Add support for Django 3.0; drop support for Django < 2.2 (django#1389)

* Add support for Django 3.0; drop support for Django < 2.2
* Do not call database operations from async code directly

This prevents `SynchronousOnlyOperation` exceptions that were
introduced in Django 3.0.  See
https://docs.djangoproject.com/en/3.0/releases/3.0/#asgi-support
for further details.

.travis.yml

@@ -3,13 +3,13 @@ dist: xenial
 language: python
 
 python:
+  - "3.8"
+  - "3.7"
   - "3.6"
-  - "3.5"
 
 env:
-  - DJANGO="Django==1.11.*"
-  - DJANGO="Django==2.1.*"
-  - DJANGO="Django==2.2.*"
+  - DJANGO="Django~=2.2.8"
+  - DJANGO="Django==3.0.*"
 
 install:
   - pip install -U pip wheel setuptools
@@ -27,11 +27,7 @@ stages:
 
 jobs:
   include:
-    - python: "3.7"
-      env: DJANGO="Django==2.1.*"
-    - python: "3.7"
-      env: DJANGO="Django==2.2.*"
-    - python: "3.8"
+    - python: "3.5"
       env: DJANGO="Django==2.2.*"
 
     - stage: lint

README.rst

@@ -36,7 +36,7 @@ Dependencies
 ------------
 
 All Channels projects currently support Python 3.5 and up. ``channels`` is
-compatible with Django 1.11, 2.1, and 2.2.
+compatible with Django 2.2 and 3.0.
 
 
 Contributing

channels/http.py

@@ -284,11 +284,6 @@ def load_middleware(self):
             )
             self._exception_middleware = self.__class__._exception_middleware
 
-            # Support additional arguments for Django 1.11 and 2.0.
-            if hasattr(self.__class__, "_request_middleware"):
-                self._request_middleware = self.__class__._request_middleware
-                self._response_middleware = self.__class__._response_middleware
-
         else:
             super(AsgiHandler, self).load_middleware()
             self.__class__._middleware_chain = self._middleware_chain
@@ -298,11 +293,6 @@ def load_middleware(self):
             )
             self.__class__._exception_middleware = self._exception_middleware
 
-            # Support additional arguments for Django 1.11 and 2.0.
-            if hasattr(self, "_request_middleware"):
-                self.__class__._request_middleware = self._request_middleware
-                self.__class__._response_middleware = self._response_middleware
-
     @classmethod
     def encode_response(cls, response):
         """

channels/routing.py

@@ -5,14 +5,10 @@
 from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 from django.urls.exceptions import Resolver404
+from django.urls.resolvers import URLResolver
 
 from channels.http import AsgiHandler
 
-try:
-    from django.urls.resolvers import URLResolver
-except ImportError:  # Django 1.11
-    from django.urls import RegexURLResolver as URLResolver
-
 
 """
 All Routing instances inside this file are also valid ASGI applications - with

channels/sessions.py

@@ -198,7 +198,7 @@ async def send(self, message):
                 and message.get("status", 200) != 500
                 and (modified or settings.SESSION_SAVE_EVERY_REQUEST)
             ):
-                self.save_session()
+                await database_sync_to_async(self.save_session)()
                 # If this is a message type that can transport cookies back to the
                 # client, then do so.
                 if message["type"] in self.middleware.cookie_response_message_types:

setup.py

@@ -7,13 +7,13 @@
     url='http://github.com/django/channels',
     author='Django Software Foundation',
     author_email='[email protected]',
-    description="Brings async, event-driven capabilities to Django. Django 1.11 and up only.",
+    description="Brings async, event-driven capabilities to Django. Django 2.2 and up only.",
     license='BSD',
     packages=find_packages(exclude=['tests']),
     include_package_data=True,
     python_requires='>=3.5',
     install_requires=[
-        'Django>=1.11',
+        'Django>=2.2',
         'asgiref~=3.2',
         'daphne~=2.3',
     ],

tests/test_http.py

@@ -10,6 +10,7 @@
 
 from asgiref.testing import ApplicationCommunicator
 from channels.consumer import AsyncConsumer
+from channels.db import database_sync_to_async
 from channels.http import AsgiHandler, AsgiRequest
 from channels.sessions import SessionMiddlewareStack
 from channels.testing import HttpCommunicator
@@ -335,7 +336,7 @@ class SimpleHttpApp(AsyncConsumer):
         """
 
         async def http_request(self, event):
-            self.scope["session"].save()
+            await database_sync_to_async(self.scope["session"].save)()
             assert self.scope["path"] == "/test/"
             assert self.scope["method"] == "GET"
             await self.send(

tests/test_routing.py

@@ -232,10 +232,7 @@ def test_invalid_routes():
     """
     Test URLRouter route validation
     """
-    try:
-        from django.urls import include
-    except ImportError:  # Django 1.11
-        from django.conf.urls import include
+    from django.urls import include
 
     with pytest.raises(ImproperlyConfigured) as exc:
         URLRouter([url(r"^$", include([]))])

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py{36,37,38}-dj{11,21,22,master}
+envlist = py{36,37,38}-dj{22,30,master}
 
 [testenv]
 usedevelop = true
@@ -10,9 +10,8 @@ commands =
     py.test -v {posargs}
 
 deps =
-    dj11: Django==1.11.*
-    dj21: Django==2.1.*
-    dj22: Django==2.2.*
+    dj22: Django~=2.2.8
+    dj30: Django==3.0.*
     djmaster: https://github.com/django/django/archive/master.tar.gz
 
 [testenv:qa]