feat: Proposer invalidates previous block if needed (#16067)

If the previous pending block on L1 has invalid attestations, the
proposer for the next slot invalidates it as part of its multicall.

Main changes involved:
- Archiver's `validateBlockAttestations` returns an object with the
validation errors that can be used for constructing the invalidate
request.
- Archiver also stores the validation result for the last block it has
fetched, so sequencer can check it to know if it needs to invalidate.
- Rollup contract wrapper can construct a state override to execute
simulations as if the pending block was different, which is used to
simulate that the invalid block has already been removed when
constructing a block proposal.
- Sequencer enqueues a call to invalidate that is executed as part of
its multicall before the block proposal lands.

Author: spalladino

yarn-project/archiver/src/archiver/archiver.test.ts

@@ -402,7 +402,7 @@ describe('Archiver', () => {
     const badBlock2BlobHashes = await makeVersionedBlobHashes(badBlock2);
     const badBlock2Blobs = await makeBlobsFromBlock(badBlock2);
 
-    // Return the archive root for the bad block 2 when queried
+    // Return the archive root for the bad block 2 when L1 is queried
     mockRollupRead.archiveAt.mockImplementation((args: readonly [bigint]) =>
       Promise.resolve((args[0] === 2n ? badBlock2 : blocks[Number(args[0] - 1n)]).archive.root.toString()),
     );
@@ -423,6 +423,14 @@ describe('Archiver', () => {
     await archiver.start(true);
     latestBlockNum = await archiver.getBlockNumber();
     expect(latestBlockNum).toEqual(1);
+    expect(await archiver.getPendingChainValidationStatus()).toEqual(
+      expect.objectContaining({
+        valid: false,
+        reason: 'invalid-attestation',
+        invalidIndex: 0,
+        committee,
+      }),
+    );
 
     // Now we go for another loop, where a proper block 2 is proposed with correct attestations
     // IRL there would be an "Invalidated" event, but we are not currently relying on it
@@ -453,6 +461,9 @@ describe('Archiver', () => {
     expect(block2.block.number).toEqual(2);
     expect(block2.block.archive.root.toString()).toEqual(blocks[1].archive.root.toString());
     expect(block2.attestations.length).toEqual(3);
+
+    // With a valid pending chain validation status
+    expect(await archiver.getPendingChainValidationStatus()).toEqual(expect.objectContaining({ valid: true }));
   }, 10_000);
 
   it('skip event search if no changes found', async () => {

yarn-project/archiver/src/archiver/archiver.ts

@@ -10,6 +10,7 @@ import {
 } from '@aztec/ethereum';
 import { maxBigint } from '@aztec/foundation/bigint';
 import { Buffer16, Buffer32 } from '@aztec/foundation/buffer';
+import { pick } from '@aztec/foundation/collection';
 import type { EthAddress } from '@aztec/foundation/eth-address';
 import { Fr } from '@aztec/foundation/fields';
 import { type Logger, createLogger } from '@aztec/foundation/log';
@@ -87,7 +88,7 @@ import { InitialBlockNumberNotSequentialError, NoBlobBodiesFoundError } from './
 import { ArchiverInstrumentation } from './instrumentation.js';
 import type { InboxMessage } from './structs/inbox_message.js';
 import type { PublishedL2Block } from './structs/published.js';
-import { validateBlockAttestations } from './validation.js';
+import { type ValidateBlockResult, validateBlockAttestations } from './validation.js';
 
 /**
  * Helper interface to combine all sources this archiver implementation provides.
@@ -119,6 +120,7 @@ export class Archiver extends (EventEmitter as new () => ArchiverEmitter) implem
 
   private l1BlockNumber: bigint | undefined;
   private l1Timestamp: bigint | undefined;
+  private pendingChainValidationStatus: ValidateBlockResult = { valid: true };
   private initialSyncComplete: boolean = false;
 
   public readonly tracer: Tracer;
@@ -356,10 +358,11 @@ export class Archiver extends (EventEmitter as new () => ArchiverEmitter) implem
       // We only do this if rollup cant prune on the next submission. Otherwise we will end up
       // re-syncing the blocks we have just unwound above. We also dont do this if the last block is invalid,
       // since the archiver will rightfully refuse to sync up to it.
-      if (!rollupCanPrune && !rollupStatus.lastBlockIsInvalid) {
+      if (!rollupCanPrune && rollupStatus.lastBlockValidationResult.valid) {
         await this.checkForNewBlocksBeforeL1SyncPoint(rollupStatus, blocksSynchedTo, currentL1BlockNumber);
       }
 
