Fix UTF-8 decoding: Guard against remaining bytes before iteration

1 files changed, 8 insertions, 10 deletions

diff --git a/include/unicode/utf.h b/include/unicode/utf.h
index 5db9cac..691d4ba 100644
--- a/include/unicode/utf.h
+++ b/include/unicode/utf.h
@@ -197,14 +197,6 @@ namespace unicode::detail {
    size_t constexpr sequence_length{sizeof...(Tbytes)};
    static_assert(sequence_length >= 1 && sequence_length <= 4);
 
-   if constexpr(sequence_length > 1) {
-    if (remaining_code_units() < sequence_length)
-#if __cplusplus >= 202002L
-     [[unlikely]]
-#endif
-     throw std::invalid_argument("Bad input: Not enough bytes left for decoding UTF-8 sequence");
-   }
-
    if (is_utf8_sequence(bytes...)) {
     std::advance(iterator, sequence_length);
     internal_type result{decode_utf8_sequence(bytes...)};
@@ -215,9 +207,15 @@ namespace unicode::detail {
      throw std::invalid_argument("Invalid Unicode character: "s + std::to_string(static_cast<uint32_t>(result)));
     return result;
    } else {
-    if constexpr(sequence_length <= 3) // template recursion break condition: UTF-8 has 1..4 code units
+    if constexpr(sequence_length <= 3) { // template recursion break condition: UTF-8 has 1..4 code units
+     if (remaining_code_units() < sequence_length + 1)
+#if __cplusplus >= 202002L
+      [[unlikely]]
+#endif
+      throw std::invalid_argument("Bad input: Not enough bytes left for decoding UTF-8 sequence");
+
      return calculate_utf8_value(bytes..., static_cast<utf8_t>(get_code_unit<sequence_length>()));
-    else
+    } else
      throw std::invalid_argument("Bad UTF-8 input: Invalid 4 byte sequence");
    }
   }