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Solid WebSockets API Spec

Note: This spec is a component of the parent Solid specification; the parent spec and all its components are versioned as a whole.

Subscribing

Live updates are currently only supported through WebSockets. This describes a subscription mechanism through which clients can be notified in real time of changes affecting a give resource.

The PubSub system is very basic. Clients only need to open a WebSocket connection and sub(scribe) to a given resource URI. If any change occurs in that resource, a pub(lish) event will be sent to all the subscribed clients.

The WebSocket server URI is the same for any resource located on a given data space (same hostname). To discover the URI of the WebSocket server, clients can send an HTTP OPTIONS. The server will then include an Updates-Via header in the response:

REQUEST:

OPTIONS /data/test HTTP/1.1
Host: example.org

RESPONSE:

HTTP/1.1 200 OK
...
Updates-Via: wss://example.org/

To subscribe to a resource, clients will need to send the keyword sub followed by an empty space and then the URI of the resource:

sub https://example.org/data/test

If a change occurs and the client is subscribed to that resource, it will receive a WebSocket message composed of the keyword pub, followed by an empty space and the URI of the resource that has changed:

pub https://example.org/data/test

Subscribing to a container can also be really useful, since all CRUD operations (POST, PUT, PATCH, DELETE) performed on resources of that container will trigger a notification for the container URI. This makes synchronization between multiple apps really easy.

For example, a client subscribes to the data/ container:

sub https://example.org/data/

If another client deletes the resource foo inside data/:

REQUEST:

DELETE /data/foo HTTP/1.1
Host: example.org

Then the following notification message will be sent:

pub https://example.org/data/

Here is a Javascript example on how to subscribe to live updates for a test resource at https://example.org/data/test:

var socket = new WebSocket('wss://example.org/');
socket.onopen = function() {
	this.send('sub https://example.org/data/test');
};
socket.onmessage = function(msg) {
	if (msg.data && msg.data.slice(0, 3) === 'pub') {
        // resource updated, refetch resource
	}
};