mb_encode_mimeheader()

(PHP 4 >= 4.0.6, PHP 5, PHP 7)

为 MIME 头编码字符串

说明

mb_encode_mimeheader (string $str[,string $charset= determined by mb_language() [,string $transfer_encoding= "B" [,string $linefeed= "\r\n" [,int $indent= 0 ]]]] ) : string

按 MIME 头编码方案将指定的字符串$str进行编码。

参数

$str

要编码的 string。 它的编码应该和 mb_internal_encoding() 一样。

$charset

$charset指定了$str的字符集名。 其默认值由当前的 NLS 设置（mbstring.language）来确定。

$transfer_encoding

$transfer_encoding指定了 MIME 的编码方案。 它可以是"B"（Base64）也可以是"Q"（Quoted-Printable）。 如果未设置，将回退为"B"。

$linefeed

$linefeed指定了 EOL（行尾）标记，使 mb_encode_mimeheader() 执行了一个换行（» RFC 文档中规定，超过长度的一行将换成多行，当前该长度硬式编码为 74 个字符）。 如果没有设定，则回退为"\r\n"(CRLF)。

$indent

首行缩进（header 里$str前的字符数目）。

返回值

转换后的字符串版本以 ASCII 形式表达。

范例

mb_encode_mimeheader() 例子

<?php
$name = ""; // kanji
$mbox = "kru";
$doma = "gtinn.mon";
$addr = mb_encode_mimeheader($name, "UTF-7", "Q") . " <" . $mbox . "@" . $doma . ">";
echo $addr;
?>

注释

Note:

这个函数没有设计成据更高级上下文的中断点来换行（单词边界等）。 这个特性将导致意外的空格可能会让原始字符串看上去很乱。

参见

• mb_decode_mimeheader()解码 MIME 头字段中的字符串

Some solution for using national chars and have problem with UTF-8 for example in mail subject. Before you use mb_encode_mimeheader with UTF-8 set mb_internal_encoding('UTF-8').

Read this FIRST: http://bugs.php.net/bug.php?id=23192 because mb_encode_mimeheaders is BUGGY!
a work around for the multibyte broken error for too long subjects for ISO-2022-JP:
$pos=0;
$split=36; // after 36 single bytes characters, if then comes MB, it is broken
while ($pos<mb_strlen($string,$encoding))
{
 $output=mb_strimwidth($string,$pos,$split,"",$encoding);
 $pos+=mb_strlen($output,$encoding);
 $_string.=(($_string)?' ':'').mb_encode_mimeheader($output,$encoding);
}
$string=$_string;
is not the best, but it works

mb_encode_mimeheader() depends on correct mbstring.internal_encoding setting. It tries to convert $str from internal encoding to $charset. If you ignore mbstring internal encoding, function might encode strings incorrectly even when $str character set matches $charset

My first post was around 2003, and still the mb_mime_header is broken. It is *NOT* usable with longer subjects, and mostly unusable with anything else than japanese.
iwakura at junx dot org is also not working for me, it produces also some gargabe.
I updated my old function (the one I posted 2003) and I tested it with overlong subjects in UTF-8, ISO-2022-JP (japanese), GB2312 (simplified chinese) and EUC-KR (korean) and I got readable results in thunderbird, mail.app, outlook, etc.
<?php
function _mb_mime_encode($string, $encoding)
{
  $pos = 0;
  // after 36 single bytes characters if then comes MB, it is broken
  // but I trimmed it down to 24, to stay 100% < 76 chars per line
  $split = 24;
  while ($pos < mb_strlen($string, $encoding))
  {
    $output = mb_strimwidth($string, $pos, $split, "", $encoding);
    $pos += mb_strlen($output, $encoding);
    $_string_encoded = "=?".$encoding."?B?".base64_encode($output)."?=";
    if ($_string)
      $_string .= "\r\n";
    $_string .= $_string_encoded;
  }
  $string = $_string;
  return $string;
}
?>

I could not find a PHP function to MIME encode the name for a n email address.
Input  = "Karl Müller<kmueller@gmx.de>"
Output = "Karl%20M%FCller<kmueller@gmx.de>"
I wrote it on my own:
<?php
// required to encode names in email addresses  
// replace " " with "%20"
// replace "ü" with "%FC" 
// replace "%" with "%25"   etc....
// Use "%" as Delimiter for MIME
// Use "=" as Delimiter for Quoted Printable
// Input string must be UTF8 encoded
public static function EncodeMime($Text, $Delimiter)
{
  $Text = utf8_decode($Text);
  $Len = strlen($Text);
  $Out = "";
  for ($i=0; $i<$Len; $i++)
  {
    $Chr = substr($Text, $i, 1);
    $Asc = ord($Chr);
    if ($Asc > 0x255) // Unicode not allowed
    {
      $Out .= "?";
    }
    else if ($Chr == " " || $Chr == $Delimiter || $Asc > 127) 
    {
      $Out .= $Delimiter . strtoupper(bin2hex($Chr));
    }
    else $Out .= $Chr;
  }
  return $Out;
}
?>

