src/Mail/mimePart.php
function _buildRFC2047Param($name, $value, $charset,
        $encoding='quoted-printable', $maxLength=76
    ) {
        // WARNING: RFC 2047 says: "An 'encoded-word' MUST NOT be used in
        // parameter of a MIME Content-Type or Content-Disposition field",
        // but... it's supported by many clients/servers
        $quoted = '';

        if ($encoding == 'base64') {
            $value = base64_encode($value);
            $prefix = '=?' . $charset . '?B?';
            $suffix = '?=';

            // 2 x SPACE, 2 x '"', '=', ';'
            $add_len = strlen($prefix . $suffix) + strlen($name) + 6;
            $len = $add_len + strlen($value);

            while ($len > $maxLength) { 
                // We can cut base64-encoded string every 4 characters
                $real_len = floor(($maxLength - $add_len) / 4) * 4;
                $_quote = substr($value, 0, $real_len);
                $value = substr($value, $real_len);

                $quoted .= $prefix . $_quote . $suffix . $this->_eol . ' ';
                $add_len = strlen($prefix . $suffix) + 4; // 2 x SPACE, '"', ';'
                $len = strlen($value) + $add_len;
            }
            $quoted .= $prefix . $value . $suffix;

        } else {
            // quoted-printable
            $value = $this->encodeQP($value);
            $prefix = '=?' . $charset . '?Q?';
            $suffix = '?=';

            // 2 x SPACE, 2 x '"', '=', ';'
            $add_len = strlen($prefix . $suffix) + strlen($name) + 6;
            $len = $add_len + strlen($value);

            while ($len > $maxLength) {
                $length = $maxLength - $add_len;
                // don't break any encoded letters
                if (preg_match("/^(.{0,$length}[^\=][^\=])/", $value, $matches)) {
                    $_quote = $matches[1];
                }

                $quoted .= $prefix . $_quote . $suffix . $this->_eol . ' ';
                $value = substr($value, strlen($_quote));
                $add_len = strlen($prefix . $suffix) + 4; // 2 x SPACE, '"', ';'
                $len = strlen($value) + $add_len;
            }

            $quoted .= $prefix . $value . $suffix;
        }

        return " {$name}=\"{$quoted}\"";
    }
function _buildRFC2047Param($name, $value, $charset,
        $encoding='quoted-printable', $maxLength=76
    ) {
        // WARNING: RFC 2047 says: "An 'encoded-word' MUST NOT be used in
        // parameter of a MIME Content-Type or Content-Disposition field",
        // but... it's supported by many clients/servers
        $quoted = '';

        if ($encoding == 'base64') {
            $value = base64_encode($value);
            $prefix = '=?' . $charset . '?B?';
            $suffix = '?=';

            // 2 x SPACE, 2 x '"', '=', ';'
            $add_len = strlen($prefix . $suffix) + strlen($name) + 6;
            $len = $add_len + strlen($value);

            while ($len > $maxLength) { 
                // We can cut base64-encoded string every 4 characters
                $real_len = floor(($maxLength - $add_len) / 4) * 4;
                $_quote = substr($value, 0, $real_len);
                $value = substr($value, $real_len);

                $quoted .= $prefix . $_quote . $suffix . $this->_eol . ' ';
                $add_len = strlen($prefix . $suffix) + 4; // 2 x SPACE, '"', ';'
                $len = strlen($value) + $add_len;
            }
            $quoted .= $prefix . $value . $suffix;

        } else {
            // quoted-printable
            $value = $this->encodeQP($value);
            $prefix = '=?' . $charset . '?Q?';
            $suffix = '?=';

            // 2 x SPACE, 2 x '"', '=', ';'
            $add_len = strlen($prefix . $suffix) + strlen($name) + 6;
            $len = $add_len + strlen($value);

            while ($len > $maxLength) {
                $length = $maxLength - $add_len;
                // don't break any encoded letters
                if (preg_match("/^(.{0,$length}[^\=][^\=])/", $value, $matches)) {
                    $_quote = $matches[1];
                }

                $quoted .= $prefix . $_quote . $suffix . $this->_eol . ' ';
                $value = substr($value, strlen($_quote));
                $add_len = strlen($prefix . $suffix) + 4; // 2 x SPACE, '"', ';'
                $len = strlen($value) + $add_len;
            }

            $quoted .= $prefix . $value . $suffix;
        }

        return " {$name}=\"{$quoted}\"";
    }
Encodes header parameter as per RFC2047 if needed

@param string $name      The parameter name
@param string $value     The parameter value
@param string $charset   The parameter charset
@param string $encoding  Encoding type (quoted-printable or base64)
@param int    $maxLength Encoded parameter max length. Default: 76

@return string Parameter line
@access private