20. solidity 发送ETH：call()

20. 发送ETH：call()

Solidity有三种方法向其他合约发送ETH，他们是：transfer()，send()和call()，其中call()是被鼓励的用法。

call没有gas限制，最为灵活，是最提倡的方法；
transfer有2300 gas限制，但是发送失败会自动revert交易，是次优选择；
send有2300 gas限制，而且发送失败不会自动revert交易，几乎没有人用它。

接收ETH合约

我们先部署一个接收ETH合约ReceiveETH。ReceiveETH合约里有一个事件Log，记录收到的ETH数量和gas剩余。还有两个函数，一个是receive()函数，收到ETH被触发，并发送Log事件；另一个是查询合约ETH余额的getBalance()函数。

contract ReceiveETH {
    // 收到eth事件，记录amount和gas
    event Log(uint amount, uint gas);
    
    // receive方法，接收eth时被触发
    receive() external payable{
        emit Log(msg.value, gasleft());
    }
    
    // 返回合约ETH余额
    function getBalance() view public returns(uint) {
        return address(this).balance;
    }
}

部署ReceiveETH合约后，运行getBalance()函数，可以看到当前合约的ETH余额为0。

20-1

发送ETH合约

我们将实现三种方法向ReceiveETH合约发送ETH。首先，先在发送ETH合约SendETH中实现payable的构造函数和receive()，让我们能够在部署时和部署后向合约转账。

contract SendETH {
    // 构造函数，payable使得部署的时候可以转eth进去
    constructor() payable{}
    // receive方法，接收eth时被触发
    receive() external payable{}
}

call：接收方地址.call{value: 发送ETH数额}(“”)

用法是接收方地址.call{value: 发送ETH数额}("")。
call()没有gas限制，可以支持对方合约fallback()或receive()函数实现复杂逻辑。
call()如果转账失败，不会revert。
call()的返回值是(bool, data)，其中bool代表着转账成功或失败，需要额外代码处理一下。

代码样例：

// call()发送ETH
function callETH(address payable _to, uint256 amount) external payable{
    // 处理下call的返回值，如果失败，revert交易并发送error
    (bool success,) = _to.call{value: amount}("");
    if(!success){
        revert CallFailed();
    }
}

对ReceiveETH合约发送ETH，此时amount为10，value为0，amount>value，转账失败，因为经过处理，所以发生revert。

20-7

此时amount为10，value为11，amount<=value，转账成功。

20-8

transfer：接收方地址.transfer(发送ETH数额)

用法是接收方地址.transfer(发送ETH数额)。
transfer()的gas限制是2300，足够用于转账，但对方合约的fallback()或receive()函数不能实现太复杂的逻辑。
transfer()如果转账失败，会自动revert（回滚交易）。

代码样例，注意里面的_to填ReceiveETH合约的地址，amount是ETH转账金额：

// 用transfer()发送ETH
function transferETH(address payable _to, uint256 amount) external payable{
    _to.transfer(amount);
}

部署SendETH合约后，对ReceiveETH合约发送ETH，此时amount为10，value为0，amount>value，转账失败，发生revert。

20-2

此时amount为10，value为10，amount<=value，转账成功。

20-3

在ReceiveETH合约中，运行getBalance()函数，可以看到当前合约的ETH余额为10。

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)]

send：接收方地址.send(发送ETH数额)

用法是接收方地址.send(发送ETH数额)。
send()的gas限制是2300，足够用于转账，但对方合约的fallback()或receive()函数不能实现太复杂的逻辑。
send()如果转账失败，不会revert。
send()的返回值是bool，代表着转账成功或失败，需要额外代码处理一下。

代码样例：

// send()发送ETH
function sendETH(address payable _to, uint256 amount) external payable{
    // 处理下send的返回值，如果失败，revert交易并发送error
    bool success = _to.send(amount);
    if(!success){
        revert SendFailed();
    }
}

对ReceiveETH合约发送ETH，此时amount为10，value为0，amount>value，转账失败，因为经过处理，所以发生revert。

20-5

此时amount为10，value为11，amount<=value，转账成功。

20-6

习题

vitalik写了一个合约，并且该合约在被部署时可以转ETH进去，那么该合约的构造函数可以是:
```
constructor() payable{}
```

vitalik写了一个用send()发送ETH的函数：
error SendFailed(); 
function sendETH(address payable _to, uint256 amount) external payable{
            ______________________________________
    }
该函数执行失败时会自动revert交易，那么填入横线处的代码可以是：
bool success = _to.send(amount); if( !success ){ revert SendFailed(); }

vitalik又写了一个用call()发送ETH的函数：
error CallFailed();
function callETH(address payable _to, uint256 amount) external payable{
            ______________________________________
    }
该函数执行失败时会自动revert交易，那么填入横线处的代码可以是：
(bool success,) = _to.call{value: amount}(" "); if( !success ){ revert CallFailed(); }

假设存在如下图所示的两个合约(sendETH和ReceiveETH)，两个合约目前ETH余额皆为0，现在vitalik想通过SendETH合约的callETH函数往ReceiveETH合约转入1ETH，他将交易的value设置为2ETH，同时交易成功执行，那么此时sendETH合约和ReceiveETH的ETH余额分别为：1ETH；1ETH

[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-nICk9N39-1680011373607)(null)]