Clean up

advanced_knowledge/saving_gas/gasless_token_transfer.sol

@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.18;
+
+// gaslless erc20 token transfer with meta transaction
+
+interface IERC20Permit {
+    function totalSupply() external view returns (uint256);
+
+    function balanceOf(address account) external view returns (uint256);
+
+    function transfer(address recipient, uint256 amount) external returns (bool);
+
+    function allowance(address owner, address spender) external view returns (uint256);
+
+    function approve(address spender, uint256 amount) external returns (bool);
+
+    function transferFrom(
+        address sender,
+        address recipient,
+        uint256 amount
+    ) external returns (bool);
+
+    function permit(
+        address owner,
+        address spender,
+        uint256 value,
+        uint256 deadline,
+        uint8 v,
+        bytes32 r,
+        bytes32 s
+    ) external;
+
+    event Transfer(address indexed from, address indexed to, uint256 value);
+    event Approval(address indexed owner, address indexed spender, uint256 value);
+}
+
+contract GaslessTokenTransfer {
+    function send(
+        address token,
+        address sender,
+        address receiver,
+        uint256 amount,
+        uint256 fee,
+        uint256 deadline,
+        // Permit signature
+        uint8 v,
+        bytes32 r,
+        bytes32 s
+    ) external {
+        // Permit
+        IERC20Permit(token).permit(
+            sender,
+            address(this),
+            amount + fee,
+            deadline,
+            v,
+            r,
+            s
+        );
+        // Send amount to receiver
+        IERC20Permit(token).transferFrom(sender, receiver, amount);
+        // Take fee - send fee to msg.sender
+        IERC20Permit(token).transferFrom(sender, msg.sender, fee);
+    }
+}