feat: update _handleCallback, add verifyCallback with docs

foundry/interfaces/ICallback.sol

@@ -2,7 +2,24 @@
 pragma solidity ^0.8.26;
 
 interface ICallback {
+    /**
+     * @notice Handles callback data from a protocol or contract interaction.
+     * @dev This method processes callback data and returns a result. Implementations
+     * should handle the specific callback logic required by the protocol.
+     *
+     * @param data The encoded callback data to be processed.
+     * @return result The encoded result of the callback processing.
+     */
     function handleCallback(
         bytes calldata data
     ) external returns (bytes memory result);
+
+    /**
+     * @notice Verifies the validity of callback data.
+     * @dev This view function checks if the provided callback data is valid according
+     * to the protocol's requirements. It should revert if the data is invalid.
+     *
+     * @param data The encoded callback data to verify.
+     */
+    function verifyCallback(bytes calldata data) external view;
 }

foundry/src/Dispatcher.sol

@@ -6,6 +6,7 @@ import "@interfaces/ICallback.sol";
 
 error Dispatcher__UnapprovedExecutor();
 error Dispatcher__NonContractExecutor();
+error Dispatcher__InvalidDataLength();
 
 /**
  * @title Dispatcher - Dispatch execution to external contracts
@@ -81,16 +82,11 @@ contract Dispatcher {
         calculatedAmount = abi.decode(result, (uint256));
     }
 
-    function _handleCallback(bytes4 selector, bytes memory data) internal {
-        // Using assembly to access the last 20 bytes of the bytes memory data
-        address executor;
-        // slither-disable-next-line assembly
-        assembly {
-            let pos := sub(add(add(data, 0x20), mload(data)), 20)
-            executor := mload(pos)
-            executor := shr(96, executor)
-        }
-
+    function _handleCallback(
+        bytes4 selector,
+        address executor,
+        bytes memory data
+    ) internal {
         if (!executors[executor]) {
             revert Dispatcher__UnapprovedExecutor();
         }

foundry/src/TychoRouter.sol

@@ -21,6 +21,7 @@ error TychoRouter__EmptySwaps();
 error TychoRouter__NegativeSlippage(uint256 amount, uint256 minAmount);
 error TychoRouter__AmountInNotFullySpent(uint256 leftoverAmount);
 error TychoRouter__MessageValueMismatch(uint256 value, uint256 amount);
+error TychoRouter__InvalidDataLength();
 
 contract TychoRouter is AccessControl, Dispatcher, Pausable, ReentrancyGuard {
     IAllowanceTransfer public immutable permit2;
@@ -215,12 +216,14 @@ contract TychoRouter is AccessControl, Dispatcher, Pausable, ReentrancyGuard {
 
     /**
      * @dev We use the fallback function to allow flexibility on callback.
-     * This function will static call a verifier contract and should revert if the
-     *  caller is not a pool.
      */
     fallback() external {
-        bytes4 selector = bytes4(msg.data[:4]);
-        _handleCallback(selector, msg.data[4:]);
+        address executor =
+            address(uint160(bytes20(msg.data[msg.data.length - 20:])));
+        bytes4 selector =
+            bytes4(msg.data[msg.data.length - 24:msg.data.length - 20]);
+        bytes memory protocolData = msg.data[:msg.data.length - 24];
+        _handleCallback(selector, executor, protocolData);
     }
 
     /**
@@ -364,22 +367,31 @@ contract TychoRouter is AccessControl, Dispatcher, Pausable, ReentrancyGuard {
     function uniswapV3SwapCallback(
         int256 amount0Delta,
         int256 amount1Delta,
-        bytes calldata msgData
+        bytes calldata data
     ) external {
+        if (data.length < 24) revert TychoRouter__InvalidDataLength();
+        address executor = address(uint160(bytes20(data[data.length - 20:])));
+        bytes4 selector = bytes4(data[data.length - 24:data.length - 20]);
+        bytes memory protocolData = data[:data.length - 24];
         _handleCallback(
-            bytes4(0), abi.encodePacked(amount0Delta, amount1Delta, msgData)
+            selector,
+            executor,
+            abi.encodePacked(amount0Delta, amount1Delta, protocolData)
         );
     }
 
