knifecycle

Manage your NodeJS processes's lifecycle automatically with an unobtrusive dependency injection implementation.

Most (maybe all) applications rely on two kinds of dependencies.

The code dependencies are fully covered by JavaScript modules in a testable manner (with mockery or System directly). There is no need for another dependency management system if those libraries are pure functions (involve no global states at all).

Unfortunately, applications often rely on global states where the JavaScript module system shows its limits. This is where knifecycle enters the game.

It is largely inspired by the Angular service system except it should not provide code but access to global states (time, filesystem, db). It also have an important additional feature to shutdown processes which is really useful for back-end servers and doesn't exists in Angular.

Last but not least, you can build your code with Knifecycle so that once in production, it do not have to resolve the dependency tree leading to better performances and reduce the bundle size (especially for tools like AWS Lambda / GCP Functions where each endpoint has its own zip).

You may want to look at the architecture notes to better handle the reasonning behind knifecycle and its implementation.

At this point you may think that a DI system is useless. My advice is that it depends. But at least, you should not make a definitive choice and allow both approaches, Knifecycle permits this, most modules made usable by Knifecycle can in fact be used without it (this is also why static build works). See this blog post for more context about this statement.

Features

• services management: start services taking their dependencies in count and shut them down the same way for graceful exits (namely dependency injection with inverted control),
• singleton: maintain singleton services across several running execution silos,
• easy end to end testing: just replace your services per your own mocks and stubs while ensuring your application integrity between testing and production,
• isolation: isolate processing in a clean manner, per concerns;
• functional programming ready: encapsulate global states allowing the rest of your application to be purely functional,
• no circular dependencies for services: while circular dependencies are not a problem within purely functional libraries (require allows it), it may be harmful for your services, knifecycle impeach that while providing an $injector service à la Angular to allow accessing existing services references if you really need to,
• generate Mermaid graphs of the dependency tree,
• auto-detect injected services names,
• build raw initialization modules to avoid embedding Knifecycle in your builds,
• optionally autoload services dependencies with custom logic.

You can find all Knifecycle comptabile modules on NPM with the knifecycle keyword.

Usage

Using knifecycle is all about declaring the services our application needs and running your application over it.

Let's say we are building a CLI script. Here is how we would proceed with Knifecycle:

// bin.js
import fs from 'fs';
import { YError } from 'YError';
import {
  Knifecycle,
  initializer,
  constant,
  inject,
  name
} from 'knifecycle';

// First of all we create a new Knifecycle instance
const $ = new Knifecycle();

// Some of our code with rely on the process environment
// let's inject it as a constant instead of directly
// pickking env vars in `process.env` to make our code
// easily testable
$.register(constant('ENV', process.env));

// Let's do so for CLI args with another constant
// in real world apps we would have created a service
// that would parse args in a complexer way
$.register(constant('ARGS', process.argv));

// We want our CLI tool to rely on some configuration
// Let's build an injectable service initializer that
// reads environment variables via an injected but
// optional `ENV` object
// In a real world app, you may use the
// `application-services` module services instead.
async function initConfig({ ENV = { CONFIG_PATH: '.' } }) {
  await fs.promises.readFile(
    ENV.CONFIG_PATH,
    'utf-8',
    (err, data) => {
      if (err) {
        reject(err);
        return;
      }
      try {
        resolve(JSON.parse(data));
      } catch (err) {
        reject(err);
      }
    },
  );
}

// We are using the `initializer` decorator to
// declare our service initializer specificities
// and register it with our Knifecycle instance
$.register(
  initializer(
    {
      // we have to give our final service a name
      // for further use in other services injections
      name: 'CONFIG',
      // we will need an `ENV` variable in the initializer
      // so adding it in the injected dependencies. The `?`
      // sign tells Knifecycle that the ENV dependency
      // is optional
      inject: ['?ENV'],
      // our initializer is simple so we use the `service`
      // type for the initializer which just indicate that
      // the initializer will return a promise of the actual
      // service
      type: 'service',
      // We don't want to read the config file everytime we
      // inject it so declaring it as a singleton
      singleton: true,
    },
    initConfig,
  ),
);

