reduce some more

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

esphome/components/improv_serial/improv_serial_component.cpp

@@ -267,16 +267,26 @@ bool ImprovSerialComponent::parse_improv_payload_(improv::ImprovCommand &command
       for (auto &scan : results) {
         if (scan.get_is_hidden())
           continue;
-        const std::string &ssid = scan.get_ssid();
-        if (std::find(networks.begin(), networks.end(), ssid) != networks.end())
+        const char *ssid_cstr = scan.get_ssid().c_str();
+        // Check if we've already sent this SSID
+        bool duplicate = false;
+        for (const auto &seen : networks) {
+          if (strcmp(seen.c_str(), ssid_cstr) == 0) {
+            duplicate = true;
+            break;
+          }
+        }
+        if (duplicate)
           continue;
+        // Only allocate std::string after confirming it's not a duplicate
+        std::string ssid(ssid_cstr);
         // Send each ssid separately to avoid overflowing the buffer
         char rssi_buf[5];  // int8_t: -128 to 127, max 4 chars + null
         *int8_to_str(rssi_buf, scan.get_rssi()) = '\0';
         std::vector<uint8_t> data =
             improv::build_rpc_response(improv::GET_WIFI_NETWORKS, {ssid, rssi_buf, YESNO(scan.get_with_auth())}, false);
         this->send_response_(data);
-        networks.push_back(ssid);
+        networks.push_back(std::move(ssid));
       }
       // Send empty response to signify the end of the list.
       std::vector<uint8_t> data =

esphome/components/wifi/wifi_component.cpp

@@ -39,6 +39,10 @@
 #include "esphome/components/esp32_improv/esp32_improv_component.h"
 #endif
 
+#ifdef USE_IMPROV_SERIAL
+#include "esphome/components/improv_serial/improv_serial_component.h"
+#endif
+
 namespace esphome::wifi {
 
 static const char *const TAG = "wifi";
@@ -347,7 +351,7 @@ bool WiFiComponent::needs_scan_results_() const {
   return this->scan_result_.empty() || !this->scan_result_[0].get_matches();
 }
 
-bool WiFiComponent::ssid_was_seen_in_scan_(const std::string &ssid) const {
+bool WiFiComponent::ssid_was_seen_in_scan_(const CompactString &ssid) const {
   // Check if this SSID is configured as hidden
   // If explicitly marked hidden, we should always try hidden mode regardless of scan results
   for (const auto &conf : this->sta_) {
@@ -365,6 +369,75 @@ bool WiFiComponent::ssid_was_seen_in_scan_(const std::string &ssid) const {
   return false;
 }
 
