Paho MQTT无法使用Flask（谷歌应用引擎）

Question

在我的Flask（谷歌应用程序引擎）应用程序中，我需要向Mosquitto代理发布消息，该代理在终端本地运行到端口1884。

    import paho.mqtt.client as mqtt
    # ...
    try:
        # publish.single("Car/Command1", dict, hostname='localhost', port=1884)
        client = mqtt.Client('Flask_Publisher')
        client.connect("localhost", 1884, 60)
        client.publish("mytopic", dict)
        client.disconnect()
    except Exception as e:
        logging.warning("Exception occurred: {}".format(e))
        error = e
    # ...

我通过键入以下命令在终端的端口1884上本地运行Mosquitto代理：sudo mosquitto -p 1884

出于测试目的，我编写了一个python脚本，它具有mqtt订阅者的角色。

但问题是，当我尝试运行Flask时，它会在尝试发布消息时给出以下错误（从Exception中捕获）：[Errno 13] Permission denied

编辑：完整的追溯

    ERROR    2018-08-30 16:47:52,665 wsgi.py:279] 
Traceback (most recent call last):
  File "/home/santoryu/Scrivania/google-cloud-sdk/platform/google_appengine/google/appengine/runtime/wsgi.py", line 267, in Handle
    result = handler(dict(self._environ), self._StartResponse)
  File "/home/santoryu/Scrivania/IOT/gae/lib/flask/app.py", line 2309, in __call__
    return self.wsgi_app(environ, start_response)
  File "/home/santoryu/Scrivania/IOT/gae/lib/flask/app.py", line 2295, in wsgi_app
    response = self.handle_exception(e)
  File "/home/santoryu/Scrivania/IOT/gae/lib/flask_cors/extension.py", line 161, in wrapped_function
    return cors_after_request(app.make_response(f(*args, **kwargs)))
  File "/home/santoryu/Scrivania/IOT/gae/lib/flask_restful/__init__.py", line 273, in error_router
    return original_handler(e)
  File "/home/santoryu/Scrivania/IOT/gae/lib/flask/app.py", line 1741, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/home/santoryu/Scrivania/IOT/gae/lib/flask/app.py", line 2292, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/santoryu/Scrivania/IOT/gae/lib/flask/app.py", line 1815, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/home/santoryu/Scrivania/IOT/gae/lib/flask_cors/extension.py", line 161, in wrapped_function
    return cors_after_request(app.make_response(f(*args, **kwargs)))
  File "/home/santoryu/Scrivania/IOT/gae/lib/flask_restful/__init__.py", line 273, in error_router
    return original_handler(e)
  File "/home/santoryu/Scrivania/IOT/gae/lib/flask/app.py", line 1718, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/home/santoryu/Scrivania/IOT/gae/lib/flask/app.py", line 1813, in full_dispatch_request
    rv = self.dispatch_request()
  File "/home/santoryu/Scrivania/IOT/gae/lib/flask/app.py", line 1799, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/home/santoryu/Scrivania/IOT/gae/app/handlers/my_handler.py", line 44, in funzione1
    client = mqtt.Client('Flask_Publisher')
  File "/home/santoryu/Scrivania/IOT/gae/lib/paho/mqtt/client.py", line 498, in __init__
    self._sockpairR, self._sockpairW = _socketpair_compat()
  File "/home/santoryu/Scrivania/IOT/gae/lib/paho/mqtt/client.py", line 238, in _socketpair_compat
    listensock.bind(("127.0.0.1", 0))
  File "/home/santoryu/Scrivania/google-cloud-sdk/platform/google_appengine/google/appengine/dist27/socket.py", line 227, in meth
    return getattr(self._sock,name)(*args)
  File "/home/santoryu/Scrivania/google-cloud-sdk/platform/google_appengine/google/appengine/api/remote_socket/_remote_socket.py", line 679, in bind
    raise _SystemExceptionFromAppError(e)
error: [Errno 13] Permission denied

Answer 1

问题是App Engine SDK提供了Python的socket模块的沙盒版本。当MQTT客户端库尝试绑定到本地端口时，它使用此沙盒模块而不是它期望的标准库模块，并且无法绑定到localhost。

在开发模式下运行时，可以通过将GAE socket模块替换为原始标准库模块来解决此问题，从而允许绑定到localhost。

在你的appengine_config.py文件中：

import os

# Only do the following if we're in development mode
if os.environ.get('SERVER_SOFTWARE', '').startswith('Development'):
    import imp
    import inspect

    # Whitelist the ssl and socket modules
    from google.appengine.tools.devappserver2.python import sandbox
    sandbox._WHITE_LIST_C_MODULES += ['_ssl', '_socket']

    # Use the standard library socket module instead
    real_os_src_path = os.path.realpath(inspect.getsourcefile(os))
    real_socket = os.path.join(os.path.dirname(real_os_src_path), 'socket.py')
    imp.load_source('socket', real_socket)