PHPMailer::encodeHeader( string $str, string $position = 'text' ): string

3706    public function encodeHeader($str, $position = 'text')3707    {3708        $position = strtolower($position);3709        if ($this->UseSMTPUTF8 && !("comment" === $position)) {3710            return trim(static::normalizeBreaks($str));3711        }3712 3713        $matchcount = 0;3714        switch (strtolower($position)) {3715            case 'phrase':3716                if (!preg_match('/[\200-\377]/', $str)) {3717                    //Can't use addslashes as we don't know the value of magic_quotes_sybase3718                    $encoded = addcslashes($str, "\0..\37\177\\\"");3719                    if (($str === $encoded) && !preg_match('/[^A-Za-z0-9!#$%&\'*+\/=?^_`{|}~ -]/', $str)) {3720                        return $encoded;3721                    }3722 3723                    return "\"$encoded\"";3724                }3725                $matchcount = preg_match_all('/[^\040\041\043-\133\135-\176]/', $str, $matches);3726                break;3727            /* @noinspection PhpMissingBreakStatementInspection */3728            case 'comment':3729                $matchcount = preg_match_all('/[()"]/', $str, $matches);3730            //fallthrough3731            case 'text':3732            default:3733                $matchcount += preg_match_all('/[\000-\010\013\014\016-\037\177-\377]/', $str, $matches);3734                break;3735        }3736 3737        if ($this->has8bitChars($str)) {3738            $charset = $this->CharSet;3739        } else {3740            $charset = static::CHARSET_ASCII;3741        }3742 3743        //Q/B encoding adds 8 chars and the charset ("` =?<charset>?[QB]?<content>?=`").3744        $overhead = 8 + strlen($charset);3745 3746        if ('mail' === $this->Mailer) {3747            $maxlen = static::MAIL_MAX_LINE_LENGTH - $overhead;3748        } else {3749            $maxlen = static::MAX_LINE_LENGTH - $overhead;3750        }3751 3752        //Select the encoding that produces the shortest output and/or prevents corruption.3753        if ($matchcount > strlen($str) / 3) {3754            //More than 1/3 of the content needs encoding, use B-encode.3755            $encoding = 'B';3756        } elseif ($matchcount > 0) {3757            //Less than 1/3 of the content needs encoding, use Q-encode.3758            $encoding = 'Q';3759        } elseif (strlen($str) > $maxlen) {3760            //No encoding needed, but value exceeds max line length, use Q-encode to prevent corruption.3761            $encoding = 'Q';3762        } else {3763            //No reformatting needed3764            $encoding = false;3765        }3766 3767        switch ($encoding) {3768            case 'B':3769                if ($this->hasMultiBytes($str)) {3770                    //Use a custom function which correctly encodes and wraps long3771                    //multibyte strings without breaking lines within a character3772                    $encoded = $this->base64EncodeWrapMB($str, "\n");3773                } else {3774                    $encoded = base64_encode($str);3775                    $maxlen -= $maxlen % 4;3776                    $encoded = trim(chunk_split($encoded, $maxlen, "\n"));3777                }3778                $encoded = preg_replace('/^(.*)$/m', ' =?' . $charset . "?$encoding?\\1?=", $encoded);3779                break;3780            case 'Q':3781                $encoded = $this->encodeQ($str, $position);3782                $encoded = $this->wrapText($encoded, $maxlen, true);3783                $encoded = str_replace('=' . static::$LE, "\n", trim($encoded));3784                $encoded = preg_replace('/^(.*)$/m', ' =?' . $charset . "?$encoding?\\1?=", $encoded);3785                break;