ethereum-input-decoder

Decodes an Ethereum input data hex string into a developer friendly JavaScript object. Optionally can be translated into an object which includes Solidity types.

Warning

This package is in alpha, use at your own risk!

Aim

The goal of ethereum-input-decoder is to facilitate dead-simple conversion of a transaction input into a JavaScript native, serializable object.

Usage

Creating a specific decoder object for decoding reuse

Here we create an instance of a decoder using a given ABI, to which we can decode inputs with. We are also able to choose the output format for decoding in this instance.

import InputDataDecoder = from 'ethereum-input-decoder'
const erc20Abi = [{ ... }]
const erc20Decoder = new InputDataDecoder(erc20Abi)
const transferInput = '0xa9059cb000...'
const result = erc20Decoder.decodeData(transferInput)
console.log(result)

{
  methodName: 'transfer',
  params: {
    _to: '0x5A1Cb5A88988cA4FEF229935db834A6781e873cB',
    _value: '1000000000000000000'
  }
}

The InputDataDecoder can take a second argument detailing the requested output format.

const erc20Decoder = new InputDataDecoder(erc20Abi, 'solidityTypes') // default is 'jsObject'
const result = erc20Decoder.decodeData(transferInput)
console.log(result)

// solidityTypes format
{
      methodName: 'transfer',
      params: [
        {
          name: '_to',
          type: 'address',
          value: '0x5A1Cb5A88988cA4FEF229935db834A6781e873cB',
        },
        {
          name: '_value',
          type: 'uint256',
          value: '1000000000000000000',
        },
      ],
    }

Passing both the ABI and the input together

Here we pass decodeInput both an ABI and an input to receive the decoded output in 'jsObject' format. This creates the decoder instance each call, it would be recommended to make a decoder instance for each contract for multiple calls.

import decodeInput from 'ethereum-input-decoder'
const erc20Abi = [{ ... }] // this may be an ABI object or an InputDataDecoder instance as above
const transferInput = '0xa9059cb000...'
const result = decodeInput(erc20Abi, transferInput)

Unable to decode example

If the input does not match the ABI, both decodeInput and InputDataDecoder.decodeData() returns null

import decodeInput from 'ethereum-input-decoder'
const erc20Abi = [{ ... }]
const failingData = '0xbitconnect'
const result = decoder.decodeData(failingData)
console.log(result)

null

Usage in node.js

When ES6 imports are not available, you may use require

const inputToObject = require('ethereum-input-decoder')

Supported types

Solidity	JavaScript equivalent used
int (all variations)	String
address	String
string	String
bool	Boolean
bytes (all variations)	String (hex formatted)
tuple	Object (with contents also converted)
array	Array (with contents also converted)

Using a type not supported? Open an issue.

Precursor work acknowledgement

This library is inspired by the great work by Miguel on ethereum-input-data-decoder, and fellow Blocknative dev Liam on ethereum-input-to-object

Todo list

• Ensure contract constructor is decoded
• Add extensive fuzzing testing (maybe)
• Have an available format that does not decode the solidity values at all, ie does not call parseCallValue()
• Add error throwing [ 'no matching function', 'incorrect inputs', ... ]