[api] Skip the listen backlog setter when it matches the default (#20066)

esphome/components/api/__init__.py

@@ -142,6 +142,7 @@ CONF_STATE_SUBSCRIPTION_ONLY = "state_subscription_only"
 DEFAULT_PORT = 6053
 DEFAULT_REBOOT_TIMEOUT = "15min"
 DEFAULT_BATCH_DELAY = "100ms"
+DEFAULT_LISTEN_BACKLOG = 4
 
 
 def _register_provisioning_source(config: ConfigType) -> ConfigType:
@@ -477,8 +478,10 @@ async def to_code(config: ConfigType) -> None:
         cg.add(var.set_reboot_timeout(reboot_timeout))
     if (batch_delay := config[CONF_BATCH_DELAY]) != cv.time_period(DEFAULT_BATCH_DELAY):
         cg.add(var.set_batch_delay(batch_delay))
-    if CONF_LISTEN_BACKLOG in config:
-        cg.add(var.set_listen_backlog(config[CONF_LISTEN_BACKLOG]))
+    if (
+        listen_backlog := config.get(CONF_LISTEN_BACKLOG)
+    ) is not None and listen_backlog != DEFAULT_LISTEN_BACKLOG:
+        cg.add(var.set_listen_backlog(listen_backlog))
     cg.add_define("MAX_API_CONNECTIONS", config[CONF_MAX_CONNECTIONS])
     cg.add_define("API_MAX_SEND_QUEUE", config[CONF_MAX_SEND_QUEUE])
 

esphome/components/api/api_server.h

@@ -357,9 +357,7 @@ class APIServer final : public Component
   // Group smaller types together
   uint16_t port_{6053};        // Keep in sync with DEFAULT_PORT in __init__.py
   uint16_t batch_delay_{100};  // Keep in sync with DEFAULT_BATCH_DELAY in __init__.py
-  // Connection limits - these defaults will be overridden by config values
-  // from cv.SplitDefault in __init__.py which sets platform-specific defaults.
-  uint8_t listen_backlog_{4};
+  uint8_t listen_backlog_{4};  // Keep in sync with DEFAULT_LISTEN_BACKLOG in __init__.py
   bool shutting_down_ = false;
   uint8_t api_connection_count_{0};
 #if defined(USE_PROVISIONING) && defined(USE_API_NOISE)

tests/component_tests/api/config/custom.yaml

@@ -13,3 +13,4 @@ api:
   port: 6054
   reboot_timeout: 0s
   batch_delay: 0ms
+  listen_backlog: 2

tests/component_tests/api/config/defaults.yaml

@@ -13,3 +13,4 @@ api:
   port: 6053
   reboot_timeout: 15min
   batch_delay: 100ms
+  listen_backlog: 4

tests/component_tests/api/config/esp8266.yaml

@@ -0,0 +1,12 @@
+---
+esphome:
+  name: test
+
+esp8266:
+  board: d1_mini
+
+wifi:
+  ssid: test
+  password: testtest
+
+api:

tests/component_tests/api/test_default_setters.py

@@ -12,7 +12,7 @@ def test_default_values_are_not_emitted(
     component_config_path: Callable[[str], Path],
     config_file: str,
 ) -> None:
-    """Port 6053, a 15 min reboot timeout and 100 ms batch delay are C++ initializers.
+    """Port 6053, a 15 min reboot timeout, 100 ms batch delay and backlog 4 are C++ initializers.
 
     Both the schema defaults and the same values written explicitly take the skip path.
     """
@@ -21,6 +21,7 @@ def test_default_values_are_not_emitted(
     assert "api_apiserver_id->set_port(" not in main_cpp
     assert "api_apiserver_id->set_reboot_timeout(" not in main_cpp
     assert "api_apiserver_id->set_batch_delay(" not in main_cpp
+    assert "api_apiserver_id->set_listen_backlog(" not in main_cpp
 
 
 def test_custom_values_are_emitted(
@@ -33,3 +34,14 @@ def test_custom_values_are_emitted(
     assert "api_apiserver_id->set_port(6054);" in main_cpp
     assert "api_apiserver_id->set_reboot_timeout(0);" in main_cpp
     assert "api_apiserver_id->set_batch_delay(0);" in main_cpp
+    assert "api_apiserver_id->set_listen_backlog(2);" in main_cpp
+
+
+def test_esp8266_listen_backlog_is_emitted(
+    generate_main: Callable[[str | Path], str],
+    component_config_path: Callable[[str], Path],
+) -> None:
+    """The ESP8266 schema default of 1 differs from the C++ initializer, so it is set."""
+    main_cpp = generate_main(component_config_path("esp8266.yaml"))
+
+    assert "api_apiserver_id->set_listen_backlog(1);" in main_cpp