proxy: preserve trailing slash through path.Join and strip_path

[c-tonneslan]

Closes #1266.

The switch to path.Join in ConfigureBackendURL drops a trailing slash from the proxied path. Combined with the existing strip_path strings.Replace, a request to /some/path/ with strip_path: /some ended up at /path on the upstream instead of /path/.

Remember whether the inbound path had a trailing slash and add it back after the strip step. Two regression cases added to TestConfigureBackendURL.

Summary by CodeRabbit

• Bug Fixes

  • Fixed an issue where trailing slashes in request paths were not being preserved during URL forwarding.

• Tests

  • Added test cases to verify proper handling of trailing slash preservation in path configurations.

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All committers have signed the CLA.

[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 Plus

Run ID: 71d4b8e8-2537-4cab-b277-742fdaf3bfd9

📥 Commits

Reviewing files that changed from the base of the PR and between 18212fc and 71f85ec.

📒 Files selected for processing (2)

• proxy/proxy.go
• proxy/proxy_test.go

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📝 Walkthrough

Walkthrough

This PR restores trailing slash semantics in upstream requests that were inadvertently lost when path.Join was introduced in version 26.2. The ConfigureBackendURL function now preserves trailing slashes by detecting them before path manipulation and re-applying them afterward.

Changes

Trailing Slash Preservation in Proxy Path Forwarding

Layer / File(s)	Summary
Trailing slash preservation in ConfigureBackendURL proxy/proxy.go, proxy/proxy_test.go	ConfigureBackendURL detects non-root trailing slashes in inbound paths, applies path.Join and StripPath removal, then conditionally restores the trailing slash. Two test cases validate the behavior for both /some-prefixed and api-style StripPath forms.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% 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 accurately and concisely describes the main change: preserving trailing slashes in the proxy path handling through path.Join and strip_path logic.
Description check	✅ Passed	The description clearly explains the bug (trailing slash removal after upgrading), references the linked issue (#1266), describes the solution, and mentions the addition of regression tests.
Linked Issues check	✅ Passed	The PR successfully addresses the primary objective from #1266: preserving trailing slashes in proxied paths by detecting inbound trailing slashes and re-appending them after strip_path processing.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to the issue: modifying ConfigureBackendURL to preserve trailing slashes and adding corresponding regression test cases to TestConfigureBackendURL.

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✨ Finishing Touches

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[xqqp]

I posted a similar MR (#1269) last month, but got no reaction from the team. I'm hoping the maintainers recognize this problem soon.

[c-tonneslan]

Thanks @xqqp, and sorry, I didn't spot #1269 when I opened this. It's the same fix and a month older, so closing mine in favour of yours.