[squirrelmail.git] / class / deliver / Deliver.class.php

<?php
/**
 * Deliver.class.php
 *
 * Copyright (c) 1999-2005 The SquirrelMail Project Team
 * Licensed under the GNU GPL. For full terms see the file COPYING.
 *
 * This contains all the functions needed to send messages through
 * a delivery backend.
 *
 * @version $Id$
 * @author  Marc Groot Koerkamp
 * @package squirrelmail
 */

/**
 * Deliver Class - called to actually deliver the message
 *
 * This class is called by compose.php and other code that needs
 * to send messages.  All delivery functionality should be centralized
 * in this class.
 *
 * Do not place UI code in this class, as UI code should be placed in templates
 * going forward.
 *
 * @author  Marc Groot Koerkamp
 * @package squirrelmail
 */
class Deliver {

    /**
     * function mail - send the message parts to the SMTP stream
     *
     * @param Message  $message  Message class to send
     * @param resource $stream   file handle to the SMTP stream
     *
     * @return integer $raw_length
     */
    function mail($message, $stream=false) {
        $rfc822_header = $message->rfc822_header;
        if (count($message->entities)) {
            $boundary = $this->mimeBoundary();
            $rfc822_header->content_type->properties['boundary']='"'.$boundary.'"';
        } else {
            $boundary='';
        }
        $raw_length = 0;
        $reply_rfc822_header = (isset($message->reply_rfc822_header)
                             ? $message->reply_rfc822_header : '');
        $header = $this->prepareRFC822_Header($rfc822_header, $reply_rfc822_header, $raw_length);

        if ($stream) {
            $this->preWriteToStream($header);
            $this->writeToStream($stream, $header);
        }
        $this->writeBody($message, $stream, $raw_length, $boundary);
        return $raw_length;
    }

    /**
     * function writeBody - generate and write the mime boundaries around each part to the stream
     *
     * Recursively formats and writes the MIME boundaries of the $message
     * to the output stream.
     *
     * @param Message   $message      Message object to transform
     * @param resource  $stream       SMTP output stream
     * @param integer  &$length_raw   raw length of the message (part)
     *                                as returned by mail fn
     * @param string    $boundary     custom boundary to call, usually for subparts
     *
     * @return void
     */
    function writeBody($message, $stream, &$length_raw, $boundary='') {
        // calculate boundary in case of multidimensional mime structures
        if ($boundary && $message->entity_id && count($message->entities)) {
            if (strpos($boundary,'_part_')) {
                $boundary = substr($boundary,0,strpos($boundary,'_part_'));

            // the next four lines use strrev to reverse any nested boundaries
            // because RFC 2046 (5.1.1) says that if a line starts with the outer
            // boundary string (doesn't matter what the line ends with), that
            // can be considered a match for the outer boundary; thus the nested
            // boundary needs to be unique from the outer one
            //
            } else if (strpos($boundary,'_trap_')) {
                $boundary = substr(strrev($boundary),0,strpos(strrev($boundary),'_part_'));
            }
            $boundary_new = strrev($boundary . '_part_'.$message->entity_id);
        } else {
            $boundary_new = $boundary;
        }
        if ($boundary && !$message->rfc822_header) {
            $s = '--'.$boundary."\r\n";
            $s .= $this->prepareMIME_Header($message, $boundary_new);
            $length_raw += strlen($s);
            if ($stream) {
                $this->preWriteToStream($s);
                $this->writeToStream($stream, $s);
            }
        }
        $this->writeBodyPart($message, $stream, $length_raw);

        $last = false;
        for ($i=0, $entCount=count($message->entities);$i<$entCount;$i++) {
            $msg = $this->writeBody($message->entities[$i], $stream, $length_raw, $boundary_new);
            if ($i == $entCount-1) $last = true;
        }
        if ($boundary && $last) {
            $s = "--".$boundary_new."--\r\n\r\n";
            $length_raw += strlen($s);
            if ($stream) {
                $this->preWriteToStream($s);
                $this->writeToStream($stream, $s);
            }
        }
    }

