A simple MQTT server

Final program for the UNIX programming in C class at MFF
UK during winter semester 23/24.

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MQTT is a simple publish-subscribe network protocol. A
server/broker recieves messages from clients and
broadcasts them to subscribers.

See the MQTT spec [1] for details.

This project implements a less-than-minimal MQTT broker
capable of servicing only the most basic requests. For
example it only supports QoS 0.

`$ make` - normal build
`$ make EXTERNFLAGS="-DDEBUG -DCOLOR -g"` - debug build

Just to make sure: DO NOT ACTUALLY USE THIS.

This is a project for me to learn about UNIX systems and
socket programming (also to get a credit). Developing a
practically usable MQTT server is a non-goal.

[1] docs.oasis-open.org/mqtt/mqtt/v3.1.1

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Author: Jan Doskočil