From dacc0f466c5f93edc1ca7f34fe6d493ed26841a3 Mon Sep 17 00:00:00 2001
From: Daniel Wang <dan@taiko.xyz>
Date: Tue, 13 Feb 2024 17:33:16 +0800
Subject: [PATCH 1/2] only keep the latest snippet

---
 packages/protocol/contracts/L1/TaikoL1.sol    |  9 ++---
 .../protocol/contracts/L1/libs/LibUtils.sol   | 14 +++++---
 .../contracts/L1/libs/LibVerifying.sol        |  4 +--
 packages/protocol/contracts/L2/TaikoL2.sol    | 33 ++++++++-----------
 .../contracts/common/ICrossChainSync.sol      | 13 ++------
 .../contracts/signal/SignalService.sol        |  4 +--
 packages/protocol/test/HelperContracts.sol    | 13 ++++----
 packages/protocol/test/L1/TaikoL1.t.sol       | 12 +++----
 packages/protocol/test/bridge/Bridge.t.sol    |  3 +-
 9 files changed, 45 insertions(+), 60 deletions(-)

diff --git a/packages/protocol/contracts/L1/TaikoL1.sol b/packages/protocol/contracts/L1/TaikoL1.sol
index 694de59b79a..921546c622e 100644
--- a/packages/protocol/contracts/L1/TaikoL1.sol
+++ b/packages/protocol/contracts/L1/TaikoL1.sol
@@ -167,13 +167,8 @@ contract TaikoL1 is
     /// @notice Important: as this contract doesn't send each block's state root as a signal when
     /// the block is verified, bridging developers should subscribe to CrossChainSynced events
     /// to ensure all synced state roots are verifiable using merkle proofs.
-    function getSyncedSnippet(uint64 blockId)
-        public
-        view
-        override
-        returns (ICrossChainSync.Snippet memory)
-    {
-        return LibUtils.getSyncedSnippet(state, getConfig(), blockId);
+    function getSyncedSnippet() public view override returns (ICrossChainSync.Snippet memory) {
+        return LibUtils.getSyncedSnippet(state, getConfig());
     }
 
     /// @notice Gets the state variables of the TaikoL1 contract.
diff --git a/packages/protocol/contracts/L1/libs/LibUtils.sol b/packages/protocol/contracts/L1/libs/LibUtils.sol
index 8824f4aa5b3..d443fd05ce0 100644
--- a/packages/protocol/contracts/L1/libs/LibUtils.sol
+++ b/packages/protocol/contracts/L1/libs/LibUtils.sol
@@ -53,16 +53,21 @@ library LibUtils {
         ts = state.transitions[slot][tid];
     }
 
+    struct Snippet {
+        uint64 blockId;
+        bytes32 blockHash;
+        bytes32 stateRoot;
+    }
+
     function getSyncedSnippet(
         TaikoData.State storage state,
-        TaikoData.Config memory config,
-        uint64 blockId
+        TaikoData.Config memory config
     )
         external
         view
         returns (ICrossChainSync.Snippet memory)
     {
-        uint64 _blockId = blockId == 0 ? state.slotB.lastVerifiedBlockId : blockId;
+        uint64 _blockId = state.slotB.lastVerifiedBlockId;
         uint64 slot = _blockId % config.blockRingBufferSize;
 
         TaikoData.Block storage blk = state.blocks[slot];
@@ -74,8 +79,7 @@ library LibUtils {
             state.transitions[slot][blk.verifiedTransitionId];
 
         return ICrossChainSync.Snippet({
-            remoteBlockId: blockId,
-            syncedInBlock: blk.proposedIn,
+            blockId: _blockId,
             blockHash: transition.blockHash,
             stateRoot: transition.stateRoot
         });
diff --git a/packages/protocol/contracts/L1/libs/LibVerifying.sol b/packages/protocol/contracts/L1/libs/LibVerifying.sol
index b88040edf4a..36a79abdd4b 100644
--- a/packages/protocol/contracts/L1/libs/LibVerifying.sol
+++ b/packages/protocol/contracts/L1/libs/LibVerifying.sol
@@ -247,9 +247,7 @@ library LibVerifying {
                     config.chainId, "state_root", stateRoot
                 );
 
