fix: override transfer to with transfer fee behavior (#7264)

Author: yorhodes

solidity/contracts/token/TokenBridgeCctpBase.sol

@@ -366,6 +366,17 @@ abstract contract TokenBridgeCctpBase is
         // do not transfer to recipient as the CCTP transfer will do it
     }
 
+    /**
+     * @inheritdoc TokenRouter
+     * @dev Overrides to transfer fees directly from the router balance since CCTP handles token delivery.
+     */
+    function _transferFee(
+        address _recipient,
+        uint256 _amount
+    ) internal override {
+        wrappedToken.safeTransfer(_recipient, _amount);
+    }
+
     function _bridgeViaCircle(
         uint32 _destination,
         bytes32 _recipient,

solidity/contracts/token/bridge/EverclearTokenBridge.sol

@@ -404,6 +404,17 @@ contract EverclearTokenBridge is EverclearBridge {
         // Do nothing (tokens transferred to recipient directly)
     }
 
+    /**
+     * @inheritdoc TokenRouter
+     * @dev Transfers fees directly from router balance using ERC20 transfer.
+     */
+    function _transferFee(
+        address _recipient,
+        uint256 _amount
+    ) internal override {
+        wrappedToken._transferTo(_recipient, _amount);
+    }
+
     /**
      * @notice Encodes the intent calldata for ETH transfers
      * @return The encoded calldata for the everclear intent.
@@ -429,16 +440,17 @@ contract EverclearEthBridge is EverclearBridge {
     using Address for address payable;
     using TypeCasts for bytes32;
 
+    uint256 private constant SCALE = 1;
+
     /**
      * @notice Constructor to initialize the Everclear ETH bridge
      * @param _everclearAdapter The address of the Everclear adapter contract
      */
     constructor(
         IWETH _weth,
-        uint256 _scale,
         address _mailbox,
         IEverclearAdapter _everclearAdapter
-    ) EverclearBridge(_everclearAdapter, IERC20(_weth), _scale, _mailbox) {}
+    ) EverclearBridge(_everclearAdapter, IERC20(_weth), SCALE, _mailbox) {}
 
     /**
      * @inheritdoc EverclearBridge

solidity/contracts/token/libs/TokenCollateral.sol

@@ -24,6 +24,7 @@ library NativeCollateral {
 
 /**
  * @title Handles deposits and withdrawals of WETH collateral.
+ * @dev TokenRouters must have `token() == address(0)` to use this library.
  */
 library WETHCollateral {
     function _transferFromSender(IWETH token, uint256 _amount) internal {

solidity/contracts/token/libs/TokenRouter.sol

@@ -189,7 +189,7 @@ abstract contract TokenRouter is GasRouter, ITokenBridge {
         if (feeAmount > 0) {
             // transfer atomically so we don't need to keep track of collateral
             // and fee balances separately
-            _transferTo(_feeRecipient, feeAmount);
+            _transferFee(_feeRecipient, feeAmount);
         }
         remainingNativeValue = token() != address(0)
             ? _msgValue
@@ -249,6 +249,7 @@ abstract contract TokenRouter is GasRouter, ITokenBridge {
      * param _recipient The address of the recipient on the destination chain.
      * param _amount The amount or identifier of tokens to be sent to the remote recipient
      * @return feeAmount The external fee amount.
+     * @dev This fee must be denominated in the `token()` defined by this router.
      * @dev The default implementation returns 0, meaning no external fees are charged.
      * This function is intended to be overridden by derived contracts that have additional fees.
      * Known overrides:
@@ -362,6 +363,25 @@ abstract contract TokenRouter is GasRouter, ITokenBridge {
         uint256 _amountOrId
     ) internal virtual;
 
+    /**
+     * @dev Should transfer `_amount` of tokens from this token router to the fee recipient.
+     * @dev Called by `_calculateFeesAndCharge` when fee recipient is set and feeAmount > 0.
+     * @dev The default implementation delegates to `_transferTo`, which works for most token routers
+     * where tokens are held by the router (e.g., collateral routers, synthetic token routers).
+     * @dev Override this function for bridges where tokens are NOT held by the router but fees still
+     * need to be paid (e.g., CCTP, Everclear). In those cases, use direct token transfers from the
+     * router's balance collected via `_transferFromSender`.
+     * Known overrides:
+     * - TokenBridgeCctpBase: Directly transfers tokens from router balance.
+     * - EverclearTokenBridge: Directly transfers tokens from router balance.
+     */
+    function _transferFee(
+        address _recipient,
+        uint256 _amount
+    ) internal virtual {
+        _transferTo(_recipient, _amount);
+    }
+
     /**
      * @dev Scales local amount to message amount (up by scale factor).
      * Known overrides:

solidity/test/token/EverclearTokenBridge.t.sol

@@ -28,6 +28,7 @@ import {IEverclearAdapter, IEverclear, IEverclearSpoke} from "../../contracts/in
 import {Quote} from "../../contracts/interfaces/ITokenBridge.sol";
 import {TokenMessage} from "../../contracts/token/libs/TokenMessage.sol";
 import {IWETH} from "contracts/token/interfaces/IWETH.sol";
+import {LinearFee} from "../../contracts/token/fees/LinearFee.sol";
 
 import {ECDSA} from "@openzeppelin/contracts/utils/cryptography/ECDSA.sol";
 /**
@@ -400,6 +401,56 @@ contract EverclearTokenBridgeTest is Test {
         assertEq(sig, feeSignature);
     }
 