+bool WiFiComponent::needs_full_scan_results_() const {
+  // Components that require full scan results (for example, scan result listeners)
+  // are expected to call request_wifi_scan_results(), which sets keep_scan_results_.
+  if (this->keep_scan_results_) {
+    return true;
+  }
+
+#ifdef USE_CAPTIVE_PORTAL
+  // Captive portal needs full results when active (showing network list to user)
+  if (captive_portal::global_captive_portal != nullptr && captive_portal::global_captive_portal->is_active()) {
+    return true;
+  }
+#endif
+
+#ifdef USE_IMPROV_SERIAL
+  // Improv serial needs results during provisioning (before connected)
+  if (improv_serial::global_improv_serial_component != nullptr && !this->is_connected()) {
+    return true;
+  }
+#endif
+
+#ifdef USE_IMPROV
+  // BLE improv also needs results during provisioning
+  if (esp32_improv::global_improv_component != nullptr && esp32_improv::global_improv_component->is_active()) {
+    return true;
+  }
+#endif
+
+  return false;
+}
+
+bool WiFiComponent::matches_configured_network_(const char *ssid, const uint8_t *bssid) const {
+  // Hidden networks in scan results have empty SSIDs - skip them
+  if (ssid[0] == '\0') {
+    return false;
+  }
+  for (const auto &sta : this->sta_) {
+    // Skip hidden network configs (they don't appear in normal scans)
+    if (sta.get_hidden()) {
+      continue;
+    }
+    // For BSSID-only configs (empty SSID), match by BSSID
+    if (sta.get_ssid().empty()) {
+      if (sta.has_bssid() && std::memcmp(sta.get_bssid().data(), bssid, 6) == 0) {
+        return true;
+      }
+      continue;
+    }
+    // Match by SSID
+    if (sta.get_ssid() == ssid) {
+      return true;
+    }
+  }
+  return false;
+}
+
+void WiFiComponent::log_discarded_scan_result_(const char *ssid, const uint8_t *bssid, int8_t rssi, uint8_t channel) {
+#if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERBOSE
+  // Skip logging during roaming scans to avoid log buffer overflow
+  // (roaming scans typically find many networks but only care about same-SSID APs)
+  if (this->roaming_state_ == RoamingState::SCANNING) {
+    return;
+  }
+  char bssid_s[MAC_ADDRESS_PRETTY_BUFFER_SIZE];
+  format_mac_addr_upper(bssid, bssid_s);
+  ESP_LOGV(TAG, "- " LOG_SECRET("'%s'") " " LOG_SECRET("(%s)") " %ddB Ch:%u", ssid, bssid_s, rssi, channel);
+#endif
+}
+
 int8_t WiFiComponent::find_next_hidden_sta_(int8_t start_index) {
   // Find next SSID to try in RETRY_HIDDEN phase.
   //
@@ -656,8 +729,12 @@ void WiFiComponent::loop() {
         ESP_LOGI(TAG, "Starting fallback AP");
         this->setup_ap_config_();
 #ifdef USE_CAPTIVE_PORTAL
-        if (captive_portal::global_captive_portal != nullptr)
+        if (captive_portal::global_captive_portal != nullptr) {
+          // Reset so we force one full scan after captive portal starts
+          // (previous scans were filtered because captive portal wasn't active yet)
+          this->has_completed_scan_after_captive_portal_start_ = false;
           captive_portal::global_captive_portal->start();
+        }
 #endif
       }
     }
@@ -862,9 +939,12 @@ WiFiAP WiFiComponent::get_sta() const {
   return config ? *config : WiFiAP{};
 }
 void WiFiComponent::save_wifi_sta(const std::string &ssid, const std::string &password) {
+  this->save_wifi_sta(ssid.c_str(), password.c_str());
+}
+void WiFiComponent::save_wifi_sta(const char *ssid, const char *password) {
   SavedWifiSettings save{};  // zero-initialized - all bytes set to \0, guaranteeing null termination
-  strncpy(save.ssid, ssid.c_str(), sizeof(save.ssid) - 1);              // max 32 chars, byte 32 remains \0
-  strncpy(save.password, password.c_str(), sizeof(save.password) - 1);  // max 64 chars, byte 64 remains \0
+  strncpy(save.ssid, ssid, sizeof(save.ssid) - 1);              // max 32 chars, byte 32 remains \0
+  strncpy(save.password, password, sizeof(save.password) - 1);  // max 64 chars, byte 64 remains \0
   this->pref_.save(&save);
   // ensure it's written immediately
   global_preferences->sync();
@@ -1179,7 +1259,7 @@ template<typename VectorType> static void insertion_sort_scan_results(VectorType
 // has overhead from UART transmission, so combining INFO+DEBUG into one line halves
 // the blocking time. Do NOT split this into separate ESP_LOGI/ESP_LOGD calls.
 __attribute__((noinline)) static void log_scan_result(const WiFiScanResult &res) {
-  char bssid_s[18];
+  char bssid_s[MAC_ADDRESS_PRETTY_BUFFER_SIZE];
   auto bssid = res.get_bssid();
   format_mac_addr_upper(bssid.data(), bssid_s);
 
@@ -1195,18 +1275,6 @@ __attribute__((noinline)) static void log_scan_result(const WiFiScanResult &res)
 #endif
 }
 
-#if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERBOSE
-// Helper function to log non-matching scan results at verbose level
-__attribute__((noinline)) static void log_scan_result_non_matching(const WiFiScanResult &res) {
-  char bssid_s[18];
-  auto bssid = res.get_bssid();
-  format_mac_addr_upper(bssid.data(), bssid_s);
-
-  ESP_LOGV(TAG, "- " LOG_SECRET("'%s'") " " LOG_SECRET("(%s) ") "%s", res.get_ssid().c_str(), bssid_s,
-           LOG_STR_ARG(get_signal_bars(res.get_rssi())));
-}
-#endif
-
 void WiFiComponent::check_scanning_finished() {
   if (!this->scan_done_) {
     if (millis() - this->action_started_ > WIFI_SCAN_TIMEOUT_MS) {
@@ -1216,6 +1284,8 @@ void WiFiComponent::check_scanning_finished() {
     return;
   }
   this->scan_done_ = false;
+  this->has_completed_scan_after_captive_portal_start_ =
+      true;  // Track that we've done a scan since captive portal started
   this->retry_hidden_mode_ = RetryHiddenMode::SCAN_BASED;
 
   if (this->scan_result_.empty()) {
@@ -1243,21 +1313,12 @@ void WiFiComponent::check_scanning_finished() {
   // Sort scan results using insertion sort for better memory efficiency
   insertion_sort_scan_results(this->scan_result_);
 
-  size_t non_matching_count = 0;
+  // Log matching networks (non-matching already logged at VERBOSE in scan callback)
   for (auto &res : this->scan_result_) {
     if (res.get_matches()) {
       log_scan_result(res);
-    } else {
-#if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERBOSE
-      log_scan_result_non_matching(res);
-#else
-      non_matching_count++;
-#endif
     }
   }
-  if (non_matching_count > 0) {
-    ESP_LOGD(TAG, "- %zu non-matching (VERBOSE to show)", non_matching_count);
-  }
 
