refactor(bridge): use deterministic message status slot (w/o mapping)

packages/protocol/contracts/bridge/Bridge.sol

@@ -15,6 +15,7 @@ import "./libs/LibBridgeProcess.sol";
 import "./libs/LibBridgeRetry.sol";
 import "./libs/LibBridgeSend.sol";
 import "./libs/LibBridgeSignal.sol";
+import "./libs/LibBridgeStatus.sol";
 
 /**
  * Bridge contract which is deployed on both L1 and L2. Mostly a thin wrapper
@@ -39,7 +40,7 @@ contract Bridge is EssentialContract, IBridge {
 
     event MessageStatusChanged(
         bytes32 indexed signal,
-        LibBridgeData.MessageStatus status
+        LibBridgeStatus.MessageStatus status
     );
 
     event DestChainEnabled(uint256 indexed chainId, bool enabled);
@@ -159,8 +160,8 @@ contract Bridge is EssentialContract, IBridge {
 
     function getMessageStatus(
         bytes32 signal
-    ) public view virtual returns (LibBridgeData.MessageStatus) {
-        return state.messageStatus[signal];
+    ) public view virtual returns (LibBridgeStatus.MessageStatus) {
+        return LibBridgeStatus.getMessageStatus(signal);
     }
 
     function context() public view returns (Context memory) {

packages/protocol/contracts/bridge/libs/LibBridgeData.sol

@@ -19,69 +19,24 @@ import "../IBridge.sol";
  * @author dantaik <[email protected]>
  */
 library LibBridgeData {
-    /*********************
-     * Structs           *
-     *********************/
-    enum MessageStatus {
-        NEW,
-        RETRIABLE,
-        DONE,
-        FAILED
-    }
-
     struct State {
         // chainId => isEnabled
         mapping(uint256 => bool) destChains;
-        // message hash => status
-        mapping(bytes32 => MessageStatus) messageStatus;
         uint256 nextMessageId;
         IBridge.Context ctx; // 3 slots
-        uint256[44] __gap;
+        uint256[45] __gap;
     }
 
-    /*********************
-     * Constants         *
-     *********************/
-
-    // TODO: figure out this value
     bytes32 internal constant SIGNAL_PLACEHOLDER = bytes32(uint256(1));
     uint256 internal constant CHAINID_PLACEHOLDER = type(uint256).max;
     address internal constant SRC_CHAIN_SENDER_PLACEHOLDER =
         0x0000000000000000000000000000000000000001;
 
-    /*********************
-     * Events            *
-     *********************/
-
     // Note: These events must match the ones defined in Bridge.sol.
     event MessageSent(bytes32 indexed signal, IBridge.Message message);
 
-    event MessageStatusChanged(bytes32 indexed signal, MessageStatus status);
-
     event DestChainEnabled(uint256 indexed chainId, bool enabled);
 
-    /*********************
-     * Internal Functions*
-     *********************/
-
-    /**
-     * @dev If messageStatus is same as in the messageStatus mapping,
-     *      does nothing.
-     * @param state The current bridge state.
-     * @param signal The messageHash of the message.
-     * @param status The status of the message.
-     */
-    function updateMessageStatus(
-        State storage state,
-        bytes32 signal,
-        MessageStatus status
-    ) internal {
-        if (state.messageStatus[signal] != status) {
-            state.messageStatus[signal] = status;
-            emit LibBridgeData.MessageStatusChanged(signal, status);
-        }
-    }
-
     /**
      * @dev Hashes messages and returns the hash signed with
      * "TAIKO_BRIDGE_MESSAGE" for verification.

packages/protocol/contracts/bridge/libs/LibBridgeProcess.sol

@@ -12,6 +12,7 @@ import "../EtherVault.sol";
 import "./LibBridgeData.sol";
 import "./LibBridgeInvoke.sol";
 import "./LibBridgeSignal.sol";
+import "./LibBridgeStatus.sol";
 
 /**
  * Process bridge messages on the destination chain.
@@ -55,7 +56,8 @@ library LibBridgeProcess {
         // LibBridgeRetry.sol
         bytes32 signal = message.hashMessage();
         require(
-            state.messageStatus[signal] == LibBridgeData.MessageStatus.NEW,
+            LibBridgeStatus.getMessageStatus(signal) ==
+                LibBridgeStatus.MessageStatus.NEW,
             "B:status"
         );
         // Message must have been "received" on the destChain (current chain)
@@ -83,13 +85,13 @@ library LibBridgeProcess {
         // will actually consume the Ether.
         message.owner.sendEther(message.depositValue);
 
