PHP web crawler: how to use HTTP and HTTPS protocols

With the development of the Internet, the information on the Internet is becoming more and more abundant, but it is not easy to obtain valuable information on the Internet. For some applications that need to obtain web page information, web crawlers have become one of the indispensable tools. In web crawler technology, PHP has also become a widely used language.

This article will focus on how to use HTTP and HTTPS protocols to crawl web information.

1. HTTP protocol

HTTP is the Hypertext Transfer Protocol, which is an application layer protocol used to transmit hypermedia documents. Usually used on the World Wide Web, its main function is communication between the client and the server based on the TCP protocol. Due to its simplicity and speed, it has become an indispensable part in web crawler-related applications.

In PHP, you can use the cURL extension to crawl the HTTP protocol. Taking the HTTP GET request as an example, the following is a simple sample code:

$url = 'http://example.com';
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$output = curl_exec($ch);
curl_close($ch);
echo $output;

As shown above, first define the URL address that needs to obtain information, then initialize the cURL handle and set related options. Among them, the CURLOPT_URL option indicates the URL address that needs to be accessed, and the CURLOPT_RETURNTRANSFER option indicates that the response result is returned instead of output. Finally, after the execution is completed, the cURL handle is closed and the obtained results are output.

In addition, when crawling the HTTP protocol, you also need to pay attention to the following points:

1. You need to set a timeout to prevent a timeout from occurring during the process of obtaining web page information and causing a request fail.

curl_setopt($ch, CURLOPT_TIMEOUT, 10); // 设置超时时间为10秒

2. For some web pages that require login or carry request headers, relevant parameters need to be set during the request.

curl_setopt($ch, CURLOPT_COOKIE, 'key=value'); // 设置cookie
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: application/json')); // 设置请求头

2. HTTPS protocol

HTTPS is a protocol that implements HTTP secure transmission through the SSL/TLS protocol, which can ensure the security and integrity of the data transmission process. Compared with the HTTP protocol, the HTTPS protocol can prevent malicious attacks and espionage activities. When crawling web pages, using the HTTPS protocol can also make data transmission more secure.

In PHP, you can also use the cURL extension to crawl the HTTPS protocol. The following is a simple sample code:

$url = 'https://example.com';
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0); // 关闭SSL证书校验
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0); // 关闭SSL证书校验
$output = curl_exec($ch);
curl_close($ch);
echo $output;

It should be noted that in crawling the HTTPS protocol, the CURLOPT_SSL_VERIFYHOST and CURLOPT_SSL_VERIFYPEER options need to be set to 0 to turn off SSL certificate verification. If you do not turn off SSL certificate verification, cURL will not be able to recognize the certificate when connecting, causing the request to fail.

In addition, when crawling via HTTPS protocol, you also need to pay attention to the following points:

1. Use the correct URL address. The format of HTTPS URL is https://example.com. Pay attention to the case of the protocol header.
2. For some websites that require client certificates, relevant parameters need to be set when requesting.

curl_setopt($ch, CURLOPT_SSLCERT, '/path/to/client/cert'); // 设置客户端证书路径
curl_setopt($ch, CURLOPT_SSLKEY, '/path/to/client/key'); // 设置客户端证书的key路径

3. Summary

The above are the methods and precautions for using HTTP and HTTPS protocols to crawl web page information. Whether it is HTTP or HTTPS, they are essential protocols in web crawler technology. Through the use of cURL extension, we can easily crawl all kinds of information on the Internet, making our applications richer and more powerful.

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