Alternative flash loan entry point without function pointers

README.md

@@ -1,6 +1,8 @@
 # ERC7399 Flash Lender Wrappers
 
-This repository contains contracts that work as [ERC7399](https://github.com/ethereum/EIPs/blob/d072207e24e3cc12b6315909e6a65275a38e1984/EIPS/eip-7399.md) entry points for popular flash lenders.
+This repository contains contracts that work as
+[ERC7399](https://github.com/ethereum/EIPs/blob/d072207e24e3cc12b6315909e6a65275a38e1984/EIPS/eip-7399.md) entry points
+for popular flash lenders.
 
 ## How Do These Wrappers Work
 
@@ -20,23 +22,28 @@ sequenceDiagram
     Wrapper --> Wrapper: approves token repayment to lender †
     Wrapper -->> Lender: lender calls transferFrom(wrapper, amount + fee) †
 ```
-† For the BalancerWrapper and Uniswap v3 the borrower transfers the repayment to the lender and the wrapper skips the repayment approval.
+
+† For the BalancerWrapper and Uniswap v3 the borrower transfers the repayment to the lender and the wrapper skips the
+repayment approval.
 
 ## Addresses
 
 Contracts are deployed at the same address for all supported networks.
 
-| Contract | Lender | Address | Networks |
-| ---- | ---- | ---- | ---- |
-|[AaveWrapper](src/aave/AaveWrapper.sol)|Aave v3|0x02C7632b84B3447845531541d0285D67E656e50c|Arbitrum One, Optimism|
-|[BalancerWrapper](src/balancer/BalancerWrapper.sol)|Balancer v2|0x3d4DF8596e5750A4F721c8764d585dcc8623d009|Arbitrum One, Optimism|
-|[UniswapV3Wrapper](src/uniswapV3/UniswapV3Wrapper.sol)|Uniswap v3|0x23de8e0bB91A105bEFf9d40d8d75C1A9fE40f523|Arbitrum One, Optimism|
+| Contract                                               | Lender      | Address                                    | Networks               |
+| ------------------------------------------------------ | ----------- | ------------------------------------------ | ---------------------- |
+| [AaveWrapper](src/aave/AaveWrapper.sol)                | Aave v3     | 0x02C7632b84B3447845531541d0285D67E656e50c | Arbitrum One, Optimism |
+| [BalancerWrapper](src/balancer/BalancerWrapper.sol)    | Balancer v2 | 0x3d4DF8596e5750A4F721c8764d585dcc8623d009 | Arbitrum One, Optimism |
+| [UniswapV3Wrapper](src/uniswapV3/UniswapV3Wrapper.sol) | Uniswap v3  | 0x23de8e0bB91A105bEFf9d40d8d75C1A9fE40f523 | Arbitrum One, Optimism |
 
-When a contract requires constructor parameters which vary per network, these are supplied by the [Registry](https://github.com/alcueca/registry) deployed at 0x05caE14d1A348B29d2b169697b4BE51009a9C4dF in each supported network.
+When a contract requires constructor parameters which vary per network, these are supplied by the
+[Registry](https://github.com/alcueca/registry) deployed at 0x05caE14d1A348B29d2b169697b4BE51009a9C4dF in each supported
+network.
 
 ## Flash Loans
 
-For detail on executing flash loans, please refer to the [ERC7399](https://github.com/ethereum/EIPs/blob/d072207e24e3cc12b6315909e6a65275a38e1984/EIPS/eip-7399.md) EIP.
+For detail on executing flash loans, please refer to the
+[ERC7399](https://github.com/ethereum/EIPs/blob/d072207e24e3cc12b6315909e6a65275a38e1984/EIPS/eip-7399.md) EIP.
 
 ## Using This Repository
 

src/BaseWrapper.sol

@@ -5,6 +5,7 @@ pragma solidity ^0.8.19;
 import "erc7399/IERC7399.sol";
 
 import { TransferHelper, ERC20 } from "./utils/TransferHelper.sol";
+import { FunctionCodec } from "./utils/FunctionCodec.sol";
 
 /// @dev All ERC7399 flash loan wrappers have the same general structure.
 /// - The ERC7399 `flash` function is the entry point for the flash loan.
@@ -52,6 +53,34 @@ abstract contract BaseWrapper is IERC7399 {
             initiatorData: initiatorData
         });
 
+        return _flash(asset, amount, data);
+    }
+
+    /// @dev Alternative entry point for the ERC7399 flash loan, without function pointers. Packs data to convert the
+    /// legacy flash loan into an ERC7399 flash loan. Then it calls the legacy flash loan. Once the flash loan is done,
+    /// checks if there is any return data and returns it.
+    function flash(
+        address loanReceiver,
+        address asset,
+        uint256 amount,
+        bytes calldata initiatorData,
+        address callbackTarget,
+        bytes4 callbackSelector
+    )
+        external
+        returns (bytes memory result)
+    {
+        Data memory data = Data({
+            loanReceiver: loanReceiver,
+            initiator: msg.sender,
