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python - 组和通道层使流程停止而不会引发异常

问题描述

从这个非常简单的工作代码示例开始：

from channels.generic.websocket import JsonWebsocketConsumer

class IsacomptaManagementFeesConsumer(JsonWebsocketConsumer):
    pass

从 javascript 连接到此 websocket 使用者时，这按预期工作。连接正确发出，我得到以下日志：

WebSocket HANDSHAKING /manager/accounting/isacompta/2020/03/management-fees.ws [192.168.96.1:38108]
WebSocket CONNECT /manager/accounting/isacompta/2020/03/management-fees.ws [192.168.96.1:38108]
WebSocket DISCONNECT /manager/accounting/isacompta/2020/03/management-fees.ws [192.168.96.1:38108]

现在，如果我将代码更改为以下代码，以使用组：

from channels.generic.websocket import JsonWebsocketConsumer

class IsacomptaManagementFeesConsumer(JsonWebsocketConsumer):
    groups = ['foobar']

然后，连接失败。JavaScript 控制台告诉我：

Firefox can’t establish a connection to the server at ws://antoine.cocoonr.hq:3001/manager/accounting/isacompta/2020/03/management-fees.ws.
error { target: WebSocket, isTrusted: true, srcElement: WebSocket, currentTarget: WebSocket, eventPhase: 2, bubbles: false, cancelable: false, defaultPrevented: false, composed: false, timeStamp: 7804, … }

服务器日志如下所示：

WebSocket HANDSHAKING /manager/accounting/isacompta/2020/03/management-fees.ws [192.168.96.1:38128]
WebSocket DISCONNECT /manager/accounting/isacompta/2020/03/management-fees.ws [192.168.96.1:38128]

但在服务器端没有引发异常。

我也可以在不使用组的情况下获得类似的行为。让我们看一个更大的工作代码示例：

from channels.generic.websocket import JsonWebsocketConsumer

class IsacomptaManagementFeesConsumer(JsonWebsocketConsumer):

    def connect(self):
        print("one")
        self.accept()
        print("two")
        self.send_json({'text': "Foobar"})
        print("three")

此代码工作正常，连接正确发出，这里是服务器日志：

WebSocket HANDSHAKING /manager/accounting/isacompta/2020/03/management-fees.ws [192.168.96.1:38168]
one
WebSocket CONNECT /manager/accounting/isacompta/2020/03/management-fees.ws [192.168.96.1:38168]
two
three
WebSocket DISCONNECT /manager/accounting/isacompta/2020/03/management-fees.ws [192.168.96.1:38168]

但是，如果我对我的代码进行以下小改动：

from asgiref.sync import async_to_sync
from channels.generic.websocket import JsonWebsocketConsumer

class IsacomptaManagementFeesConsumer(JsonWebsocketConsumer):

    def connect(self):
        print("one")
        self.accept()
        print("two")
        async_to_sync(self.channel_layer.send)(self.channel_name, {
            'type': 'foobar.send',
            'text': "Foobar",
        })
        print("three")

    def foobar_send(self, event):
        print("AAA")
        self.send_json({'text': event['text'])
        print("BBB")

然后，连接正确发出但立即关闭，进程停止，没有机会打印“三”，函数“foobar_send”也没有执行。

WebSocket HANDSHAKING /manager/accounting/isacompta/2020/03/management-fees.ws [192.168.96.1:38224]                                                                                                                                                                             
one                                                                                                                                                                                                                                                                             
WebSocket CONNECT /manager/accounting/isacompta/2020/03/management-fees.ws [192.168.96.1:38224]                                                                                                                                                                                 
two                                                                                                                                                                                                                                                                             
WebSocket DISCONNECT /manager/accounting/isacompta/2020/03/management-fees.ws [192.168.96.1:38224]

我不明白为什么没有打印“三”，同时也没有引发异常。这意味着异常被?self.channel_layers.send()的调用者引发并静默捕获。IsacomptaManagementFeesConsumer.connect()

写完最后一段后，我决定试一试：

import traceback

from asgiref.sync import async_to_sync
from channels.generic.websocket import JsonWebsocketConsumer

class IsacomptaManagementFeesConsumer(JsonWebsocketConsumer):

    def connect(self):
        print("one")
        self.accept()
        print("two")
        try:
            async_to_sync(self.channel_layer.send)(self.channel_name, {
                'type': 'foobar.send',
                'text': "Foobar",
            })
        except Exception as e:
            print(e)
            traceback.print_stack()
        print("three")

    def foobar_send(self, event):
        print("AAA")
        self.send_json({'text': event['text'])
        print("BBB")

就是这样，有一个隐藏的“找不到文件”错误：

WebSocket HANDSHAKING /manager/accounting/isacompta/2020/03/management-fees.ws [192.168.96.1:42562]
one
WebSocket CONNECT /manager/accounting/isacompta/2020/03/management-fees.ws [192.168.96.1:42562]
two
[Errno 2] No such file or directory
  File "/usr/lib64/python3.6/threading.py", line 884, in _bootstrap
    self._bootstrap_inner()
  File "/usr/lib64/python3.6/threading.py", line 916, in _bootstrap_inner
    self.run()
  File "/usr/lib64/python3.6/threading.py", line 864, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/lib64/python3.6/concurrent/futures/thread.py", line 69, in _worker
    work_item.run()
  File "/usr/lib64/python3.6/concurrent/futures/thread.py", line 56, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/home/tony/.venvs/cocoonr/lib/python3.6/site-packages/channels/db.py", line 14, in thread_handler
    return super().thread_handler(loop, *args, **kwargs)
  File "/home/tony/.venvs/cocoonr/lib/python3.6/site-packages/asgiref/sync.py", line 277, in thread_handler
    return func(*args, **kwargs)
  File "/home/tony/.venvs/cocoonr/lib/python3.6/site-packages/channels/consumer.py", line 105, in dispatch
    handler(message)
  File "/home/tony/.venvs/cocoonr/lib/python3.6/site-packages/channels/generic/websocket.py", line 39, in websocket_connect
    self.connect()
  File "/home/tony/Workspace/cocoonr/billing/consumers.py", line 32, in connect
    traceback.print_stack()
three
WebSocket DISCONNECT /manager/accounting/isacompta/2020/03/management-fees.ws [192.168.96.1:42562]

我将 Django 3.0 与 Channels 2.4.0 和 channels-redis 2.4.2 一起使用。这是我的 CHANNEL_LAYERS 设置：

 CHANNEL_LAYERS = {                                                                                                                                                          
     'default': {                                                                                                                                                                                                                                                         
         'BACKEND': 'channels_redis.core.RedisChannelLayer',                                                                                                                                                                                                                
         'CONFIG': {                                                                                                                                                                                                                                                       
             'hosts': [                                                                                                                                                                                                                                            
                 {                                                                                                                                                                                                                                                 
                     'address': get_env('CHANNELS_REDIS_HOST',                                                                                                                                                                                          
                                        default='localhost:6379'),                                                                                                                                                                             
                     'password': get_env('CHANNELS_REDIS_PASSWORD',                                                                                                                                                                             
                                         default=None),                                                                                                                                                                                          
                     'db': 1,            
                 },                                                                                                                                  
             ],                                                                                                                                   
         },                                                                                                                                                        
     },                                                                                                                                                        
 }

标签： pythondjangoredisdjango-channelsasgi

解决方案

问题 #1340已经解决了错误被隐藏的事实。

至于 FileNotFoundError 本身，它是由错误的address值引起的。它应该传递为'redis://localhost:6379/'，而不是'localhost:6379'。

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