fix: preserve UTF-8 advert names

src/helpers/AdvertDataHelpers.cpp

@@ -1,4 +1,5 @@
 #include <helpers/AdvertDataHelpers.h>
+#include <helpers/UTF8Helpers.h>
 
   uint8_t AdvertDataBuilder::encodeTo(uint8_t app_data[]) {
     app_data[0] = _type;
@@ -16,11 +17,12 @@
       app_data[0] |= ADV_FEAT2_MASK;
       memcpy(&app_data[i], &_extra2, 2); i += 2;
     }
-    if (_name && *_name != 0) { 
-      app_data[0] |= ADV_NAME_MASK;
-      const char* sp = _name;
-      while (*sp && i < MAX_ADVERT_DATA_SIZE) {
-        app_data[i++] = *sp++;
+    if (_name && *_name != 0) {
+      size_t name_len = mesh::validUtf8PrefixLength(_name, MAX_ADVERT_DATA_SIZE - i);
+      if (name_len > 0) {
+        app_data[0] |= ADV_NAME_MASK;
+        memcpy(&app_data[i], _name, name_len);
+        i += name_len;
       }
     }
     return i;
@@ -84,4 +86,4 @@ void AdvertTimeHelper::formatRelativeTimeDiff(char dest[], int32_t seconds_from_
       }
     }
   }
-}
+}

src/helpers/UTF8Helpers.h

@@ -0,0 +1,56 @@
+#pragma once
+
+#include <stddef.h>
+#include <stdint.h>
+
+namespace mesh {
+
+inline bool isUtf8Continuation(uint8_t byte) {
+  return (byte & 0xC0) == 0x80;
+}
+
+inline size_t validUtf8PrefixLength(const char* text, size_t max_bytes) {
+  if (text == nullptr) return 0;
+
+  size_t offset = 0;
+  while (text[offset] != '\0') {
+    const uint8_t first = static_cast<uint8_t>(text[offset]);
+    size_t sequence_length = 0;
+
+    if (first <= 0x7F) {
+      sequence_length = 1;
+    } else if (first >= 0xC2 && first <= 0xDF) {
+      sequence_length = 2;
+    } else if (first >= 0xE0 && first <= 0xEF) {
+      sequence_length = 3;
+    } else if (first >= 0xF0 && first <= 0xF4) {
+      sequence_length = 4;
+    } else {
+      break;
+    }
+
+    if (offset + sequence_length > max_bytes) break;
+
+    bool complete = true;
+    for (size_t i = 1; i < sequence_length; i++) {
+      if (text[offset + i] == '\0' || !isUtf8Continuation(static_cast<uint8_t>(text[offset + i]))) {
+        complete = false;
+        break;
+      }
+    }
+    if (!complete) break;
+
+    if (sequence_length == 3) {
+      const uint8_t second = static_cast<uint8_t>(text[offset + 1]);
+      if ((first == 0xE0 && second < 0xA0) || (first == 0xED && second > 0x9F)) break;
+    } else if (sequence_length == 4) {
+      const uint8_t second = static_cast<uint8_t>(text[offset + 1]);
+      if ((first == 0xF0 && second < 0x90) || (first == 0xF4 && second > 0x8F)) break;
+    }
+
+    offset += sequence_length;
+  }
+  return offset;
+}
+
+}  // namespace mesh