-        LibBridgeData.MessageStatus status;
+        LibBridgeStatus.MessageStatus status;
         uint256 refundAmount;
 
         if (message.to == address(this) || message.to == address(0)) {
             // For these two special addresses, the call will not be actually
             // invoked but will be marked DONE. The callValue will be refunded.
-            status = LibBridgeData.MessageStatus.DONE;
+            status = LibBridgeStatus.MessageStatus.DONE;
             refundAmount = message.callValue;
         } else {
             uint256 gasLimit = msg.sender == message.owner
@@ -104,16 +106,16 @@ library LibBridgeProcess {
             });
 
             if (success) {
-                status = LibBridgeData.MessageStatus.DONE;
+                status = LibBridgeStatus.MessageStatus.DONE;
             } else {
-                status = LibBridgeData.MessageStatus.RETRIABLE;
+                status = LibBridgeStatus.MessageStatus.RETRIABLE;
                 if (ethVault != address(0)) {
                     ethVault.sendEther(message.callValue);
                 }
             }
         }
 
-        state.updateMessageStatus(signal, status);
+        LibBridgeStatus.updateMessageStatus(signal, status);
 
         address refundAddress = message.refundAddress == address(0)
             ? message.owner

packages/protocol/contracts/bridge/libs/LibBridgeRetry.sol

@@ -11,6 +11,7 @@ pragma solidity ^0.8.9;
 import "../EtherVault.sol";
 import "./LibBridgeInvoke.sol";
 import "./LibBridgeData.sol";
+import "./LibBridgeStatus.sol";
 
 /**
  * Retry bridge messages.
@@ -50,8 +51,8 @@ library LibBridgeRetry {
 
         bytes32 signal = message.hashMessage();
         require(
-            state.messageStatus[signal] ==
-                LibBridgeData.MessageStatus.RETRIABLE,
+            LibBridgeStatus.getMessageStatus(signal) ==
+                LibBridgeStatus.MessageStatus.RETRIABLE,
             "B:notFound"
         );
 
@@ -69,11 +70,14 @@ library LibBridgeRetry {
                 gasLimit: gasleft()
             })
         ) {
-            state.updateMessageStatus(signal, LibBridgeData.MessageStatus.DONE);
+            LibBridgeStatus.updateMessageStatus(
+                signal,
+                LibBridgeStatus.MessageStatus.DONE
+            );
         } else if (isLastAttempt) {
-            state.updateMessageStatus(
+            LibBridgeStatus.updateMessageStatus(
                 signal,
-                LibBridgeData.MessageStatus.FAILED
+                LibBridgeStatus.MessageStatus.FAILED
             );
 
             address refundAddress = message.refundAddress == address(0)

packages/protocol/contracts/bridge/libs/LibBridgeSignal.sol

@@ -12,6 +12,8 @@ import "../../common/AddressResolver.sol";
 import "../../common/IHeaderSync.sol";
 import "../../libs/LibBlockHeader.sol";
 import "../../libs/LibTrieProof.sol";
+import "./LibBridgeData.sol";
+import "./LibBridgeStatus.sol";
 
 /**
  * Library for working with bridge signals.
@@ -43,9 +45,9 @@ library LibBridgeSignal {
         address sender,
         bytes32 signal
     ) internal onlyValidSenderAndSignal(sender, signal) {
-        bytes32 key = _key(sender, signal);
+        bytes32 k = _signalSlot(sender, signal);
         assembly {
-            sstore(key, 1)
+            sstore(k, 1)
         }
     }
 
@@ -59,10 +61,10 @@ library LibBridgeSignal {
         address sender,
         bytes32 signal
     ) internal view onlyValidSenderAndSignal(sender, signal) returns (bool) {
-        bytes32 key = _key(sender, signal);
+        bytes32 k = _signalSlot(sender, signal);
         uint256 v;
         assembly {
-            v := sload(key)
+            v := sload(k)
         }
         return v == 1;
     }
@@ -87,30 +89,27 @@ library LibBridgeSignal {
     ) internal view onlyValidSenderAndSignal(sender, signal) returns (bool) {
         require(srcBridge != address(0), "B:srcBridge");
 
-        SignalProof memory mkp = abi.decode(proof, (SignalProof));
+        SignalProof memory sp = abi.decode(proof, (SignalProof));
         LibTrieProof.verify({
-            stateRoot: mkp.header.stateRoot,
+            stateRoot: sp.header.stateRoot,
             addr: srcBridge,
-            key: _key(sender, signal),
+            key: _signalSlot(sender, signal),
             value: bytes32(uint256(1)),
-            mkproof: mkp.proof
+            mkproof: sp.proof
         });
         // get synced header hash of the header height specified in the proof
         bytes32 syncedHeaderHash = IHeaderSync(resolver.resolve("taiko"))
-            .getSyncedHeader(mkp.header.height);
+            .getSyncedHeader(sp.header.height);
         // check header hash specified in the proof matches the current chain
         return
             syncedHeaderHash != 0 &&
-            syncedHeaderHash == mkp.header.hashBlockHeader();
+            syncedHeaderHash == sp.header.hashBlockHeader();
     }
 