-                emit CrossChainSynced(
-                    uint64(block.number), lastVerifiedBlockId, blockHash, stateRoot
-                );
+                emit CrossChainSynced(uint64(block.number), lastVerifiedBlockId, blockHash, stateRoot);
             }
         }
     }
diff --git a/packages/protocol/contracts/L2/TaikoL2.sol b/packages/protocol/contracts/L2/TaikoL2.sol
index 0fa9ad55537..15e4b9b6989 100644
--- a/packages/protocol/contracts/L2/TaikoL2.sol
+++ b/packages/protocol/contracts/L2/TaikoL2.sol
@@ -45,15 +45,16 @@ contract TaikoL2 is CrossChainOwned, ICrossChainSync {
 
     // Mapping from L2 block numbers to their block hashes.
     // All L2 block hashes will be saved in this mapping.
-    mapping(uint256 blockId => bytes32 blockHash) public l2Hashes;
-    mapping(uint256 l1height => ICrossChainSync.Snippet) public snippets;
+    mapping(uint256 blockId => bytes32 blockHash) public l2Hashes; // slot 1
 
     // A hash to check the integrity of public inputs.
-    bytes32 public publicInputHash; // slot 3
-    uint64 public gasExcess; // slot 4
+    bytes32 public publicInputHash; // slot 2
+    uint64 public gasExcess; // slot 3
     uint64 public latestSyncedL1Height;
 
-    uint256[146] private __gap;
+    ICrossChainSync.Snippet private _chainData; // slot 4, 5, 6
+
+    uint256[144] private __gap;
 
     event Anchored(bytes32 parentHash, uint64 gasExcess);
 
@@ -147,20 +148,18 @@ contract TaikoL2 is CrossChainOwned, ICrossChainSync {
             ownerChainId, "state_root", l1StateRoot
         );
 
-        emit CrossChainSynced(uint64(block.number), l1Height, l1BlockHash, l1StateRoot);
+        emit CrossChainSynced(l1Height, l1BlockHash, l1StateRoot);
 
         // Update state variables
         l2Hashes[parentId] = blockhash(parentId);
-        snippets[l1Height] = ICrossChainSync.Snippet({
-            remoteBlockId: l1Height,
-            syncedInBlock: uint64(block.number),
-            blockHash: l1BlockHash,
-            stateRoot: l1StateRoot
-        });
 
         publicInputHash = publicInputHashNew;
         latestSyncedL1Height = l1Height;
 
+        _chainData.blockId = l1Height;
+        _chainData.blockHash = l1BlockHash;
+        _chainData.stateRoot = l1StateRoot;
+
         emit Anchored(blockhash(parentId), gasExcess);
     }
 
@@ -175,14 +174,8 @@ contract TaikoL2 is CrossChainOwned, ICrossChainSync {
     }
 
     /// @inheritdoc ICrossChainSync
-    function getSyncedSnippet(uint64 blockId)
-        public
-        view
-        override
-        returns (ICrossChainSync.Snippet memory)
-    {
-        uint256 id = blockId == 0 ? latestSyncedL1Height : blockId;
-        return snippets[id];
+    function getSyncedSnippet() public view returns (ICrossChainSync.Snippet memory) {
+        return _chainData;
     }
 
     /// @notice Gets the basefee and gas excess using EIP-1559 configuration for
diff --git a/packages/protocol/contracts/common/ICrossChainSync.sol b/packages/protocol/contracts/common/ICrossChainSync.sol
index 97d22e8af9a..43126b51312 100644
--- a/packages/protocol/contracts/common/ICrossChainSync.sol
+++ b/packages/protocol/contracts/common/ICrossChainSync.sol
@@ -22,25 +22,18 @@ pragma solidity 0.8.24;
 /// both chains remain consistent and can be cross-referenced with integrity.
 interface ICrossChainSync {
     struct Snippet {
-        uint64 remoteBlockId;
-        uint64 syncedInBlock;
+        uint64 blockId;
         bytes32 blockHash;
         bytes32 stateRoot;
     }
 
