Reintroduce timeout and is production check

Summary:
For dev, let's not kill the server.
Also, reintroduce a timeout of 60 seconds before disconnecting.

Reviewed By: antonk52

Differential Revision: D48432317

fbshipit-source-id: bac6f67101e5be481af06a5ea6ccb3b3134c4075

desktop/flipper-server-core/src/server/attachSocketServer.tsx

@@ -17,6 +17,7 @@ import {
   SystemError,
   getLogger,
   CompanionEventWebSocketMessage,
+  isProduction,
 } from 'flipper-common';
 import {FlipperServerImpl} from '../FlipperServerImpl';
 import {RawData, WebSocketServer} from 'ws';
@@ -38,6 +39,7 @@ const safe = (f: () => void) => {
 };
 
 let numberOfConnectedClients = 0;
+let disconnectTimeout: NodeJS.Timeout | undefined;
 
 /**
  * Attach and handle incoming messages from clients.
@@ -239,10 +241,19 @@ export function attachSocketServer(
       flipperServerCompanion?.destroyAll();
 
       if (getFlipperServerConfig().environmentInfo.isHeadlessBuild) {
-        if (numberOfConnectedClients === 0) {
-          console.info('Shutdown as no clients are currently connected');
-          process.exit(0);
+        if (disconnectTimeout) {
+          clearTimeout(disconnectTimeout);
         }
+
+        /**
+         * If, after 60 seconds, there are no more connected clients, we exit the process.
+         */
+        disconnectTimeout = setTimeout(() => {
+          if (numberOfConnectedClients === 0 && isProduction()) {
+            console.info('Shutdown as no clients are currently connected');
+            process.exit(0);
+          }
+        }, 60 * 1000);
       }
     }