如何查看渠道消费者引发的异常

Question

我开始使用django-channels，我觉得它很棒。然而调试消费者很痛苦，因为当消费者内部引发一些异常时，终端不会打印任何内容，websocket 只是断开连接。

未显示的异常类型不明显识别。 AssertionError 和其他一些系统都是这种情况，例如下面的代码：

class MexicoProgressConsumer(ProgressConsumer):
    def init(self, SSDBConfig, Sub_application):
        subappli = models.Sub_application.objects.get(pk=Sub_application)
        ...

使用错误数量的参数调用此方法不会在控制台上打印任何内容并断开 websocket。如果最后一行的 get 失败，则同上。

有没有办法将这些异常视为其他异常？

Answer 1

从 albar 的 answer 开始，我达到的解决方案是定义一个这样的装饰器

from functools import wraps
from logging import getLogger

from channels.exceptions import AcceptConnection, DenyConnection, StopConsumer

logger = getLogger("foo-logger")

def log_exceptions(f):
    @wraps(f)
    async def wrapper(*args, **kwargs):
        try:
            return await f(*args, **kwargs)
        except (AcceptConnection, DenyConnection, StopConsumer):
            raise
        except Exception as exception:
            if not getattr(exception, "logged_by_wrapper", False):
                logger.error(
                    "Unhandled exception occurred in {}:".format(f.__qualname__),
                    exc_info=exception,
                )
                setattr(exception, "logged_by_wrapper", True)
            raise

    return wrapper

这有几个改进：

• 使用 functools.wraps 使包装的函数更接近原始函数。
• 使用 async/await 语法，因为我使用的是异步消费者（如果不是，请删除）
• 不记录 django-channels 故意引发的多个异常。
• 仅在没有设置logged_by_wrapper 属性时记录异常。这导致异常只记录一次，因为我们在第一次记录后设置了属性。
• 使用python内置的logging模块来记录错误。这会自动格式化异常和回溯，因为我们在 exc_info=exception 中提供了异常。

然后，我定义了一个类装饰器来代替基类，以将其应用于消费者的方法

from inspect import iscoroutinefunction

def log_consumer_exceptions(klass):
    for method_name, method in list(klass.__dict__.items()):
        if iscoroutinefunction(method):
            setattr(klass, method_name, log_exceptions(method))

    return klass

这会将log_exceptions 应用于 Consumer 中定义的所有异步方法，但不适用于它继承的方法 - 即仅适用于我们为 Consumer 自定义的方法。

Answer 2

我找到了解决问题的方法。我先定义一个装饰器：

import traceback
def catch_exception(f):
    def wrapper(*args, **kwargs):
        try:
            return f(*args, **kwargs)
        except StopConsumer:
            raise
        except Exception as e:
            print(traceback.format_exc().strip('\n'), '<--- from consumer')
            raise
    return wrapper

然后我为我的所有消费者定义一个基类，以这种方式使用这个装饰器：

import inspect
class BaseConsumer(JsonWebsocketConsumer):
    def __getattribute__(self, name):
        value = object.__getattribute__(self, name)
        if inspect.ismethod(value):
            return catch_exception(value)
        return value

但仍然存在 2 个问题：

• 通常显示的异常会出现两次
• 其他异常重复3或4次！ （好像每个级别的类层次结构都会触发）

第一种情况（KeyError）的例子：

Traceback (most recent call last):
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 19, in wrapper
    return f(*args, **kwargs)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 31, in wrapper
    result = f(owner, **kwargs)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 110, in refresh
    data = super().refresh.__wrapped__(self)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 73, in refresh
    pvalue = round(data['toto'] * 100, 1)
KeyError: 'toto' <--- from consumer
Exception in thread Thread-3:
Traceback (most recent call last):
  File "/usr/lib/python3.6/threading.py", line 916, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.6/threading.py", line 864, in run
    self._target(*self._args, **self._kwargs)
  File "/home/alain/ADN/simutool/dbsimu/utils.py", line 193, in repeat
    self.repeat_func()
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 19, in wrapper
    return f(*args, **kwargs)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 31, in wrapper
    result = f(owner, **kwargs)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 110, in refresh
    data = super().refresh.__wrapped__(self)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 73, in refresh
    pvalue = round(data['toto'] * 100, 1)
KeyError: 'toto'

第二种情况的示例（拼写错误的变量）：

WebSocket CONNECT /ws/dbsimu/Simuflow_progress/ [127.0.0.1:55866]
Traceback (most recent call last):
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 19, in wrapper
    return f(*args, **kwargs)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 57, in receive_json
    return getattr(self, icommand)(**data)
NameError: name 'icommand' is not defined <--- from consumer
Traceback (most recent call last):
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 19, in wrapper
    return f(*args, **kwargs)
  File "/home/alain/.local/lib/python3.6/site-packages/channels/generic/websocket.py", line 125, in receive
    self.receive_json(self.decode_json(text_data), **kwargs)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 19, in wrapper
    return f(*args, **kwargs)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 57, in receive_json
    return getattr(self, icommand)(**data)
NameError: name 'icommand' is not defined <--- from consumer
Traceback (most recent call last):
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 19, in wrapper
    return f(*args, **kwargs)
  File "/home/alain/.local/lib/python3.6/site-packages/channels/generic/websocket.py", line 60, in websocket_receive
    self.receive(text_data=message["text"])
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 19, in wrapper
    return f(*args, **kwargs)
  File "/home/alain/.local/lib/python3.6/site-packages/channels/generic/websocket.py", line 125, in receive
    self.receive_json(self.decode_json(text_data), **kwargs)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 19, in wrapper
    return f(*args, **kwargs)
  File "/home/alain/ADN/simutool/dbsimu/consumers.py", line 57, in receive_json
    return getattr(self, icommand)(**data)
NameError: name 'icommand' is not defined <--- from consumer

如果有人想解决这个问题，请提出建议。