UI: Add error message for widget

ui-ngx/src/app/core/api/widget-subscription.ts

@@ -787,7 +787,38 @@ export class WidgetSubscription implements IWidgetSubscription {
     } else if (!this.targetDeviceId) {
       return throwError(new Error('Target device is not set!'));
     }
-    return this.ctx.deviceService.getPersistedRpcRequests(this.targetDeviceId, pageLink, keyFilter);
+    const rpcSubject: Subject<any> = new Subject<any>();
+
+    this.ctx.deviceService.getPersistedRpcRequests(this.targetDeviceId, pageLink, keyFilter).subscribe(
+      (responseBody) => {
+        rpcSubject.next(responseBody);
+        rpcSubject.complete();
+      },
+      (rejection: HttpErrorResponse) => {
+        const index = this.executingSubjects.indexOf(rpcSubject);
+        if (index >= 0) {
+          this.executingSubjects.splice( index, 1 );
+        }
+        this.executingRpcRequest = this.executingSubjects.length > 0;
+        this.callbacks.rpcStateChanged(this);
+        if (!this.executingRpcRequest || rejection.status === 504) {
+          this.rpcRejection = rejection;
+          if (rejection.status === 504) {
+            this.rpcErrorText = 'Request Timeout.';
+          } else {
+            this.rpcErrorText =  'Error : ' + rejection.status + ' - ' + rejection.statusText;
+            const error = this.extractRejectionErrorText(rejection);
+            if (error) {
+              this.rpcErrorText += '</br>';
+              this.rpcErrorText += error;
+            }
+          }
+          this.callbacks.onRpcFailed(this);
+        }
+        rpcSubject.error(rejection);
+      }
+    );
+    return rpcSubject.asObservable();
   }
 
   private extractRejectionErrorText(rejection: HttpErrorResponse) {