@metamask/controllers

@metamask/controllers is a collection of platform-agnostic modules for creating secure data models for cryptocurrency wallets.

Table of Contents

• Usage
• Modules
• Concepts
  • Initialization
  • Configuration
  • State management
  • Subscription
  • Composition
• TypeScript
• Linking
• API documentation
• License

Usage

1. Install the package.

yarn add @metamask/controllers

1. Compose stores to create a data model.

import {
  ComposableController,
  NetworkStatusController,
  TokenRatesController
} from '@metamask/controllers';

const datamodel = new ComposableController([
  new NetworkStatusController(),
  new TokenRatesController()
]);

datamodel.subscribe((state) => {/* data model has changed */});

Modules

@metamask/controllers consists of a collection of controller modules that each expose uniform APIs for common operations like configuration, state management, and subscription.

AccountTrackerController

import AccountTrackerController from '@metamask/controllers';

The AccountTrackerController tracks information associated with specific Ethereum accounts.

AddressBookController

import AddressBookController from '@metamask/controllers';

The AddressBookController exposes functions for managing a list of recipient addresses and associated nicknames.

ComposableController

import ComposableController from '@metamask/controllers';

The ComposableController can be used to compose multiple controllers together into a single controller.

CurrencyRateController

import CurrencyRateController from '@metamask/controllers';

The CurrencyRateController passively polls for an ETH-to-fiat exchange rate based on a chosen currency.

KeyringController

import KeyringController from '@metamask/controllers';

The KeyringController is responsible for establishing and managing Ethereum address-based identities.

NetworkController

import NetworkController from '@metamask/controllers';

The NetworkController is responsible for creating an underlying provider and for refreshing its configuration.

NetworkStatusController

import NetworkStatusController from '@metamask/controllers';

The NetworkStatusController passively polls for the status of available provider networks. The Infura network is supported by default.

PhishingController

import PhishingController from '@metamask/controllers';

The PhishingController passively polls for community-maintained lists of approved and unapproved website origins.

PreferencesController

import PreferencesController from '@metamask/controllers';

The PreferencesController manages agnostic global settings and exposes convenience methods for updating them.

TokenRatesController

import TokenRatesController from '@metamask/controllers';

The TokenRatesController passively polls on a set interval for token-to-fiat exchange rates.

TransactionController

import TransactionController from '@metamask/controllers';

The TransactionController is responsible for submitting and managing transactions.

util

import util from '@metamask/controllers';

The util module exposes a set of utility functions for common operations like gas estimation and generating crypto-buying URLs.

Concepts

Using controllers should be straightforward since each controller exposes the same minimal API. The concepts detailed in this section form the entirety of the core API: knowing these concepts will allow you to fully use @metamask/controllers to build wallet data models.

Initialization

Each controller can be initialized with an optional initial configuration argument and an optional initial state argument:

const controller = new Controller(<initial_config>, <initial_state>)

Data passed into a controller as initial state will be merged with that controller's default state; likewise, options passed into a controller as initial configuration will be merged with that controller's default configuration.

Configuration

As mentioned in the initialization section, a controller can be configured during initialization by passing in a configuration object as its first argument:

const controller = new Controller(<initial_config>, <initial_state>)

A controller can also be configured (or reconfigured) after initialization by passing a configuration object to its configure method:

const controller = new Controller()
controller.configure({ foo: 'bar', baz: 'qux' });

Regardless of how a controller is configured, whether it's during or after initialization, configuration options can always be accessed on a controller as instance variables for convenience:

const controller = new Controller()
controller.configure({ foo: 'bar', baz: 'qux' });
console.log(controller.foo, controller.baz); // "bar qux"

State management

The core purpose of every controller is to maintain an internal data object called "state". Modules are like data stores: their internal state data can be updated directly by modifying the data itself or indirectly by calling API methods that in turn modify the data.

A controller's state can be directly modified by calling its update method and passing in a new data object. By default, this data object will be merged with the controller's existing internal state; however, if the data object should overwrite the controller's internal state, a second argument of true can be passed to the update method:

const controller = new Controller();
controller.update({ foo: 'bar' }); // merge with existing state
controller.update({ foo: 'bar' }, true); // overwrite existing state

A controller's state can be indirectly modified by calling any state-modifying API methods it may expose. For example, the AddressBookController exposes a set method that accepts a new address to save and an associated nickname; calling this method will internally update its state.addressBook array.

A controller's state can always be accessed by referencing the state instance variable for convenience:

const controller = new Controller();
console.log(controller.state); // { ... }

Subscription

Since each controller maintains an internal state object, there should be a way to add listeners to be notified when state data changes. controllers expose two methods for subscription management, subscribe and unsubscribe.

