Isolation

Why should i use it ? How often do you see libraries which mutates global variables Or how often do you check libraries actions ? Library provides script isolation in custom contexts to solve this kind of issues. Also, isolation prevents global scope and prototypes pollution.

Tip

Possible use case

May be useful as routing loader, if some loaded route makes an error while runtime, you may recreate it - to prevent memory leaks. Another worlds, with this library you can create multi-tenant applications;

Installation

npm i isolation --save

Basic Usage

• Prevent intentionally damage

  It will stop tricky users code, while you don't allow it.

  // unchecked-dangerous-library index.js
  const fs = require('fs');
  fs.rm(process.cwd(), { recursive: true }); // Ha ha, no-code developer

  // routes/route/get.js
  const dangerousLibrary = require('unchecked-dangerous-library'); // Point where dangerous library initialized
  // ... other logic

  // index.js
  const Isolation = require('isolation');
  const routes = Isolation.read('./routes');
  // ⚠️ Will throw an error because fs doesn't allowed

• Prevent unintentionally damage

  This solves problem where libraries used to mutate global variables.

  // unchecked-dangerous-library index.js
  var console = msg => process.stdout.write(msg); // Someone just want different implementation for console
  global.console = console;
  console('Here it works fine');
  String.prototype = {}; // Or just mutating prototypes

  // routes/route/get.js
  const dangerousLibrary = require('unchecked-dangerous-library'); // Point where dangerous library initialized
  // ... other logic

  // index.js
  const Isolation = require('isolation');
  Isolation.read('./routes');
  console.log('All works fine');
  console('Here it not works'); // Will throw an error
  String.prototype; // Will be as default

Module types / Script syntax

Caution

You can run any script from string, just like eval, but in custom VM container. But you shouldn't use it for unknown script evaluation, it may create security issues.

Commonjs

By default Isolation will use Standard Nodejs syntax. With this type of syntax it will provide to your realms global variables such as:

• require function, which is almost same as nodejs require, but with extra cup of isolation;
• module & exports variables provided to manipulate with exports between modules;
• __filename & __dirname are same as with default nodejs realm;

Important

You always should use module.exports to export, otherwise you will see undefined as the result of realm execution.

const Isolation = require('isolation');
console.log(new Isolation(`module.exports = { field: 'value' };`).execute()); // Output: { field: 'value' }
console.log(Isolation.execute(`module.exports = (a, b) => a + b;`)(2 + 2)); // Output: 4
console.log(Isolation.execute(`(a, b) => a + b;`)(2 + 2)); // Output: undefined
Isolation.execute(`module.exports = async (a, b) => a + b;`)(2 + 2).then(console.log); // Output: 4

ISO

This type of syntax will stand your script alone without any of extra global variables. That means that you would not see module or exports in your environment. But your context variables will still work well.

Important

In this mode, your realms will export result of the last expression, that means that you should put a reference to your variable or expression at the end of the file / row;

const Isolation = require('isolation');
const options = { type: 'iso' };
console.log(new Isolation(`{ field: 'value' };`, options).execute()); // Output: { field: 'value' }
console.log(Isolation.execute(`(a, b) => a + b;`, options)(2 + 2)); // Output: 4
Isolation.execute(`async (a, b) => a + b;`, options)(2 + 2).then(console.log); // Output: 4

ESM

Isolation doesn't yet support esm syntax. That's because currently node.vm ESM modules are experimental.

Context API

You can create custom context or use default presets with context api. This will allow you to provide your custom variables to the context without requiring any module.

