【翻译】Django Channels 官方文档 -- Tutorial

Django Channels 官方文档

https://channels.readthedocs.io/en/latest/index.html

前言：

最近课程设计需要用到 WebSocket，而原生的 Django 又不支持 WebSocket，仅有 Django Channels 库支持 WebSocket，但是  Django Channels 的资料，特别是中文资料异常稀缺，因此我在自己理解的基础上，整理翻译了这一篇 官方入门教程，仅作参考，如有疑问可以在下方留言。感谢大家的查看！

Tutorial
教程

Channels allows you to use WebSockets and other non-HTTP protocols in your Django site. For example you might want to use WebSockets to allow a page on your site to immediately receive updates from your Django server without using HTTP long-polling or other expensive techniques.
Channels 允许您在 Django 站点中使用 Websockets 和其他非 HTTP 协议。例如, 您可能希望 Websockets 允许网站上的页面立即从 Django 服务器接收更新, 而无需使用 HTTP 长轮询或其他昂贵的技术。

In this tutorial we will build a simple chat server, where you can join an online room, post messages to the room, and have others in the same room see those messages immediately.
在本教程中, 我们将建立一个简单的聊天服务器, 在那里你可以加入一个在线房间, 张贴消息到房间, 并让其他人在同一房间看到这些消息立即。

• Tutorial Part 1: Basic Setup
• 教程1部分: 基本设置
• Tutorial Part 2: Implement a Chat Server
• 教程2部分: 实现聊天服务器
• Tutorial Part 3: Rewrite Chat Server as Asynchronous
• 教程3部分: 将聊天服务器重写为异步
• Tutorial Part 4: Automated Testing
• 教程4部分: 自动化测试

Tutorial Part 1: Basic Setup

教程1部分: 基本设置

In this tutorial we will build a simple chat server. It will have two pages:
在本教程中, 我们将构建一个简单的聊天服务器。它将有两个页面:

• An index view that lets you type the name of a chat room to join.
• 一个 index 视图, 用于输入要加入的聊天室的名称。
• A room view that lets you see messages posted in a particular chat room.
• 一个可以查看在特定聊天室中发送的消息的房间视图。

The room view will use a WebSocket to communicate with the Django server and listen for any messages that are posted.
房间视图将使用 WebSocket 与 Django 服务器进行通信, 并监听任何发送出来的消息。

We assume that you are familar with basic concepts for building a Django site. If not we recommend you complete the Django tutorial first and then come back to this tutorial.
我们假设您熟悉构建 Django 站点的基本概念。如果不是, 我们建议您先完成 Django 教程, 然后再回到本教程。

We assume that you have Django installed already. You can tell Django is installed and which version by running the following command in a shell prompt (indicated by the $ prefix):
我们假设你已经安装了 Django。您可以通过在 shell 提示符下运行以下命令 (用 $ 前缀表示) 来查看 您安装的 Django 版本:

$ python3 -m django --version

We also assume that you have Channels installed already. You can tell Channels is installed by running the following command:
我们还假设您已经安装了 Channels。您可以通过运行以下命令来查看 Channels 安装与否:

$ python3 -c 'import channels; print(channels.__version__)'

This tutorial is written for Channels 2.0, which supports Python 3.5+ and Django 1.11+. If the Channels version does not match, you can refer to the tutorial for your version of Channels by using the version switcher at the bottom left corner of this page, or update Channels to the newest version.
本教程是为 Channels 2.0 编写的, 它支持 Python 3.5 + 和 Django 1.11 +。如果 Channels 版本不匹配, 你可以使用本页左下角的版本切换器, 或将 Channels 更新到最新版本, 以参考您的 Channels 版本的教程。

This tutorial also uses Docker to install and run Redis. We use Redis as the backing store for the channel layer, which is an optional component of the Channels library that we use in the tutorial. Install Docker from its official website - there are official runtimes for Mac OS and Windows that make it easy to use, and packages for many Linux distributions where it can run natively.
本教程还使用 Docker 安装和运行 Redis。我们使用 Redis 作为 Channels 层的后备存储, 它是我们在教程中使用的 Channels 库的可选组件。从其官方网站安装 Docker --有用于 Mac OS 和 Windows 的易于使用的正式运行版, 并为许多 Linux 发行版提供了可本地运行的软件包。

Note
提醒
While you can run the standard Django runserver without the need for Docker, the channels features we’ll be using in later parts of the tutorial will need Redis to run, and we recommend Docker as the easiest way to do this.
虽然您可以运行标准的 Django runserver 不需要 Docker , 我们将使用的 channels 功能在后面的教程将需要 Redis 运行, 我们建议使用 Docker 这一最简单的方式来做到这一点。

Creating a project
新建一个项目

If you don’t already have a Django project, you will need to create one.
如果您还没有 Django 项目, 您将需要创建一个。

From the command line, cd into a directory where you’d like to store your code, then run the following command:
从命令行, 将 cd 放入要存储代码的目录中, 然后运行以下命令:

$ django-admin startproject mysite

This will create a mysite directory in your current directory with the following contents:
这将在当前目录中创建一个 mysite 目录, 其中有以下内容:

mysite/
    manage.py
    mysite/
        __init__.py
        settings.py
        urls.py
        wsgi.py

Creating the Chat app
创建聊天应用程序

We will put the code for the chat server in its own app.
我们会将聊天服务器的代码放在它自己的应用程序中。

Make sure you’re in the same directory as manage.py and type this command:
请确保您位于与 manage.py 相同的目录中. 然后输入以下命令:

$ python3 manage.py startapp chat

That’ll create a directory chat, which is laid out like this:
这将创建一个 chat 文件夹, 它是像这样的:

chat/
    __init__.py
    admin.py
    apps.py
    migrations/
        __init__.py
    models.py
    tests.py
    views.py

For the purposes of this tutorial, we will only be working with chat/views.py and chat/__init__.py. So remove all other files from the chat directory.
为了达到本教程的目的, 我们将只使用 chat/views.py 和 chat/__init__.py。因此, 从 chat 目录中删除所有其他文件。

After removing unnecessary files, the chat directory should look like:
删除不必要的文件后, chat 目录应如下所示:

chat/
    __init__.py
    views.py

We need to tell our project that the chat app is installed. Edit the mysite/settings.py file and add 'chat' to the INSTALLED_APPS setting. It’ll look like this:
我们需要告诉我们的项目 chat app 已经安装。编辑 mysite/settings.py 文件并将 'chat' 添加到 INSTALLED_APPS 设置中。它看起来像这样:

