[sntp] Store server strings in flash memory

esphome/components/sntp/sntp_component.cpp

@@ -27,7 +27,7 @@ void SNTPComponent::setup() {
   esp_sntp_setoperatingmode(ESP_SNTP_OPMODE_POLL);
   size_t i = 0;
   for (auto &server : this->servers_) {
-    esp_sntp_setservername(i++, server.c_str());
+    esp_sntp_setservername(i++, server);
   }
   esp_sntp_set_sync_interval(this->get_update_interval());
   esp_sntp_set_time_sync_notification_cb([](struct timeval *tv) {
@@ -42,7 +42,16 @@ void SNTPComponent::setup() {
 
   size_t i = 0;
   for (auto &server : this->servers_) {
-    sntp_setservername(i++, server.c_str());
+#if defined(USE_ESP8266)
+    // On ESP8266, server is PGM_P pointing to PROGMEM
+    // LWIP's sntp_setservername is not PROGMEM-aware, so copy to stack buffer first
+    char server_buf[64];
+    strncpy_P(server_buf, server, sizeof(server_buf) - 1);
+    server_buf[sizeof(server_buf) - 1] = '\0';
+    sntp_setservername(i++, server_buf);
+#else
+    sntp_setservername(i++, server);
+#endif
   }
 
 #if defined(USE_ESP8266)
@@ -59,7 +68,8 @@ void SNTPComponent::dump_config() {
   ESP_LOGCONFIG(TAG, "SNTP Time:");
   size_t i = 0;
   for (auto &server : this->servers_) {
-    ESP_LOGCONFIG(TAG, "  Server %zu: '%s'", i++, server.c_str());
+    // LOG_STR_ARG handles both PROGMEM (ESP8266) and regular pointers
+    ESP_LOGCONFIG(TAG, "  Server %zu: '%s'", i++, LOG_STR_ARG(server));
   }
 }
 void SNTPComponent::update() {

esphome/components/sntp/sntp_component.h

@@ -2,10 +2,18 @@
 
 #include "esphome/core/component.h"
 #include "esphome/components/time/real_time_clock.h"
+#include <array>
+
+#ifdef USE_ESP8266
+#include <pgmspace.h>
+#endif
 
 namespace esphome {
 namespace sntp {
 
+// Server count is calculated at compile time by Python codegen
+// SNTP_SERVER_COUNT will always be defined
+
 /// The SNTP component allows you to configure local timekeeping via Simple Network Time Protocol.
 ///
 /// \note
@@ -14,10 +22,7 @@ namespace sntp {
 /// \see https://www.gnu.org/software/libc/manual/html_node/TZ-Variable.html
 class SNTPComponent : public time::RealTimeClock {
  public:
-  SNTPComponent(const std::vector<std::string> &servers) : servers_(servers) {}
-
-  // Note: set_servers() has been removed and replaced by a constructor - calling set_servers after setup would
-  // have had no effect anyway, and making the strings immutable avoids the need to strdup their contents.
+  SNTPComponent() = default;
 
   void setup() override;
   void dump_config() override;
@@ -28,8 +33,15 @@ class SNTPComponent : public time::RealTimeClock {
 
   void time_synced();
 
+#ifdef USE_ESP8266
+  // On ESP8266, store pointers to PROGMEM strings to save RAM
+  std::array<PGM_P, SNTP_SERVER_COUNT> servers_{};
+#else
+  // On other platforms, store regular const char pointers
+  std::array<const char *, SNTP_SERVER_COUNT> servers_{};
+#endif
+
  protected:
-  std::vector<std::string> servers_;
   bool has_time_{false};
 
 #if defined(USE_ESP32)

esphome/components/sntp/time.py

@@ -12,6 +12,7 @@ from esphome.const import (
     PLATFORM_RTL87XX,
 )
 from esphome.core import CORE
+from esphome.cpp_generator import ProgmemAssignmentExpression
 
 DEPENDENCIES = ["network"]
 sntp_ns = cg.esphome_ns.namespace("sntp")
@@ -43,11 +44,34 @@ CONFIG_SCHEMA = cv.All(
 
 async def to_code(config):
     servers = config[CONF_SERVERS]
-    var = cg.new_Pvariable(config[CONF_ID], servers)
+    server_count = len(servers)
+
+    # Define server count at compile time
+    cg.add_define("SNTP_SERVER_COUNT", server_count)
+
+    var = cg.new_Pvariable(config[CONF_ID])
 
     await cg.register_component(var, config)
     await time_.register_time(var, config)
 
+    # Generate PROGMEM strings for ESP8266, regular strings for other platforms
+    if CORE.is_esp8266:
+        # On ESP8266, use PROGMEM to store strings in flash
+        # Use ProgmemAssignmentExpression to generate: static const char name[] PROGMEM = "value";
+        for i, server in enumerate(servers):
+            var_name = f"{config[CONF_ID].id}_server_{i}"
+            # Create PROGMEM string: static const char var_name[] PROGMEM = "server";
+            assignment = ProgmemAssignmentExpression(
+                "char", var_name, cg.safe_exp(server)
+            )
+            cg.add(assignment)
+            # Assign pointer to array element
+            cg.add(cg.RawStatement(f"{var}->servers_[{i}] = {var_name};"))
+    else:
+        # On other platforms, use regular string literals
+        for i, server in enumerate(servers):
+            cg.add(cg.RawStatement(f"{var}->servers_[{i}] = {cg.safe_exp(server)};"))
+
     if CORE.is_esp8266 and len(servers) > 1:
         # We need LwIP features enabled to get 3 SNTP servers (not just one)
         cg.add_build_flag("-DPIO_FRAMEWORK_ARDUINO_LWIP2_LOW_MEMORY")