source: trunk/library/Mail/Mail/RFC822.php @ 7688

<?php
/**
 * RFC 822 Email address list validation Utility
 *
 * PHP versions 4 and 5
 *
 * LICENSE:
 *
 * Copyright (c) 2001-2010, Richard Heyes
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * o Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * o Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * o The names of the authors may not be used to endorse or promote
 *   products derived from this software without specific prior written
 *   permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * @category    Mail
 * @package     Mail
 * @author      Richard Heyes <richard@phpguru.org>
 * @author      Chuck Hagenbuch <chuck@horde.org
 * @copyright   2001-2010 Richard Heyes
 * @license     http://opensource.org/licenses/bsd-license.php New BSD License
 * @version     CVS: $Id: RFC822.php 294749 2010-02-08 08:22:25Z clockwerx $
 * @link        http://pear.php.net/package/Mail/
 */

/**
 * RFC 822 Email address list validation Utility
 *
 * What is it?
 *
 * This class will take an address string, and parse it into it's consituent
 * parts, be that either addresses, groups, or combinations. Nested groups
 * are not supported. The structure it returns is pretty straight forward,
 * and is similar to that provided by the imap_rfc822_parse_adrlist(). Use
 * print_r() to view the structure.
 *
 * How do I use it?
 *
 * $address_string = 'My Group: "Richard" <richard@localhost> (A comment), ted@example.com (Ted Bloggs), Barney;';
 * $structure = Mail_RFC822::parseAddressList($address_string, 'example.com', true)
 * print_r($structure);
 *
 * @author  Richard Heyes <richard@phpguru.org>
 * @author  Chuck Hagenbuch <chuck@horde.org>
 * @version $Revision: 294749 $
 * @license BSD
 * @package Mail
 */
if(!class_exists('Mail_RFC822'))
{
    class Mail_RFC822 {

        /**
         * The address being parsed by the RFC822 object.
         * @var string $address
         */
        var $address = '';

        /**
         * The default domain to use for unqualified addresses.
         * @var string $default_domain
         */
        var $default_domain = 'localhost';

        /**
         * Should we return a nested array showing groups, or flatten everything?
         * @var boolean $nestGroups
         */
        var $nestGroups = true;

        /**
         * Whether or not to validate atoms for non-ascii characters.
         * @var boolean $validate
         */
        var $validate = true;

        /**
         * The array of raw addresses built up as we parse.
         * @var array $addresses
         */
        var $addresses = array();

        /**
         * The final array of parsed address information that we build up.
         * @var array $structure
         */
        var $structure = array();

        /**
         * The current error message, if any.
         * @var string $error
         */
        var $error = null;

        /**
         * An internal counter/pointer.
         * @var integer $index
         */
        var $index = null;

        /**
         * The number of groups that have been found in the address list.
         * @var integer $num_groups
         * @access public
         */
        var $num_groups = 0;

        /**
         * A variable so that we can tell whether or not we're inside a
         * Mail_RFC822 object.
         * @var boolean $mailRFC822
         */
        var $mailRFC822 = true;

        /**
         * A limit after which processing stops
         * @var int $limit
         */
        var $limit = null;

        /**
         * Sets up the object. The address must either be set here or when
         * calling parseAddressList(). One or the other.
         *
         * @access public
         * @param string  $address         The address(es) to validate.
         * @param string  $default_domain  Default domain/host etc. If not supplied, will be set to localhost.
         * @param boolean $nest_groups     Whether to return the structure with groups nested for easier viewing.
         * @param boolean $validate        Whether to validate atoms. Turn this off if you need to run addresses through before encoding the personal names, for instance.
         *
         * @return object Mail_RFC822 A new Mail_RFC822 object.
         */
        function Mail_RFC822($address = null, $default_domain = null, $nest_groups = null, $validate = null, $limit = null)
        {
            if (isset($address))        $this->address        = $address;
            if (isset($default_domain)) $this->default_domain = $default_domain;
            if (isset($nest_groups))    $this->nestGroups     = $nest_groups;
            if (isset($validate))       $this->validate       = $validate;
            if (isset($limit))          $this->limit          = $limit;
        }

