[logger] Use StaticVector for log listeners with compile-time sizing (#13196)

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

esphome/components/api/__init__.py

@@ -4,6 +4,7 @@ import logging
 from esphome import automation
 from esphome.automation import Condition
 import esphome.codegen as cg
+from esphome.components.logger import request_log_listener
 from esphome.config_helpers import get_logger_level
 import esphome.config_validation as cv
 from esphome.const import (
@@ -326,6 +327,9 @@ async def to_code(config: ConfigType) -> None:
     # Track controller registration for StaticVector sizing
     CORE.register_controller()
 
+    # Request a log listener slot for API log streaming
+    request_log_listener()
+
     cg.add(var.set_port(config[CONF_PORT]))
     cg.add(var.set_reboot_timeout(config[CONF_REBOOT_TIMEOUT]))
     cg.add(var.set_batch_delay(config[CONF_BATCH_DELAY]))

esphome/components/ble_nus/__init__.py

@@ -1,4 +1,5 @@
 import esphome.codegen as cg
+from esphome.components.logger import request_log_listener
 from esphome.components.zephyr import zephyr_add_prj_conf
 import esphome.config_validation as cv
 from esphome.const import CONF_ID, CONF_LOGS, CONF_TYPE
@@ -25,5 +26,8 @@ CONFIG_SCHEMA = cv.All(
 async def to_code(config):
     var = cg.new_Pvariable(config[CONF_ID])
     zephyr_add_prj_conf("BT_NUS", True)
-    cg.add(var.set_expose_log(config[CONF_TYPE] == CONF_LOGS))
+    expose_log = config[CONF_TYPE] == CONF_LOGS
+    cg.add(var.set_expose_log(expose_log))
+    if expose_log:
+        request_log_listener()  # Request a log listener slot for BLE NUS log streaming
     await cg.register_component(var, config)

esphome/components/logger/__init__.py

@@ -421,6 +421,7 @@ async def to_code(config):
     await cg.register_component(log, config)
 
     for conf in config.get(CONF_ON_MESSAGE, []):
+        request_log_listener()  # Each on_message trigger needs a listener slot
         trigger = cg.new_Pvariable(
             conf[CONF_TRIGGER_ID], log, LOG_LEVEL_SEVERITY.index(conf[CONF_LEVEL])
         )
@@ -546,6 +547,7 @@ FILTER_SOURCE_FILES = filter_source_files_from_platform(
 # Keys for CORE.data storage
 DOMAIN = "logger"
 KEY_LEVEL_LISTENERS = "level_listeners"
+KEY_LOG_LISTENERS = "log_listeners"
 
 
 def request_logger_level_listeners() -> None:
@@ -558,8 +560,26 @@ def request_logger_level_listeners() -> None:
     CORE.data.setdefault(DOMAIN, {})[KEY_LEVEL_LISTENERS] = True
 
 
+def request_log_listener() -> None:
+    """Request a log listener slot.
+
+    Components that need to receive log messages should call this function
+    during their code generation. This increments the listener count used
+    to size the StaticVector.
+    """
+    data = CORE.data.setdefault(DOMAIN, {})
+    data[KEY_LOG_LISTENERS] = data.get(KEY_LOG_LISTENERS, 0) + 1
+
+
 @coroutine_with_priority(CoroPriority.FINAL)
 async def final_step():
     """Final code generation step to configure optional logger features."""
-    if CORE.data.get(DOMAIN, {}).get(KEY_LEVEL_LISTENERS, False):
+    domain_data = CORE.data.get(DOMAIN, {})
+    if domain_data.get(KEY_LEVEL_LISTENERS, False):
         cg.add_define("USE_LOGGER_LEVEL_LISTENERS")
+
+    # Only generate log listener code if any component needs it
+    log_listener_count = domain_data.get(KEY_LOG_LISTENERS, 0)
+    if log_listener_count > 0:
+        cg.add_define("USE_LOG_LISTENERS")
+        cg.add_define("ESPHOME_LOG_MAX_LISTENERS", log_listener_count)

esphome/components/logger/logger.cpp

@@ -178,8 +178,10 @@ void Logger::log_vprintf_(uint8_t level, const char *tag, int line, const __Flas
       this->tx_buffer_at_ - msg_start;  // Don't subtract 1 - tx_buffer_at_ is already at the null terminator position
 
   // Listeners get message first (before console write)
+#ifdef USE_LOG_LISTENERS
   for (auto *listener : this->log_listeners_)
     listener->on_log(level, tag, this->tx_buffer_ + msg_start, msg_length);
+#endif
 
   // Write to console starting at the msg_start
   this->write_tx_buffer_to_console_(msg_start, &msg_length);

esphome/components/logger/logger.h

@@ -212,8 +212,13 @@ class Logger : public Component {
 
   inline uint8_t level_for(const char *tag);
 
+#ifdef USE_LOG_LISTENERS
   /// Register a log listener to receive log messages
   void add_log_listener(LogListener *listener) { this->log_listeners_.push_back(listener); }
+#else
+  /// No-op when log listeners are disabled
+  void add_log_listener(LogListener *listener) {}
+#endif
 