     /// @dev Emitted when a block has been synced across chains.
-    /// @param syncedInBlock The ID of this chain's block where the sync
-    /// happened.
     /// @param blockId The ID of the remote block whose block hash are synced.
     /// @param blockHash The hash of the synced block.
     /// @param stateRoot The block's state root.
-    event CrossChainSynced(
-        uint64 indexed syncedInBlock, uint64 indexed blockId, bytes32 blockHash, bytes32 stateRoot
-    );
+    event CrossChainSynced(uint64 indexed blockId, bytes32 blockHash, bytes32 stateRoot);
 
     /// @notice Fetches the hash of a block from the opposite chain.
-    /// @param blockId The target block id. Specifying 0 retrieves the hash
-    /// of the latest block.
     /// @return snippet The block hash and signal root synced.
-    function getSyncedSnippet(uint64 blockId) external view returns (Snippet memory snippet);
+    function getSyncedSnippet() external view returns (Snippet memory snippet);
 }
diff --git a/packages/protocol/contracts/signal/SignalService.sol b/packages/protocol/contracts/signal/SignalService.sol
index 8a53675f879..5581359b907 100644
--- a/packages/protocol/contracts/signal/SignalService.sol
+++ b/packages/protocol/contracts/signal/SignalService.sol
@@ -45,7 +45,7 @@ contract SignalService is EssentialContract, ISignalService {
     uint256[49] private __gap;
 
     event TrustedRelayUpdated(uint64 indexed hopChainId, uint64 indexed srcChainId, address hop);
-    event ChainDataRelayed(
+    event SnippetRelayed(
         uint64 indexed chainid, bytes32 indexed kind, bytes32 data, bytes32 signal
     );
 
@@ -211,7 +211,7 @@ contract SignalService is EssentialContract, ISignalService {
         returns (bytes32 slot)
     {
         bytes32 signal = signalForChainData(chainId, kind, data);
-        emit ChainDataRelayed(chainId, kind, data, signal);
+        emit SnippetRelayed(chainId, kind, data, signal);
         return _sendSignal(address(this), signal);
     }
 
diff --git a/packages/protocol/test/HelperContracts.sol b/packages/protocol/test/HelperContracts.sol
index f3ad1801960..3b4d7829716 100644
--- a/packages/protocol/test/HelperContracts.sol
+++ b/packages/protocol/test/HelperContracts.sol
@@ -53,14 +53,15 @@ contract SkipProofCheckSignal is SignalService {
 }
 
 contract DummyCrossChainSync is EssentialContract, ICrossChainSync {
-    Snippet private _snippet;
+    Snippet private _chainData;
 
-    function setSyncedData(bytes32 blockHash, bytes32 stateRoot) external {
-        _snippet.blockHash = blockHash;
-        _snippet.stateRoot = stateRoot;
+    function setSnippet(uint64 blockId, bytes32 blockHash, bytes32 stateRoot) external {
+        _chainData.blockId = blockId;
+        _chainData.blockHash = blockHash;
+        _chainData.stateRoot = stateRoot;
     }
 
-    function getSyncedSnippet(uint64) external view returns (Snippet memory) {
-        return _snippet;
+    function getSyncedSnippet() public view returns (Snippet memory) {
+        return _chainData;
     }
 }
diff --git a/packages/protocol/test/L1/TaikoL1.t.sol b/packages/protocol/test/L1/TaikoL1.t.sol
index 86ade3ceea4..881353a7305 100644
--- a/packages/protocol/test/L1/TaikoL1.t.sol
+++ b/packages/protocol/test/L1/TaikoL1.t.sol
@@ -193,12 +193,12 @@ contract TaikoL1Test is TaikoL1TestBase {
 
     /// @dev getCrossChainBlockHash tests
     function test_L1_getCrossChainBlockHash0() external {
-        bytes32 genHash = L1.getSyncedSnippet(0).blockHash;
+        bytes32 genHash = L1.getSyncedSnippet().blockHash;
         assertEq(GENESIS_BLOCK_HASH, genHash);
 
         // Reverts if block is not yet verified!
         vm.expectRevert(TaikoErrors.L1_BLOCK_MISMATCH.selector);
-        L1.getSyncedSnippet(1);
+        L1.getSyncedSnippet();
     }
 
     /// @dev getSyncedSnippet tests
@@ -236,7 +236,7 @@ contract TaikoL1Test is TaikoL1TestBase {
             verifyBlock(Carol, 1);
 
