feat(pkg): introduce blob.go (#644)

Co-authored-by: maskpp <[email protected]>

driver/txlist_fetcher/blob.go

@@ -56,7 +56,8 @@ func (d *BlobFetcher) Fetch(
 			sha256.New(),
 			&commitment,
 		) == common.BytesToHash(meta.BlobHash[:]) {
-			return rpc.DecodeBlob(common.FromHex(sidecar.Blob))
+			blob := rpc.Blob(common.FromHex(sidecar.Blob))
+			return blob.ToData()
 		}
 	}
 

pkg/rpc/beaconclient.go

@@ -66,7 +66,8 @@ func (c *BeaconClient) GetBlobByHash(ctx context.Context, slot *big.Int, blobHas
 			sha256.New(),
 			&commitment,
 		) == blobHash {
-			return DecodeBlob(common.FromHex(sidecar.Blob))
+			blob := Blob(common.FromHex(sidecar.Blob))
+			return blob.ToData()
 		}
 	}
 

pkg/rpc/blob.go

@@ -0,0 +1,291 @@
+package rpc
+
+import (
+	"crypto/sha256"
+	"errors"
+	"fmt"
+	"reflect"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/hexutil"
+	"github.com/ethereum/go-ethereum/crypto/kzg4844"
+)
+
+// Taken from:
+// https://github.com/ethereum-optimism/optimism/blob/develop/op-service/eth/blob.go
+const (
+	BlobSize          = 4096 * 32
+	MaxBlobDataSize   = (4*31+3)*1024 - 4
+	EncodingVersion   = 0
+	VersionOffset     = 1    // offset of the version byte in the blob encoding
+	Rounds            = 1024 // number of encode/decode rounds
+	BlobTxHashVersion = 0x01 // Version byte of the commitment hash
+)
+
+type Data = hexutil.Bytes
+
+var (
+	ErrBlobInvalidFieldElement        = errors.New("invalid field element")
+	ErrBlobInvalidEncodingVersion     = errors.New("invalid encoding version")
+	ErrBlobInvalidLength              = errors.New("invalid length for blob")
+	ErrBlobInputTooLarge              = errors.New("too much data to encode in one blob")
+	ErrBlobExtraneousData             = errors.New("non-zero data encountered where blob should be empty")
+	ErrBlobExtraneousDataFieldElement = errors.New("non-zero data encountered where field element should be empty")
+)
+
+type Blob [BlobSize]byte
+
+func (b *Blob) KZGBlob() *kzg4844.Blob {
+	return (*kzg4844.Blob)(b)
+}
+
+func (b *Blob) UnmarshalJSON(text []byte) error {
+	return hexutil.UnmarshalFixedJSON(reflect.TypeOf(b), text, b[:])
+}
+
+func (b *Blob) UnmarshalText(text []byte) error {
+	return hexutil.UnmarshalFixedText("Bytes32", text, b[:])
+}
+
+func (b *Blob) MarshalText() ([]byte, error) {
+	return hexutil.Bytes(b[:]).MarshalText()
+}
+
+func (b *Blob) String() string {
+	return hexutil.Encode(b[:])
+}
+
+// TerminalString implements log.TerminalStringer, formatting a string for console
+// output during logging.
+func (b *Blob) TerminalString() string {
+	return fmt.Sprintf("%x..%x", b[:3], b[BlobSize-3:])
+}
+
+func (b *Blob) ComputeKZGCommitment() (kzg4844.Commitment, error) {
+	return kzg4844.BlobToCommitment(*b.KZGBlob())
+}
+
+// KZGToVersionedHash computes the "blob hash" (a.k.a. versioned-hash) of a blob-commitment, as used in a blob-tx.
+// We implement it here because it is unfortunately not (currently) exposed by geth.
+func KZGToVersionedHash(commitment kzg4844.Commitment) (out common.Hash) {
+	// EIP-4844 spec:
+	//	def kzg_to_versioned_hash(commitment: KZGCommitment) -> VersionedHash:
+	//		return VERSIONED_HASH_VERSION_KZG + sha256(commitment)[1:]
+	h := sha256.New()
+	h.Write(commitment[:])
+	_ = h.Sum(out[:0])
+	out[0] = BlobTxHashVersion
+	return out
+}
+
+// VerifyBlobProof verifies that the given blob and proof corresponds to the given commitment,
+// returning error if the verification fails.
+func VerifyBlobProof(blob *Blob, commitment kzg4844.Commitment, proof kzg4844.Proof) error {
+	return kzg4844.VerifyBlobProof(*blob.KZGBlob(), commitment, proof)
+}
+