   // SYNCHRONIZATION POINT: Establish link between scan_result_[0] and selected_sta_index_
   // After sorting, scan_result_[0] contains the best network. Now find which sta_[i] config
@@ -1516,7 +1577,10 @@ WiFiRetryPhase WiFiComponent::determine_next_phase_() {
       if (this->went_through_explicit_hidden_phase_()) {
         return WiFiRetryPhase::EXPLICIT_HIDDEN;
       }
-      // Skip scanning when captive portal/improv is active to avoid disrupting AP.
+      // Skip scanning when captive portal/improv is active to avoid disrupting AP,
+      // BUT only if we've already completed at least one scan AFTER the portal started.
+      // When captive portal first starts, scan results may be filtered/stale, so we need
+      // to do one full scan to populate available networks for the captive portal UI.
       //
       // WHY SCANNING DISRUPTS AP MODE:
       // WiFi scanning requires the radio to leave the AP's channel and hop through
@@ -1533,7 +1597,16 @@ WiFiRetryPhase WiFiComponent::determine_next_phase_() {
       //
       // This allows users to configure WiFi via captive portal while the device keeps
       // attempting to connect to all configured networks in sequence.
-      if (this->is_captive_portal_active_() || this->is_esp32_improv_active_()) {
+      // Captive portal needs scan results to show available networks.
+      // If captive portal is active, only skip scanning if we've done a scan after it started.
+      // If only improv is active (no captive portal), skip scanning since improv doesn't need results.
+      if (this->is_captive_portal_active_()) {
+        if (this->has_completed_scan_after_captive_portal_start_) {
+          return WiFiRetryPhase::RETRY_HIDDEN;
+        }
+        // Need to scan for captive portal
+      } else if (this->is_esp32_improv_active_()) {
+        // Improv doesn't need scan results
         return WiFiRetryPhase::RETRY_HIDDEN;
       }
       return WiFiRetryPhase::SCAN_CONNECTING;
@@ -1716,11 +1789,11 @@ void WiFiComponent::log_and_adjust_priority_for_failed_connect_() {
   }
 
   // Get SSID for logging (use pointer to avoid copy)
-  const std::string *ssid = nullptr;
+  const char *ssid = nullptr;
   if (this->retry_phase_ == WiFiRetryPhase::SCAN_CONNECTING && !this->scan_result_.empty()) {
-    ssid = &this->scan_result_[0].get_ssid();
+    ssid = this->scan_result_[0].get_ssid().c_str();
   } else if (const WiFiAP *config = this->get_selected_sta_()) {
-    ssid = &config->get_ssid();
+    ssid = config->get_ssid().c_str();
   }
 
   // Only decrease priority on the last attempt for this phase
@@ -1740,8 +1813,8 @@ void WiFiComponent::log_and_adjust_priority_for_failed_connect_() {
   }
   char bssid_s[18];
   format_mac_addr_upper(failed_bssid.value().data(), bssid_s);
-  ESP_LOGD(TAG, "Failed " LOG_SECRET("'%s'") " " LOG_SECRET("(%s)") ", priority %d → %d",
-           ssid != nullptr ? ssid->c_str() : "", bssid_s, old_priority, new_priority);
+  ESP_LOGD(TAG, "Failed " LOG_SECRET("'%s'") " " LOG_SECRET("(%s)") ", priority %d → %d", ssid != nullptr ? ssid : "",
+           bssid_s, old_priority, new_priority);
 
   // After adjusting priority, check if all priorities are now at minimum
   // If so, clear the vector to save memory and reset for fresh start
@@ -1989,10 +2062,14 @@ void WiFiComponent::save_fast_connect_settings_() {
 }
 #endif
 
-void WiFiAP::set_ssid(const std::string &ssid) { this->ssid_ = ssid; }
+void WiFiAP::set_ssid(const std::string &ssid) { this->ssid_ = CompactString(ssid.c_str(), ssid.size()); }
+void WiFiAP::set_ssid(const char *ssid) { this->ssid_ = CompactString(ssid, strlen(ssid)); }
 void WiFiAP::set_bssid(const bssid_t &bssid) { this->bssid_ = bssid; }
 void WiFiAP::clear_bssid() { this->bssid_ = {}; }
-void WiFiAP::set_password(const std::string &password) { this->password_ = password; }
+void WiFiAP::set_password(const std::string &password) {
+  this->password_ = CompactString(password.c_str(), password.size());
+}
+void WiFiAP::set_password(const char *password) { this->password_ = CompactString(password, strlen(password)); }
 #ifdef USE_WIFI_WPA2_EAP
 void WiFiAP::set_eap(optional<EAPAuth> eap_auth) { this->eap_ = std::move(eap_auth); }
 #endif
@@ -2002,10 +2079,8 @@ void WiFiAP::clear_channel() { this->channel_ = 0; }
 void WiFiAP::set_manual_ip(optional<ManualIP> manual_ip) { this->manual_ip_ = manual_ip; }
 #endif
 void WiFiAP::set_hidden(bool hidden) { this->hidden_ = hidden; }
-const std::string &WiFiAP::get_ssid() const { return this->ssid_; }
 const bssid_t &WiFiAP::get_bssid() const { return this->bssid_; }
 bool WiFiAP::has_bssid() const { return this->bssid_ != bssid_t{}; }
-const std::string &WiFiAP::get_password() const { return this->password_; }
 #ifdef USE_WIFI_WPA2_EAP
 const optional<EAPAuth> &WiFiAP::get_eap() const { return this->eap_; }
 #endif
@@ -2016,12 +2091,12 @@ const optional<ManualIP> &WiFiAP::get_manual_ip() const { return this->manual_ip
 #endif
 bool WiFiAP::get_hidden() const { return this->hidden_; }
 