    /**
     * function writeBodyPart - write each individual mimepart
     *
     * Recursively called by WriteBody to write each mime part to the SMTP stream
     *
     * @param Message   $message      Message object to transform
     * @param resource  $stream       SMTP output stream
     * @param integer  &$length       length of the message part
     *                                as returned by mail fn
     *
     * @return void
     */
    function writeBodyPart($message, $stream, &$length) {
        if ($message->mime_header) {
            $type0 = $message->mime_header->type0;
        } else {
            $type0 = $message->rfc822_header->content_type->type0;
        }

        $body_part_trailing = $last = '';
        switch ($type0)
        {
        case 'text':
        case 'message':
            if ($message->body_part) {
                $body_part = $message->body_part;
                // remove NUL characters
                $body_part = str_replace("\0",'',$body_part);
                $length += $this->clean_crlf($body_part);
                if ($stream) {
                    $this->preWriteToStream($body_part);
                    $this->writeToStream($stream, $body_part);
                }
                $last = $body_part;
            } elseif ($message->att_local_name) {
                $filename = $message->att_local_name;
                $file = fopen ($filename, 'rb');
                while ($body_part = fgets($file, 4096)) {
                    // remove NUL characters
                    $body_part = str_replace("\0",'',$body_part);
                    $length += $this->clean_crlf($body_part);
                    if ($stream) {
                        $this->preWriteToStream($body_part);
                        $this->writeToStream($stream, $body_part);
                    }
                    $last = $body_part;
                }
                fclose($file);
            }
            break;
        default:
            if ($message->body_part) {
                $body_part = $message->body_part;
                // remove NUL characters
                $body_part = str_replace("\0",'',$body_part);
                $length += $this->clean_crlf($body_part);
                if ($stream) {
                    $this->writeToStream($stream, $body_part);
                }
            } elseif ($message->att_local_name) {
                $filename = $message->att_local_name;
                $file = fopen ($filename, 'rb');
                while ($tmp = fread($file, 570)) {
                   $body_part = chunk_split(base64_encode($tmp));
                    $length += $this->clean_crlf($body_part);
                    if ($stream) {
                        $this->writeToStream($stream, $body_part);
                    }
                }
                fclose($file);
            }
            break;
        }
        $body_part_trailing = '';
        if ($last && substr($last,-1) != "\n") {
            $body_part_trailing = "\r\n";
        }
        if ($body_part_trailing) {
            $length += strlen($body_part_trailing);
            if ($stream) {
                $this->preWriteToStream($body_part_trailing);
                $this->writeToStream($stream, $body_part_trailing);
            }
        }
    }

    /**
     * function clean_crlf - change linefeeds and newlines to legal characters
     *
     * The SMTP format only allows CRLF as line terminators.
     * This function replaces illegal teminators with the correct terminator.
     *
     * @param string &$s string to clean linefeeds on
     *
     * @return void
     */
    function clean_crlf(&$s) {
        $s = str_replace("\r\n", "\n", $s);
        $s = str_replace("\r", "\n", $s);
        $s = str_replace("\n", "\r\n", $s);
        return strlen($s);
    }

    /**
     * function strip_crlf - strip linefeeds and newlines from a string
     *
     * The SMTP format only allows CRLF as line terminators.
     * This function strips all line terminators from the string.
     *
     * @param string &$s string to clean linefeeds on
     *
     * @return void
     */
    function strip_crlf(&$s) {
        $s = str_replace("\r\n ", '', $s);
        $s = str_replace("\r", '', $s);
        $s = str_replace("\n", '', $s);
    }

    /**
     * function preWriteToStream - reserved for extended functionality
     *
     * This function is not yet implemented.
     * Reserved for extended functionality.
     *
     * @param string &$s string to operate on
     *
     * @return void
     */
    function preWriteToStream(&$s) {
    }

    /**
     * function writeToStream - write data to the SMTP stream
     *
     * @param resource $stream  SMTP output stream
     * @param string   $data    string with data to send to the SMTP stream
     *
     * @return void
     */
    function writeToStream($stream, $data) {
        fputs($stream, $data);
    }

    /**
     * function initStream - reserved for extended functionality
     *
     * This function is not yet implemented.
     * Reserved for extended functionality.
     *
     * @param Message $message  Message object
     * @param string  $host     host name or IP to connect to
     * @param string  $user     username to log into the SMTP server with
     * @param string  $pass     password to log into the SMTP server with
     * @param integer $length
     *
     * @return handle $stream file handle resource to SMTP stream
     */
    function initStream($message, $length=0, $host='', $port='', $user='', $pass='') {
        return $stream;
    }