             // Querying written blockhash
-            assertEq(L1.getSyncedSnippet(blockId).blockHash, blockHash);
+            assertEq(L1.getSyncedSnippet().blockHash, blockHash);
 
             mine(5);
             parentHashes[blockId] = blockHash;
@@ -245,16 +245,16 @@ contract TaikoL1Test is TaikoL1TestBase {
         uint64 queriedBlockId = 1;
         bytes32 expectedSR = bytes32(1e9 + uint256(queriedBlockId));
 
-        assertEq(expectedSR, L1.getSyncedSnippet(queriedBlockId).stateRoot);
+        assertEq(expectedSR, L1.getSyncedSnippet().stateRoot);
 
         // 2nd
         queriedBlockId = 2;
         expectedSR = bytes32(1e9 + uint256(queriedBlockId));
-        assertEq(expectedSR, L1.getSyncedSnippet(queriedBlockId).stateRoot);
+        assertEq(expectedSR, L1.getSyncedSnippet().stateRoot);
 
         // Not found -> reverts
         vm.expectRevert(TaikoErrors.L1_BLOCK_MISMATCH.selector);
-        L1.getSyncedSnippet((count + 1));
+        L1.getSyncedSnippet();
     }
 
     function test_L1_deposit_hash_creation() external {
diff --git a/packages/protocol/test/bridge/Bridge.t.sol b/packages/protocol/test/bridge/Bridge.t.sol
index c7dd95a4992..616ff7d72ad 100644
--- a/packages/protocol/test/bridge/Bridge.t.sol
+++ b/packages/protocol/test/bridge/Bridge.t.sol
@@ -643,7 +643,8 @@ contract BridgeTest is TaikoTest {
 
         addressManager.setAddress(dest, "signal_service", address(mockProofSignalService));
 
-        crossChainSync.setSyncedData(
+        crossChainSync.setSnippet(
+            123,
             0xd5f5d8ac6bc37139c97389b00e9cf53e89c153ad8a5fc765ffe9f44ea9f3d31e,
             0x631b214fb030d82847224f0b3d3b906a6764dded176ad3c7262630204867ba85
         );

From e539427b374c6edebef533aa6a772a3143f0d940 Mon Sep 17 00:00:00 2001
From: Daniel Wang <dan@taiko.xyz>
Date: Tue, 13 Feb 2024 17:50:27 +0800
Subject: [PATCH 2/2] fix

---
 .../protocol/contracts/L1/libs/LibUtils.sol   |  6 ----
 .../contracts/L1/libs/LibVerifying.sol        |  4 ++-
 packages/protocol/contracts/L2/TaikoL2.sol    | 22 ++++++--------
 .../contracts/signal/SignalService.sol        |  6 ++--
 packages/protocol/test/HelperContracts.sol    | 10 +++----
 packages/protocol/test/L1/TaikoL1.t.sol       | 29 +++++--------------
 .../protocol/test/signal/SignalService.t.sol  |  1 +
 7 files changed, 28 insertions(+), 50 deletions(-)

diff --git a/packages/protocol/contracts/L1/libs/LibUtils.sol b/packages/protocol/contracts/L1/libs/LibUtils.sol
index d443fd05ce0..dd61849aba7 100644
--- a/packages/protocol/contracts/L1/libs/LibUtils.sol
+++ b/packages/protocol/contracts/L1/libs/LibUtils.sol
@@ -53,12 +53,6 @@ library LibUtils {
         ts = state.transitions[slot][tid];
     }
 
-    struct Snippet {
-        uint64 blockId;
-        bytes32 blockHash;
-        bytes32 stateRoot;
-    }
-
     function getSyncedSnippet(
         TaikoData.State storage state,
         TaikoData.Config memory config
diff --git a/packages/protocol/contracts/L1/libs/LibVerifying.sol b/packages/protocol/contracts/L1/libs/LibVerifying.sol
index 36a79abdd4b..b88040edf4a 100644
--- a/packages/protocol/contracts/L1/libs/LibVerifying.sol
+++ b/packages/protocol/contracts/L1/libs/LibVerifying.sol
@@ -247,7 +247,9 @@ library LibVerifying {
                     config.chainId, "state_root", stateRoot
                 );
 
