0-indexed Checkpoints (#344)

* Checkpoints are zero indexed

* Checkpoints are not one-indexed anymore

* Agent changes for 0-indexed checkpoints

* Disallow checkpoint index 0

* Can just check indicies again

* Proper isCheckpoint

* Dispatch dummy message

* fix before

* PR review

Co-authored-by: Asa Oines <asaoines@Asas-MacBook-Pro.local>

rust/agents/checkpointer/src/submit.rs

@@ -49,8 +49,9 @@ impl CheckpointSubmitter {
                     "Got latest checkpoint and count"
                 );
                 // If there are any new messages, the count will be greater than
-                // the latest checkpoint index.
-                if count > latest_checkpoint_index {
+                // the latest checkpoint index + 1. Don't checkpoint for count < 2
+                // since checkpoints with index 0 are disallowed
+                if count > latest_checkpoint_index + 1 && count > 1 {
                     debug!("Creating checkpoint");
                     self.outbox.create_checkpoint().await?;
                     // Sleep to ensure that another checkpoint isn't made until

rust/agents/relayer/src/checkpoint_relayer.rs

@@ -40,7 +40,7 @@ impl CheckpointRelayer {
     }
 
     /// Only gets the messages desinated for the Relayers inbox
-    /// Exclusive the to_checkpoint_index
+    /// Inclusive the to_checkpoint_index
     async fn get_messages_between(
         &self,
         from_leaf_index: u32,
@@ -48,7 +48,7 @@ impl CheckpointRelayer {
     ) -> Result<Option<Vec<CommittedMessage>>> {
         let mut messages: Vec<CommittedMessage> = vec![];
         let mut current_leaf_index = from_leaf_index;
-        while current_leaf_index < to_checkpoint_index {
+        while current_leaf_index <= to_checkpoint_index {
             // Relies on the indexer finding this message eventually
             self.db.wait_for_leaf(current_leaf_index).await?;
             let maybe_message = self
@@ -138,8 +138,11 @@ impl CheckpointRelayer {
             let latest_inbox_checkpoint =
                 self.inbox_contracts.inbox.latest_checkpoint(None).await?;
             let mut onchain_checkpoint_index = latest_inbox_checkpoint.index;
-            // Checkpoints are 1-indexed, while leaves are 0-indexed
-            let mut next_inbox_leaf_index = onchain_checkpoint_index;
+            let mut next_inbox_leaf_index = if onchain_checkpoint_index == 0 {
+                0
+            } else {
+                onchain_checkpoint_index + 1
+            };
             loop {
                 sleep(Duration::from_secs(self.polling_interval)).await;
 
@@ -161,11 +164,11 @@ impl CheckpointRelayer {
                     {
                         None => debug!("Couldn't fetch the relevant messages, retry this range"),
                         Some(messages) if messages.is_empty() => {
-                            next_inbox_leaf_index = signed_checkpoint_index;
+                            next_inbox_leaf_index = signed_checkpoint_index + 1;
                             debug!("New checkpoint does not include messages for inbox")
                         }
                         Some(messages) => {
-                            next_inbox_leaf_index = signed_checkpoint_index;
+                            next_inbox_leaf_index = signed_checkpoint_index + 1;
                             debug!(
                                 len = messages.len(),
                                 "Signed checkpoint allows for processing of new messages"

rust/agents/relayer/src/merkle_tree_builder.rs

@@ -144,7 +144,7 @@ impl MerkleTreeBuilder {
             return Ok(());
         }
         let starting_index = self.prover.count() as u32;
-        for i in starting_index..checkpoint.index {
+        for i in starting_index..=checkpoint.index {
             self.db.wait_for_leaf(i).await?;
             self.ingest_leaf_index(i)?;
         }
@@ -168,7 +168,7 @@ impl MerkleTreeBuilder {
         &mut self,
         batch: &MessageBatch,
     ) -> Result<(), MerkleTreeBuilderError> {
-        if self.prover.count() as u32 > batch.current_checkpoint_index {
+        if self.prover.count() as u32 > batch.current_checkpoint_index + 1 {
             error!("Prover was already ahead of MessageBatch, something went wrong");
             return Err(MerkleTreeBuilderError::UnexpectedProverState {
                 prover_count: self.prover.count() as u32,
@@ -185,8 +185,8 @@ impl MerkleTreeBuilder {
             count = self.prover.count(),
             "update_from_batch fast forward"
         );
-        // prove the until target (checkpoints are 1-indexed)
-        for i in (batch.current_checkpoint_index + 1)..batch.target_checkpoint.index {
+        // prove the until target
+        for i in (batch.current_checkpoint_index + 1)..=batch.target_checkpoint.index {
             self.ingest_leaf_index(i)?;
         }
 

