Subscriptions

A client can subscribe to a resource and be told when it changes, so it reads the new version instead of polling.

Clients can subscribe to resources to receive notifications when they change. This enables real-time updates without polling.

Server Capabilities

NitroStack declares subscription support in server capabilities:

{
  capabilities: {
    resources: {
      subscribe: true,
      listChanged: true
    }
  }
}

Handling Subscriptions

When a client subscribes to a resource, your application can track subscriptions and notify clients of changes:

import { McpApplicationFactory } from '@nitrostack/core';

const app = await McpApplicationFactory.create(AppModule);
const server = app.getServer();

// When a resource changes, notify subscribers
function onResourceUpdated(uri: string) {
  server.notifyResourceUpdated(uri);
}

// Example: Update product and notify
async function updateProduct(productId: string, data: ProductData) {
  await this.productRepo.update(productId, data);
  onResourceUpdated(`product://${productId}`);
}

Subscription Flow

1. Client subscribes: resources/subscribe with resource URI
2. Server tracks: Maintains list of subscribed URIs
3. Resource changes: Your code detects the change
4. Server notifies: Sends notifications/resources/updated with URI
5. Client refreshes: Fetches updated resource content

List Changed Notifications

When resources are added or removed, notify clients:

// After adding a new resource
server.notifyResourcesListChanged();

// After removing a resource
server.notifyResourcesListChanged();

Next steps