用PHP模拟登陆

<?php
/* 
* 得到网页内容 
* 参数：$host [in] string
*      主机名称（例如： www.imsorry.com.cn）
* 参数：$method [in] string
*      提交方法：post, get, head ... 并加上相应的参数( 具体语法参见 rfc1945，rfc2068 )
* 参数：$str [in] string
*      提交的内容
* 参数：$sessid [in] string
*      php的sessionid
*
* @返回 网页内容 string
*/
function getwebcontent($host, $method, $str, $sessid = '')
{
    $ip = gethostbyname($host);
    $fp = fsockopen($ip, 80);
    if (!$fp) return;
    fputs($fp, "$method/r/n");
    fputs($fp, "host: $host/r/n");
    if (!empty($sessid))
    {
        fputs($fp, "cookie: phpsessid=$sessid; path=/;/r/n");
    }
    if ( substr(trim($method),0, 4) == "post")
    {
        fputs($fp, "content-length: ". strlen($str) . "/r/n"); //  别忘了指定长度
    }
    fputs($fp, "content-type: application/x-www-form-urlencoded/r/n/r/n");
    if ( substr(trim($method),0, 4) == "post")
    {
        fputs($fp, $str."/r/n");
    }
    while(!feof($fp))
    {
        $response .= fgets($fp, 1024);
    }
    $hlen = strpos($response,"/r/n/r/n"); // linux下是 "/n/n"
    $header = substr($response, 0, $hlen);
    $entity = substr($response, $hlen + 4);
    if ( preg_match('/phpsessid=([0-9a-z]+);/i', $header, $matches))
    {
        $a['sessid'] = $matches[1];
    }
    if ( preg_match('/location: ([0-9a-z/_/?/=/&/#/.]+)/i', $header, $matches))
    {
        $a['location'] = $matches[1];
    }
    $a['content'] = $entity;    
    fclose($fp);
    return $a;
}

/* 构造用户名，密码字符串 */
$str = ("username=test&password=test");
$response = getwebcontent("localhost","post /login.php http/1.0", $str);
echo $response['location'].$response['content']."<br>";
echo $response['sessid']."<br>";
if ( preg_match('/error/.php/i',$response['location']))
{
    echo "登陆失败<br>";
} else {
    echo "登陆成功<br>";
    // 不可以访问user.php，因为不带sessid参数
    $response = getwebcontent("localhost","get /user.php http/1.0", '', '');
    echo $response['location']."<br>"; // 结果：error.php?errcode=2

    // 可以访问user.php
    $response = getwebcontent("localhost","get /user.php http/1.0", '', $response['sessid']);
    echo $response['location']."<br>"; // 结果：user.php
}
?>