《纸上谈兵·solidity》第 10 课：Solidity `fallback` / `receive` 函数 —— 合约如何收 ETH 和响应未知调用？

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract Sender {
    function transferTo(address payable target) public payable {
        target.transfer(msg.value);
    }

    function sendTo(address payable target) public payable returns (bool) {
        return target.send(msg.value);
    }

    function callTo(address payable target) public payable returns (bool, bytes memory) {
        (bool success, bytes memory data) = target.call{value: msg.value}("");
        return (success, data);
    }

    function callWithData(address target, bytes calldata data) public payable returns (bool, bytes memory) {
        (bool success, bytes memory ret) = target.call{value: msg.value}(data);
        return (success, ret);
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract SimpleReceiver {
    event GotReceive(address indexed sender, uint256 amount);
    event GotFallback(address indexed sender, uint256 amount, bytes data);

    receive() external payable {
        emit GotReceive(msg.sender, msg.value);
    }

    fallback() external payable {
        emit GotFallback(msg.sender, msg.value, msg.data);
    }
}

contract WriterReceiver {
    uint256 public counter;
    event GotAny(address indexed sender, uint256 amount);

    receive() external payable {
        counter += 1;
        emit GotAny(msg.sender, msg.value);
    }

    fallback() external payable {
        counter += 1;
        emit GotAny(msg.sender, msg.value);
    }
}

contract NonPayableFallback {
    fallback() external {
        // 非 payable，不能收 ETH
    }
}

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.0;

import "forge-std/Test.sol";
import "../src/Sender.sol";
import "../src/Receivers.sol";

contract FallbackReceiveTest is Test {
    Sender sender;
    SimpleReceiver simple;
    WriterReceiver writer;
    NonPayableFallback nonPayable;

    function setUp() public {
        sender = new Sender();
        simple = new SimpleReceiver();
        writer = new WriterReceiver();
        nonPayable = new NonPayableFallback();
        vm.deal(address(this), 10 ether);
    }

    function testTransferToSimpleReceiver() public {
        sender.transferTo{value: 1 ether}(payable(address(simple)));
        assertEq(address(simple).balance, 1 ether);
    }

    function testTransferToWriterReceiverFails() public {
        vm.expectRevert();
        sender.transferTo{value: 1 ether}(payable(address(writer)));
    }

    function testCallToWriterReceiverSucceeds() public {
        (bool ok, ) = sender.callTo{value: 1 ether}(payable(address(writer)));
        assertTrue(ok);
        assertEq(address(writer).balance, 1 ether);
        assertEq(writer.counter(), 1);
    }

    function testSendToWriterReceiverReturnsFalse() public {
        bool sent = sender.sendTo{value: 1 ether}(payable(address(writer)));
        assertFalse(sent);
        assertEq(address(writer).balance, 0);
    }

    function testCallTriggersReceiveWhenNoData() public {
        (bool ok, ) = sender.callTo{value: 1 ether}(payable(address(simple)));
        assertTrue(ok);
        assertEq(address(simple).balance, 1 ether);
    }

    function testCallWithDataTriggersFallback() public {
        bytes memory someData = abi.encodeWithSignature("nonexistent()");
        (bool ok, ) = sender.callWithData{value: 0}(address(simple), someData);
        assertTrue(ok);
    }

    function testCallToNonPayableFallbackWithValueFails() public {
        (bool ok, ) = sender.callTo{value: 1 ether}(payable(address(nonPayable)));
        assertFalse(ok);
    }
}

➜  counter git:(main) ✗ forge test --match-path test/FallbackReceive.t.sol -vvv
[⠊] Compiling...
[⠒] Compiling 3 files with Solc 0.8.30
[⠑] Solc 0.8.30 finished in 540.39ms
Compiler run successful!

Ran 7 tests for test/FallbackReceive.t.sol:FallbackReceiveTest
[PASS] testCallToNonPayableFallbackWithValueFails() (gas: 28887)
[PASS] testCallToWriterReceiverSucceeds() (gas: 55238)
[PASS] testCallTriggersReceiveWhenNoData() (gas: 31262)
[PASS] testCallWithDataTriggersFallback() (gas: 18734)
[PASS] testSendToWriterReceiverReturnsFalse() (gas: 30670)
[PASS] testTransferToSimpleReceiver() (gas: 29019)
[PASS] testTransferToWriterReceiverFails() (gas: 29210)
Suite result: ok. 7 passed; 0 failed; 0 skipped; finished in 4.74ms (5.49ms CPU time)

Ran 1 test suite in 212.40ms (4.74ms CPU time): 7 tests passed, 0 failed, 0 skipped (7 total tests)