    /**
     * function getBCC - reserved for extended functionality
     *
     * This function is not yet implemented.
     * Reserved for extended functionality.
     *
     */
    function getBCC() {
        return false;
    }

    /**
     * function prepareMIME_Header - creates the mime header
     *
     * @param Message $message  Message object to act on
     * @param string  $boundary mime boundary from fn MimeBoundary
     *
     * @return string $header properly formatted mime header
     */
    function prepareMIME_Header($message, $boundary) {
        $mime_header = $message->mime_header;
        $rn="\r\n";
        $header = array();

        $contenttype = 'Content-Type: '. $mime_header->type0 .'/'.
                        $mime_header->type1;
        if (count($message->entities)) {
            $contenttype .= ';' . 'boundary="'.$boundary.'"';
        }
        if (isset($mime_header->parameters['name'])) {
            $contenttype .= '; name="'.
            encodeHeader($mime_header->parameters['name']). '"';
        }
        if (isset($mime_header->parameters['charset'])) {
            $charset = $mime_header->parameters['charset'];
            $contenttype .= '; charset="'.
            encodeHeader($charset). '"';
        }

        $header[] = $contenttype . $rn;
        if ($mime_header->description) {
            $header[] = 'Content-Description: ' . $mime_header->description . $rn;
        }
        if ($mime_header->encoding) {
            $header[] = 'Content-Transfer-Encoding: ' . $mime_header->encoding . $rn;
        } else {
            if ($mime_header->type0 == 'text' || $mime_header->type0 == 'message') {
                $header[] = 'Content-Transfer-Encoding: 8bit' .  $rn;
            } else {
                $header[] = 'Content-Transfer-Encoding: base64' .  $rn;
            }
        }
        if ($mime_header->id) {
            $header[] = 'Content-ID: ' . $mime_header->id . $rn;
        }
        if ($mime_header->disposition) {
            $disposition = $mime_header->disposition;
            $contentdisp = 'Content-Disposition: ' . $disposition->name;
            if ($disposition->getProperty('filename')) {
                $contentdisp .= '; filename="'.
                encodeHeader($disposition->getProperty('filename')). '"';
            }
            $header[] = $contentdisp . $rn;
        }
        if ($mime_header->md5) {
            $header[] = 'Content-MD5: ' . $mime_header->md5 . $rn;
        }
        if ($mime_header->language) {
            $header[] = 'Content-Language: ' . $mime_header->language . $rn;
        }

        $cnt = count($header);
        $hdr_s = '';
        for ($i = 0 ; $i < $cnt ; $i++)    {
            $hdr_s .= $this->foldLine($header[$i], 78,str_pad('',4));
        }
        $header = $hdr_s;
        $header .= $rn; /* One blank line to separate mimeheader and body-entity */
        return $header;
    }

    /**
     * function prepareRFC822_Header - prepares the RFC822 header string from Rfc822Header object(s)
     *
     * This function takes the Rfc822Header object(s) and formats them
     * into the RFC822Header string to send to the SMTP server as part
     * of the SMTP message.
     *
     * @param Rfc822Header  $rfc822_header
     * @param Rfc822Header  $reply_rfc822_header
     * @param integer      &$raw_length length of the message
     *
     * @return string $header
     */
    function prepareRFC822_Header($rfc822_header, $reply_rfc822_header, &$raw_length) {
        global $domain, $version, $username, $encode_header_key, $edit_identity, $hide_auth_header;

        /* if server var SERVER_NAME not available, use $domain */
        if(!sqGetGlobalVar('SERVER_NAME', $SERVER_NAME, SQ_SERVER)) {
            $SERVER_NAME = $domain;
        }

        sqGetGlobalVar('REMOTE_ADDR', $REMOTE_ADDR, SQ_SERVER);
        sqGetGlobalVar('REMOTE_PORT', $REMOTE_PORT, SQ_SERVER);
        sqGetGlobalVar('REMOTE_HOST', $REMOTE_HOST, SQ_SERVER);
        sqGetGlobalVar('HTTP_VIA',    $HTTP_VIA,    SQ_SERVER);
        sqGetGlobalVar('HTTP_X_FORWARDED_FOR', $HTTP_X_FORWARDED_FOR, SQ_SERVER);