True, function is broken (PHP5.1, encoding from UTF-8 with pl_PL charset). Below is about 15% faster version of proposed _mb_mime_encode. Also it has header more like othe mb_* functions and doesn't trigger any errors/warnings/notices.
<?php
function mb_mime_header($string, $encoding=null, $linefeed="\r\n") {
 if(!$encoding) $encoding = mb_internal_encoding();
 $encoded = '';
 while($length = mb_strlen($string)) {
  $encoded .= "=?$encoding?B?"
       . base64_encode(mb_substr($string,0,24,$encoding))
       . "?=$linefeed";
  $string = mb_substr($string,24,$length,$encoding);
 }
 return $encoded;
}
?>

If mb_ version doesn't work for you in MIME-B mode:
function encode_mimeheader($string, $charset=null, $linefeed="\r\n") {
  if (!$charset)
    $charset = mb_internal_encoding();
  $start = "=?$charset?B?";
  $end = "?=";
  $encoded = '';
  /* Each line must have length <= 75, including $start and $end */
  $length = 75 - strlen($start) - strlen($end);
  /* Average multi-byte ratio */
  $ratio = mb_strlen($string, $charset) / strlen($string);
  /* Base64 has a 4:3 ratio */
  $magic = $avglength = floor(3 * $length * $ratio / 4);
  for ($i=0; $i <= mb_strlen($string, $charset); $i+=$magic) {
    $magic = $avglength;
    $offset = 0;
    /* Recalculate magic for each line to be 100% sure */
    do {
      $magic -= $offset;
      $chunk = mb_substr($string, $i, $magic, $charset);
      $chunk = base64_encode($chunk);
      $offset++;
    } while (strlen($chunk) > $length);
    if ($chunk)
      $encoded .= ' '.$start.$chunk.$end.$linefeed;
  }
  /* Chomp the first space and the last linefeed */
  $encoded = substr($encoded, 1, -strlen($linefeed));
  return $encoded;
}

In countries where there's non-us ASCII, it's a very good example, for sending mail:
mb_internal_encoding('iso-8859-2');
setlocale(LC_CTYPE, 'hu_HU');
function encode($str,$charset){
  $str=mb_encode_mimeheader(trim($str),$charset, 'Q', "\n\t");
  return $str;
}
print encode('the text with spec. chars: ő Ű Ő ű, ','iso-8859-2');
It creates a 7bit string

i think mb_encode_mimeheader still have bug. here is sample code:
function mb_encode_mimeheader2($string, $encoding = "ISO-2022-JP") {
  $string_array = array();
  $pos = 0;
  $row = 0;
  $mode = 0;
  
  while ($pos < mb_strlen($string)) {
    $word = mb_strimwidth($string, $pos, 1);
    if (!$word) {
      $word = mb_strimwidth($string, $pos, 2);
    }
    if (mb_ereg_match("[ -~]", $word)) {  // ascii
      if ($mode != 1) {
        $row++;
        $mode = 1;
        $string_array[$row] = NULL;
      }
    } else {                // multibyte
      if ($mode != 2) {
        $row++;
        $mode = 2;
        $string_array[$row] = NULL;
      }
    }
    $string_array[$row] .= $word;
    $pos++;
  }
  
  //echo "<pre>";
  //print_r($string_array);
  //echo "</pre>";
  
  foreach ($string_array as $key => $value) {
    $value = mb_convert_encoding($value, $encoding);
    $string_array[$key] = mb_encode_mimeheader($value, $encoding);
  }
  
  //echo "<pre>";
  //print_r($string_array);
  //echo "</pre>";
  
  return implode("", $string_array);
}
is not the best, but it works

At least for Q encoding, this function is unsafe and does not encode correctly. Raw characters which appear as RFC2047 sequences are simply left as is.
Ex:
mb_encode_mimeheader( '=?iso-8859-1?q?this=20is=20some=20text?=' );
returns '=?iso-8859-1?q?this=20is=20some=20text?='
The exact same string, which is obviously not the encoding for the source string. That is, mb_encode_mimeheader does not do any type of escaping.
That is, the following condition is not always true:
  mb_decode_mimeheader( mb_encode_mimeheader( $text ) ) == $text

I found a bad function. 
<?php
function encodeHeader($input, $charset = 'ISO-8859-2')
{
  preg_match_all('/(\\w*[\\x80-\\xFF]+\\w*)/', $input, $matches);
  foreach ($matches[1] as $value) {
    $replacement = preg_replace('/([\\x80-\\xFF])/e', '"=" . strtoupper(dechex(ord("\\1")))', $value);
    $input = str_replace($value, '=?' . $charset . '?Q?' . $replacement . '?=', $input);
  }
  return $input;
}
?>
This function should be used:
<?php
function encodeHeader($input, $charset = 'ISO-8859-2')
{
  $m=preg_match_all('/(\w*[\x80-\xFF]+\w*)/', $input, $matches);
  if($m)$input=mb_encode_mimeheader($input,$charset, 'Q');
  return $input;
}
?>

second parameter 'charset' is character encoding name, but default must be UTF-8 on PHP4.3.1.