        /**
         * Starts the whole process. The address must either be set here
         * or when creating the object. One or the other.
         *
         * @access public
         * @param string  $address         The address(es) to validate.
         * @param string  $default_domain  Default domain/host etc.
         * @param boolean $nest_groups     Whether to return the structure with groups nested for easier viewing.
         * @param boolean $validate        Whether to validate atoms. Turn this off if you need to run addresses through before encoding the personal names, for instance.
         *
         * @return array A structured array of addresses.
         */
        function parseAddressList($address = null, $default_domain = null, $nest_groups = null, $validate = null, $limit = null)
        {
            if (!isset($this) || !isset($this->mailRFC822)) {
                $obj = new Mail_RFC822($address, $default_domain, $nest_groups, $validate, $limit);
                return $obj->parseAddressList();
            }

            if (isset($address))        $this->address        = $address;
            if (isset($default_domain)) $this->default_domain = $default_domain;
            if (isset($nest_groups))    $this->nestGroups     = $nest_groups;
            if (isset($validate))       $this->validate       = $validate;
            if (isset($limit))          $this->limit          = $limit;

            $this->structure  = array();
            $this->addresses  = array();
            $this->error      = null;
            $this->index      = null;

            // Unfold any long lines in $this->address.
            $this->address = preg_replace('/\r?\n/', "\r\n", $this->address);
            $this->address = preg_replace('/\r\n(\t| )+/', ' ', $this->address);

            while ($this->address = $this->_splitAddresses($this->address));

            if ($this->address === false || isset($this->error)) {
                require_once dirname(__FILE__).'/../../PEAR/PEAR.php';
                return PEAR::raiseError($this->error);
            }

            // Validate each address individually.  If we encounter an invalid
            // address, stop iterating and return an error immediately.
            foreach ($this->addresses as $address) {
                $valid = $this->_validateAddress($address);

                if ($valid === false || isset($this->error)) {
                    require_once 'PEAR.php';
                    return PEAR::raiseError($this->error);
                }

                if (!$this->nestGroups) {
                    $this->structure = array_merge($this->structure, $valid);
                } else {
                    $this->structure[] = $valid;
                }
            }

            return $this->structure;
        }

        /**
         * Splits an address into separate addresses.
         *
         * @access private
         * @param string $address The addresses to split.
         * @return boolean Success or failure.
         */
        function _splitAddresses($address)
        {
            if (!empty($this->limit) && count($this->addresses) == $this->limit) {
                return '';
            }

            if ($this->_isGroup($address) && !isset($this->error)) {
                $split_char = ';';
                $is_group   = true;
            } elseif (!isset($this->error)) {
                $split_char = ',';
                $is_group   = false;
            } elseif (isset($this->error)) {
                return false;
            }

            // Split the string based on the above ten or so lines.
            $parts  = explode($split_char, $address);
            $string = $this->_splitCheck($parts, $split_char);

            // If a group...
            if ($is_group) {
                // If $string does not contain a colon outside of
                // brackets/quotes etc then something's fubar.

                // First check there's a colon at all:
                if (strpos($string, ':') === false) {
                    $this->error = 'Invalid address: ' . $string;
                    return false;
                }

                // Now check it's outside of brackets/quotes:
                if (!$this->_splitCheck(explode(':', $string), ':')) {
                    return false;
                }

                // We must have a group at this point, so increase the counter:
                $this->num_groups++;
            }

            // $string now contains the first full address/group.
            // Add to the addresses array.
            $this->addresses[] = array(
                'address' => trim($string),
                'group'   => $is_group
            );

            // Remove the now stored address from the initial line, the +1
            // is to account for the explode character.
            $address = trim(substr($address, strlen($string) + 1));

