异常捕获

Solidity 将异常情况分为三类：前置（require）、后置（assert）、抛出异常（revert）: 三种异常通过 try-catch 捕获处理

require 前置判断

require(condition,"ErrorMsg“), which throws if the condition is false
- 条件不满足时就会抛出异常，输出异常字符串(ErrorMsg)
- gas 花销和描述异常的字符串的长度正相关

        require(
            address(this).balance >= value,
            "Address: insufficient balance for call"
        );

assert 后置判断

assert(condition), which throws if the condition is false
一般作为后置条件判断，但是无法抛出具体的异常信息

        assert (balanceAfter < balanceBefore);

revert

revert() | revert(ErrorMsg) | revert Error()
- 可以通过 revert() 直接抛出异常
- 异常内支持添加异常信息 revert(ErrorMsg)
- 允许抛出自定义的 Error(), 通过 revert Error() 抛出

error TransferNotOwner(); // 自定义error
function transferOwner1(uint256 tokenId, address newOwner) public {
    if(_owners[tokenId] != msg.sender){
        revert TransferNotOwner();
    }
     _owners[tokenId] = newOwner;
}

try catch

Lower-level

lower-level的调用在EVM层面，直接返回 boolean,bytes,让用户自行捕获异常：

外部调用的合约函数执行出现了 revert
外部调用的合约函数执行了非法逻辑（/0，out-of-bound）
外部调用的合约函数 out-of-gas

异常捕获

try external function calls and contract creation calls{}catch

try 用户捕获外部函数调用的异常
不可用于 selector 调用的异常捕获
catch 匹配异常
- Panic(errorCode) via assert
  - 0x00,编译器错误
  - 0x01,assert 报错
  - 0x11,数字越界错误
  - 0x12,/0
  - 0x21,转化枚举类型时：传参负数或越界
  - 0x22,访问错误编码的bytes数组
  - 0x31,空数组pop
  - 0x32,数组越界
  - 0x41,申请内存超额或数组太大
  - 0x51,访问局部变量
  - 返回数据： bytes4(keccak256(”Panic(uint256)”))) + encode_uint256
- Error via require|revert
  - require(bool) = if(bool){revert()}，直接 revert(),返回数据为空
  - require(bool, string) = if(bool){revert(string)}，返回数据是 Error(string) 的编码
  - require(bool, UserCustomError()) = if(bool){revert UserCustomError()}，报用户自定义错误，返回数据是 bytes4(keccak256("UserCustomError()")))

function callContractB() external view {
  try functionFromAnotherContract() {
    //<-- Handle the success case if needed
  } catch Panic(uint256 errorCode) {
    //<-- handle Panic errors
  } catch Error(string memory reason) { //revert(string), require(false, “reason”)
    //<-- handle revert with a reason
  } catch (bytes memory lowLevelData) { //revert UserCustomError(),require(bool, UserCustomError())
    //<-- handle every other errors apart from Panic and Error with a reason
    // revert without a message
    if (lowLevelData.length == 0) {
      console.log("revert without a message occured");
    }

    // Decode the error data to check if it's the custom error
    if (bytes4(abi.encodeWithSignature("CustomError(uint256)")) ==bytes4(lowLevelData)
    ) {
      // handle custom error
      console.log("CustomError occured here");
    }
  }
}

Preference

https://www.rareskills.io/post/try-catch-solidity

Solidity Development Book