Merge pull request #22529 from drodil/signals_improvements

fix: signal disconnect loop on server start

plugins/signals-react/api-report.md

@@ -7,21 +7,27 @@ import { ApiRef } from '@backstage/core-plugin-api';
 import { JsonObject } from '@backstage/types';
 
 // @public (undocumented)
-export type SignalApi = {
+export interface SignalApi {
+  // (undocumented)
   subscribe(
     channel: string,
     onMessage: (message: JsonObject) => void,
-  ): {
-    unsubscribe: () => void;
-  };
-};
+  ): SignalSubscriber;
+}
 
 // @public (undocumented)
 export const signalApiRef: ApiRef<SignalApi>;
 
+// @public (undocumented)
+export interface SignalSubscriber {
+  // (undocumented)
+  unsubscribe(): void;
+}
+
 // @public (undocumented)
 export const useSignal: (channel: string) => {
   lastSignal: JsonObject | null;
+  isSignalsAvailable: boolean;
 };
 
 // (No @packageDocumentation comment for this package)

plugins/signals-react/src/api/SignalApi.ts

@@ -22,9 +22,14 @@ export const signalApiRef = createApiRef<SignalApi>({
 });
 
 /** @public */
-export type SignalApi = {
+export interface SignalSubscriber {
+  unsubscribe(): void;
+}
+
+/** @public */
+export interface SignalApi {
   subscribe(
     channel: string,
     onMessage: (message: JsonObject) => void,
-  ): { unsubscribe: () => void };
-};
+  ): SignalSubscriber;
+}

plugins/signals-react/src/hooks/useSignal.ts

@@ -16,7 +16,7 @@
 import { signalApiRef } from '../api';
 import { useApiHolder } from '@backstage/core-plugin-api';
 import { JsonObject } from '@backstage/types';
-import { useEffect, useState } from 'react';
+import { useEffect, useMemo, useState } from 'react';
 
 /** @public */
 export const useSignal = (channel: string) => {
@@ -40,5 +40,8 @@ export const useSignal = (channel: string) => {
     };
   }, [signals, channel]);
 
-  return { lastSignal };
+  // Can be used to fallback (for example to long polling) if signals are not available in the system
+  const isSignalsAvailable = useMemo(() => !signals, [signals]);
+
+  return { lastSignal, isSignalsAvailable };
 };