EIP-4844: Generate valid blobsBundle in execution engine mock

packages/beacon-node/src/execution/engine/mock.ts

@@ -1,7 +1,13 @@
 import crypto from "node:crypto";
+import {blobToKzgCommitment, BYTES_PER_FIELD_ELEMENT, FIELD_ELEMENTS_PER_BLOB} from "c-kzg";
+import {
+  kzgCommitmentToVersionedHash,
+  OPAQUE_TX_BLOB_VERSIONED_HASHES_OFFSET,
+  OPAQUE_TX_MESSAGE_OFFSET,
+} from "@lodestar/state-transition";
 import {allForks, bellatrix, eip4844, RootHex, ssz} from "@lodestar/types";
 import {fromHex, toHex} from "@lodestar/utils";
-import {ForkName} from "@lodestar/params";
+import {BLOB_TX_TYPE, ForkName, ForkSeq} from "@lodestar/params";
 import {ZERO_HASH_HEX} from "../../constants/index.js";
 import {
   ExecutePayloadStatus,
@@ -215,7 +221,17 @@ export class ExecutionEngineMock implements IExecutionEngine {
       const kzgs: eip4844.KZGCommitment[] = [];
       const blobs: eip4844.Blob[] = [];
 
-      // TODO EIP-4844: Populate blobs and KZG commitments
+      // if post eip4844, add between 0 and 2 blob transactions
+      if (ForkSeq[payloadAttributes.fork] >= ForkSeq.eip4844) {
+        const eip4844TxCount = Math.round(2 * Math.random());
+        for (let i = 0; i < eip4844TxCount; i++) {
+          const blob = generateRandomBlob();
+          const kzg = blobToKzgCommitment(blob);
+          executionPayload.transactions.push(transactionForKzgCommitment(kzg));
+          kzgs.push(kzg);
+          blobs.push(blob);
+        }
+      }
 
       this.preparingPayloads.set(payloadId, {
         executionPayload,
@@ -302,3 +318,38 @@ export class ExecutionEngineMock implements IExecutionEngine {
     });
   }
 }
+
+function transactionForKzgCommitment(kzgCommitment: eip4844.KZGCommitment): bellatrix.Transaction {
+  // Some random value that after the offset's position
+  const blobVersionedHashesOffset = OPAQUE_TX_BLOB_VERSIONED_HASHES_OFFSET + 64;
+
+  // +32 for the size of versionedHash
+  const ab = new ArrayBuffer(blobVersionedHashesOffset + 32);
+  const dv = new DataView(ab);
+  const ua = new Uint8Array(ab);
+
+  // Set tx type
+  dv.setUint8(0, BLOB_TX_TYPE);
+
+  // Set offset to hashes array
+  // const blobVersionedHashesOffset =
+  //   OPAQUE_TX_MESSAGE_OFFSET + opaqueTxDv.getUint32(OPAQUE_TX_BLOB_VERSIONED_HASHES_OFFSET, true);
+  dv.setUint32(OPAQUE_TX_BLOB_VERSIONED_HASHES_OFFSET, blobVersionedHashesOffset - OPAQUE_TX_MESSAGE_OFFSET, true);
+
+  const versionedHash = kzgCommitmentToVersionedHash(kzgCommitment);
+  ua.set(versionedHash, blobVersionedHashesOffset);
+
+  return ua;
+}
+
+/**
+ * Generate random blob of sequential integers such that each element is < BLS_MODULUS
+ */
+function generateRandomBlob(): eip4844.Blob {
+  const blob = new Uint8Array(FIELD_ELEMENTS_PER_BLOB * BYTES_PER_FIELD_ELEMENT);
+  const dv = new DataView(blob.buffer, blob.byteOffset, blob.byteLength);
+  for (let i = 0; i < FIELD_ELEMENTS_PER_BLOB; i++) {
+    dv.setUint32(i * BYTES_PER_FIELD_ELEMENT, i);
+  }
+  return blob;
+}