function-selectors.js

const explorer = require('sol-explore');
const SolidityParser = require('solparse');
const _ = require('underscore');
const soltar = require('soltar');
const Web3 = require('web3');


const web3 = new Web3();


function generateFunctionSignatures(file) {
  const ast = SolidityParser.parseFile(`${file}`, false);
  // Preprocess with table for structs
  let structSignatureTable = {};
  explorer.traverse(ast, (node, parent) => {
    if (node.type === 'StructDeclaration') {
      let structName = node.name;
      let structSignature = '(';
      let structTypes = _.map(node.body, _.property(['literal', 'literal']));
      structSignature += structTypes.join(',');
      structSignature += ')';
      structSignatureTable[structName] = structSignature;
    }
  });

  let functionSignatureList = [];
  explorer.traverse(ast, (node, parent) => {
    if (node.type === 'FunctionDeclaration') {
      let functionSignature = '';
      functionSignature += node.name + '(';
      let params = [];
      _.each(node.params, (param) => {
        // Handle struct types
        let type = _.property(['literal', 'literal'])(param);
        // Hack for struct defined in other contract
        if (_.property(['literal', 'members'])(param).length > 0) {
          type = _.property(['literal', 'members'])(param)[0];
        }
        if (_.contains(Object.keys(structSignatureTable), type)) {
          type = structSignatureTable[type];
        }
        // Handle multi-dimensional arrays
        for (let i = 0; i < param.literal.array_parts.length; i++) {
          type += '[]';
        }
        params.push(type);
      });
      functionSignature += params.join(',');
      functionSignature += ')';
      functionSignatureList.push(functionSignature);
    }
  });
  return functionSignatureList;
}

function computeFunctionSelector(functionSignature) {
  let functionSelector = web3.utils.keccak256(functionSignature).substring(0, 10);  // 10 because '0x' is included
  return functionSelector;
}

// Main

let functionSignatureList = generateFunctionSignatures('./contracts/Forwarder.sol')
_.each(functionSignatureList, (functionSignature, index) => {
  let functionSelector = computeFunctionSelector(functionSignature);
  console.log(`${functionSelector}: ${functionSignature}`);
});