# Learn MQTT with Go

Learning MQTT with Golang by doing. This repo is a simple example of using a Golang application as a client (pub & sub) of an MQTT broker.

1883, Eclipse Mosquitto unsecured (opening the port on the internet is not recommended).


## Architecture

![mqtt-arch](./img/mqtt-architecture.svg)

Ideally I would like this application to resemble the above design. Conceptually, there 

## Development

For local development we use [Mosquitto](https://mosquitto.org/) as our MQTT broker, with TLS enabled. 

```
sudo apt install mosquitto-clients
```

First generate local development certs using:

```
make gen-local-tls-certs
```

This will create CA, server, and client certificates suitable for local development. Server and CA certs are created in `./.mosquitto/certs`. The client cert is create in the project root. 

Start the local development environment with:

```
make start-dev
```

Stop the local development environment with:

```
make stop-dev
```

### Testing

Unit tests can be run with:

```
make test
```

Integration tests are run via:

```
make test-integration
```

## Usage

To run the application end to end first start the development server:

```
make start-dev
```

Next we can start our subscriber. The following command connects to the TLS listener port.

```
go run cmd/subscriber/main.go --host 0.0.0.0 --port 8883
```


## Design Considerations

See [DESIGN_CONCIDERATIONS.md](./DESIGN_CONCIDERATIONS.md)

## Resources:

- [Mosquitto Docs](https://mosquitto.org/man/mosquitto-8.html)
- [Mosquitto TLS Tutorial](https://cedalo.com/blog/mqtt-tls-configuration-guide/)
- [Golang MQTT Tutorial](https://www.emqx.com/en/blog/how-to-use-mqtt-in-golang)
- [MQTT as a Service](https://cedalo.com/mqtt-broker-pro-mosquitto/)
- [Using Wireshark for MQTT Analysis](https://cedalo.com/blog/wireshark-mqtt-guide/)
- [Caddy as reverse proxy](https://github.com/caddyserver/caddy)
- [Using Python paho MQTT client with TLS](https://cedalo.com/blog/configuring-paho-mqtt-python-client-with-examples/)
- [ESP32 Micropython MQTT with TLS](https://dev.to/bassparanoya/esp32-micropython-mqtt-tls-28fd): Note cert file format for uPy MQTT client needs to be in .der format which is a binary format.
- [TLS refresher](http://www.steves-internet-guide.com/ssl-certificates-explained/)
- [HA Mosquitto in K8s](https://sko.ai/blog/how-to-run-ha-mosquitto/)
- [Lamport Timestamps Tutorial](https://towardsdatascience.com/understanding-lamport-timestamps-with-pythons-multiprocessing-library-12a6427881c6)
- [Vector Clocks Lecture](https://www.youtube.com/watch?v=x-D8iFU1d-o)