@loopback/rest/src/parse-json.ts

Expose controllers as REST endpoints and route REST API requests to controller methods

// Copyright IBM Corp. and LoopBack contributors 2019. All Rights Reserved.
// Node module: @loopback/rest
// This file is licensed under the MIT License.
// License text available at https://opensource.org/licenses/MIT

/* eslint-disable @typescript-eslint/no-explicit-any */

// These utilities are introduced to mitigate the prototype pollution issue
// with `JSON.parse`.
// See https://hueniverse.com/a-tale-of-prototype-poisoning-2610fa170061
//
// The [bourne](https://github.com/hapijs/bourne) module provides a drop-in
// replacement for `JSON.parse` but we need to instruct `body-parser` to honor
// a `reviver` function.

const isMatched = (key: string, pattern: string) =>
  pattern === key || key.indexOf(`${pattern}.`) === 0;

/**
 * Factory to create a reviver function for `JSON.parse` to sanitize keys
 * @param reviver - Reviver function
 * @param prohibitedKeys - An array of keys to be rejected
 */
export function sanitizeJsonParse(
  reviver?: (key: any, value: any) => any,
  prohibitedKeys?: string[],
) {
  return (key: string, value: any) => {
    if (key === '__proto__') {
      // Reject `__proto__`
      throw new Error(`JSON string cannot contain "${key}" key.`);
    }
    if (
      key === 'constructor' &&
      value != null &&
      Object.keys(value).some(k => isMatched(k, 'prototype'))
    ) {
      // Reject `constructor/prototype.*`
      throw new Error(
        `JSON string cannot contain "constructor.prototype" key.`,
      );
    }
    if (prohibitedKeys?.some(pattern => isMatched(key, pattern))) {
      throw new Error(`JSON string cannot contain "${key}" key.`);
    }
    if (reviver) {
      return reviver(key, value);
    } else {
      return value;
    }
  };
}

/**
 * Parse a json string that rejects prohibited keys
 * @param text - JSON string
 * @param reviver - Optional reviver function for `JSON.parse`
 * @param prohibitedKeys - An array of keys to be rejected
 */
export function parseJson(
  text: string,
  reviver?: (key: any, value: any) => any,
  prohibitedKeys?: string[],
) {
  prohibitedKeys = [
    '__proto__',
    'constructor.prototype',
    ...(prohibitedKeys ?? []),
  ];
  return JSON.parse(text, sanitizeJsonParse(reviver, prohibitedKeys));
}