From 74281b93c4491f80bfd02db9e56696a86081083c Mon Sep 17 00:00:00 2001
From: kahrendt <kahrendt@gmail.com>
Date: Thu, 21 Dec 2023 02:19:15 -0500
Subject: [PATCH] Reduce memory usage with StringRef in MQTT Components (#5719)

---
 esphome/components/mqtt/mqtt_binary_sensor.cpp |  2 +-
 esphome/components/mqtt/mqtt_component.cpp     | 12 ++++++------
 esphome/components/mqtt/mqtt_component.h       | 13 ++++++++-----
 3 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/esphome/components/mqtt/mqtt_binary_sensor.cpp b/esphome/components/mqtt/mqtt_binary_sensor.cpp
index 79e6989a8f..6d12e88391 100644
--- a/esphome/components/mqtt/mqtt_binary_sensor.cpp
+++ b/esphome/components/mqtt/mqtt_binary_sensor.cpp
@@ -25,7 +25,7 @@ void MQTTBinarySensorComponent::dump_config() {
 MQTTBinarySensorComponent::MQTTBinarySensorComponent(binary_sensor::BinarySensor *binary_sensor)
     : binary_sensor_(binary_sensor) {
   if (this->binary_sensor_->is_status_binary_sensor()) {
-    this->set_custom_state_topic(mqtt::global_mqtt_client->get_availability().topic);
+    this->set_custom_state_topic(mqtt::global_mqtt_client->get_availability().topic.c_str());
   }
 }
 
diff --git a/esphome/components/mqtt/mqtt_component.cpp b/esphome/components/mqtt/mqtt_component.cpp
index af4d6f13a5..8855b4d8e3 100644
--- a/esphome/components/mqtt/mqtt_component.cpp
+++ b/esphome/components/mqtt/mqtt_component.cpp
@@ -34,13 +34,13 @@ std::string MQTTComponent::get_default_topic_for_(const std::string &suffix) con
 
 std::string MQTTComponent::get_state_topic_() const {
   if (this->has_custom_state_topic_)
-    return this->custom_state_topic_;
+    return this->custom_state_topic_.str();
   return this->get_default_topic_for_("state");
 }
 
 std::string MQTTComponent::get_command_topic_() const {
   if (this->has_custom_command_topic_)
-    return this->custom_command_topic_;
+    return this->custom_command_topic_.str();
   return this->get_default_topic_for_("command");
 }
 
@@ -180,12 +180,12 @@ MQTTComponent::MQTTComponent() = default;
 
 float MQTTComponent::get_setup_priority() const { return setup_priority::AFTER_CONNECTION; }
 void MQTTComponent::disable_discovery() { this->discovery_enabled_ = false; }
-void MQTTComponent::set_custom_state_topic(const std::string &custom_state_topic) {
-  this->custom_state_topic_ = custom_state_topic;
+void MQTTComponent::set_custom_state_topic(const char *custom_state_topic) {
+  this->custom_state_topic_ = StringRef(custom_state_topic);
   this->has_custom_state_topic_ = true;
 }
-void MQTTComponent::set_custom_command_topic(const std::string &custom_command_topic) {
-  this->custom_command_topic_ = custom_command_topic;
+void MQTTComponent::set_custom_command_topic(const char *custom_command_topic) {
+  this->custom_command_topic_ = StringRef(custom_command_topic);
   this->has_custom_command_topic_ = true;
 }
 void MQTTComponent::set_command_retain(bool command_retain) { this->command_retain_ = command_retain; }
diff --git a/esphome/components/mqtt/mqtt_component.h b/esphome/components/mqtt/mqtt_component.h
index aacfe8891f..9fc8c795d3 100644
--- a/esphome/components/mqtt/mqtt_component.h
+++ b/esphome/components/mqtt/mqtt_component.h
@@ -8,6 +8,7 @@
 
 #include "esphome/core/component.h"
 #include "esphome/core/entity_base.h"
+#include "esphome/core/string_ref.h"
 #include "mqtt_client.h"
 
 namespace esphome {
@@ -88,9 +89,9 @@ class MQTTComponent : public Component {
   virtual std::string component_type() const = 0;
 
   /// Set a custom state topic. Set to "" for default behavior.
-  void set_custom_state_topic(const std::string &custom_state_topic);
+  void set_custom_state_topic(const char *custom_state_topic);
   /// Set a custom command topic. Set to "" for default behavior.
-  void set_custom_command_topic(const std::string &custom_command_topic);
+  void set_custom_command_topic(const char *custom_command_topic);
   /// Set whether command message should be retained.
   void set_command_retain(bool command_retain);
 
@@ -188,15 +189,17 @@ class MQTTComponent : public Component {
   /// Generate the Home Assistant MQTT discovery object id by automatically transforming the friendly name.
   std::string get_default_object_id_() const;
 
-  std::string custom_state_topic_{};
-  std::string custom_command_topic_{};
+  StringRef custom_state_topic_{};
+  StringRef custom_command_topic_{};
+
+  std::unique_ptr<Availability> availability_;
+
   bool has_custom_state_topic_{false};
   bool has_custom_command_topic_{false};
 
   bool command_retain_{false};
   bool retain_{true};
   bool discovery_enabled_{true};
-  std::unique_ptr<Availability> availability_;
   bool resend_state_{false};
 };