-WiFiScanResult::WiFiScanResult(const bssid_t &bssid, std::string ssid, uint8_t channel, int8_t rssi, bool with_auth,
-                               bool is_hidden)
+WiFiScanResult::WiFiScanResult(const bssid_t &bssid, const char *ssid, size_t ssid_len, uint8_t channel, int8_t rssi,
+                               bool with_auth, bool is_hidden)
     : bssid_(bssid),
       channel_(channel),
       rssi_(rssi),
-      ssid_(std::move(ssid)),
+      ssid_(ssid, ssid_len),
       with_auth_(with_auth),
       is_hidden_(is_hidden) {}
 bool WiFiScanResult::matches(const WiFiAP &config) const {
@@ -2064,7 +2139,6 @@ bool WiFiScanResult::matches(const WiFiAP &config) const {
 bool WiFiScanResult::get_matches() const { return this->matches_; }
 void WiFiScanResult::set_matches(bool matches) { this->matches_ = matches; }
 const bssid_t &WiFiScanResult::get_bssid() const { return this->bssid_; }
-const std::string &WiFiScanResult::get_ssid() const { return this->ssid_; }
 uint8_t WiFiScanResult::get_channel() const { return this->channel_; }
 int8_t WiFiScanResult::get_rssi() const { return this->rssi_; }
 bool WiFiScanResult::get_with_auth() const { return this->with_auth_; }
@@ -2080,7 +2154,7 @@ void WiFiComponent::clear_roaming_state_() {
 
 void WiFiComponent::release_scan_results_() {
   if (!this->keep_scan_results_) {
-#ifdef USE_RP2040
+#if defined(USE_RP2040) || defined(USE_ESP32)
     // std::vector - use swap trick since shrink_to_fit is non-binding
     decltype(this->scan_result_)().swap(this->scan_result_);
 #else
@@ -2137,7 +2211,7 @@ void WiFiComponent::process_roaming_scan_() {
 
   for (const auto &result : this->scan_result_) {
     // Must be same SSID, different BSSID
-    if (current_ssid != result.get_ssid() || result.get_bssid() == current_bssid)
+    if (result.get_ssid() != current_ssid.c_str() || result.get_bssid() == current_bssid)
       continue;
 
 #if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERBOSE

esphome/components/wifi/wifi_component.h

@@ -161,9 +161,12 @@ struct EAPAuth {
 
 using bssid_t = std::array<uint8_t, 6>;
 
-// Use std::vector for RP2040 since scan count is unknown (callback-based)
-// Use FixedVector for other platforms where count is queried first
-#ifdef USE_RP2040
+/// Initial reserve size for filtered scan results (typical: 1-3 matching networks per SSID)
+static constexpr size_t WIFI_SCAN_RESULT_FILTERED_RESERVE = 8;
+
+// Use std::vector for RP2040 (callback-based) and ESP32 (destructive scan API)
+// Use FixedVector for ESP8266 and LibreTiny where two-pass exact allocation is possible
+#if defined(USE_RP2040) || defined(USE_ESP32)
 template<typename T> using wifi_scan_vector_t = std::vector<T>;
 #else
 template<typename T> using wifi_scan_vector_t = FixedVector<T>;
@@ -172,9 +175,13 @@ template<typename T> using wifi_scan_vector_t = FixedVector<T>;
 class WiFiAP {
  public:
   void set_ssid(const std::string &ssid);
+  void set_ssid(const char *ssid);
+  void set_ssid(const CompactString &ssid) { this->ssid_ = ssid; }
   void set_bssid(const bssid_t &bssid);
   void clear_bssid();
   void set_password(const std::string &password);
+  void set_password(const char *password);
+  void set_password(const CompactString &password) { this->password_ = password; }
 #ifdef USE_WIFI_WPA2_EAP
   void set_eap(optional<EAPAuth> eap_auth);
 #endif  // USE_WIFI_WPA2_EAP
@@ -185,10 +192,10 @@ class WiFiAP {
   void set_manual_ip(optional<ManualIP> manual_ip);
 #endif
   void set_hidden(bool hidden);
-  const std::string &get_ssid() const;
+  const CompactString &get_ssid() const { return this->ssid_; }
+  const CompactString &get_password() const { return this->password_; }
   const bssid_t &get_bssid() const;
   bool has_bssid() const;
-  const std::string &get_password() const;
 #ifdef USE_WIFI_WPA2_EAP
   const optional<EAPAuth> &get_eap() const;
 #endif  // USE_WIFI_WPA2_EAP
@@ -201,8 +208,8 @@ class WiFiAP {
   bool get_hidden() const;
 
  protected:
-  std::string ssid_;
-  std::string password_;
+  CompactString ssid_;
+  CompactString password_;
 #ifdef USE_WIFI_WPA2_EAP
   optional<EAPAuth> eap_;
 #endif  // USE_WIFI_WPA2_EAP
@@ -218,14 +225,15 @@ class WiFiAP {
 
