From c779e24fbc5f64d401bca31848596da434993d07 Mon Sep 17 00:00:00 2001
From: Rubilmax <rmilon@gmail.com>
Date: Mon, 24 Jul 2023 15:51:24 +0200
Subject: [PATCH 01/12] feat(flash-loan): add flash loan

---
 src/Blue.sol                      | 21 +++++++++++++++++++++
 src/interfaces/IFlashBorrower.sol | 18 ++++++++++++++++++
 src/libraries/Errors.sol          |  2 ++
 3 files changed, 41 insertions(+)
 create mode 100644 src/interfaces/IFlashBorrower.sol

diff --git a/src/Blue.sol b/src/Blue.sol
index 9c864cfde..6977b7dbd 100644
--- a/src/Blue.sol
+++ b/src/Blue.sol
@@ -3,6 +3,7 @@ pragma solidity 0.8.20;
 
 import {IIrm} from "src/interfaces/IIrm.sol";
 import {IERC20} from "src/interfaces/IERC20.sol";
+import {IFlashBorrower} from "src/interfaces/IFlashBorrower.sol";
 
 import {Errors} from "./libraries/Errors.sol";
 import {SharesMath} from "src/libraries/SharesMath.sol";
@@ -13,6 +14,9 @@ import {SafeTransferLib} from "src/libraries/SafeTransferLib.sol";
 uint256 constant WAD = 1e18;
 uint256 constant ALPHA = 0.5e18;
 
+/// @dev The expected success hash returned by the FlashBorrower.
+bytes32 constant FLASH_BORROWER_SUCCESS_HASH = keccak256("FlashBorrower.onFlashLoan");
+
 contract Blue {
     using SharesMath for uint256;
     using FixedPointMathLib for uint256;
@@ -244,6 +248,23 @@ contract Blue {
         market.borrowableAsset.safeTransferFrom(msg.sender, address(this), repaid);
     }
 
+    // Flash Loans.
+
+    function flashLoan(IFlashBorrower receiver, IERC20 token, uint256 amount, bytes calldata data)
+        public
+        virtual
+        returns (bytes memory)
+    {
+        token.safeTransfer(address(receiver), amount);
+
+        (bytes32 successHash, bytes memory returnData) = receiver.onFlashLoan(msg.sender, token, amount, data);
+        require(successHash == FLASH_BORROWER_SUCCESS_HASH, Errors.INVALID_SUCCESS_HASH);
+
+        token.safeTransferFrom(address(receiver), address(this), amount);
+
+        return returnData;
+    }
+
     // Position management.
 
     function setApproval(address manager, bool isAllowed) external {
diff --git a/src/interfaces/IFlashBorrower.sol b/src/interfaces/IFlashBorrower.sol
new file mode 100644
index 000000000..543ff4ec7
--- /dev/null
+++ b/src/interfaces/IFlashBorrower.sol
@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+pragma solidity ^0.8.0;
+
+import {IERC20} from "src/interfaces/IERC20.sol";
+
+/// @dev Interface of the FlashBorrower, inspired by https://eips.ethereum.org/EIPS/eip-3156.
+///      The FlashLender's `flashLoan` function now returns the FlashBorrower's return data.
+interface IFlashBorrower {
+    /// @dev Receive a flash loan.
+    /// @param initiator The initiator of the loan.
+    /// @param token The loan currency.
+    /// @param amount The amount of tokens lent.
+    /// @param data Arbitrary data structure, intended to contain user-defined parameters.
+    /// @return The keccak256 hash of "FlashBorrower.onFlashLoan" and any additional arbitrary data.
+    function onFlashLoan(address initiator, IERC20 token, uint256 amount, bytes calldata data)
+        external
+        returns (bytes32, bytes memory);
+}
diff --git a/src/libraries/Errors.sol b/src/libraries/Errors.sol
index c7c2235d8..ca5d27fe2 100644
--- a/src/libraries/Errors.sol
+++ b/src/libraries/Errors.sol
@@ -23,4 +23,6 @@ library Errors {
     string internal constant INSUFFICIENT_LIQUIDITY = "insufficient liquidity";
 
     string internal constant HEALTHY_POSITION = "position is healthy";
+
+    string internal constant INVALID_SUCCESS_HASH = "invalid success hash";
 }

From 33c390b68675a6d895c46d5f4d3a1d0b85c9faae Mon Sep 17 00:00:00 2001
From: Rubilmax <rmilon@gmail.com>
Date: Mon, 24 Jul 2023 16:07:31 +0200
Subject: [PATCH 02/12] test(flash-loan): add flash borrower mock

---
 src/Blue.sol                      |  5 +---
 src/interfaces/IFlashBorrower.sol |  5 +++-
 src/interfaces/IFlashLender.sol   | 18 +++++++++++++++
 src/libraries/SafeTransferLib.sol | 29 +++++++++++++++++++++++
 src/mocks/FlashBorrowerMock.sol   | 38 +++++++++++++++++++++++++++++++
 test/hardhat/Blue.spec.ts         | 16 +++++++++++++
 6 files changed, 106 insertions(+), 5 deletions(-)
 create mode 100644 src/interfaces/IFlashLender.sol
 create mode 100644 src/mocks/FlashBorrowerMock.sol

diff --git a/src/Blue.sol b/src/Blue.sol
index 6977b7dbd..d6ab32758 100644
--- a/src/Blue.sol
+++ b/src/Blue.sol
@@ -3,7 +3,7 @@ pragma solidity 0.8.20;
 
 import {IIrm} from "src/interfaces/IIrm.sol";
 import {IERC20} from "src/interfaces/IERC20.sol";
-import {IFlashBorrower} from "src/interfaces/IFlashBorrower.sol";
+import {IFlashBorrower, FLASH_BORROWER_SUCCESS_HASH} from "src/interfaces/IFlashBorrower.sol";
 
 import {Errors} from "./libraries/Errors.sol";
 import {SharesMath} from "src/libraries/SharesMath.sol";
@@ -14,9 +14,6 @@ import {SafeTransferLib} from "src/libraries/SafeTransferLib.sol";
 uint256 constant WAD = 1e18;
 uint256 constant ALPHA = 0.5e18;
 
-/// @dev The expected success hash returned by the FlashBorrower.
-bytes32 constant FLASH_BORROWER_SUCCESS_HASH = keccak256("FlashBorrower.onFlashLoan");
-
 contract Blue {
     using SharesMath for uint256;
     using FixedPointMathLib for uint256;
diff --git a/src/interfaces/IFlashBorrower.sol b/src/interfaces/IFlashBorrower.sol
index 543ff4ec7..a5b41d482 100644
--- a/src/interfaces/IFlashBorrower.sol
+++ b/src/interfaces/IFlashBorrower.sol
@@ -1,8 +1,11 @@
-// SPDX-License-Identifier: AGPL-3.0-only
+// SPDX-License-Identifier: UNLICENSED
 pragma solidity ^0.8.0;
 
 import {IERC20} from "src/interfaces/IERC20.sol";
 