# mysite/settings.py
INSTALLED_APPS = [
    'chat',
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
]

Add the index view
添加 index 视图

We will now create the first view, an index view that lets you type the name of a chat room to join.
现在, 我们将创建第一个视图, 这个 index 视图允许您输入要加入的聊天室的名称。

Create a templates directory in your chat directory. Within the templates directory you have just created, create another directory called chat, and within that create a file called index.html to hold the template for the index view.
在 chat 目录中创建 templates 目录。在刚刚创建的 templates 目录中, 创建另一个名为 chat 的目录, 并在其中创建一个名为 index.html 的文件。

Your chat directory should now look like:
您的 chat 目录现在应该看起来像:

chat/
    __init__.py
    templates/
        chat/
            index.html
    views.py

Put the following code in chat/templates/chat/index.html:
将下面的代码写进 chat/templates/chat/index.html 文件中：

<!-- chat/templates/chat/index.html -->
<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8"/>
    <title>Chat Rooms</title>
</head>
<body>
    What chat room would you like to enter?<br/>
    <input id="room-name-input" type="text" size="100"/><br/>
    <input id="room-name-submit" type="button" value="Enter"/>
</body>
<script>
    document.querySelector('#room-name-input').focus();
    document.querySelector('#room-name-input').onkeyup = function(e) {
        if (e.keyCode === 13) {  // enter, return
            document.querySelector('#room-name-submit').click();
        }
    };

    document.querySelector('#room-name-submit').onclick = function(e) {
        var roomName = document.querySelector('#room-name-input').value;
        window.location.pathname = '/chat/' + roomName + '/';
    };
</script>
</html>

Create the view function for the room view. Put the following code in chat/views.py:
为 room 视图创建视图函数。将下面的代码写进 chat/views.py 文件中：

# chat/views.py
from django.shortcuts import render

def index(request):
    return render(request, 'chat/index.html', {})

To call the view, we need to map it to a URL - and for this we need a URLconf.
为了调用这个视图，我们需要把它映射到一个 URL -- 因此我们需要一个 URL 配置文件。

To create a URLconf in the chat directory, create a file called urls.py. Your app directory should now look like:
为了在 chat 目录下创建一个 URL 配置文件，我们需要新建一个名为 urls.py 的文件。你的 app 目录应该像现在这样子：

chat/
    __init__.py
    templates/
        chat/
            index.html
    urls.py
    views.py

In the chat/urls.py file include the following code:
在 chat/urls.py 文件中包含以下代码：

# chat/urls.py
from django.conf.urls import url

from . import views

urlpatterns = [
    url(r'^$', views.index, name='index'),
]

The next step is to point the root URLconf at the chat.urls module. In mysite/urls.py, add an import for django.conf.urls.include and insert an include() in the urlpatterns list, so you have:
下一步是将根目录下的 URLconf 文件指向 chat.urls 模块。在 mysite/urls.py 中, 导入 django.conf.urls.include模块，并在 urlpatterns 列表中插入一个 include() 函数, 因此您需要写入以下代码:

# mysite/urls.py
from django.conf.urls import include, url
from django.contrib import admin

urlpatterns = [
    url(r'^chat/', include('chat.urls')),
    url(r'^admin/', admin.site.urls),
]

Let’s verify that the index view works. Run the following command:
让我们验证 index 视图是否有效。运行以下命令:

$ python3 manage.py runserver

You’ll see the following output on the command line:
您将在命令行中看到以下输出:

Performing system checks...

System check identified no issues (0 silenced).

You have 13 unapplied migration(s). Your project may not work properly until you apply the migrations for app(s): admin, auth, contenttypes, sessions.
Run 'python manage.py migrate' to apply them.

February 18, 2018 - 22:08:39
Django version 1.11.10, using settings 'mysite.settings'
Starting development server at http://127.0.0.1:8000/
Quit the server with CONTROL-C.

Note
提醒
Ignore the warning about unapplied database migrations. We won’t be using a database in this tutorial.
忽略有关未应用数据库迁移的警告。我们将不会在本教程中使用数据库。

Go to http://127.0.0.1:8000/chat/ in your browser and you should see the text “What chat room would you like to enter?” along with a text input to provide a room name.
在浏览器中转到 http://127.0.0.1:8000/chat/, 您应该看到文本 "What chat room would you like to enter?" 以及一个用于输入房间名字的文本输入框。

Type in “lobby” as the room name and press enter. You should be redirected to the room view at http://127.0.0.1:8000/chat/lobby/ but we haven’t written the room view yet, so you’ll get a “Page not found” error page.
输入 "lobby" 作为房间名称, 然后按 enter 键。你应该被重定向到 http://127.0.0.1:8000/chat/lobby/的房间视图, 但我们还没有写的房间视图, 所以你会得到一个 "页面找不到" 错误页面。

Go to the terminal where you ran the runserver command and press Control-C to stop the server.
转到运行 runserver 命令的终端, 然后按下 Control+C 以停止服务器。

Integrate the Channels library
集成 Channels 库

So far we’ve just created a regular Django app; we haven’t used the Channels library at all. Now it’s time to integrate Channels.
到目前为止, 我们刚刚创建了一个常规的 Django 应用程序;我们根本就没有使用 Channels 库。现在是时候集成 Channels 库了。

Let’s start by creating a root routing configuration for Channels. A Channels routing configuration is similar to a Django URLconf in that it tells Channels what code to run when an HTTP request is received by the Channels server.
让我们从创建 Channels 的根路由配置文件开始。Channels 路由配置类似于 Django URLconf，它会告诉 Channels 当收到由 Channels 服务器发过来的 HTTP 请求时，应该执行什么代码。

We’ll start with an empty routing configuration. Create a file mysite/routing.py and include the following code:
我们将从一个空的路由配置文件开始。创建文件 mysite/routing.py, 并写入以下代码:

# mysite/routing.py
from channels.routing import ProtocolTypeRouter

application = ProtocolTypeRouter({
    # (http->django views is added by default)
})

