Proof-of-concept of a fully distributed MQTT broker for the IoT. Uses Twister platform, Bitcoin and Bittorrent protocols.
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README.md
alice.json
bob.json
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README.md

A fully distributed MQTT broker proof-of-concept, based on Mosquitto and Twister.

Motivation

See here. Now, let's get started.

Disclaimer

It's only a proof-of-concept, and uses Twister network for illustration purposes, as it provides all the required features. But please, please, don't bother the users of this service. Thank you.

Installation

Instructions are available for Linux only, for now. Sorry about that. Note that as this project is only a single Python script, the issues you may encounter are more likely to come from somewhere else. :)

Assuming you'll have everything installed into your $HOME:

  • You'll need a working Python 3 installation.
  • Grab the latest Mosquitto source from the official repository, and compile it. Don't run "make install" as it is not required.
  • Grab the latest Twister source (twister-core) from GitHub, and compile it. That's often a bit trickier, but YMMV. Again, there is no need to run "make install".
  • Clone this repository.

You should end up with three directories: "mosquitto", "twister-core" and "mosquitto-twister", all located under your $HOME.

Now run:

./twister-core/src/twisterd

and follow the instructions. Use the recommended defaults. Now you will have to create two users. I created mqtt_alice and mqtt_bob on purpose, but obviously, you can't use them. Use your imagination and create two different users. Follow the instructions here. Basically, all yo have to do (twice) is:

./twisterd createwalletuser myname
./twisterd sendnewusertransaction myname
./twisterd newpostmsg myname 1 "hello world"

Please note that you might have to wait a bit before the third command actually works, as it may take some time for your username to be validated at the blockchain level.

Now install the required Python libraries:

pip install paho-mqtt
pip install git+https://github.com/jgarzik/python-bitcoinrpc.git

and you should be ready to go.

Running the software

Here is the parts involved, from end-to-end:

  • A first MQTT client (1), that will pulish a message, using...
  • A first MQTT broker (2), to which will be also connected...
  • A first instance of the mosquitto-twister bridge (3), associated to the first Twister user, that will relay the message through the Twister network through...
  • A single instance of the Twister daemon (4), assuming you're using one single box. If you want to test with two boxes, you'll have to run one instance per box. The daemon is responsible for relaying the messages of the network to...
  • A second instance of the mosquitto-twister bridge (5), associated to the second Twister user, connected to...
  • A second MQTT broker (6), that will relay messages to...
  • A second MQTT client (7), that subscribed to the MQTT topic the message belongs to.

You'll have to run the involved parts in this order: (4) then (2),(6) then (3),(5) then (7) then (1) at the very end. Phew!

You'll end up running (in a different shell per command):

cd $HOME; ./twister-core/src/twisterd
cd $HOME/mosquitto; ./src/mosquitto -p 1883
cd $HOME/mosquitto; ./src/mosquitto -p 2883
cd $HOME/mosquitto-twister; python main.py alice.json
cd $HOME/mosquitto-twister; python main.py bob.json
cd $HOME/mosquitto; LD_LIBRARY_PATH=./lib ./client/mosquitto_sub -p 2883 -t doors/\#
cd $HOME/mosquitto; LD_LIBRARY_PATH=./lib ./client/mosquitto_pub -t doors/1 -m empty

Here are the expected output of the first bridge:

Checking user status for [mqtt_alice]...
Checking following list...
Expecting at least: mqtt_alice, mqtt_bob
Got: mqtt_alice, mqtt_bob, torlus
Checking subscriptions...
Got: fridges/#, earrings/#
Getting latest public posts...
Getting latest direct messages...
MQTT: Connected successfully.
MQTT: Message received.
Sending direct message to mqtt_bob:{"topic": "doors/1", "payload": "ZW1wdHk=", "qos": 0}
Done.

And here what you should expect from the second bridge:

Checking user status for [mqtt_bob]...
Checking following list...
Expecting at least: mqtt_bob, mqtt_alice
Got: mqtt_alice, mqtt_bob
Checking subscriptions...
Got: doors/#
Getting latest public posts...
Getting latest direct messages...
MQTT: Connected successfully.
match(sub): doors/#:sensors/temperature/sensor1
match(sub): doors/#:doors/1
b'empty'
MQTT: Message 2 published.

Details

General idea

My first idea has been to patch Mosquitto to add support for Kademlia DHT, and that's why I started this fork.

However, apart form getting a distributed set of nodes, there were many other issues to address. Some of them are perfectly addressed by Twister, some others are yet to be figured out:

  • User identification. This one's addressed by a Bitcoin-like blockchain, where transactions correspond to user registrations. Incentive here is the ability given to whoever find the hash value to get the right to publish an advertising message.
  • Topics subscriptions. Here, they are stored in a per-user basis, in their profile. Which, well, does the job, as crawling the user base isn't so expensive, as you have to retreive the blockchain locally anyway. Then the profile details, stored in the DHT, carry the list of topics in which the user is interested in.
  • In my initial idea, the concept of Users wasn't as central as it is in Twister. But it seems that is not really an issue. Even more, the "following/followers" model fits nicely with the "publisher/subscriber" one. And it even makes more sense when dealing with private data (mapped to direct messages), where both parts need to follow each other.
  • One thing I'd like to address somehow is the ability to publish data "anonymously", i.e that data be really distributed across the network, with a location-specific addressing based on the topic, instead of the users. This rises up some issues about searching. I'm looking forward to make something with this kind oh hash functions.

Implementation

Finding the Twister project (and Mosquitto's Python library as well, donated to Eclipse Paho) allowed me to write a proof-of-concept in two days by hcking some Python, instead of spending months with C or C++ which is fine. :)

However there are of course some limitations:

  • MQTT QoS levels > 0 are not handled properly, as the delivery is ack'ed at the broker level by the mosquitto-twister bridge which is seen as a client. To properly handle that, some modifications should be done at the broker/bridge level, and an acknowledgment message should be carried across the Twister network for QoS = 2 type of messages.
  • The "Retain" rules haven't been taken into account as well. I haven't check the rules about multiple subscribers/topics delivery.
  • For more efficiency, I guess that messages batching should be considered at some point.

Acknowledgments

Developers working on Mosquitto, Twister, Bittorrent, Bitcoin.

Juliusz Chroboczek for his DHT code.

And to all the people fighting against "control freaks".


Gregory Estrade