Refactor DOHClient URL completion

[SukkaW]

Follows #96, cc @lsongdev

📑 Description

• Re-add pathname auto completion, but this time only for input w/o any /
  • So 1.0.0.1 and dns.google will become https://1.0.0.1/dns-query and https://dns.google/dns-query
  • But https://1.0.0.1 will still be https://1.0.0.1
• URL.searchParams is mutable and manipulatable, we don't need to re-assign a string to .search
• Prefer URL.href over URL.toString()
• Passes URL object directly to http.get, https.get, and h2.get
  • All three implementations accept URL type; we don't need to convert the URL to a string here.

✅ Checks

• My pull request adheres to the code style of this project
• My code requires changes to the documentation
• I have updated the documentation as required
• All the tests have passed

[lsongdev]

I’m a bit concerned this behavior might be too implicit. For example, dns.google and https://dns.google would resolve differently (one gets /dns-query appended, the other not), which could be confusing.

Any thoughts please let me know.

[SukkaW]

I’m a bit concerned this behavior might be too implicit. For example, dns.google and https://dns.google would resolve differently (one gets /dns-query appended, the other not), which could be confusing.

Any thoughts please let me know.

While the vast majority of DoH servers serve at the /dns-query path, there are some edge cases where a DoH server serves at the root path. Here are a few examples:

• dns.nextdns.io (and anycast.dns.nextdns.io)
• zero.dns0.eu (which is also powered by NextDNS)
• basic.rethinkdns.com

While many of those examples actually also serve on /dns-query as well, such edge cases should not be overlooked.

On the other hand, there are many DoH servers serving at other paths:

• https://dns.bebasid.com/unfiltered
• https://internetsehat.bebasid.com/adblock (also https://dns.bebasid.com/dns-oisd and https://dns.bebasid.com/dns-hagezi)
• https://doh.cleanbrowsing.org/doh/family-filter (also https://doh.cleanbrowsing.org/doh/adult-filter)
• https://freedns.controld.com/p0 (also https://freedns.controld.com/p1, https://freedns.controld.com/p2, and https://freedns.controld.com/p3)
• https://odvr.nic.cz/doh
• https://dns.dnswarden.com/uncensored

So we expect:

• We can auto-complete https:// and /dns-query for the vast majority of DoH servers:
  • dns.google -> https://dns.google/dns-query
  • 1.0.0.1-> https://1.0.0.1/dns-query
  • [2a09::] -> https://[2a09::]/dns-query
• We can not auto-complete the path for input with a specified path, but we still can auto-complete the HTTPS protocol:
  • odvr.nic.cz/doh -> https://odvr.nic.cz/doh
  • dns.bebasid.com/unfiltered -> https://dns.bebasid.com/unfiltered
  • Actually, we want this to work as well: zero.dns0.eu/ -> https://zero.dns0.eu/
• We can not auto-complete the path for an input that looks like an exact URL (since the path might/could be explicit):
  • https://dns.google/dns-query -> do nothing
  • https://doh.cleanbrowsing.org/doh/family-filter -> do nothing
  • https://dns.nextdns.io and https://dns.nextdns.io/ -> should also do nothing because those servers serve at the root path as well.