JSON hashing, canonicalization, digests, SHA, MD5

json_hashing.js

function json_canonical(obj) {
  return JSON.stringify(obj, (key, value) => {
    if ('object' !== typeof value)
      return value // it is a value of some kind

    if (value instanceof Array)
      return value // Arrays are (already) ordered

    // normalize into new object initializing via sorted keys
    let result = {}
    for(let k of Object.keys(value).sort())
      result[k] = value[k]
    return result }) }

function json_hash(obj, hash_algorithm='sha1') {
  let src_json = json_canonical(obj)
  let hash = crypto.createHash(hash_algorithm)
    .update(src_json, 'utf8')
  hash.src_json = src_json
  return hash }

function json_digest(obj, encoding='hex', hash_algorithm='sha1') {
  return json_hash(obj, hash_algorithm).digest(encoding) }

test_json_hashing.js

'use strict'
const assert = require('assert')
let {json_digest, json_canonical} = require('./json_hashing')

class MyClass { toJSON() { return {lst: [1,2,3], msg: 'was here'} }}
let myObj = new MyClass()

let ans = [
  {b: 'bee', c: myObj, a: {z: 'zzeee', d: 'ddeeee'}},
  {b: 'bee', a: {z: 'zzeee', d: 'ddeeee'}, c: myObj},
  {a: {z: 'zzeee', d: 'ddeeee'}, c: myObj, b: 'bee'},
  {a: {d: 'ddeeee', z: 'zzeee'}, c: myObj, b: 'bee'},
].map(e => json_digest(e))

assert.deepEqual(ans, [
  '316944236441fe58d5ad02c5d494ffef284657f8',
  '316944236441fe58d5ad02c5d494ffef284657f8',
  '316944236441fe58d5ad02c5d494ffef284657f8',
  '316944236441fe58d5ad02c5d494ffef284657f8'])

assert.equal(ans.reduce((k,v) => k==v ? k : null),
  '316944236441fe58d5ad02c5d494ffef284657f8')