router_condition: Fix unconditional route check in routing

[cosmo0920]

The PR #11055 removed the routes_mask guard, which exposed a design flaw in the previous logic. Unconditional routes were being forced through prepare_logs() first. The proper fix is to allow unconditional routes to short-circuit early, so that chunk_trace routes are wired correctly.
With this change, the core_chunk_trace unit test will no longer fail.

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

Summary by CodeRabbit

• Refactor
  • Improved routing condition evaluation logic with optimized control flow to handle edge cases more efficiently.

[coderabbitai]

Walkthrough

This PR refactors the flb_router_path_should_route function in src/flb_router_condition.c by adding an early guard that returns FLB_TRUE when a path exists but path->route is NULL, and removes a duplicate check that appeared later, resulting in optimized early short-circuit behavior.

Changes

Cohort / File(s)	Summary
Router condition early return optimization src/flb_router_condition.c	Added early guard in flb_router_path_should_route to return FLB_TRUE when path->route is NULL; removed duplicate NULL check that appeared after LOGS chunk context handling, consolidating the logic path.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

• Single file with focused guard clause repositioning
• Verify that early return for NULL path->route is semantically correct across all calling contexts
• Confirm removal of duplicate check doesn't mask any conditional logic that depended on later evaluation

Suggested labels

backport to v4.0.x

Suggested reviewers

• koleini
• fujimotos

Poem

🐰 A path without a route to show,
Now caught before the function's flow,
Early guard hops in with might,
One true return does set things right,
Hopping faster, cleaner code—we go!

Pre-merge checks and finishing touches

❌ 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%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title Check	✅ Passed	The pull request title "router_condition: Fix unconditional route check in routing" directly addresses the main change in the codebase. The PR modifies the flb_router_path_should_route function in src/flb_router_condition.c to add an early guard that handles the case where path->route is NULL (unconditional routes), which is precisely what the title describes as "unconditional route check." The title is specific to the router_condition component, concise at 58 characters and 7 words, and clearly conveys the primary purpose of the fix without vague terminology or noise. It accurately summarizes the bug fix from a developer's perspective by identifying both the component and the nature of the correction.

✨ 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 cosmo0920-fix-failing-core_chunk_trace-test

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📜 Recent review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between f879a93 and 6f9b009.

📒 Files selected for processing (1)

• src/flb_router_condition.c (1 hunks)

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🔇 Additional comments (1)

src/flb_router_condition.c (1)

268-270: LGTM! Early return correctly implements unconditional routing.

The early guard properly handles unconditional routes (where path->route is NULL) by returning FLB_TRUE immediately. This fixes the reported bug where unconditional routes were incorrectly forced through prepare_logs() (line 277), and aligns with the semantic expectation that a NULL route means "route unconditionally."

The behavior change is significant but correct:

• Before: NULL path->route would call flb_route_condition_eval() with NULL, which returns FLB_FALSE (line 226)
• After: NULL path->route short-circuits to return FLB_TRUE (unconditional routing)

This also provides a performance benefit by avoiding unnecessary log preparation for unconditional routes.

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[edsiper]

great catch! thank you