fix(websockets): add ping responses to avoid timeouts from tornado websockets

Author: Taran Rorem

packages/voila/src/plugins/outputs/plugins.ts

@@ -154,6 +154,10 @@ export const renderOutputsProgressivelyPlugin: JupyterFrontEndPlugin<void> = {
           console.error(`Execution error: ${payload.error}`);
           break;
         }
+        case 'ping': {
+          ws.send(JSON.stringify({ action: 'pong' }));
+          break;
+        }
         default:
           break;
       }

packages/voila/src/plugins/outputs/tools.ts

@@ -27,6 +27,14 @@ export interface IExecutionErrorMessage {
   };
 }
 
+/**
+ * Interface representing the structure of an execution's ping and pong message.
+ */
+export interface IExecutionResultPingMessage {
+  action: 'ping';
+  payload: any;
+}
+
 /**
  * Interface representing a received widget model
  * containing output and execution models.
@@ -39,7 +47,8 @@ export interface IReceivedWidgetModel {
 }
 export type IExecutionMessage =
   | IExecutionResultMessage
-  | IExecutionErrorMessage;
+  | IExecutionErrorMessage
+  | IExecutionResultPingMessage;
 
 export function getExecutionURL(kernelId?: string): string {
   const wsUrl = PageConfig.getWsUrl();