+/// @dev The expected success hash returned by the FlashBorrower.
+bytes32 constant FLASH_BORROWER_SUCCESS_HASH = keccak256("FlashBorrower.onFlashLoan");
+
 /// @dev Interface of the FlashBorrower, inspired by https://eips.ethereum.org/EIPS/eip-3156.
 ///      The FlashLender's `flashLoan` function now returns the FlashBorrower's return data.
 interface IFlashBorrower {
diff --git a/src/interfaces/IFlashLender.sol b/src/interfaces/IFlashLender.sol
new file mode 100644
index 000000000..59e21c675
--- /dev/null
+++ b/src/interfaces/IFlashLender.sol
@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.0;
+
+import {IERC20} from "src/interfaces/IERC20.sol";
+import {IFlashBorrower} from "./IFlashBorrower.sol";
+
+/// @dev Interface of the Flash Lender, inspired by https://eips.ethereum.org/EIPS/eip-3156.
+///      The FlashLender's `flashLoan` function now returns the FlashBorrower's return data.
+interface IFlashLender {
+    /// @dev Initiate a flash loan.
+    /// @param receiver The receiver of the tokens in the loan, and the receiver of the callback.
+    /// @param token The loan currency.
+    /// @param amount The amount of tokens lent.
+    /// @param data Arbitrary data structure, intended to contain user-defined parameters.
+    function flashLoan(IFlashBorrower receiver, IERC20 token, uint256 amount, bytes calldata data)
+        external
+        returns (bytes memory);
+}
diff --git a/src/libraries/SafeTransferLib.sol b/src/libraries/SafeTransferLib.sol
index 016cd598a..eba51ba20 100644
--- a/src/libraries/SafeTransferLib.sol
+++ b/src/libraries/SafeTransferLib.sol
@@ -66,4 +66,33 @@ library SafeTransferLib {
 
         require(success, "TRANSFER_FAILED");
     }
+
+    function safeApprove(IERC20 token, address to, uint256 amount) internal {
+        bool success;
+
+        /// @solidity memory-safe-assembly
+        assembly {
+            // Get a pointer to some free memory.
+            let freeMemoryPointer := mload(0x40)
+
+            // Write the abi-encoded calldata into memory, beginning with the function selector.
+            mstore(freeMemoryPointer, 0x095ea7b300000000000000000000000000000000000000000000000000000000)
+            mstore(add(freeMemoryPointer, 4), and(to, 0xffffffffffffffffffffffffffffffffffffffff)) // Append and mask the "to" argument.
+            mstore(add(freeMemoryPointer, 36), amount) // Append the "amount" argument. Masking not required as it's a full 32 byte type.
+
+            success :=
+                and(
+                    // Set success to whether the call reverted, if not we check it either
+                    // returned exactly 1 (can't just be non-zero data), or had no return data.
+                    or(and(eq(mload(0), 1), gt(returndatasize(), 31)), iszero(returndatasize())),
+                    // We use 68 because the length of our calldata totals up like so: 4 + 32 * 2.
+                    // We use 0 and 32 to copy up to 32 bytes of return data into the scratch space.
+                    // Counterintuitively, this call must be positioned second to the or() call in the
+                    // surrounding and() call or else returndatasize() will be zero during the computation.
+                    call(gas(), token, 0, freeMemoryPointer, 68, 0, 32)
+                )
+        }
+
+        require(success, "APPROVE_FAILED");
+    }
 }
diff --git a/src/mocks/FlashBorrowerMock.sol b/src/mocks/FlashBorrowerMock.sol
new file mode 100644
index 000000000..9e64eed63
--- /dev/null
+++ b/src/mocks/FlashBorrowerMock.sol
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.0;
+
+import {IERC20} from "src/interfaces/IERC20.sol";
+import {IFlashLender} from "src/interfaces/IFlashLender.sol";
+import {IFlashBorrower, FLASH_BORROWER_SUCCESS_HASH} from "src/interfaces/IFlashBorrower.sol";
+
+import {SafeTransferLib} from "src/libraries/SafeTransferLib.sol";
+
+contract FlashBorrowerMock is IFlashBorrower {
+    using SafeTransferLib for IERC20;
+
+    IFlashLender private immutable _LENDER;
+
+    constructor(IFlashLender lender) {
+        _LENDER = lender;
+    }
+
+    /* EXTERNAL */
+
+    function flashLoan(IERC20 token, uint256 amount, bytes calldata data) external virtual returns (bytes memory) {
+        return _LENDER.flashLoan(this, token, amount, data);
+    }
+
+    /// @inheritdoc IFlashBorrower
+    function onFlashLoan(address initiator, IERC20 token, uint256 amount, bytes calldata)
+        external
+        virtual
+        returns (bytes32, bytes memory)
+    {
+        require(msg.sender == address(_LENDER), "invalid lender");
+        require(initiator == address(this), "invalid initiator");
+
+        token.safeApprove(address(_LENDER), amount);
+
+        return (FLASH_BORROWER_SUCCESS_HASH, bytes(""));
+    }
+}
diff --git a/test/hardhat/Blue.spec.ts b/test/hardhat/Blue.spec.ts
index 08193f88e..bc92c7974 100644
--- a/test/hardhat/Blue.spec.ts
+++ b/test/hardhat/Blue.spec.ts
@@ -5,6 +5,7 @@ import { expect } from "chai";
 import { BigNumber, constants, utils } from "ethers";
 import hre from "hardhat";
 import { Blue, OracleMock, ERC20Mock, IrmMock } from "types";
+import { FlashBorrowerMock } from "types/src/mocks/FlashBorrowerMock";
 
 const closePositions = false;
 const initBalance = constants.MaxUint256.div(2);
@@ -51,6 +52,8 @@ describe("Blue", () => {
 
   let nbLiquidations: number;
 
+  let flashBorrower: FlashBorrowerMock;
+
   const updateMarket = (newMarket: Partial<Market>) => {
     market = { ...market, ...newMarket };
     id = identifier(market);
@@ -110,6 +113,10 @@ describe("Blue", () => {
 
     await borrowable.setBalance(liquidator.address, initBalance);
     await borrowable.connect(liquidator).approve(blue.address, constants.MaxUint256);
+
+    const FlashBorrowerFactory = await hre.ethers.getContractFactory("FlashBorrowerMock", admin);
+
+    flashBorrower = await FlashBorrowerFactory.deploy(blue.address);
   });
 
   it("should simulate gas cost [main]", async () => {
@@ -185,4 +192,13 @@ describe("Blue", () => {
       await borrowableOracle.setPrice(BigNumber.WAD);
     }
   });
+
+  it("should simuate gas cost [flashloan]", async () => {
+    const user = signers[0];
+    const amount = BigNumber.WAD;
+
+    await blue.connect(user).supply(market, amount, user.address);
+
+    await flashBorrower.flashLoan(borrowable.address, amount.div(2), []);
+  });
 });