-                emit CrossChainSynced(uint64(block.number), lastVerifiedBlockId, blockHash, stateRoot);
+                emit CrossChainSynced(
+                    uint64(block.number), lastVerifiedBlockId, blockHash, stateRoot
+                );
             }
         }
     }
diff --git a/packages/protocol/contracts/L2/TaikoL2.sol b/packages/protocol/contracts/L2/TaikoL2.sol
index 15e4b9b6989..8f70d392cac 100644
--- a/packages/protocol/contracts/L2/TaikoL2.sol
+++ b/packages/protocol/contracts/L2/TaikoL2.sol
@@ -50,9 +50,8 @@ contract TaikoL2 is CrossChainOwned, ICrossChainSync {
     // A hash to check the integrity of public inputs.
     bytes32 public publicInputHash; // slot 2
     uint64 public gasExcess; // slot 3
-    uint64 public latestSyncedL1Height;
 
-    ICrossChainSync.Snippet private _chainData; // slot 4, 5, 6
+    Snippet private _l1Snippet; // slot 4, 5, 6
 
     uint256[144] private __gap;
 
@@ -148,17 +147,14 @@ contract TaikoL2 is CrossChainOwned, ICrossChainSync {
             ownerChainId, "state_root", l1StateRoot
         );
 
-        emit CrossChainSynced(l1Height, l1BlockHash, l1StateRoot);
-
         // Update state variables
         l2Hashes[parentId] = blockhash(parentId);
-
         publicInputHash = publicInputHashNew;
-        latestSyncedL1Height = l1Height;
 
-        _chainData.blockId = l1Height;
-        _chainData.blockHash = l1BlockHash;
-        _chainData.stateRoot = l1StateRoot;
+        _l1Snippet.blockId = l1Height;
+        _l1Snippet.blockHash = l1BlockHash;
+        _l1Snippet.stateRoot = l1StateRoot;
+        emit CrossChainSynced(l1Height, l1BlockHash, l1StateRoot);
 
         emit Anchored(blockhash(parentId), gasExcess);
     }
@@ -175,7 +171,7 @@ contract TaikoL2 is CrossChainOwned, ICrossChainSync {
 
     /// @inheritdoc ICrossChainSync
     function getSyncedSnippet() public view returns (ICrossChainSync.Snippet memory) {
-        return _chainData;
+        return _l1Snippet;
     }
 
     /// @notice Gets the basefee and gas excess using EIP-1559 configuration for
@@ -267,10 +263,10 @@ contract TaikoL2 is CrossChainOwned, ICrossChainSync {
             // Calculate how much more gas to issue to offset gas excess.
             // after each L1 block time, config.gasTarget more gas is issued,
             // the gas excess will be reduced accordingly.
-            // Note that when latestSyncedL1Height is zero, we skip this step.
+            // Note that when _l1Snippet.blockId is zero, we skip this step.
             uint256 numL1Blocks;
-            if (latestSyncedL1Height > 0 && l1Height > latestSyncedL1Height) {
-                numL1Blocks = l1Height - latestSyncedL1Height;
+            if (_l1Snippet.blockId > 0 && l1Height > _l1Snippet.blockId) {
+                numL1Blocks = l1Height - _l1Snippet.blockId;
             }
 
             if (numL1Blocks > 0) {
diff --git a/packages/protocol/contracts/signal/SignalService.sol b/packages/protocol/contracts/signal/SignalService.sol
index 5581359b907..db2f2bddb07 100644
--- a/packages/protocol/contracts/signal/SignalService.sol
+++ b/packages/protocol/contracts/signal/SignalService.sol
@@ -49,16 +49,16 @@ contract SignalService is EssentialContract, ISignalService {
         uint64 indexed chainid, bytes32 indexed kind, bytes32 data, bytes32 signal
     );
 