 #ifdef USE_LOGGER_LEVEL_LISTENERS
   /// Register a listener for log level changes
@@ -318,8 +323,10 @@ class Logger : public Component {
                                                 this->tx_buffer_size_);
 
     // Listeners get message WITHOUT newline (for API/MQTT/syslog)
+#ifdef USE_LOG_LISTENERS
     for (auto *listener : this->log_listeners_)
       listener->on_log(level, tag, this->tx_buffer_, this->tx_buffer_at_);
+#endif
 
     // Console gets message WITH newline (if platform needs it)
     this->write_tx_buffer_to_console_();
@@ -336,8 +343,10 @@ class Logger : public Component {
     this->write_body_to_buffer_(text, text_length, this->tx_buffer_, &this->tx_buffer_at_, this->tx_buffer_size_);
     this->write_footer_to_buffer_(this->tx_buffer_, &this->tx_buffer_at_, this->tx_buffer_size_);
     this->tx_buffer_[this->tx_buffer_at_] = '\0';
+#ifdef USE_LOG_LISTENERS
     for (auto *listener : this->log_listeners_)
       listener->on_log(level, tag, this->tx_buffer_, this->tx_buffer_at_);
+#endif
   }
 #endif
 
@@ -394,7 +403,10 @@ class Logger : public Component {
 #ifdef USE_LOGGER_RUNTIME_TAG_LEVELS
   std::map<const char *, uint8_t, CStrCompare> log_levels_{};
 #endif
-  std::vector<LogListener *> log_listeners_;  // Log message listeners (API, MQTT, syslog, etc.)
+#ifdef USE_LOG_LISTENERS
+  StaticVector<LogListener *, ESPHOME_LOG_MAX_LISTENERS>
+      log_listeners_;  // Log message listeners (API, MQTT, syslog, etc.)
+#endif
 #ifdef USE_LOGGER_LEVEL_LISTENERS
   std::vector<LoggerLevelListener *> level_listeners_;  // Log level change listeners
 #endif

esphome/components/mqtt/__init__.py

@@ -350,6 +350,7 @@ def exp_mqtt_message(config):
 async def to_code(config):
     var = cg.new_Pvariable(config[CONF_ID])
     await cg.register_component(var, config)
+
     # Add required libraries for ESP8266 and LibreTiny
     if CORE.is_esp8266 or CORE.is_libretiny:
         # https://github.com/heman/async-mqtt-client/blob/master/library.json
@@ -432,6 +433,8 @@ async def to_code(config):
         cg.add(var.disable_log_message())
     else:
         cg.add(var.set_log_message_template(exp_mqtt_message(log_topic)))
+        # Request a log listener slot only when log topic is enabled
+        logger.request_log_listener()
 
         if CONF_LEVEL in log_topic:
             cg.add(var.set_log_level(logger.LOG_LEVELS[log_topic[CONF_LEVEL]]))

esphome/components/syslog/__init__.py

@@ -1,6 +1,6 @@
 import esphome.codegen as cg
 from esphome.components import udp
-from esphome.components.logger import LOG_LEVELS, is_log_level
+from esphome.components.logger import LOG_LEVELS, is_log_level, request_log_listener
 from esphome.components.time import RealTimeClock
 from esphome.components.udp import CONF_UDP_ID
 import esphome.config_validation as cv
@@ -36,6 +36,7 @@ async def to_code(config):
     level = LOG_LEVELS[config[CONF_LEVEL]]
     var = cg.new_Pvariable(config[CONF_ID], level, time)
     await cg.register_component(var, config)
+    request_log_listener()  # Request a log listener slot for syslog
     await cg.register_parented(var, parent)
     cg.add(var.set_strip(config[CONF_STRIP]))
     cg.add(var.set_facility(config[CONF_FACILITY]))

esphome/components/web_server/__init__.py

@@ -4,6 +4,7 @@ import gzip
 
 import esphome.codegen as cg
 from esphome.components import web_server_base
+from esphome.components.logger import request_log_listener
 from esphome.components.web_server_base import CONF_WEB_SERVER_BASE_ID
 import esphome.config_validation as cv
 from esphome.const import (
@@ -313,6 +314,8 @@ async def to_code(config):
     if config.get(CONF_OTA) is False:
         cg.add_define("USE_WEBSERVER_OTA_DISABLED")
     cg.add(var.set_expose_log(config[CONF_LOG]))
+    if config[CONF_LOG]:
+        request_log_listener()  # Request a log listener slot for web server log streaming
     if config[CONF_ENABLE_PRIVATE_NETWORK_ACCESS]:
         cg.add_define("USE_WEBSERVER_PRIVATE_NETWORK_ACCESS")
     if CONF_AUTH in config:

esphome/core/defines.h

@@ -20,6 +20,8 @@
 
 // logger
 #define ESPHOME_LOG_LEVEL ESPHOME_LOG_LEVEL_VERY_VERBOSE
+#define USE_LOG_LISTENERS
+#define ESPHOME_LOG_MAX_LISTENERS 8
 
 // Feature flags
 #define USE_ALARM_CONTROL_PANEL