        $rn = "\r\n";

        /* This creates an RFC 822 date */
        $date = date('D, j M Y H:i:s ', mktime()) . $this->timezone();
        /* Create a message-id */
        $message_id = '<' . $REMOTE_PORT . '.';
        if (isset($encode_header_key) && trim($encode_header_key)!='') {
            // use encrypted form of remote address
            $message_id.= OneTimePadEncrypt($this->ip2hex($REMOTE_ADDR),base64_encode($encode_header_key));
        } else {
            $message_id.= $REMOTE_ADDR;
        }
        $message_id .= '.' . time() . '.squirrel@' . $SERVER_NAME .'>';
        /* Make an RFC822 Received: line */
        if (isset($REMOTE_HOST)) {
            $received_from = "$REMOTE_HOST ([$REMOTE_ADDR])";
        } else {
            $received_from = $REMOTE_ADDR;
        }
        if (isset($HTTP_VIA) || isset ($HTTP_X_FORWARDED_FOR)) {
            if (!isset($HTTP_X_FORWARDED_FOR) || $HTTP_X_FORWARDED_FOR == '') {
                $HTTP_X_FORWARDED_FOR = 'unknown';
            }
            $received_from .= " (proxying for $HTTP_X_FORWARDED_FOR)";
        }
        $header = array();

        /**
         * SquirrelMail header
         *
         * This Received: header provides information that allows to track
         * user and machine that was used to send email. Don't remove it
         * unless you understand all possible forging issues or your
         * webmail installation does not prevent changes in user's email address.
         * See SquirrelMail bug tracker #847107 for more details about it.
         */
        if (isset($encode_header_key) && 
            trim($encode_header_key)!='') {
            // use encoded headers, if encryption key is set and not empty
            $header[] = 'X-Squirrel-UserHash: '.OneTimePadEncrypt($username,base64_encode($encode_header_key)).$rn;
            $header[] = 'X-Squirrel-FromHash: '.OneTimePadEncrypt($this->ip2hex($REMOTE_ADDR),base64_encode($encode_header_key)).$rn;
            if (isset($HTTP_X_FORWARDED_FOR))
                $header[] = 'X-Squirrel-ProxyHash:'.OneTimePadEncrypt($this->ip2hex($HTTP_X_FORWARDED_FOR),base64_encode($encode_header_key)).$rn;
        } else {
            // use default received headers
            $header[] = "Received: from $received_from" . $rn;
            if ($edit_identity || ! isset($hide_auth_header) || ! $hide_auth_header)
                $header[] = "        (SquirrelMail authenticated user $username)" . $rn;
            $header[] = "        by $SERVER_NAME with HTTP;" . $rn;
            $header[] = "        $date" . $rn;
        }

        /* Insert the rest of the header fields */
        $header[] = 'Message-ID: '. $message_id . $rn;
        if ($reply_rfc822_header->message_id) {
            $rep_message_id = $reply_rfc822_header->message_id;
        //        $this->strip_crlf($message_id);
            $header[] = 'In-Reply-To: '.$rep_message_id . $rn;
            $references = $this->calculate_references($reply_rfc822_header);
            $header[] = 'References: '.$references . $rn;
        }
        $header[] = "Date: $date" . $rn;
        $header[] = 'Subject: '.encodeHeader($rfc822_header->subject) . $rn;
        $header[] = 'From: '. $rfc822_header->getAddr_s('from',",$rn ",true) . $rn;

        // folding address list [From|To|Cc|Bcc] happens by using ",$rn<space>" as delimiter
        // Do not use foldLine for that.

