Bidirectional payment channel

bidirectional_payment_channel/.env.example

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+ALCHEMY_API_KEY=
+ROPSTEN_PRIVATE_KEY=

bidirectional_payment_channel/.gitignore

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+node_modules
+.env
+
+#Hardhat files
+cache
+artifacts
+dist
+typechain

bidirectional_payment_channel/.prettierrc

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+{
+  "overrides": [
+    {
+      "files": "*.sol",
+      "options": {
+        "printWidth": 120,
+        "tabWidth": 4,
+        "useTabs": false,
+        "singleQuote": false,
+        "bracketSpacing": false,
+        "explicitTypes": "always",
+        "semi": true
+      }
+    }
+  ]
+}

bidirectional_payment_channel/contracts/PaymentChannel.sol

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+// SPDX-License-Identifier: GPL-3.0
+pragma solidity ^0.8.7;
+
+import "@openzeppelin/contracts/utils/cryptography/ECDSA.sol";
+
+contract PaymentChannel {
+    using ECDSA for bytes32;
+
+    event ChallengedExit(address indexed sender, uint256 nonce);
+    event Withdrawn(address indexed to, uint256 amount);
+
+    address payable[2] public users;
+    mapping(address => bool) public isUser;
+
+    mapping(address => uint256) public balances;
+
+    uint256 public immutable challengeTime;
+    uint256 public expiresAt;
+    uint256 public nonce;
+
+    modifier checkBalances(uint256[2] memory _balances) {
+        require(address(this).balance >= _balances[0] + _balances[1], "contract balance not enough");
+        _;
+    }
+
+    constructor(
+        address payable[2] memory _users,
+        uint256[2] memory _balances,
+        uint256 _expiresAt,
+        uint256 _challengeTime
+    ) payable checkBalances(_balances) {
+        require(_expiresAt > block.timestamp);
+        require(_challengeTime > 0);
+
+        expiresAt = _expiresAt;
+        challengeTime = _challengeTime;
+
+        for (uint256 i = 0; i < _users.length; i++) {
+            address payable user = _users[i];
+
+            require(!isUser[user], "duplicate users");
+
+            users[i] = user;
+            isUser[user] = true;
+            balances[user] = _balances[i];
+        }
+    }
+
+    function verify(
+        bytes[2] memory _signatures,
+        address _contract,
+        address[2] memory _signers,
+        uint256[2] memory _balances,
+        uint256 _nonce
+    ) public pure returns (bool) {
+        for (uint256 i = 0; i < _signatures.length; i++) {
+            bytes memory signature = _signatures[i];
+            address signer = _signers[i];
+
+            address recovered = keccak256(abi.encodePacked(_contract, _balances, _nonce))
+                .toEthSignedMessageHash()
+                .recover(signature);
+
+            if (recovered != signer) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    modifier checkSignatures(
+        bytes[2] memory _signatures,
+        uint256[2] memory _balances,
+        uint256 _nonce
+    ) {
+        address[2] memory signers;
+
+        // Copy users from storage to memory
+        for (uint256 i = 0; i < users.length; i++) {
+            signers[i] = users[i];
+        }
+
+        require(verify(_signatures, address(this), signers, _balances, _nonce), "Invalid signatures");
+
+        _;
+    }
+
+    modifier onlyUser() {
+        require(isUser[msg.sender], "only users");
+        _;
+    }
+
+    function challengeExit(
+        uint256[2] memory _balances,
+        uint256 _nonce,
+        bytes[2] memory _signatures
+    ) public onlyUser checkSignatures(_signatures, _balances, _nonce) checkBalances(_balances) {
+        require(block.timestamp < expiresAt, "challenge period expired");
+        require(_nonce > nonce, "nonce must be greater than the current nonce");
+
+        for (uint256 i = 0; i < _balances.length; i++) {
+            balances[users[i]] = _balances[i];
+        }
+
+        nonce = _nonce;
+        expiresAt = block.timestamp + challengeTime;
+
+        emit ChallengedExit(msg.sender, nonce);
+    }
+
+    function withdraw() public onlyUser {
+        require(block.timestamp >= expiresAt, "Challenge period not expired yet");
+
+        uint256 amount = balances[msg.sender];
+        balances[msg.sender] = 0;
+
+        payable(msg.sender).transfer(amount);
+
+        emit Withdrawn(msg.sender, amount);
+    }
+}

bidirectional_payment_channel/hardhat.config.ts

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+import { config as dotenvConfig } from "dotenv";
+import "@typechain/hardhat";
+import "@nomiclabs/hardhat-ethers";
+import "@nomiclabs/hardhat-waffle";
+import "@nomiclabs/hardhat-etherscan";
+import "solidity-coverage";
+import "hardhat-gas-reporter";
+import { HardhatUserConfig } from "hardhat/types/config";
+
+dotenvConfig();
+
+const gasPrice = parseInt(process.env.GAS_PRICE || "1000000000");
+
+const config: HardhatUserConfig = {
+  solidity: {
+    compilers: [
+      {
+        version: "0.8.10",
+        settings: {
+          optimizer: {
+            enabled: true,
+            runs: 200,
+          },
+        },
+      },
+    ],
+  },
+  networks: {
+    hardhat: {
+      initialBaseFeePerGas: 0,
+    },
+    rinkeby: {
+      url: process.env.RINKEBY_URL || "",
+      accounts:
+        process.env.PRIVATE_KEY !== undefined ? [process.env.PRIVATE_KEY] : [],
+      gasPrice,
+    },
+    mainnet: {
+      url: process.env.MAINNET_URL || "",
+      accounts:
+        process.env.PRIVATE_KEY !== undefined ? [process.env.PRIVATE_KEY] : [],
+      gasPrice,
+    },
+  },
+  gasReporter: {
+    enabled: process.env.REPORT_GAS !== undefined,
+    currency: "USD",
+    gasPrice: 120,
+    coinmarketcap: process.env.COINMARKETCAP_API_KEY,
+  },
+  etherscan: {
+    apiKey: process.env.ETHERSCAN_API_KEY,
+  },
+};
+
+export default config;