// Our CLI also uses a database so let's write an
// initializer for it (in a real world app you
// can use `postgresql-service` instead):
const initDB = initializer(
  {
    name: 'db',
    // Here we are injecting the previous `CONFIG` service
    // as required so that our DB cannot be connected without
    // having a proper config.
    inject: ['CONFIG', 'DB_URI', '?log'],
    // The initializer type is slightly different. Indeed,
    // we need to manage the database connection errors
    // and wait for it to flush before shutting down the
    // process.
    // A service provider returns a promise of a provider
    // descriptor exposing:
    // - a mandatory `service` property containing the
    // actual service;
    // - an optional `dispose` function allowing to
    // gracefully close the service;
    // - an optional `fatalErrorPromise` property to
    // handle the service unrecoverable failure.
    type: 'provider',
    singleton: true,
  },
  async ({ CONFIG, DB_URI, log }) => {
    const db = await MongoClient.connect(DB_URI, CONFIG.databaseOptions);
    let fatalErrorPromise = new Promise((resolve, reject) => {
      db.once('error', reject);
    });

    // Logging only if the `log` service is defined
    log && log('info', 'db service initialized!');

    return {
      service: db,
      dispose: db.close.bind(db, true),
      fatalErrorPromise,
    };
  },
);

// Here we are registering our initializer apart to
// be able to reuse it, we also declare the required
// DB_URI constant it needs
$.register(constant('DB_URI', 'posgresql://xxxx'));
$.register(initDB);

// Say we need to use two different DB server
// We can reuse our initializer by tweaking
// some of its properties
$.register(constant('DB_URI2', 'posgresql://yyyy'));
$.register(
  // First we remap the injected dependencies. It will
  // take the `DB_URI2` constant and inject it as
  // `DB_URI`
  inject(
    ['CONFIG', 'DB_URI2>DB_URI', '?log'],
    // Then we override its name to make it
    // available as a different service
    name('db2', initDB),
  ),
);

// A lot of NodeJS functions have some side effects
// declaring them as constants allows you to easily
// mock/monitor/patch it. The `common-services` NPM
// module contains a few useful ones
$.register(constant('now', Date.now.bind(Date)))
  .register(constant('log', console.log.bind(console)))
  .register(constant('exit', process.exit.bind(process)));

// Finally, let's declare an `$autoload` service
// to allow us to load only the initializers needed
// to run the given commands
$.register(
  initializer(
    {
      name: '$autoload',
      type: 'service',
      inject: ['CONFIG', 'ARGS'],
      // Note that the auto loader must be a singleton
      singleton: true,
    },
    async ({ CONFIG, ARGS }) =>
      async (serviceName) => {
        if ('command' !== serviceName) {
          // Allows to signal that the dependency is not found
          // so that optional dependencies doesn't impeach the
          // injector to resolve the dependency tree
          throw new YError('E_UNMATCHED_DEPENDENCY', serviceName);
        }
        try {
          const path = CONFIG.commands + '/' + ARGS[2];
          return {
            path,
            initializer: require(path).default,
          };
        } catch (err) {
          throw new Error(`Cannot load ${serviceName}: ${ARGS[2]}!`);
        }
      },
  ),
);

// At this point, nothing is running. To instanciate the
// services, we have to create an execution silo using
// them. Note that we required the `$instance` service
// implicitly created by `knifecycle`
$.run(['command', '$instance', 'exit', 'log'])
  // Here, command contains the initializer eventually
  // found by automatically loading a NodeJS module
  // in the above `$autoload` service. The db connection
  // will only be instanciated if that command needs it
  .then(async ({ command, $instance, exit, log }) => {
    try {
      command();

      log('It worked!');
    } catch (err) {
      log('It failed!', err);
    } finally {
      // Here we ensure every db connections are closed
      // properly. We could have use `$.destroy()` the same
      // way but this is to illustrate that the Knifecycle
      // instance can be injected in services contexts
      // (rarely done but good to know it exists)
      await $instance.destroy().catch((err) => {
        console.error('Could not exit gracefully:', err);
        exit(1);
      });
    }
  })
  .catch((err) => {
    console.error('Could not launch the app:', err);
    process.exit(1);
  });

Running the following should make the magic happen:

cat "{ commands: './commands'}" > config.json
DEBUG=knifecycle CONFIG_PATH=./config.json node -r @babel/register bin.js mycommand test
// Prints: Could not launch the app: Error: Cannot load command: mycommand!
// (...stack trace)

