第4节：abi.encode、abi.decode、abi.encodePacked

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1. abi.encode：可以将data编码成bytes，生成的bytes总是32字节的倍数，不足32为会自动填充（用于给合约调用）；
2. abi.decode：可以将bytes解码成data（可以只解析部分字段）
3. abi.encodePacked：与abi.encode类似，但是生成的bytes是压缩过的（有些类型不会自动填充，无法传递给合约调用）。
4. 手册：https://docs.soliditylang.org/en/v0.8.13/abi-spec.html?highlight=abi.encodePacked#non-standard-packed-mode

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.13;

contract AbiDecode {
    struct MyStruct {
        string name;
        uint[2] nums;
    }

    // input: 10, 0x5B38Da6a701c568545dCfcB03FcB875f56beddC4, [1,"2",3], ["duke", [10,20]]
    // output: 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
    //  output长度：832位16进制字符（去除0x)，832 / 32 = 26 （一定是32字节的整数倍，不足填0）
    function encode(
        uint x,
        address addr,
        uint[] calldata arr,
        MyStruct calldata myStruct
    ) external pure returns (bytes memory) {
        return abi.encode(x, addr, arr, myStruct);
    }

    function decode(bytes calldata data)
        external
        pure
        returns (
            uint x,
            address addr,
            uint[] memory arr,
            MyStruct memory myStruct
        )
    {
        (x, addr, arr, myStruct) = abi.decode(data, (uint, address, uint[], MyStruct));

        /* decode output: 
            0: uint256: x 10
            1: address: addr 0x5B38Da6a701c568545dCfcB03FcB875f56beddC4
            2: uint256[]: arr 1,2,3
            3: tuple(string,uint256[2]): myStruct ,10,20
        */
    }

    // 可以只decode其中部分字段，而不用全部decode，当前案例中，只有第一个字段被解析了，其余为默认值
    function decodeLess(bytes calldata data)
        external
        pure
        returns (
            uint x,
            address addr,
            uint[] memory arr,
            MyStruct memory myStruct
        )
    {
        (x) = abi.decode(data, (uint));

        /* decode output: 
            0: uint256: x 10
            1: address: addr 0x0000000000000000000000000000000000000000
            2: uint256[]: arr
            3: tuple(string,uint256[2]): myStruct ,0,0
        */
    }

    // input: -1, 0x42, 0x03, "Hello, world!"
    function encodePacked(
        int16 x,
        bytes1 y,
        uint16 z,
        string memory s
    ) external view returns (bytes memory) {

        // encodePacked 不支持struct和mapping
        return abi.encodePacked(x, y, z, s);

        /*
        0xffff42000348656c6c6f2c20776f726c6421
          ^^^^                                 int16(-1)
              ^^                               bytes1(0x42)
                ^^^^                           uint16(0x03)
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^ string("Hello, world!") without a length field
        */
    }

      // 可以用encodePacked来拼接字符串
      // output string: ipfs://bafybeidmrsvehl4ehipm5qqvgegi33r6/100.json
      function encodePackedTest() public  pure returns (string memory) {
        string memory uri = "ipfs://bafybeidmrsvehl4ehipm5qqvgegi33r6/";
        return string(abi.encodePacked(uri, "100", ".json"));
    }
}

使用三方库：

web3js编码：

// encodeFunctionCall( abi ,参数 ) 得到编码

web3.eth.abi.encodeFunctionCall({
    name: 'myMethod',
    type: 'function',
    inputs: [{
        type: 'uint256',
        name: 'myNumber'
    },{
        type: 'string',
        name: 'myString'
    }]
}, ['2345675643', 'Hello!%']);
> "0x24ee0097000000000000000000000000000000000000000000000000000000008bd02b7b0000000000000000000000000000000000000000000000000000000000000040000000000000000000000000000000000000000000000000000000000000000748656c6c6f212500000000000000000000000000000000000000000000000000"

web3js解码：

解码时，要将得到的calldata的前四字节去掉，那是函数的selector，不应该参与参数解析。

//  let res = web3.eth.abi.decodeParameters(abi, calldata)

async function main() {
  let calldata = '' //太大了，删除，去下面线上链接中获取
  let abi = [{ "internalType": "string", "name": "_id", "type": "string" }, { "internalType": "string", "name": "_uniqueId", "type": "string" }, { "internalType": "uint8", "name": "_assetFrom", "type": "uint8" }, { "internalType": "uint8", "name": "_action", "type": "uint8" }, { "internalType": "address", "name": "_srcToken", "type": "address" }, { "internalType": "address", "name": "_dstToken", "type": "address" }, { "internalType": "uint256", "name": "_srcAmount", "type": "uint256" }, { "internalType": "uint256", "name": "_srcFeeAmount", "type": "uint256" }, { "internalType": "bytes", "name": "_data", "type": "bytes" }]


  let res = web3.eth.abi.decodeParameters(abi, calldata)
  console.log('res:', res)
}

在线案例：https://web3playground.io/QmSeHtJPLFxweiGB8ocFDXkCZao6Mt5oEJ4Ej66iY3RL1R

ethersjs

let bytes2 = mock1Inch.interface.encodeFunctionData("swap", [ETH_ADDR, daiToken.address, 90])