[mdns][openthread] Use StaticVector for services storage with compile-time capacity (#10976)

esphome/components/mdns/__init__.py

@@ -17,6 +17,11 @@ from esphome.coroutine import CoroPriority
 CODEOWNERS = ["@esphome/core"]
 DEPENDENCIES = ["network"]
 
+# Components that create mDNS services at runtime
+# IMPORTANT: If you add a new component here, you must also update the corresponding
+# #ifdef blocks in mdns_component.cpp compile_records_() method
+COMPONENTS_WITH_MDNS_SERVICES = ("api", "prometheus", "web_server")
+
 mdns_ns = cg.esphome_ns.namespace("mdns")
 MDNSComponent = mdns_ns.class_("MDNSComponent", cg.Component)
 MDNSTXTRecord = mdns_ns.struct("MDNSTXTRecord")
@@ -91,12 +96,20 @@ async def to_code(config):
 
     cg.add_define("USE_MDNS")
 
-    var = cg.new_Pvariable(config[CONF_ID])
-    await cg.register_component(var, config)
+    # Calculate compile-time service count
+    service_count = sum(
+        1 for key in COMPONENTS_WITH_MDNS_SERVICES if key in CORE.config
+    ) + len(config[CONF_SERVICES])
 
     if config[CONF_SERVICES]:
         cg.add_define("USE_MDNS_EXTRA_SERVICES")
 
+    # Ensure at least 1 service (fallback service)
+    cg.add_define("MDNS_SERVICE_COUNT", max(1, service_count))
+
+    var = cg.new_Pvariable(config[CONF_ID])
+    await cg.register_component(var, config)
+
     for service in config[CONF_SERVICES]:
         txt = [
             cg.StructInitializer(

esphome/components/mdns/mdns_component.cpp

@@ -74,32 +74,12 @@ MDNS_STATIC_CONST_CHAR(NETWORK_THREAD, "thread");
 void MDNSComponent::compile_records_() {
   this->hostname_ = App.get_name();
 
-  // Calculate exact capacity needed for services vector
-  size_t services_count = 0;
-#ifdef USE_API
-  if (api::global_api_server != nullptr) {
-    services_count++;
-  }
-#endif
-#ifdef USE_PROMETHEUS
-  services_count++;
-#endif
-#ifdef USE_WEBSERVER
-  services_count++;
-#endif
-#ifdef USE_MDNS_EXTRA_SERVICES
-  services_count += this->services_extra_.size();
-#endif
-  // Reserve for fallback service if needed
-  if (services_count == 0) {
-    services_count = 1;
-  }
-  this->services_.reserve(services_count);
+  // IMPORTANT: The #ifdef blocks below must match COMPONENTS_WITH_MDNS_SERVICES
+  // in mdns/__init__.py. If you add a new service here, update both locations.
 
 #ifdef USE_API
   if (api::global_api_server != nullptr) {
-    this->services_.emplace_back();
-    auto &service = this->services_.back();
+    auto &service = this->services_.emplace_next();
     service.service_type = MDNS_STR(SERVICE_ESPHOMELIB);
     service.proto = MDNS_STR(SERVICE_TCP);
     service.port = api::global_api_server->get_port();
@@ -178,30 +158,23 @@ void MDNSComponent::compile_records_() {
 #endif  // USE_API
 
 #ifdef USE_PROMETHEUS
-  this->services_.emplace_back();
-  auto &prom_service = this->services_.back();
+  auto &prom_service = this->services_.emplace_next();
   prom_service.service_type = MDNS_STR(SERVICE_PROMETHEUS);
   prom_service.proto = MDNS_STR(SERVICE_TCP);
   prom_service.port = USE_WEBSERVER_PORT;
 #endif
 
 #ifdef USE_WEBSERVER
-  this->services_.emplace_back();
-  auto &web_service = this->services_.back();
+  auto &web_service = this->services_.emplace_next();
   web_service.service_type = MDNS_STR(SERVICE_HTTP);
   web_service.proto = MDNS_STR(SERVICE_TCP);
   web_service.port = USE_WEBSERVER_PORT;
 #endif
 