From 4f498386be16dea5ca90dd044f8a63788e77c144 Mon Sep 17 00:00:00 2001
From: Romain Milon <rmilon@gmail.com>
Date: Tue, 25 Jul 2023 09:55:51 +0200
Subject: [PATCH 03/12] refactor(flash-loan): remove virtual modifier

Co-authored-by: MathisGD <74971347+MathisGD@users.noreply.github.com>
Signed-off-by: Romain Milon <rmilon@gmail.com>
---
 src/Blue.sol | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/Blue.sol b/src/Blue.sol
index d6ab32758..899d746f7 100644
--- a/src/Blue.sol
+++ b/src/Blue.sol
@@ -249,7 +249,6 @@ contract Blue {
 
     function flashLoan(IFlashBorrower receiver, IERC20 token, uint256 amount, bytes calldata data)
         public
-        virtual
         returns (bytes memory)
     {
         token.safeTransfer(address(receiver), amount);

From f36fdf095abd7f74d96f6d6d4b9a1ac6daff5138 Mon Sep 17 00:00:00 2001
From: Romain Milon <rmilon@gmail.com>
Date: Tue, 25 Jul 2023 09:56:18 +0200
Subject: [PATCH 04/12] docs(flash-loan): modify natspecs

Co-authored-by: MathisGD <74971347+MathisGD@users.noreply.github.com>
Signed-off-by: Romain Milon <rmilon@gmail.com>
---
 src/interfaces/IFlashBorrower.sol | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/interfaces/IFlashBorrower.sol b/src/interfaces/IFlashBorrower.sol
index a5b41d482..71e12b9e4 100644
--- a/src/interfaces/IFlashBorrower.sol
+++ b/src/interfaces/IFlashBorrower.sol
@@ -13,7 +13,7 @@ interface IFlashBorrower {
     /// @param initiator The initiator of the loan.
     /// @param token The loan currency.
     /// @param amount The amount of tokens lent.
-    /// @param data Arbitrary data structure, intended to contain user-defined parameters.
+    /// @param data Arbitrary data, intended to contain user-defined parameters.
     /// @return The keccak256 hash of "FlashBorrower.onFlashLoan" and any additional arbitrary data.
     function onFlashLoan(address initiator, IERC20 token, uint256 amount, bytes calldata data)
         external

From cf7e86b5a7b470423dc2b42417798aecb4cfb891 Mon Sep 17 00:00:00 2001
From: Romain Milon <rmilon@gmail.com>
Date: Tue, 25 Jul 2023 10:05:36 +0200
Subject: [PATCH 05/12] docs(flash-borrower): update natspecs

Co-authored-by: Merlin Egalite <44097430+MerlinEgalite@users.noreply.github.com>
Signed-off-by: Romain Milon <rmilon@gmail.com>
---
 src/interfaces/IFlashBorrower.sol | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/interfaces/IFlashBorrower.sol b/src/interfaces/IFlashBorrower.sol
index 71e12b9e4..a026c138c 100644
--- a/src/interfaces/IFlashBorrower.sol
+++ b/src/interfaces/IFlashBorrower.sol
@@ -9,7 +9,7 @@ bytes32 constant FLASH_BORROWER_SUCCESS_HASH = keccak256("FlashBorrower.onFlashL
 /// @dev Interface of the FlashBorrower, inspired by https://eips.ethereum.org/EIPS/eip-3156.
 ///      The FlashLender's `flashLoan` function now returns the FlashBorrower's return data.
 interface IFlashBorrower {
-    /// @dev Receive a flash loan.
+    /// @dev Receives a flash loan.
     /// @param initiator The initiator of the loan.
     /// @param token The loan currency.
     /// @param amount The amount of tokens lent.

From c6d46f3b64d5c9cdd6699197883611fb9c4c1fa0 Mon Sep 17 00:00:00 2001
From: Romain Milon <rmilon@gmail.com>
Date: Tue, 25 Jul 2023 10:06:00 +0200
Subject: [PATCH 06/12] docs(flash-borrower): update natspecs

Co-authored-by: Merlin Egalite <44097430+MerlinEgalite@users.noreply.github.com>
Signed-off-by: Romain Milon <rmilon@gmail.com>
---
 src/interfaces/IFlashBorrower.sol | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/interfaces/IFlashBorrower.sol b/src/interfaces/IFlashBorrower.sol
index a026c138c..259ff7ba0 100644
--- a/src/interfaces/IFlashBorrower.sol
+++ b/src/interfaces/IFlashBorrower.sol
@@ -11,7 +11,7 @@ bytes32 constant FLASH_BORROWER_SUCCESS_HASH = keccak256("FlashBorrower.onFlashL
 interface IFlashBorrower {
     /// @dev Receives a flash loan.
     /// @param initiator The initiator of the loan.
-    /// @param token The loan currency.
+    /// @param token The token lent.
     /// @param amount The amount of tokens lent.
     /// @param data Arbitrary data, intended to contain user-defined parameters.
     /// @return The keccak256 hash of "FlashBorrower.onFlashLoan" and any additional arbitrary data.

From eee3cfdf9883ab7ccbfa264ac51cfe93661b8c28 Mon Sep 17 00:00:00 2001
From: Romain Milon <rmilon@gmail.com>
Date: Tue, 25 Jul 2023 10:06:15 +0200
Subject: [PATCH 07/12] docs(flash-lender): update natspecs

Co-authored-by: Merlin Egalite <44097430+MerlinEgalite@users.noreply.github.com>
Signed-off-by: Romain Milon <rmilon@gmail.com>
---
 src/interfaces/IFlashLender.sol | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/interfaces/IFlashLender.sol b/src/interfaces/IFlashLender.sol
index 59e21c675..6c91e2eb7 100644
--- a/src/interfaces/IFlashLender.sol
+++ b/src/interfaces/IFlashLender.sol
@@ -7,7 +7,7 @@ import {IFlashBorrower} from "./IFlashBorrower.sol";
 /// @dev Interface of the Flash Lender, inspired by https://eips.ethereum.org/EIPS/eip-3156.
 ///      The FlashLender's `flashLoan` function now returns the FlashBorrower's return data.
 interface IFlashLender {
-    /// @dev Initiate a flash loan.
+    /// @dev Initiates a flash loan.
     /// @param receiver The receiver of the tokens in the loan, and the receiver of the callback.
     /// @param token The loan currency.
     /// @param amount The amount of tokens lent.