+// FromData encodes the given input data into this blob. The encoding scheme is as follows:
+//
+// In each round we perform 7 reads of input of lengths (31,1,31,1,31,1,31) bytes respectively for
+// a total of 127 bytes. This data is encoded into the next 4 field elements of the output by
+// placing each of the 4x31 byte chunks into bytes [1:32] of its respective field element. The
+// three single byte chunks (24 bits) are split into 4x6-bit chunks, each of which is written into
+// the top most byte of its respective field element, leaving the top 2 bits of each field element
+// empty to avoid modulus overflow.  This process is repeated for up to 1024 rounds until all data
+// is encoded.
+//
+// For only the very first output field, bytes [1:5] are used to encode the version and the length
+// of the data.
+func (b *Blob) FromData(data Data) error {
+	if len(data) > MaxBlobDataSize {
+		return fmt.Errorf("%w: len=%v", ErrBlobInputTooLarge, data)
+	}
+	b.Clear()
+
+	readOffset := 0
+
+	// read 1 byte of input, 0 if there is no input left
+	read1 := func() byte {
+		if readOffset >= len(data) {
+			return 0
+		}
+		out := data[readOffset]
+		readOffset++
+		return out
+	}
+
+	writeOffset := 0
+	var buf31 [31]byte
+	var zero31 [31]byte
+
+	// Read up to 31 bytes of input (left-aligned), into buf31.
+	read31 := func() {
+		if readOffset >= len(data) {
+			copy(buf31[:], zero31[:])
+			return
+		}
+		n := copy(buf31[:], data[readOffset:]) // copy as much data as we can
+		copy(buf31[n:], zero31[:])             // pad with zeroes (since there might not be enough data)
+		readOffset += n
+	}
+	// Write a byte, updates the write-offset.
+	// Asserts that the write-offset matches encoding-algorithm expectations.
+	// Asserts that the value is 6 bits.
+	write1 := func(v byte) {
+		if writeOffset%32 != 0 {
+			panic(fmt.Errorf("blob encoding: invalid byte write offset: %d", writeOffset))
+		}
+		if v&0b1100_0000 != 0 {
+			panic(fmt.Errorf("blob encoding: invalid 6 bit value: 0b%b", v))
+		}
+		b[writeOffset] = v
+		writeOffset++
+	}
+	// Write buf31 to the blob, updates the write-offset.
+	// Asserts that the write-offset matches encoding-algorithm expectations.
+	write31 := func() {
+		if writeOffset%32 != 1 {
+			panic(fmt.Errorf("blob encoding: invalid bytes31 write offset: %d", writeOffset))
+		}
+		copy(b[writeOffset:], buf31[:])
+		writeOffset += 31
+	}
+
+	for round := 0; round < Rounds && readOffset < len(data); round++ {
+		// The first field element encodes the version and the length of the data in [1:5].
+		// This is a manual substitute for read31(), preparing the buf31.
+		if round == 0 {
+			buf31[0] = EncodingVersion
+			// Encode the length as big-endian uint24.
+			// The length check at the start above ensures we can always fit the length value into only 3 bytes.
+			ilen := uint32(len(data))
+			buf31[1] = byte(ilen >> 16)
+			buf31[2] = byte(ilen >> 8)
+			buf31[3] = byte(ilen)
+
+			readOffset += copy(buf31[4:], data[:])
+		} else {
+			read31()
+		}
+
+		x := read1()
+		A := x & 0b0011_1111
+		write1(A)
+		write31()
+
+		read31()
+		y := read1()
+		B := (y & 0b0000_1111) | ((x & 0b1100_0000) >> 2)
+		write1(B)
+		write31()
+
+		read31()
+		z := read1()
+		C := z & 0b0011_1111
+		write1(C)
+		write31()
+
+		read31()
+		D := ((z & 0b1100_0000) >> 2) | ((y & 0b1111_0000) >> 4)
+		write1(D)
+		write31()
+	}
+
+	if readOffset < len(data) {
+		panic(fmt.Errorf("expected to fit data but failed, read offset: %d, data: %d", readOffset, len(data)))
+	}
+	return nil
+}
+
+// ToData decodes the blob into raw byte data. See FromData above for details on the encoding
