From b730056dbc9f1555fabc30ade64ae19d7dddbb88 Mon Sep 17 00:00:00 2001
From: Yury Semikhatsky <yurys@chromium.org>
Date: Wed, 8 Apr 2026 18:17:42 -0700
Subject: [PATCH] fix(run-server): handle malformed JSON frames without
 crashing

A malformed WebSocket text frame caused JSON.parse to throw an
uncaught SyntaxError from the async message listener, terminating
the run-server process. Catch the parse error, close the offending
connection with code 1007, and keep the server running.
---
 .../src/remote/playwrightConnection.ts           |  9 ++++++++-
 tests/library/browsertype-connect.spec.ts        | 16 ++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/packages/playwright-core/src/remote/playwrightConnection.ts b/packages/playwright-core/src/remote/playwrightConnection.ts
index dbf41ceaa2551..cc1b1de751062 100644
--- a/packages/playwright-core/src/remote/playwrightConnection.ts
+++ b/packages/playwright-core/src/remote/playwrightConnection.ts
@@ -64,7 +64,14 @@ export class PlaywrightConnection {
     transport.on('message', async (message: string) => {
       await lock;
       const messageString = Buffer.from(message).toString();
-      const jsonMessage = JSON.parse(messageString);
+      let jsonMessage: any;
+      try {
+        jsonMessage = JSON.parse(messageString);
+      } catch (e) {
+        debugLogger.log('server', `[${this._id}] failed to parse message: ${e}`);
+        this.close({ code: 1007, reason: 'Malformed message' });
+        return;
+      }
       if (debugLogger.isEnabled('server:channel'))
         debugLogger.log('server:channel', `[${this._id}] ${monotonicTime() * 1000} ◀ RECV ${messageString}`);
       if (debugLogger.isEnabled('server:metadata'))
diff --git a/tests/library/browsertype-connect.spec.ts b/tests/library/browsertype-connect.spec.ts
index e3eb616dce533..d4d3c184b2762 100644
--- a/tests/library/browsertype-connect.spec.ts
+++ b/tests/library/browsertype-connect.spec.ts
@@ -158,6 +158,22 @@ for (const kind of ['launchServer', 'run-server'] as const) {
       }
     });
 
+    test('should not crash on malformed json frame', async ({ connect, startRemoteServer }) => {
+      const remoteServer = await startRemoteServer(kind);
+      const ws = new WebSocket(remoteServer.wsEndpoint());
+      await new Promise<void>((resolve, reject) => {
+        ws.once('open', resolve);
+        ws.once('error', reject);
+      });
+      ws.send(']');
+      await new Promise<void>(resolve => ws.once('close', () => resolve()));
+      // Server should still be alive and accept new connections.
+      const browser = await connect(remoteServer.wsEndpoint());
+      const page = await browser.newPage();
+      expect(await page.evaluate('1 + 2')).toBe(3);
+      await browser.close();
+    });
+
     test('should be able to visit ipv6', async ({ connect, startRemoteServer, ipV6ServerPort, channel }) => {
       test.fail(!!process.env.INSIDE_DOCKER, 'docker does not support IPv6 by default');
       test.fail(channel === 'webkit-wsl', 'WebKit on WSL does not support IPv6: https://github.com/microsoft/WSL/issues/10803');