How to generate the full list of function selectors for a contract?

Question

A contract has many functions and how to automatically generate the full selector list, including inherited functions, for the whole contract?

Preferred solution shouldn’t require more than a web browser.

Answer 1

Maybe you can use the online Ethereum IDE (Remix):

• Paste the whole code of the address you posted.
• Select the same compiler version: v0.4.25+commit.59dbf8f1.
• Select the contract by name: SaiProxyCreateAndExecute.

Press on Compilation Details and check the functionHashes section. You will get something like the following:

{
    "581f3c50": "createAndOpen(address,address)",
    "eefe3818": "createOpenAndLock(address,address)",
    "d3140a65": "createOpenLockAndDraw(address,address,uint256)",
    "0344a36f": "draw(address,bytes32,uint256)",
    "f9ef04be": "free(address,bytes32,uint256)",
    "da93dfcf": "give(address,bytes32,address)",
    "bc25a810": "lock(address,bytes32)",
    "1edf0c1e": "lockAndDraw(address,bytes32,uint256)",
    "516e9aec": "lockAndDraw(address,uint256)",
    "b95460f8": "open(address)",
    "bc244c11": "shut(address,bytes32)",
    "792037e3": "shut(address,bytes32,address)",
    "a3dc65a7": "wipe(address,bytes32,uint256)",
    "8a9fc475": "wipe(address,bytes32,uint256,address)",
    "faed77ab": "wipeAndFree(address,bytes32,uint256,uint256)",
    "1b968160": "wipeAndFree(address,bytes32,uint256,uint256,address)"
}

Answer 2

For every function, you want to calculate keccak256(signature) (try https://emn178.github.io/online-tools/keccak_256.html)

signature is a concatenation of function's name and parameters' types in parentheses, omitting all spaces and parameter names.

For example function

transfer(address to, uint256 amount)

has signature

transfer(address,uint256)

keccak256(signature) result is

a9059cbb2ab09eb219583f4a59a5d0623ade346d962bcd4e46b11da047c9049b

Function selector is first 4 bytes (according to https://solidity.readthedocs.io/en/v0.4.24/abi-spec.html#function-selector) which is

a9059cbb

As ABI can be interpreted in JavaScript as simple array of JSON objects, it would be simple to iterate through this array and compose signature for every function and calculate selectors

Answer 3

It's kind of ridiculous that it's not part of the artifacts. Here's a quick js script that will extract them out of the artifacts/build-info json data:

#!/usr/bin/env node

// Reads JSON from stdin and writes equivalent
// nicely-formatted JSON to stdout.

var stdin = process.stdin,
    stdout = process.stdout,
    inputChunks = [];

stdin.resume();
stdin.setEncoding('utf8');

stdin.on('data', function (chunk) {
    inputChunks.push(chunk);
});

// Search for  path of item with name and value
function path(c, name, currentPath, t){
    var currentPath = currentPath || "root";

    for(var i in c){
      if(i == name){
        t = currentPath;
        console.log(t + "." + name + ' -> ' + JSON.stringify(c[name], null, '    '));
      }
      else if(typeof c[i] == "object"){
        path(c[i], name, currentPath + "." + i);
      }
    }
};


stdin.on('end', function () {
    var inputJSON = inputChunks.join("");
    var parsedData = JSON.parse(inputJSON);

    path(parsedData,"methodIdentifiers", '');
});

It works on stdin so , just run like this: cat artifacts/build-info/2e388aff5c540fc7cba05810417a6a1d.json | ./extractSelectors.js

Answer 4

There you go (using web3.js v1.0.0-beta.34):

const Web3    = require("web3");
const request = require("request");
request("http://api.etherscan.io/api?module=contract&action=getabi&address=0x526af336d614ade5cc252a407062b8861af998f5&format=raw", function(error, response, body) {
    const web3 = new Web3();
    for (const func of JSON.parse(body))
        console.log(func.name, web3.eth.abi.encodeFunctionSignature(func));
});

Answer 5

This can get tricky for functions that have complex argument definitions. slither has a feature that can help here, though:

slither --print function-id .