Make DaphneProcess pickleable (#440)

CHANGELOG.txt

@@ -41,6 +41,9 @@ This is a beta release to allow testing compatibility with the upcoming Channels
 
 * Removed deprecated ``--ws_protocols`` CLI option.
 
+* Made the ``DaphneProcess`` tests helper class compatible with the ``spawn``
+  process start method, which is used on macOS and Windows.
+
 3.0.2 (2021-04-07)
 ------------------
 

daphne/testing.py

@@ -26,6 +26,9 @@ class BaseDaphneTestingInstance:
         self.request_buffer_size = request_buffer_size
         self.application = application
 
+    def get_application(self):
+        return self.application
+
     def __enter__(self):
         # Option Daphne features
         kwargs = {}
@@ -41,7 +44,7 @@ class BaseDaphneTestingInstance:
         # Start up process
         self.process = DaphneProcess(
             host=self.host,
-            application=self.application,
+            get_application=self.get_application,
             kwargs=kwargs,
             setup=self.process_setup,
             teardown=self.process_teardown,
@@ -123,13 +126,13 @@ class DaphneProcess(multiprocessing.Process):
     port it ends up listening on back to the parent process.
     """
 
-    def __init__(self, host, application, kwargs=None, setup=None, teardown=None):
+    def __init__(self, host, get_application, kwargs=None, setup=None, teardown=None):
         super().__init__()
         self.host = host
-        self.application = application
+        self.get_application = get_application
         self.kwargs = kwargs or {}
-        self.setup = setup or (lambda: None)
-        self.teardown = teardown or (lambda: None)
+        self.setup = setup
+        self.teardown = teardown
         self.port = multiprocessing.Value("i")
         self.ready = multiprocessing.Event()
         self.errors = multiprocessing.Queue()
@@ -146,11 +149,13 @@ class DaphneProcess(multiprocessing.Process):
         from .endpoints import build_endpoint_description_strings
         from .server import Server
 
+        application = self.get_application()
+
         try:
             # Create the server class
             endpoints = build_endpoint_description_strings(host=self.host, port=0)
             self.server = Server(
-                application=self.application,
+                application=application,
                 endpoints=endpoints,
                 signal_handlers=False,
                 **self.kwargs
@@ -158,10 +163,12 @@ class DaphneProcess(multiprocessing.Process):
             # Set up a poller to look for the port
             reactor.callLater(0.1, self.resolve_port)
             # Run with setup/teardown
+            if self.setup is not None:
                 self.setup()
             try:
                 self.server.run()
             finally:
+                if self.teardown is not None:
                     self.teardown()
         except BaseException as e:
             # Put the error on our queue so the parent gets it

tests/test_websocket.py

@@ -288,7 +288,7 @@ async def cancelling_application(scope, receive, send):
     from twisted.internet import reactor
 
     # Stop the server after a short delay so that the teardown is run.
-    reactor.callLater(2, lambda: reactor.stop())
+    reactor.callLater(2, reactor.stop)
     await send({"type": "websocket.accept"})
     raise asyncio.CancelledError()