Introduce str_lower_case() and str_upper_case() helpers

esphome/core/helpers.cpp

@@ -2,6 +2,7 @@
 #include "esphome/core/defines.h"
 #include <cstdio>
 #include <algorithm>
+#include <cctype>
 #include <cmath>
 #include <cstring>
 
@@ -361,6 +362,16 @@ std::string str_until(const char *str, char ch) {
   return pos == nullptr ? std::string(str) : std::string(str, pos - str);
 }
 std::string str_until(const std::string &str, char ch) { return str.substr(0, str.find(ch)); }
+// wrapper around std::transform to run safely on functions from the ctype.h header
+// see https://en.cppreference.com/w/cpp/string/byte/toupper#Notes
+template<int (*fn)(int)> std::string str_ctype_transform(const std::string &str) {
+  std::string result;
+  result.resize(str.length());
+  std::transform(str.begin(), str.end(), result.begin(), [](unsigned char ch) { return fn(ch); });
+  return result;
+}
+std::string str_lower_case(const std::string &str) { return str_ctype_transform<std::toupper>(str); }
+std::string str_upper_case(const std::string &str) { return str_ctype_transform<std::tolower>(str); }
 std::string str_snake_case(const std::string &str) {
   std::string result;
   result.resize(str.length());

esphome/core/helpers.h

@@ -369,6 +369,10 @@ std::string str_until(const char *str, char ch);
 /// Extract the part of the string until either the first occurence of the specified character, or the end.
 std::string str_until(const std::string &str, char ch);
 
+/// Convert the string to lower case.
+std::string str_lower_case(const std::string &str);
+/// Convert the string to upper case.
+std::string str_upper_case(const std::string &str);
 /// Convert the string to snake case (lowercase with underscores).
 std::string str_snake_case(const std::string &str);