Now add the Channels library to the list of installed apps. Edit the mysite/settings.py file and add 'channels' to the INSTALLED_APPS setting. It’ll look like this:
现在, 将 Channels 库添加到已安装的应用程序列表中。编辑 mysite/settings.py 文件并将 'channels' 添加到 INSTALLED_APPS 设置。它看起来像这样:

# mysite/settings.py
INSTALLED_APPS = [
    'channels',
    'chat',
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
]

You’ll also need to point Channels at the root routing configuration. Edit the mysite/settings.py file again and add the following to the bottom of it:
您同样需要在根路由配置中指向 Channels。再次编辑 mysite/settings.py 文件, 并将以下内容添加到底部:

# mysite/settings.py
# Channels
ASGI_APPLICATION = 'mysite.routing.application'

With Channels now in the installed apps, it will take control of the runserver command, replacing the standard Django development server with the Channels development server.
现在已安装的应用程序中有 Channels, 它将控制 runserver 命令, 用 Channels 开发服务器替换标准的 Django 开发服务器。

Note
提醒

The Channels development server will conflict with any other third-party apps that require an overloaded or replacement runserver command. An example of such a conflict is with whitenoise.runserver_nostatic from whitenoise. In order to solve such issues, try moving channels to the top of your INSTALLED_APPS or remove the offending app altogether.
Channels 开发服务器将与需要重载或替换 runserver 命令的任何其他第三方应用程序冲突。whitenoise 中的 whitenoise.runserver_nostatic是一个冲突的例子。为了解决这些问题, 请尝试将 Channels 移动到您的 INSTALLED_APPS 的顶部, 或者完全删除与其发生冲突的应用程序。

Let’s ensure that the Channels development server is working correctly. Run the following command:
让我们确保 Channels 开发服务器工作正常。运行以下命令:

$ python3 manage.py runserver

You’ll see the following output on the command line:
您将在命令行中看到以下输出:

Performing system checks...

System check identified no issues (0 silenced).

You have 13 unapplied migration(s). Your project may not work properly until you apply the migrations for app(s): admin, auth, contenttypes, sessions.
Run 'python manage.py migrate' to apply them.

February 18, 2018 - 22:16:23
Django version 1.11.10, using settings 'mysite.settings'
Starting ASGI/Channels development server at http://127.0.0.1:8000/
Quit the server with CONTROL-C.
2018-02-18 22:16:23,729 - INFO - server - HTTP/2 support not enabled (install the http2 and tls Twisted extras)
2018-02-18 22:16:23,730 - INFO - server - Configuring endpoint tcp:port=8000:interface=127.0.0.1
2018-02-18 22:16:23,731 - INFO - server - Listening on TCP address 127.0.0.1:8000

Note
提醒

Ignore the warning about unapplied database migrations. We won’t be using a database in this tutorial.
忽略有关未应用数据库迁移的警告。我们将不会在本教程中使用数据库。

Notice the line beginning with Starting ASGI/Channels development server at http://127.0.0.1:8000/. This indicates that the Channels development server has taken over from the Django development server.
留意从 Starting ASGI/Channels development server at http://127.0.0.1:8000/ 开始的内容。这表明 Channels 开发服务器已接管了 Django 开发服务器。

Go to http://127.0.0.1:8000/chat/ in your browser and you should still see the index page that we created before.
在浏览器中转到 http://127.0.0.1:8000/chat/, 您仍然应该看到我们以前创建的 index 页面。

Go to the terminal where you ran the runserver command and press Control-C to stop the server.
转到运行 runserver 命令的终端, 然后按下 Control+C 以停止服务器。

 

Tutorial Part 2: Implement a Chat Server
教程2部分: 实现聊天服务器

This tutorial begins where Tutorial 1 left off. We’ll get the room page working so that you can chat with yourself and others in the same room.
本教程在教程1的基础上开始。我们会让房间页面工作, 这样你可以和你自己或者其他人在同一个房间里聊天。

Add the room view
添加房间视图

We will now create the second view, a room view that lets you see messages posted in a particular chat room.
现在, 我们将创建第二个视图, 即一个允许您查看在特定聊天室中发布消息的房间视图。

Create a new file chat/templates/chat/room.html. Your app directory should now look like:
创建新的文件 chat/templates/chat/room.html。您的应用程序目录现在应该看起来像:

chat/
    __init__.py
    templates/
        chat/
            index.html
            room.html
    urls.py
    views.py

Create the view template for the room view in chat/templates/chat/room.html:
在 chat/templates/chat/room.html 中填入一下代码：

<!-- chat/templates/chat/room.html -->
<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8"/>
    <title>Chat Room</title>
</head>
<body>
    <textarea id="chat-log" cols="100" rows="20"></textarea><br/>
    <input id="chat-message-input" type="text" size="100"/><br/>
    <input id="chat-message-submit" type="button" value="Send"/>
</body>
<script>
    var roomName = {{ room_name_json }};

    var chatSocket = new WebSocket(
        'ws://' + window.location.host +
        '/ws/chat/' + roomName + '/');

    chatSocket.onmessage = function(e) {
        var data = JSON.parse(e.data);
        var message = data['message'];
        document.querySelector('#chat-log').value += (message + '\n');
    };

    chatSocket.onclose = function(e) {
        console.error('Chat socket closed unexpectedly');
    };

    document.querySelector('#chat-message-input').focus();
    document.querySelector('#chat-message-input').onkeyup = function(e) {
        if (e.keyCode === 13) {  // enter, return
            document.querySelector('#chat-message-submit').click();
        }
    };

    document.querySelector('#chat-message-submit').onclick = function(e) {
        var messageInputDom = document.querySelector('#chat-message-input');
        var message = messageInputDom.value;
        chatSocket.send(JSON.stringify({
            'message': message
        }));

        messageInputDom.value = '';
    };
</script>
</html>

Create the view function for the room view in chat/views.py. Add the imports of mark_safe and json and add the room view function:
在 chat/views.py 中为房间视图创建视图函数。添加导入 mark_safe 和 json 模块, 并添加 房间视图的视图函数:

# chat/views.py
from django.shortcuts import render
from django.utils.safestring import mark_safe
import json

def index(request):
    return render(request, 'chat/index.html', {})

def room(request, room_name):
    return render(request, 'chat/room.html', {
        'room_name_json': mark_safe(json.dumps(room_name))
    })

