feat: Cast client

[mbellehumeur]

Context

Cast package - @cornerstonejs/cast

Cast hub networking for browser-based viewers: OAuth client-credentials token, HTTP subscribe/unsubscribe, WebSocket receive, and publish. This package contains transport only; application-specific message handling stays in the host app to implement FHIRcast or other messaging. Handles token acquisition, subscribe/unsubscribe lifecycle, websocket message processing, publish, websocket heartbeats , message echo and optional auto-reconnect of the websocket.

Example

The Cast client example under examples/castClient mirrors the python Slicer Cast test-client.html flow (subscribe, log incoming events, publish) using CastClient for all network calls.

From the monorepo root:

yarn example castClient

Optional query parameter: ?topic=your-topic pre-fills the topic fields.

Example:

const client = new CastClient({
  hub: {
    name: 'demo',
    version: '1',
    hub_endpoint: 'https://host/api/hub',
    token_endpoint: 'https://host/oauth/token',
    client_id: 'client_id',
    client_secret: 'client_secret',
  },
  session: {
    events: ['*'],
    lease: 7200,
    subscriberName: 'CS3D-EXAMPLE',
    topic: 'my-topic',
  },
  autoReconnect: true,
});

client.onMessage((message) => {
  console.log(message);
});

 const tokenOk = await client.getToken();
 if (tokenOk) {
   await client.subscribe();
   await client.publish({
     event: {
       'hub.event': 'custom',
       'hub.topic': 'my-topic',
       context: [],
     },
   });
 }

Changes & Results

Testing

yarn run example castClient

online test:

https://cs3d-castclientexample-anczasf2c7fghhgp.westeurope-01.azurewebsites.net/castClient

Screen.Recording.2026-04-05.175423.mp4

• Click Authenticate to obtain a user id and access token (use ?topic= to choose a mock user id).
• Click Subscribe to open a WebSocket connection and start receiving events from the hub.
• Click Open viewer with this topic button to open an image display in the workflow.
• Click Publish to send an ImagingStudy-open event to the hub -> the study opens in the image display.
• Change the event to dicom-send and click Publish to send an AI result SEG object to the hub -> the result is displayed in the image display.
• Use Get to fetch context from a FHIRCast hub or other data from cast compliant IHE actors (in this case the worklist-client).
• Change the event to ImagingStudy-close and click Publish to send an ImagingStudy-close event to the hub -> the image display goes back to home screen.
• Use Collaborate to open a conference client to create a multi-topic session.

Checklist

PR

• My Pull Request title is descriptive, accurate and follows the
  semantic-release format and guidelines.

Code

• My code has been well-documented (function documentation, inline comments,
  etc.)

Public Documentation Updates

• The documentation page has been updated as necessary for any public API
  additions or removals.

Tested Environment

• "OS: Windows/Chrome

[sedghi]

I'm not sure why this is in cornerstone. Cornerstone scope is limited and described here https://www.cornerstonejs.org/docs/getting-started/scope