phpSpider advanced guide: How to deal with the anti-crawler page anti-crawling mechanism?

phpSpider Advanced Guide: How to deal with the anti-crawler page anti-crawling mechanism?

1. Introduction
In the development of web crawlers, we often encounter various anti-crawler page anti-crawling mechanisms. These mechanisms are designed to prevent crawlers from accessing and crawling website data. For developers, breaking through these anti-crawling mechanisms is an essential skill. This article will introduce some common anti-crawler mechanisms and give corresponding response strategies and code examples to help readers better deal with these challenges.

2. Common anti-crawler mechanisms and countermeasures

1. User-Agent detection:
   By detecting the User-Agent field of the HTTP request, the server can determine whether the request is made by the browser Initiated or initiated by crawler program. To deal with this mechanism, we can set up a reasonable User-Agent in the crawler program to make it look like the request is initiated by a real browser.

Code sample:

$ch = curl_init();
$url = "http://example.com";
$user_agent = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.3";
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_USERAGENT, $user_agent);
$result = curl_exec($ch);
curl_close($ch);

2. Cookie verification:
   Some websites will set a cookie when the user visits, and then verify the cookie in subsequent requests. If it is missing or not If correct, it will be judged as a crawler program and access will be denied. To solve this problem, we can obtain cookies in the crawler program by simulating login, etc., and carry cookies with each request.

Code example:

$ch = curl_init();
$url = "http://example.com";
$cookie = "sessionid=xyz123";
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_COOKIE, $cookie);
$result = curl_exec($ch);
curl_close($ch);

3. IP restriction:
   Some websites will limit requests based on IP address. For example, the same IP sends too many requests in a short period of time. The request will be blocked. In response to this situation, we can use a proxy IP pool and regularly change the IP for crawling to bypass IP restrictions.

Code example:

$ch = curl_init();
$url = "http://example.com";
$proxy = "http://127.0.0.1:8888";
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_PROXY, $proxy);
$result = curl_exec($ch);
curl_close($ch);

4. JavaScript encryption:
   Some websites use JavaScript in the page to encrypt data, which prevents crawlers from directly parsing the page to obtain data. To deal with this mechanism, we can use third-party libraries such as PhantomJS to implement JavaScript rendering and then crawl data.

Code examples:

$js_script = 'var page = require("webpage").create();
page.open("http://example.com", function(status) {
  var content = page.content;
  console.log(content);
  phantom.exit();
});';
exec('phantomjs -e ' . escapeshellarg($js_script), $output);
$result = implode("
", $output);

3. Summary
This article introduces some common anti-crawler page anti-crawling mechanisms, and gives corresponding countermeasures and code examples. Of course, in order to better break through the anti-crawler mechanism, we also need to carry out targeted analysis and solutions based on specific situations. I hope this article can help readers to better cope with the challenge of anti-crawling and successfully complete the crawling task. In the process of developing crawler programs, please be sure to comply with relevant laws and regulations and use crawler technology rationally. Protecting user privacy and website security is our shared responsibility.

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