add util::crop_utf8 (stringutil)

src/util/stringutil.cpp

@@ -141,6 +141,19 @@ extern uint32_t util::decode_utf8(uint& size, const char* chr) {
     return code;
 }
 
+size_t util::crop_utf8(std::string_view s, size_t maxSize) {
+    size_t pos = 0;
+    uint size = 0;
+    while (pos < s.length()) {
+        decode_utf8(size, &s.at(pos));
+        if (pos + size > maxSize) {
+            return pos;
+        }
+        pos += size;
+    }
+    return pos;
+}
+
 std::string util::wstr2str_utf8(const std::wstring& ws) {
     std::vector<char> chars;
     char buffer[4];

src/util/stringutil.hpp

@@ -17,8 +17,23 @@ namespace util {
 
     uint encode_utf8(uint32_t c, ubyte* bytes);
     uint32_t decode_utf8(uint& size, const char* bytes);
+
+    /// @brief Encode raw wstring to UTF-8
+    /// @param ws source raw wstring
+    /// @return new UTF-8 encoded string
     std::string wstr2str_utf8(const std::wstring& ws);
+
+    /// @brief Decode UTF
+    /// @param s source encoded string
+    /// @return new raw decoded string
     std::wstring str2wstr_utf8(const std::string& s);
+
+    /// @brief Calculated length of UTF-8 encoded string that fits into maxSize
+    /// @param s source UTF-8 encoded string view
+    /// @param maxSize max encoded string length after crop
+    /// @return cropped string size (less or equal to maxSize)
+    size_t crop_utf8(std::string_view s, size_t maxSize);
+    
     bool is_integer(const std::string& text);
     bool is_integer(const std::wstring& text);
     bool is_valid_filename(const std::wstring& name);

test/util/stringutil.cpp

@@ -0,0 +1,10 @@
+#include "util/stringutil.hpp"
+
+#include <gtest/gtest.h>
+
+TEST(stringutil, crop_utf8) {
+    // Project source files must be UTF-8 encoded
+    std::string str = "пример";
+    str = str.substr(0, util::crop_utf8(str, 7));
+    EXPECT_EQ(str, "при");
+}