 class WiFiScanResult {
  public:
-  WiFiScanResult(const bssid_t &bssid, std::string ssid, uint8_t channel, int8_t rssi, bool with_auth, bool is_hidden);
+  WiFiScanResult(const bssid_t &bssid, const char *ssid, size_t ssid_len, uint8_t channel, int8_t rssi, bool with_auth,
+                 bool is_hidden);
 
   bool matches(const WiFiAP &config) const;
 
   bool get_matches() const;
   void set_matches(bool matches);
   const bssid_t &get_bssid() const;
-  const std::string &get_ssid() const;
+  const CompactString &get_ssid() const { return this->ssid_; }
   uint8_t get_channel() const;
   int8_t get_rssi() const;
   bool get_with_auth() const;
@@ -239,7 +247,7 @@ class WiFiScanResult {
   bssid_t bssid_;
   uint8_t channel_;
   int8_t rssi_;
-  std::string ssid_;
+  CompactString ssid_;
   int8_t priority_{0};
   bool matches_{false};
   bool with_auth_;
@@ -378,6 +386,10 @@ class WiFiComponent : public Component {
   void set_passive_scan(bool passive);
 
   void save_wifi_sta(const std::string &ssid, const std::string &password);
+  void save_wifi_sta(const char *ssid, const char *password);
+  void save_wifi_sta(const CompactString &ssid, const CompactString &password) {
+    this->save_wifi_sta(ssid.c_str(), password.c_str());
+  }
 
   // ========== INTERNAL METHODS ==========
   // (In most use cases you won't need these)
@@ -538,7 +550,14 @@ class WiFiComponent : public Component {
   int8_t find_first_non_hidden_index_() const;
   /// Check if an SSID was seen in the most recent scan results
   /// Used to skip hidden mode for SSIDs we know are visible
-  bool ssid_was_seen_in_scan_(const std::string &ssid) const;
+  bool ssid_was_seen_in_scan_(const CompactString &ssid) const;
+  /// Check if full scan results are needed (captive portal active, improv, listeners)
+  bool needs_full_scan_results_() const;
+  /// Check if network matches any configured network (for scan result filtering)
+  /// Matches by SSID when configured, or by BSSID for BSSID-only configs
+  bool matches_configured_network_(const char *ssid, const uint8_t *bssid) const;
+  /// Log a discarded scan result at VERBOSE level (skipped during roaming scans to avoid log overflow)
+  void log_discarded_scan_result_(const char *ssid, const uint8_t *bssid, int8_t rssi, uint8_t channel);
   /// Find next SSID that wasn't in scan results (might be hidden)
   /// Returns index of next potentially hidden SSID, or -1 if none found
   /// @param start_index Start searching from index after this (-1 to start from beginning)
@@ -710,6 +729,8 @@ class WiFiComponent : public Component {
   bool enable_on_boot_{true};
   bool got_ipv4_address_{false};
   bool keep_scan_results_{false};
+  bool has_completed_scan_after_captive_portal_start_{
+      false};  // Tracks if we've completed a scan after captive portal started
   RetryHiddenMode retry_hidden_mode_{RetryHiddenMode::BLIND_RETRY};
   bool skip_cooldown_next_cycle_{false};
   bool post_connect_roaming_{true};  // Enabled by default

esphome/components/wifi/wifi_component_esp8266.cpp

@@ -756,20 +756,35 @@ void WiFiComponent::wifi_scan_done_callback_(void *arg, STATUS status) {
     return;
   }
 
-  // Count the number of results first
   auto *head = reinterpret_cast<bss_info *>(arg);
+  bool needs_full = this->needs_full_scan_results_();
+
+  // First pass: count matching networks (linked list is non-destructive)
+  size_t total = 0;
   size_t count = 0;
   for (bss_info *it = head; it != nullptr; it = STAILQ_NEXT(it, next)) {
-    count++;
+    total++;
+    const char *ssid_cstr = reinterpret_cast<const char *>(it->ssid);
+    if (needs_full || this->matches_configured_network_(ssid_cstr, it->bssid)) {
+      count++;
+    }
   }
 
-  this->scan_result_.init(count);
+  this->scan_result_.init(count);  // Exact allocation
+
+  // Second pass: store matching networks
   for (bss_info *it = head; it != nullptr; it = STAILQ_NEXT(it, next)) {
-    this->scan_result_.emplace_back(
-        bssid_t{it->bssid[0], it->bssid[1], it->bssid[2], it->bssid[3], it->bssid[4], it->bssid[5]},
-        std::string(reinterpret_cast<char *>(it->ssid), it->ssid_len), it->channel, it->rssi, it->authmode != AUTH_OPEN,
-        it->is_hidden != 0);
+    const char *ssid_cstr = reinterpret_cast<const char *>(it->ssid);
+    if (needs_full || this->matches_configured_network_(ssid_cstr, it->bssid)) {
+      this->scan_result_.emplace_back(
+          bssid_t{it->bssid[0], it->bssid[1], it->bssid[2], it->bssid[3], it->bssid[4], it->bssid[5]}, ssid_cstr,
+          it->ssid_len, it->channel, it->rssi, it->authmode != AUTH_OPEN, it->is_hidden != 0);
+    } else {
+      this->log_discarded_scan_result_(ssid_cstr, it->bssid, it->rssi, it->channel);
+    }
   }
+  ESP_LOGV(TAG, "Scan complete: %zu found, %zu stored%s", total, this->scan_result_.size(),
+           needs_full ? "" : " (filtered)");
   this->scan_done_ = true;
 #ifdef USE_WIFI_SCAN_RESULTS_LISTENERS
   for (auto *listener : global_wifi_component->scan_results_listeners_) {

