README.md

web3-input-decoder

A simple offline web3 transaction input decoder for functions and constructors.

Install

pip install web3-input-decoder

Quick start

Let's take a USDT transfer transaction and the USDT contract creator transaction as an example:

>>> import json
>>> import urllib.request
>>> from web3_input_decoder import decode_constructor, decode_function
>>> f = urllib.request.urlopen("https://api.etherscan.io/api?module=contract&action=getabi&address=0xdac17f958d2ee523a2206206994597c13d831ec7")
>>> TETHER_ABI = json.loads(json.load(f)["result"])
>>> decode_function(
        TETHER_ABI, "0xa9059cbb000000000000000000000000f050227be1a7ce587aa83d5013f900dbc3be0611000000000000000000000000000000000000000000000000000000000ecdd350",
    )
[('address', '_to', '0xf050227be1a7ce587aa83d5013f900dbc3be0611'),
 ('uint256', '_value', 248370000)]
>>> decode_constructor(
        TETHER_ABI, "000000000000000000000000000000000000000000000000000000174876e800000000000000000000000000000000000000000000000000000000000000008000000000000000000000000000000000000000000000000000000000000000c00000000000000000000000000000000000000000000000000000000000000006000000000000000000000000000000000000000000000000000000000000000a546574686572205553440000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000045553445400000000000000000000000000000000000000000000000000000000"
    )
[('uint256', '_initialSupply', 100000000000),
 ('string', '_name', 'Tether USD'),
 ('string', '_symbol', 'USDT'),
 ('uint256', '_decimals', 6)]

You can also play with it here.

Performance enhancement

If you have lots of inputs in the same contract to decode, consider using InputDecoder.

>>> from web3_input_decoder import InputDecoder
>>> decoder = InputDecoder(TETHER_ABI)
>>> for _ in range(10000):
>>>    decoder.decode_function(
          (
            "0xa9059cbb000000000000000000000000f050227be1a7ce587aa83d5013f900dbc3b"
            "e0611000000000000000000000000000000000000000000000000000000000ecdd350"
          ),
        )

API

• decode_constructor

  def decode_constructor(
      abi: List[dict],
      tx_input: Union[str, bytes],
      bytecode: Optional[Union[str, bytes]] = None,
  ) -> List[Tuple[str, str, Any]]

  Parameters:

  • abi: Contract ABI
  • tx_input: Transaction input to decode, with or without deployed contract bytecode
  • bytecode: Optional deployed contract bytecode. If this is set, tx_input should include bytecode

  Returns:

  • List[Tuple[str, str, Any]]: Decoded type-name-value tuples

• decode_function

  def decode_function(
      abi: List[dict], tx_input: Union[str, bytes]
  ) -> List[Tuple[str, str, Any]]

  Parameters:

  • abi: Contract ABI
  • tx_input: Transaction input to decode

  Returns:

  • List[Tuple[str, str, Any]]: Decoded type-name-value tuples

Rationale

Existing solutions are not satisfying to me, e.g.:

1. web3py can only decode function calls and it's necessary to be online to set up a provider first.
2. ethereum-input-decoder is not maintained and it contains several glitches.