        // RFC2822 if from contains more then 1 address
        if (count($rfc822_header->from) > 1) {
            $header[] = 'Sender: '. $rfc822_header->getAddr_s('sender',',',true) . $rn;
        }
        if (count($rfc822_header->to)) {
            $header[] = 'To: '. $rfc822_header->getAddr_s('to',",$rn ",true) . $rn;
        }
        if (count($rfc822_header->cc)) {
            $header[] = 'Cc: '. $rfc822_header->getAddr_s('cc',",$rn ",true) . $rn;
        }
        if (count($rfc822_header->reply_to)) {
            $header[] = 'Reply-To: '. $rfc822_header->getAddr_s('reply_to',',',true) . $rn;
        }
        /* Sendmail should return true. Default = false */
        $bcc = $this->getBcc();
        if (count($rfc822_header->bcc)) {
            $s = 'Bcc: '. $rfc822_header->getAddr_s('bcc',",$rn ",true) . $rn;
            if (!$bcc) {
                $raw_length += strlen($s);
            } else {
                $header[] = $s;
            }
        }
        /* Identify SquirrelMail */
        $header[] = 'User-Agent: SquirrelMail/' . $version . $rn;
        /* Do the MIME-stuff */
        $header[] = 'MIME-Version: 1.0' . $rn;
        $contenttype = 'Content-Type: '. $rfc822_header->content_type->type0 .'/'.
                                         $rfc822_header->content_type->type1;
        if (count($rfc822_header->content_type->properties)) {
            foreach ($rfc822_header->content_type->properties as $k => $v) {
                if ($k && $v) {
                    $contenttype .= ';' .$k.'='.$v;
                }
            }
        }
        $header[] = $contenttype . $rn;
        if ($encoding = $rfc822_header->encoding) {
            $header[] = 'Content-Transfer-Encoding: ' . $encoding .  $rn;
        }
        if ($rfc822_header->dnt) {
            $dnt = $rfc822_header->getAddr_s('dnt');
            /* Pegasus Mail */
            $header[] = 'X-Confirm-Reading-To: '.$dnt. $rn;
            /* RFC 2298 */
            $header[] = 'Disposition-Notification-To: '.$dnt. $rn;
        }
        if ($rfc822_header->priority) {
            switch($rfc822_header->priority)
            {
            case 1:
                $header[] = 'X-Priority: 1 (Highest)'.$rn;
                $header[] = 'Importance: High'. $rn; break;
            case 5:
                $header[] = 'X-Priority: 5 (Lowest)'.$rn;
                $header[] = 'Importance: Low'. $rn; break;
            default: break;
            }
        }
        /* Insert headers from the $more_headers array */
        if(count($rfc822_header->more_headers)) {
            reset($rfc822_header->more_headers);
            foreach ($rfc822_header->more_headers as $k => $v) {
                $header[] = $k.': '.$v .$rn;
            }
        }
        $cnt = count($header);
        $hdr_s = '';

        for ($i = 0 ; $i < $cnt ; $i++) {
            $sKey = substr($header[$i],0,strpos($header[$i],':'));
            switch ($sKey)
            {
            case 'Message-ID':
            case 'In-Reply_To':
                $hdr_s .= $header[$i];
                break;
            case 'References':
                $sRefs = substr($header[$i],12);
                $aRefs = explode(' ',$sRefs);
                $sLine = 'References:';
                foreach ($aRefs as $sReference) {
                    if (strlen($sLine)+strlen($sReference) >76) {
                        $hdr_s .= $sLine;
                        $sLine = $rn . '    ' . $sReference;
                    } else {
                        $sLine .= ' '. $sReference;
                    }
                }
                $hdr_s .= $sLine;
                break;
            case 'To':
            case 'Cc':
            case 'Bcc':
            case 'From':
                $hdr_s .= $header[$i];
                break;
            default: $hdr_s .= $this->foldLine($header[$i], 78, str_pad('',4)); break;
            }
        }
        $header = $hdr_s;
        $header .= $rn; /* One blank line to separate header and body */
        $raw_length += strlen($header);
        return $header;
    }