From 47b5ffdfda03d1b0d14a5a2410745eb86fae5a92 Mon Sep 17 00:00:00 2001
From: Romain Milon <rmilon@gmail.com>
Date: Tue, 25 Jul 2023 11:04:29 +0200
Subject: [PATCH 08/12] docs(flash-lender): update natspecs

Co-authored-by: Merlin Egalite <44097430+MerlinEgalite@users.noreply.github.com>
Signed-off-by: Romain Milon <rmilon@gmail.com>
---
 src/interfaces/IFlashLender.sol | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/interfaces/IFlashLender.sol b/src/interfaces/IFlashLender.sol
index 6c91e2eb7..4110e247a 100644
--- a/src/interfaces/IFlashLender.sol
+++ b/src/interfaces/IFlashLender.sol
@@ -9,7 +9,7 @@ import {IFlashBorrower} from "./IFlashBorrower.sol";
 interface IFlashLender {
     /// @dev Initiates a flash loan.
     /// @param receiver The receiver of the tokens in the loan, and the receiver of the callback.
-    /// @param token The loan currency.
+    /// @param token The token lent.
     /// @param amount The amount of tokens lent.
     /// @param data Arbitrary data structure, intended to contain user-defined parameters.
     function flashLoan(IFlashBorrower receiver, IERC20 token, uint256 amount, bytes calldata data)

From 0b6bfad5574d1fcc2476860d5c579166c73a5de2 Mon Sep 17 00:00:00 2001
From: Rubilmax <rmilon@gmail.com>
Date: Tue, 25 Jul 2023 11:36:30 +0200
Subject: [PATCH 09/12] refactor(flash-loan): stick to eip3156

---
 src/Blue.sol                             | 30 +++++++++++++++-------
 src/interfaces/IERC20.sol                |  4 ++-
 src/interfaces/IERC3156FlashBorrower.sol | 20 +++++++++++++++
 src/interfaces/IERC3156FlashLender.sol   | 32 ++++++++++++++++++++++++
 src/interfaces/IFlashBorrower.sol        | 21 ----------------
 src/interfaces/IFlashLender.sol          | 18 -------------
 src/mocks/FlashBorrowerMock.sol          | 26 ++++++++-----------
 test/forge/Blue.t.sol                    | 12 +++++++++
 test/hardhat/Blue.spec.ts                |  5 ++--
 9 files changed, 100 insertions(+), 68 deletions(-)
 create mode 100644 src/interfaces/IERC3156FlashBorrower.sol
 create mode 100644 src/interfaces/IERC3156FlashLender.sol
 delete mode 100644 src/interfaces/IFlashBorrower.sol
 delete mode 100644 src/interfaces/IFlashLender.sol

diff --git a/src/Blue.sol b/src/Blue.sol
index 9f009cd0d..3a87b131b 100644
--- a/src/Blue.sol
+++ b/src/Blue.sol
@@ -3,7 +3,8 @@ pragma solidity 0.8.20;
 
 import {IIrm} from "src/interfaces/IIrm.sol";
 import {IERC20} from "src/interfaces/IERC20.sol";
-import {IFlashBorrower, FLASH_BORROWER_SUCCESS_HASH} from "src/interfaces/IFlashBorrower.sol";
+import {IERC3156FlashLender} from "src/interfaces/IERC3156FlashLender.sol";
+import {IERC3156FlashBorrower, FLASH_BORROWER_SUCCESS_HASH} from "src/interfaces/IERC3156FlashBorrower.sol";
 
 import {Errors} from "./libraries/Errors.sol";
 import {SharesMath} from "src/libraries/SharesMath.sol";
@@ -15,7 +16,7 @@ uint256 constant WAD = 1e18;
 uint256 constant MAX_FEE = 0.2e18;
 uint256 constant ALPHA = 0.5e18;
 
-contract Blue {
+contract Blue is IERC3156FlashLender {
     using SharesMath for uint256;
     using FixedPointMathLib for uint256;
     using SafeTransferLib for IERC20;
@@ -248,18 +249,29 @@ contract Blue {
 
     // Flash Loans.
 
-    function flashLoan(IFlashBorrower receiver, IERC20 token, uint256 amount, bytes calldata data)
-        public
-        returns (bytes memory)
+    /// @inheritdoc IERC3156FlashLender
+    function maxFlashLoan(address token) external view returns (uint256) {
+        return IERC20(token).balanceOf(address(this));
+    }
+
+    /// @inheritdoc IERC3156FlashLender
+    function flashFee(address, uint256) external pure returns (uint256) {
+        return 0;
+    }
+
+    /// @inheritdoc IERC3156FlashLender
+    function flashLoan(IERC3156FlashBorrower receiver, address token, uint256 amount, bytes calldata data)
+        external
+        returns (bool)
     {
-        token.safeTransfer(address(receiver), amount);
+        IERC20(token).safeTransfer(address(receiver), amount);
 
-        (bytes32 successHash, bytes memory returnData) = receiver.onFlashLoan(msg.sender, token, amount, data);
+        bytes32 successHash = receiver.onFlashLoan(msg.sender, token, amount, 0, data);
         require(successHash == FLASH_BORROWER_SUCCESS_HASH, Errors.INVALID_SUCCESS_HASH);
 
-        token.safeTransferFrom(address(receiver), address(this), amount);
+        IERC20(token).safeTransferFrom(address(receiver), address(this), amount);
 
-        return returnData;
+        return true;
     }
 
     // Position management.
diff --git a/src/interfaces/IERC20.sol b/src/interfaces/IERC20.sol
index 31f0cc95f..b7610676f 100644
--- a/src/interfaces/IERC20.sol
+++ b/src/interfaces/IERC20.sol
@@ -3,4 +3,6 @@ pragma solidity >=0.5.0;
 
