Fix websocket error when closing the server

Fix #634

gns3server/controller/compute.py

@@ -299,6 +299,7 @@ class Compute:
         # https://www.python.org/dev/peps/pep-0492/
         # that why we wrap the answer
         class StreamResponse:
+
             def __init__(self, response):
                 self._response = response
 
@@ -350,7 +351,11 @@ class Compute:
         """
         self._ws = yield from self._session().ws_connect(self._getUrl("/notifications/ws"))
         while True:
-            response = yield from self._ws.receive()
+            try:
+                response = yield from self._ws.receive()
+            except aiohttp.errors.WSServerHandshakeError:
+                self._ws = None
+                return
             if response.tp == aiohttp.MsgType.closed or response.tp == aiohttp.MsgType.error:
                 self._connected = False
                 break

gns3server/controller/link.py

@@ -165,7 +165,7 @@ class Link:
 
     @property
     def nodes(self):
-        return [ node['node'] for node in self._nodes ]
+        return [node['node'] for node in self._nodes]
 
     @property
     def capturing(self):

gns3server/utils/asyncio/__init__.py

@@ -127,4 +127,3 @@ def wait_for_named_pipe_creation(pipe_path, timeout=60):
         else:
             return
     raise asyncio.TimeoutError()
-

tests/utils/test_asyncio.py

@@ -67,5 +67,3 @@ def test_wait_for_process_termination(loop):
     exec = wait_for_process_termination(process, timeout=0.5)
     with pytest.raises(asyncio.TimeoutError):
         loop.run_until_complete(asyncio.async(exec))
-
-