单向支付通道

支付通道允许参与者反复将以太币转移到链下。

以下是该合约的使用方式：

• Alice部署合约，并用一些以太币为其提供资金。
• Alice通过签署消息（链下）来授权付款并将签名发送到Bob。
• Bob通过向智能合约出示签名消息来索取付款。
• 如果Bob不领取付款，Alice请在合同到期后取回她的以太币

这称为单向支付通道，因为支付只能沿从Alice到 的单一方向进行Bob。

Payment channels allow participants to repeatedly transfer Ether off chain.

Here is how this contract is used:

• Alice deploys the contract, funding it with some Ether.
• Alice authorizes a payment by signing a message (off chain) and sends the signature to Bob.
• Bob claims his payment by presenting the signed message to the smart contract.
• If Bob does not claim his payment, Alice get her Ether back after the contract expires

This is called a uni-directional payment channel since the payment can go only in a single direction from Alice to Bob.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "github.com/OpenZeppelin/openzeppelin-contracts/blob/release-v4.5/contracts/utils/cryptography/ECDSA.sol";
import "github.com/OpenZeppelin/openzeppelin-contracts/blob/release-v4.5/contracts/security/ReentrancyGuard.sol";

contract UniDirectionalPaymentChannel is ReentrancyGuard {
    using ECDSA for bytes32;

    address payable public sender;
    address payable public receiver;

    uint private constant DURATION = 7 * 24 * 60 * 60;
    uint public expiresAt;

    constructor(address payable _receiver) payable {
        require(_receiver != address(0), "receiver = zero address");
        sender = payable(msg.sender);
        receiver = _receiver;
        expiresAt = block.timestamp + DURATION;
    }

    function _getHash(uint _amount) private view returns (bytes32) {
        // NOTE: sign with address of this contract to protect agains
        // replay attack on other contracts
        return keccak256(abi.encodePacked(address(this), _amount));
    }

    function getHash(uint _amount) external view returns (bytes32) {
        return _getHash(_amount);
    }

    function _getEthSignedHash(uint _amount) private view returns (bytes32) {
        return _getHash(_amount).toEthSignedMessageHash();
    }

    function getEthSignedHash(uint _amount) external view returns (bytes32) {
        return _getEthSignedHash(_amount);
    }

    function _verify(uint _amount, bytes memory _sig) private view returns (bool) {
        return _getEthSignedHash(_amount).recover(_sig) == sender;
    }

    function verify(uint _amount, bytes memory _sig) external view returns (bool) {
        return _verify(_amount, _sig);
    }

    function close(uint _amount, bytes memory _sig) external nonReentrant {
        require(msg.sender == receiver, "!receiver");
        require(_verify(_amount, _sig), "invalid sig");

        (bool sent, ) = receiver.call{value: _amount}("");
        require(sent, "Failed to send Ether");
        selfdestruct(sender);
    }

    function cancel() external {
        require(msg.sender == sender, "!sender");
        require(block.timestamp >= expiresAt, "!expired");
        selfdestruct(sender);
    }
}