code: private static boolean isAscii(ByteBuf buf, int index, int length) {
          return buf.forEachByte(index, length, FIND_NON_ASCII) == -1;
      }
docs: Returns {@code true} if the specified {@link ByteBuf} starting at {@code index} with {@code length} is valid
  ASCII text, otherwise return {@code false}.
  
  @param buf    The given {@link ByteBuf}.
  @param index  The start index of the specified buffer.
  @param length The length of the specified buffer.