feat: allow custom service name for mDNS

[erhant]

Description

The mdns protocol always uses _p2p._udp (see here) as its service name.

We should be able to provide our own service name for mDNS instead.

Motivation

Multiple protocols on a single node using libp2p-mdns will collide due to service name, and have to resolve their collision at application level / other protocol's level (e.g. different gossipsub topic).

It makes most sense to allow a specific service name for the developer, also makes diagnostics with dns-sd command much easier.

Requirements

• Allow service name to be provided from Config
• Ensure that service name is well-formed (RFC6763 section 7)

Open questions

No response

Are you planning to do it yourself in a pull request?

Maybe

[elenaf9]

The hardcoded _p2p._udp.local service name is part of the libp2p specs¹.

Still, I agree that it is a realistic use-case that multiple protocols, or even multiple nodes in the same private network, need isolated mDNS discovery.
The default should still be _p2p._udp.local, but we can make it part of the config that a user can overwrite.

CC @jxs wdyt?

Footnotes

1. https://github.com/libp2p/specs/blob/master/discovery/mdns.md#request ↩

[erhant]

I would like to piggyback this issue with another question as well, is there a way for the user to add their custom TXT records? This would be reaaaallllly useful for my case, if possible 🙏🏻

[jxs]

Hi, thanks for the ping @elenaf9, this has been discussed before on #2898 and a spec issue was opened libp2p/specs#620 I think this should be discussed at the spec level.