router: apply input routes with a single input and output

[edsiper]

Problem

With exactly one input and one output, flb_router_io_set() connects the two
directly and returns before applying the routes of the configuration. The
input gets no direct routes, so route conditions are never evaluated: records
that match no route still reach the output.

pipeline:
  inputs:
    - name: dummy
      dummy: '{"topic":"topic2"}'
      routes:
        logs:
          - name: topic1
            condition:
              op: and
              rules:
                - field: $topic
                  op: eq
                  value: topic1
            to:
              outputs:
                - out1
  outputs:
    - name: stdout
      alias: out1

Before this change the record is printed. After it, it is not, the same as
when the pipeline has more inputs or outputs.

Change

Take the 1:1 shortcut only when no input has routes. Inputs with routes go
through the regular setup and the router configuration.

Testing

New integration tests in tests/integration/scenarios/out_stdout for a
matching and a non-matching route with one input and one output. Both fail on
master and pass with this change.

ctest --test-dir build -R 'rout|condition'          # 8/8 passed
pytest scenarios/out_stdout                          # 16 passed
VALGRIND=1 VALGRIND_STRICT=1 pytest scenarios/out_stdout -n 4   # 16 passed, no errors

Summary by CodeRabbit

• Bug Fixes
  • Conditional routes are now applied when a configuration has one input and one output, preventing records from being sent unconditionally. Matching records are delivered, while records that do not meet the route condition are not sent.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-17T20:29:58.475743Z	ea76030	PR opened

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ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: defaults
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• Plan: Advanced
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📥 Commits

Reviewing files that changed from the base of the PR and between f5374f7 and ea76030.

📒 Files selected for processing: 4

• src/flb_router.c
• tests/integration/scenarios/out_stdout/config/out_stdout_single_pair_conditional_match.yaml
• tests/integration/scenarios/out_stdout/config/out_stdout_single_pair_conditional_miss.yaml
• tests/integration/scenarios/out_stdout/tests/test_out_stdout_001.py

Included review availability: This review used your included allowance. Your plan provides up to 8 included reviews per hour; 7 remain after this review.

📝 Walkthrough

The router now uses the single-input/one-output shortcut only when no input routes are configured. Integration tests check conditional routes with matching and unmatched records.

Changes: Conditional routing

Layer / File(s)	Summary
Route application and validation src/flb_router.c, tests/integration/scenarios/out_stdout/config/out_stdout_single_pair_conditional_*.yaml, tests/integration/scenarios/out_stdout/tests/test_out_stdout_001.py	The router applies configured input routes for single-input/one-output pairs. Integration tests check that a matching route delivers a record and an unmatched route does not.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to ea760

The routing change has tests for both matching and unmatched records, with no identified issue preventing merge after normal checks.

Pre-merge checks: 5

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly describes the main change: applying input routes when one input and one output are configured.
Docstring Coverage		Docstring coverage is 80.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 2 files. (2 skipped: 2 u…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 80.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 2 files. (2 skipped: 2 unsupported.)

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