+      this.pendingChainValidationStatus = rollupStatus.lastBlockValidationResult;
       this.instrumentation.updateL1BlockHeight(currentL1BlockNumber);
     }
 
@@ -617,7 +620,7 @@ export class Archiver extends (EventEmitter as new () => ArchiverEmitter) implem
       provenArchive,
       pendingBlockNumber: Number(pendingBlockNumber),
       pendingArchive,
-      lastBlockIsInvalid: false,
+      lastBlockValidationResult: { valid: true } as ValidateBlockResult,
     };
     this.log.trace(`Retrieved rollup status at current L1 block ${currentL1BlockNumber}.`, {
       localPendingBlockNumber,
@@ -793,16 +796,19 @@ export class Archiver extends (EventEmitter as new () => ArchiverEmitter) implem
 
       for (const block of publishedBlocks) {
         const isProven = block.block.number <= provenBlockNumber;
-        if (!isProven && !(await validateBlockAttestations(block, this.epochCache, this.l1constants, this.log))) {
+        rollupStatus.lastBlockValidationResult = isProven
+          ? { valid: true }
+          : await validateBlockAttestations(block, this.epochCache, this.l1constants, this.log);
+
+        if (!rollupStatus.lastBlockValidationResult.valid) {
           this.log.warn(`Skipping block ${block.block.number} due to invalid attestations`, {
             blockHash: block.block.hash(),
             l1BlockNumber: block.l1.blockNumber,
+            ...pick(rollupStatus.lastBlockValidationResult, 'reason'),
           });
-          rollupStatus.lastBlockIsInvalid = true;
           continue;
         }
 
-        rollupStatus.lastBlockIsInvalid = false;
         validBlocks.push(block);
         this.log.debug(`Ingesting new L2 block ${block.block.number} with ${block.block.body.txEffects.length} txs`, {
           blockHash: block.block.hash(),
@@ -1200,6 +1206,14 @@ export class Archiver extends (EventEmitter as new () => ArchiverEmitter) implem
     return this.store.getDebugFunctionName(address, selector);
   }
 
+  getPendingChainValidationStatus(): Promise<ValidateBlockResult> {
+    return Promise.resolve(this.pendingChainValidationStatus);
+  }
+
+  isPendingChainInvalid(): Promise<boolean> {
+    return Promise.resolve(this.pendingChainValidationStatus.valid === false);
+  }
+
   async getL2Tips(): Promise<L2Tips> {
     const [latestBlockNumber, provenBlockNumber] = await Promise.all([
       this.getBlockNumber(),

yarn-project/archiver/src/archiver/validation.test.ts

@@ -45,15 +45,17 @@ describe('validateBlockAttestations', () => {
       const block = await makeBlock([], []);
       const result = await validateBlockAttestations(block, epochCache, constants, logger);
 
-      expect(result).toBe(true);
+      expect(result.valid).toBe(true);
+      expect(result.block).toBe(block);
       expect(epochCache.getCommitteeForEpoch).toHaveBeenCalledWith(0n);
     });
 
     it('validates a block with no attestations if no committee is found', async () => {
       const block = await makeBlock(signers, committee);
       const result = await validateBlockAttestations(block, epochCache, constants, logger);
 
-      expect(result).toBe(true);
+      expect(result.valid).toBe(true);
+      expect(result.block).toBe(block);
       expect(epochCache.getCommitteeForEpoch).toHaveBeenCalledWith(0n);
     });
   });
@@ -73,19 +75,33 @@ describe('validateBlockAttestations', () => {
       const badSigner = Secp256k1Signer.random();
       const block = await makeBlock([...signers, badSigner], [...committee, badSigner.address]);
       const result = await validateBlockAttestations(block, epochCache, constants, logger);
-      expect(result).toBe(false);
+      expect(result.valid).toBe(false);
+      if (!result.valid) {
+        expect(result.reason).toBe('invalid-attestation');
+        expect(result.block).toBe(block);
+        expect(result.committee).toEqual(committee);
+        if (result.reason === 'invalid-attestation') {
+          expect(result.invalidIndex).toBe(5); // The bad signer is at index 5
+        }
+      }
     });
 
     it('returns false if insufficient attestations', async () => {
       const block = await makeBlock(signers.slice(0, 2), committee);
       const result = await validateBlockAttestations(block, epochCache, constants, logger);
-      expect(result).toBe(false);
+      expect(result.valid).toBe(false);
+      if (!result.valid) {
+        expect(result.reason).toBe('insufficient-attestations');
+        expect(result.block).toBe(block);
+        expect(result.committee).toEqual(committee);
+      }
     });
 
