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，RFC2616 )
* 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");

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    }
    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))
    { 中国网管联盟bitsCN.com
        $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;
}

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/* 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

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    // 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
}
?>