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mqtt-kat

mqtt-kat is an attempt at an MQTT broker based on the concepts of http-kit. As http-kit this means low level java code to do the handling of the NIO and decoding and encoding of the MQTT packets. MQTT packets are en/decoded to Clojure maps and handled by Clojure code to do all the clever stuff a broker needs to do.

The idea is to see if a MQTT Broker could be as scalable as http-kit and handle as many concurrent connection as http-kit does.

What does it do at the moment?

Well... with the latest push it can actually forward a PUBLISHed message to multiple clients that have SUBSCRIBEd to a particular topic. I have tested this with three subscribers concurrently.

Are there any bugs?

Yes!

Loads. Too many to mention actually. But here are a few I know of:

  • Disconnecting clients in error cases is not fully implemented.
  • At the moment the message flows for good path QOS 0, 1 and 2 is in place. But there is no error recovery if one of the packets gets lost. So no resending of packets.
  • Also latency is rather high, to be investigated.

What about the name?

I first thought of calling it mqtt-kit... but then decide that mqtt-kat made more sense. Somehow.

Will it ever be a proper MQTT broker supporting QOS > 0?

Probably not.

Will it ever support MQTT version 5?

Probably not.

And here are some links with info to help me:

https://gist.github.com/Botffy/3860641

http://tutorials.jenkov.com/java-nio/non-blocking-server.html

http://docs.oasis-open.org/mqtt/mqtt/v5.0/csprd01/mqtt-v5.0-csprd01.html

http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/errata01/os/mqtt-v3.1.1-errata01-os-complete.html#_Toc442180846

https://github.com/http-kit/http-kit

https://github.com/eclipse/paho.mqtt.java

https://lispcast.com/3-things-java-can-steal-from-clojure/

https://gist.github.com/yukaizhao/155d931326e298d6404f

https://crunchify.com/java-nio-non-blocking-io-with-server-client-example-java-nio-bytebuffer-and-channels-selector-java-nio-vs-io/

http://rox-xmlrpc.sourceforge.net/niotut/

Usage

I call (start) function in the repl and then use an MQTT client to send packets to it and wait for it to crash.

Thank you

First of all an extra big thank you to Feng Shen for making http-kit. I have borrowed heavily from his code. And also a big thank you to the Eclipse Paho Project. I have used their code as inspiration as well and yes I have copied the MQTT packet length code from them.

And also a big thank you for the people from ClojureWerkz for their triennium library. It just works.

License

Copyright © 2018 Thomas van der Veen

Distributed under the Apache License Version 2.0.