Create the route for the room view in chat/urls.py:
在 chat/urls.py 中创建房间视图的路由：

# chat/urls.py
from django.conf.urls import url

from . import views

urlpatterns = [
    url(r'^$', views.index, name='index'),
    url(r'^(?P<room_name>[^/]+)/$', views.room, name='room'),
]

Start the Channels development server:
启动 Channels 开发服务器:

$ python3 manage.py runserver

Go to http://127.0.0.1:8000/chat/ in your browser and to see the index page.
在浏览器中转到 http://127.0.0.1:8000/chat/并查看 index 页面。

Type in “lobby” as the room name and press enter. You should be redirected to the room page at http://127.0.0.1:8000/chat/lobby/ which now displays an empty chat log.
输入 “lobby” 作为房间名称, 然后按 enter 键。您将会重定向到 http://127.0.0.1:8000/chat/lobby/, 该页面现在显示一个空的聊天日志。

Type the message “hello” and press enter. Nothing happens. In particular the message does not appear in the chat log. Why?
键入消息 "hello", 然后按 enter 键。什么也没有发生。尤其是，消息并不会出现在聊天日志中。为什么？

The room view is trying to open a WebSocket to the URL ws://127.0.0.1:8000/ws/chat/lobby/ but we haven’t created a consumer that accepts WebSocket connections yet. If you open your browser’s JavaScript console, you should see an error that looks like:
房间视图试图打开一个 WebSocket 连接到 URL ws://127.0.0.1:8000/ws/chat/lobby/，但我们还没有创建一个接受 WebSocket 连接的 consumer。如果打开浏览器的 JavaScript 控制台, 您应该会看到如下所示的错误:

WebSocket connection to 'ws://127.0.0.1:8000/ws/chat/lobby/' failed: Unexpected response code: 500

Write your first consumer
编写您的第一个用户

When Django accepts an HTTP request, it consults the root URLconf to lookup a view function, and then calls the view function to handle the request. Similarly, when Channels accepts a WebSocket connection, it consults the root routing configuration to lookup a consumer, and then calls various functions on the consumer to handle events from the connection.
当 Django 接受 HTTP 请求时, 它会根据根 URLconf 以查找视图函数, 然后调用视图函数来处理请求。同样, 当 Channels 接受 WebSocket 连接时, 它会根据根路由配置以查找对应的 consumer, 然后调用 consumer 上的各种函数来处理来自这个连接的事件。

We will write a basic consumer that accepts WebSocket connections on the path /ws/chat/ROOM_NAME/ that takes any message it receives on the WebSocket and echos it back to the same WebSocket.
我们将编写一个简单的 consumer, 它会在路径 /ws/chat/ROOM_NAME/ 接收 WebSocket 连接，然后把接收任意的消息, 回送给同一个 WebSocket 连接。

Note
提醒

It is good practice to use a common path prefix like /ws/ to distinguish WebSocket connections from ordinary HTTP connections because it will make deploying Channels to a production environment in certain configurations easier.
使用常见的路径前缀 (如/ws) 来区分 WebSocket 连接与普通 HTTP 连接是很好的做法, 因为它将使在某些配置中部署 Channels 更容易。

In particular for large sites it will be possible to configure a production-grade HTTP server like nginx to route requests based on path to either a production-grade WSGI server like Gunicorn+Django for ordinary HTTP requests or a production-grade ASGI server like Daphne+Channels for WebSocket requests.
特别是大型网站, 它们很有可能配置像 nginx 这样的生产级别 HTTP 服务器，根据路径将请求发送到生产级别的 WSGI 服务器，例如用于处理普通 HTTP 请求的 Gunicorn + Django, 或生产级别的 ASGI 服务器，例如用于处理 WebSocket 请求的 Daphne + Channels。

Note that for smaller sites you can use a simpler deployment strategy where Daphne serves all requests - HTTP and WebSocket - rather than having a separate WSGI server. In this deployment configuration no common path prefix like is /ws/ is necessary.
请注意, 对于较小的站点, 您可以使用更简单的部署策略, 其中 Daphne 服务器处理所有的请求--HTTP 和 WebSocket--而不是单独的 WSGI 服务器。在这种部署配置策略中, 不需要使用 /ws/ 这样的通用路径前缀。

Create a new file chat/consumers.py. Your app directory should now look like:
创建新文件 chat/consumers.py。您的应用程序目录现在应该看起来像:

chat/
    __init__.py
    consumers.py
    templates/
        chat/
            index.html
            room.html
    urls.py
    views.py

Put the following code in chat/consumers.py:
在 chat/consumers.py 中写入以下代码：

# chat/consumers.py
from channels.generic.websocket import WebsocketConsumer
import json

class ChatConsumer(WebsocketConsumer):
    def connect(self):
        self.accept()

    def disconnect(self, close_code):
        pass

    def receive(self, text_data):
        text_data_json = json.loads(text_data)
        message = text_data_json['message']

        self.send(text_data=json.dumps({
            'message': message
        }))

This is a synchronous WebSocket consumer that accepts all connections, receives messages from its client, and echos those messages back to the same client. For now it does not broadcast messages to other clients in the same room.
这是一个同步 WebSocket consumer, 它接受所有连接, 接收来自其客户端的消息, 并将这些消息回送到同一客户端。现在, 它不向同一个房间的其他客户端广播消息。

Note
提醒

Channels also supports writing asynchronous consumers for greater performance. However any asynchronous consumer must be careful to avoid directly performing blocking operations, such as accessing a Django model. See the Consumers reference for more information about writing asynchronous consumers.
Channels 还支持编写异步 consumers 以提高性能。但是, 任何异步 consumers 都必须小心, 避免直接执行阻塞操作, 例如访问 Django 的 model。有关编写异步 consumers 的详细信息, 请参阅 Consumers。

We need to create a routing configuration for the chat app that has a route to the consumer. Create a new file chat/routing.py. Your app directory should now look like:
我们需要为 chat app 创建一个路由配置, 它有一个通往 consumer 的路由。创建新文件 chat/routing.py。您的应用程序目录现在应该看起来像:

chat/
    __init__.py
    consumers.py
    routing.py
    templates/
        chat/
            index.html
            room.html
    urls.py
    views.py

Put the following code in chat/routing.py:
在 chat/routing.py 中输入以下代码：

# chat/routing.py
from django.conf.urls import url

from . import consumers

websocket_urlpatterns = [
    url(r'^ws/chat/(?P<room_name>[^/]+)/$', consumers.ChatConsumer),
]