-#ifdef USE_MDNS_EXTRA_SERVICES
-  this->services_.insert(this->services_.end(), this->services_extra_.begin(), this->services_extra_.end());
-#endif
-
 #if !defined(USE_API) && !defined(USE_PROMETHEUS) && !defined(USE_WEBSERVER) && !defined(USE_MDNS_EXTRA_SERVICES)
   // Publish "http" service if not using native API or any other services
   // This is just to have *some* mDNS service so that .local resolution works
-  this->services_.emplace_back();
-  auto &fallback_service = this->services_.back();
+  auto &fallback_service = this->services_.emplace_next();
   fallback_service.service_type = "_http";
   fallback_service.proto = "_tcp";
   fallback_service.port = USE_WEBSERVER_PORT;
@@ -214,7 +187,7 @@ void MDNSComponent::dump_config() {
                 "mDNS:\n"
                 "  Hostname: %s",
                 this->hostname_.c_str());
-#if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERY_VERBOSE
+#if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERBOSE
   ESP_LOGV(TAG, "  Services:");
   for (const auto &service : this->services_) {
     ESP_LOGV(TAG, "  - %s, %s, %d", service.service_type.c_str(), service.proto.c_str(),
@@ -227,8 +200,6 @@ void MDNSComponent::dump_config() {
 #endif
 }
 
-std::vector<MDNSService> MDNSComponent::get_services() { return this->services_; }
-
 }  // namespace mdns
 }  // namespace esphome
 #endif

esphome/components/mdns/mdns_component.h

@@ -2,13 +2,16 @@
 #include "esphome/core/defines.h"
 #ifdef USE_MDNS
 #include <string>
-#include <vector>
 #include "esphome/core/automation.h"
 #include "esphome/core/component.h"
+#include "esphome/core/helpers.h"
 
 namespace esphome {
 namespace mdns {
 
+// Service count is calculated at compile time by Python codegen
+// MDNS_SERVICE_COUNT will always be defined
+
 struct MDNSTXTRecord {
   std::string key;
   TemplatableValue<std::string> value;
@@ -36,18 +39,15 @@ class MDNSComponent : public Component {
   float get_setup_priority() const override { return setup_priority::AFTER_CONNECTION; }
 
 #ifdef USE_MDNS_EXTRA_SERVICES
-  void add_extra_service(MDNSService service) { services_extra_.push_back(std::move(service)); }
+  void add_extra_service(MDNSService service) { this->services_.emplace_next() = std::move(service); }
 #endif
 
-  std::vector<MDNSService> get_services();
+  const StaticVector<MDNSService, MDNS_SERVICE_COUNT> &get_services() const { return this->services_; }
 
   void on_shutdown() override;
 
  protected:
-#ifdef USE_MDNS_EXTRA_SERVICES
-  std::vector<MDNSService> services_extra_{};
-#endif
-  std::vector<MDNSService> services_{};
+  StaticVector<MDNSService, MDNS_SERVICE_COUNT> services_{};
   std::string hostname_;
   void compile_records_();
 };

esphome/components/openthread/openthread.cpp

@@ -143,11 +143,10 @@ void OpenThreadSrpComponent::setup() {
     return;
   }
 
-  // Copy the mdns services to our local instance so that the c_str pointers remain valid for the lifetime of this
-  // component
-  this->mdns_services_ = this->mdns_->get_services();
-  ESP_LOGD(TAG, "Setting up SRP services. count = %d\n", this->mdns_services_.size());
-  for (const auto &service : this->mdns_services_) {
+  // Get mdns services and copy their data (strings are copied with strdup below)
+  const auto &mdns_services = this->mdns_->get_services();
+  ESP_LOGD(TAG, "Setting up SRP services. count = %d\n", mdns_services.size());
+  for (const auto &service : mdns_services) {
     otSrpClientBuffersServiceEntry *entry = otSrpClientBuffersAllocateService(instance);
     if (!entry) {
       ESP_LOGW(TAG, "Failed to allocate service entry");

esphome/components/openthread/openthread.h

@@ -57,7 +57,6 @@ class OpenThreadSrpComponent : public Component {
 
  protected:
   esphome::mdns::MDNSComponent *mdns_{nullptr};
-  std::vector<esphome::mdns::MDNSService> mdns_services_;
   std::vector<std::unique_ptr<uint8_t[]>> memory_pool_;
   void *pool_alloc_(size_t size);
 };

esphome/core/defines.h

@@ -82,6 +82,7 @@
 #define USE_LVGL_TILEVIEW
 #define USE_LVGL_TOUCHSCREEN
 #define USE_MDNS
+#define MDNS_SERVICE_COUNT 3
 #define USE_MEDIA_PLAYER
 #define USE_NEXTION_TFT_UPLOAD
 #define USE_NUMBER

esphome/core/helpers.h

@@ -127,6 +127,16 @@ template<typename T, size_t N> class StaticVector {
     }
   }
 
+  // Return reference to next element and increment count (with bounds checking)
+  T &emplace_next() {
+    if (count_ >= N) {
+      // Should never happen with proper size calculation
+      // Return reference to last element to avoid crash
+      return data_[N - 1];
+    }
+    return data_[count_++];
+  }
+
   size_t size() const { return count_; }
   bool empty() const { return count_ == 0; }