expose if there are any connected devices to dev middleware and adding event on if this changes (facebook#54447)

Summary:

Changelog: [Internal]

Expose `unstable_hasConnectedDevices` and `unstable_addHasConnectedDevicesListener` from both `InspectorProxy` and `DevMiddleware` that tells the user if any devices are connected to `devMiddleware` and allows to listen to whenever this state changes.

Reviewed By: motiz88

Differential Revision: D86319965

Author: vzaidman

packages/dev-middleware/src/createDevMiddleware.js

@@ -9,6 +9,7 @@
  */
 
 import type {CreateCustomMessageHandlerFn} from './inspector-proxy/CustomMessageHandler';
+import type {HasConnectedDevicesListener} from './inspector-proxy/InspectorProxy';
 import type {BrowserLauncher} from './types/BrowserLauncher';
 import type {EventReporter, ReportableEvent} from './types/EventReporter';
 import type {Experiments, ExperimentsConfig} from './types/Experiments';
@@ -73,6 +74,8 @@ type Options = $ReadOnly<{
 type DevMiddlewareAPI = $ReadOnly<{
   middleware: NextHandleFunction,
   websocketEndpoints: {[path: string]: ws$WebSocketServer},
+  unstable_hasConnectedDevices(): boolean,
+  unstable_addHasConnectedDevicesListener: HasConnectedDevicesListener,
 }>;
 
 export default function createDevMiddleware({
@@ -131,6 +134,10 @@ export default function createDevMiddleware({
   return {
     middleware,
     websocketEndpoints: inspectorProxy.createWebSocketListeners(),
+    unstable_hasConnectedDevices: () =>
+      inspectorProxy.unstable_hasConnectedDevices(),
+    unstable_addHasConnectedDevicesListener: cb =>
+      inspectorProxy.unstable_addHasConnectedDevicesListener(cb),
   };
 }
 

packages/dev-middleware/src/inspector-proxy/InspectorProxy.js

@@ -71,6 +71,12 @@ export interface InspectorProxyQueries {
   ): Array<PageDescription>;
 }
 
+export type RemoveHasConnectedDevicesListener = () => void;
+
+export type HasConnectedDevicesListener = (
+  callback: (hasConnectedDevices: boolean) => void,
+) => RemoveHasConnectedDevicesListener;
+
 /**
  * Main Inspector Proxy class that connects JavaScript VM inside Android/iOS apps and JS debugger.
  */
@@ -97,6 +103,8 @@ export default class InspectorProxy implements InspectorProxyQueries {
 
   #eventLoopPerfTracker: EventLoopPerfTracker;
 
+  #onHasConnectedDevicesChangedFns: Set<(boolean) => void>;
+
   constructor(
     serverBaseUrl: string,
     eventReporter: ?EventReporter,
@@ -111,6 +119,7 @@ export default class InspectorProxy implements InspectorProxyQueries {
     this.#experiments = experiments;
     this.#logger = logger;
     this.#customMessageHandler = customMessageHandler;
+    this.#onHasConnectedDevicesChangedFns = new Set();
     if (trackEventLoopPerf) {
       this.#eventLoopPerfTracker = new EventLoopPerfTracker({
         perfMeasurementDuration: EVENT_LOOP_PERF_MEASUREMENT_MS,
@@ -142,6 +151,18 @@ export default class InspectorProxy implements InspectorProxyQueries {
     }
   }
 
+  unstable_hasConnectedDevices(): boolean {
+    return this.#devices.size > 0;
+  }
+
+  unstable_addHasConnectedDevicesListener: HasConnectedDevicesListener =
+    onDevicesChanged => {
+      this.#onHasConnectedDevicesChangedFns.add(onDevicesChanged);
+      return () => {
+        this.#onHasConnectedDevicesChangedFns.delete(onDevicesChanged);
+      };
+    };
+
   getPageDescriptions({
     requestorRelativeBaseUrl,
     logNoPagesForConnectedDevice = false,
@@ -365,6 +386,9 @@ export default class InspectorProxy implements InspectorProxyQueries {
         }
 
         this.#devices.set(deviceId, newDevice);
+        if (this.#devices.size === 1) {
+          this.#onHasConnectedDevicesChangedFns.forEach(cb => cb(true));
+        }
 
         debug(
           "Got new device connection: name='%s', app=%s, device=%s, via=%s",
@@ -457,6 +481,9 @@ export default class InspectorProxy implements InspectorProxyQueries {
 
           if (this.#devices.get(deviceId)?.dangerouslyGetSocket() === socket) {
             this.#devices.delete(deviceId);
+            if (this.#devices.size === 0) {
+              this.#onHasConnectedDevicesChangedFns.forEach(cb => cb(false));
+            }
           }
         });
       } catch (error) {