MQTT server for Erlang.

Introduction

The server implements MQTT messaging protocol version 3.1, 3.1.1, 5.0 and allows communicate with MQTT clients to send/receive messages. The server is written in Erlang. The server was tested with following clients:

1. Mosquitto command line tools subscriber and publisher
2. Javascript web-socket MQTT client HiveMQ
3. Erlang MQTT client

Messenger implementation based on the MQTT server.

Simple Instant messenger SIM was created to test functionality of the MQTT server and prove good performance of the code. Live demo of SIM is running here.

Architecture

The server consist of two OTP applications: core MQTT server and restful HTTP server for managing users DB. The both apps are combined in one release and are working closely.

Core MQTT server

Core MQTT server is an OTP application that implements MQTT protocol versions 3.1, 3.1.1 and 5.0. It depends on other Erlang applications:

1. lager for logging service,
2. cowboy for tcp, tls and web-socket (ws and wss) connections,
3. msql_client for connection to MySQL server see,
4. mqtt_common that is library keeping code that is common for MQTT client and server implementation.

Resful Http server

Http server implements Restful API described in OpenAPI configuration file mqtt_rest_v3.yaml. There is swagger page of running instance of MQTT Rest Http server.

Backend database implementation

Session state data is storing in database (DETS or MySQL in current version). Developing of Mnesia support is in progress.

Connection types

Server can establish connection using different network protocols:

1. clear it/tcp
2. tls/ssl
3. web socket
4. secure web socket

Getting started

Installation

To start with the server you have to complete two steps below:

1. Install Erlang.
2. Install Rebar3.

Building

Download or clone from SourceForge GIT repository or from GitHub

Download source code to local host. Type command

$ git clone https://git.code.sf.net/p/mqtt-server/code erl.mqtt.server

or

$ git clone https://github.com/alekras/erl.mqtt.server.git erl.mqtt.server

Compiling

After you have got source code of the server then change directory to the erl.mqtt.server:

$ cd erl.mqtt.server

Run rebar3 for this project. You have to add path to rebar3 to OS PATH variable or just use the whole path:

$ /opt/local/bin/rebar3 compile

Rebar will fetch code of all dependencies and compile source files of main project and all dependencies.

Starting

To start server run bash script:

$ ./start_mqtt_server.sh

Erlang shell will open and log statements are appearing in console.

Using relx

To make release of the application for development run command:

$ /opt/local/bin/rebar3 release -n mqtt_server_dev

for production:

$ /opt/local/bin/rebar3 release -n mqtt_server

Go to folder:

$ cd _build/prod/rel/mqtt_server_dev

and run command to start server:

$ bin/mqtt_server_dev console

Example of script to make release and start server is here

Testing

You can test the server with any MQTT client complained with protocol version 3.1.1 or 5.0. I recommend to try Erlang MQTT client or client.

Testing with Mosquitto tools

To test with Mosquitto tools you need to open two terminal windows. One for subscribing and other for publishing. Open the first terminal windows and change directory to folder where Mosquitto is installed:

$ cd /usr/local/Cellar/mosquitto/1.4.10/

Now subscribe to "test/c" topic:

$ bin/mosquitto_sub -t test/c -p 18883 -i test -u guest -P guest -V mqttv5

Open the second terminal windows and change directory to Mosquitto installation:

$ cd /usr/local/Cellar/mosquitto/1.4.10/

Publish some message to "test/c" topic:

$ bin/mosquitto_pub -t test/c -p 18883 -i test1 -u guest -P guest -m "Test message from mosquitto tools QoS=2" -q 2 -V mqttv5

In first terminal you will see incoming message:

$ Test message from mosquitto tools QoS=2

Testing with other MQTT clients

The server was tested with other clients:

1. Websocket MQTT client from HiveMQ [http://www.hivemq.com/demos/websocket-client/].
2. MQTT Erlang client [https://github.com/alekras/mqtt_client.git].

Configuration

To set up ports for TCP and TLS socket connection go to config[-dev]/sys.config. This is OTP application configuration file contained startup data for lager, ranch and mqtt server backend type and connection details.

Add/Remove users

Rest HTTP server allows to manage users table on backend DB. If you start server on local environment you can reach swagger page as http://localhost:8080/rest/v3/swagger-ui.

References

1. [https://mosquitto.org/] - Mosquitto MQTT server.
2. [https://www.rabbitmq.com/] - RabbitMQ server with MQTT plugin.
3. [https://sourceforge.net/projects/mqtt-client/] - Erlang MQTT client.
4. [http://www.hivemq.com/demos/websocket-client/] - MQTT websocket client.