Arpen

Arpen is a Node.js micro-framework with class autoloading and dependency injection. Its purpose is to aid in creation of non-Express.js applications.

Dependency injection

Arpen application consists of services. Here is how service looks like:

class MyService {
    constructor(otherService, anotherService) {
        this._otherService = otherService;
        this._anotherService = anotherService;
    }
    
    static get provides() { return 'myService'; }
    static get requires() { return ['otherService', 'anotherService?']; }
    
    doStuff() {
        // do something with this._otherService
        // and this._anotherService
    }
}
 
module.exports = MyService;

This is a service which is registered in the system by key 'myService' (provides static property). It requires two other services known as 'otherService' and 'anotherService' (requires static property). The second one is marked by '?' sign which means that this dependency is optional: if Arpen won't be able to instantiate it (i.e. it is not registered) then null will be passed to the constructor instead (for non-optional dependencies error will be thrown).

Arpen will first instantiate dependencies of the service and pass the instances to your constructor in the same order as specified by requires property. You can use this service as a dependency of another service or just instantiate it with app.get('myService').

Life cycle

The third (optional) static property you can define on a service is lifecycle. Consider the following example: we have a service A that depends on B and C, both B and C depend on fourth service - D.

When lifecycle of D is 'perRequest' or not specified then both B and C dependencies of A will receive the same instance of D when A is instantiated. So D is instantiated only once per request of instantiating A.

But if you run app.get('A') another time it will be new request and B and C of A will receive different instance of D when instantiating new A (but, again, both B and C will receive the same D just like in previous app.get('A')).

Another possible value of lifecycle is 'unique': B and C will always receive brand new D. And another one is 'singleton': D will be instantiated only once during the whole life of the app.

Additional parameters

If you change the constructor in the example above to this, you can pass additional parameters to your service.

    constructor(otherService, anotherService, value1, value2) {
        // ...
    }

Now you can run app.get('A', 'abc', 123) and value1 will be 'abc' and value2 will be 123.

Services instantiated as dependencies (via requires property) and not via app.get() cannot have additional parameters (they will be undefined).

Manual registration and instantiation

Usually you let Arpen find, load and register your services. But you can also do this by hand. Add a dependency on 'app' service which is instance of the application. Now your service can call app.get() to instantiate a known service or app.registerClass(classFunc) and app.registerInstance(obj, name) to register services.

.get() accepts a string or a regular expression of the service(s) to instantiate. In RegExp case a Map of services is returned.

.registerClass() is what is called on your class-exportig files. .registerInstance() will register any JavaScript variable as a service. For example:

// In one service
let map = new Map();
map.add('key', 'value');
app.registerInstance(map, 'myMapService');
 
// In another service
let map = app.get('myMapService');
console.log(map.get('key'));

Basically instance services behave just like singleton classes.

Class autoloading

At the top level of your application 'config' directory should exit. It must contain at least 'global.js' file and optionally 'local.js' file.

When application is started global and local files are merged to create configuration object of the application (both files should export plain JS object with the configuration parameters). Usually global file is submitted into the repository and the local one is excluded from the repo so passwords can be stored in it.

One possible configuration is to put 'autoload' parameter to global file. This is an array of paths relative to project root that will be searched for services. If path starts with '~' symbol then it is loaded from 'node_modules' directory and not from the project root. Paths starting with '!' symbol define what will be excluded when autoloading.

autoload: [
    '~arpen/src',               // load Arpen services
    'src',                      // app services are in 'src' subdir
    '!src/not-this-one',        // skip 'not-this-one' dir in 'src'
],

Another important configuration parameter is 'modules' (you can put it into local configuration file, for example). This is a list of modules of your application.

Modules defined in your configuration are searched for in 'modules' subdirectory relative to project root. Each module is a directory with the same 'config' subdirectory just like the main project. It should contain at least 'global.js' with 'autoload' parameter.

Usually you put project-wide files in 'src' directory of project root and module-specific code in 'src' relative to a module directory (don't forget to autoload it!)

Your module should define one service with service name like 'modules.someModule' - replace 'someModule' with a unique name (no dots).

During initialization of the app this service will be instantiated and its .bootstrap() method will be called (if it exists) which should return a Promise.

See it in action!

$ sudo npm install arpen -g --unsafe-perm

--unsafe-perm is needed for some C++ dependencies to compile.

$ arpen new my-project
$ cd my-project
$ npm install
$ ./bin/run udp

This is how to create and run a skeleton project. It includes one simple server Udp which listens for UDP commands. Test it:

$ nc -u localhost 3000
uppercase hello world
HELLO WORLD
^C

To keep it simple it understands just one command: uppercase.

This sample project has just one module 'udp' which defines one server (Udp) which listens for one event (Uppercase).

Have a look at modules/udp/src/servers/udp.js file - it is the server. Directory modules/udp/src/events contains the events of the server.

Servers

Server is a service which has these methods:

.init(name) — called when app is instantiated

.start(name) — called when the app is started

.stop(name) — called when the app is stopped

name is the name of the server in the configuration. If you look at the skeleton project local.js config you will find the following section:

    // Servers
    servers: {
        udp: {
            class: 'servers.udp',
            host: "0.0.0.0",
            port: 3000,
        },
    },

This is how you define your servers, each entry should have at least class key, which is the service name of the server. The rest of keys are all up to you: they depend on what your server expects.

You can retrieve this configuration by adding dependency on 'config' service:

let name = 'udp';
let port = config.get(`servers.${name}.port`);

Commands

Another feature of Arpen is console commands. The skeleton project includes a couple of them, you can find them in src/commands directory.

Try running:

$ ./bin/cmd help create-cert
$ ./bin/cmd create-cert 192.168.0.1

Bundled services

See jsDoc: https://basarevych.github.io/arpen

• filer
• runner
• logger
• mongo
• mysql
• postgres
• postgres-pubsub
• redis
• redis-pubsub
• cacher
• emailer
• session
• ini
• util