public function base64EncodeWrapMB($str, $linebreak = null)
{
$start = '=?' . $this->CharSet . '?B?';
$end = '?=';
$encoded = '';
if ($linebreak === null) {
$linebreak = $this->LE;
}
$mb_length = mb_strlen($str, $this->CharSet);
// Each line must have length <= 75, including $start and $end
$length = 75 - strlen($start) - strlen($end);
// Average multi-byte ratio
$ratio = $mb_length / strlen($str);
// Base64 has a 4:3 ratio
$avgLength = floor($length * $ratio * 0.75);
for ($i = 0; $i < $mb_length; $i += $offset) {
$lookBack = 0;
do {
$offset = $avgLength - $lookBack;
$chunk = mb_substr($str, $i, $offset, $this->CharSet);
$chunk = base64_encode($chunk);
$lookBack++;
} while (strlen($chunk) > $length);
$encoded .= $chunk . $linebreak;
}
// Chomp the last linefeed
$encoded = substr($encoded, 0, -strlen($linebreak));
return $encoded;
}