dns: return localhost IP directly

[LiviaMedeiros]

Fixes: #44804
Fixes: #54111
Not fully fixes yet: #50871
Partially related to: #44003

As per RFC 6761 6.3,

2. Application software MAY recognize localhost names as special, or
   MAY pass them to name resolution APIs as they would for other
   domain names.

3. Name resolution APIs and libraries SHOULD recognize localhost
   names as special and SHOULD always return the IP loopback address
   for address queries and negative responses for all other query
   types. Name resolution APIs SHOULD NOT send queries for
   localhost names to their configured caching DNS server(s).

I think we should recognize localhost. zone as special and return immediately, without relying on getaddrinfo(3), /etc/hosts, etc..

[nodejs-github-bot]

Review requested:

• @nodejs/net
• @nodejs/security-wg

[mcollina]

We can't return an ipv6 address if we don't have the matching interface.

Also, this can be customized by the host, and I think it would be better
to leave as is.

[LiviaMedeiros]

We can't return an ipv6 address if we don't have the matching interface.

Agreed. I think something similar can also be done within net subsystem or libuv; if low-enough-cost check for IPv6 support is feasible there.

We can also make fast-path exclusively for cases where we must return only IPv4 (which would add inconsistency, i'd be -1 myself).

Also, this can be customized by the host, and I think it would be better
to leave as is.

Not sure how spec-compliant customizations are... But if it might break on some systems, probably not worth changing it.

---

Closing this. For future references, proper check here would be something closer to RegExpPrototypeExec(/^(?:.+\.)?localhost\.?$/i, hostname)

[codecov]

Codecov Report

❌ Patch coverage is 84.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.04%. Comparing base (a6696e2) to head (86d24c8).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/dns.js	86.66%	1 Missing and 1 partial ⚠️
lib/internal/dns/promises.js	80.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #63368      +/-   ##
==========================================
- Coverage   90.06%   90.04%   -0.02%     
==========================================
  Files         714      714              
  Lines      225522   225589      +67     
  Branches    42636    42662      +26     
==========================================
+ Hits       203110   203128      +18     
- Misses      14196    14259      +63     
+ Partials     8216     8202      -14     

Files with missing lines	Coverage Δ
lib/dns.js	98.17% <86.66%> (-0.47%)	⬇️
lib/internal/dns/promises.js	97.85% <80.00%> (-0.44%)	⬇️

... and 45 files with indirect coverage changes

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