使用ABI解码以太坊Transaction input数据，减少gas free

妖狐艹你老母 2022-12-03 09:43 57阅读 0赞

在写智能合约的时候，之前我的习惯是把需要查询的数据记录在合约的event中，这些event的字段有些就是方法的入参。虽然以太坊log数据gas free相对较少，但积累起来就可观了。经过思考后，我给自己定了一些规则：

1.  需要索引的字段，计算的中间结果，可以保留在event中
2.  无后台的DApp可以在event中保留更多的字段
3.  具有复杂功能（比如分账明细）的DApp，如需要多次查询大量数据，可以考虑使用后台来查询区块链。此时event中含有的函数入参就没有必要保留了，数据可以通过transaction的input字段恢复。

拿我发送的一个transaction为例

{
      hash: '0xcc1c866186ff39555936ea007a63ead761aef80d4301eb4e0081e8fc8f6fe18d',
      nonce: 892,
      blockHash: '0xbfff2fc0dd268dfce90417a3ea3b5da3a9e59703d8d4ec6a5be3ba2dce59b924',
      blockNumber: 987,
      transactionIndex: 0,
      from: '0x40FB66078a2e688f83002930B7EbA981323d4bef',
      to: '0x2C71AC97716A17E66D7E524Cfeb28B97A3728250',
      value: '0',
      gas: 5000000,
      gasPrice: '10000000000',
      input: '0x70a1495c00000000000000000000000000000000000000000000000000000000000000a0000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000003782dace9d900000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000000000000056f70656e31000000000000000000000000000000000000000000000000000000',
      v: '0x1b',
      r: '0xbfbd3aef6c6777598847de0aa1ffcaf50470f785054771a54e2e274b89d1a633',
      s: '0x27aea35dd4d462598ac909b55444ec0131c7977fe2ad244eaac0cc28b70e07f1'
    }

可以看到很长的input字段，这个字段以`0x70a1495c`开头，这其实就是函数签名，后面的数据则是按类型把数据拼接起来而已。我们再来看这个函数的abi

{
      constant: false,
      inputs: [
        { internalType: 'bytes', name: 'name', type: 'bytes' },
        { internalType: 'bool', name: 'isOpen', type: 'bool' },
        { internalType: 'bool', name: 'isCustom', type: 'bool' },
        { internalType: 'uint256', name: 'cusPrice', type: 'uint256' },
        { internalType: 'uint8', name: 'durationInYear', type: 'uint8' }
      ],
      name: 'registerRoot',
      outputs: [],
      payable: false,
      stateMutability: 'nonpayable',
      type: 'function',
      signature: '0x70a1495c'
    }

可以看到signature也是`0x70a1495c`  
这个签名是怎么生成的呢，其实很简单:  
`web3.eth.abi.encodeFunctionSignature("registerRoot(bytes,bool,bool,uint256,uint8)")`  
就是一个短Hash，去掉`0x70a1495c`后，我们把剩下数据解码：

web3.eth.abi.decodeParameters(["bytes","bool","bool","uint256","uint8"],"0x00000000000000000000000000000000000000000000000000000000000000a0000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000003782dace9d900000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000000000000000000000000000000000000000056f70656e31000000000000000000000000000000000000000000000000000000")
    Result {
      '0': '0x6f70656e31',
      '1': true,
      '2': true,
      '3': '4000000000000000000',
      '4': '1',

最后再拼上字段名称就可以了。  
自己写了个解析函数，如下：

async function decodeParamsOfTransaction(txHash, func_abi){
        var txData = await web3.eth.getTransaction(txHash);
        var input = txData.input;
        var types = func_abi.inputs.map(x=>x.internalType);
        var _d = "0x"+input.replace(func_abi.signature,"");
        var names = func_abi.inputs.map(x=>x.name);
        var r = web3.eth.abi.decodeParameters(types, _d);
        var dic = {}
        for(var i=0; i<names.length; i++){
            dic[names[i]] = r[i];
        }
        return dic
    }

可得到例如下面的结果：

{
      name: '0x6f70656e31',
      isOpen: true,
      isCustom: true,
      cusPrice: '4000000000000000000',
      durationInYear: '1'
    }