+    /**
+     * @dev Called by UniswapV4 pool manager after achieving unlock state.
+     */
     function unlockCallback(bytes calldata data)
         external
         returns (bytes memory)
     {
-        require(data.length >= 20, "Invalid data length");
-        bytes4 selector = bytes4(data[data.length - 24:data.length - 20]);
+        if (data.length < 24) revert TychoRouter__InvalidDataLength();
         address executor = address(uint160(bytes20(data[data.length - 20:])));
+        bytes4 selector = bytes4(data[data.length - 24:data.length - 20]);
         bytes memory protocolData = data[:data.length - 24];
-        _handleCallback(selector, abi.encodePacked(protocolData, executor));
+        _handleCallback(selector, executor, protocolData);
         return "";
     }
 }

foundry/src/executors/UniswapV3Executor.sol

@@ -29,11 +29,10 @@ contract UniswapV3Executor is IExecutor, ICallback {
     }
 
     // slither-disable-next-line locked-ether
-    function swap(uint256 amountIn, bytes calldata data)
-        external
-        payable
-        returns (uint256 amountOut)
-    {
+    function swap(
+        uint256 amountIn,
+        bytes calldata data
+    ) external payable returns (uint256 amountOut) {
         (
             address tokenIn,
             address tokenOut,
@@ -76,7 +75,9 @@ contract UniswapV3Executor is IExecutor, ICallback {
             abi.encodeWithSelector(
                 ICallback.handleCallback.selector,
                 abi.encodePacked(
-                    amount0Delta, amount1Delta, data[:data.length - 20]
+                    amount0Delta,
+                    amount1Delta,
+                    data[:data.length - 20]
                 )
             )
         );
@@ -91,28 +92,43 @@ contract UniswapV3Executor is IExecutor, ICallback {
         }
     }
 
-    function handleCallback(bytes calldata msgData)
-        external
-        returns (bytes memory result)
-    {
-        (int256 amount0Delta, int256 amount1Delta) =
-            abi.decode(msgData[:64], (int256, int256));
+    function handleCallback(
+        bytes calldata msgData
+    ) external returns (bytes memory result) {
+        (int256 amount0Delta, int256 amount1Delta) = abi.decode(
+            msgData[:64],
+            (int256, int256)
+        );
 
         address tokenIn = address(bytes20(msgData[64:84]));
-        address tokenOut = address(bytes20(msgData[84:104]));
-        uint24 poolFee = uint24(bytes3(msgData[104:107]));
 
-        // slither-disable-next-line unused-return
-        CallbackValidationV2.verifyCallback(factory, tokenIn, tokenOut, poolFee);
+        verifyCallback(msgData[64:]);
 
-        uint256 amountOwed =
-            amount0Delta > 0 ? uint256(amount0Delta) : uint256(amount1Delta);
+        uint256 amountOwed = amount0Delta > 0
+            ? uint256(amount0Delta)
+            : uint256(amount1Delta);
 
         IERC20(tokenIn).safeTransfer(msg.sender, amountOwed);
         return abi.encode(amountOwed, tokenIn);
     }
 
-    function _decodeData(bytes calldata data)
+    function verifyCallback(bytes calldata data) public view {
+        address tokenIn = address(bytes20(data[0:20]));
+        address tokenOut = address(bytes20(data[20:40]));
+        uint24 poolFee = uint24(bytes3(data[40:43]));
+
+        // slither-disable-next-line unused-return
+        CallbackValidationV2.verifyCallback(
+            factory,
+            tokenIn,
+            tokenOut,
+            poolFee
+        );
+    }
+
+    function _decodeData(
+        bytes calldata data
+    )
         internal
         pure
         returns (
@@ -135,11 +151,18 @@ contract UniswapV3Executor is IExecutor, ICallback {
         zeroForOne = uint8(data[83]) > 0;
     }
 
-    function _makeV3CallbackData(address tokenIn, address tokenOut, uint24 fee)
-        internal
-        view
-        returns (bytes memory)
-    {
-        return abi.encodePacked(tokenIn, tokenOut, fee, self);
+    function _makeV3CallbackData(
+        address tokenIn,
+        address tokenOut,
+        uint24 fee
+    ) internal view returns (bytes memory) {
+        return
+            abi.encodePacked(
+                tokenIn,
+                tokenOut,
+                fee,
+                ICallback.handleCallback.selector,
+                self
+            );
     }
 }