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SRV records

Sean Conner sean at conman.org

Sun Jun 28 03:55:52 BST 2020

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It was thus said that the Great Evert Pot once stated:

Dear list,

I would like to play around with Gemini and build a personal site. I'd

love to be able to host it on my main domain at gemini://evertpot.com/

Okay, so you are running a service on port 1965 that *isn't* Gemini, andyou would like to run a Gemini server on a different port, but not have tospecify the port number on the URL. Okay, got it.

It occurred to me that it would be nice if I could use DNS SRV records

to point gemini:// clients to a different host. However, after reading

the spec it doesn't seem like there is support for this.

I would love support for this, but or that to be realistically useful,

it would have to be in the spec and required. I know a lot of HTTP folks

wish they had that from the start too, as it's a pain to adopt later.

Like you, I wouldn't mind seeing SRV records used more often, but thereare considerations. First off, the dismal state of DNS resolution libariesout there. For the most part, they pretty much do too much (have their ownnetwork driver that is hard to integrate into an existing network basedprogram) and do too little (very little support for non A/AAAA records---youmight get lucky and get MX support).

I was fed up enough to write my own DNS encoding/decoding library [1] butthat only helps if you use C (or Lua---I include Lua bindings in thelibrary) and you still need to integrate your own networking with it [3].

Second, the code needs to be aware that multiple SRV records for a givenservice can exist, and how to order the results and pick one.

And the use of SRV records impact clients more than servers. Instead ofnow, where a client can go:

location = breakdown(url) address = getaddrinfo(location.host,location.port or 1965)

you now need:

results = lookup(RR_SRV,location.host) if results then sort(results) /* based upon priority and weight */ /* if not done by the lookup() routine */ for each result in results do address = getaddrinfo(result.host,result.port) if address then break end end if not address then address = getaddrinfo(location.host,location.port or 1965) end

Keep in mind the above is "get the idea" pseudocode, not real code.

I couldn't find in the archives if this has been asked before.

It has not.

-spc (The client now needs to know which DNS server to query, and how does it obtain *that* information?)

[1] https://github.com/spc476/SPCDNS [2]

[2] My most popular Github project if going by stars.

[3] A lot easier than with the other DNS libraries I've come across, but it still needs to be done.