Curl library and HTTP request technology in PHP

With the popularity and development of the Internet, and the increasing number and complexity of websites, the development of network-oriented applications has attracted more and more attention. In this process, HTTP request technology and Curl library have become important technologies that developers must master. This article will introduce the basic knowledge, application scenarios and usage of the Curl library and HTTP request technology in PHP.

1. HTTP request technology

1.1 HTTP protocol

HyperText Transfer Protocol (HTTP) is a protocol used to transmit hypertext data (such as HTML). HTTP is a client-server protocol. The client obtains resources from the server through HTTP requests, and the server returns the requested data through HTTP responses. The HTTP protocol is built on the TCP/IP protocol and uses the TCP protocol to provide reliable transmission services.

1.2 HTTP request methods

HTTP defines some methods for specifying the operations that the client wants the server to perform. Commonly used HTTP request methods include:

• GET: Obtain the specified resource from the server;
• POST: Submit data to the specified server resource;
• PUT: Send the request The data is stored in the specified server resource;
• DELETE: Requests the server to delete the specified resource;
• HEAD: Gets the header information of the specified resource;
• OPTIONS: Gets server support Which HTTP request methods and header information.

1.3 HTTP request header

HTTP request header contains the request information sent by the client to the server, which is used to tell the server how to interpret the request and response. Commonly used HTTP request headers include:

• User-Agent: specifies the client type;
• Content-Type: specifies the MIME type of the requested data;
• Accept : Specify the MIME type acceptable to the client;
• Authorization: Specify the authentication information provided by the client;
• Referer: Specify the URL from which the client links;
• Cookie: Specify the cookie information of the client.

1.4 HTTP response

HTTP response is the response information returned by the server to the client, usually including a status code and corresponding text information. HTTP status codes are used to indicate the processing results of requests. Commonly used HTTP status codes include:

• 200 OK: The request is successful;
• 301 Moved Permanently: The requested resource has been moved. to the new URL;
• 404 Not Found: The specified resource was not found;
• 500 Internal Server Error: There was an internal error in the server.

2. Curl library in PHP

2.1 Curl library overview

Curl is an excellent open source library that supports various protocols, including HTTP, HTTPS, and FTP , SMTP, etc. It allows developers to upload and download files, as well as send HTTP requests, in a simple, unified way. In PHP, Curl can be used to access remote servers, handle file uploads and downloads, obtain network content, etc.

2.2 Using Curl in PHP

The basic form of using Curl to make HTTP requests is:

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

The above code demonstrates the basic process of using Curl. The first step is to initialize a Curl handle and set the appropriate options. Among them, CURLOPT_URL is used to set the URL to be accessed, and CURLOPT_RETURNTRANSFER is used to configure whether to return data in string form (generally set to 1). Then use curl_exec() to get the response result of the request, and use curl_close() to release the Curl handle.

3. Application Case

3.1 Obtain remote interface data

Curl can be used to obtain remote interface data. The following is a sample code snippet:

$curl = curl_init();

curl_setopt_array($curl, array(
  CURLOPT_URL => "https://api.example.com/products?search=foo",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "GET",
  CURLOPT_HTTPHEADER => array(
    "Authorization: Token abcdefghijklmnopqrstuvwxyz",
    "Content-Type: application/json"
  ),
));

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

The above code will send an HTTP GET request to the https://api.example.com/products?search=foo interface and store the returned result in the $response variable middle.

3.2 File upload

Curl can also be used to upload files. The following is a sample code snippet:

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "http://example.com/upload.php");
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS,
            array('file' => '@/path/to/file', 'file_name' => 'new_file_name'));

$result = curl_exec($ch);
curl_close($ch);

The above code will upload the /path/to/file file to http://example.com/upload.php in POST mode, and save the file as new_file_name.

4. Summary

This article introduces the application of HTTP request technology and Curl library in PHP. HTTP request technology, as a client-server protocol, is critical to the development of Internet applications. The Curl library provides developers with a simple and unified way to access remote servers, handle file uploads and downloads, and obtain network content. The process of using Curl is relatively simple, and developers can flexibly configure relevant parameters according to actual needs. In future development, developers can deeply study the API of the Curl library and gradually master more advanced functions.

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