* [x] Support custom Modbus transports (Sungrow WiNet-S has been implemented)
* Modbus RTU has not been tested because I don't have a serial Modbus device, but in principle it should work. Please let me know
* [x] Support reading input registers
* [x] Support reading holding registers
* [ ] Support _setting_ holding registers
* [ ] Support optional auto-configuration of Home Assistant entities, including using [MQTT Number](https://www.home-assistant.io/integrations/number.mqtt/) et al for holding registers, to allow setting the value.
* [ ] TLS MQTT connections
* [ ] WebSocket MQTT connections
NOTE: For the time being, this does not support MQTTv5.
For now, `cargo install` is the easiest way to install. Either run it in a checkout for the latest development version, or run `cargo install modbus-mqtt` to install the latest release version.
If you don't want to set up the Rust toolchain, you can likely found built binaries as build artifacts in the GitHub Actions tab above.
In the future, there will also be Docker images made available for convenience.
The supported protocols are currently just `tcp://`/`mqtt://`, but with intent to support: `mqtts://`, `ssl://`/`tls://`, `ws://`, and `wss://`.
The default topic which ModbusMQTT monitors and to which it publishes is `modbus-mqtt`. You can vary that by changing the path portion of the MQTT URL.
Further, you can change other MQTT options by using query params, such as setting a custom client_id:
```sh
"mqtt://1.2.3.4/?client_id=$CUSTOM_CLIENT_ID"
```
For a full list of supported options, check [the MQTT client library's source code](https://github.com/bytebeamio/rumqtt/blob/c6dc1f7cfb26f6c1f676954a51b398708d49091a/rumqttc/src/lib.rs#L680-L768).
### Connecting to Modbus devices
To connect to a Modbus device, you need to post the connection details to MQTT under a topic of `$prefix/$connection_id/connect`. It is intended that such messages are marked as **retained** so that ModbusMQTT reconnects to your devices when it restarts.
For instance, a simple config might be:
```jsonc
// PUBLISH modbus-mqtt/solar-inverter/connect
{
"host": "10.10.10.219",
"proto": "tcp",
}
```
If the connection is successful, you will see the following message like the following sent to the MQTT server:
```jsonc
// modbus-mqtt/solar-inverter/state
"connected"
```
#### Full connection examples
All fields accepted (optional fields show defaults)
```jsonc
{
// Common fields
"address_offset": 0, // optional
"unit": 1, // optional, aliased to "slave"
// TCP:
"proto": "tcp",
"host": "1.2.3.4",
"port": 502, // optional
// RTU / Serial:
"proto": "rtu",
"tty": "/dev/ttyACM0",
"data_bits": "Eight", // optional (TODO: accept numeric and lowercase)
// valid: Five, Six, Seven, Eight
"stop_bits": "One", // optional (TODO: accept numeric and lowercase)
Post to `$MODBUS_MQTT_TOPIC/$CONNECTION_ID/$TYPE/$ADDRESS` where `$TYPE` is one of `input` or `holding` with the following payload (optional fields show defaults):
When issuing the `connect` payload, you can optionally include a top-level `registers` array, containing the above register schema. When present, these payloads will be replayed to the MQTT server as if the user had specified each register separately, as above.
