From 4dbe60a9f71791b17e7af851de50ad6fa71f2e84 Mon Sep 17 00:00:00 2001
From: puddly <32534428+puddly@users.noreply.github.com>
Date: Tue, 10 Sep 2024 16:23:59 -0400
Subject: [PATCH] Guard to make sure we can't send data while the transport is
 closing

---
 bellows/ash.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/bellows/ash.py b/bellows/ash.py
index 06156eb0..2f9c8212 100644
--- a/bellows/ash.py
+++ b/bellows/ash.py
@@ -579,6 +579,9 @@ def _write_frame(
         prefix: tuple[Reserved] = (),
         suffix: tuple[Reserved] = (Reserved.FLAG,),
     ) -> None:
+        if self._transport is None or self._transport.is_closing():
+            raise NcpFailure("Transport is closed, cannot send frame")
+
         if _LOGGER.isEnabledFor(logging.DEBUG):
             prefix_str = "".join([f"{r.name} + " for r in prefix])
             suffix_str = "".join([f" + {r.name}" for r in suffix])