@fanoutio/pubcontrol

PubControl for JavaScript

Authors: Katsuyuki Ohmuro [e-mail], Konstantin Bokarius [e-mail]

Description

An EPCP library for NodeJS

HTTP Extensible Pubsub Control Protocol (EPCP) defines a generalized and extensible data publishing protocol using HTTP. Data is published by way of HTTP POST, whose content is the JSON string representation of an object that follows certain structural guidelines.

Each message consists of one or more data items, and is always sent to a specified channel. The messages are associated with that channel and will only be delivered to those listeners subscribed to the channel.

This library contains a Format base class and a PubControl class that is used to send messages. This library also supports the case when the EPCP endpoint requires certain types of authentication.

Sample Usage

This example illustrates the process of instantiating the PubControl publisher class, defining a data format, and then publishing some data.

import PubControl, { Format, Item } from '@fanoutio/pubcontrol';

// Instantiate PubControl publisher.
const pub = new PubControl({
    'uri': 'http://www.example.com/path/to/endpoint'
});

// Define a data format.
class HttpResponseFormat extends Format {
    body;
    constructor(body) {
        super();
        this.body = body;
    }
    name() {
        return 'http-response';
    }
    export() {
        return { body: this.body, };
    }
}

// Publish across all configured endpoints.
const item = new Item(new HttpResponseFormat('Test Publish!'));
pub.publish('my-channel', item)
    .then(() => {
        console.log('Publish successful!');
    })
    .catch(({message, context}) => {
        console.log('Publish failed!');
        console.log('Message: ' + message);
        console.log('Context: ');
        console.dir(context); 
    });

Configuration

PubControl offers several ways of configuring endpoints. The simplest way is by specifying an object with a uri and optional iss and key fields.

const pub = new PubControl({
    'uri': 'https://api.fanout.io/realm/<myrealm>',
    'iss': '<myrealm>',
    'key': Buffer.from('<myrealmkey>', 'base64'),
});

// In a browser setting, use the following, as Buffer is not available to
// browser scripts.
// 'key': PubControl.base64ToBuffer('<myrealmkey>'),

An advanced usage is to create an instance of a PubControlClient and add it to the PubControl instance yourself. This allows for finer tuning of authentication used by the client.

import PubControl, { PubControlClient } from '@fanoutio/pubcontrol';

const pub = new PubControl();

// Define the endpoint:
const pubclient = new PubControlClient('<myendpoint_uri>');
// Optionally set JWT auth: pubclient.setAuthJwt(<claim>, '<key>');
// Optionally set basic auth: pubclient.setAuthBasic('<user>', '<password>');
pub.addClient(pubclient);

Additionally, multiple endpoints can be included in a single configuration.

// Initialize PubControl with a single endpoint:
const pub = new PubControl();

// Add new endpoints by applying an endpoint configuration:
pub.applyConfig([
    {'uri': '<myendpoint_uri_1>'},
    {'uri': '<myendpoint_uri_2>'},
]);

If you ever need to clear all configured endpoints, call the removeAllClients function.

// Remove all configured endpoints:
pub.removeAllClients();

Authentication

In some cases, the EPCP endpoint requires authentication before allowing its use. This library can provide Basic and JWT authentication for these cases.

To use Basic authentication, create an instance of the PubControlClient class, use setBasicAuth() to set the username and password, and add the instance to the PubControl instance via addClient() as shown in the example above.

To use JWT authentication, pass a configuration to PubControl when instantiating it or via applyConfig() and provide the claim as shown in the example above.

If the claim does not contain an exp value, then this library will create an appropriate value for that field on each use. Since the header is generated from the authorization object each time it needs to be used, the library is able to generate a new authorization header, even from the same auth object.

It is also possible to use a literal JWT string for JWT authentication. This may be useful in certain cases, such as when you are performing a push request on behalf of another service. That service can pre-encode the JWT token and hand it to you in its string representation. This way, that service does not need to hand the JWT signing key to you.

pubClient.setAuthJwt('######.######.######'); // Literal JWT string

Tests

The tests in this package require Node.js 12 or newer to run. This is because the tests run against the source JavaScript modules directly, which is a feature that was supported starting with Node.js 12.

(The runtime will work with lower versions of node and with browsers since they go through a transpile step.)

Running pubcontrol in web browsers

A build for browsers is available by running npm run build-browser to build the /browser/pubcontrol.js artifact. This may be included as a normal <script> tag on your web page.

In this usage, PubControl is introduced to the global namespace.

const pub = new PubControl({uri: "<endpoint_uri>"});
const { Format, Item } = PubControl;

An example for this is included at ./demo/index.html. Open this page in your browser after you have built the /browser/pubcontrol.js file.

For another example, js-pubcontrol-demo-webworkers contains a demo of this library for the web browser, running it in a separate service worker. The same service worker can be used with Cloudflare Workers as a way of building real-time serverless apps with fanout.io and Cloudflare Workers.

CommonJS

Although this package is distributed as an ESM module, this package is a hybrid package, and a CommonJS version of the library is available by specifying a deep path.

const PubControl = require('@fanoutio/pubcontrol/commonjs');
const { Format, Item } = PubControl;

License

(C) 2015, 2019 Fanout, Inc.
Licensed under the MIT License, see file COPYING for details.