DNS-SD Service Discovery

[besmarsh]

Is your enhancement proposal related to a problem? Please describe.

DNS-SD (DNS-based Service Discovery) is a standard method for enabling discovery of services on a local IP network. DNS-SD consists of two parts, Service Advertisement, and Service Discovery. Zephyr currently supports the Service Advertisement part of DNS-SD, but does not support the Service Discovery part.

DNS-SD is one of the 3 core aspects of Zero-Configuration Networking, along with IP Autoconfiguration and mDNS, both of which are supported by Zephyr. The Service Discovery part of DNS-SD is the missing part to enable a Zephyr device to fully work in a Zero-Configuration Networking environment.

Describe the solution you'd like

This enhancement proposal is for implementing the Service Discovery part of DNS-SD. Much of the groundwork is already present, as DNS-SD builds on top of standard DNS, which is already implemented.

The implementation should likely provide an API to discover services through DNS-SD, similar to the existing DNS API for resolving hostnames. As multiple instances can exist for a given service, a consumer of the API should in some way be provided with a list of discovered service instances, from which a service instance can be chosen and resolved using the standard DNS API.

The DNS-SD implementation should work with both unicast DNS and multicast DNS (mDNS).

Describe alternatives you've considered

DNS-SD is the accepted standard solution for local IP network service discovery. I don't know of any alternatives which would be better to support.

Additional context

• RFC 6763 is the IETF RFC for DNS-SD
• Some experimentation was done earlier this year by another Zephyr contributor - main...Ayush1325:zephyr:zeroconf

[Ayush1325]

Great proposal. I would love this in the mainline.

I had to pause the previous work since I came across some problems with networking on beagleconnect freedom in Zephyr mainline (#71191, #68674). I can pick it up again once I get all the other parts of networking on bcf resolved. Of course, it is also fine if someone else wants to pick it up (since it might take me a few weeks to get around to working on this).