Modify simulated beacon to service blobs in nitro system_tests

eth/catalyst/simulated_beacon.go

@@ -96,6 +96,8 @@ type SimulatedBeacon struct {
 	engineAPI          *ConsensusAPI
 	curForkchoiceState engine.ForkchoiceStateV1
 	lastBlockTime      uint64
+
+	blobsBundleProvider map[common.Hash]*engine.BlobsBundleV1
 }
 
 func payloadVersion(config *params.ChainConfig, time uint64, header *types.Header) engine.PayloadVersion {
@@ -264,6 +266,10 @@ func (c *SimulatedBeacon) sealBlock(withdrawals []*types.Withdrawal, timestamp u
 		return err
 	}
 	c.lastBlockTime = payload.Timestamp
+
+	if c.blobsBundleProvider != nil && envelope.BlobsBundle != nil {
+		c.blobsBundleProvider[payload.BlockHash] = envelope.BlobsBundle
+	}
 	return nil
 }
 

eth/catalyst/simulated_beacon_blob_provider.go

@@ -0,0 +1,92 @@
+package catalyst
+
+import (
+	"context"
+	"crypto/sha256"
+	"errors"
+	"fmt"
+
+	"github.com/ethereum/go-ethereum/beacon/engine"
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/crypto/kzg4844"
+)
+
+// GetBlobs is a mimic of blobSidecars function (https://github.com/OffchainLabs/nitro/blob/a4b72abd63df46de920580685842491d550dfc20/util/headerreader/blob_client.go#L199)
+// in nitro, a mel related system test uses simulated beacon as blob reader, if that were to fail we need to update this function to be similar to the above referenced function
+func (c *SimulatedBeacon) GetBlobs(ctx context.Context, batchBlockHash common.Hash, versionedHashes []common.Hash) ([]kzg4844.Blob, error) {
+	bundle, ok := c.blobsBundleProvider[batchBlockHash]
+	if !ok {
+		return nil, errors.New("blobs not found")
+	}
+
+	if len(bundle.Blobs) < len(versionedHashes) {
+		return nil, fmt.Errorf("expected at least %d blobs but only got %d", len(versionedHashes), len(bundle.Blobs))
+	}
+
+	output := make([]kzg4844.Blob, len(versionedHashes))
+	outputsFound := make([]bool, len(versionedHashes))
+
+	for i := 0; i < len(bundle.Blobs); i++ {
+		var commitment kzg4844.Commitment
+		copy(commitment[:], bundle.Commitments[i])
+		versionedHash := commitmentToVersionedHash(commitment)
+
+		// The versioned hashes of the blob commitments are produced in the by HASH_OPCODE_BYTE,
+		// presumably in the order they were added to the tx. The spec is unclear if the blobs
+		// need to be returned in any particular order from the beacon API, so we put them back in
+		// the order from the tx.
+		var outputIdx int
+		var found bool
+		for outputIdx = range versionedHashes {
+			if versionedHashes[outputIdx] == versionedHash {
+				if outputsFound[outputIdx] {
+					// Duplicate, skip this one
+					break
+				}
+				found = true
+				outputsFound[outputIdx] = true
+				break
+			}
+		}
+		if !found {
+			continue
+		}
+
+		copy(output[outputIdx][:], bundle.Blobs[i])
+
+		var proof kzg4844.Proof
+		copy(proof[:], bundle.Proofs[i])
+
+		if err := kzg4844.VerifyBlobProof(&output[outputIdx], commitment, proof); err != nil {
+			return nil, fmt.Errorf("failed to verify blob proof for blob index(%d), blob(%s)", i, firstFewChars(bundle.Blobs[i].String()))
+		}
+	}
+
+	for i, found := range outputsFound {
+		if !found {
+			return nil, fmt.Errorf("missing blob %v, can't reconstruct batch payload", versionedHashes[i])
+		}
+	}
+
+	return output, nil
+}
+
+func (c *SimulatedBeacon) Initialize(ctx context.Context) error {
+	c.blobsBundleProvider = make(map[common.Hash]*engine.BlobsBundleV1)
+	return nil
+}
+
+func commitmentToVersionedHash(commitment kzg4844.Commitment) common.Hash {
+	// As per the EIP-4844 spec, the versioned hash is the SHA-256 hash of the commitment with the first byte set to 1.
+	hash := sha256.Sum256(commitment[:])
+	hash[0] = 1
+	return hash
+}
+
+func firstFewChars(s string) string {
+	if len(s) < 9 {
+		return fmt.Sprintf("\"%s\"", s)
+	} else {
+		return fmt.Sprintf("\"%s...\"", s[:8])
+	}
+}