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php – 如何检测伪装用户/爬虫/cURL

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问题描述

其他一些网站可能会使用cURL和伪造的http Referer复制我的网站内容。

我们是否可以检测出请求是cURL而不是真正的Web浏览器？

 

最佳思路

没有任何完美的方法可以避免自动爬取网页。因为人可以做到的一切，机器人也可以模拟做到。但是有很多能让机器抓取变得更困难的做法，从而防止绝大部分人的专区，不过对于非常精通技术的极客效果有限。

这里介绍几种不同类型的反爬技术。

1.每个IP的会话数

如果用户每分钟使用50个新会话，则可以认为该用户可能是不处理Cookie的爬虫程序。当然，curl可以完美地管理cookie，但是如果您将其与每个会话的访问计数器结合使用(稍后说明)，或者爬虫对cookie处理得不好，那么这个方法可能是有效的。

一般不太可能有50个具有相同共享连接的人会同时在您的网站上访问。如果发生这种情况，则认为是爬虫在抓取，您可以锁定网站页面，直到输入验证码为止。

具体步骤：

1)创建2个表：1个保存禁用的ips，1个保存ip和会话

create table if not exists sessions_per_ip (
  ip int unsigned,
  session_id varchar(32),
  creation timestamp default current_timestamp,
  primary key(ip, session_id)
);

create table if not exists banned_ips (
  ip int unsigned,
  creation timestamp default current_timestamp,
  primary key(ip)
);

2)在脚本的开头，您从两个表中删除了太旧的条目

3)接下来，您检查用户的IP是否被禁止(将标志设置为true)

4)如果没有，您可以计算出他的IP会话数

5)如果TA的会话过多，则将其插入到被禁止的表中并设置一个标志

6)如果尚未插入sessions_per_ip表，则将其ip插入

我编写了一个代码示例，以更好地显示我的想法。

<?php

try
{

    // Some configuration (small values for demo)
    $max_sessions = 5; // 5 sessions/ip simultaneousely allowed
    $check_duration = 30; // 30 secs max lifetime of an ip on the sessions_per_ip table
    $lock_duration = 60; // time to lock your website for this ip if max_sessions is reached

    // Mysql connection
    require_once("config.php");
    $dbh = new PDO("mysql:host={$host};dbname={$base}", $user, $password);
    $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    // Delete old entries in tables
    $query = "delete from sessions_per_ip where timestampdiff(second, creation, now()) > {$check_duration}";
    $dbh->exec($query);

    $query = "delete from banned_ips where timestampdiff(second, creation, now()) > {$lock_duration}";
    $dbh->exec($query);

    // Get useful info attached to our user...
    session_start();
    $ip = ip2long($_SERVER['REMOTE_ADDR']);
    $session_id = session_id();

    // Check if IP is already banned
    $banned = false;
    $count = $dbh->query("select count(*) from banned_ips where ip = '{$ip}'")->fetchColumn();
    if ($count > 0)
    {
        $banned = true;
    }
    else
    {
        // Count entries in our db for this ip
        $query = "select count(*)  from sessions_per_ip where ip = '{$ip}'";
        $count = $dbh->query($query)->fetchColumn();
        if ($count >= $max_sessions)
        {
            // Lock website for this ip
            $query = "insert ignore into banned_ips ( ip ) values ( '{$ip}' )";
            $dbh->exec($query);
            $banned = true;
        }

        // Insert a new entry on our db if user's session is not already recorded
        $query = "insert ignore into sessions_per_ip ( ip, session_id ) values ('{$ip}', '{$session_id}')";
        $dbh->exec($query);
    }

    // At this point you have a $banned if your user is banned or not.
    // The following code will allow us to test it...