solidity/apps/test/governance/governanceRouter.test.ts

@@ -21,13 +21,14 @@ describe('GovernanceRouter', async () => {
     remote: GovernanceRouter,
     testSet: TestSet,
     governance: GovernanceDeploy;
+  let outbox: Outbox;
+  let interchainGasPaymaster: InterchainGasPaymaster;
 
   before(async () => {
     [governor, recoveryManager] = await ethers.getSigners();
 
     const testSetFactory = new TestSet__factory(governor);
     testSet = await testSetFactory.deploy();
-    await abacus.deploy(domains, governor);
   });
 
   beforeEach(async () => {
@@ -40,10 +41,13 @@ describe('GovernanceRouter', async () => {
         address: governor.address,
       },
     };
+    await abacus.deploy(domains, governor);
     governance = new GovernanceDeploy(config);
     await governance.deploy(abacus);
     router = governance.router(localDomain);
     remote = governance.router(remoteDomain);
+    outbox = abacus.outbox(localDomain);
+    interchainGasPaymaster = abacus.interchainGasPaymaster(localDomain);
   });
 
   it('Cannot be initialized twice', async () => {
@@ -425,14 +429,6 @@ describe('GovernanceRouter', async () => {
   describe('interchain gas payments for dispatched messages', async () => {
     const testInterchainGasPayment = 123456789;
 
-    let outbox: Outbox;
-    let interchainGasPaymaster: InterchainGasPaymaster;
-
-    before(() => {
-      outbox = abacus.outbox(localDomain);
-      interchainGasPaymaster = abacus.interchainGasPaymaster(localDomain);
-    });
-
     it('allows interchain gas payment for remote calls', async () => {
       const leafIndex = await outbox.count();
       const call = formatCall(testSet, 'set', [13]);

solidity/core/contracts/Common.sol

@@ -21,6 +21,8 @@ abstract contract Common is ICommon, OwnableUpgradeable {
     // ============ Public Variables ============
 
     // Checkpoints of root => leaf index
+    // Checkpoints of index 0 have to be disallowed as the existence of such
+    // a checkpoint cannot be distinguished from their non-existence
     mapping(bytes32 => uint256) public checkpoints;
     // The latest checkpointed root
     bytes32 public checkpointedRoot;
@@ -121,7 +123,7 @@ abstract contract Common is ICommon, OwnableUpgradeable {
     /**
      * @notice Store the provided checkpoint.
      * @param _root The merkle root
-     * @param _index The next available leaf index of the merkle tree.
+     * @param _index The leaf index of the latest message in the merkle tree.
      */
     function _checkpoint(bytes32 _root, uint256 _index) internal {
         checkpoints[_root] = _index;

solidity/core/contracts/Outbox.sol

@@ -133,14 +133,16 @@ contract Outbox is IOutbox, Version0, MerkleTreeManager, Common {
     /**
      * @notice Checkpoints the latest root and index.
      * Validators are expected to sign this checkpoint so that it can be
-     * relayed to the Inbox contracts.
+     * relayed to the Inbox contracts. Checkpoints for a single message (i.e.
+     * count = 1) are disallowed since they make checkpoint tracking more
+     * difficult.
      * @dev emits Checkpoint event
      */
     function checkpoint() external override notFailed {
         uint256 count = count();
-        require(count > 0, "!count");
+        require(count > 1, "!count");
         bytes32 root = root();
-        _checkpoint(root, count);
+        _checkpoint(root, count - 1);
     }
 
