[client] Always log dns forwader responses

[lixmal]

Describe your changes

The forwarder was missing logging for cases like REFUSED when a domain was queried that was not (yet) configured.

Issue ticket number and link

Stack

Checklist

• Is it a bug fix
• Is a typo/documentation fix
• Is a feature enhancement
• It is a refactor
• Created tests that fail without the change (if possible)

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Documentation

Select exactly one:

• I added/updated documentation for this change
• Documentation is not needed for this change (explain why)

Docs PR URL (required if "docs added" is checked)

Paste the PR link from https://github.com/netbirdio/docs here:

https://github.com/netbirdio/docs/pull/__

Summary by CodeRabbit

• Improvements
  • Enhanced DNS response handling with improved timing accuracy and consistency.
  • Optimized UDP response processing for better reliability.
  • Improved error handling and logging during DNS forwarding operations.

[coderabbitai]

📝 Walkthrough

Walkthrough

The pull request refactors DNS forwarder's response handling by propagating timing information through the query handler chain, centralizing response writing via a new helper function, and introducing UDP-specific truncation logic through a wrapper. Method signatures are updated to pass timing context throughout.

Changes

Cohort / File(s)	Summary
Core DNS Forwarding Logic client/internal/dnsfwd/forwarder.go	Propagated startTime parameter into handleDNSQuery and handleDNSError for time-aware logging. Centralized DNS response writing through new writeResponse helper, eliminating inline response writes. Introduced udpResponseWriter wrapper for UDP-specific EDNS0 size truncation. Unified domain variable naming to lowercased qname. Adjusted call flow between UDP/TCP handlers to funnel through updated handlers with timing context.
Test Updates client/internal/dnsfwd/forwarder_test.go	Updated test calls to handleDNSQuery to include time.Time parameter. Changed response retrieval from method return values to GetLastResponse on writer object. Adjusted assertions to work with new response retrieval pattern and nil/non-nil expectations.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• [client] Fix DNS forwarder returning broken records on 4 to 6 mapped IP addresses #4887: Also modifies client/internal/dnsfwd/forwarder.go's handleDNSQuery function, with potential interaction between timing changes and address unmapping logic.

Suggested reviewers

• pappz

Poem

🐰 Hops of timing, writes consolidated clear,
Response helpers funnel far and near,
UDP truncation wraps with care,
DNS flows with freshened flair! ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 44.44% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the main change: improving DNS forwarder logging to always log responses, which aligns with the raw summary's description of propagating startTime for time-aware logging and centralizing response writing.
Description check	✅ Passed	The PR description covers the key section (Describe your changes) explaining the bug fix intent, marks it as a bug fix, and confirms documentation is not needed. However, the Issue ticket number section is empty and no explanation is provided for why documentation isn't needed.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch improve-dns-forwarder-logs

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
1 Accepted issue

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarQube Cloud