 /// @dev Empty because we only call functions in assembly. It prevents calling
 /// transfer (transferFrom) instead of safeTransfer (safeTransferFrom).
-interface IERC20 {}
+interface IERC20 {
+    function balanceOf(address owner) external view returns (uint256);
+}
diff --git a/src/interfaces/IERC3156FlashBorrower.sol b/src/interfaces/IERC3156FlashBorrower.sol
new file mode 100644
index 000000000..98cdea7b9
--- /dev/null
+++ b/src/interfaces/IERC3156FlashBorrower.sol
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity >=0.5.0;
+
+/// @dev The expected success hash returned by the FlashBorrower.
+bytes32 constant FLASH_BORROWER_SUCCESS_HASH = keccak256("ERC3156FlashBorrower.onFlashLoan");
+
+interface IERC3156FlashBorrower {
+    /**
+     * @dev Receives a flash loan.
+     * @param initiator The initiator of the loan.
+     * @param token The token lent.
+     * @param amount The amount of tokens lent.
+     * @param fee The additional amount of tokens to repay.
+     * @param data Arbitrary data structure, intended to contain user-defined parameters.
+     * @return The keccak256 hash of "ERC3156FlashBorrower.onFlashLoan"
+     */
+    function onFlashLoan(address initiator, address token, uint256 amount, uint256 fee, bytes calldata data)
+        external
+        returns (bytes32);
+}
diff --git a/src/interfaces/IERC3156FlashLender.sol b/src/interfaces/IERC3156FlashLender.sol
new file mode 100644
index 000000000..fa9d7a852
--- /dev/null
+++ b/src/interfaces/IERC3156FlashLender.sol
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity >=0.5.0;
+
+import {IERC3156FlashBorrower} from "src/interfaces/IERC3156FlashBorrower.sol";
+
+interface IERC3156FlashLender {
+    /**
+     * @dev The amount of currency available to be lent.
+     * @param token The token lent.
+     * @return The amount of `token` that can be borrowed.
+     */
+    function maxFlashLoan(address token) external view returns (uint256);
+
+    /**
+     * @dev The fee to be charged for a given loan.
+     * @param token The token lent.
+     * @param amount The amount of tokens lent.
+     * @return The amount of `token` to be charged for the loan, on top of the returned principal.
+     */
+    function flashFee(address token, uint256 amount) external view returns (uint256);
+
+    /**
+     * @dev Initiate a flash loan.
+     * @param receiver The receiver of the tokens in the loan, and the receiver of the callback.
+     * @param token The token lent.
+     * @param amount The amount of tokens lent.
+     * @param data Arbitrary data structure, intended to contain user-defined parameters.
+     */
+    function flashLoan(IERC3156FlashBorrower receiver, address token, uint256 amount, bytes calldata data)
+        external
+        returns (bool);
+}
diff --git a/src/interfaces/IFlashBorrower.sol b/src/interfaces/IFlashBorrower.sol
deleted file mode 100644
index 259ff7ba0..000000000
--- a/src/interfaces/IFlashBorrower.sol
+++ /dev/null
@@ -1,21 +0,0 @@
-// SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.8.0;
-
-import {IERC20} from "src/interfaces/IERC20.sol";
-
-/// @dev The expected success hash returned by the FlashBorrower.
-bytes32 constant FLASH_BORROWER_SUCCESS_HASH = keccak256("FlashBorrower.onFlashLoan");
-
-/// @dev Interface of the FlashBorrower, inspired by https://eips.ethereum.org/EIPS/eip-3156.
-///      The FlashLender's `flashLoan` function now returns the FlashBorrower's return data.
-interface IFlashBorrower {
-    /// @dev Receives a flash loan.
-    /// @param initiator The initiator of the loan.
-    /// @param token The token lent.
-    /// @param amount The amount of tokens lent.
-    /// @param data Arbitrary data, intended to contain user-defined parameters.
-    /// @return The keccak256 hash of "FlashBorrower.onFlashLoan" and any additional arbitrary data.
-    function onFlashLoan(address initiator, IERC20 token, uint256 amount, bytes calldata data)
-        external
-        returns (bytes32, bytes memory);
-}
diff --git a/src/interfaces/IFlashLender.sol b/src/interfaces/IFlashLender.sol
deleted file mode 100644
index 4110e247a..000000000
--- a/src/interfaces/IFlashLender.sol
+++ /dev/null
@@ -1,18 +0,0 @@
-// SPDX-License-Identifier: UNLICENSED
-pragma solidity ^0.8.0;
-
-import {IERC20} from "src/interfaces/IERC20.sol";
-import {IFlashBorrower} from "./IFlashBorrower.sol";
-
-/// @dev Interface of the Flash Lender, inspired by https://eips.ethereum.org/EIPS/eip-3156.
-///      The FlashLender's `flashLoan` function now returns the FlashBorrower's return data.
-interface IFlashLender {
-    /// @dev Initiates a flash loan.
-    /// @param receiver The receiver of the tokens in the loan, and the receiver of the callback.
-    /// @param token The token lent.
-    /// @param amount The amount of tokens lent.
-    /// @param data Arbitrary data structure, intended to contain user-defined parameters.
-    function flashLoan(IFlashBorrower receiver, IERC20 token, uint256 amount, bytes calldata data)
-        external
-        returns (bytes memory);
-}
diff --git a/src/mocks/FlashBorrowerMock.sol b/src/mocks/FlashBorrowerMock.sol
index 9e64eed63..0d60e3f21 100644
--- a/src/mocks/FlashBorrowerMock.sol
+++ b/src/mocks/FlashBorrowerMock.sol
@@ -2,37 +2,31 @@
 pragma solidity ^0.8.0;
 
 import {IERC20} from "src/interfaces/IERC20.sol";
-import {IFlashLender} from "src/interfaces/IFlashLender.sol";
-import {IFlashBorrower, FLASH_BORROWER_SUCCESS_HASH} from "src/interfaces/IFlashBorrower.sol";
+import {IERC3156FlashLender} from "src/interfaces/IERC3156FlashLender.sol";
+import {IERC3156FlashBorrower, FLASH_BORROWER_SUCCESS_HASH} from "src/interfaces/IERC3156FlashBorrower.sol";
 
 import {SafeTransferLib} from "src/libraries/SafeTransferLib.sol";
 
-contract FlashBorrowerMock is IFlashBorrower {
+contract FlashBorrowerMock is IERC3156FlashBorrower {
     using SafeTransferLib for IERC20;
 
-    IFlashLender private immutable _LENDER;
+    IERC3156FlashLender private immutable _LENDER;
 
-    constructor(IFlashLender lender) {
+    constructor(IERC3156FlashLender lender) {
         _LENDER = lender;
     }
 
     /* EXTERNAL */
 
-    function flashLoan(IERC20 token, uint256 amount, bytes calldata data) external virtual returns (bytes memory) {
-        return _LENDER.flashLoan(this, token, amount, data);
-    }
-
-    /// @inheritdoc IFlashBorrower
-    function onFlashLoan(address initiator, IERC20 token, uint256 amount, bytes calldata)
+    /// @inheritdoc IERC3156FlashBorrower
+    function onFlashLoan(address, address token, uint256 amount, uint256 fee, bytes calldata)
         external
-        virtual
-        returns (bytes32, bytes memory)
+        returns (bytes32)
     {
         require(msg.sender == address(_LENDER), "invalid lender");
-        require(initiator == address(this), "invalid initiator");
 
-        token.safeApprove(address(_LENDER), amount);
+        IERC20(token).safeApprove(address(_LENDER), amount + fee);
 
