nfroidureknifecycle
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,
knifecycleimpeach that while providing an$injectorservice 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
pgmodule, - jwt-service: a simple wrapper
around the
jwtmodule 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
Functions
- initInitializerBuilder(services) ⇒
Promise.<function()> Instantiate the initializer builder service
- initDispose()
Allow to dispose the services of an initialized silo content.
- 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
- 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']);
initDispose()
Allow to dispose the services of an initialized silo content.
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 information |
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 information |
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 |
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'