Server shutdown only if no errors

Summary:
The socket will close as the endpoint is terminating the connection.

Status code 1000 and 1001 are used for normal closures. Either the connection is no longer needed or the endpoint is going away i.e. browser navigating away from the current page.

WS RFC: https://www.rfc-editor.org/rfc/rfc6455

Reviewed By: LukeDefeo

Differential Revision: D48896696

fbshipit-source-id: 22070ae34b7f35d35589db06108feb718e73e866

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

@@ -227,11 +227,8 @@ export function attachSocketServer(
       safe(() => onClientMessage(data));
     });
 
-    async function onClientClose(error: Error | undefined = undefined) {
+    async function onClientClose(closeOnIdle: boolean) {
       console.log(`Client disconnected ${clientAddress}`);
-      if (error) {
-        console.error('Client disconnected with error', error);
-      }
 
       numberOfConnectedClients--;
 
@@ -244,24 +241,43 @@ export function attachSocketServer(
           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);
+        if (closeOnIdle) {
+          /**
+           * 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);
+        }
       }
     }
 
-    client.on('close', () => {
-      safe(() => onClientClose());
+    client.on('close', (code, _reason) => {
+      /**
+       * The socket will close as the endpoint is terminating
+       * the connection. Status code 1000 and 1001 are used for normal
+       * closures. Either the connection is no longer needed or the
+       * endpoint is going away i.e. browser navigating away from the
+       * current page.
+       * WS RFC: https://www.rfc-editor.org/rfc/rfc6455
+       */
+      const closeOnIdle = code === 1000 || code === 1001;
+      safe(() => onClientClose(closeOnIdle));
     });
 
     client.on('error', (error) => {
-      safe(() => onClientClose(error));
+      safe(() => {
+        /**
+         * The socket will close due to an error. In this case,
+         * do not close on idle as there's a high probability the
+         * client will attempt to connect again.
+         */
+        onClientClose(false);
+        console.error('Client disconnected with error', error);
+      });
     });
   });
 }