now-cli/lib/hash.js

// Native
import {createHash} from 'crypto'
import path from 'path'

// Packages
import {readFile} from 'fs-promise'

const listPackage = {
  name: 'static',
  version: '0.0.0',
  scripts: {
    start: 'list ./content'
  },
  dependencies: {
    list: 'latest'
  }
}

 /**
  * Computes hashes for the contents of each file given.
  *
  * @param {Array} of {String} full paths
  * @return {Map}
  */

export default async function hashes(files, isStatic) {
  const map = new Map()
  await Promise.all(files.map(async name => {
    const filename = path.basename(name)
    let data

    if (isStatic && filename === 'package.json') {
      const packageString = JSON.stringify(listPackage, null, 2)
      data = Buffer.from(packageString)
    } else {
      data = await readFile(name)
    }

    const h = hash(data)
    const entry = map.get(h)
    if (entry) {
      entry.names.push(name)
    } else {
      map.set(hash(data), {names: [name], data})
    }
  }))
  return map
}

/**
 * Computes a hash for the given buf.
 *
 * @param {Buffer} file data
 * @return {String} hex digest
 */

function hash(buf) {
  return createHash('sha1')
    .update(buf)
    .digest('hex')
}