The next step is to point the root routing configuration at the chat.routing module. In mysite/routing.py, import AuthMiddlewareStack, URLRouter, and chat.routing; and insert a 'websocket' key in the ProtocolTypeRouter list in the following format:
下一步是将根路由指向 chat.routing 模块。在 mysite/routing.py 中, 导入 AuthMiddlewareStack、URLRouter 和 chat.routing ;并在 ProtocolTypeRouter 列表中插入一个 "websocket" 键, 格式如下:

# mysite/routing.py
from channels.auth import AuthMiddlewareStack
from channels.routing import ProtocolTypeRouter, URLRouter
import chat.routing

application = ProtocolTypeRouter({
    # (http->django views is added by default)
    'websocket': AuthMiddlewareStack(
        URLRouter(
            chat.routing.websocket_urlpatterns
        )
    ),
})

This root routing configuration specifies that when a connection is made to the Channels development server, the ProtocolTypeRouter will first inspect the type of connection. If it is a WebSocket connection (ws:// or wss://), the connection will be given to the AuthMiddlewareStack.
这个根路由配置指定，当与 Channels 开发服务器建立连接的时候, ProtocolTypeRouter 将首先检查连接的类型。如果是 WebSocket 连接 (ws://或 wss://), 则连接会交给 AuthMiddlewareStack。

The AuthMiddlewareStack will populate the connection’s scope with a reference to the currently authenticated user, similar to how Django’s AuthenticationMiddleware populates the request object of a view function with the currently authenticated user. (Scopes will be discussed later in this tutorial.) Then the connection will be given to the URLRouter.
AuthMiddlewareStack 将使用对当前经过身份验证的用户的引用来填充连接的 scope, 类似于 Django 的 AuthenticationMiddleware 用当前经过身份验证的用户填充视图函数的请求对象。（Scopes 将在本教程后面讨论。）然后连接将被给到 URLRouter。

The URLRouter will examine the HTTP path of the connection to route it to a particular consumer, based on the provided url patterns.
根据提供的 url 模式, URLRouter 将检查连接的 HTTP 路径, 以将其路由指定到到特定的 consumer。

Let’s verify that the consumer for the /ws/chat/ROOM_NAME/ path works. Start the Channels development server:
让我们验证 consumer 的 /ws/chat/ROOM_NAME/ 路径是否工作。启动 Channels 开发服务器:

$ python3 manage.py runserver

Go to the room page at http://127.0.0.1:8000/chat/lobby/ which now displays an empty chat log.
转到 http://127.0.0.1:8000/chat/lobby/ 中的 房间页面, 该页现在显示一个空的聊天日志。

Type the message “hello” and press enter. You should now see “hello” echoed in the chat log.
输入消息 "hello", 然后按 enter 键。您现在应该看到 "hello" 在聊天日志中显示。

However if you open a second browser tab to the same room page at http://127.0.0.1:8000/chat/lobby/ and type in a message, the message will not appear in the first tab. For that to work, we need to have multiple instances of the same ChatConsumer be able to talk to each other. Channels provides a channel layer abstraction that enables this kind of communication between consumers.
但是, 如果您打开第二个浏览器选项卡输入 http://127.0.0.1:8000/chat/lobby/进入同一房间页面上并输入消息, 则消息并不会出现在第一个选项卡中。为了做到这一点, 我们需要有多个相同 ChatConsumer 实例才能互相交谈。Channels 提供了一种 channel layer 抽象, 使 consumers 之间能够进行这种通信。

Go to the terminal where you ran the runserver command and press Control-C to stop the server.
转到运行 runserver 命令的终端, 然后按下 Control+C 以停止服务器。

Enable a channel layer
启用 channel layer

A channel layer is a kind of communication system. It allows multiple consumer instances to talk with each other, and with other parts of Django.
channel layer 是一种通信系统。它允许多个 consumer 实例互相交谈, 以及与 Django 的其他部分进行通信。

A channel layer provides the following abstractions:
channel layer 提供以下抽象:

• A channel is a mailbox where messages can be sent to. Each channel has a name. Anyone who has the name of a channel can send a message to the channel.
• channel 是可以发送消息的邮箱。每个 channel 都有一个名称。任何有名称的 channel 都可以向 channel 发送消息。
• A group is a group of related channels. A group has a name. Anyone who has the name of a group can add/remove a channel to the group by name and send a message to all channels in the group. It is not possible to enumerate what channels are in a particular group.
• group 是一组相关的 channels。group 具有名称。任何具有名字的 group 都可以按名称向 group 中添加/删除 channel, 也可以向 group 中的所有 channel 发送消息。无法列举特定 group 中的 channel。

Every consumer instance has an automatically generated unique channel name, and so can be communicated with via a channel layer.
每个 consumer 实例都有一个自动生成的唯一的 channel 名称, 因此可以通过 channel layer 进行通信。

In our chat application we want to have multiple instances of ChatConsumer in the same room communicate with each other. To do that we will have each ChatConsumer add its channel to a group whose name is based on the room name. That will allow ChatConsumers to transmit messages to all other ChatConsumers in the same room.
在我们的聊天应用程序中, 我们希望在同一房间中有多个 ChatConsumer 的实例相互通信。要做到这一点, 我们将有每个 ChatConsumer 添加它的 channel 到一个 group, 其名称是基于房间的名称。这将允许 ChatConsumers 将消息传输到同一个房间中的所有其他 ChatConsumers。

We will use a channel layer that uses Redis as its backing store. To start a Redis server on port 6379, run the following command:
我们将使用一个 channel layer, 使用 Redis 作为其后备存储。要在端口6379上启动 Redis 服务器, 请运行以下命令:

$ docker run -p 6379:6379 -d redis:2.8

We need to install channels_redis so that Channels knows how to interface with Redis. Run the following command:
我们需要安装 channels_redis, 以便 Channels 知道如何调用 redis。运行以下命令:

$ pip3 install channels_redis

Before we can use a channel layer, we must configure it. Edit the mysite/settings.py file and add a CHANNEL_LAYERS setting to the bottom. It should look like:
在使用 channel layer 之前, 必须对其进行配置。编辑 mysite/settings.py 文件并将 CHANNEL_LAYERS 设置添加到底部。它应该看起来像:

# mysite/settings.py
# Channels
ASGI_APPLICATION = 'mysite.routing.application'
CHANNEL_LAYERS = {
    'default': {
        'BACKEND': 'channels_redis.core.RedisChannelLayer',
        'CONFIG': {
            "hosts": [('127.0.0.1', 6379)],
        },
    },
}

Note
提醒

It is possible to have multiple channel layers configured. However most projects will just use a single 'default' channel layer.
可以配置多个 channel layer。然而, 大多数项目只使用一个 "默认" 的 channel layer。

Let’s make sure that the channel layer can communicate with Redis. Open a Django shell and run the following commands:
让我们确保 channel layer 可以与 Redis 通信。打开 Django shell 并运行以下命令:

$ python3 manage.py shell
>>> import channels.layers
>>> channel_layer = channels.layers.get_channel_layer()
>>> from asgiref.sync import async_to_sync
>>> async_to_sync(channel_layer.send)('test_channel', {'type': 'hello'})
>>> async_to_sync(channel_layer.receive)('test_channel')
{'type': 'hello'}

Type Control-D to exit the Django shell.
输入 Control+D 退出 Django shell。

Now that we have a channel layer, let’s use it in ChatConsumer. Put the following code in chat/consumers.py, replacing the old code:
现在我们有了一个 channel layer, 让我们在 ChatConsumer 中使用它。将以下代码放在 chat/consumers.py 中, 替换旧代码:

# chat/consumers.py
from asgiref.sync import async_to_sync
from channels.generic.websocket import WebsocketConsumer
import json

class ChatConsumer(WebsocketConsumer):
    def connect(self):
        self.room_name = self.scope['url_route']['kwargs']['room_name']
        self.room_group_name = 'chat_%s' % self.room_name

        # Join room group
        async_to_sync(self.channel_layer.group_add)(
            self.room_group_name,
            self.channel_name
        )

        self.accept()

    def disconnect(self, close_code):
        # Leave room group
        async_to_sync(self.channel_layer.group_discard)(
            self.room_group_name,
            self.channel_name
        )

    # Receive message from WebSocket
    def receive(self, text_data):
        text_data_json = json.loads(text_data)
        message = text_data_json['message']

        # Send message to room group
        async_to_sync(self.channel_layer.group_send)(
            self.room_group_name,
            {
                'type': 'chat_message',
                'message': message
            }
        )

    # Receive message from room group
    def chat_message(self, event):
        message = event['message']

        # Send message to WebSocket
        self.send(text_data=json.dumps({
            'message': message
        }))

When a user posts a message, a JavaScript function will transmit the message over WebSocket to a ChatConsumer. The ChatConsumer will receive that message and forward it to the group corresponding to the room name. Every ChatConsumer in the same group (and thus in the same room) will then receive the message from the group and forward it over WebSocket back to JavaScript, where it will be appended to the chat log.
当用户发布消息时, JavaScript 函数将通过 WebSocket 将消息传输到 ChatConsumer。ChatConsumer 将接收该消息并将其转发到与房间名称对应的 group。在同一 group 中的每个 ChatConsumer (并因此在同一个房间中) 将接收来自该 group 的消息, 通过 WebSocket 将其转发并返回到 JavaScript, 它将会追加到聊天日志中。

Several parts of the new ChatConsumer code deserve further explanation:
新的 ChatConsumer 代码中有几个部分需要进一步解释:

• self.scope[‘url_route’][‘kwargs’][‘room_name’]
  • Obtains the 'room_name' parameter from the URL route in chat/routes.py that opened the WebSocket connection to the consumer.
  • 从给 consumer 打开 WebSocket 连接的 chat/routes.py 中的 URL 路由中获取 "room_name" 参数。
  • Every consumer has a scope that contains information about its connection, including in particular any positional or keyword arguments from the URL route and the currently authenticated user if any.
  • 每个 consumer 都有一个 scope, 其中包含有关其连接的信息, 特别是来自 URL 路由和当前经过身份验证的用户 (如果有的话) 中的任何位置或关键字参数。
• self.room_group_name = ‘chat_%s’ % self.room_name
  • Constructs a Channels group name directly from the user-specified room name, without any quoting or escaping.
  • 直接从用户指定的房间名称构造一个 Channels group 名称, 无需任何引用或转义。
  • Group names may only contain letters, digits, hyphens, and periods. Therefore this example code will fail on room names that have other characters.
  • 组名可能只包含字母、数字、连字符和句点。因此, 此示例代码将在具有其他字符的房间名称上发生失败。
• async_to_sync(self.channel_layer.group_add)(…)
  • Joins a group.
  • 加入一个 group。
  • The async_to_sync(…) wrapper is required because ChatConsumer is a synchronous WebsocketConsumer but it is calling an asynchronous channel layer method. (All channel layer methods are asynchronous.)
  • async_to_sync(…) wrapper 是必需的, 因为 ChatConsumer 是同步 WebsocketConsumer, 但它调用的是异步 channel layer 方法。（所有 channel layer 方法都是异步的）
  • Group names are restricted to ASCII alphanumerics, hyphens, and periods only. Since this code constructs a group name directly from the room name, it will fail if the room name contains any characters that aren’t valid in a group name.
  • group 名称仅限于 ASCII 字母、连字符和句点。由于此代码直接从房间名称构造 group 名称, 因此如果房间名称中包含的其他无效的字符, 代码运行则会失败。
• self.accept()
  • Accepts the WebSocket connection.
  • 接收 WebSocket 连接。
  • If you do not call accept() within the connect() method then the connection will be rejected and closed. You might want to reject a connection for example because the requesting user is not authorized to perform the requested action.
  • 如果你在 connect() 方法中不调用 accept(), 则连接将被拒绝并关闭。例如，您可能希望拒绝连接, 因为请求的用户未被授权执行请求的操作。
  • It is recommended that accept() be called as the last action in connect() if you choose to accept the connection.
  • 如果你选择接收连接, 建议 accept() 作为在 connect() 方法中的最后一个操作。
• async_to_sync(self.channel_layer.group_discard)(…)
  • Leaves a group.
  • 离开一个 group。
• async_to_sync(self.channel_layer.group_send)
  • Sends an event to a group.
  • 将 event 发送到一个 group。
  • An event has a special 'type' key corresponding to the name of the method that should be invoked on consumers that receive the event.
  • event 具有一个特殊的键 'type' 对应接收 event 的 consumers 调用的方法的名称。

