[core] Add str_contains_ignore_case_p for PROGMEM needle strings

esphome/core/helpers.cpp

@@ -233,6 +233,28 @@ bool str_contains_ignore_case_fallback(const char *haystack, const char *needle)
   return false;
 }
 
+bool str_contains_ignore_case_p(const char *haystack, const char *needle) {
+  if (haystack == nullptr || needle == nullptr) {
+    return false;
+  }
+  const auto *needle_p = reinterpret_cast<const uint8_t *>(needle);
+  if (progmem_read_byte(needle_p) == '\0') {
+    return true;
+  }
+  for (const char *p = haystack; *p != '\0'; p++) {
+    size_t i = 0;
+    uint8_t n;
+    // Never reads past the haystack terminator: comparing '\0' against a non-'\0' needle byte fails
+    while ((n = progmem_read_byte(needle_p + i)) != '\0' && ::tolower(static_cast<uint8_t>(p[i])) == ::tolower(n)) {
+      i++;
+    }
+    if (n == '\0') {
+      return true;
+    }
+  }
+  return false;
+}
+
 // str_truncate, str_until, str_lower_case, str_upper_case, str_snake_case moved to alloc_helpers.cpp
 char *str_sanitize_to(char *buffer, size_t buffer_size, const char *str) {
   if (buffer_size == 0) {

esphome/core/helpers.h

@@ -1000,6 +1000,11 @@ inline bool str_contains_ignore_case(const char *haystack, const char *needle) {
 #endif  // defined(USE_LIBRETINY) || defined(USE_RP2) || defined(USE_ZEPHYR)
 }
 
+/// Case-insensitive check if needle string is contained in haystack (no heap allocation).
+/// The needle may live in flash (PROGMEM) on ESP8266 — wrap literals with PSTR().
+/// On all other platforms PROGMEM reads are plain dereferences, so any string works.
+bool str_contains_ignore_case_p(const char *haystack, const char *needle);
+
 // str_truncate moved to alloc_helpers.h - remove this include before 2026.11.0
 
 // str_until, str_lower_case, str_upper_case moved to alloc_helpers.h - remove this comment before 2026.11.0

tests/components/core/helpers_test.cpp

@@ -129,4 +129,24 @@ TEST(StringContainsIgnoreCaseTest, FallbackMatchesLibc) {
   EXPECT_EQ(str_contains_ignore_case_fallback("ab", "abc"), str_contains_ignore_case("ab", "abc"));
 }
 
+TEST(StringContainsIgnoreCaseTest, ProgmemVariantNullPointerAlwaysFalse) {
+  const char *haystack = nullptr;
+  const char *needle = nullptr;
+
+  EXPECT_FALSE(str_contains_ignore_case_p(haystack, needle));
+  EXPECT_FALSE(str_contains_ignore_case_p("Hello World", needle));
+  EXPECT_FALSE(str_contains_ignore_case_p(haystack, "anything"));
+}
+
+TEST(StringContainsIgnoreCaseTest, ProgmemVariantMatchesFallback) {
+  const char *haystack = "Hello World";
+  for (const char *needle : {"", "Hello", "hELLO", "HELLO", "Hell", "world", "World", "Heaven", "Hello!", "d"}) {
+    EXPECT_EQ(str_contains_ignore_case_p(haystack, needle), str_contains_ignore_case_fallback(haystack, needle))
+        << "needle: " << needle;
+  }
+  EXPECT_TRUE(str_contains_ignore_case_p("", ""));
+  EXPECT_FALSE(str_contains_ignore_case_p("", "a"));
+  EXPECT_FALSE(str_contains_ignore_case_p("ab", "abc"));
+}
+
 }  // namespace esphome