that its length must be a multiple of 32 (common.HashLength).
+// For messages with a length that does not comply to that, this delimiter is used to
+// append/remove padding.
+var PredicateEndByte = byte(0xff)
+
+// PackPredicate packs [predicate] by delimiting the actual message with [PredicateEndByte]
+// and zero padding to reach a length that is a multiple of 32.
+func PackPredicate(predicate []byte) []byte {
+	predicate = append(predicate, PredicateEndByte)
+	return common.RightPadBytes(predicate, (len(predicate)+31)/32*32)
+}
+
+// UnpackPredicate unpacks a predicate by stripping right padded zeroes, checking for the delimter,
+// ensuring there is not excess padding, and returning the original message.
+// Returns an error if it finds an incorrect encoding.
+func UnpackPredicate(paddedPredicate []byte) ([]byte, error) {
+	trimmedPredicateBytes := common.TrimRightZeroes(paddedPredicate)
+	if len(trimmedPredicateBytes) == 0 {
+		return nil, fmt.Errorf("predicate specified invalid all zero bytes: 0x%x", paddedPredicate)
+	}
+
+	if expectedPaddedLength := (len(trimmedPredicateBytes) + 31) / 32 * 32; expectedPaddedLength != len(paddedPredicate) {
+		return nil, fmt.Errorf("predicate specified invalid padding with length (%d), expected length (%d)", len(paddedPredicate), expectedPaddedLength)
+	}
+
+	if trimmedPredicateBytes[len(trimmedPredicateBytes)-1] != PredicateEndByte {
+		return nil, fmt.Errorf("invalid end delimiter")
+	}
+
+	return trimmedPredicateBytes[:len(trimmedPredicateBytes)-1], nil
+}
+
+// HashSliceToBytes serializes a []common.Hash into a tightly packed byte array.
+func HashSliceToBytes(hashes []common.Hash) []byte {
+	bytes := make([]byte, common.HashLength*len(hashes))
+	for i, hash := range hashes {
+		copy(bytes[i*common.HashLength:], hash[:])
+	}
+	return bytes
+}
+
+// BytesToHashSlice packs [b] into a slice of hash values with zero padding
+// to the right if the length of b is not a multiple of 32.
+func BytesToHashSlice(b []byte) []common.Hash {
+	var (
+		numHashes = (len(b) + 31) / 32
+		hashes    = make([]common.Hash, numHashes)
+	)
+
+	for i := range hashes {
+		start := i * common.HashLength
+		copy(hashes[i][:], b[start:])
+	}
+	return hashes
+}

utils/predicate_bytes_test.go

@@ -0,0 +1,73 @@
+// (c) 2023, Ava Labs, Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package utils
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/ava-labs/avalanchego/utils"
+	"github.com/stretchr/testify/require"
+)
+
+func testBytesToHashSlice(t testing.TB, b []byte) {
+	hashSlice := BytesToHashSlice(b)
+
+	copiedBytes := HashSliceToBytes(hashSlice)
+
+	if len(b)%32 == 0 {
+		require.Equal(t, b, copiedBytes)
+	} else {
+		require.Equal(t, b, copiedBytes[:len(b)])
+		// Require that any additional padding is all zeroes
+		padding := copiedBytes[len(b):]
+		require.Equal(t, bytes.Repeat([]byte{0x00}, len(padding)), padding)
+	}
+}
+
+func FuzzHashSliceToBytes(f *testing.F) {
+	for i := 0; i < 100; i++ {
+		f.Add(utils.RandomBytes(i))
+	}
+
+	f.Fuzz(func(t *testing.T, b []byte) {
+		testBytesToHashSlice(t, b)
+	})
+}
+
+func testPackPredicate(t testing.TB, b []byte) {
+	packedPredicate := PackPredicate(b)
+	unpackedPredicated, err := UnpackPredicate(packedPredicate)
+	require.NoError(t, err)
+	require.Equal(t, b, unpackedPredicated)
+}
+
+func FuzzPackPredicate(f *testing.F) {
+	for i := 0; i < 100; i++ {
+		f.Add(utils.RandomBytes(i))
+	}
+
+	f.Fuzz(func(t *testing.T, b []byte) {
+		testPackPredicate(t, b)
+	})
+}
+
+func FuzzUnpackInvalidPredicate(f *testing.F) {
+	// Seed the fuzzer with non-zero length padding of zeroes or non-zeroes.
+	for i := 1; i < 100; i++ {
+		f.Add(utils.RandomBytes(i))
+		f.Add(make([]byte, i))
+	}
+
+	f.Fuzz(func(t *testing.T, b []byte) {
+		// Ensure that adding the invalid padding to any length correctly packed predicate
+		// results in failing to unpack it.
+		for _, l := range []int{0, 1, 31, 32, 33, 63, 64, 65} {
+			validPredicate := PackPredicate(utils.RandomBytes(l))
+			invalidPredicate := append(validPredicate, b...)
+			_, err := UnpackPredicate(invalidPredicate)
+			require.Error(t, err)
+		}
+	})
+}