Metadata-Version: 1.1
Name: micropython-umqtt.robust2
Version: 2.1.1
Summary: MQTT client for MicroPython ("robust" version).
Home-page: https://github.com/fizista/micropython-umqtt.robust2
Author: Wojciech Banaś
Author-email: fizista+umqtt.robust2@gmail.com
License: MIT
Description: .. role:: bash(code)
           :language: bash
        
        .. role:: python(code)
           :language: python
        
        umqtt.robust2
        =============
        
        umqtt.robust2 is a MQTT client for MicroPython. (Note that it uses some
        MicroPython shortcuts and doesn't work with CPython). It consists of
        two submodules: umqtt.simple2_ and umqtt.robust2_. umqtt.robust2_ is built
        on top of umqtt.simple2_.
        
        Features of this library
        ------------------------
        * allows you to resume connection with the MQTT broker
        * allows you to send unsent messages when you resume a connection
        * allows you to subscribe to all previously subscribed topics once the connection is resumed
        * is resistant to errors in connections
        * you have clear information about the type of errors
        
        Differences between umqtt.robust and umqtt.robust2
        --------------------------------------------------
        
        * allows for easy programming of different strategies to maintain communication with the MQTT broker
        * works without blocking app
        * in case of network problems, it can send the data itself at a later time
        * we have the ability to track down errors
        * is larger than the previous one, so I recommend compiling this
          library to MPY files (especially for esp8266)
        
        Problems and solutions
        ----------------------
        * ImportError: no module named 'umqtt.robust2'
        
          Versions of micropython from http://micropython.org/download/ since version 1.12 include
          the umqtt library, which conflicts with the current library.
          To avoid conflicts, you need to change the order of importing libraries.
          You need to import the '/lib' libraries first and then the system libraries.
          Just add the following lines of code to the boot.py file:
        
        .. code-block:: python
        
            import sys
            sys.path.reverse()
        
        How and where to install this code?
        -----------------------------------
        This library requires the umqtt.simple2_ library.
        Therefore, please read this required library first,
        and then you can install this one.
        
        You can install using the upip:
        
        .. code-block:: python
        
            import upip
            upip.install("micropython-umqtt.robust2")
        
        or
        
        .. code-block:: bash
        
            micropython -m upip install -p modules micropython-umqtt.robust2
        
        
        You can also clone this repository, and install it manually:
        
        .. code-block:: bash
        
            git clone https://github.com/fizista/micropython-umqtt.robust2.git
        
        Manual installation gives you more possibilities:
        
        * You can compile this library into MPY files using the :bash:`compile.sh` script.
        * You can remove comments from the code with the command: :bash:`python setup.py minify`
        * You can of course copy the code as it is, if you don't mind.
        
        **Please note that the PyPi repositories contain optimized code (no comments).**
        
        **For more detailed information about API please see the source code
        (which is quite short and easy to review) and provided examples.**
        
        What does it mean to be "robust" ?
        ----------------------------------
        
        Modern computing systems are sufficiently complex and have multiple
        points of failure. Consider for example that nothing will work if
        there's no power (mains outage or battery ran out). As you may imagine,
        umqtt.robust2 won't help you with your flat battery. Most computing
        systems are now networked, and communication is another weak link.
        This is especially true for wireless communications. If two of your
        systems can't connect reliably communicate via WiFi, umqtt.robust2
        can't magically resolve that (but it may help with intermittent
        WiFi issues).
        
        What umqtt.robust2 tries to do is very simple - if while trying to
        perform some operation, it detects that connection to MQTT breaks,
        it tries to reconnect to it. That's good direction towards "robustness",
        but the problem that there is no single definition of what "robust"
        is. Let's consider following usecase:
        
        1. A temperature reading gets transmitted once a minute. Then the
        best option in case of a transmission error might be not doing
        anything at all - in a minute, another reading will be transmitted,
        and for slowly-changing parameter like a temperature, a one-minute
        lost reading is not a problem. Actually, if the sending device is
        battery-powered, any connection retries will just drain battery and
        make device "less robust" (it will run out of juice sooner and more
        unexpectedly, which may be a criteria for "robustness").
        
