In web development, we need to interact with other services from time to time, such as requesting APIs, crawling web pages, etc. cURL is a very powerful tool that can be used to perform HTTP requests and FTP uploads and downloads. In PHP, we can use the cURL library to make network requests.

This article will introduce how to use the cURL library to make network requests in PHP.

Installing cURL

First, we need to install the cURL extension on the server. Under Ubuntu, you can use the following command to install:

sudo apt-get install php-curl

Under CentOS, you can use the following command to install:

sudo yum install php-curl

After the installation is complete, you can use the following command to verify:

php -i | grep -i curl

If the cURL extension was successfully installed, the output should contain the following information:

curl
cURL support => enabled
cURL Information => 7.50.1

Sending a GET request

Sending a GET request is the simplest request method. In PHP, we can use the curl_init() function to initialize, use the curl_setopt() function to set the parameters of the request, and finally use the curl_exec() function to send the request. The following is a simple example of sending a GET request:

$url = 'https://example.com/api/get_data';
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($ch);
curl_close($ch);

echo $response;

In the above code, we first define the requested URL. Then use the curl_init() function to initialize a cURL session and pass in the request URL as a parameter. Then use the curl_setopt() function to set the CURLOPT_RETURNTRANSFER parameter to true, indicating that the request result needs to be returned. Finally, use the curl_exec() function to send the request and save the result to the $response variable. Finally, use the curl_close() function to close the session.

Sending a POST request

Sending a POST request is slightly more complicated than sending a GET request. We need to use the curl_setopt() function to set the CURLOPT_POST parameter to true and send the requested data as the CURLOPT_POSTFIELDS parameter. The following is an example of sending a POST request:

$url = 'https://example.com/api/post_data';
$data = array(
    'name' => 'John',
    'age' => 30,
);
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($data));
$response = curl_exec($ch);
curl_close($ch);

echo $response;

In the above code, we first define the requested URL and requested data. Then use the curl_init() function to initialize a cURL session and pass in the request URL as a parameter. Then use the curl_setopt() function to set the CURLOPT_RETURNTRANSFER parameter to true, indicating that the request result needs to be returned. Then use the curl_setopt() function to set the CURLOPT_POST parameter to true, which means sending a POST request. Finally, use the curl_setopt() function to set the CURLOPT_POSTFIELDS parameter to the requested data, and use the http_build_query() function to convert the data into a URL-encoded string. Finally, the curl_exec() function is used to send the request and the result is saved in the $response variable.

Set request headers

Some APIs require us to set specific request headers for normal interaction. For this case, we can use the curl_setopt() function to set the CURLOPT_HTTPHEADER parameter to set the request header. The following is an example of setting request headers:

$url = 'https://example.com/api/get_data';
$headers = array(
    'Authorization: Bearer xxxxxxx',
    'Content-Type: application/json',
);
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
$response = curl_exec($ch);
curl_close($ch);

echo $response;

In the above code, we first define the requested URL and request headers. Then use the curl_init() function to initialize a cURL session and pass in the request URL as a parameter. Then use the curl_setopt() function to set the CURLOPT_RETURNTRANSFER parameter to true, indicating that the request result needs to be returned. Then use the curl_setopt() function to set the CURLOPT_HTTPHEADER parameter to the set request header and pass it in an array. Finally, the curl_exec() function is used to send the request and the result is saved in the $response variable.

Using proxy

Sometimes, we need to send requests through a proxy server. For this case, we can use the curl_setopt() function to set the CURLOPT_PROXY parameter to set the proxy server. The following is an example of using a proxy server:

$url = 'https://example.com/api/get_data';
$proxy = 'http://proxy.example.com:8080';
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_PROXY, $proxy);
$response = curl_exec($ch);
curl_close($ch);

echo $response;

In the above code, we first define the requested URL and proxy server address. Then use the curl_init() function to initialize a cURL session and pass in the request URL as a parameter. Then use the curl_setopt() function to set the CURLOPT_RETURNTRANSFER parameter to true, indicating that the request result needs to be returned. Then use the curl_setopt() function to set the CURLOPT_PROXY parameter to the proxy server address. Finally, the curl_exec() function is used to send the request and the result is saved in the $response variable.

To sum up, the cURL library is a very powerful tool that can be used to perform operations such as HTTP requests. In PHP, we can use the cURL library to send network requests and set request parameters to meet different needs.

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