esphome/components/wifi/wifi_component_esp_idf.cpp

@@ -827,7 +827,14 @@ void WiFiComponent::wifi_process_event_(IDFWiFiEvent *data) {
     }
 
     uint16_t number = it.number;
-    scan_result_.init(number);
+    bool needs_full = this->needs_full_scan_results_();
+
+    // Smart reserve: full capacity if needed, small reserve otherwise
+    if (needs_full) {
+      this->scan_result_.reserve(number);
+    } else {
+      this->scan_result_.reserve(WIFI_SCAN_RESULT_FILTERED_RESERVE);
+    }
 
     // Process one record at a time to avoid large buffer allocation
     wifi_ap_record_t record;
@@ -838,12 +845,22 @@ void WiFiComponent::wifi_process_event_(IDFWiFiEvent *data) {
         esp_wifi_clear_ap_list();  // Free remaining records not yet retrieved
         break;
       }
-      bssid_t bssid;
-      std::copy(record.bssid, record.bssid + 6, bssid.begin());
-      std::string ssid(reinterpret_cast<const char *>(record.ssid));
-      scan_result_.emplace_back(bssid, ssid, record.primary, record.rssi, record.authmode != WIFI_AUTH_OPEN,
-                                ssid.empty());
+
+      // Check C string first - avoid std::string construction for non-matching networks
+      const char *ssid_cstr = reinterpret_cast<const char *>(record.ssid);
+
+      // Only construct std::string and store if needed
+      if (needs_full || this->matches_configured_network_(ssid_cstr, record.bssid)) {
+        bssid_t bssid;
+        std::copy(record.bssid, record.bssid + 6, bssid.begin());
+        this->scan_result_.emplace_back(bssid, ssid_cstr, strlen(ssid_cstr), record.primary, record.rssi,
+                                        record.authmode != WIFI_AUTH_OPEN, ssid_cstr[0] == '\0');
+      } else {
+        this->log_discarded_scan_result_(ssid_cstr, record.bssid, record.rssi, record.primary);
+      }
     }
+    ESP_LOGV(TAG, "Scan complete: %u found, %zu stored%s", number, this->scan_result_.size(),
+             needs_full ? "" : " (filtered)");
 #ifdef USE_WIFI_SCAN_RESULTS_LISTENERS
     for (auto *listener : this->scan_results_listeners_) {
       listener->on_wifi_scan_results(this->scan_result_);

esphome/components/wifi/wifi_component_libretiny.cpp

@@ -666,18 +666,39 @@ void WiFiComponent::wifi_scan_done_callback_() {
   if (num < 0)
     return;
 
-  this->scan_result_.init(static_cast<unsigned int>(num));
-  for (int i = 0; i < num; i++) {
-    String ssid = WiFi.SSID(i);
-    wifi_auth_mode_t authmode = WiFi.encryptionType(i);
-    int32_t rssi = WiFi.RSSI(i);
-    uint8_t *bssid = WiFi.BSSID(i);
-    int32_t channel = WiFi.channel(i);
+  bool needs_full = this->needs_full_scan_results_();
 
-    this->scan_result_.emplace_back(bssid_t{bssid[0], bssid[1], bssid[2], bssid[3], bssid[4], bssid[5]},
-                                    std::string(ssid.c_str()), channel, rssi, authmode != WIFI_AUTH_OPEN,
-                                    ssid.length() == 0);
+  // Access scan results directly via WiFi.scan struct to avoid Arduino String allocations
+  // WiFi.scan is public in LibreTiny for WiFiEvents & WiFiScan static handlers
+  auto *scan = WiFi.scan;
+
+  // First pass: count matching networks
+  size_t count = 0;
+  for (int i = 0; i < num; i++) {
+    const char *ssid_cstr = scan->ap[i].ssid;
+    if (needs_full || this->matches_configured_network_(ssid_cstr, scan->ap[i].bssid.addr)) {
+      count++;
+    }
   }
+
+  this->scan_result_.init(count);  // Exact allocation
+
+  // Second pass: store matching networks
+  for (int i = 0; i < num; i++) {
+    const char *ssid_cstr = scan->ap[i].ssid;
+    if (needs_full || this->matches_configured_network_(ssid_cstr, scan->ap[i].bssid.addr)) {
+      auto &ap = scan->ap[i];
+      this->scan_result_.emplace_back(bssid_t{ap.bssid.addr[0], ap.bssid.addr[1], ap.bssid.addr[2], ap.bssid.addr[3],
+                                              ap.bssid.addr[4], ap.bssid.addr[5]},
+                                      ssid_cstr, strlen(ssid_cstr), ap.channel, ap.rssi, ap.auth != WIFI_AUTH_OPEN,
+                                      ssid_cstr[0] == '\0');
+    } else {
+      auto &ap = scan->ap[i];
+      this->log_discarded_scan_result_(ssid_cstr, ap.bssid.addr, ap.rssi, ap.channel);
+    }
+  }
+  ESP_LOGV(TAG, "Scan complete: %d found, %zu stored%s", num, this->scan_result_.size(),
+           needs_full ? "" : " (filtered)");
   WiFi.scanDelete();
 #ifdef USE_WIFI_SCAN_RESULTS_LISTENERS
   for (auto *listener : this->scan_results_listeners_) {

