序言

三天前，Django 3.0 正式发布了。
发布节点链接
在众多改动中，我对增加 ASGI 的支持非常感兴趣，
我真的想亲自试用一下。

補充一下：ASGI是什麼？

ASGI（非同期サーバーゲートウェイインターフェイス）は、WSGIの精神的な後継者であり、非同期対応のPython Webサーバー、フレームワーク、およびアプリケーション間の標準インターフェイスを提供することを目的としています。

WSGIが同期Pythonアプリの標準を提供したのに対し、ASGIは、WSGIの下位互換性の実装と複数のサーバーとアプリケーションフレームワークを備えた非同期アプリと同期アプリの両方を提供します。

文档链接

全新的项目

我将创建一个用于测试的虚拟环境。

 mkvirtualenv django3.0

安装Django

 pip3 install django

安装完成后，确认Django3.0已经安装好。

(django3.0) ~ $ pip3 list
Package    Version
---------- -------
asgiref    3.2.3  
Django     3.0    
pip        19.3.1 
pytz       2019.3 
setuptools 42.0.2 
sqlparse   0.3.0  
wheel      0.33.6

我们随意创建一个新项目，然后启动服务器看看。

mkdir django-test
&&
django-admin startproject newtest
&&
cd newtest/
&&
python3 manage.py runserver

我們試著將訪存取8000番，您將能夠看到熟悉的火箭。

我们来看一下公式文档。

How to deploy with ASGI¶
As well as WSGI, Django also supports deploying on ASGI, the emerging Python standard for asynchronous web servers and applications.

Django’s startproject management command sets up a default ASGI configuration for you, which you can tweak as needed for your project, and direct any ASGI-compliant application server to use.

Django includes getting-started documentation for the following ASGI servers:

How to use Django with Daphne
How to use Django with Uvicorn
The application object¶
Like WSGI, ASGI has you supply an application callable which the application server uses to communicate with your code. It’s commonly provided as an object named application in a Python module accessible to the server.

The startproject command creates a file <project_name>/asgi.py that contains such an application callable.

It’s not used by the development server (runserver), but can be used by any ASGI server either in development or in production.

ASGI servers usually take the path to the application callable as a string; for most Django projects, this will look like myproject.asgi:application.

Warning

While Django’s default ASGI handler will run all your code in a synchronous thread, if you choose to run your own async handler you must be aware of async-safety.

Do not call blocking synchronous functions or libraries in any async code. Django prevents you from doing this with the parts of Django that are not async-safe, but the same may not be true of third-party apps or Python libraries.

Configuring the settings module¶
When the ASGI server loads your application, Django needs to import the settings module — that’s where your entire application is defined.

Django uses the DJANGO_SETTINGS_MODULE environment variable to locate the appropriate settings module. It must contain the dotted path to the settings module. You can use a different value for development and production; it all depends on how you organize your settings.

If this variable isn’t set, the default asgi.py sets it to mysite.settings, where mysite is the name of your project.

Applying ASGI middleware¶
To apply ASGI middleware, or to embed Django in another ASGI application, you can wrap Django’s application object in the asgi.py file. For example:

from some_asgi_library import AmazingMiddleware
application = AmazingMiddleware(application)

Link
链接

总之可以概括为

python manage.py runserverでサーバー起動してはいけない、いつものwsgiのサーバー起動することになります。
サーバー起動時にDaphneかUvicorn使用することお勧めします。

让我们打开官方链接来看看Daphne是什么。

How to use Django with Daphne¶
Daphne is a pure-Python ASGI server for UNIX, maintained by members of the Django project. It acts as the reference server for ASGI.

Installing Daphne¶
You can install Daphne with pip:

python -m pip install daphne
Running Django in Daphne¶
When Daphne is installed, a daphne command is available which starts the Daphne server process. At its simplest, Daphne needs to be called with the location of a module containing an ASGI application object, followed by what the application is called (separated by a colon).

For a typical Django project, invoking Daphne would look like:

daphne myproject.asgi:application
This will start one process listening on 127.0.0.1:8000. It requires that your project be on the Python path; to ensure that run this command from the same directory as your manage.py file.

以下是将其翻译成中文的版本：
– 使用pip安装daphne
– 运行daphne myproject.asgi:application启动ASGI服务器
– 访问127.0.0.1:8000

让我们试试看

启动ASGI服务器

安装Daphne

 pip3 install daphne

启动服务器

daphne [プロジェクト名].asgi:application

当我访问了8000次后，又看到了火箭，尽管文字略有不同。

WebSocket测试

收到了错误代码500，错误信息如下。

2019-12-05 11:02:09,533 ERROR    Exception inside application: Django can only handle ASGI/HTTP connections, not websocket.
  File "/Envs/django3.0/lib/python3.7/site-packages/daphne/cli.py", line 30, in asgi
    await self.app(scope, receive, send)
  File "/Envs/django3.0/lib/python3.7/site-packages/django/core/handlers/asgi.py", line 146, in __call__
    % scope['type']
  Django can only handle ASGI/HTTP connections, not websocket.

让我们看看 asgi.py 的第 146 行，似乎有些内容。

 async def __call__(self, scope, receive, send):
        """
        Async entrypoint - parses the request and hands off to get_response.
        """
        # Serve only HTTP connections.
        # FIXME: Allow to override this.
        if scope['type'] != 'http':
            raise ValueError(
                'Django can only handle ASGI/HTTP connections, not %s.'
                % scope['type']
            )
        # Receive the HTTP request body as a stream object.
        try:
            body_file = await self.read_body(receive)
        except RequestAborted:
            return
        # Request is complete and can be served.
        set_script_prefix(self.get_script_prefix(scope))

请注意以下两行的评论。

 # Serve only HTTP connections.
 # FIXME: Allow to override this.

目前只允许HTTP通信。请根据需要自行修正！

最终

以下是可能的原因的推测。

• 多分私はDjangoのことまたわかっていない

• Websocketではなくて、他の手段でASGI通信を実現している

ASGIの完全サポートはこれから

如果想要在当前的Django 3.0版本中使用WebSocket，建议使用django-channels包。