Solid Notification Client

This library implements the disovery and subscription to a Notication Channel following the Solid Notifications Protocol.

Discovery

A first step for having Solid Notifications is having a resource of interest to which you want to subscribe, we will call this resource the topic. To discover whether the topic supports a certain channel type, you can use the DiscoveryClient. (A list of channel types can be found here)

Following piece of code shows how to use this class.

import { DiscoveryClient } from '@solid-notifications/discovery';

const topic = "http://localhost:3000/topic.ttl";
const channelType = "http://www.w3.org/ns/solid/notifications#WebSocketChannel2023";

const client = new DiscoveryClient(fetch);
const subscriptionService = await client.findService(topic, channelType);

console.log(subscriptionService);

If the subscriptionService is not null, then subscriptionService.id contains the URL to which a Solid Notification Subscription can be made for the given channel type.

Subscription

When you know that a given topic resource has support for your chosen channel type, you follow the Subscription flow from the Solid Notification Protocol, which is implemented in the SubscriptionClient class.

Following piece of (ESM) code shows how to use this class.

import { SubscriptionClient } from '@solid-notifications/subscription';

const topic = "http://localhost:3000/topic.ttl";
const channelType = "http://www.w3.org/ns/solid/notifications#WebSocketChannel2023";

const client = new SubscriptionClient(fetch);
const notificationChannel = await client.subscribe(topic, channelType);

console.log(notificationChannel);

In this example, a subscription to a WebSocketChannel2023 has been made. So this variable can now be used to set up a WebSocket connection to listen to updates of the topic resource in the Solid Server. For this, the receiveFrom property is used from the notificationChannel from the above sample code.

import { WebSocket } from 'ws';

// set up a WebSocket using the notificationChannel
const socket = new WebSocket(notificationChannel.receiveFrom)
// print all notifications, which in this case will be notifications from the topic resource
socket.onmessage = (message) => console.log(message.data.toString());

Development Setup

This repository is managed as a monorepo using Lerna.

It can be set up and installed by cloning this repository and installing:

git clone https://github.com/o-development/solid-notification-client.git
cd solid-notification-client
npm i 

Building the project can be achieved through the following command:

npm run build

Additional information

Authenticated fetch

The classes DiscoveryClient and SubscriptionClient require a fetch function to be passed as constructor argument. The default fetch function results into sending unauthenticated requests to a Solid Server.

However, when the topic is a resource which has authorization requirements, you need to pass an authenticated fetch function. Inrupt provides libraries to which you can log in with your WebID following the Solid-OIDC Protocol:

• @inrupt/solid-client-authn-node can be used in NodeJs
• @inrupt/solid-client-authn-browser can be used in the browser

After logging in, you can use the Session object to get an authenticated fetch function: session.fetch.

Notification Sender

For channel types where the Notification Sender opens the connection e.g., WebhookChannel2023), an extra argument (an URL) must be provided to announce to the Subscription Server the sendTo property.

Setting up a solid server which supports WebSocketChannel2023 and WebhookChannel2023

This can be done with the Community Solid Server (CSS).

Install the Solid Server:

npm i @solid/community-server

Start a server without setup, with memory storage and with both WebSocketChannel2023 and WebHookSubscription2021 channel types for solid notifications:

wget https://raw.githubusercontent.com/woutslabbinck/Solid-Notification/main/config/memory-config.json
npx @solid/community-server -c memory-config.json 

Feedback and questions

Do not hesitate to report a bug