From 43d2c920e0e3f3586aae47026fde7dc04e4f479f Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Tue, 12 Mar 2024 10:53:21 +0100
Subject: [PATCH] LibWeb: Ignore MessagePort.start() on already-closed port

This matches other browsers, and fixes an assertion found by Domato.
---
 .../Messaging/MessagePort-start-after-close.txt        |  1 +
 .../input/Messaging/MessagePort-start-after-close.html | 10 ++++++++++
 Userland/Libraries/LibWeb/HTML/MessagePort.cpp         |  3 +++
 3 files changed, 14 insertions(+)
 create mode 100644 Tests/LibWeb/Text/expected/Messaging/MessagePort-start-after-close.txt
 create mode 100644 Tests/LibWeb/Text/input/Messaging/MessagePort-start-after-close.html

diff --git a/Tests/LibWeb/Text/expected/Messaging/MessagePort-start-after-close.txt b/Tests/LibWeb/Text/expected/Messaging/MessagePort-start-after-close.txt
new file mode 100644
index 0000000000..aaecaf93c4
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/Messaging/MessagePort-start-after-close.txt
@@ -0,0 +1 @@
+PASS (didn't crash)
diff --git a/Tests/LibWeb/Text/input/Messaging/MessagePort-start-after-close.html b/Tests/LibWeb/Text/input/Messaging/MessagePort-start-after-close.html
new file mode 100644
index 0000000000..4c36d3af5e
--- /dev/null
+++ b/Tests/LibWeb/Text/input/Messaging/MessagePort-start-after-close.html
@@ -0,0 +1,10 @@
+<script src="../include.js"></script>
+<script>
+    test(() => {
+        let channel = new MessageChannel();
+        let port = channel.port2;
+        port.close();
+        port.start();
+        println("PASS (didn't crash)");
+    });
+</script>
diff --git a/Userland/Libraries/LibWeb/HTML/MessagePort.cpp b/Userland/Libraries/LibWeb/HTML/MessagePort.cpp
index a66850f95b..defc64969b 100644
--- a/Userland/Libraries/LibWeb/HTML/MessagePort.cpp
+++ b/Userland/Libraries/LibWeb/HTML/MessagePort.cpp
@@ -364,6 +364,9 @@ void MessagePort::post_message_task_steps(SerializedTransferRecord& serialize_wi
 // https://html.spec.whatwg.org/multipage/web-messaging.html#dom-messageport-start
 void MessagePort::start()
 {
+    if (!is_entangled())
+        return;
+
     VERIFY(m_socket);
     VERIFY(m_fd_passing_socket);