            // If the next char is a comma and this was a group, then
            // there are more addresses, otherwise, if there are any more
            // chars, then there is another address.
            if ($is_group && substr($address, 0, 1) == ','){
                $address = trim(substr($address, 1));
                return $address;

            } elseif (strlen($address) > 0) {
                return $address;

            } else {
                return '';
            }

            // If you got here then something's off
            return false;
        }

        /**
         * Checks for a group at the start of the string.
         *
         * @access private
         * @param string $address The address to check.
         * @return boolean Whether or not there is a group at the start of the string.
         */
        function _isGroup($address)
        {
            // First comma not in quotes, angles or escaped:
            $parts  = explode(',', $address);
            $string = $this->_splitCheck($parts, ',');

            // Now we have the first address, we can reliably check for a
            // group by searching for a colon that's not escaped or in
            // quotes or angle brackets.
            if (count($parts = explode(':', $string)) > 1) {
                $string2 = $this->_splitCheck($parts, ':');
                return ($string2 !== $string);
            } else {
                return false;
            }
        }

        /**
         * A common function that will check an exploded string.
         *
         * @access private
         * @param array $parts The exloded string.
         * @param string $char  The char that was exploded on.
         * @return mixed False if the string contains unclosed quotes/brackets, or the string on success.
         */
        function _splitCheck($parts, $char)
        {
            $string = $parts[0];

            $parts_count = count($parts);
            for ($i = 0; $i < $parts_count; ++$i) {
                if ($this->_hasUnclosedQuotes($string)
                    || $this->_hasUnclosedBrackets($string, '<>')
                    || $this->_hasUnclosedBrackets($string, '[]')
                    || $this->_hasUnclosedBrackets($string, '()')
                    || substr($string, -1) == '\\') {
                    if (isset($parts[$i + 1])) {
                        $string = $string . $char . $parts[$i + 1];
                    } else {
                        $this->error = 'Invalid address spec. Unclosed bracket or quotes';
                        return false;
                    }
                } else {
                    $this->index = $i;
                    break;
                }
            }

            return $string;
        }

        /**
         * Checks if a string has unclosed quotes or not.
         *
         * @access private
         * @param string $string  The string to check.
         * @return boolean  True if there are unclosed quotes inside the string,
         *                  false otherwise.
         */
        function _hasUnclosedQuotes($string)
        {
            $string = trim($string);
            $iMax = strlen($string);
            $in_quote = false;
            $i = $slashes = 0;

            for (; $i < $iMax; ++$i) {
                switch ($string[$i]) {
                    case '\\':
                        ++$slashes;
                        break;

                    case '"':
                        if ($slashes % 2 == 0) {
                            $in_quote = !$in_quote;
                        }
                    // Fall through to default action below.

                    default:
                        $slashes = 0;
                        break;
                }
            }

            return $in_quote;
        }

        /**
         * Checks if a string has an unclosed brackets or not. IMPORTANT:
         * This function handles both angle brackets and square brackets;
         *
         * @access private
         * @param string $string The string to check.
         * @param string $chars  The characters to check for.
         * @return boolean True if there are unclosed brackets inside the string, false otherwise.
         */
        function _hasUnclosedBrackets($string, $chars)
        {
            $num_angle_start = substr_count($string, $chars[0]);
            $num_angle_end   = substr_count($string, $chars[1]);

            $this->_hasUnclosedBracketsSub($string, $num_angle_start, $chars[0]);
            $this->_hasUnclosedBracketsSub($string, $num_angle_end, $chars[1]);

            if ($num_angle_start < $num_angle_end) {
                $this->error = 'Invalid address spec. Unmatched quote or bracket (' . $chars . ')';
                return false;
            } else {
                return ($num_angle_start > $num_angle_end);
            }
        }

