PHP 访问LDAP

/**
 * @file ldap_util.php
 *
 * @author Li Yongfeng
 */
function getUserEmail($userId) {
    $ldap_host = "ldap://***/"; 
    $ldap_user = "***";
    $ldap_pwd = "***";
    $ldap_conn = ldap_connect($ldap_host) or die("Can't connect to LDAP server");
    ldap_set_option($ldap_conn, LDAP_OPT_REFERRALS, 0);        //this is necessary
    ldap_set_option($ldap_conn, LDAP_OPT_PROTOCOL_VERSION, 3); //this is necessary
    ldap_bind($ldap_conn, $ldap_user, base64_decode($ldap_pwd)) or die("Can't bind to LDAP server.");
    $base_dn = "DC=corpusers,DC=net";
    $filter = "(samaccountname=$userId)";
    $justthese = array("name","mail");
    //$result= ldap_search($ldap_conn, $base_dn, $filter) or exit(">>Unable to search ldap server<<");
    $result= ldap_search($ldap_conn, $base_dn, $filter, $justthese) or exit(">>Unable to search ldap server<<");
    if (!$result) {
        echo "LDAP-Errno: " . ldap_errno($ldap_conn) . "<br />\n";
        echo "LDAP-Error: " . ldap_error($ldap_conn) . "<br />\n";
        die("Argh!<br />\n");
    }
    $entry= ldap_get_entries($ldap_conn, $result);
    ldap_unbind($ldap_conn) or die("Can't unbind from LDAP server.");
    $ret = new stdClass();
    if ($entry['count'] > 0) {
        $ret->name = $entry[0]['name'][0];
        $ret->mail = $entry[0]['mail'][0];
    }
    //error_log(json_encode($ret));
    return $ret;
    
}