Or at least, we still have to create commands, let's create the mycommand one:

// commands/mycommand.js
import { initializer } from './dist';

// A simple command that prints the given args
export default initializer(
  {
    name: 'command',
    type: 'service',
    // Here we could have injected whatever we declared
    // in the previous file: db, now, exit...
    inject: ['ARGS', 'log'],
  },
  async ({ ARGS, log }) => {
    return () => log('Command args:', ARGS.slice(2));
  },
);

So now, it works:

DEBUG=knifecycle CONFIG_PATH=./config.json node -r @babel/register bin.js mycommand test
// Prints: Command args: [ 'mycommand', 'test' ]
// It worked!

This is a very simple example but you can find a complexer CLI usage with (metapak)[https://github.com/nfroidure/metapak/blob/master/bin/metapak.js].

Auto detection

Knifecycle also provide some utility function to automatically assign the initializer property declarations, the following 3 ways to declare the getUser service are equivalent:

import noop from 'noop';
import { autoInject, inject, initializer, autoService } from 'knifecycle';

initializer({
  name: 'getUser',
  inject: ['db', '?log'],
  type: 'service',
}, getUser);

service('getUser', autoInject(getUser)));

autoService(getUser);

async function getUser({ db, log = noop}) {}

That said, if you need to build your code with webpack/babel you may have to convert auto-detections to raw declarations with the babel-plugin-knifecycle plugin. You can also do this only for the performance improvements it brings.

Also, keep in mind that the auto-detection is based on a simple regular expression so you should care to keep initializer signatures simple to avoid having a E_AUTO_INJECTION_FAILURE error. As a rule of thumb, avoid setting complex default values.

// Won't work
autoInject(async ({ log = () => {} }) => {});

// Will work
function noop() {}
autoInject(async ({ log = noop }) => {});

Debugging

Simply use the DEBUG environment variable by setting it to 'knifecycle':

DEBUG=knifecycle npm t

The output is very verbose but lead to a deep understanding of mechanisms that take place under the hood.

Plans

The scope of this library won't change. However the plan is:

• improve performances;
• track bugs ;).

I'll also share most of my own initializers and their stubs/mocks in order to let you reuse it through your projects easily. Here are the current projects that use this DI lib:

• common-services: contains the services I use the most in my apps,
• memory-kv-store: a simple in memory key-value store,
• whook: a framework to build REST web services.
• postgresql-service: a simple wrapper around the pg module,
• jwt-service: a simple wrapper around the jwt module to simplify its use,
• ftp-service: a FTP client with clean defaults.

Notice that those modules remains usable without using Knifecycle at all which is maybe the best feature of this library 😉.

API

Classes

Knifecycle

Functions

initInitializerBuilder(services) ⇒ Promise.<function()>

Instantiate the initializer builder service

constant(name, value) ⇒ function

Decorator that creates an initializer for a constant value

service(serviceBuilder, [name], [dependencies], [singleton], [extra]) ⇒ function

Decorator that creates an initializer from a service builder

autoService(serviceBuilder) ⇒ function

Decorator that creates an initializer from a service builder by automatically detecting its name and dependencies

provider(providerBuilder, [name], [dependencies], [singleton], [extra]) ⇒ function

Decorator that creates an initializer for a provider builder

autoProvider(providerBuilder) ⇒ function

Decorator that creates an initializer from a provider builder by automatically detecting its name and dependencies

handler(handlerFunction, [name], [dependencies], [options]) ⇒ function

Shortcut to create an initializer with a simple handler

autoHandler(handlerFunction) ⇒ function

Allows to create an initializer with a simple handler automagically

parseDependencyDeclaration(dependencyDeclaration) ⇒ Object

Explode a dependency declaration an returns its parts.

stringifyDependencyDeclaration(dependencyDeclarationParts) ⇒ String

Stringify a dependency declaration from its parts.

