Use advertisement data in publish_topic name using placeholders

[konfilios]

Hi there and thanks for the great work!

I am using gateway in order to convert BLE advertisments to MQTT and then mostly consume the MQTT messages from telegraf for further processing. I have enough BLE devices to publish tens to hundreds of messages per scan.

The problem is that the per-id topic is too fine whereas the top-level topic of gateway is too coarse.

It would be very helpful if one could define a publish_topic in the settings which contains placeholders (in whatever format or convention) corresponding to fields of the advertisment packet. For example, one could define a publish topic as follows:

• home/TheengsGateway/BTtoMQTT/{address_safe} that would be what you get now, i.e. a fixed prefix plus the MAC/id in uppercase without the colons
• home/{local_name:none}/{address_safe} where {local_name} would be the device name advertised in the BLE packet or none if it is not set
• home/{manufacturer_id}-
• etc

Following this idea, one could define placeholders even for vendor- or device- specific payload fields and just use a predefined string as default value in case that field is not defined in the message

This way I could define a much more focused topic e.g. in telegraf (let's say that would only match the manufacturer or a device local name) and reduce further processing requirements