     it('returns true if all attestations are valid and sufficient', async () => {
       const block = await makeBlock(signers.slice(0, 4), committee);
       const result = await validateBlockAttestations(block, epochCache, constants, logger);
-      expect(result).toBe(true);
+      expect(result.valid).toBe(true);
+      expect(result.block).toBe(block);
     });
   });
 });

yarn-project/archiver/src/archiver/validation.ts

@@ -1,18 +1,24 @@
 import type { EpochCache } from '@aztec/epoch-cache';
 import type { Logger } from '@aztec/foundation/log';
-import { type PublishedL2Block, getAttestationsFromPublishedL2Block } from '@aztec/stdlib/block';
+import {
+  type PublishedL2Block,
+  type ValidateBlockResult,
+  getAttestationsFromPublishedL2Block,
+} from '@aztec/stdlib/block';
 import { type L1RollupConstants, getEpochAtSlot } from '@aztec/stdlib/epoch-helpers';
 
+export type { ValidateBlockResult };
+
 /**
  * Validates the attestations submitted for the given block.
  * Returns true if the attestations are valid and sufficient, false otherwise.
  */
 export async function validateBlockAttestations(
-  publishedBlock: Pick<PublishedL2Block, 'attestations' | 'block'>,
+  publishedBlock: PublishedL2Block,
   epochCache: EpochCache,
   constants: Pick<L1RollupConstants, 'epochDuration'>,
   logger?: Logger,
-): Promise<boolean> {
+): Promise<ValidateBlockResult> {
   const attestations = getAttestationsFromPublishedL2Block(publishedBlock);
   const { block } = publishedBlock;
   const blockHash = await block.hash().then(hash => hash.toString());
@@ -33,17 +39,18 @@ export async function validateBlockAttestations(
   if (!committee || committee.length === 0) {
     // Q: Should we accept blocks with no committee?
     logger?.warn(`No committee found for epoch ${epoch} at slot ${slot}. Accepting block without validation.`, logData);
-    return true;
+    return { valid: true, block: publishedBlock };
   }
 
   const committeeSet = new Set(committee.map(member => member.toString()));
   const requiredAttestationCount = Math.floor((committee.length * 2) / 3) + 1;
 
-  for (const attestation of attestations) {
+  for (let i = 0; i < attestations.length; i++) {
+    const attestation = attestations[i];
     const signer = attestation.getSender().toString();
     if (!committeeSet.has(signer)) {
       logger?.warn(`Attestation from non-committee member ${signer} at slot ${slot}`, { committee });
-      return false;
+      return { valid: false, reason: 'invalid-attestation', invalidIndex: i, block: publishedBlock, committee };
     }
   }
 
@@ -53,9 +60,9 @@ export async function validateBlockAttestations(
       actualAttestations: attestations.length,
       ...logData,
     });
-    return false;
+    return { valid: false, reason: 'insufficient-attestations', block: publishedBlock, committee };
   }
 
   logger?.debug(`Block attestations validated successfully for block ${block.number} at slot ${slot}`, logData);
-  return true;
+  return { valid: true, block: publishedBlock };
 }

yarn-project/archiver/src/test/mock_l2_block_source.ts

@@ -5,7 +5,7 @@ import type { Fr } from '@aztec/foundation/fields';
 import { createLogger } from '@aztec/foundation/log';
 import type { FunctionSelector } from '@aztec/stdlib/abi';
 import type { AztecAddress } from '@aztec/stdlib/aztec-address';
-import { L2Block, L2BlockHash, type L2BlockSource, type L2Tips } from '@aztec/stdlib/block';
+import { L2Block, L2BlockHash, type L2BlockSource, type L2Tips, type ValidateBlockResult } from '@aztec/stdlib/block';
 import type { ContractClassPublic, ContractDataSource, ContractInstanceWithAddress } from '@aztec/stdlib/contract';
 import { EmptyL1RollupConstants, type L1RollupConstants, getSlotRangeForEpoch } from '@aztec/stdlib/epoch-helpers';
 import { type BlockHeader, TxHash, TxReceipt, TxStatus } from '@aztec/stdlib/tx';
@@ -271,4 +271,12 @@ export class MockL2BlockSource implements L2BlockSource, ContractDataSource {
   syncImmediate(): Promise<void> {
     return Promise.resolve();
   }
+
+  isPendingChainInvalid(): Promise<boolean> {
+    return Promise.resolve(false);
+  }
+
+  getPendingChainValidationStatus(): Promise<ValidateBlockResult> {
+    return Promise.resolve({ valid: true });
+  }
 }