router: apply input routes with a single input and output

src/flb_router.c

@@ -198,8 +198,12 @@ int flb_router_io_set(struct flb_config *config)
     in_count = mk_list_size(&config->inputs);
     out_count = mk_list_size(&config->outputs);
 
-    /* Mostly used for command line tests */
-    if (in_count == 1 && out_count == 1) {
+    /*
+     * Mostly used for command line tests. Inputs with routes are connected by
+     * the router configuration below.
+     */
+    if (in_count == 1 && out_count == 1 &&
+        cfl_list_is_empty(&config->input_routes)) {
         i_ins = mk_list_entry_first(&config->inputs, struct flb_input_instance, _head);
         o_ins = mk_list_entry_first(&config->outputs, struct flb_output_instance, _head);
 

tests/integration/scenarios/out_stdout/config/out_stdout_single_pair_conditional_match.yaml

@@ -0,0 +1,30 @@
+service:
+  flush: 1
+  grace: 1
+  log_level: debug
+  http_server: on
+  http_port: ${FLUENT_BIT_HTTP_MONITORING_PORT}
+
+pipeline:
+  inputs:
+    - name: dummy
+      alias: single_pair_dummy
+      tag: single.pair
+      dummy: '{"message":"single pair record","topic":"topic1"}'
+      samples: 1
+      routes:
+        logs:
+          - name: single_pair_topic1
+            condition:
+              op: and
+              rules:
+                - field: $topic
+                  op: eq
+                  value: topic1
+            to:
+              outputs:
+                - single_pair_stdout
+
+  outputs:
+    - name: stdout
+      alias: single_pair_stdout

tests/integration/scenarios/out_stdout/config/out_stdout_single_pair_conditional_miss.yaml

@@ -0,0 +1,30 @@
+service:
+  flush: 1
+  grace: 1
+  log_level: debug
+  http_server: on
+  http_port: ${FLUENT_BIT_HTTP_MONITORING_PORT}
+
+pipeline:
+  inputs:
+    - name: dummy
+      alias: single_pair_dummy
+      tag: single.pair
+      dummy: '{"message":"single pair record","topic":"topic2"}'
+      samples: 1
+      routes:
+        logs:
+          - name: single_pair_topic1
+            condition:
+              op: and
+              rules:
+                - field: $topic
+                  op: eq
+                  value: topic1
+            to:
+              outputs:
+                - single_pair_stdout
+
+  outputs:
+    - name: stdout
+      alias: single_pair_stdout

tests/integration/scenarios/out_stdout/tests/test_out_stdout_001.py

@@ -1,5 +1,6 @@
 import json
 import os
+import time
 from pathlib import Path
 
 import pytest
@@ -347,3 +348,28 @@ def test_out_stdout_conditional_routing_corner_cases(mode, label, config_file):
     )
     assert _stdout_lines_for_tag(log_text, f"{mode}_default_topic1") == []
     assert _stdout_lines_for_tag(log_text, f"{mode}_miss_topic1") == []
+
+
+def test_out_stdout_single_pair_conditional_route_matches():
+    """With one input and one output, a matching route still delivers."""
+    service = Service("out_stdout_single_pair_conditional_match.yaml")
+    service.start()
+    log_text = service.wait_for_log_contains("[0] single_pair_topic1:", timeout=10)
+    service.stop()
+
+    assert "connected input 'single_pair_dummy' route 'single_pair_topic1'" in log_text
+    assert "\"message\"=>\"single pair record\"" in log_text
+
+
+def test_out_stdout_single_pair_conditional_route_drops_unmatched():
+    """With one input and one output, records matching no route are not delivered."""
+    service = Service("out_stdout_single_pair_conditional_miss.yaml")
+    service.start()
+    service.wait_for_log_contains(
+        "connected input 'single_pair_dummy' route 'single_pair_topic1'", timeout=10)
+    # several flushes for the sample to reach the output if it were routed
+    time.sleep(4)
+    log_text = service.read_log()
+    service.stop()
+
+    assert "single pair record" not in log_text