Fix 503 request flags in unservicable connections

cheroot/server.py

@@ -1893,7 +1893,12 @@ def _serve_unservicable(self):
             conn = self._unservicable_conns.get()
             if conn is _STOPPING_FOR_INTERRUPT:
                 return
-            request = HTTPRequest(self, conn)
+            request = HTTPRequest(
+                self,
+                conn,
+                proxy_mode=self.proxy_mode,
+                strict_mode=self.strict_mode,
+            )
             try:
                 request.simple_response('503 Service Unavailable')
             except (OSError, errors.FatalSSLAlert):

cheroot/test/test_server.py

@@ -127,6 +127,67 @@ def test_stop_interrupts_serve():
     assert not serve_thread.is_alive()
 
 
+def test_unservicable_conn_uses_server_proxy_and_strict_mode(monkeypatch):
+    """Check that 503 requests inherit proxy/strict mode from the server."""
+    httpserver = HTTPServer(
+        bind_addr=(ANY_INTERFACE_IPV4, EPHEMERAL_PORT),
+        gateway=Gateway,
+    )
+    close_calls = []
+    request_init_args = []
+
+    class CapturingHTTPRequest:
+        """Capture request constructor args used for 503 responses."""
+
+        def __init__(
+            self,
+            server,
+            conn,
+            proxy_mode=False,
+            strict_mode=True,
+        ):
+            request_init_args.append(
+                {
+                    'server': server,
+                    'conn': conn,
+                    'proxy_mode': proxy_mode,
+                    'strict_mode': strict_mode,
+                },
+            )
+
+        def simple_response(self, _status):
+            return None
+
+    def close_conn():
+        close_calls.append(None)
+
+    conn = types.SimpleNamespace(linger=False, close=close_conn)
+    stopping_sentinel = object()
+    httpserver.proxy_mode = True
+    httpserver.strict_mode = False
+    httpserver.ready = True
+    httpserver._unservicable_conns.put(conn)
+    httpserver._unservicable_conns.put(stopping_sentinel)
+    monkeypatch.setattr(
+        'cheroot.server._STOPPING_FOR_INTERRUPT',
+        stopping_sentinel,
+    )
+    monkeypatch.setattr('cheroot.server.HTTPRequest', CapturingHTTPRequest)
+
+    httpserver._serve_unservicable()
+
+    assert request_init_args == [
+        {
+            'server': httpserver,
+            'conn': conn,
+            'proxy_mode': True,
+            'strict_mode': False,
+        },
+    ]
+    assert conn.linger is True
+    assert close_calls == [None]
+
+
 @pytest.mark.parametrize(
     'exc_cls',
     (