        /**
         * Sub function that is used only by hasUnclosedBrackets().
         *
         * @access private
         * @param string $string The string to check.
         * @param integer &$num    The number of occurences.
         * @param string $char   The character to count.
         * @return integer The number of occurences of $char in $string, adjusted for backslashes.
         */
        function _hasUnclosedBracketsSub($string, &$num, $char)
        {
            $parts = explode($char, $string);
            $parts_count = count($parts);
            for ($i = 0; $i < $parts_count; ++$i){
                if (substr($parts[$i], -1) == '\\' || $this->_hasUnclosedQuotes($parts[$i]))
                    $num--;
                if (isset($parts[$i + 1]))
                    $parts[$i + 1] = $parts[$i] . $char . $parts[$i + 1];
            }

            return $num;
        }

        /**
         * Function to begin checking the address.
         *
         * @access private
         * @param string $address The address to validate.
         * @return mixed False on failure, or a structured array of address information on success.
         */
        function _validateAddress($address)
        {
            $is_group = false;
            $addresses = array();

            if ($address['group']) {
                $is_group = true;

                // Get the group part of the name
                $parts     = explode(':', $address['address']);
                $groupname = $this->_splitCheck($parts, ':');
                $structure = array();

                // And validate the group part of the name.
                if (!$this->_validatePhrase($groupname)){
                    $this->error = 'Group name did not validate.';
                    return false;
                } else {
                    // Don't include groups if we are not nesting
                    // them. This avoids returning invalid addresses.
                    if ($this->nestGroups) {
                        $structure = new stdClass;
                        $structure->groupname = $groupname;
                    }
                }

                $address['address'] = ltrim(substr($address['address'], strlen($groupname . ':')));
            }

            // If a group then split on comma and put into an array.
            // Otherwise, Just put the whole address in an array.
            if ($is_group) {
                while (strlen($address['address']) > 0) {
                    $parts       = explode(',', $address['address']);
                    $addresses[] = $this->_splitCheck($parts, ',');
                    $address['address'] = trim(substr($address['address'], strlen(end($addresses) . ',')));
                }
            } else {
                $addresses[] = $address['address'];
            }

            // Check that $addresses is set, if address like this:
            // Groupname:;
            // Then errors were appearing.
            if (!count($addresses)){
                $this->error = 'Empty group.';
                return false;
            }

            // Trim the whitespace from all of the address strings.
            array_map('trim', $addresses);

            // Validate each mailbox.
            // Format could be one of: name <geezer@domain.com>
            //                         geezer@domain.com
            //                         geezer
            // ... or any other format valid by RFC 822.
            $addresses_count = count($addresses);
            for ($i = 0; $i < $addresses_count; ++$i) {
                if (!$this->validateMailbox($addresses[$i])) {
                    if (empty($this->error)) {
                        $this->error = 'Validation failed for: ' . $addresses[$i];
                    }
                    return false;
                }
            }

            // Nested format
            if ($this->nestGroups) {
                if ($is_group) {
                    $structure->addresses = $addresses;
                } else {
                    $structure = $addresses[0];
                }

                // Flat format
            } else {
                if ($is_group) {
                    $structure = array_merge($structure, $addresses);
                } else {
                    $structure = $addresses;
                }
            }

            return $structure;
        }

        /**
         * Function to validate a phrase.
         *
         * @access private
         * @param string $phrase The phrase to check.
         * @return boolean Success or failure.
         */
        function _validatePhrase($phrase)
        {
            // Splits on one or more Tab or space.
            $parts = preg_split('/[ \\x09]+/', $phrase, -1, PREG_SPLIT_NO_EMPTY);

            $phrase_parts = array();
            while (count($parts) > 0){
                $phrase_parts[] = $this->_splitCheck($parts, ' ');
                for ($i = 0; $i < $this->index + 1; ++$i)
                    array_shift($parts);
            }

            foreach ($phrase_parts as $part) {
                // If quoted string:
                if (substr($part, 0, 1) == '"') {
                    if (!$this->_validateQuotedString($part)) {
                        return false;
                    }
                    continue;
                }

