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Live update

Live update is a way to be notified of changes to a Pod in real time. For now, the main mechanism for live update are Solid Notifications.

Solid Notifications

Added in: activitypods@2.0

Thanks to the Solid Notifications Protocol, you can listen to LDP resources, LDP containers or ActivityStreams collections.

We support discovering the notification subscription services through the storage description resource. This can be found by doing a HEAD request on any resource in your pod and looking for the Link header with the http://www.w3.org/ns/solid/terms#storageDescription relationship.

This leads to the /.well-known/solid endpoint which includes links to available subscription services.

{
  "@context": { "notify": "http://www.w3.org/ns/solid/notifications#" },
  "@id": "http://localhost:3000/.well-known/solid",
  "@type": "http://www.w3.org/ns/pim/space#Storage",
  "notify:subscription": [
    "http://localhost:3000/.notifications/WebSocketChannel2023",
    "http://localhost:3000/.notifications/WebhookChannel2023"
  ]
}

Webhooks subscription

To subscribe to the http://localhost:3000/foo resource using webhooks, you use an authenticated POST request to send the following JSON-LD document to the server, at http://localhost:3000/.notifications/WebhookChannel2023/:

{
  "@context": ["https://www.w3.org/ns/solid/notifications-context/v1"],
  "type": "WebhookChannel2023",
  "topic": "http://localhost:3000/foo",
  "sendTo": "https://example.com/webhook"
}

The sendTo predicate is the Webhook URL of your server, the URL to which you want the notifications to be sent.

WebSockets subscription

To subscribe to the http://localhost:3000/foo resource using WebSockets, you use an authenticated POST request to send the following JSON-LD document to the server, at http://localhost:3000/.notifications/WebSocketChannel2023/:

{
  "@context": ["https://www.w3.org/ns/solid/notifications-context/v1"],
  "type": "WebhookChannel2023",
  "topic": "http://localhost:3000/foo"
}

The server will send back a subscription resource, in which the notify:receiveFrom predicate indicates the WebSocket channel.

Notification types

Just like the Community Solid Server, we support five different notification types that the client can receive. The format of the notification can slightly change depending on the type.

  • Create: When the resource is created.
  • Update: When the existing resource is changed.
  • Delete: When the resource is deleted. Does not have a state field.

Additionally, when listening to a LDP container or an ActivityStreams collection, there are two extra notifications that are sent out when the contents of the container or collection change. For these notifications, the object field references the resource that was added or removed, while the new target field references the container or collection itself.

  • Add: When a new resource is added to the container or collection.
  • Remove: When a resource is removed from the container or collection.