-        return (FLASH_BORROWER_SUCCESS_HASH, bytes(""));
+        return FLASH_BORROWER_SUCCESS_HASH;
     }
 }
diff --git a/test/forge/Blue.t.sol b/test/forge/Blue.t.sol
index 6df98903c..387c734ce 100644
--- a/test/forge/Blue.t.sol
+++ b/test/forge/Blue.t.sol
@@ -8,6 +8,7 @@ import "src/Blue.sol";
 import {ERC20Mock as ERC20} from "src/mocks/ERC20Mock.sol";
 import {OracleMock as Oracle} from "src/mocks/OracleMock.sol";
 import {IrmMock as Irm} from "src/mocks/IrmMock.sol";
+import {FlashBorrowerMock} from "src/mocks/FlashBorrowerMock.sol";
 
 contract BlueTest is Test {
     using FixedPointMathLib for uint256;
@@ -25,6 +26,7 @@ contract BlueTest is Test {
     Irm private irm;
     Market public market;
     Id public id;
+    FlashBorrowerMock internal flashBorrower;
 
     function setUp() public {
         // Create Blue.
@@ -35,6 +37,7 @@ contract BlueTest is Test {
         collateralAsset = new ERC20("collateral", "C", 18);
         borrowableOracle = new Oracle();
         collateralOracle = new Oracle();
+        flashBorrower = new FlashBorrowerMock(blue);
 
         irm = new Irm(blue);
         market = Market(
@@ -685,6 +688,15 @@ contract BlueTest is Test {
 
         vm.stopPrank();
     }
+
+    function testFlashLoan(uint256 amount) public {
+        amount = bound(amount, 1, 2 ** 64);
+
+        borrowableAsset.setBalance(address(this), amount);
+        blue.supply(market, amount, address(this));
+
+        blue.flashLoan(flashBorrower, address(borrowableAsset), amount, bytes(""));
+    }
 }
 
 function neq(Market memory a, Market memory b) pure returns (bool) {
diff --git a/test/hardhat/Blue.spec.ts b/test/hardhat/Blue.spec.ts
index bc92c7974..062ca4651 100644
--- a/test/hardhat/Blue.spec.ts
+++ b/test/hardhat/Blue.spec.ts
@@ -46,14 +46,13 @@ describe("Blue", () => {
   let borrowableOracle: OracleMock;
   let collateralOracle: OracleMock;
   let irm: IrmMock;
+  let flashBorrower: FlashBorrowerMock;
 
   let market: Market;
   let id: Buffer;
 
   let nbLiquidations: number;
 
-  let flashBorrower: FlashBorrowerMock;
-
   const updateMarket = (newMarket: Partial<Market>) => {
     market = { ...market, ...newMarket };
     id = identifier(market);
@@ -199,6 +198,6 @@ describe("Blue", () => {
 
     await blue.connect(user).supply(market, amount, user.address);
 
-    await flashBorrower.flashLoan(borrowable.address, amount.div(2), []);
+    await blue.flashLoan(flashBorrower.address, borrowable.address, amount.div(2), []);
   });
 });

From e54f7b0e3bd6588fd5adfad41d9fe0b8e9bfef6b Mon Sep 17 00:00:00 2001
From: Rubilmax <rmilon@gmail.com>
Date: Tue, 25 Jul 2023 11:50:59 +0200
Subject: [PATCH 10/12] refactor(libraries): use solmate in mocks

---
 src/libraries/SafeTransferLib.sol | 29 -----------------------------
 src/mocks/FlashBorrowerMock.sol   |  7 +++----
 2 files changed, 3 insertions(+), 33 deletions(-)

diff --git a/src/libraries/SafeTransferLib.sol b/src/libraries/SafeTransferLib.sol
index eba51ba20..016cd598a 100644
--- a/src/libraries/SafeTransferLib.sol
+++ b/src/libraries/SafeTransferLib.sol
@@ -66,33 +66,4 @@ library SafeTransferLib {
 
         require(success, "TRANSFER_FAILED");
     }
-
-    function safeApprove(IERC20 token, address to, uint256 amount) internal {
-        bool success;
-
-        /// @solidity memory-safe-assembly
-        assembly {
-            // Get a pointer to some free memory.
-            let freeMemoryPointer := mload(0x40)
-
-            // Write the abi-encoded calldata into memory, beginning with the function selector.
-            mstore(freeMemoryPointer, 0x095ea7b300000000000000000000000000000000000000000000000000000000)
-            mstore(add(freeMemoryPointer, 4), and(to, 0xffffffffffffffffffffffffffffffffffffffff)) // Append and mask the "to" argument.
-            mstore(add(freeMemoryPointer, 36), amount) // Append the "amount" argument. Masking not required as it's a full 32 byte type.
-
-            success :=
-                and(
-                    // Set success to whether the call reverted, if not we check it either
-                    // returned exactly 1 (can't just be non-zero data), or had no return data.
-                    or(and(eq(mload(0), 1), gt(returndatasize(), 31)), iszero(returndatasize())),
-                    // We use 68 because the length of our calldata totals up like so: 4 + 32 * 2.
-                    // We use 0 and 32 to copy up to 32 bytes of return data into the scratch space.
-                    // Counterintuitively, this call must be positioned second to the or() call in the
-                    // surrounding and() call or else returndatasize() will be zero during the computation.
-                    call(gas(), token, 0, freeMemoryPointer, 68, 0, 32)
-                )
-        }
-
-        require(success, "APPROVE_FAILED");
-    }
 }
diff --git a/src/mocks/FlashBorrowerMock.sol b/src/mocks/FlashBorrowerMock.sol
index 0d60e3f21..227b0d9c4 100644
--- a/src/mocks/FlashBorrowerMock.sol
+++ b/src/mocks/FlashBorrowerMock.sol
@@ -1,14 +1,13 @@
 // SPDX-License-Identifier: UNLICENSED
 pragma solidity ^0.8.0;
 
-import {IERC20} from "src/interfaces/IERC20.sol";
 import {IERC3156FlashLender} from "src/interfaces/IERC3156FlashLender.sol";
 import {IERC3156FlashBorrower, FLASH_BORROWER_SUCCESS_HASH} from "src/interfaces/IERC3156FlashBorrower.sol";
 
-import {SafeTransferLib} from "src/libraries/SafeTransferLib.sol";
+import {ERC20, SafeTransferLib} from "solmate/utils/SafeTransferLib.sol";
 
 contract FlashBorrowerMock is IERC3156FlashBorrower {
-    using SafeTransferLib for IERC20;
+    using SafeTransferLib for ERC20;
 
     IERC3156FlashLender private immutable _LENDER;
 
@@ -25,7 +24,7 @@ contract FlashBorrowerMock is IERC3156FlashBorrower {
     {
         require(msg.sender == address(_LENDER), "invalid lender");
 
-        IERC20(token).safeApprove(address(_LENDER), amount + fee);
+        ERC20(token).safeApprove(address(_LENDER), amount + fee);
 
         return FLASH_BORROWER_SUCCESS_HASH;
     }

From 762b88dc9fd136b020d7e90a092548a30e0da4c8 Mon Sep 17 00:00:00 2001
From: Rubilmax <rmilon@gmail.com>
Date: Tue, 25 Jul 2023 12:16:57 +0200
Subject: [PATCH 11/12] refactor(flash-loan): remove erc3156

