FOTToken: canonical way of implementation, following SETH example

contracts/experimental/FOTToken.sol

@@ -10,19 +10,30 @@ import {
 } from "@superfluid-finance/ethereum-contracts/contracts/interfaces/superfluid/ISuperfluid.sol";
 import { Ownable } from "@openzeppelin/contracts/access/Ownable.sol";
 
+// Custom methods of this token, to be inherited from by both the proxy and interface.
+interface IFOTTokenCustom {
+    // admin interface
+    function setFeeConfig(uint256 _feePerTx, address _feeRecipient) external /*onlyOwner*/;
+}
+
+// Methods included in ISuperToken, but intercepted by the proxy in order to change its behaviour.
+// This dedicated interface can be inherited only by the proxy.
+interface IFOTTokenIntercepted {
+    // subset of IERC20 intercepted in the proxy in order to add a fee
+    function transferFrom(address holder, address recipient, uint256 amount) external returns (bool);
+    function transfer(address recipient, uint256 amount) external returns (bool);
+}
+
 /// @title FOT (Fee on Transfer) Token
 /// trivial implementation using a fixed fee amount per tx, added to the actual transfer amount.
 /// @notice CustomSuperTokenBase MUST be the first inherited contract, otherwise the storage layout may get corrupted
-contract FOTTokenProxy is CustomSuperTokenBase, UUPSProxy, Ownable {
-    uint256 public feePerTx;
-    address public feeRecipient;
+contract FOTTokenProxy is CustomSuperTokenBase, UUPSProxy, Ownable, IFOTTokenCustom, IFOTTokenIntercepted {
+    uint256 public feePerTx; // amount detracted as fee per tx
+    address public feeRecipient; // receiver of the fee
 
-    constructor(uint256 _feePerTx, address _feeRecipient) {
-        feePerTx = _feePerTx;
-        feeRecipient = _feeRecipient;
-    }
+    event FeeConfigSet(uint256 feePerTx, address feeRecipient);
 
-    function setFeeConfig(uint256 _feePerTx, address _feeRecipient) external onlyOwner {
+    constructor(uint256 _feePerTx, address _feeRecipient) {
         feePerTx = _feePerTx;
         feeRecipient = _feeRecipient;
     }
@@ -36,25 +47,42 @@ contract FOTTokenProxy is CustomSuperTokenBase, UUPSProxy, Ownable {
 		ISuperToken(address(this)).initialize(IERC20(address(0)), 18, name, symbol);
     }
 
-    // ERC20 functions we want to intercept and add custom behavior to
+    // ======= IFOTTokenCustom =======
+
+    function setFeeConfig(uint256 _feePerTx, address _feeRecipient) external override onlyOwner {
+        feePerTx = _feePerTx;
+        feeRecipient = _feeRecipient;
+        emit FeeConfigSet(_feePerTx, _feeRecipient);
+    }
+
+    // ======= IFOTTokenIntercepted =======
 
     function transferFrom(address holder, address recipient, uint256 amount)
-        public returns (bool)
+        external override returns (bool)
     {
+        _transferFrom(holder, recipient, amount);
+        return true; // returns true if it didn't revert
+    }
+
+    function transfer(address recipient, uint256 amount)
+        external override returns (bool)
+    {
+        _transferFrom(msg.sender, recipient, amount);
+        return true;
+    }
+
+
+    // ======= Internal =======
+
+    function _transferFrom(address holder, address recipient, uint256 amount) internal {
         // get the fee
         ISuperToken(address(this)).selfTransferFrom(holder, msg.sender, feeRecipient, feePerTx);
         // (external) call into the implementation contract.
 
         // do the actual tx
         ISuperToken(address(this)).selfTransferFrom(holder, msg.sender, recipient, amount);
-        return true; // returns true if it didn't revert
-    }
-
-    function transfer(address recipient, uint256 amount)
-        public returns (bool)
-    {
-        return transferFrom(msg.sender, recipient, amount);
     }
 }
 
 // TODO: create interfaces IFOTTokenCustom, IFOTToken - see https://github.com/superfluid-finance/protocol-monorepo/blob/dev/packages/ethereum-contracts/contracts/interfaces/tokens/ISETH.sol
+interface IFOTToken is ISuperToken, IFOTTokenCustom {}

test/foundry/FOTToken.t.sol

@@ -2,18 +2,13 @@
 pragma solidity 0.8.19;
 
 import "forge-std/Test.sol";
-import {
-    FOTTokenProxy,
-    ISuperToken
-} from "../../contracts/experimental/FOTToken.sol";
-import {ISuperfluid} from "@superfluid-finance/ethereum-contracts/contracts/interfaces/superfluid/ISuperfluid.sol";
-import {
-    SuperfluidFrameworkDeployer
-} from "@superfluid-finance/ethereum-contracts/contracts/utils/SuperfluidFrameworkDeployer.sol";
-import {ERC1820RegistryCompiled} from "@superfluid-finance/ethereum-contracts/contracts/libs/ERC1820RegistryCompiled.sol";
+import { FOTTokenProxy, IFOTToken } from "../../contracts/experimental/FOTToken.sol";
+import { ISuperfluid } from "@superfluid-finance/ethereum-contracts/contracts/interfaces/superfluid/ISuperfluid.sol";
+import { SuperfluidFrameworkDeployer } from "@superfluid-finance/ethereum-contracts/contracts/utils/SuperfluidFrameworkDeployer.sol";
+import { ERC1820RegistryCompiled } from "@superfluid-finance/ethereum-contracts/contracts/libs/ERC1820RegistryCompiled.sol";
 
 contract FOTTokenTest is Test {
-    ISuperToken public fotToken;
+    IFOTToken public fotToken;
     SuperfluidFrameworkDeployer.Framework sf;
     uint256 public txFee = 1e16;
 
@@ -34,7 +29,7 @@ contract FOTTokenTest is Test {
         vm.startPrank(admin);
         FOTTokenProxy fotTokenProxy = new FOTTokenProxy(txFee, txFeeRecipient);
         fotTokenProxy.initialize(sf.superTokenFactory, "FOTToken", "FOT");
-        fotToken = ISuperToken(address(fotTokenProxy));
+        fotToken = IFOTToken(address(fotTokenProxy));
     }
 
     function testTransfer() public {
@@ -84,10 +79,10 @@ contract FOTTokenTest is Test {
         vm.startPrank(dan);
         vm.expectRevert("Ownable: caller is not the owner"); // dan isn't the owner
         // casting to payable needed because the proxy contains a payable fallback function
-        FOTTokenProxy(payable(address(fotToken))).setFeeConfig(newTxFee, dan);
+        fotToken.setFeeConfig(newTxFee, dan);
 
         vm.startPrank(admin);
-        FOTTokenProxy(payable(address(fotToken))).setFeeConfig(newTxFee, dan);
+        fotToken.setFeeConfig(newTxFee, dan);
 
         deal(address(fotToken), alice, 100 ether);