    /**
     * function foldLine - for cleanly folding of headerlines
     *
     * @param   string  $line
     * @param   integer $length length to fold the line at
     * @param   string  $pre    prefix the line with...
     *
     * @return string   $line folded line with trailing CRLF
     */
    function foldLine($line, $length, $pre='') {
        $line = substr($line,0, -2);
        $length -= 2; /* do not fold between \r and \n */
        $cnt = strlen($line);
        if ($cnt > $length) { /* try folding */
            $fold_string = "\r\n " . $pre;
            $bFirstFold = false;
            $aFoldLine = array();
            while (strlen($line) > $length) {
                $fold = false;
                /* handle encoded parts */
                if (preg_match('/(=\?([^?]*)\?(Q|B)\?([^?]*)\?=)(\s+|.*)/Ui',$line,$regs)) {
                    $fold_tmp = $regs[1];
                    if (!trim($regs[5])) {
                        $fold_tmp .= $regs[5];
                    }
                    $iPosEnc = strpos($line,$fold_tmp);
                    $iLengthEnc = strlen($fold_tmp);
                    $iPosEncEnd = $iPosEnc+$iLengthEnc;
                    if ($iPosEnc < $length && (($iPosEncEnd) > $length)) {
                        $fold = true;
                        /* fold just before the start of the encoded string */
                        if ($iPosEnc) {
                            $aFoldLine[] = substr($line,0,$iPosEnc);
                        }
                        $line = substr($line,$iPosEnc);
                        if (!$bFirstFold) {
                            $bFirstFold = true;
                            $length -= strlen($fold_string);
                        }
                        if ($iLengthEnc > $length) { /* place the encoded
                            string on a separate line and do not fold inside it*/
                            /* minimize foldstring */
                            $fold_string = "\r\n ";
                            $aFoldLine[] = substr($line,0,$iLengthEnc);
                            $line = substr($line,$iLengthEnc);
                        }
                    } else if ($iPosEnc < $length) { /* the encoded string fits into the foldlength */
                        /*remainder */
                        $sLineRem = substr($line,$iPosEncEnd,$length - $iPosEncEnd);
                        if (preg_match('/^(=\?([^?]*)\?(Q|B)\?([^?]*)\?=)(.*)/Ui',$sLineRem) || !preg_match('/[=,;\s]/',$sLineRem)) {
                            /*impossible to fold clean in the next part -> fold after the enc string */
                            $aFoldLine[] = substr($line,0,$iPosEncEnd);
                            $line = substr($line,$iPosEncEnd);
                            $fold = true;
                            if (!$bFirstFold) {
                                $bFirstFold = true;
                                $length -= strlen($fold_string);
                            }
                        }
                    }
                }
                if (!$fold) {
                    $line_tmp = substr($line,0,$length);
                    $iFoldPos = false;
                    /* try to fold at logical places */
                    switch (true)
                    {
                    case ($iFoldPos = strrpos($line_tmp,',')): break;
                    case ($iFoldPos = strrpos($line_tmp,';')): break;
                    case ($iFoldPos = strrpos($line_tmp,' ')): break;
                    case ($iFoldPos = strrpos($line_tmp,'=')): break;
                    default: break;
                    }

                    if (!$iFoldPos) { /* clean folding didn't work */
                        $iFoldPos = $length;
                    }
                    $aFoldLine[] = substr($line,0,$iFoldPos+1);
                    $line = substr($line,$iFoldPos+1);
                    if (!$bFirstFold) {
                        $bFirstFold = true;
                        $length -= strlen($fold_string);
                    }
                }
            }
            /*$reconstruct the line */
            if ($line) {
                $aFoldLine[] = $line;
            }
            $line = implode($fold_string,$aFoldLine);
        }
        return $line."\r\n";
    }

    /**
     * function mimeBoundary - calculates the mime boundary to use
     *
     * This function will generate a random mime boundary base part
     * for the message if the boundary has not already been set.
     *
     * @return string $mimeBoundaryString random mime boundary string
     */
    function mimeBoundary () {
        static $mimeBoundaryString;

        if ( !isset( $mimeBoundaryString ) ||
            $mimeBoundaryString == '') {
            $mimeBoundaryString = '----=_' . date( 'YmdHis' ) . '_' .
            mt_rand( 10000, 99999 );
        }
        return $mimeBoundaryString;
    }

    /**
     * function timezone - Time offset for correct timezone
     *
     * @return string $result with timezone and offset
     */
    function timezone () {
        global $invert_time;

