python - 使用 django channel 从 python 3.6 升级到 python 3.7 时出现 SynchronousOnlyOperation 错误

Question

我一直在尝试将我们的 Django 和 Django channel 应用程序的 python 从 3.6 升级到 3.7。有了这个更改，Django 会在任何 HTTP 请求发出时抛出一个 SynchronousOnlyOperation(即使它与 WebSockets 无关)。我的猜测是 python 升级以某种方式使 Django 检查更加严格。

我相信 Django channel 同时服务于 HTTP 请求和 WebSocket 请求，因此它希望所有代码都异步兼容。

如何让 Django channel runserver 同步运行 wsgi 应用程序，同时异步使用 channel ？

# project/asgi.py
application = ProtocolTypeRouter({"http": get_asgi_application(), "websocket": routing})

# project/wsgi.py
application = get_wsgi_application()

堆栈跟踪: 我很清楚，为普通 wsgi View 运行的 auth 中间件不兼容异步，我怎样才能让它在同步环境中运行？

ERROR    Internal Server Error: /a/api
Traceback (most recent call last):
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/contrib/sessions/backends/base.py", line 233, in _get_session
    return self._session_cache
AttributeError: 'SessionStore' object has no attribute '_session_cache'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "/___/___/___/___/apps/core/middleware.py", line 60, in __call__
    request.is_user_verified = request.user.is_verified()
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/utils/functional.py", line 240, in inner
    self._setup()
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/utils/functional.py", line 376, in _setup
    self._wrapped = self._setupfunc()
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django_otp/middleware.py", line 38, in _verify_user
    user.otp_device = None
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/utils/functional.py", line 270, in __setattr__
    self._setup()
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/utils/functional.py", line 376, in _setup
    self._wrapped = self._setupfunc()
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/contrib/auth/middleware.py", line 24, in <lambda>
    request.user = SimpleLazyObject(lambda: get_user(request))
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/contrib/auth/middleware.py", line 12, in get_user
    request._cached_user = auth.get_user(request)
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/contrib/auth/__init__.py", line 174, in get_user
    user_id = _get_user_session_key(request)
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/contrib/auth/__init__.py", line 58, in _get_user_session_key
    return get_user_model()._meta.pk.to_python(request.session[SESSION_KEY])
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/contrib/sessions/backends/base.py", line 65, in __getitem__
    return self._session[key]
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/contrib/sessions/backends/base.py", line 238, in _get_session
    self._session_cache = self.load()
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/contrib/sessions/backends/db.py", line 43, in load
    s = self._get_session_from_db()
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/contrib/sessions/backends/db.py", line 34, in _get_session_from_db
    expire_date__gt=timezone.now()
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/db/models/manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/db/models/query.py", line 425, in get
    num = len(clone)
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/db/models/query.py", line 269, in __len__
    self._fetch_all()
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/db/models/query.py", line 1303, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/db/models/query.py", line 53, in __iter__
    results = compiler.execute_sql(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size)
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/db/models/sql/compiler.py", line 1154, in execute_sql
    cursor = self.connection.cursor()
  File "/___/___/.pyenv/versions/pd37/lib/python3.7/site-packages/django/utils/asyncio.py", line 24, in inner
    raise SynchronousOnlyOperation(message)
django.core.exceptions.SynchronousOnlyOperation: You cannot call this from an async context - use a thread or sync_to_async.

版本

Django==3.1.1
channels==3.0.2
channels-redis==3.2.0

Answer 1

总结一下我的尝试:

• 首先，我有一个 channel 应用程序，它根本没有数据库，除了静态文件之外没有贡献应用程序。
• 我添加了数据库、DRF 和一个具有单一模型和列表/详细 View 的应用
• 启用同步 http 消费者:

# dwtools.routing
from channels.routing import ProtocolTypeRouter, URLRouter
from django.core.asgi import get_asgi_application

import romanize.routing

application = ProtocolTypeRouter(
    {
        "websocket": URLRouter(romanize.routing.websocket_urlpatterns),
        "http": get_asgi_application(),
    },
)

• 设置:

INSTALLED_APPS = [
    "channels",
    "romanize.apps.RomanizeConfig",
    "django.contrib.staticfiles",
    "rest_framework",
    "agencies.apps.AgenciesConfig",
]
WSGI_APPLICATION = "dwtools.wsgi.application"
ASGI_APPLICATION = "dwtools.routing.application"

我可以调出 DRF 的标准 View 、创建条目等。

然后添加一个访问数据库的简单中间件(获取代理数量并将其放入请求中)。甚至不使用 MiddlewareMixin，只需要简单的 init 就可以调用协议(protocol)。

System check identified no issues (0 silenced).
December 07, 2020 - 14:38:56
Django version 3.1.4, using settings 'dwtools.settings'
Starting ASGI/Channels version 3.0.2 development server at http://127.0.0.1:3401/
#             ^^^^^^^^               ^^^^^^^^^^^ ( Channels runserver)
Quit the server with CONTROL-C.
HTTP GET /agencies/ 200 [0.05, 127.0.0.1:60460]

堆栈使用本地 nginx 为 /ws (websocket) 和 /agencies (http) 路由到端口 3401。也许你发现了什么......