esphome/components/wifi/wifi_component_pico_w.cpp

@@ -21,6 +21,7 @@ static const char *const TAG = "wifi_pico_w";
 // Track previous state for detecting changes
 static bool s_sta_was_connected = false;  // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
 static bool s_sta_had_ip = false;         // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
+static size_t s_scan_result_count = 0;    // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
 
 bool WiFiComponent::wifi_mode_(optional<bool> sta, optional<bool> ap) {
   if (sta.has_value()) {
@@ -137,10 +138,19 @@ int WiFiComponent::s_wifi_scan_result(void *env, const cyw43_ev_scan_result_t *r
 }
 
 void WiFiComponent::wifi_scan_result(void *env, const cyw43_ev_scan_result_t *result) {
+  s_scan_result_count++;
+  const char *ssid_cstr = reinterpret_cast<const char *>(result->ssid);
+
+  // Skip networks that don't match any configured network (unless full results needed)
+  if (!this->needs_full_scan_results_() && !this->matches_configured_network_(ssid_cstr, result->bssid)) {
+    this->log_discarded_scan_result_(ssid_cstr, result->bssid, result->rssi, result->channel);
+    return;
+  }
+
   bssid_t bssid;
   std::copy(result->bssid, result->bssid + 6, bssid.begin());
-  std::string ssid(reinterpret_cast<const char *>(result->ssid));
-  WiFiScanResult res(bssid, ssid, result->channel, result->rssi, result->auth_mode != CYW43_AUTH_OPEN, ssid.empty());
+  WiFiScanResult res(bssid, ssid_cstr, strlen(ssid_cstr), result->channel, result->rssi,
+                     result->auth_mode != CYW43_AUTH_OPEN, ssid_cstr[0] == '\0');
   if (std::find(this->scan_result_.begin(), this->scan_result_.end(), res) == this->scan_result_.end()) {
     this->scan_result_.push_back(res);
   }
@@ -149,6 +159,7 @@ void WiFiComponent::wifi_scan_result(void *env, const cyw43_ev_scan_result_t *re
 bool WiFiComponent::wifi_scan_start_(bool passive) {
   this->scan_result_.clear();
   this->scan_done_ = false;
+  s_scan_result_count = 0;
   cyw43_wifi_scan_options_t scan_options = {0};
   scan_options.scan_type = passive ? 1 : 0;
   int err = cyw43_wifi_scan(&cyw43_state, &scan_options, nullptr, &s_wifi_scan_result);
@@ -244,7 +255,9 @@ void WiFiComponent::wifi_loop_() {
   // Handle scan completion
   if (this->state_ == WIFI_COMPONENT_STATE_STA_SCANNING && !cyw43_wifi_scan_active(&cyw43_state)) {
     this->scan_done_ = true;
-    ESP_LOGV(TAG, "Scan done");
+    bool needs_full = this->needs_full_scan_results_();
+    ESP_LOGV(TAG, "Scan complete: %zu found, %zu stored%s", s_scan_result_count, this->scan_result_.size(),
+             needs_full ? "" : " (filtered)");
 #ifdef USE_WIFI_SCAN_RESULTS_LISTENERS
     for (auto *listener : this->scan_results_listeners_) {
       listener->on_wifi_scan_results(this->scan_result_);

esphome/components/wifi_info/wifi_info_text_sensor.cpp

@@ -89,7 +89,7 @@ void ScanResultsWiFiInfo::on_wifi_scan_results(const wifi::wifi_scan_vector_t<wi
   for (const auto &scan : results) {
     if (scan.get_is_hidden())
       continue;
-    const std::string &ssid = scan.get_ssid();
+    const auto &ssid = scan.get_ssid();
     // Max space: ssid + ": " (2) + "-128" (4) + "dB\n" (3) = ssid + 9
     if (ptr + ssid.size() + 9 > end)
       break;

esphome/core/helpers.cpp

@@ -12,6 +12,7 @@
 #include <cstdarg>
 #include <cstdio>
 #include <cstring>
+#include <new>
 
 #ifdef USE_ESP32
 #include "rom/crc.h"
@@ -857,4 +858,60 @@ void IRAM_ATTR HOT delay_microseconds_safe(uint32_t us) {
     ;
 }
 