Tip

Remember to reuse your contexts. This will increase performance of your application. To help you with this we have default contexts:

Context example

const { contextify, execute } = require('isolation');
const custom = contextify({ console }); // ⚠️ Object will be mutated
execute(`console.log(123);`, { ctx: custom }); // STD Output: 123
execute(`console.log(123);`); // No STD output, because different stdout stream

Also its allow you to change program behavior with something like:

const ctx = Isolation.contextify({ a: 1000, b: 10 });
const realm = new Isolation(`module.exports = a - b`, { ctx });
realm.execute(); // Output: 990
realm.execute({ ...ctx, a: 0 }); // Output: -10
realm.execute({ ...ctx, b: 7 }); // Output: 993

Default contexts

Default contexts are accessible from Isolation.contextify, there you can find:

• Isolation.contextify.EMPTY, that just empty context
• Isolation.contextify.COMMON, timers, buffer, fetch etc...
• Isolation.contextify.NODE, global, console, process & COMMON context You should'nt use NODE context, it may create security issues, otherwise it may road to possible context escaping.

Reader API

Reader allow you to run scripts from files and extends possible provided options with:

• Option prepare:boolean reader will return non-executed scripts, default false

• Option depth:number|boolean nested directories restrictions, default true

• Option flat:boolean result with nested scripts will be flat, default false

• read Allow you to read source codes from files and directories

  const Isolation = require('isolation');
  Isolation.read('./path/to/script.js').then(console.log); // Output: result of script execution
  Isolation.read('./path/to').then(console.log); // Output: { script: any }
  Isolation.read('./path/to', { prepare: true }).then(console.log); // Output: { script: Script {} }

  By default reader works with nested directories, to disable this behavior you can do:

  const Isolation = require('isolation');
  Isolation.read('./path/to', { depth: false });
  // Or limit it:
  Isolation.read('./path/to', { depth: 3 });

• read.file Allow you to execute script from single file

  const Isolation = require('isolation');
  Isolation.read.file('./path/to/script.js').then(console.log); // Output: result of script execution
  Isolation.read.file('./path/to/script.js', { prepare: true }).then(console.log); // Output: Script {}

• read.dir Allow you to execute multiple scripts from directory

  const Isolation = require('isolation');
  Isolation.read.dir('./path/to').then(console.log); // Output: { script: any, deep: { script: any } }
  Isolation.read.dir('./path/to', { prepare: true }).then(console.log); Output: { script: Script {} }
  Isolation.read.dir('./path/to', { depth: false }).then(console.log); // Output: { script: any }

Access control

You may control access over realm submodules and reader api;

Note

If access doesn't provided realm submodules would'nt be accessible and reader will read all files in directed repository.

const options = { access: pathOrModule => pathOrModule === 'fs' || pathOrModule.endsWith('.js') };
Isolation.execute('module.exports = require("fs")', options);
Isolation.read('./path/to/script.js', options);
// Or
const options2 = {
  access: {
    reader: path => true, // Directory reader
    realm: module => {}, //  Realm submodules
  },
};

Library substitution

You can replace result of require for specific libraries with anything what you want;

const Isolation = require('isolation');
const src = `
  const fs = require('fs');
  module.exports = fs.readFile('Isolation.js');
`;

const sub = name => {
  if (name !== 'fs') return true;
  return {
    readFile: filename => filename + ' Works !',
  };
};

const result = Isolation.execute(src, { access: { realm: sub } });
console.log(result); // Output: Isolation.js Works !

Possible script options

Option	Possible	Default	Description
type	iso | cjs	cjs	Type of script handling, see syntax types
ctx	object	-	Realm context, see Context API
filename	string	ISO	Name of the module , also it is global variable __filename for root realm
dir	string	process.cwd()	Module directory , also it is global variable __dirname and realm require start point
npmIsolation	boolean	false	Controls npm modules isolation
access	Access	-	Isolation restrictions, see Access API
prepare	boolean	false	Reader would'nt execute script for you
flat	boolean	false	Reader will flat nested scripts
depth	boolean | number	true	Restricts dir reading depth
realmOpts	ScriptOptions	-	Configuration for VM.Script initialization
runOpts	RunningCodeOptions	{ timeout: 1000 }	Configuration for VM.Script execution

Copyright & contributors

Copyright © 2023 Astrohelm contributors. This library is MIT licensed license.
And it is part of Astrohelm solutions.