fix(dns): allow http:// DoH resolvers

[lidel]

This PR allows people to run own DNS over HTTP(S) resolver on the same box or within same secure LAN, without setting up unnecessary TLS certs.

Main use case is to simplify self-hosting of ENS resolves by gateway operations etc.

• relax https://github.com/libp2p/go-doh-resolver/blob/f2e25860684789200e3a3a911dc9a74d01771d5b/resolver.go#L55
• [ ] relax https://github.com/multiformats/go-multiaddr-dns (if needed) (doesn't appear to be needed)
• test end-to-end with localhost resolver

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 60.56%. Comparing base (17db35a) to head (3a62179).

Files with missing lines	Patch %	Lines
gateway/dns.go	0.00%	1 Missing and 1 partial ⚠️

@@            Coverage Diff             @@
##             main     #645      +/-   ##
==========================================
+ Coverage   60.55%   60.56%   +0.01%     
==========================================
  Files         245      245              
  Lines       31126    31126              
==========================================
+ Hits        18848    18853       +5     
+ Misses      10607    10598       -9     
- Partials     1671     1675       +4     

Files with missing lines	Coverage Δ
gateway/dns.go	60.00% <0.00%> (+22.22%)	⬆️

... and 11 files with indirect coverage changes

[aschmahmann]

I don't think this is going to be enough:
https://github.com/libp2p/go-doh-resolver/blob/f2e25860684789200e3a3a911dc9a74d01771d5b/resolver.go#L55

Note: AFAICT there is no DNS-over-HTTP spec for some reason it's specified as being over HTTPS, however I definitely see your point and have definitely felt the pain over the self-signed cert dance just to run local resolvers

[lidel]

Yep, filled this PR because I am looking at https://github.com/libp2p/go-doh-resolver and https://github.com/multiformats/go-multiaddr-dns to wire up TTL (to fix #329 (comment) for DNSLinks), so likely will relax things there as well, and get back to this PR draft.

[aschmahmann]

TODO: Fix after libp2p/go-doh-resolver#28 is released

[aschmahmann]

Main use case is to simplify self-hosting of ENS resolves by gateway operations etc.

This PR works and for tools like CoreDNS that support DNS over HTTP (and not just HTTPS) this might be enough. If there's not enough support here folks might end up asking us for DNS over UDP / TCP support, but we can tackle that as the need arises.

For what it's worth a nice thing about pushing on DNS-over-HTTP is that it makes it easier for folks who want to self-host while also using web-browsers since UDP/TCP are not available to javascript in browsers. For some cases like ENS this might not be a big deal since they can wrap the Ethereum JSON-RPC, but it might matter for other name systems.

[aschmahmann]

Updated the comment above given that CoreDNS does support DNS-over-HTTP in addition to DNS-over-HTTPS.

FYI CoreDNS (and therefore the CoreDNS ENS resolver) supports DNS-over-HTTP, although the UX for this is that you configure listening on "https://" rather than "http://" and just not pass a certificate (which is what tripped me up initially 😅).

I think we should be good to go on a merge here, pending reviews.