Using `dns-sd` with `libp2p-mdns`

Summary

I am unable to use dns-sd tool with libp2p-mdns. See below for more info.

Expected behavior

I will give an example over another crate, mdns-sd. Suppose we register a service _p2p._udp with our hostname foobar there. Then, we will see ourself with:

$ dns-sd -B _p2p._udp
A/R    Flags  if Domain               Service Type         Instance Name
Add        3  11 local.               _p2p._udp.           foobar

We can then query that service instance as well:

$ dns-sd -Q _p2p._udp.local. PTR
A/R  Flags         IF  Name                          Type   Class  Rdata
Add  40000003      11  _p2p._udp.local.            PTR    IN     foobar._p2p._udp.local.

We can follow that PTR value to get SRV and TXT records:

# service records
$ dns-sd -Q foobar._p2p._udp.local. SRV
A/R  Flags         IF  Name                          Type   Class  Rdata
Add  40000003       1  foobar._p2p._udp.local.     SRV    IN     0 0 3456 <something-here>

# additional records
$ dns-sd -Q foobar._p2p._udp.local. TXT
A/R  Flags         IF  Name                          Type   Class  Rdata
Add  40000003      11  foobar._p2p._udp.local.     TXT    IN     9 bytes: <some bytes here>

Actual behavior

Looking at the chat example, I would expect to how the mDNS implementation responds to the dns-sd tool.

Of course at first nothing appears when we are not running the service:

# see a p2p related service
dns-sd -Q _services._dns-sd._udp.local PTR | grep p2p

# or directly query the service name:
dns-sd -Q _p2p._udp.local. PTR  

Then I do cargo run within the chat example, and we can immediately see some results:

$ dns-sd -Q _services._dns-sd._udp.local PTR | grep p2p 
Add  2             12  _services._dns-sd._udp.local. PTR    IN     _p2p._udp.local.

$ dns-sd -Q _p2p._udp.local. PTR    
A/R  Flags         IF  Name                          Type   Class  Rdata
Add  40000003      12  _p2p._udp.local.              PTR    IN     PJ2Adr3Zp8KKry1ftPa0wckURooHtuaQq9abVx2ZjL.
Add  40000003      12  _p2p._udp.local.              PTR    IN     BtLsbrMhFqOLJxqb4IH91BWuy4PmXIHkJDWZr8VE.
Add  40000003      12  _p2p._udp.local.              PTR    IN     evwca28w1FbzKvilNd3entoeSD2OYf0XZZfC.
Add  40000003      12  _p2p._udp.local.              PTR    IN     akG3qYT6xxTfmEIl8c0akPhB7HeaUb4l86CuW.
Add  40000003      12  _p2p._udp.local.              PTR    IN     hsEIRIw3O9gwZSUAvtoFIG5nVTxHyWpR.
Add  40000002      12  _p2p._udp.local.              PTR    IN     Ip5EpyxGobOBKCgTItmJAK0mRgEoNyNXV.
Add  3             12  _p2p._udp.local.              PTR    IN     4AEDDykQHCi7lnaZAlhRtOZ2PElE9PENgEouK4HiMRubEhXJK0bMObeGYHr.
Add  2             12  _p2p._udp.local.              PTR    IN     b8Kl6NpZR7HLZqbgYVqHKAV6u2Xwso8Z52fmdmxmXhlzmacyQE.

At this point, I couldn't see how I could query the SRV and TXT records as is expected in the standard. Normally we should be able to query those records, like:

dns-sd -Q 4AEDDykQHCi7lnaZAlhRtOZ2PElE9PENgEouK4HiMRubEhXJK0bMObeGYHr. SRV  
dns-sd -Q 4AEDDykQHCi7lnaZAlhRtOZ2PElE9PENgEouK4HiMRubEhXJK0bMObeGYHr. TXT 

but these do not return any response.

When we look at the libp2p mdns spec we also see that we should be able to query with <peer-id>.<service>, but I wasn't able to get any response with that as well.

It also does not respond to dns-sd -B _p2p._udp. with an instance name.

Relevant log output

Possible Solution

Not a solution for this library maybe, but I would love to have info one how one can perhaps integrate the mentioned mdns-sd crate as a Behaviour for libp2p.

Version

0.55.0

Would you like to work on fixing this bug?

Maybe

Start with the chat example and the libp2p-mdns implementation referenced by the report, then compare its responses with the linked libp2p mDNS specification. Reproduce the dns-sd PTR, SRV, TXT, and browsing queries against the example. Done means the expected query behavior is implemented or the compatibility limitation and integration guidance are documented.