Added topic filtering Plugin

[romancardenas]

I have developed a new version of HBMQTT which supports topic filtering. This is: you can define a topic filtering plugin in order to grant or deny subscriptions to certain topics, depending on the policy you want.
For that, I have created the hbmqtt/plugins/topic_checking.py file, where I developed a very silly topic filtering policy: If you want to subscribe to prohibited, top-secret or data/classified topics, your username must be admin. Otherwise, you will not be subscribed. You may take this example as a template for designing your own topic policy.

How to try it

After downloading this fork, execute the following python commands on the hbmqtt directory:

python3 setup.py build
python3 setup.py install

You can notice that this commit also adds a line in this script: This is necessary for the namespace to being able to detect the new plugin.

After that, you will execute three processes:

• python3 samples/broker_taboo.py
  This starts an MQTT broker with topic_taboo plugin enabled. This can be configured via the configuration parameter of the broker:

config = {
    'listeners': {
        'default': {
            'type': 'tcp',
            'bind': '0.0.0.0:1883',
        },
        'ws-mqtt': {
            'bind': '127.0.0.1:8080',
            'type': 'ws',
            'max_connections': 10,
        },
    },
    'sys_interval': 10,
    'auth': {
        'allow-anonymous': True,
        'password-file': os.path.join(os.path.dirname(os.path.realpath(__file__)), "passwd"),
        'plugins': [
            'auth_file', 'auth_anonymous'
        ]

    },
    'topic-check': {
        'enabled': True,
        'plugins': [
            'topic_taboo'
        ]
    }
}

• python3 samples/client_subscribe_taboo.py
  This starts an MQTT client that will try to subscribe to a valid topic and a forbidden topic

• python3 samples/client_publish_taboo.py
  This starts an MQTT client that will publish two messages in the valid and the forbidden topic.
  The console of the client subscribed will only receive the valid message.

[coveralls]

Coverage remained the same at ?% when pulling 59f9d28 on romancardenas:master into 0d6030c on beerfactory:master.

[coveralls]

Coverage remained the same at ?% when pulling 59f9d28 on romancardenas:master into 0d6030c on beerfactory:master.

[PythonLinks]

This is a really good idea for corporate chat servers. Have a tree of topics, but only allow certain users to see certain topics. Perhaps some of the MQTT servers support access control lists, but that becomes very cumbersome. Much better to call a Python function.

The next thing I need are tools to store the messages by topic, one file for each topic. I would think that this is a very common need, and yet I am having difficulty finding such a tool . Here is the only such tool I have found.
http://www.steves-internet-guide.com/simple-python-mqtt-data-logger/
Are any others out there?

[romancardenas]

I will check that upgrade. I am now working on a project where security and privacy is very important, so I really need a broker able to filter subscriptions.
I am working now on a new version able to filter publications, but I would prefer this repository to accept my contributions one by one. In this way, the upgrades would be maintained by the whole community, which is a great opportunity to enrich this project.