-    error SS_INVALID_PARAMS();
-    error SS_INVALID_PROOF();
     error SS_EMPTY_PROOF();
     error SS_INVALID_APP();
     error SS_INVALID_HOP_PROOF();
     error SS_INVALID_LAST_HOP_CHAINID();
     error SS_INVALID_MID_HOP_CHAINID();
+    error SS_INVALID_PARAMS();
+    error SS_INVALID_PROOF();
     error SS_INVALID_RELAY();
-    error SS_INVALID_SIGNAL();
     error SS_INVALID_STATE_ROOT();
+    error SS_INVALID_SIGNAL();
     error SS_LOCAL_CHAIN_DATA_NOT_FOUND();
     error SS_UNSUPPORTED();
 
diff --git a/packages/protocol/test/HelperContracts.sol b/packages/protocol/test/HelperContracts.sol
index 3b4d7829716..1b8e93cd1a2 100644
--- a/packages/protocol/test/HelperContracts.sol
+++ b/packages/protocol/test/HelperContracts.sol
@@ -53,15 +53,15 @@ contract SkipProofCheckSignal is SignalService {
 }
 
 contract DummyCrossChainSync is EssentialContract, ICrossChainSync {
-    Snippet private _chainData;
+    Snippet private _snippet;
 
     function setSnippet(uint64 blockId, bytes32 blockHash, bytes32 stateRoot) external {
-        _chainData.blockId = blockId;
-        _chainData.blockHash = blockHash;
-        _chainData.stateRoot = stateRoot;
+        _snippet.blockId = blockId;
+        _snippet.blockHash = blockHash;
+        _snippet.stateRoot = stateRoot;
     }
 
     function getSyncedSnippet() public view returns (Snippet memory) {
-        return _chainData;
+        return _snippet;
     }
 }
diff --git a/packages/protocol/test/L1/TaikoL1.t.sol b/packages/protocol/test/L1/TaikoL1.t.sol
index 881353a7305..92e3e43f436 100644
--- a/packages/protocol/test/L1/TaikoL1.t.sol
+++ b/packages/protocol/test/L1/TaikoL1.t.sol
@@ -192,13 +192,11 @@ contract TaikoL1Test is TaikoL1TestBase {
     }
 
     /// @dev getCrossChainBlockHash tests
-    function test_L1_getCrossChainBlockHash0() external {
-        bytes32 genHash = L1.getSyncedSnippet().blockHash;
-        assertEq(GENESIS_BLOCK_HASH, genHash);
-
-        // Reverts if block is not yet verified!
-        vm.expectRevert(TaikoErrors.L1_BLOCK_MISMATCH.selector);
-        L1.getSyncedSnippet();
+    function test_L1_getCrossChainSnippet_Genesis() external {
+        ICrossChainSync.Snippet memory snippet = L1.getSyncedSnippet();
+        assertEq(snippet.blockId, 0);
+        assertEq(snippet.blockHash, GENESIS_BLOCK_HASH);
+        assertEq(snippet.stateRoot, 0);
     }
 
     /// @dev getSyncedSnippet tests
@@ -235,26 +233,13 @@ contract TaikoL1Test is TaikoL1TestBase {
 
             verifyBlock(Carol, 1);
 
-            // Querying written blockhash
+            assertEq(L1.getSyncedSnippet().blockId, blockId);
             assertEq(L1.getSyncedSnippet().blockHash, blockHash);
+            assertEq(L1.getSyncedSnippet().stateRoot, stateRoot);
 
             mine(5);
             parentHashes[blockId] = blockHash;
         }
-
-        uint64 queriedBlockId = 1;
-        bytes32 expectedSR = bytes32(1e9 + uint256(queriedBlockId));
-
-        assertEq(expectedSR, L1.getSyncedSnippet().stateRoot);
-
-        // 2nd
-        queriedBlockId = 2;
-        expectedSR = bytes32(1e9 + uint256(queriedBlockId));
-        assertEq(expectedSR, L1.getSyncedSnippet().stateRoot);
-
-        // Not found -> reverts
-        vm.expectRevert(TaikoErrors.L1_BLOCK_MISMATCH.selector);
-        L1.getSyncedSnippet();
     }
 
     function test_L1_deposit_hash_creation() external {
diff --git a/packages/protocol/test/signal/SignalService.t.sol b/packages/protocol/test/signal/SignalService.t.sol
index 2b218c871aa..9eb77b2c8b5 100644
--- a/packages/protocol/test/signal/SignalService.t.sol
+++ b/packages/protocol/test/signal/SignalService.t.sol
@@ -12,6 +12,7 @@ contract MockSignalService is SignalService {
         address /*relay*/
     )
         internal
+        pure
         override
         returns (bytes32)
     {