                // Otherwise it's an atom:
                if (!$this->_validateAtom($part)) return false;
            }

            return true;
        }

        /**
         * Function to validate an atom which from rfc822 is:
         * atom = 1*<any CHAR except specials, SPACE and CTLs>
         *
         * If validation ($this->validate) has been turned off, then
         * validateAtom() doesn't actually check anything. This is so that you
         * can split a list of addresses up before encoding personal names
         * (umlauts, etc.), for example.
         *
         * @access private
         * @param string $atom The string to check.
         * @return boolean Success or failure.
         */
        function _validateAtom($atom)
        {
            if (!$this->validate) {
                // Validation has been turned off; assume the atom is okay.
                return true;
            }

            // Check for any char from ASCII 0 - ASCII 127
            if (!preg_match('/^[\\x00-\\x7E]+$/i', $atom, $matches)) {
                return false;
            }

            // Check for specials:
            if (preg_match('/[][()<>@,;\\:". ]/', $atom)) {
                return false;
            }

            // Check for control characters (ASCII 0-31):
            if (preg_match('/[\\x00-\\x1F]+/', $atom)) {
                return false;
            }

            return true;
        }

        /**
         * Function to validate quoted string, which is:
         * quoted-string = <"> *(qtext/quoted-pair) <">
         *
         * @access private
         * @param string $qstring The string to check
         * @return boolean Success or failure.
         */
        function _validateQuotedString($qstring)
        {
            // Leading and trailing "
            $qstring = substr($qstring, 1, -1);

            // Perform check, removing quoted characters first.
            return !preg_match('/[\x0D\\\\"]/', preg_replace('/\\\\./', '', $qstring));
        }

        /**
         * Function to validate a mailbox, which is:
         * mailbox =   addr-spec         ; simple address
         *           / phrase route-addr ; name and route-addr
         *
         * @access public
         * @param string &$mailbox The string to check.
         * @return boolean Success or failure.
         */
        function validateMailbox(&$mailbox)
        {
            // A couple of defaults.
            $phrase  = '';
            $comment = '';
            $comments = array();

            // Catch any RFC822 comments and store them separately.
            $_mailbox = $mailbox;
            while (strlen(trim($_mailbox)) > 0) {
                $parts = explode('(', $_mailbox);
                $before_comment = $this->_splitCheck($parts, '(');
                if ($before_comment != $_mailbox) {
                    // First char should be a (.
                    $comment    = substr(str_replace($before_comment, '', $_mailbox), 1);
                    $parts      = explode(')', $comment);
                    $comment    = $this->_splitCheck($parts, ')');
                    $comments[] = $comment;

                    // +2 is for the brackets
                    $_mailbox = substr($_mailbox, strpos($_mailbox, '('.$comment)+strlen($comment)+2);
                } else {
                    break;
                }
            }

            foreach ($comments as $comment) {
                $mailbox = str_replace("($comment)", '', $mailbox);
            }

            $mailbox = trim($mailbox);

            // Check for name + route-addr
            if (substr($mailbox, -1) == '>' && substr($mailbox, 0, 1) != '<') {
                $parts  = explode('<', $mailbox);
                $name   = $this->_splitCheck($parts, '<');

                $phrase     = trim($name);
                $route_addr = trim(substr($mailbox, strlen($name.'<'), -1));

                if ($this->_validatePhrase($phrase) === false || ($route_addr = $this->_validateRouteAddr($route_addr)) === false) {
                    return false;
                }

                // Only got addr-spec
            } else {
                // First snip angle brackets if present.
                if (substr($mailbox, 0, 1) == '<' && substr($mailbox, -1) == '>') {
                    $addr_spec = substr($mailbox, 1, -1);
                } else {
                    $addr_spec = $mailbox;
                }

                if (($addr_spec = $this->_validateAddrSpec($addr_spec)) === false) {
                    return false;
                }
            }

