metamask-extension/app/scripts/lib/util.js

const extension = require('extensionizer')
const ethUtil = require('ethereumjs-util')
const assert = require('assert')
const BN = require('bn.js')
const {
  ENVIRONMENT_TYPE_POPUP,
  ENVIRONMENT_TYPE_NOTIFICATION,
  ENVIRONMENT_TYPE_FULLSCREEN,
  ENVIRONMENT_TYPE_BACKGROUND,
  PLATFORM_FIREFOX,
  PLATFORM_OPERA,
  PLATFORM_CHROME,
  PLATFORM_EDGE,
  PLATFORM_BRAVE,
} = require('./enums')

/**
 * Used to determine the window type through which the app is being viewed.
 *  - 'popup' refers to the extension opened through the browser app icon (in top right corner in chrome and firefox)
 *  - 'responsive' refers to the main browser window
 *  - 'notification' refers to the popup that appears in its own window when taking action outside of metamask
 *  - 'background' refers to the background page
 *
 * @returns {string} A single word label that represents the type of window through which the app is being viewed
 *
 */
const getEnvironmentType = (url = window.location.href) => {
  const parsedUrl = new URL(url)
  if (parsedUrl.pathname === '/popup.html') {
    return ENVIRONMENT_TYPE_POPUP
  } else if (['/home.html', '/phishing.html'].includes(parsedUrl.pathname)) {
    return ENVIRONMENT_TYPE_FULLSCREEN
  } else if (parsedUrl.pathname === '/notification.html') {
    return ENVIRONMENT_TYPE_NOTIFICATION
  } else {
    return ENVIRONMENT_TYPE_BACKGROUND
  }
}

/**
 * Returns the platform (browser) where the extension is running.
 *
 * @returns {string} the platform ENUM
 *
 */
const getPlatform = _ => {
  const ua = navigator.userAgent
  if (ua.search('Firefox') !== -1) {
    return PLATFORM_FIREFOX
  } else {
    if (window && window.chrome && window.chrome.ipcRenderer) {
      return PLATFORM_BRAVE
    } else if (ua.search('Edge') !== -1) {
      return PLATFORM_EDGE
    } else if (ua.search('OPR') !== -1) {
      return PLATFORM_OPERA
    } else {
      return PLATFORM_CHROME
    }
  }
}

/**
 * Checks whether a given balance of ETH, represented as a hex string, is sufficient to pay a value plus a gas fee
 *
 * @param {object} txParams Contains data about a transaction
 * @param {string} txParams.gas The gas for a transaction
 * @param {string} txParams.gasPrice The price per gas for the transaction
 * @param {string} txParams.value The value of ETH to send
 * @param {string} hexBalance A balance of ETH represented as a hex string
 * @returns {boolean} Whether the balance is greater than or equal to the value plus the value of gas times gasPrice
 *
 */
function sufficientBalance (txParams, hexBalance) {
  // validate hexBalance is a hex string
  assert.equal(typeof hexBalance, 'string', 'sufficientBalance - hexBalance is not a hex string')
  assert.equal(hexBalance.slice(0, 2), '0x', 'sufficientBalance - hexBalance is not a hex string')

  const balance = hexToBn(hexBalance)
  const value = hexToBn(txParams.value)
  const gasLimit = hexToBn(txParams.gas)
  const gasPrice = hexToBn(txParams.gasPrice)

  const maxCost = value.add(gasLimit.mul(gasPrice))
  return balance.gte(maxCost)
}

/**
 * Converts a BN object to a hex string with a '0x' prefix
 *
 * @param {BN} inputBn The BN to convert to a hex string
 * @returns {string} A '0x' prefixed hex string
 *
 */
function bnToHex (inputBn) {
  return ethUtil.addHexPrefix(inputBn.toString(16))
}

/**
 * Converts a hex string to a BN object
 *
 * @param {string} inputHex A number represented as a hex string
 * @returns {Object} A BN object
 *
 */
function hexToBn (inputHex) {
  return new BN(ethUtil.stripHexPrefix(inputHex), 16)
}

/**
 * Used to multiply a BN by a fraction
 *
 * @param {BN} targetBN The number to multiply by a fraction
 * @param {number|string} numerator The numerator of the fraction multiplier
 * @param {number|string} denominator The denominator of the fraction multiplier
 * @returns {BN} The product of the multiplication
 *
 */
function BnMultiplyByFraction (targetBN, numerator, denominator) {
  const numBN = new BN(numerator)
  const denomBN = new BN(denominator)
  return targetBN.mul(numBN).div(denomBN)
}

function removeListeners (listeners, emitter) {
  Object.keys(listeners).forEach((key) => {
    emitter.removeListener(key, listeners[key])
  })
}

function getRandomArrayItem (array) {
  return array[Math.floor((Math.random() * array.length))]
}

function mapObjectValues (object, cb) {
  const mappedObject = {}
  Object.keys(object).forEach(key => {
    mappedObject[key] = cb(key, object[key])
  })
  return mappedObject
}

/**
 * Returns an Error if extension.runtime.lastError is present
 * this is a workaround for the non-standard error object thats used
 * @returns {Error}
 */
function checkForError () {
  const lastError = extension.runtime.lastError
  if (!lastError) {
    return
  }
  // if it quacks like an Error, its an Error
  if (lastError.stack && lastError.message) {
    return lastError
  }
  // repair incomplete error object (eg chromium v77)
  return new Error(lastError.message)
}

module.exports = {
  removeListeners,
  getPlatform,
  getEnvironmentType,
  sufficientBalance,
  hexToBn,
  bnToHex,
  BnMultiplyByFraction,
  getRandomArrayItem,
  mapObjectValues,
  checkForError,
}