---
 src/Blue.sol                             | 28 +++++----------------
 src/interfaces/IERC3156FlashBorrower.sol | 20 ---------------
 src/interfaces/IERC3156FlashLender.sol   | 32 ------------------------
 src/interfaces/IFlashBorrower.sol        | 13 ++++++++++
 src/interfaces/IFlashLender.sol          | 15 +++++++++++
 src/mocks/FlashBorrowerMock.sol          | 21 ++++++----------
 test/forge/Blue.t.sol                    |  2 ++
 7 files changed, 44 insertions(+), 87 deletions(-)
 delete mode 100644 src/interfaces/IERC3156FlashBorrower.sol
 delete mode 100644 src/interfaces/IERC3156FlashLender.sol
 create mode 100644 src/interfaces/IFlashBorrower.sol
 create mode 100644 src/interfaces/IFlashLender.sol

diff --git a/src/Blue.sol b/src/Blue.sol
index 3a87b131b..acb639d4f 100644
--- a/src/Blue.sol
+++ b/src/Blue.sol
@@ -3,8 +3,8 @@ pragma solidity 0.8.20;
 
 import {IIrm} from "src/interfaces/IIrm.sol";
 import {IERC20} from "src/interfaces/IERC20.sol";
-import {IERC3156FlashLender} from "src/interfaces/IERC3156FlashLender.sol";
-import {IERC3156FlashBorrower, FLASH_BORROWER_SUCCESS_HASH} from "src/interfaces/IERC3156FlashBorrower.sol";
+import {IFlashLender} from "src/interfaces/IFlashLender.sol";
+import {IFlashBorrower} from "src/interfaces/IFlashBorrower.sol";
 
 import {Errors} from "./libraries/Errors.sol";
 import {SharesMath} from "src/libraries/SharesMath.sol";
@@ -16,7 +16,7 @@ uint256 constant WAD = 1e18;
 uint256 constant MAX_FEE = 0.2e18;
 uint256 constant ALPHA = 0.5e18;
 
-contract Blue is IERC3156FlashLender {
+contract Blue is IFlashLender {
     using SharesMath for uint256;
     using FixedPointMathLib for uint256;
     using SafeTransferLib for IERC20;
@@ -249,29 +249,13 @@ contract Blue is IERC3156FlashLender {
 
     // Flash Loans.
 
-    /// @inheritdoc IERC3156FlashLender
-    function maxFlashLoan(address token) external view returns (uint256) {
-        return IERC20(token).balanceOf(address(this));
-    }
-
-    /// @inheritdoc IERC3156FlashLender
-    function flashFee(address, uint256) external pure returns (uint256) {
-        return 0;
-    }
-
-    /// @inheritdoc IERC3156FlashLender
-    function flashLoan(IERC3156FlashBorrower receiver, address token, uint256 amount, bytes calldata data)
-        external
-        returns (bool)
-    {
+    /// @inheritdoc IFlashLender
+    function flashLoan(IFlashBorrower receiver, address token, uint256 amount, bytes calldata data) external {
         IERC20(token).safeTransfer(address(receiver), amount);
 
-        bytes32 successHash = receiver.onFlashLoan(msg.sender, token, amount, 0, data);
-        require(successHash == FLASH_BORROWER_SUCCESS_HASH, Errors.INVALID_SUCCESS_HASH);
+        receiver.onFlashLoan(msg.sender, token, amount, data);
 
         IERC20(token).safeTransferFrom(address(receiver), address(this), amount);
-
-        return true;
     }
 
     // Position management.
diff --git a/src/interfaces/IERC3156FlashBorrower.sol b/src/interfaces/IERC3156FlashBorrower.sol
deleted file mode 100644
index 98cdea7b9..000000000
--- a/src/interfaces/IERC3156FlashBorrower.sol
+++ /dev/null
@@ -1,20 +0,0 @@
-// SPDX-License-Identifier: UNLICENSED
-pragma solidity >=0.5.0;
-
-/// @dev The expected success hash returned by the FlashBorrower.
-bytes32 constant FLASH_BORROWER_SUCCESS_HASH = keccak256("ERC3156FlashBorrower.onFlashLoan");
-
-interface IERC3156FlashBorrower {
-    /**
-     * @dev Receives a flash loan.
-     * @param initiator The initiator of the loan.
-     * @param token The token lent.
-     * @param amount The amount of tokens lent.
-     * @param fee The additional amount of tokens to repay.
-     * @param data Arbitrary data structure, intended to contain user-defined parameters.
-     * @return The keccak256 hash of "ERC3156FlashBorrower.onFlashLoan"
-     */
-    function onFlashLoan(address initiator, address token, uint256 amount, uint256 fee, bytes calldata data)
-        external
-        returns (bytes32);
-}
diff --git a/src/interfaces/IERC3156FlashLender.sol b/src/interfaces/IERC3156FlashLender.sol
deleted file mode 100644
index fa9d7a852..000000000
--- a/src/interfaces/IERC3156FlashLender.sol
+++ /dev/null
@@ -1,32 +0,0 @@
-// SPDX-License-Identifier: UNLICENSED
-pragma solidity >=0.5.0;
-
-import {IERC3156FlashBorrower} from "src/interfaces/IERC3156FlashBorrower.sol";
-
-interface IERC3156FlashLender {
-    /**
-     * @dev The amount of currency available to be lent.
-     * @param token The token lent.
-     * @return The amount of `token` that can be borrowed.
-     */
-    function maxFlashLoan(address token) external view returns (uint256);
-
-    /**
-     * @dev The fee to be charged for a given loan.
-     * @param token The token lent.
-     * @param amount The amount of tokens lent.
-     * @return The amount of `token` to be charged for the loan, on top of the returned principal.
-     */
-    function flashFee(address token, uint256 amount) external view returns (uint256);
-
-    /**
-     * @dev Initiate a flash loan.
-     * @param receiver The receiver of the tokens in the loan, and the receiver of the callback.
-     * @param token The token lent.
-     * @param amount The amount of tokens lent.
-     * @param data Arbitrary data structure, intended to contain user-defined parameters.
-     */
-    function flashLoan(IERC3156FlashBorrower receiver, address token, uint256 amount, bytes calldata data)
-        external
-        returns (bool);
-}
diff --git a/src/interfaces/IFlashBorrower.sol b/src/interfaces/IFlashBorrower.sol
new file mode 100644
index 000000000..65a3cf88b
--- /dev/null
+++ b/src/interfaces/IFlashBorrower.sol
@@ -0,0 +1,13 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity >=0.5.0;
+
+interface IFlashBorrower {
+    /**
+     * @dev Receives a flash loan.
+     * @param initiator The initiator of the loan.
+     * @param token The token lent.
+     * @param amount The amount of tokens lent.
+     * @param data Arbitrary data structure, intended to contain user-defined parameters.
+     */
+    function onFlashLoan(address initiator, address token, uint256 amount, bytes calldata data) external;
+}
diff --git a/src/interfaces/IFlashLender.sol b/src/interfaces/IFlashLender.sol
new file mode 100644
index 000000000..1cba63ca5
--- /dev/null
+++ b/src/interfaces/IFlashLender.sol
@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity >=0.5.0;
+
+import {IFlashBorrower} from "src/interfaces/IFlashBorrower.sol";
+
+interface IFlashLender {
+    /**
+     * @dev Initiate a flash loan.
+     * @param receiver The receiver of the tokens in the loan, and the receiver of the callback.
+     * @param token The token lent.
+     * @param amount The amount of tokens lent.
+     * @param data Arbitrary data structure, intended to contain user-defined parameters.
+     */
+    function flashLoan(IFlashBorrower receiver, address token, uint256 amount, bytes calldata data) external;
+}
diff --git a/src/mocks/FlashBorrowerMock.sol b/src/mocks/FlashBorrowerMock.sol
index 227b0d9c4..08c5aa869 100644
--- a/src/mocks/FlashBorrowerMock.sol
+++ b/src/mocks/FlashBorrowerMock.sol
@@ -1,31 +1,26 @@
 // SPDX-License-Identifier: UNLICENSED
 pragma solidity ^0.8.0;
 
