About

An Elixir app to investigate the possibility of building RSMP 4 on top of MQTT.

Initial code from: https://www.emqx.com/en/blog/mqtt-for-elixir

Prerequisites

Elixir >= 1.15 Erlang 25 (not 26)

Dependencies

emqtt is an Erlang MQTT library (Erlang can be used in Elixir).

NOTE: The emqtt libriary is currently incompatible with the latest Erlang 26, see: emqx/emqtt#196

Instead you must install Erlang 25, and a version of Elixir is compiled with that OTP version. The easiest way to do this is to install Erlang and Elixir with rtx, see e.g: https://github.com/jdx/rtx

After installing rtx, you can install the correct version of Elixir and Erlang (which is specified in .tool-versions) with:

rtx install`

If you're on macOS 14 Sonoma, Erlang 25 does work unless you build if without JIT. You can do this with:

KERL_CONFIGURE_OPTIONS="--disable-jit" rtx install

If you downgrade an existing Erlang 26, you might need to remove all project dependencies and reinstall.

Once Elixir and Erlang are installed, you can install project dependencies with:

% mix deps.get

Run Broker

Run the EMQX mqtt broker in a docker container, see https://www.emqx.io:

docker run -d --name emqx -p 1883:1883 emqx/emqx

Run app

% mix run --no-halt

Troubleshooting

If you get the error Application rsmp exited: shutdown, then please check that the broker is running and reachable on port 1883 - see above.

Interacting

You can interact with the RMSP client using iex, the interactive Elixir shell.

code/rsmp_mqtt (main) % iex -S mix
Erlang/OTP 25 [erts-13.2.2.3] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1] [jit:ns]

10:34:54.354 [info] Starting RSMP with pid #PID<0.190.0>
Interactive Elixir (1.15.5) - press Ctrl+C to exit (type h() ENTER for help)

iex(2)> rsmp = Process.whereis(RSMP)
#PID<0.190.0>

iex(3)> :sys.get_state(RSMP)        
%{
  interval: 1000,
  pid: #PID<0.191.0>,
  plan: 1,
  status: %{1 => 0},
  timer: #Reference<0.1086325504.2114453507.137317>
}
iex(4)> RSMP.set_status(rsmp,1,3)   
:ok