feat: add apply msg

src/Gateway.sol

@@ -24,6 +24,7 @@ contract Gateway is IGateway, ReentrancyGuard {
     using FilAddress for address payable;
     using AccountHelper for address;
     using SubnetIDHelper for SubnetID;
+    using CrossMsgHelper for CrossMsg;
     using CheckpointHelper for Checkpoint;
     using CheckpointMappingHelper for mapping(int64 => Checkpoint);
     using StorableMsgHelper for StorableMsg;
@@ -90,6 +91,8 @@ contract Gateway is IGateway, ReentrancyGuard {
     /// @notice fee amount charged per cross message
     uint256 public crossMsgFee;
 
+    mapping(uint64 => bytes4) public methodSelectors;
+
     /// epoch => SubnetID => [childIndex, exists(0 - no, 1 - yes)]
     mapping(int64 => mapping(bytes32 => uint256[2])) internal children;
     /// epoch => SubnetID => check => exists
@@ -119,6 +122,14 @@ contract Gateway is IGateway, ReentrancyGuard {
             : DEFAULT_CHECKPOINT_PERIOD;
         appliedBottomUpNonce = MAX_NONCE;
         crossMsgFee = msgFee;
+
+        methodSelectors[2] = IGateway.register.selector;
+        methodSelectors[3] = IGateway.addStake.selector;
+        methodSelectors[4] = IGateway.releaseStake.selector;
+        methodSelectors[5] = IGateway.kill.selector;
+        methodSelectors[6] = IGateway.commitChildCheck.selector;
+        methodSelectors[9] = IGateway.sendCross.selector;
+        methodSelectors[10] = IGateway.applyMsg.selector;
     }
 
     function getCrossMsgsLength(
@@ -387,6 +398,57 @@ contract Gateway is IGateway, ReentrancyGuard {
         payable(down.getActor()).sendValue(topDownFee);
     }
 
+    function applyMsg(
+        CrossMsg calldata crossMsg
+    ) external returns (bool success) {
+        require(
+            crossMsg.message.to.rawAddress != address(0),
+            "error getting raw address from msg"
+        );
+        require(
+            crossMsg.message.to.subnetId.route.length > 0,
+            "error getting subnet from msg"
+        );
+        require(
+            crossMsg.message.to.subnetId.equals(networkName),
+            "the message being applied doesn't belong to this subnet"
+        );
+        require(
+            methodSelectors[crossMsg.message.method] != bytes4(0),
+            "method not found"
+        );
+
+        if (crossMsg.message.applyType(networkName) == IPCMsgType.BottomUp) {
+            _bottomUpStateTransition(crossMsg.message);
+        } else {
+            require(
+                appliedTopDownNonce == crossMsg.message.nonce,
+                "the top-down message being applied doesn't hold the subsequent nonce"
+            );
+            appliedTopDownNonce += 1;
+        }
+
+        // execute the message
+        success = crossMsg.execute(methodSelectors[crossMsg.message.method]);
+
+        //todo postbox
+    }
+
+    function _bottomUpStateTransition(
+        StorableMsg calldata storableMsg
+    ) internal {
+        if (appliedBottomUpNonce == 2 ** 64 - 1 && storableMsg.nonce == 0) {
+            appliedBottomUpNonce = 0;
+        } else if (appliedBottomUpNonce + 1 == storableMsg.nonce) {
+            appliedBottomUpNonce += 1;
+        }
+
+        require(
+            appliedBottomUpNonce == storableMsg.nonce,
+            "the bottom-up message being applied doesn't hold the subsequent nonce"
+        );
+    }
+
     function _commitCrossMessage(
         CrossMsg memory crossMessage
     ) internal returns (bool, uint256) {
@@ -396,14 +458,15 @@ contract Gateway is IGateway, ReentrancyGuard {
             !crossMessage.message.to.subnetId.equals(networkName),
             "should already be committed"
         );
-        
+
         SubnetID memory from = crossMessage.message.from.subnetId;
         IPCMsgType applyType = crossMessage.message.applyType(networkName);
         bool shouldCommitBottomUp;
 
         if (applyType == IPCMsgType.BottomUp) {
             require(from.route.length > 0, "error getting subnet from msg");
-            shouldCommitBottomUp = to.commonParent(from).equals(networkName) == false;
+            shouldCommitBottomUp =
+                to.commonParent(from).equals(networkName) == false;
         }
 
         if (shouldCommitBottomUp) {
@@ -413,7 +476,7 @@ contract Gateway is IGateway, ReentrancyGuard {
 
         appliedTopDownNonce += applyType == IPCMsgType.TopDown ? 1 : 0;
         _commitTopDownMsg(crossMessage);
-    
+
         return (false, crossMsgFee);
     }
 

src/interfaces/IGateway.sol

@@ -58,4 +58,13 @@ interface IGateway {
         external
         payable;
 
+    /// ApplyMessage triggers the execution of a cross-subnet message validated through the consensus.
+    ///
+    /// This function can only be triggered using `ApplyImplicitMessage`, and the source needs to
+    /// be the SystemActor. Cross messages are applied similarly to how rewards are applied once
+    /// a block has been validated. This function:
+    /// - Determines the type of cross-message.
+    /// - Performs the corresponding state changes.
+    /// - And updated the latest nonce applied for future checks.
+    function applyMsg(CrossMsg calldata crossMsg) external returns (bool);
 }

src/lib/CrossMsgHelper.sol

@@ -67,4 +67,16 @@ library CrossMsgHelper {
     ) internal pure returns (bytes32) {
         return keccak256(abi.encode(crossMsgs));
     }
+
+    function execute(
+        CrossMsg calldata crossMsg,
+        bytes4 methodSelector
+    ) public returns (bool success) {
+        bytes memory params = crossMsg.wrapped
+            ? abi.encode(crossMsg)
+            : crossMsg.message.params;
+        (success, ) = crossMsg.message.to.rawAddress.call{
+            value: crossMsg.message.value
+        }(abi.encodeWithSelector(methodSelector, params));
+    }
 }