        We can also cache some of the results, as far as memory allows,
        until we try to connect again. This will increase the reliability
        of data delivery.
        
        2. If there's a button, which communicates its press event, then
        perhaps it's really worth to retry to deliver this event (a user
        expects something to happen when they press the button, right?).
        But if a button is battery-power, unconstrained retries won't do
        much good still. Consider mains power outage for several hours,
        MQTT server down all this time, and battery-powered button trying
        to re-publish event every second. It will likely drain battery
        during this time, which is very non-robust. Perhaps, if a press
        isn't delivered in 15 seconds, it's no longer relevant (depending
        on what press does, the above may be good for a button turning
        on lights, but not for something else!)
        
        3. Finally, let's consider security sensors, like a window broken
        sensor. That's the hardest case. Apparently, those events are
        important enough to be delivered no matter what. But if done with
        short, dumb retries, it will only lead to quick battery drain. So,
        a robust device would retry, but in smart manner, to let battery
        run for as long as possible, to maximize the chance of the message
        being delivered.
        
        Let's sum it up:
        
        a) There's no single definition of what "robust" is. It depends on
           a particular application.
        b) Robustness is a complex measure, it doesn't depend on one single
           feature, but rather many different features working together.
           Consider for example that to make button from the case 2 above
           work better, it would help to add a visual feedback, so a user
           knew what happens.
        
        As you may imagine, umqtt.robust2 doesn't, and can't, cover all possible
        "robustness" scenarios, nor it alone can make your MQTT application
        "robust". Rather, it's a barebones example of how to reconnect to an
        MQTT server in case of a connection error. As such, it's just one
        of many steps required to make your app robust, and majority of those
        steps lie on *your application* side. With that in mind, any realistic
        application would subclass umqtt.robust2.MQTTClient class and override
        add_msg_to_send() and reconnect() methods and will use the
        socket_timeout/message_timeout parameters to suit particular usage scenario.
        It may even happen that umqtt.robust2 won't even suit your needs, and you
        will need to implement your "robust" handling from scratch.
        
        
        Persistent and non-persistent MQTT servers
        ------------------------------------------
        
        Consider an example: you subscribed to some MQTT topics, then connection
        went down. If we talk "robust", then once you reconnect, you want any
        messages which arrived when the connection was down, to be still delivered
        to you. That requires retainment and persistency enabled on MQTT server.
        As umqtt.robust2 tries to achieve as much "robustness" as possible, it
        makes a requirement that the MQTT server it communicates to has persistency
        enabled. This include persistent sessions, meaning that any client
        subscriptions are retained across disconnect, and if you subscribed once,
        you no longer need to resubscribe again on next connection(s). This makes
        it more robust, minimizing amount of traffic to transfer on each connection
        (the more you transfer, the higher probability of error), and also saves
        battery power.
        
        However, not all broker offer true, persistent MQTT support:
        
        * If you use self-hosted broker, you may need to configure it for
          persistency. E.g., a popular open-source broker Mosquitto requires
          following line::
        
            persistence true
        
          to be added to ``mosquitto.conf``. Please consult documentation of
          your broker.
        
        * Many so-called "cloud providers" offer very limited subset of MQTT for
          their free/inexpensive tiers. Persistence and QoS are features usually
          not supported. It's hard to achieve any true robustness with these
          demo-like offerings, and umqtt.robust2 isn't designed to work with them.
        
        
        .. _umqtt.simple2: https://github.com/fizista/micropython-umqtt.simple2
        .. _umqtt.robust2: https://github.com/fizista/micropython-umqtt.robust2
Keywords: mqtt micropython
Platform: UNKNOWN
Classifier: Programming Language :: Python :: Implementation :: MicroPython