Let’s verify that the new consumer for the /ws/chat/ROOM_NAME/ path works. To start the Channels development server, run the following command:
让我们验证新 consumer 的 /ws/chat/ROOM_NAME/ 路径是否工作。要启动 Channels 开发服务器, 请运行以下命令:

$ python3 manage.py runserver

Open a browser tab to the room page at http://127.0.0.1:8000/chat/lobby/. Open a second browser tab to the same room page.
打开浏览器选项卡到 http://127.0.0.1:8000/chat/lobby/的房间页面。打开另一个浏览器选项卡到同一个房间页面。

In the second browser tab, type the message “hello” and press enter. You should now see “hello” echoed in the chat log in both the second browser tab and in the first browser tab.
在第二个浏览器选项卡中, 输入消息 "hello", 然后按 enter 键。在第二个浏览器选项卡和第一个浏览器选项卡中, 您现在应该看到 "hello" 在聊天日志中显示。

You now have a basic fully-functional chat server!
您现在有一个基本的功能齐全的聊天服务器!

Tutorial Part 3: Rewrite Chat Server as Asynchronous
教程3部分: 将聊天服务器重写为异步方式

This tutorial begins where Tutorial 2 left off. We’ll rewrite the consumer code to be asynchronous rather than synchronous to improve its performance.
本教程在教程2的基础上开始。我们将重写 consumer 代码使其变成是异步的而不是同步的, 以提高其性能。

Rewrite the consumer to be asynchronous
将 consumer 改写为异步

The ChatConsumer that we have written is currently synchronous. Synchronous consumers are convenient because they can call regular synchronous I/O functions such as those that access Django models without writing special code. However asynchronous consumers can provide a higher level of performance since they don’t need create additional threads when handling requests.
我们编写的 ChatConsumer 当前是同步的。同步的 consumers 很方便, 因为它们可以调用常规的同步 I/O 函数, 例如访问 Django models 而不用编写特殊的代码。但是, 异步的 consumers 可以提供更高级别的性能, 因为它们在处理请求时不需要创建其他线程。

ChatConsumer only uses async-native libraries (Channels and the channel layer) and in particular it does not access synchronous Django models. Therefore it can be rewritten to be asynchronous without complications.
ChatConsumer 只使用 async-native 库 (Channels 和 channel layer), 特别是它不访问同步的 Django models。因此, 它可以被改写为异步的而不会变得复杂化。

Note
提醒

Even if ChatConsumer did access Django models or other synchronous code it would still be possible to rewrite it as asynchronous. Utilities like asgiref.sync.sync_to_async and channels.db.database_sync_to_async can be used to call synchronous code from an asynchronous consumer. The performance gains however would be less than if it only used async-native libraries.
即使 ChatConsumer 访问 Django models 或其他同步的代码, 它仍然可以将其重写为异步的。像 asgiref.sync.sync_to_async 和 channels.db.database_sync_to_async 这样的实用工具可以用来从异步 consumer 那里调用同步的代码。但是, 性能增益将小于仅使用 async-native 库的方式。

Let’s rewrite ChatConsumer to be asynchronous. Put the following code in chat/consumers.py:
让我们重写 ChatConsumer 使其变为异步的。在 chat/consumers.py 中输入以下代码:

# chat/consumers.py
from channels.generic.websocket import AsyncWebsocketConsumer
import json

class ChatConsumer(AsyncWebsocketConsumer):
    async def connect(self):
        self.room_name = self.scope['url_route']['kwargs']['room_name']
        self.room_group_name = 'chat_%s' % self.room_name

        # Join room group
        await self.channel_layer.group_add(
            self.room_group_name,
            self.channel_name
        )

        await self.accept()

    async def disconnect(self, close_code):
        # Leave room group
        await self.channel_layer.group_discard(
            self.room_group_name,
            self.channel_name
        )

    # Receive message from WebSocket
    async def receive(self, text_data):
        text_data_json = json.loads(text_data)
        message = text_data_json['message']

        # Send message to room group
        await self.channel_layer.group_send(
            self.room_group_name,
            {
                'type': 'chat_message',
                'message': message
            }
        )

    # Receive message from room group
    async def chat_message(self, event):
        message = event['message']

        # Send message to WebSocket
        await self.send(text_data=json.dumps({
            'message': message
        }))

This new code is for ChatConsumer is very similar to the original code, with the following differences:
这些用于 ChatConsumer 的新代码与原始代码非常相似, 它们具有以下差异:

• ChatConsumer now inherits from AsyncWebsocketConsumer rather than WebsocketConsumer.
• 现在 ChatConsumer 继承自 AsyncWebsocketConsumer 而不是 WebsocketConsumer。
• All methods are async def rather than just def.
• 所有方法都是 async def, 而不仅仅是 def。
• await is used to call asynchronous functions that perform I/O.
• await 被用于调用执行 I/O 的异步函数。
• async_to_sync is no longer needed when calling methods on the channel layer.
• 在 channel layer 上调用方法时, 不再需要 async_to_sync。

Let’s verify that the consumer for the /ws/chat/ROOM_NAME/ path still works. To start the Channels development server, run the following command:
让我们验证 consumer 的 /ws/chat/ROOM_NAME/ 路径是否仍然有效。启动 Channels 开发服务器, 运行以下命令:

$ python3 manage.py runserver

Open a browser tab to the room page at http://127.0.0.1:8000/chat/lobby/. Open a second browser tab to the same room page.
打开浏览器选项卡到 http://127.0.0.1:8000/chat/lobby/的房间页面。打开另一个浏览器选项卡到同一个房间页面。

In the second browser tab, type the message “hello” and press enter. You should now see “hello” echoed in the chat log in both the second browser tab and in the first browser tab.
在第二个浏览器选项卡中, 输入消息 "hello", 然后按 enter 键。在第二个浏览器选项卡和第一个浏览器选项卡中, 您现在应该看到 "hello" 在聊天日志中显示。

Now your chat server is fully asynchronous!
现在, 您的聊天服务器是完全异步的了!

