连接数据库并向应用程序发送回复的微小脚本逻辑

Question

我在以下代码中遇到了一个痛苦的问题。我的应用程序连接到名为main.php的脚本，并向其发送用户名和密码。然后，该脚本将检查数据库中的凭据，如果凭据正确则会对我的应用程序作出肯定回复，如果不正确，则会回复。更具体地说，它只检查用户组成员身份并发送回复。现在的问题是它总是发送否定回复。你能告诉我我哪里错了吗？

    <?php

    function append_file( $filename, $newdata )
    {
            $f = fopen( $filename, "a" );
            fwrite( $f, $newdata );
            fclose( $f );
    }


$userAgent          =   $_SERVER['HTTP_USER_AGENT'];


$m_pUsername            =   $_POST['user'];
$m_pPassword                =   $_POST['pass'];
    $m_pDate                        =   date(DATE_RFC822);
    $m_pIP                          =   $_SERVER[ 'REMOTE_ADDR' ];


    $conf['host']           = 'localhost';
    $conf['user']           = 'XXX';
    $conf['pass']           = 'XXX';
    $conf['database']       = 'XXX';



if( !$m_pUsername || !$m_pPassword )
    die("g_requireUpdate");



    $con = mysql_connect($conf['host'],$conf['user'],$conf['pass']) or die ("cannot connect");
    mysql_select_db($conf['database'])or die("cannot select DB");
$sql = mysql_query("SELECT * FROM `user`");

while($row = mysql_fetch_array($sql))
{

    $salt = $row['salt'];
    $md5_pass = MD5(md5($m_pPassword) . $salt);
    if($m_pUsername == $row['username'] &&  $md5_pass == $row['password'] )
    {

        if( $row['usergroupid'] == '5' || $row['usergroupid'] == '9' || $row['usergroupid'] ==     '7' || $row['usergroupid'] == '6' || $row['usergroupid'] == '71' || $row['usergroupid'] == '72'      )//VIPS + STAFF
{
            print("g_userValid ");

            append_file( "access_log.txt", "($m_pUsername) \t  ($m_pIP) \n");
        }
        if( $row['usergroupid'] == '2')//NON VIP
                    {
            print("g_userNormal ");
            exit;
                    }
        if( $row['usergroupid'] == '8')//BANNED
                    {
            print("g_userBanned ");
            exit;
                    }
    }
}


append_file( "access_log.txt", "($m_pUsername) \t  ($m_pIP) \t \n");
mysql_close();
?>