Change handlers can be registered with a controller by passing a function to its subscribe method. This function will be called anytime the controller's underlying state changes and will be passed the current state as its only function argument:

function onChange(state) { /* state data changed */ }
const controller = new Controller();
controller.subscribe(onChange);

Change handlers can be removed from a controller by passing a function to its unsubscribe method. Any function passed to unsubscribe will be removed from the internal list of handlers and will no longer be called when state data changes:

function onChange(state) { /* state data changed */ }
const controller = new Controller();
controller.subscribe(onChange);
// ...
controller.unsubscribe(onChange);

Composition

Because each controller maintains its own state and subscriptions, it would be tedious to initialize and subscribe to every available controller independently. To solve this issue, the ComposableController can be used to compose multiple controllers into a single controller.

The ComposableController is initialized by passing an array of controller instances:

import {
  ComposableController,
  NetworkStatusController,
  TokenRatesController
} from '@metamask/controllers';

const datamodel = new ComposableController([
  new NetworkStatusController(),
  new TokenRatesController()
]);

The resulting composed controller exposes the same APIs as every other controller for configuration, state management, and subscription:

datamodel.subscribe((state) => { /* some child state has changed */ });

The internal state maintained by a ComposableController will be keyed by child controller class name. It's also possible to access the flatState instance variable that is a convenience accessor for merged child state:

console.log(datamodel.state); // {NetworkController: {...}, TokenRatesController: {...}}
console.log(datamodel.flatState); // {infura: {...}, contractExchangeRates: [...]}

Advanced Note: The ComposableController builds a map of all child controllers keyed by controller name. This object is cached as a context instance variable on both the ComposableController itself as well as all child controllers. This means that child controllers can call methods on other sibling controllers through the context variable, e.g. this.context.SomeController.someMethod().

Why TypeScript?

@metamask/controllers is written using TypeScript. Despite its arguably steeper learning curve compared to JavaScript, TypeScript offers an objectively safer development experience that directly improves the reliability and maintainability of a large codebase.

Eliminate unintentionally broken APIs

TypeScript eliminates the ability to introduce changes to a codebase that break the APIs between or within components. If the signature changes for a specific function in a given class, every use of that function will immediately fail to compile until updated to match the new signature. This same idea applies to every other construct of the language: if the type of a property on an object is changed from string to boolean, every invalid use of that property will immediately fail to compile, etc. This is one of the most powerful features of a statically typed language for a mission-critical, modular package like @metamask/controller: it's extremely difficult to unknowingly introduce side effects.

Share custom types and interfaces

The ability to describe the shape that code must adhere to allows for the safe consumption and sharing of code without the need for duck typing. An underwhelming but point-driving comparison could be that TypeScript provides an enforced and very advanced form of JSDoc. Common or complex object formats with type-checked members can be shared and guaranteed across a codebase. This eliminates logic paths that only serve to check for the existence or the type of certain properties on an object, which usually account for a large portion of the code paths in a JavaScript application. Codebases become pragmatic and composable.

Eliminate errors caused by misnamed code

TypeScript exposes a powerful language services API used by most major editors for code introspection features such as member autocompletion. This drastically reduces the chance of misnaming a function or property from an imported module, and in the off chance that a typo or misnaming does occur, the codebase would again immediately fail to compile instead of causing a user-facing bug at runtime.

Use transpiled language-forward features

TypeScript automatically transpiles the latest ECMAScript language features to any desired target gracefully down to ES3. Microsoft directly monitors, supports, and heavily steers the implementation progress of the latest ES2018 specification through its development of TypeScript and adds opt-in support for features as their API churn settles down even before official TC39 finalization. This means that even implementation-heavy features like async / await are down-emitted without the hassle of manually managing polyfills or build tools like babel.

Other general OOP features

• Generics
• Member visibility
• Enums
• Advanced types (e.g. union, intersection)
• Easy 3rd-party typings management
• Mixins
• Superset of JavaScript, so all JS is valid TS

All of these features of a statically-typed language like TypeScript combine to form codebases consisting of strict contractural relationships between every module in an application. Changes are less intimidating since unnoticed side effects are difficult to introduce, documentation can be generated with less verbose syntax (TSDoc is JSDoc without the types since it can infer them), editors provide autocompletion of both public module members and of local and NPM dependencies, and an upgrade to TypeScript can be incremental as demonstrated in this PR.

Linking during development

Linking @metamask/controller into other projects involves a special NPM command to ensure that dependencies are not duplicated. This is because @metamask/controller ships modules that are transpiled but not bundled, and NPM does not deduplicate linked dependency trees.

1. Link @metamask/controller.

$ yarn build:link
# or
$ npm run build:link

1. Link into other projects.

$ yarn link @metamask/controllers
# or
$ npm link @metamask/controllers

Release Steps

• Create branch from develop named v${version}
• push remote branch
• Run npx release <major|minor|patch>. major for breaking changes, patch for bugfixes, minor for backwards compatible features.
• Then select which PRs will be added to generate the changelog
• Github page will be opened in your browser with the new generated tag and changelog, press the green button to release.
• Then merge v${version} branch to develop, then make master up to date with develop
• enable "create merge commit" option
• do a normal merge to maintain history
• disable "create merge commit" option
• On a clean master run yarn build, then run npm publish in the project root and @metamask/controller will be on npm

API documentation

API documentation is auto-generated for the @metamask/controller package on every commit to the master branch.

View API documentation

License

MIT