+// CompactString implementation
+CompactString::CompactString(const char *str, size_t len) {
+  if (len > MAX_LENGTH) {
+    len = MAX_LENGTH;  // Clamp to max valid length
+  }
+
+  this->length_ = len;
+  if (len <= INLINE_CAPACITY) {
+    // Store inline with null terminator
+    this->is_heap_ = 0;
+    if (len > 0) {
+      std::memcpy(this->storage_, str, len);
+    }
+    this->storage_[len] = '\0';
+  } else {
+    // Heap allocate with null terminator
+    this->is_heap_ = 1;
+    char *heap_data = new char[len + 1];  // NOLINT(cppcoreguidelines-owning-memory)
+    std::memcpy(heap_data, str, len);
+    heap_data[len] = '\0';
+    this->set_heap_ptr_(heap_data);
+  }
+}
+
+CompactString::CompactString(const CompactString &other) : CompactString(other.data(), other.size()) {}
+
+CompactString &CompactString::operator=(const CompactString &other) {
+  if (this != &other) {
+    this->~CompactString();
+    new (this) CompactString(other);
+  }
+  return *this;
+}
+
+CompactString::CompactString(CompactString &&other) noexcept : length_(other.length_), is_heap_(other.is_heap_) {
+  // Copy full storage (includes null terminator for inline, or pointer for heap)
+  std::memcpy(this->storage_, other.storage_, INLINE_CAPACITY + 1);
+  other.length_ = 0;
+  other.is_heap_ = 0;
+  other.storage_[0] = '\0';
+}
+
+CompactString &CompactString::operator=(CompactString &&other) noexcept {
+  if (this != &other) {
+    this->~CompactString();
+    new (this) CompactString(std::move(other));
+  }
+  return *this;
+}
+
+CompactString::~CompactString() {
+  if (this->is_heap_) {
+    delete[] this->get_heap_ptr_();  // NOLINT(cppcoreguidelines-owning-memory)
+  }
+}
+
 }  // namespace esphome

esphome/core/helpers.h

@@ -1749,4 +1749,58 @@ template<typename T, enable_if_t<std::is_pointer<T *>::value, int> = 0> T &id(T
 
 ///@}
 
+/// 20-byte string: 18 chars inline + null, heap for longer. Always null-terminated.
+class CompactString {
+ public:
+  static constexpr uint8_t MAX_LENGTH = 127;
+  static constexpr uint8_t INLINE_CAPACITY = 18;          // 18 chars + null terminator fits in 19 bytes
+  static constexpr uint8_t BUFFER_SIZE = MAX_LENGTH + 1;  // For external buffer (128 bytes)
+
+  CompactString() : length_(0), is_heap_(0) { this->storage_[0] = '\0'; }
+  CompactString(const char *str, size_t len);
+  CompactString(const CompactString &other);
+  CompactString(CompactString &&other) noexcept;
+  CompactString &operator=(const CompactString &other);
+  CompactString &operator=(CompactString &&other) noexcept;
+  ~CompactString();
+
+  const char *data() const { return this->is_heap_ ? this->get_heap_ptr_() : this->storage_; }
+  const char *c_str() const { return this->data(); }  // Always null-terminated
+  size_t size() const { return this->length_; }
+  bool empty() const { return this->length_ == 0; }
+
+  // Implicit conversion to std::string for backwards compatibility
+  operator std::string() const { return std::string(this->data(), this->size()); }
+
+  bool operator==(const CompactString &other) const {
+    return this->size() == other.size() && std::memcmp(this->data(), other.data(), this->size()) == 0;
+  }
+  bool operator==(const std::string &other) const {
+    return this->size() == other.size() && std::memcmp(this->data(), other.data(), this->size()) == 0;
+  }
+  bool operator==(const char *other) const {
+    return this->size() == std::strlen(other) && std::memcmp(this->data(), other, this->size()) == 0;
+  }
+  bool operator!=(const CompactString &other) const { return !(*this == other); }
+  bool operator!=(const std::string &other) const { return !(*this == other); }
+  bool operator!=(const char *other) const { return !(*this == other); }
+
+ protected:
+  char *get_heap_ptr_() const {
+    char *ptr;
+    std::memcpy(&ptr, this->storage_, sizeof(ptr));
+    return ptr;
+  }
+  void set_heap_ptr_(char *ptr) { std::memcpy(this->storage_, &ptr, sizeof(ptr)); }
+
+  // Storage for string data. When is_heap_=0, contains the string directly (null-terminated).
+  // When is_heap_=1, first sizeof(char*) bytes contain pointer to heap allocation.
+  char storage_[INLINE_CAPACITY + 1];  // 19 bytes: 18 chars + null terminator
+  uint8_t length_ : 7;                 // String length (0-127)
+  uint8_t is_heap_ : 1;                // 1 if using heap pointer, 0 if using inline storage
+  // Total size: 20 bytes (19 bytes storage + 1 byte bitfields)
+};
+
+static_assert(sizeof(CompactString) == 20, "CompactString must be exactly 20 bytes");
+
 }  // namespace esphome