    // We do not display anything now because we'll play with sessions :
    // to make the demo more readable I prefer going step by step like
    // this.
    ob_start();

    // Displays your current sessions
    echo "Your current sessions keys are : <br/>";
    $query = "select session_id from sessions_per_ip where ip = '{$ip}'";
    foreach ($dbh->query($query) as $row) {
        echo "{$row['session_id']}<br/>";
    }

    // Display and handle a way to create new sessions
    echo str_repeat('<br/>', 2);
    echo '<a href="' . basename(__FILE__) . '?new=1">Create a new session / reload</a>';
    if (isset($_GET['new']))
    {
        session_regenerate_id();
        session_destroy();
        header("Location: " . basename(__FILE__));
        die();
    }

    // Display if you're banned or not
    echo str_repeat('<br/>', 2);
    if ($banned)
    {
        echo '<span style="color:red;">You are banned: wait 60secs to be unbanned... a captcha must be more friendly of course!</span>';
        echo '<br/>';
        echo '<img src="http://4.bp.blogspot.com/-PezlYVgEEvg/TadW2e4OyHI/AAAAAAAAAAg/QHZPVQcBNeg/s1600/feu-rouge.png" />';
    }
    else
    {
        echo '<span style="color:blue;">You are not banned!</span>';
        echo '<br/>';
        echo '<img src="http://identityspecialist.files.wordpress.com/2010/06/traffic_light_green.png" />';
    }
    ob_end_flush();
}
catch (PDOException $e)
{
    /*echo*/ $e->getMessage();
}

?>

2.访问计数

如果您的用户使用相同的Cookie来抓取您的页面，则可以使用其会话来阻止它。这个想法很简单：您的用户是否有可能在60秒内访问60页？

步骤：

  1. 在用户会话中创建一个数组，其中将包含每次访问时间。
  2. 删除此数组中早于X秒的访问
  3. 为实际访问添加新条目
  4. 计算此数组中的条目
  5. 如果用户访问了Y页，则禁止该用户

样例代码：

<?php

$visit_counter_pages = 5; // maximum number of pages to load
$visit_counter_secs = 10; // maximum amount of time before cleaning visits

session_start();

// initialize an array for our visit counter
if (array_key_exists('visit_counter', $_SESSION) == false)
{
    $_SESSION['visit_counter'] = array();
}

// clean old visits
foreach ($_SESSION['visit_counter'] as $key => $time)
{
    if ((time() - $time) > $visit_counter_secs) {
        unset($_SESSION['visit_counter'][$key]);
    }
}

// we add the current visit into our array
$_SESSION['visit_counter'][] = time();

// check if user has reached limit of visited pages
$banned = false;
if (count($_SESSION['visit_counter']) > $visit_counter_pages)
{
    // puts ip of our user on the same "banned table" as earlier...
    $banned = true;
}

// At this point you have a $banned if your user is banned or not.
// The following code will allow us to test it...

echo '<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js"></script>';

// Display counter
$count = count($_SESSION['visit_counter']);
echo "You visited {$count} pages.";
echo str_repeat('<br/>', 2);

echo <<< EOT

<a id="reload" href="#">Reload</a>

<script type="text/javascript">

  $('#reload').click(function(e) {
    e.preventDefault();
    window.location.reload();
  });

</script>

EOT;

echo str_repeat('<br/>', 2);

// Display if you're banned or not
echo str_repeat('<br/>', 2);
if ($banned)
{
    echo '<span style="color:red;">You are banned! Wait for a short while (10 secs in this demo)...</span>';
    echo '<br/>';
    echo '<img src="http://4.bp.blogspot.com/-PezlYVgEEvg/TadW2e4OyHI/AAAAAAAAAAg/QHZPVQcBNeg/s1600/feu-rouge.png" />';
}
else
{
    echo '<span style="color:blue;">You are not banned!</span>';
    echo '<br/>';
    echo '<img src="http://identityspecialist.files.wordpress.com/2010/06/traffic_light_green.png" />';
}
?>

3.图片下载

爬虫通常要在很短的时间内获取大量数据，一般不会下载页面上的图像，原因是：图像占用了太多带宽，会使抓取速度变慢。

这个方法的具体做法是：(我认为是最简洁，最容易实现的)