+    function testTransferRemoteWithFeeRecipient() public {
+        // Create a LinearFee contract as the fee recipient
+        // LinearFee(token, maxFee, halfAmount, owner)
+        address feeCollector = makeAddr("feeCollector");
+        LinearFee feeContract = new LinearFee(
+            address(token),
+            1e6, // maxFee
+            TRANSFER_AMT / 2, // halfAmount
+            feeCollector
+        );
+
+        // Set fee recipient to the LinearFee contract
+        vm.prank(OWNER);
+        bridge.setFeeRecipient(address(feeContract));
+
+        uint256 initialAliceBalance = token.balanceOf(ALICE);
+        uint256 initialFeeContractBalance = token.balanceOf(
+            address(feeContract)
+        );
+        uint256 initialBridgeBalance = token.balanceOf(address(bridge));
+
+        // Get the expected fee from the feeContract
+        uint256 expectedFeeRecipientFee = feeContract
+        .quoteTransferRemote(DESTINATION, RECIPIENT, TRANSFER_AMT)[0].amount;
+
+        vm.prank(ALICE);
+        bridge.transferRemote(DESTINATION, RECIPIENT, TRANSFER_AMT);
+
+        // Check Alice paid the transfer amount + external fee + fee recipient fee
+        assertEq(
+            token.balanceOf(ALICE),
+            initialAliceBalance -
+                TRANSFER_AMT -
+                FEE_AMOUNT -
+                expectedFeeRecipientFee
+        );
+
+        // Check fee contract received the fee recipient fee (this tests the fix!)
+        assertEq(
+            token.balanceOf(address(feeContract)),
+            initialFeeContractBalance + expectedFeeRecipientFee
+        );
+
+        // Check bridge only holds the transfer amount + external fee, not the fee recipient fee
+        assertEq(
+            token.balanceOf(address(bridge)),
+            initialBridgeBalance + TRANSFER_AMT + FEE_AMOUNT
+        );
+    }
+
     function testTransferRemoteOutputAssetNotSet() public {
         vm.expectRevert("ETB: Output asset not set");
         vm.prank(ALICE);
@@ -797,10 +848,9 @@ contract EverclearTokenBridgeForkTest is BaseEverclearTokenBridgeForkTest {
 contract MockEverclearEthBridge is EverclearEthBridge {
     constructor(
         IWETH _weth,
-        uint256 _scale,
         address _mailbox,
         IEverclearAdapter _everclearAdapter
-    ) EverclearEthBridge(_weth, _scale, _mailbox, _everclearAdapter) {}
+    ) EverclearEthBridge(_weth, _mailbox, _everclearAdapter) {}
 
     bytes public lastIntent;
     function _createIntent(
@@ -835,7 +885,6 @@ contract EverclearEthBridgeForkTest is BaseEverclearTokenBridgeForkTest {
         // Deploy ETH bridge implementation
         MockEverclearEthBridge implementation = new MockEverclearEthBridge(
             IWETH(ARBITRUM_WETH),
-            1,
             address(0x979Ca5202784112f4738403dBec5D0F3B9daabB9), // Mailbox
             everclearAdapter
         );
@@ -927,7 +976,6 @@ contract EverclearEthBridgeForkTest is BaseEverclearTokenBridgeForkTest {
     function testEthBridgeConstructor() public {
         EverclearEthBridge newBridge = new EverclearEthBridge(
             IWETH(ARBITRUM_WETH),
-            1,
             address(0x979Ca5202784112f4738403dBec5D0F3B9daabB9), // Mailbox
             everclearAdapter
         );

solidity/test/token/TokenBridgeCctp.t.sol

@@ -339,6 +339,12 @@ contract TokenBridgeCctpV1Test is Test {
         vm.startPrank(user);
         tokenOrigin.approve(address(tbOrigin), charge);
 
+        uint256 initialUserBalance = tokenOrigin.balanceOf(user);
+        uint256 initialFeeContractBalance = tokenOrigin.balanceOf(
+            address(feeContract)
+        );
+        uint256 initialBridgeBalance = tokenOrigin.balanceOf(address(tbOrigin));
+
         uint64 cctpNonce = tokenMessengerOrigin.nextNonce();
 
         vm.expectCall(
@@ -358,6 +364,27 @@ contract TokenBridgeCctpV1Test is Test {
             user.addressToBytes32(),
             amount
         );
+
+        // Verify fee recipient received the fee (tests the fix!)
+        assertEq(
+            tokenOrigin.balanceOf(address(feeContract)),
+            initialFeeContractBalance + feeRecipientFee,
+            "Fee contract should receive fee"
+        );
+
+        // Verify user was charged correctly
+        assertEq(
+            tokenOrigin.balanceOf(user),
+            initialUserBalance - charge,
+            "User should be charged transfer amount + fees"
+        );
+
+        // Verify bridge doesn't hold the fee
+        assertEq(
+            tokenOrigin.balanceOf(address(tbOrigin)),
+            initialBridgeBalance,
+            "Bridge should not hold fee recipient fee"
+        );
     }
 
     function test_verify() public {