        $diff_second = date('Z');
        if ($invert_time) {
            $diff_second = - $diff_second;
        }
        if ($diff_second > 0) {
            $sign = '+';
        } else {
            $sign = '-';
        }
        $diff_second = abs($diff_second);
        $diff_hour = floor ($diff_second / 3600);
        $diff_minute = floor (($diff_second-3600*$diff_hour) / 60);
        $zonename = '('.strftime('%Z').')';
        $result = sprintf ("%s%02d%02d %s", $sign, $diff_hour, $diff_minute,
                       $zonename);
        return ($result);
    }

    /**
     * function calculate_references - calculate correct Referer string
     *
     * @param   Rfc822Header $hdr    message header to calculate from
     *
     * @return  string       $refer  concatenated and trimmed Referer string
     */
    function calculate_references($hdr) {
        $refer = $hdr->references;
        $message_id = $hdr->message_id;
        $in_reply_to = $hdr->in_reply_to;
        if (strlen($refer) > 2) {
            $refer .= ' ' . $message_id;
        } else {
            if ($in_reply_to) {
                $refer .= $in_reply_to . ' ' . $message_id;
            } else {
                $refer .= $message_id;
            }
        }
        trim($refer);
        return $refer;
    }

    /**
     * Converts ip address to hexadecimal string
     *
     * Function is used to convert ipv4 and ipv6 addresses to hex strings.
     * It removes all delimiter symbols from ip addresses, converts decimal
     * ipv4 numbers to hex and pads strings in order to present full length
     * address. ipv4 addresses are represented as 8 byte strings, ipv6 addresses 
     * are represented as 32 byte string.
     *
     * If function fails to detect address format, it returns unprocessed string.
     * @param string $string ip address string
     * @return string processed ip address string
     * @since 1.5.1 and 1.4.5
     */
    function ip2hex($string) {
        if (preg_match("/^(\d+)\.(\d+)\.(\d+)\.(\d+)$/",$string,$match)) {
            // ipv4 address
            $ret = str_pad(dechex($match[1]),2,'0',STR_PAD_LEFT)
                . str_pad(dechex($match[2]),2,'0',STR_PAD_LEFT)
                . str_pad(dechex($match[3]),2,'0',STR_PAD_LEFT)
                . str_pad(dechex($match[4]),2,'0',STR_PAD_LEFT);
        } elseif (preg_match("/^([0-9a-h]+)\:([0-9a-h]+)\:([0-9a-h]+)\:([0-9a-h]+)\:([0-9a-h]+)\:([0-9a-h]+)\:([0-9a-h]+)\:([0-9a-h]+)$/i",$string,$match)) {
            // full ipv6 address
            $ret = str_pad($match[1],4,'0',STR_PAD_LEFT)
                . str_pad($match[2],4,'0',STR_PAD_LEFT)
                . str_pad($match[3],4,'0',STR_PAD_LEFT)
                . str_pad($match[4],4,'0',STR_PAD_LEFT)
                . str_pad($match[5],4,'0',STR_PAD_LEFT)
                . str_pad($match[6],4,'0',STR_PAD_LEFT)
                . str_pad($match[7],4,'0',STR_PAD_LEFT)
                . str_pad($match[8],4,'0',STR_PAD_LEFT);
        } elseif (preg_match("/^\:\:([0-9a-h\:]+)$/i",$string,$match)) {
            // short ipv6 with all starting symbols nulled
            $aAddr=explode(':',$match[1]);
            $ret='';
            foreach ($aAddr as $addr) {
                $ret.=str_pad($addr,4,'0',STR_PAD_LEFT);
            }
            $ret=str_pad($ret,32,'0',STR_PAD_LEFT);
        } elseif (preg_match("/^([0-9a-h\:]+)::([0-9a-h\:]+)$/i",$string,$match)) {
            // short ipv6 with middle part nulled
            $aStart=explode(':',$match[1]);
            $sStart='';
            foreach($aStart as $addr) {
                $sStart.=str_pad($addr,4,'0',STR_PAD_LEFT);
            }
            $aEnd = explode(':',$match[2]);
            $sEnd='';
            foreach($aEnd as $addr) {
                $sEnd.=str_pad($addr,4,'0',STR_PAD_LEFT);
            }
            $ret = $sStart
                . str_pad('',(32 - strlen($sStart . $sEnd)),'0',STR_PAD_LEFT)
                . $sEnd;
        } else {
            // unknown addressing
            $ret = $string;
        }
        return $ret;
    }
}
?>