sanitize_rfc1035: return early on error at start

[rsmarples]

Fixes a heap overflow found by runnint test with a sanitizer. Fixes #5

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: ed510202-8ee6-4735-8035-9f865778a2a9

📥 Commits

Reviewing files that changed from the base of the PR and between 6d411f2 and a3ac70a.

📒 Files selected for processing (1)

• src/common.c

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Walkthrough

Modified sanitize_rfc1035() in src/common.c to return an error value immediately when an invalid condition is detected at the start of the input buffer, rather than continuing with sanitization steps.

Changes

Cohort / File(s)	Summary
Heap overflow fix src/common.c	Added early return statements in sanitize_rfc1035() to exit the function immediately when p == start triggers an error condition, preventing further buffer processing.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main change: returning early from sanitize_rfc1035 when an error occurs at the start of input.
Description check	✅ Passed	The description relates to the changeset by referencing the heap overflow fix in sanitize_rfc1035 and linking to issue #5, which documents the overflow problem.
Linked Issues check	✅ Passed	The PR addresses the heap-buffer-overflow in sanitize_rfc1035 reported in issue #5 by returning early on error at the start, preventing the overflow condition.
Out of Scope Changes check	✅ Passed	All changes are scoped to fixing the heap overflow in sanitize_rfc1035 as required by issue #5; no out-of-scope modifications are present.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch sanitize

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