Knifecycle

Kind: global class

• Knifecycle
  • new Knifecycle(options)
  • .register(initializer) ⇒ Knifecycle
  • .toMermaidGraph(options) ⇒ String
  • .run(dependenciesDeclarations) ⇒ Promise
  • .destroy() ⇒ Promise

new Knifecycle(options)

Create a new Knifecycle instance

Returns: Knifecycle - The Knifecycle instance

Param	Type	Description
options	Object	An object with options
options.sequential	boolean	Allows to load dependencies sequentially (usefull for debugging)

Example

import Knifecycle from 'knifecycle'

const $ = new Knifecycle();

knifecycle.register(initializer) ⇒ Knifecycle

Register an initializer

Kind: instance method of Knifecycle
Returns: Knifecycle - The Knifecycle instance (for chaining)

Param	Type	Description
initializer	function	An initializer

knifecycle.toMermaidGraph(options) ⇒ String

Outputs a Mermaid compatible dependency graph of the declared services. See Mermaid docs

Kind: instance method of Knifecycle
Returns: String - Returns a string containing the Mermaid dependency graph

Param	Type	Description
options	Object	Options for generating the graph (destructured)
options.shapes	Array.<Object>	Various shapes to apply
options.styles	Array.<Object>	Various styles to apply
options.classes	Object	A hash of various classes contents

Example

import Knifecycle, { inject, constant, service } from 'knifecycle';
import appInitializer from './app';

const $ = new Knifecycle();

$.register(constant('ENV', process.env));
$.register(constant('OS', require('os')));
$.register(service('app', inject(['ENV', 'OS'], appInitializer)));
$.toMermaidGraph();

// returns
graph TD
  app-->ENV
  app-->OS

knifecycle.run(dependenciesDeclarations) ⇒ Promise

Creates a new execution silo

Kind: instance method of Knifecycle
Returns: Promise - Service descriptor promise

Param	Type	Description
dependenciesDeclarations	Array.<String>	Service name.

Example

import Knifecycle, { constant } from 'knifecycle'

const $ = new Knifecycle();

$.register(constant('ENV', process.env));
$.run(['ENV'])
.then(({ ENV }) => {
 // Here goes your code
})

knifecycle.destroy() ⇒ Promise

Destroy the Knifecycle instance

Kind: instance method of Knifecycle
Returns: Promise - Full destruction promise
Example

import Knifecycle, { constant } from 'knifecycle'

const $ = new Knifecycle();

$.register(constant('ENV', process.env));
$.run(['ENV'])
.then(({ ENV }) => {
   // Here goes your code

   // Finally destroy the instance
   $.destroy()
})

initInitializerBuilder(services) ⇒ Promise.<function()>

Instantiate the initializer builder service

Kind: global function
Returns: Promise.<function()> - A promise of the buildInitializer function

Param	Type	Description
services	Object	The services to inject
services.$autoload	Object	The dependencies autoloader

Example

import initInitializerBuilder from 'knifecycle/dist/build';

const buildInitializer = await initInitializerBuilder({
  $autoload: async () => {},
});

initInitializerBuilder~buildInitializer(dependencies) ⇒ Promise.<String>

Create a JavaScript module that initialize a set of dependencies with hardcoded import/awaits.

Kind: inner method of initInitializerBuilder
Returns: Promise.<String> - The JavaScript module content

Param	Type	Description
dependencies	Array.<String>	The main dependencies

Example

import initInitializerBuilder from 'knifecycle/dist/build';

const buildInitializer = await initInitializerBuilder({
  $autoload: async () => {},
});

const content = await buildInitializer(['entryPoint']);

constant(name, value) ⇒ function

Decorator that creates an initializer for a constant value

Kind: global function
Returns: function - Returns a new constant initializer

Param	Type	Description
name	String	The constant's name.
value	any	The constant's value

Example

import Knifecycle, { constant, service } from 'knifecycle';

const { printAnswer } = new Knifecycle()
  .register(constant('THE_NUMBER', value))
  .register(constant('log', console.log.bind(console)))
  .register(service(
    async ({ THE_NUMBER, log }) => () => log(THE_NUMBER),
    'printAnswer',
    ['THE_NUMBER', 'log'],
  ))
  .run(['printAnswer']);

printAnswer(); // 42

service(serviceBuilder, [name], [dependencies], [singleton], [extra]) ⇒ function

Decorator that creates an initializer from a service builder

Kind: global function
Returns: function - Returns a new initializer

Param	Type	Description
serviceBuilder	function	An async function to build the service
[name]	String	The service's name
[dependencies]	Array.<String>	The service's injected dependencies
[singleton]	Boolean	Whether the service is a singleton or not
[extra]	any	Eventual extra informations

