fix: preserve trailing slash in joinURL when path is "/" (#134)

[SAY-5]

Closes #134. The path === "/" early-return dropped the slash so joinURL("/maildev", "/") returned "/maildev" instead of "/maildev/", causing redirect loops with sub-path-mounted upstreams. Treat root-path as a real path and let the trailing/leading slash logic produce the correct join. Per @pi0 in #134 ("PR welcome!").

Summary by CodeRabbit

• Bug Fixes

  • Fixed URL path joining to correctly preserve single trailing slashes in certain cases.

• Tests

  • Added tests to verify trailing-slash handling in URL path operations.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 0c3cd289-29e3-4bd9-bfad-57a423ec690f

📥 Commits

Reviewing files that changed from the base of the PR and between 9dc2425 and 79703f8.

📒 Files selected for processing (2)

• src/_utils.ts
• test/_utils.test.ts

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📝 Walkthrough

Walkthrough

The joinURL function is refined to handle trailing slashes more precisely. Previously, the function treated both falsy path and path === "/" as early-return cases; now only falsy path triggers early return, allowing "/" to be joined normally. Two test cases verify the behavior for both a standalone "/" path and the case where both base and path end with "/".

Changes

Trailing slash handling in joinURL

Layer / File(s)	Summary
joinURL trailing slash logic and validation src/_utils.ts, test/_utils.test.ts	The early-return condition in joinURL is narrowed to only trigger on falsy path, allowing path === "/" to proceed through normal joining logic. Two new test cases validate that "/" paths are joined correctly and that multiple trailing slashes are collapsed to a single slash.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Possibly related issues

• joinURL drops trailing slash when path is "/", breaks proxying to apps mounted on a sub-path #134: Directly related; both changes modify joinURL to stop treating path === "/" as an early-return case and preserve trailing slash behavior.

Poem

🐰 A slash was treated like a ghost,
But now it joins the joining post.
With logic refined, the path flows true,
Single slashes shine right through! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and accurately describes the main change: fixing joinURL to preserve trailing slashes when the path is "/". It directly addresses the core issue and aligns perfectly with the PR objectives.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
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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✨ Finishing Touches

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