Distinguishing erc721 transactions from the response of txlist on etherscan

Question

I am making some erc721 transactions. I can retrieve those transactions using the etherscan api like this

https://api.etherscan.io/api?module=contract&action=txlist&address=0xb30c5db4ca271653535b846f237c4a8d0d6fb32d&startblock=0&endblock=99999999&page=1&offset=20&sort=desc&apikey=

{"blockNumber":"6878479","timeStamp":"1544697153","hash":"0x68dffa9cd6b2f408a5bc1bb9c3cc9a0344e9e7e71029e551f3a5b35673bad362","nonce":"53","blockHash":"0x2e0968d71243a531b80db3a1feba3b0b16f664ae16cf3a992e4fd3fd8a40667c","transactionIndex":"153","from":"0xb30c5db4ca271653535b846f237c4a8d0d6fb32d","to":"0x06012c8cf97bead5deae237070f9587f8e7a266d","value":"0","gas":"69379","gasPrice":"5100000000","isError":"0","txreceipt_status":"1","input":"0xa9059cbb0000000000000000000000003b7b6f8c1b9fe9be5b59326a3e8c695fce3a4e0800000000000000000000000000000000000000000000000000000000000c90c4","contractAddress":"","cumulativeGasUsed":"7480061","gasUsed":"69379","confirmations":"4750"}

This is a cryptokitties transaction. However, how do I distinguish this from a erc20 transaction. I checked their other apis https://etherscan.io/apis#contracts

but, none of them seem to explicitly state the type of contract/transaction.

Answer 1

That link is broken, but I'll give it a whirl.

The problem

We would like to use the Etherscan Developer API to review transactions against a given contract address and find out:

1. Does this contract implement ERC-721?
2. What is the list of token transfers on this contract or other useful info.

There is a lot you can do with the Etherscan Developer API. For example, here's one URL that pulls data from Ethereum Mainnet -> Etherscan -> JSON parser -> Shields.io and renders it as an image to calculate the number of Su Squares remaining for sale:

Source: https://img.shields.io/badge/dynamic/json.svg?label=Su+Squares+available&url=https%3A%2F%2Fapi.etherscan.io%2Fapi%3Fmodule%3Daccount%26action%3Dtokenbalance%26contractaddress%3D0xE9e3F9cfc1A64DFca53614a0182CFAD56c10624F%26address%3D0xE9e3F9cfc1A64DFca53614a0182CFAD56c10624F%26tag%3Dlatest%26apikey%3DYourApiKeyToken&query=%24.result

Solution

First, the source documentation is at https://etherscan.io/apis

It is not possible to determine which contracts support ERC-721. Source: The ERC-721 Validator. So we are going to have to use some approximation.

Here is a some ERC-721 contract, I won't tell you which one: 0xE9e3F9cfc1A64DFca53614a0182CFAD56c10624F.

We can use a special query against Etherscan to guess if it is ERC-721 compliant. This will check the original contract creation code (limiting the page and offset parameters).

http://api.etherscan.io/api?module=account&action=txlist&address=0xE9e3F9cfc1A64DFca53614a0182CFAD56c10624F&startblock=0&endblock=99999999&sort=asc&apikey=YourApiKeyToken&page=1&offset=1

Just load that file and grep that code for 42842e0e, the function signature for safeTransferFrom(address,address,uint256) and boom you found it! This makes me pretty confident because I don't expect non-721 contracts to implement that method. This approach is not fail-safe, because there are function signature collisions (expect to try 500k attempts* to collide with that one), because contracts can lie, and because a contract can use a proxy to another backing implementation.

Likewise, you can query more transactions and filter on input begins with 42842e0e to find transfers. This is still a big approximation because those transfers might fail and also because there are many ways (including internal transactions) to transfer rather than using the 42842e0e function.

Discussion

This is a fun tool to test and have fun with, but for actual analysis you will want to use a real tool.

• 2^32 byte combinations * 0.5 collision luck factor / ~5000 bytes per contract initialization