-    /**
-     * Generate the storage key for a signal.
-     */
-    function _key(
+    function _signalSlot(
         address sender,
         bytes32 signal
     ) private pure returns (bytes32) {
-        return keccak256(abi.encodePacked(sender, signal));
+        return keccak256(abi.encodePacked("SIGNAL", sender, signal));
     }
 }

packages/protocol/contracts/bridge/libs/LibBridgeStatus.sol

@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: MIT
+//
+// ╭━━━━╮╱╱╭╮╱╱╱╱╱╭╮╱╱╱╱╱╭╮
+// ┃╭╮╭╮┃╱╱┃┃╱╱╱╱╱┃┃╱╱╱╱╱┃┃
+// ╰╯┃┃┣┻━┳┫┃╭┳━━╮┃┃╱╱╭━━┫╰━┳━━╮
+// ╱╱┃┃┃╭╮┣┫╰╯┫╭╮┃┃┃╱╭┫╭╮┃╭╮┃━━┫
+// ╱╱┃┃┃╭╮┃┃╭╮┫╰╯┃┃╰━╯┃╭╮┃╰╯┣━━┃
+// ╱╱╰╯╰╯╰┻┻╯╰┻━━╯╰━━━┻╯╰┻━━┻━━╯
+pragma solidity ^0.8.9;
+
+/**
+ * @author dantaik <[email protected]>
+ */
+library LibBridgeStatus {
+    enum MessageStatus {
+        NEW,
+        RETRIABLE,
+        DONE,
+        FAILED
+    }
+
+    event MessageStatusChanged(bytes32 indexed signal, MessageStatus status);
+
+    /**
+     * @dev If messageStatus is same as in the messageStatus mapping,
+     *      does nothing.
+     * @param signal The messageHash of the message.
+     * @param status The status of the message.
+     */
+    function updateMessageStatus(
+        bytes32 signal,
+        MessageStatus status
+    ) internal {
+        if (getMessageStatus(signal) != status) {
+            _setMessageStatus(signal, status);
+            emit LibBridgeStatus.MessageStatusChanged(signal, status);
+        }
+    }
+
+    function getMessageStatus(
+        bytes32 signal
+    ) internal view returns (MessageStatus) {
+        bytes32 k = _statusSlot(signal);
+        uint256 v;
+        assembly {
+            v := sload(k)
+        }
+        return MessageStatus(v);
+    }
+
+    function _setMessageStatus(bytes32 signal, MessageStatus status) private {
+        bytes32 k = _statusSlot(signal);
+        uint256 v = uint256(status);
+        assembly {
+            sstore(k, v)
+        }
+    }
+
+    function _statusSlot(bytes32 signal) private pure returns (bytes32) {
+        return keccak256(abi.encodePacked("MESSAGE_STATUS", signal));
+    }
+}

packages/protocol/contracts/test/bridge/libs/TestLibBridgeData.sol

@@ -9,21 +9,20 @@
 pragma solidity ^0.8.9;
 
 import "../../../bridge/libs/LibBridgeData.sol";
+import "../../../bridge/libs/LibBridgeStatus.sol";
 
 contract TestLibBridgeData {
-    LibBridgeData.State public state;
-
     function updateMessageStatus(
         bytes32 signal,
-        LibBridgeData.MessageStatus status
+        LibBridgeStatus.MessageStatus status
     ) public {
-        LibBridgeData.updateMessageStatus(state, signal, status);
+        LibBridgeStatus.updateMessageStatus(signal, status);
     }
 
     function getMessageStatus(
         bytes32 signal
-    ) public view returns (LibBridgeData.MessageStatus) {
-        return state.messageStatus[signal];
+    ) public view returns (LibBridgeStatus.MessageStatus) {
+        return LibBridgeStatus.getMessageStatus(signal);
     }
 
     function hashMessage(

packages/protocol/docs/bridge/Bridge.md

@@ -20,7 +20,7 @@ uint256[50] __gap
 ### MessageStatusChanged
 
 ```solidity
-event MessageStatusChanged(bytes32 signal, enum LibBridgeData.MessageStatus status)
+event MessageStatusChanged(bytes32 signal, enum LibBridgeStatus.MessageStatus status)
 ```
 
 ### DestChainEnabled
@@ -120,7 +120,7 @@ by the specified sender.
 ### getMessageStatus
 
 ```solidity
-function getMessageStatus(bytes32 signal) public view virtual returns (enum LibBridgeData.MessageStatus)
+function getMessageStatus(bytes32 signal) public view virtual returns (enum LibBridgeStatus.MessageStatus)
 ```
 
 ### context