     /**
@@ -166,7 +168,7 @@ contract Outbox is IOutbox, Version0, MerkleTreeManager, Common {
         override
         returns (bool)
     {
-        // Checkpoint indices are one-indexed.
+        // Checkpoints are zero-indexed, but checkpoints of index 0 are disallowed
         return _index > 0 && checkpoints[_root] == _index;
     }
 

solidity/core/test/outbox.test.ts

@@ -124,15 +124,30 @@ describe('Outbox', async () => {
 
   it('Checkpoints the latest root', async () => {
     const message = ethers.utils.formatBytes32String('message');
+    const count = 2;
+    for (let i = 0; i < count; i++) {
       await outbox.dispatch(
         destDomain,
         utils.addressToBytes32(recipient.address),
         message,
       );
+    }
     await outbox.checkpoint();
     const [root, index] = await outbox.latestCheckpoint();
     expect(root).to.not.equal(ethers.constants.HashZero);
-    expect(index).to.equal(1);
+    expect(index).to.equal(count - 1);
+
+    expect(await outbox.isCheckpoint(root, index)).to.be.true;
+  });
+
+  it('does not allow a checkpoint of index 0', async () => {
+    const message = ethers.utils.formatBytes32String('message');
+    await outbox.dispatch(
+      destDomain,
+      utils.addressToBytes32(recipient.address),
+      message,
+    );
+    await expect(outbox.checkpoint()).to.be.revertedWith('!count');
   });
 
   it('Correctly calculates destinationAndNonce', async () => {

solidity/core/test/validator-manager/outboxValidatorManager.test.ts

@@ -85,6 +85,12 @@ describe('OutboxValidatorManager', () => {
 
     it('reverts if the checkpoint is not improper', async () => {
       const message = `0x${Buffer.alloc(10).toString('hex')}`;
+      // Send two messages to allow checkpointing
+      await outbox.dispatch(
+        INBOX_DOMAIN,
+        utils.addressToBytes32(signer.address),
+        message,
+      );
       await outbox.dispatch(
         INBOX_DOMAIN,
         utils.addressToBytes32(signer.address),

typescript/hardhat/src/TestAbacusDeploy.ts

@@ -13,6 +13,7 @@ import {
   AbacusConnectionManager__factory,
 } from "@abacus-network/core";
 import { TestDeploy } from "./TestDeploy";
+import { addressToBytes32 } from "@abacus-network/utils/dist/src/utils";
 
 export type TestAbacusConfig = {
   signer: Record<types.Domain, ethers.Signer>;
@@ -98,6 +99,13 @@ export class TestAbacusDeploy extends TestDeploy<
       inboxes[remote] = inbox;
     });
     await Promise.all(deploys);
+
+    // dispatch a dummy event to allow a consumer to checkpoint/process a single message
+    await outbox.dispatch(
+      remotes.find((_) => _ !== domain)!,
+      addressToBytes32(ethers.constants.AddressZero),
+      "0x"
+    );
     return {
       outbox,
       abacusConnectionManager,
@@ -162,8 +170,14 @@ export class TestAbacusDeploy extends TestDeploy<
       new Map();
     const outbox = this.outbox(origin);
     const [, checkpointedIndex] = await outbox.latestCheckpoint();
-    const latestIndex = await outbox.count();
-    if (latestIndex.eq(checkpointedIndex)) return responses;
+    const messageCount = await outbox.count();
+    // Message count does allow for a checkpoint
+    if (messageCount.lte(checkpointedIndex.add(1))) return responses;
+
+    // Can't checkpoint a single message
+    if (messageCount.toNumber() <= 1) {
+      return responses;
+    }
 
     await outbox.checkpoint();
     const [root, index] = await outbox.latestCheckpoint();
@@ -183,6 +197,10 @@ export class TestAbacusDeploy extends TestDeploy<
       const inbox = this.inbox(origin, destination);
       const status = await inbox.messages(dispatch.args.messageHash);
       if (status !== types.MessageStatus.PROCESSED) {
+        if (dispatch.args.leafIndex.toNumber() == 0) {
+          // disregard the dummy message
+          continue;
+        }
         const response = await inbox.testProcess(
           dispatch.args.message,
           dispatch.args.leafIndex.toNumber()