+// format. If error is returned it will be one of InvalidFieldElementError,
+// InvalidEncodingVersionError and InvalidLengthError.
+func (b *Blob) ToData() (Data, error) {
+	// check the version
+	if b[VersionOffset] != EncodingVersion {
+		return nil, fmt.Errorf(
+			"%w: expected version %d, got %d", ErrBlobInvalidEncodingVersion, EncodingVersion, b[VersionOffset])
+	}
+
+	// decode the 3-byte big-endian length value into a 4-byte integer
+	outputLen := uint32(b[2])<<16 | uint32(b[3])<<8 | uint32(b[4])
+	if outputLen > MaxBlobDataSize {
+		return nil, fmt.Errorf("%w: got %d", ErrBlobInvalidLength, outputLen)
+	}
+
+	// round 0 is special cased to copy only the remaining 27 bytes of the first field element into
+	// the output due to version/length encoding already occupying its first 5 bytes.
+	output := make(Data, MaxBlobDataSize)
+	copy(output[0:27], b[5:])
+
+	// now process remaining 3 field elements to complete round 0
+	opos := 28 // current position into output buffer
+	ipos := 32 // current position into the input blob
+	var err error
+	encodedByte := make([]byte, 4) // buffer for the 4 6-bit chunks
+	encodedByte[0] = b[0]
+	for i := 1; i < 4; i++ {
+		encodedByte[i], opos, ipos, err = b.decodeFieldElement(opos, ipos, output)
+		if err != nil {
+			return nil, err
+		}
+	}
+	opos = reassembleBytes(opos, encodedByte, output)
+
+	// in each remaining round we decode 4 field elements (128 bytes) of the input into 127 bytes
+	// of output
+	for i := 1; i < Rounds && opos < int(outputLen); i++ {
+		for j := 0; j < 4; j++ {
+			// save the first byte of each field element for later re-assembly
+			encodedByte[j], opos, ipos, err = b.decodeFieldElement(opos, ipos, output)
+			if err != nil {
+				return nil, err
+			}
+		}
+		opos = reassembleBytes(opos, encodedByte, output)
+	}
+	for i := int(outputLen); i < len(output); i++ {
+		if output[i] != 0 {
+			return nil, fmt.Errorf("fe=%d: %w", opos/32, ErrBlobExtraneousDataFieldElement)
+		}
+	}
+	output = output[:outputLen]
+	for ; ipos < BlobSize; ipos++ {
+		if b[ipos] != 0 {
+			return nil, fmt.Errorf("pos=%d: %w", ipos, ErrBlobExtraneousData)
+		}
+	}
+	return output, nil
+}
+
+// decodeFieldElement decodes the next input field element by writing its lower 31 bytes into its
+// appropriate place in the output and checking the high order byte is valid. Returns an
+// InvalidFieldElementError if a field element is seen with either of its two high order bits set.
+func (b *Blob) decodeFieldElement(opos, ipos int, output []byte) (byte, int, int, error) {
+	// two highest order bits of the first byte of each field element should always be 0
+	if b[ipos]&0b1100_0000 != 0 {
+		return 0, 0, 0, fmt.Errorf("%w: field element: %d", ErrBlobInvalidFieldElement, ipos)
+	}
+	copy(output[opos:], b[ipos+1:ipos+32])
+	return b[ipos], opos + 32, ipos + 32, nil
+}
+
+// reassembleBytes takes the 4x6-bit chunks from encodedByte, reassembles them into 3 bytes of
+// output, and places them in their appropriate output positions.
+func reassembleBytes(opos int, encodedByte []byte, output []byte) int {
+	opos-- // account for fact that we don't output a 128th byte
+	x := (encodedByte[0] & 0b0011_1111) | ((encodedByte[1] & 0b0011_0000) << 2)
+	y := (encodedByte[1] & 0b0000_1111) | ((encodedByte[3] & 0b0000_1111) << 4)
+	z := (encodedByte[2] & 0b0011_1111) | ((encodedByte[3] & 0b0011_0000) << 2)
+	// put the re-assembled bytes in their appropriate output locations
+	output[opos-32] = z
+	output[opos-(32*2)] = y
+	output[opos-(32*3)] = x
+	return opos
+}
+
+func (b *Blob) Clear() {
+	for i := 0; i < BlobSize; i++ {
+		b[i] = 0
+	}
+}