使用mod_rewrite将.jpg /.png /…等格式的图像文件隐藏在网页中。该图像应该在您要保护的每个页面上可用：它可能是您的网站LOGO，一般选择尺寸较小的图像(因为该图像不得缓存)。

步骤：

1. 将这些行添加到您的.htaccess中

RewriteEngine On
RewriteBase /tests/anticrawl/
RewriteRule ^logo\.jpg$ logo.php

2.使用安全性创建您的logo.php

<?php

// start session and reset counter
session_start();
$_SESSION['no_logo_count'] = 0;

// forces image to reload next time
header("Cache-Control: no-store, no-cache, must-revalidate");

// displays image
header("Content-type: image/jpg");
readfile("logo.jpg");
die();

3.在需要增加安全性的每个页面上增加no_logo_count，并检查其是否达到限制。

样例代码：

<?php

$no_logo_limit = 5; // number of allowd pages without logo

// start session and initialize
session_start();
if (array_key_exists('no_logo_count', $_SESSION) == false)
{
    $_SESSION['no_logo_count'] = 0;
}
else
{
    $_SESSION['no_logo_count']++;
}

// check if user has reached limit of "undownloaded image"
$banned = false;
if ($_SESSION['no_logo_count'] >= $no_logo_limit)
{
    // puts ip of our user on the same "banned table" as earlier...
    $banned = true;
}

// At this point you have a $banned if your user is banned or not.
// The following code will allow us to test it...

echo '<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js"></script>';

// Display counter
echo "You did not loaded image {$_SESSION['no_logo_count']} times.";
echo str_repeat('<br/>', 2);

// Display "reload" link
echo <<< EOT

<a id="reload" href="#">Reload</a>

<script type="text/javascript">

  $('#reload').click(function(e) {
    e.preventDefault();
    window.location.reload();
  });

</script>

EOT;

echo str_repeat('<br/>', 2);

// Display "show image" link : note that we're using .jpg file
echo <<< EOT

<div id="image_container">
    <a id="image_load" href="#">Load image</a>
</div>
<br/>

<script type="text/javascript">

  // On your implementation, you'llO of course use <img src="logo.jpg" />
  $('#image_load').click(function(e) {
    e.preventDefault();
    $('#image_load').html('<img src="logo.jpg" />');
  });

</script>

EOT;

// Display if you're banned or not
echo str_repeat('<br/>', 2);
if ($banned)
{
    echo '<span style="color:red;">You are banned: click on "load image" and reload...</span>';
    echo '<br/>';
    echo '<img src="http://4.bp.blogspot.com/-PezlYVgEEvg/TadW2e4OyHI/AAAAAAAAAAg/QHZPVQcBNeg/s1600/feu-rouge.png" />';
}
else
{
    echo '<span style="color:blue;">You are not banned!</span>';
    echo '<br/>';
    echo '<img src="http://identityspecialist.files.wordpress.com/2010/06/traffic_light_green.png" />';
}
?>

4.Cookie检查

您可以在javascript端创建cookie，以检查您的用户是否执行了javascript(例如，使用Curl的抓取工具不会)。

这个想法很简单：这与图像检查大致相同。

  1. 将$ _SESSION值设置为1，并在每次访问中将其递增
  2. 如果存在cookie(在JavaScript中设置)，请将会话值设置为0
  3. 如果此值达到限制，择禁止用户访问

代码：

<?php

$no_cookie_limit = 5; // number of allowd pages without cookie set check

// Start session and reset counter
session_start();

if (array_key_exists('cookie_check_count', $_SESSION) == false)
{
    $_SESSION['cookie_check_count'] = 0;
}

// Initializes cookie (note: rename it to a more discrete name of course) or check cookie value
if ((array_key_exists('cookie_check', $_COOKIE) == false) || ($_COOKIE['cookie_check'] != 42))
{
    // Cookie does not exist or is incorrect...
    $_SESSION['cookie_check_count']++;
}
else
{
    // Cookie is properly set so we reset counter
    $_SESSION['cookie_check_count'] = 0;
}

