Recover from args argument being uniterable

Summary:
Another kind of error that can easily be triggered during testing that will kill the server otherwise.

Changelog: Make it possible to recover from malformed JSON in server requests

Reviewed By: timur-valiev

Differential Revision: D34932896

fbshipit-source-id: 7c6acfd53ffbd85a54a786d74c99bcccb64d85cb

desktop/flipper-server/src/startSocketServer.tsx

@@ -65,6 +65,21 @@ export function startSocketServer(
         case 'exec': {
           const {id, command, args} = payload;
 
+          if (typeof args[Symbol.iterator] !== 'function') {
+            console.warn(
+              'flipperServer -> exec: args argument in payload is not iterable',
+            );
+            const responseError: ExecResponseErrorWebSocketMessage = {
+              event: 'exec-response-error',
+              payload: {
+                id,
+                data: 'Payload args argument is not an iterable.',
+              },
+            };
+            client.send(JSON.stringify(responseError));
+            return;
+          }
+
           flipperServer
             .exec(command, ...args)
             .then((result: any) => {