-import {IERC3156FlashLender} from "src/interfaces/IERC3156FlashLender.sol";
-import {IERC3156FlashBorrower, FLASH_BORROWER_SUCCESS_HASH} from "src/interfaces/IERC3156FlashBorrower.sol";
+import {IFlashLender} from "src/interfaces/IFlashLender.sol";
+import {IFlashBorrower} from "src/interfaces/IFlashBorrower.sol";
 
 import {ERC20, SafeTransferLib} from "solmate/utils/SafeTransferLib.sol";
 
-contract FlashBorrowerMock is IERC3156FlashBorrower {
+contract FlashBorrowerMock is IFlashBorrower {
     using SafeTransferLib for ERC20;
 
-    IERC3156FlashLender private immutable _LENDER;
+    IFlashLender private immutable _LENDER;
 
-    constructor(IERC3156FlashLender lender) {
+    constructor(IFlashLender lender) {
         _LENDER = lender;
     }
 
     /* EXTERNAL */
 
-    /// @inheritdoc IERC3156FlashBorrower
-    function onFlashLoan(address, address token, uint256 amount, uint256 fee, bytes calldata)
-        external
-        returns (bytes32)
-    {
+    /// @inheritdoc IFlashBorrower
+    function onFlashLoan(address, address token, uint256 amount, bytes calldata) external {
         require(msg.sender == address(_LENDER), "invalid lender");
 
-        ERC20(token).safeApprove(address(_LENDER), amount + fee);
-
-        return FLASH_BORROWER_SUCCESS_HASH;
+        ERC20(token).safeApprove(address(_LENDER), amount);
     }
 }
diff --git a/test/forge/Blue.t.sol b/test/forge/Blue.t.sol
index 387c734ce..caa9d8635 100644
--- a/test/forge/Blue.t.sol
+++ b/test/forge/Blue.t.sol
@@ -696,6 +696,8 @@ contract BlueTest is Test {
         blue.supply(market, amount, address(this));
 
         blue.flashLoan(flashBorrower, address(borrowableAsset), amount, bytes(""));
+
+        assertEq(borrowableAsset.balanceOf(address(blue)), amount, "balanceOf");
     }
 }
 

From 5e8be49b994160ad36d6518bf5c0ece95b6a72a8 Mon Sep 17 00:00:00 2001
From: MerlinEgalite <egalite.merlin@gmail.com>
Date: Thu, 27 Jul 2023 09:09:13 +0200
Subject: [PATCH 12/12] chore: remove function in interface + small modif
 NATSPECs

---
 src/interfaces/IERC20.sol         |  4 +---
 src/interfaces/IFlashBorrower.sol | 12 +++++-------
 src/interfaces/IFlashLender.sol   | 12 +++++-------
 3 files changed, 11 insertions(+), 17 deletions(-)

diff --git a/src/interfaces/IERC20.sol b/src/interfaces/IERC20.sol
index b7610676f..31f0cc95f 100644
--- a/src/interfaces/IERC20.sol
+++ b/src/interfaces/IERC20.sol
@@ -3,6 +3,4 @@ pragma solidity >=0.5.0;
 
 /// @dev Empty because we only call functions in assembly. It prevents calling
 /// transfer (transferFrom) instead of safeTransfer (safeTransferFrom).
-interface IERC20 {
-    function balanceOf(address owner) external view returns (uint256);
-}
+interface IERC20 {}
diff --git a/src/interfaces/IFlashBorrower.sol b/src/interfaces/IFlashBorrower.sol
index 65a3cf88b..eb0d490d6 100644
--- a/src/interfaces/IFlashBorrower.sol
+++ b/src/interfaces/IFlashBorrower.sol
@@ -2,12 +2,10 @@
 pragma solidity >=0.5.0;
 
 interface IFlashBorrower {
-    /**
-     * @dev Receives a flash loan.
-     * @param initiator The initiator of the loan.
-     * @param token The token lent.
-     * @param amount The amount of tokens lent.
-     * @param data Arbitrary data structure, intended to contain user-defined parameters.
-     */
+    /// @dev Receives a flash loan.
+    /// @param initiator The initiator of the loan.
+    /// @param token The token lent.
+    /// @param amount The amount of tokens lent.
+    /// @param data Arbitrary data structure, intended to contain user-defined parameters.
     function onFlashLoan(address initiator, address token, uint256 amount, bytes calldata data) external;
 }
diff --git a/src/interfaces/IFlashLender.sol b/src/interfaces/IFlashLender.sol
index 1cba63ca5..603e18902 100644
--- a/src/interfaces/IFlashLender.sol
+++ b/src/interfaces/IFlashLender.sol
@@ -4,12 +4,10 @@ pragma solidity >=0.5.0;
 import {IFlashBorrower} from "src/interfaces/IFlashBorrower.sol";
 
 interface IFlashLender {
-    /**
-     * @dev Initiate a flash loan.
-     * @param receiver The receiver of the tokens in the loan, and the receiver of the callback.
-     * @param token The token lent.
-     * @param amount The amount of tokens lent.
-     * @param data Arbitrary data structure, intended to contain user-defined parameters.
-     */
+    /// @dev Initiate a flash loan.
+    /// @param receiver The receiver of the tokens in the loan, and the receiver of the callback.
+    /// @param token The token lent.
+    /// @param amount The amount of tokens lent.
+    /// @param data Arbitrary data structure, intended to contain user-defined parameters.
     function flashLoan(IFlashBorrower receiver, address token, uint256 amount, bytes calldata data) external;
 }