Handle case when websocket client disconnects before websocket connection is accepted

pyproject.toml

@@ -9,9 +9,7 @@ description = "The lightning-fast ASGI server."
 readme = "README.md"
 license = "BSD-3-Clause"
 requires-python = ">=3.8"
-authors = [
-    { name = "Tom Christie", email = "[email protected]" },
-]
+authors = [{ name = "Tom Christie", email = "[email protected]" }]
 classifiers = [
     "Development Status :: 4 - Beta",
     "Environment :: Web Environment",
@@ -90,16 +88,14 @@ filterwarnings = [
     "error",
     'ignore: \"watchgod\" is deprecated\, you should switch to watchfiles \(`pip install watchfiles`\)\.:DeprecationWarning',
     "ignore:Uvicorn's native WSGI implementation is deprecated.*:DeprecationWarning",
-    "ignore: 'cgi' is deprecated and slated for removal in Python 3.13:DeprecationWarning"
+    "ignore: 'cgi' is deprecated and slated for removal in Python 3.13:DeprecationWarning",
 ]
 
 [tool.coverage.run]
+branch = true
 source_pkgs = ["uvicorn", "tests"]
 plugins = ["coverage_conditional_plugin"]
-omit = [
-    "uvicorn/workers.py",
-    "uvicorn/__main__.py",
-]
+omit = ["uvicorn/workers.py", "uvicorn/__main__.py"]
 
 [tool.coverage.report]
 precision = 2
@@ -124,7 +120,7 @@ py-not-win32 = "sys_platform != 'win32'"
 py-linux = "sys_platform == 'linux'"
 py-darwin = "sys_platform == 'darwin'"
 py-gte-38 = "sys_version_info >= (3, 8)"
-py-lt-38 =  "sys_version_info < (3, 8)"
+py-lt-38 = "sys_version_info < (3, 8)"
 py-gte-39 = "sys_version_info >= (3, 9)"
 py-lt-39 = "sys_version_info < (3, 9)"
 py-gte-310 = "sys_version_info >= (3, 10)"

tests/protocols/test_websocket.py

@@ -69,7 +69,7 @@ async def asgi(self):
                 break
 
 
-async def wsresponse(url):
+async def wsresponse(url: str):
     """
     A simple websocket connection request and response helper
     """
@@ -507,6 +507,34 @@ async def connect(url: str):
         assert exc_info.value.status_code == 500
 
 
+@pytest.mark.anyio
+async def test_do_not_send_500_on_closed_transport(
+    ws_protocol_cls: WSProtocol, http_protocol_cls: HTTPProtocol, unused_tcp_port: int
+):
+    is_disconnected = asyncio.Event()
+    is_inside_app = asyncio.Event()
+
+    async def app(scope: Scope, receive: ASGIReceiveCallable, send: ASGISendCallable):
+        # The client can only disconnect after we've reached the application.
+        is_inside_app.set()
+        await asyncio.sleep(0.1)
+        # Wait for client to disconnect.
+        await is_disconnected.wait()
+
+    async def connect(url: str):
+        await websockets.client.connect(url)
+
+    config = Config(app=app, ws=ws_protocol_cls, http=http_protocol_cls, lifespan="off", port=unused_tcp_port)
+    async with run_server(config):
+        task = asyncio.create_task(connect(f"ws://127.0.0.1:{unused_tcp_port}"))
+        await is_inside_app.wait()
+        task.cancel()
+        is_disconnected.set()
+        # Sleep here so the server has a chance to react before shutting down.
+        await asyncio.sleep(0.1)
+        assert task.cancelled()
+
+
 @pytest.mark.anyio
 async def test_send_before_handshake(
     ws_protocol_cls: WSProtocol, http_protocol_cls: HTTPProtocol, unused_tcp_port: int
@@ -1069,11 +1097,6 @@ async def app(scope, receive, send):
         }
         await send(message)
 
-    async def websocket_session(url):
-        response = await wsresponse(url)
-        assert response.status_code == 500
-        assert response.content == b"Internal Server Error"
-
     config = Config(
         app=app,
         ws=ws_protocol_cls,
@@ -1082,7 +1105,9 @@ async def websocket_session(url):
         port=unused_tcp_port,
     )
     async with run_server(config):
-        await websocket_session(f"ws://127.0.0.1:{unused_tcp_port}")
+        response = await wsresponse(f"ws://127.0.0.1:{unused_tcp_port}")
+        assert response.status_code == 500
+        assert response.content == b"Internal Server Error"
 
 
 @pytest.mark.anyio

uvicorn/protocols/websockets/websockets_impl.py

@@ -215,7 +215,8 @@ def send_500_response(self) -> None:
             b"\r\n",
             msg,
         ]
-        self.transport.write(b"".join(content))
+        if not self.transport.is_closing():
+            self.transport.write(b"".join(content))
         # Allow handler task to terminate cleanly, as websockets doesn't cancel it by
         # itself (see https://github.com/encode/uvicorn/issues/920)
         self.handshake_started_event.set()

uvicorn/protocols/websockets/wsproto_impl.py

@@ -226,6 +226,7 @@ def send_500_response(self) -> None:
         ]
         output = self.conn.send(wsproto.events.RejectConnection(status_code=500, headers=headers, has_body=True))
         output += self.conn.send(wsproto.events.RejectData(data=b"Internal Server Error"))
+        print('is here')
         self.transport.write(output)
 
     async def run_asgi(self) -> None: