@backstage/plugin-signals-node

Welcome to the Node.js library package for the signals plugin!

Signals plugin allows backend plugins to publish messages to frontend plugins.

Getting started

New backend system

In packages/backend/index.ts, add the signals backend:

backend.add(import('@backstage/plugin-signals-backend'));
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To use signals in your plugin, add it as a dependency to my-plugin/plugin.ts:

import {
  coreServices,
  createBackendPlugin,
} from '@backstage/backend-plugin-api';
import { signalsServiceRef } from '@backstage/plugin-signals-node';

export const myPlugin = createBackendPlugin({
  pluginId: 'my-plugin',
  register(env) {
    env.registerInit({
      deps: {
        httpRouter: coreServices.httpRouter,
        signals: signalsServiceRef,
      },
      async init({ httpRouter, signals }) {
        httpRouter.use(
          await createRouter({
            signals,
          }),
        );
      },
    });
  },
});
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Old backend system

Add SignalService to your plugin environment in packages/backend/src/types.ts:

import { SignalsService } from '@backstage/plugin-signals-node';

export type PluginEnvironment = {
  // ...
  signals: SignalsService;
};
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Add it also to your makeCreateEnv to allow access from the other plugins:

import {
  SignalsService,
  DefaultSignalsService,
} from '@backstage/plugin-signals-node';
import { DefaultEventBroker } from '@backstage/plugin-events-backend';

function makeCreateEnv(config: Config) {
  // ...

  const eventBroker = new DefaultEventBroker(root.child({ type: 'plugin' }));
  const signalsService = DefaultSignalsService.create({
    eventBroker,
  });

  return (plugin: string): PluginEnvironment => {
    const logger = root.child({ type: 'plugin', plugin });
    return {
      logger,
      eventBroker,
      signals: signalsService,
      // ...
    };
  };
}
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To allow connections from the frontend, you should also install the @backstage/plugin-signals-backend.

Using the service

Once you have both of the backend plugins installed, you can utilize the signal service by calling the publish method. This will publish the message to all subscribers in the frontend. To send message to all subscribers, you can use broadcast type:

// Periodic sending example
setInterval(async () => {
  await signals.publish({
    recipients: { type: 'broadcast' },
    channel: 'my_plugin',
    message: {
      message: 'hello world',
    },
  });
}, 5000);
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To receive this message in the frontend, check the documentation of @backstage/plugin-signals and @backstage/plugin-signals-react.

Using event broker directly

Other way to send signals is to utilize the EventBroker directly. This requires that the payload is correct for it to work:

eventBroker.publish({
  topic: 'signals',
  eventPayload: {
    recipients: { type: 'user', entityRef: 'user:default/user1' },
    message: {
      message: 'hello world',
    },
    channel: 'my_plugin',
  },
});
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