+            callback: FunctionCodec.decodeFunction(callbackTarget, callbackSelector),
+            initiatorData: initiatorData
+        });
+
+        return _flash(asset, amount, data);
+    }
+
+    function _flash(address asset, uint256 amount, Data memory data) internal virtual returns (bytes memory result) {
         _flashLoan(asset, amount, abi.encode(data));
 
         result = _callbackResult;
@@ -63,7 +92,7 @@ abstract contract BaseWrapper is IERC7399 {
     }
 
     /// @dev Call the legacy flashloan function in the child contract. This is where we borrow from Aave, Uniswap, etc.
-    function _flashLoan(address asset, uint256 amount, bytes memory params) internal virtual;
+    function _flashLoan(address asset, uint256 amount, bytes memory data) internal virtual;
 
     /// @dev Handle the common parts of bridging the callback from legacy to ERC7399. Transfer the funds to the loan
     /// receiver. Call the callback supplied by the original borrower. Approve the repayment if necessary. If there is

src/utils/FunctionCodec.sol

@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.19;
+
+library FunctionCodec {
+    function encodeParams(address contractAddr, bytes4 selector) internal pure returns (bytes24) {
+        return bytes24(bytes20(contractAddr)) | bytes24(selector) >> 160;
+    }
+
+    function decodeParams(bytes24 encoded) internal pure returns (address contractAddr, bytes4 selector) {
+        contractAddr = address(bytes20(encoded));
+        selector = bytes4(encoded << 160);
+    }
+
+    function encodeFunction(
+        function(address, address, address, uint256, uint256, bytes memory) external returns (bytes memory) f
+    )
+        internal
+        pure
+        returns (bytes24)
+    {
+        return encodeParams(f.address, f.selector);
+    }
+
+    function decodeFunction(
+        address contractAddr,
+        bytes4 selector
+    )
+        internal
+        pure
+        returns (function(address, address, address, uint256, uint256, bytes memory) external returns (bytes memory) f)
+    {
+        uint32 s = uint32(selector);
+        // solhint-disable-next-line no-inline-assembly
+        assembly {
+            f.address := contractAddr
+            f.selector := s
+        }
+    }
+
+    function decodeFunction(bytes24 encoded)
+        internal
+        pure
+        returns (function(address, address, address, uint256, uint256, bytes memory) external returns (bytes memory) f)
+    {
+        (address contractAddr, bytes4 selector) = decodeParams(encoded);
+        return decodeFunction(contractAddr, selector);
+    }
+}

test/BaseWrapper.t.sol

@@ -50,6 +50,21 @@ contract BaseWrapperTest is PRBTest, StdCheats {
         assertEq(vm.load(address(wrapper), bytes32(uint256(0))), "");
     }
 
+    function test_flashLoanNoPointers() external {
+        console2.log("test_flashLoan");
+        uint256 loan = 1e18;
+        uint256 fee = wrapper.flashFee(dai, loan);
+        ERC20(dai).transfer(address(borrower), fee);
+        bytes memory result = borrower.flashBorrow(dai, loan);
+
+        // Test the return values passed through the wrapper
+        (bytes32 callbackReturn) = abi.decode(result, (bytes32));
+        assertEq(uint256(callbackReturn), uint256(borrower.ERC3156PP_CALLBACK_SUCCESS()), "Callback failed");
+
+        // Test the wrapper state (return bytes should be cleaned up)
+        assertEq(vm.load(address(wrapper), bytes32(uint256(0))), "");
+    }
+
     function test_flashLoan_void() external {
         console2.log("test_flashLoan_void");
         uint256 loan = 1e18;

test/MockBorrower.sol

@@ -2,6 +2,7 @@
 pragma solidity ^0.8.19;
 
 import "erc7399/IERC7399.sol";
+import "src/BaseWrapper.sol";
 
 import { ERC20 } from "solmate/tokens/ERC20.sol";
 
@@ -134,6 +135,12 @@ contract MockBorrower {
         return lender.flash(address(loanReceiver), asset, amount, "", this.onFlashLoan);
     }
 
+    function flashBorrowNoPointers(address asset, uint256 amount) public returns (bytes memory) {
+        return BaseWrapper(address(lender)).flash(
+            address(loanReceiver), asset, amount, "", address(this), this.onFlashLoan.selector
+        );
+    }
+
     function flashBorrowAndSteal(address asset, uint256 amount) public returns (bytes memory) {
         return lender.flash(address(loanReceiver), asset, amount, "", this.onSteal);
     }