fix(dns): fold domain case as ASCII, matching the reverse-DNS parser

[chet]

Summary

normalize_domain folded domain case with to_lowercase (Unicode-aware), while arpa_qname_to_ip (the reverse-DNS parser from #2637) uses to_ascii_lowercase. DNS names are ASCII (RFC 1123) and case-insensitivity is ASCII-scoped (RFC 4343), so this aligns normalize_domain to the same ASCII primitive — the two now fold case identically, by construction.

• to_lowercase → to_ascii_lowercase: no change for a valid ASCII domain; the two differ only on non-ASCII input, which is not valid in a DNS name.
• The debug log moves to structured (logfmt) fields.
• The test now covers the case folding it had skipped — its only input was already lowercase — with an uppercase and a mixed-case name.

Addresses CodeRabbit's open comment on #2691. Supports #2637; part of the #2630 (reverse DNS) effort.

Draft pending review.

[chet]

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📥 Commits

Reviewing files that changed from the base of the PR and between f947966 and 6641f5f.

📒 Files selected for processing (1)

• crates/api-db/src/dns/mod.rs

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Summary by CodeRabbit

• Refactor

  • Improved DNS domain normalization logic with enhanced structured logging for better observability.

• Tests

  • Expanded test coverage for domain normalization with multiple input/output scenarios to ensure reliability across edge cases.

Walkthrough

normalize_domain is updated to use to_ascii_lowercase() instead of a generic lowercasing method, and its debug log is refactored from a formatted string to a structured tracing event with named input and normalized fields. The corresponding unit test is expanded from a single assertion to a value_scenarios!-driven parametric table.

Changes

normalize_domain: ASCII lowercasing, structured logging, and test coverage

Layer / File(s)	Summary
ASCII lowercasing, structured debug log, and parametric unit tests crates/api-db/src/dns/mod.rs	normalize_domain now calls to_ascii_lowercase() and emits a structured tracing::debug! with discrete input and normalized fields. test_normalize_domain_name is replaced by a value_scenarios! table exercising trailing-dot stripping and ASCII case folding across multiple input variants.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related PRs

• NVIDIA/infra-controller#2691: Modifies the same normalize_domain function in crates/api-db/src/dns/mod.rs, introducing to_ascii_lowercase() and expanding test coverage via value_scenarios!, directly overlapping with this PR's scope.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title directly and precisely identifies the core change: switching from Unicode-aware to ASCII case folding in the DNS domain normalization function to match the reverse-DNS parser behavior.
Description check	✅ Passed	The description thoroughly explains the rationale (RFC compliance), the technical change (to_lowercase → to_ascii_lowercase), and test improvements, demonstrating clear understanding of the changeset.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Service	Total	Critical	High	Medium	Low	Other
boot-artifacts-aarch64	3	0	0	3	0	0
boot-artifacts-x86_64	3	0	0	3	0	0
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