            // Construct the object that will be returned.
            $mbox = new stdClass();

            // Add the phrase (even if empty) and comments
            $mbox->personal = $phrase;
            $mbox->comment  = isset($comments) ? $comments : array();

            if (isset($route_addr)) {
                $mbox->mailbox = $route_addr['local_part'];
                $mbox->host    = $route_addr['domain'];
                $route_addr['adl'] !== '' ? $mbox->adl = $route_addr['adl'] : '';
            } else {
                $mbox->mailbox = $addr_spec['local_part'];
                $mbox->host    = $addr_spec['domain'];
            }

            $mailbox = $mbox;
            return true;
        }

        /**
         * This function validates a route-addr which is:
         * route-addr = "<" [route] addr-spec ">"
         *
         * Angle brackets have already been removed at the point of
         * getting to this function.
         *
         * @access private
         * @param string $route_addr The string to check.
         * @return mixed False on failure, or an array containing validated address/route information on success.
         */
        function _validateRouteAddr($route_addr)
        {
            // Check for colon.
            if (strpos($route_addr, ':') !== false) {
                $parts = explode(':', $route_addr);
                $route = $this->_splitCheck($parts, ':');
            } else {
                $route = $route_addr;
            }

            // If $route is same as $route_addr then the colon was in
            // quotes or brackets or, of course, non existent.
            if ($route === $route_addr){
                unset($route);
                $addr_spec = $route_addr;
                if (($addr_spec = $this->_validateAddrSpec($addr_spec)) === false) {
                    return false;
                }
            } else {
                // Validate route part.
                if (($route = $this->_validateRoute($route)) === false) {
                    return false;
                }

                $addr_spec = substr($route_addr, strlen($route . ':'));

                // Validate addr-spec part.
                if (($addr_spec = $this->_validateAddrSpec($addr_spec)) === false) {
                    return false;
                }
            }

            if (isset($route)) {
                $return['adl'] = $route;
            } else {
                $return['adl'] = '';
            }

            $return = array_merge($return, $addr_spec);
            return $return;
        }

        /**
         * Function to validate a route, which is:
         * route = 1#("@" domain) ":"
         *
         * @access private
         * @param string $route The string to check.
         * @return mixed False on failure, or the validated $route on success.
         */
        function _validateRoute($route)
        {
            // Split on comma.
            $domains = explode(',', trim($route));

            foreach ($domains as $domain) {
                $domain = str_replace('@', '', trim($domain));
                if (!$this->_validateDomain($domain)) return false;
            }

            return $route;
        }

        /**
         * Function to validate a domain, though this is not quite what
         * you expect of a strict internet domain.
         *
         * domain = sub-domain *("." sub-domain)
         *
         * @access private
         * @param string $domain The string to check.
         * @return mixed False on failure, or the validated domain on success.
         */
        function _validateDomain($domain)
        {
            // Note the different use of $subdomains and $sub_domains
            $subdomains = explode('.', $domain);

            while (count($subdomains) > 0) {
                $sub_domains[] = $this->_splitCheck($subdomains, '.');
                for ($i = 0; $i < $this->index + 1; ++$i)
                    array_shift($subdomains);
            }

            foreach ($sub_domains as $sub_domain) {
                if (!$this->_validateSubdomain(trim($sub_domain)))
                    return false;
            }

            // Managed to get here, so return input.
            return $domain;
        }

        /**
         * Function to validate a subdomain:
         *   subdomain = domain-ref / domain-literal
         *
         * @access private
         * @param string $subdomain The string to check.
         * @return boolean Success or failure.
         */
        function _validateSubdomain($subdomain)
        {
            if (preg_match('|^\[(.*)]$|', $subdomain, $arr)){
                if (!$this->_validateDliteral($arr[1])) return false;
            } else {
                if (!$this->_validateAtom($subdomain)) return false;
            }