Example

import Knifecycle, { constant, service } from 'knifecycle';

const { printAnswer } = new Knifecycle()
  .register(constant('THE_NUMBER', value))
  .register(constant('log', console.log.bind(console)))
  .register(service(
    async ({ THE_NUMBER, log }) => () => log(THE_NUMBER),
    'printAnswer',
    ['THE_NUMBER', 'log'],
    true
  ))
  .run(['printAnswer']);

printAnswer(); // 42

autoService(serviceBuilder) ⇒ function

Decorator that creates an initializer from a service builder by automatically detecting its name and dependencies

Kind: global function
Returns: function - Returns a new initializer

Param	Type	Description
serviceBuilder	function	An async function to build the service

provider(providerBuilder, [name], [dependencies], [singleton], [extra]) ⇒ function

Decorator that creates an initializer for a provider builder

Kind: global function
Returns: function - Returns a new provider initializer

Param	Type	Description
providerBuilder	function	An async function to build the service provider
[name]	String	The service's name
[dependencies]	Array.<String>	The service's dependencies
[singleton]	Boolean	Whether the service is a singleton or not
[extra]	any	Eventual extra informations

Example

import Knifecycle, { provider } from 'knifecycle'
import fs from 'fs';

const $ = new Knifecycle();

$.register(provider(configProvider, 'config'));

async function configProvider() {
  return new Promise((resolve, reject) {
    fs.readFile('config.js', function(err, data) {
      let config;

      if(err) {
        reject(err);
        return;
      }

      try {
        config = JSON.parse(data.toString);
      } catch (err) {
        reject(err);
        return;
      }

      resolve({
        service: config,
      });
    });
  });
}

autoProvider(providerBuilder) ⇒ function

Decorator that creates an initializer from a provider builder by automatically detecting its name and dependencies

Kind: global function
Returns: function - Returns a new provider initializer

Param	Type	Description
providerBuilder	function	An async function to build the service provider

handler(handlerFunction, [name], [dependencies], [options]) ⇒ function

Shortcut to create an initializer with a simple handler

Kind: global function
Returns: function - Returns a new initializer

Param	Type	Default	Description
handlerFunction	function		The handler function
[name]	String		The name of the handler. Default to the DI prop if exists
[dependencies]	Array.<String>	[]	The dependencies to inject in it
[options]	Object		Options attached to the built initializer

Example

import Knifecycle, { handler } from 'knifecycle';

new Knifecycle()
.register(handler(getUser, 'getUser', ['db', '?log']));

const QUERY = `SELECT * FROM users WHERE id=$1`
async function getUser({ db }, userId) {
  const [row] = await db.query(QUERY, userId);

  return row;
}

autoHandler(handlerFunction) ⇒ function

Allows to create an initializer with a simple handler automagically

Kind: global function
Returns: function - Returns a new initializer

Param	Type	Description
handlerFunction	function	The handler function

Example

import Knifecycle, { autoHandler } from 'knifecycle';

new Knifecycle()
.register(autoHandler(getUser));

const QUERY = `SELECT * FROM users WHERE id=$1`
async function getUser({ db }, userId) {
  const [row] = await db.query(QUERY, userId);

  return row;
}

parseDependencyDeclaration(dependencyDeclaration) ⇒ Object

Explode a dependency declaration an returns its parts.

Kind: global function
Returns: Object - The various parts of it

Param	Type	Description
dependencyDeclaration	String	A dependency declaration string

Example

parseDependencyDeclaration('pgsql>db');
// Returns
{
  serviceName: 'pgsql',
  mappedName: 'db',
  optional: false,
}

stringifyDependencyDeclaration(dependencyDeclarationParts) ⇒ String

Stringify a dependency declaration from its parts.

Kind: global function
Returns: String - The various parts of it

Param	Type	Description
dependencyDeclarationParts	Object	A dependency declaration string

Example

stringifyDependencyDeclaration({
  serviceName: 'pgsql',
  mappedName: 'db',
  optional: false,
});

// Returns
'pgsql>db'

Authors

• Nicolas Froidure

License

MIT