 

Tutorial Part 4: Automated Testing
Tutorial 4 部分: 自动化测试

This tutorial begins where Tutorial 3 left off. We’ve built a simple chat server and now we’ll create some automated tests for it.
本教程在教程3的基础上开始。我们已经建立了一个简单的聊天服务器, 现在我们将为它创建一些自动化测试。

Testing the views
测试视图

To ensure that the chat server keeps working, we will write some tests.
为了确保聊天服务器能够继续工作, 我们将编写一些测试。

We will write a suite of end-to-end tests using Selenium to control a Chrome web browser. These tests will ensure that:
我们将编写一套端到端的测试, 使用 Selenium 来控制 Chrome web 浏览器。这些测试将确保:

• when a chat message is posted then it is seen by everyone in the same room
• 当一个聊天信息被发布, 然后它能被大家在同一房间看到
• when a chat message is posted then it is not seen by anyone in a different room
• 当一个聊天信息被发布, 那么它在不同的房间是不会被别人看到的

Install the Chrome web browser, if you do not already have it.
如果您尚未拥有 Chrome web 浏览器, 请安装它。

Install chromedriver.
安装 chromedriver。

Install Selenium. Run the following command:
安装 Selenium。运行以下命令:

$ pip3 install selenium

Create a new file chat/tests.py. Your app directory should now look like:
创建新的文件 chat/tests.py。您的应用程序目录现在应该看起来像:

chat/
    __init__.py
    consumers.py
    routing.py
    templates/
        chat/
            index.html
            room.html
    tests.py
    urls.py
    views.py

Put the following code in chat/tests.py:
在 chat/tests.py 中输入以下代码:

# chat/tests.py
from channels.testing import ChannelsLiveServerTestCase
from selenium import webdriver
from selenium.webdriver.common.action_chains import ActionChains
from selenium.webdriver.support.wait import WebDriverWait

class ChatTests(ChannelsLiveServerTestCase):
    serve_static = True  # emulate StaticLiveServerTestCase

    @classmethod
    def setUpClass(cls):
        super().setUpClass()
        try:
            # NOTE: Requires "chromedriver" binary to be installed in $PATH
            cls.driver = webdriver.Chrome()
        except:
            super().tearDownClass()
            raise

    @classmethod
    def tearDownClass(cls):
        cls.driver.quit()
        super().tearDownClass()

    def test_when_chat_message_posted_then_seen_by_everyone_in_same_room(self):
        try:
            self._enter_chat_room('room_1')

            self._open_new_window()
            self._enter_chat_room('room_1')

            self._switch_to_window(0)
            self._post_message('hello')
            WebDriverWait(self.driver, 2).until(lambda _:
                'hello' in self._chat_log_value,
                'Message was not received by window 1 from window 1')
            self._switch_to_window(1)
            WebDriverWait(self.driver, 2).until(lambda _:
                'hello' in self._chat_log_value,
                'Message was not received by window 2 from window 1')
        finally:
            self._close_all_new_windows()

    def test_when_chat_message_posted_then_not_seen_by_anyone_in_different_room(self):
        try:
            self._enter_chat_room('room_1')

            self._open_new_window()
            self._enter_chat_room('room_2')

            self._switch_to_window(0)
            self._post_message('hello')
            WebDriverWait(self.driver, 2).until(lambda _:
                'hello' in self._chat_log_value,
                'Message was not received by window 1 from window 1')

            self._switch_to_window(1)
            self._post_message('world')
            WebDriverWait(self.driver, 2).until(lambda _:
                'world' in self._chat_log_value,
                'Message was not received by window 2 from window 2')
            self.assertTrue('hello' not in self._chat_log_value,
                'Message was improperly received by window 2 from window 1')
        finally:
            self._close_all_new_windows()

    # === Utility ===

    def _enter_chat_room(self, room_name):
        self.driver.get(self.live_server_url + '/chat/')
        ActionChains(self.driver).send_keys(room_name + '\n').perform()
        WebDriverWait(self.driver, 2).until(lambda _:
            room_name in self.driver.current_url)

    def _open_new_window(self):
        self.driver.execute_script('window.open("about:blank", "_blank");')
        self.driver.switch_to_window(self.driver.window_handles[-1])

    def _close_all_new_windows(self):
        while len(self.driver.window_handles) > 1:
            self.driver.switch_to_window(self.driver.window_handles[-1])
            self.driver.execute_script('window.close();')
        if len(self.driver.window_handles) == 1:
            self.driver.switch_to_window(self.driver.window_handles[0])

    def _switch_to_window(self, window_index):
        self.driver.switch_to_window(self.driver.window_handles[window_index])

    def _post_message(self, message):
        ActionChains(self.driver).send_keys(message + '\n').perform()

    @property
    def _chat_log_value(self):
        return self.driver.find_element_by_css_selector('#chat-log').get_property('value')

Our test suite extends ChannelsLiveServerTestCase rather than Django’s usual suites for end-to-end tests (StaticLiveServerTestCase or LiveServerTestCase) so that URLs inside the Channels routing configuration like /ws/room/ROOM_NAME/ will work inside the suite.
我们的测试套件扩展了 ChannelsLiveServerTestCase, 而不是 Django 常用来进行端到端测试的套件 (StaticLiveServerTestCase 或 LiveServerTestCase), 这样, Channels 路由配置里面的 URLs(如 /ws/room/ROOM_NAME/ ) 将会在套件里面工作。

To run the tests, run the following command:
要运行测试, 请运行以下命令:

$ python3 manage.py test chat.tests

You should see output that looks like:
您应该看到如下所示的输出:

Creating test database for alias 'default'...
System check identified no issues (0 silenced).
..
----------------------------------------------------------------------
Ran 2 tests in 5.014s

OK
Destroying test database for alias 'default'...

You now have a tested chat server!
你现在有一个经过测试的聊天服务器了!

What’s next?
接下来应该做什么呢？

Congratulations! You’ve fully implemented a chat server, made it performant by writing it in asynchronous style, and written automated tests to ensure it won’t break.
祝贺！您已经完全实现了一个聊天服务器, 通过在异步样式中编写它来高性能, 并编写了自动测试以确保它不会中断。

This is the end of the tutorial. At this point you should know enough to start an app of your own that uses Channels and start fooling around. As you need to learn new tricks, come back to rest of the documentation.
这是教程的结尾。现在，你应该清楚地知道如何启动一个使用了 Channels 的你自己的应用程序和做其他的操作。当您需要学习新的技巧时, 请回到文档的其余部分。

 

作者： 守护窗明守护爱

出处： https://www.cnblogs.com/chuangming/p/9222794.html

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