asrpc

AS-RPC

A tool to make your class as an RPC service.

Idea

AS first means English word as, that this package will make your class as an RPC service, And secondly, it also means as-is, that no matter how you use the instance of the class, the usage (syntax) is the same on the server and the client. You don't have to change any API of the class, this package is meant to wrap your ordinary classes RPC-like.

Example

// SimpleCalculator.js
// for convenience, all remote methods should be async
class SimpleCalculator {
    async sum(...args) {
        console.log(args.join(" + "));
        return args.reduce((a, b) => a + b);
    }

    async sub(...args) {
        console.log(args.join(" - "));
        return args.reduce((a, b) => a - b);
    }

    async multiply(...args) {
        console.log(args.join(" * "));
        return args.reduce((a, b) => a * b);
    }

    async div(...args) {
        console.log(args.join(" / "));
        return args.reduce((a, b) => a / b);
    }
}

exports.SimpleCalculator = SimpleCalculator;

// server.js
const { createInstance } = require("asrpc");
const { SimpleCalculator } = require("./SimpleCalculator");

var ins = createInstance(2018); // bind port 2018

ins.register(SimpleCalculator); // register service

(async () => {
    await ins.start(); // start service instance
});

// client.js
const { createInstance } = require("asrpc");
const { SimpleCalculator } = require("./SimpleCalculator");

var ins = createInstance(2018); // also bind port 2018

(async () => {
    var calc = await ins.connect(SimpleCalculator); // connect service
    console.log(await calc.sum(1, 2, 3, 4, 5)); // => 15
    console.log(await calc.sub(15, 5, 4, 3, 2)); // => 1
    console.log(await calc.multiply(1, 2, 3, 4, 5)); // => 120
    console.log(await calc.div(120, 5, 4, 3, 2)); // => 1
});

First run server.js then run client.js.

server.js will output:

1 + 2 + 3 + 4 + 5
15 - 5 - 4 - 3 - 2
1 * 2 * 3 * 4 * 5
120 / 5 / 4 / 3 / 2

and client.js will output:

15
1
120
1

API

createInstance

This is the only useful function in JavaScript that exposed from this package, other objects and interfaces are for TypeScript programming.

signatures:

• createInstance(path: string): ServiceInstance
• createInstance(port: number, host?: string): ServiceInstance
• createInstance(options: ServiceOptions): ServiceInstance

Creates a ServiceInstance according to the given arguments.

If path is provided, the instance binds to a UNIX domain socket or named pipe on Windows, and communicate via IPC channels. This is very useful and efficient when the client and server are both run in the same machine. BUT must be aware that Windows named pipe has no support in cluster mode.

If port is provided, the instance binds to an network port, and communicate through network card. This is mainly used when the server and client are run in different machines, or in cluster on Windows. If the server and client are in different machines (even under different domain), the host option must be provided (on the client side, optional on the server side).

If options is provided, it is an object that contains path, port, host and timeout (all optional), the first three are corresponding to the individual options talked above, while timeout is a number in milliseconds and the default value is 5000.

ServiceInstance

A type that represents a service instance shipped on the server. This is a class exposed in JavaScript as well, but not recommended in use, it should only for typing usage, since function createInstance() provides a more suitable interface.

ServiceInstance.prototype.register<T>(target: ServiceClass<T>): void

Registers an ordinary JavaScript class (either in ES6 and ES5) as an RPC service. This method doesn't do any other job, just make a reference in the internal map with a unique-supposed string id generated according to the class definition itself.

This method should only be called on the server side.

ServiceInstance.prototype.deregister<T>(target: ServiceClass<T>): void

De-registers the target class bound by register(). Once a class is de-registered, it can no longer be connected on the client.

This method should only be called on the server side.

ServiceInstance.prototype.start(): Promise<void>

Starts the service server, listening for connections and requests from a client.

This method can only be called on the server side.

ServiceInstance.prototype.close(): Promise<void>

Closes the service server shipped by the current instance. Once the server is closed, no more connections and requests should be delivered.

This method can only be called on the server side.

ServiceInstance.prototype.connect<T>(target: ServiceClass<T>, ...args: any[]): Promise<T>

Connects to the service server and returns a new instance of target. If args is provided, it is any number of arguments passed to the class constructor. When the service is connected, they will be assigned to the instance on the server as well.

This method can only be called on the client side.

ServiceInstance.prototype.disconnect(service: any): Promise<void>

Disconnects the given service returned by connect(). Once a service is disconnected, no more operations should be called on it.

This method can only be called on the client side.

ServiceInstance.prototype.onError(handler: (err: Error) => void): void

Binds an error handler to be invoked whenever an error occurred in asynchronous operations which can't be caught during run-time.

Efficiency

Once the start() method is called, a Domain/TCP socket will be created, and the first time connect() is called, a socket client will be created, and ONLY one client will be created in one ServiceInstance, every connected service shares this client. There is no need and no reason to separate client for each service. The requests and responses are distinguished by the service itself, you don't have to worry connecting to much services might causing multiple connections, it will not.

Supported Data Types

Since the operation will be delivered to the server rather than calling locally, so not all JavaScript types are supported through socket communication, but this package uses encoded-buffer to transfer data in socket, it supports many common types (more than JSON, BSON), currently, these types are supported:

• string
• number
• boolean
• symbol not the same symbol as original, just a new symbol with the same description.
• undefined
• null
• object
• Array only the enumerable elements will be transferred.
• Buffer
• Date
• Error
• RegExp

Any other types, will be transferred as an standard object or not transferred at all. Any method called remotely should only accept these types of arguments, and the returning value should match one of these types as well.

Error Handle

If any error occurred on the server side in a service, the error will be send back to the client, and it will be just like the error the occurred on the client side, you will not see any difference between them, so just focus on your design as usual.

But not all errors can't be caught, like an error occurred inside the socket itself, these errors can be handled via onError() method.

Warning

Although this package will try to bring the most familiar experience for your code to use as RPC service as used ordinarily. BUT, due to the program runs in different processes, so are instances. The reason why you can access methods on the client but fetch results from the server is that this package wrapped your client service in a Proxy constructor, and when you call a method, the operation will be delivered to the server and call the version on the server instead. But only the methods can do this, that means if you try to access other properties, you will get the value in the local service, instead of the one on the server.

So it's recommended the properties, except constants or readonly properties, should be set private or protected, since they should only be accessed inside the class itself. There is not point you will access those properties on the server side, since the instance is handled by ServiceInstance, not by human. And on the client side, you will never get the real property value outside the class, also no point to set them public. If you really need to get the properties, define a method to do so.

class TestService {
    constructor() {
        this.name = "TestService"; // this is a readonly property
        this.text = "Hello, World!";
    }

    async set(prop, value) {
        this[prop] = value;
    }

    async get(prop) {
        return this[prop];
    }
}

// on the client side
(async () => {
    var ins = createInstance(2018);
    var srv = await ins.connect(TestService);

    console.log(srv.name); // TestService
    console.log(await srv.get("text")); // Hello, World!
    await srv.set("text", "Hi, there!");
    console.log(srv.text); // still: Hello, World!
    console.log(await srv.get("text")); // Hi, there!
})();