            // Got here, so return successful.
            return true;
        }

        /**
         * Function to validate a domain literal:
         *   domain-literal =  "[" *(dtext / quoted-pair) "]"
         *
         * @access private
         * @param string $dliteral The string to check.
         * @return boolean Success or failure.
         */
        function _validateDliteral($dliteral)
        {
            return !preg_match('/(.)[][\x0D\\\\]/', $dliteral, $matches) && $matches[1] != '\\';
        }

        /**
         * Function to validate an addr-spec.
         *
         * addr-spec = local-part "@" domain
         *
         * @access private
         * @param string $addr_spec The string to check.
         * @return mixed False on failure, or the validated addr-spec on success.
         */
        function _validateAddrSpec($addr_spec)
        {
            $addr_spec = trim($addr_spec);

            // Split on @ sign if there is one.
            if (strpos($addr_spec, '@') !== false) {
                $parts      = explode('@', $addr_spec);
                $local_part = $this->_splitCheck($parts, '@');
                $domain     = substr($addr_spec, strlen($local_part . '@'));

                // No @ sign so assume the default domain.
            } else {
                $local_part = $addr_spec;
                $domain     = $this->default_domain;
            }

            if (($local_part = $this->_validateLocalPart($local_part)) === false) return false;
            if (($domain     = $this->_validateDomain($domain)) === false) return false;

            // Got here so return successful.
            return array('local_part' => $local_part, 'domain' => $domain);
        }

        /**
         * Function to validate the local part of an address:
         *   local-part = word *("." word)
         *
         * @access private
         * @param string $local_part
         * @return mixed False on failure, or the validated local part on success.
         */
        function _validateLocalPart($local_part)
        {
            $parts = explode('.', $local_part);
            $words = array();

            // Split the local_part into words.
            while (count($parts) > 0){
                $words[] = $this->_splitCheck($parts, '.');
                for ($i = 0; $i < $this->index + 1; ++$i) {
                    array_shift($parts);
                }
            }

            // Validate each word.
            foreach ($words as $word) {
                // If this word contains an unquoted space, it is invalid. (6.2.4)
                if (strpos($word, ' ') && $word[0] !== '"')
                {
                    return false;
                }

                if ($this->_validatePhrase(trim($word)) === false) return false;
            }

            // Managed to get here, so return the input.
            return $local_part;
        }

        /**
         * Returns an approximate count of how many addresses are in the
         * given string. This is APPROXIMATE as it only splits based on a
         * comma which has no preceding backslash. Could be useful as
         * large amounts of addresses will end up producing *large*
         * structures when used with parseAddressList().
         *
         * @param  string $data Addresses to count
         * @return int          Approximate count
         */
        function approximateCount($data)
        {
            return count(preg_split('/(?<!\\\\),/', $data));
        }

        /**
         * This is a email validating function separate to the rest of the
         * class. It simply validates whether an email is of the common
         * internet form: <user>@<domain>. This can be sufficient for most
         * people. Optional stricter mode can be utilised which restricts
         * mailbox characters allowed to alphanumeric, full stop, hyphen
         * and underscore.
         *
         * @param  string  $data   Address to check
         * @param  boolean $strict Optional stricter mode
         * @return mixed           False if it fails, an indexed array
         *                         username/domain if it matches
         */
        function isValidInetAddress($data, $strict = false)
        {
            $regex = $strict ? '/^([.0-9a-z_+-]+)@(([0-9a-z-]+\.)+[0-9a-z]{2,})$/i' : '/^([*+!.&#$|\'\\%\/0-9a-z^_`{}=?~:-]+)@(([0-9a-z-]+\.)+[0-9a-z]{2,})$/i';
            if (preg_match($regex, trim($data), $matches)) {
                return array($matches[1], $matches[2]);
            } else {
                return false;
            }
        }

    }
}