解码mime

function decode_mime_string ($string) {
$pos = strpos($string, '=?');
if (!is_int($pos)) {
return $string;
}

$preceding = substr($string, 0, $pos); // save any preceding text

$search = substr($string, $pos+2, 75); /* the mime header spec says this is the longest a single encoded word can be */
$d1 = strpos($search, '?');
if (!is_int($d1)) {
return $string;
}

$charset = substr($string, $pos+2, $d1);
$search = substr($search, $d1+1);

$d2 = strpos($search, '?');
if (!is_int($d2)) {
return $string;
}

$encoding = substr($search, 0, $d2);
$search = substr($search, $d2+1);

$end = strpos($search, '?=');
if (!is_int($end)) {
return $string;
}

$encoded_text = substr($search, 0, $end);
$rest = substr($string, (strlen($preceding . $charset . $encoding . $encoded_text)+6));

switch ($encoding) {
case 'Q':
case 'q':
$encoded_text = str_replace('_', '%20', $encoded_text);
$encoded_text = str_replace('=', '%', $encoded_text);
$decoded = urldecode($encoded_text);

if (strtolower($charset) == 'windows-1251') {
$decoded = convert_cyr_string($decoded, 'w', 'k');
}
break;

case 'B':
case 'b':
$decoded = urldecode(base64_decode($encoded_text));

if (strtolower($charset) == 'windows-1251') {
$decoded = convert_cyr_string($decoded, 'w', 'k');
}
break;

default:
$decoded = '=?' . $charset . '?' . $encoding . '?' . $encoded_text . '?=';
break;
}

return $preceding . $decoded . decode_mime_string($rest);
} // decode_mime_string()