Consolidiffication of DNS requests for a host.

[Jorropo]

TL;DR:

While implementing DNS over Tor for anonymity we faced the impossibilities to proxy the DNS requests made by libp2p and libs using it, we should try to fix that.

Current status

I've identified 3 resolver spots and each one has a problem :

• basichost#Host.maResolver: no codepath available to set it with a custom DialFunc or resolver, underused.
• go-dnslink#defaultResolver: no codepath available to set it, unsafe to set (racy), mixed Parser + Resolver object
• go-multiaddr-dns#DefaultResolver: unsafe to set (racy)

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Proposed changes

Important (non breaking, or minor breaking):

• go-dnslink:
  • split the dns / parsing part, sets the default exposed methods to use go-multiaddr-dns#DefaultResolver as backend.

Need more discussion:

• Basic Host:
  • Add an DNSResolver options to go-libp2p#New, this would sets the basichost#Host.maResolver with a custom *madns.Resolver as argument.
  • Changes all internal usages in a host to using this internal resolver (might already be done idk, I will have to check).
• host#Host
  • Exposes an API on the interface (maybe an optional extension of the interface ?) for dns, madns and dnslink releated requests.
  • Change go-ipfs to use this new API.

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When we came to a consensus about that I'll be happy to implement it (I'll probably throw an ugly api and many replace go.mod rules since).

[aschmahmann]

I agree that having a more configurable way to issue DNS requests that doesn't involve setting a global variable is a reasonable idea 👍.

However, I think a good deal of this is either done already or is an application level issue (e.g. ipfs/kubo#6532).

• go-dnslink: I'm up for accepting changes here but AFAICT nobody is using is this library. Perhaps with some changes here we could use it instead of separately doing DNSLink resolution in go-ipfs's namesys module (e.g. https://github.com/ipfs/go-ipfs/blob/2ed9254426e900cf00a9b35304dc5b5de8173208/namesys/dns.go#L28)
• BasicHost: It seems like this can be set by utilizing a custom MultiaddrResolver

  go-libp2p/p2p/host/basic/basic_host.go

  Line 230 in fcf6964

  h.maResolver = opts.MultiaddrResolver

@Jorropo is there something I'm missing here, and if not is this issue closable?

[Jorropo]

BasicHost: It seems like this can be set by utilizing a custom MultiaddrResolver

There isn't any go-libp2p#Option who sets opts.MultiaddrResolver, I guess I can add one.

[Stebalien]

Fixed by

go-libp2p/options.go

Line 469 in d38694b

func MultiaddrResolver(rslv *madns.Resolver) Option {

.