// Check if user has reached limit of "cookie check"
$banned = false;
if ($_SESSION['cookie_check_count'] >= $no_cookie_limit)
{
    // puts ip of our user on the same "banned table" as earlier...
    $banned = true;
}

// At this point you have a $banned if your user is banned or not.
// The following code will allow us to test it...

echo '<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js"></script>';

// Display counter
echo "Cookie check failed {$_SESSION['cookie_check_count']} times.";
echo str_repeat('<br/>', 2);

// Display "reload" link
echo <<< EOT

<br/>
<a id="reload" href="#">Reload</a>
<br/>

<script type="text/javascript">

  $('#reload').click(function(e) {
    e.preventDefault();
    window.location.reload();
  });

</script>

EOT;

// Display "set cookie" link
echo <<< EOT

<br/>
<a id="cookie_link" href="#">Set cookie</a>
<br/>

<script type="text/javascript">

  // On your implementation, you'll of course put the cookie set on a $(document).ready()
  $('#cookie_link').click(function(e) {
    e.preventDefault();
    var expires = new Date();
    expires.setTime(new Date().getTime() + 3600000);
    document.cookie="cookie_check=42;expires=" + expires.toGMTString();
  });

</script>
EOT;


// Display "unset cookie" link
echo <<< EOT

<br/>
<a id="unset_cookie" href="#">Unset cookie</a>
<br/>

<script type="text/javascript">

  // On your implementation, you'll of course put the cookie set on a $(document).ready()
  $('#unset_cookie').click(function(e) {
    e.preventDefault();
    document.cookie="cookie_check=;expires=Thu, 01 Jan 1970 00:00:01 GMT";
  });

</script>
EOT;

// Display if you're banned or not
echo str_repeat('<br/>', 2);
if ($banned)
{
    echo '<span style="color:red;">You are banned: click on "Set cookie" and reload...</span>';
    echo '<br/>';
    echo '<img src="http://4.bp.blogspot.com/-PezlYVgEEvg/TadW2e4OyHI/AAAAAAAAAAg/QHZPVQcBNeg/s1600/feu-rouge.png" />';
}
else
{
    echo '<span style="color:blue;">You are not banned!</span>';
    echo '<br/>';
    echo '<img src="http://identityspecialist.files.wordpress.com/2010/06/traffic_light_green.png" />';
}

5.防止代理

我们可以在网上找到有关不同种类的代理的一些信息：

  • 普通代理显示有关用户连接(尤其是其IP)的信息。 （“normal” proxy）
  • 匿名代理不显示IP，但在标头上提供有关代理使用的信息。(anonymous proxy)
  • 高度匿名代理不显示用户IP，也不显示浏览器可能无法发送的任何信息。(high-anonyous proxy)

发现连接任何网站的代理很容易，但是很难发现high-anonymous代理。

一些$ _SERVER变量可能包含密钥，特别是如果您的用户位于代理之后(详尽列表来自this question)：

  • CLIENT_IP
  • FORWARDED
  • FORWARDED_FOR
  • FORWARDED_FOR_IP
  • HTTP_CLIENT_IP
  • HTTP_FORWARDED
  • HTTP_FORWARDED_FOR
  • HTTP_FORWARDED_FOR_IP
  • HTTP_PC_REMOTE_ADDR
  • HTTP_PROXY_CONNECTION’
  • HTTP_VIA
  • HTTP_X_FORWARDED
  • HTTP_X_FORWARDED_FOR
  • HTTP_X_FORWARDED_FOR_IP
  • HTTP_X_IMFORWARDS
  • HTTP_XROXY_CONNECTION
  • VIA
  • X_FORWARDED
  • X_FORWARDED_FOR

如果您检测到$_SERVER变量中有上述字段，就可以为反爬制定相应的反代理安全策略。

爬虫

结论

综上，有很多方法可以检测到您网站上的爬虫行为。但是，需要精确地了解网站的使用方式，从而您的安全策略误伤正常用户。

 

参考资料

 

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