From e842971da67b224a794ce7800e5bb656000c3cdd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Joan=20Fabr=C3=A9gat?= <joan@fabreg.at>
Date: Thu, 4 Jun 2026 16:55:29 -0700
Subject: [PATCH] Handle plain OSError when waiting for the writer to close

A peer that becomes unreachable mid-connection (e.g. EHOSTUNREACH when
the client host vanishes) raises a plain OSError from wait_closed(),
which the except tuple in TCPServer._close() missed - only
ConnectionError subclasses were caught. The exception then escaped the
client_connected_cb task via run()'s finally block, or propagated into
the ASGI application's send path via protocol_send(Closed).

Catch OSError instead: BrokenPipeError, ConnectionAbortedError and
ConnectionResetError are all OSError subclasses, so the tuple collapses
to (OSError, RuntimeError, asyncio.CancelledError) - consistent with
run()'s existing `except OSError`.

Fixes #361

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 src/hypercorn/asyncio/tcp_server.py |  4 +---
 tests/asyncio/test_tcp_server.py    | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/src/hypercorn/asyncio/tcp_server.py b/src/hypercorn/asyncio/tcp_server.py
index 5612214c..55d744d6 100644
--- a/src/hypercorn/asyncio/tcp_server.py
+++ b/src/hypercorn/asyncio/tcp_server.py
@@ -119,9 +119,7 @@ async def _close(self) -> None:
             self.writer.close()
             await self.writer.wait_closed()
         except (
-            BrokenPipeError,
-            ConnectionAbortedError,
-            ConnectionResetError,
+            OSError,  # Includes Connection*Errors and e.g. EHOSTUNREACH for a vanished peer
             RuntimeError,
             asyncio.CancelledError,
         ):
diff --git a/tests/asyncio/test_tcp_server.py b/tests/asyncio/test_tcp_server.py
index 1aa2898b..cb361f8b 100644
--- a/tests/asyncio/test_tcp_server.py
+++ b/tests/asyncio/test_tcp_server.py
@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import asyncio
+import errno
 
 import pytest
 
@@ -12,6 +13,11 @@
 from ..helpers import echo_framework
 
 
+class UnreachableHostWriter(MemoryWriter):
+    async def wait_closed(self) -> None:
+        raise OSError(errno.EHOSTUNREACH, "No route to host")
+
+
 @pytest.mark.asyncio
 async def test_completes_on_closed() -> None:
     event_loop: asyncio.AbstractEventLoop = asyncio.get_running_loop()
@@ -31,6 +37,25 @@ async def test_completes_on_closed() -> None:
     # hanging.
 
 
+@pytest.mark.asyncio
+async def test_completes_on_unreachable_host_close() -> None:
+    event_loop: asyncio.AbstractEventLoop = asyncio.get_running_loop()
+
+    server = TCPServer(
+        ASGIWrapper(echo_framework),
+        event_loop,
+        Config(),
+        WorkerContext(None),
+        {},
+        MemoryReader(),  # type: ignore
+        UnreachableHostWriter(),  # type: ignore
+    )
+    server.reader.close()  # type: ignore
+    await server.run()
+    # Key is that this line is reached, rather than the above line
+    # raising the OSError from the writer close.
+
+
 @pytest.mark.asyncio
 async def test_complets_on_half_close() -> None:
     event_loop: asyncio.AbstractEventLoop = asyncio.get_running_loop()