How to use PHP cURL for data transfer

The biggest benefit of PHP cURL is its cap­ab­il­ity to handle various data transfer needs and seam­lessly integrate with APIs. In this article, you’ll gain insights into PHP cURL’s syntax and func­tion­al­ity.

What is PHP cURL?

PHP cURL, short for ‘Curl URL Request Library’, is a PHP extension. It offers a way to send HTTP requests and com­mu­nic­ate using different network protocols, including HTTP, HTTPS, and FTP. With cURL, you can adjust and manage headers, para­met­ers, and data to fulfill API needs.

How to install PHP cURL?

To utilise cURL in PHP, you typically don’t have to install cURL sep­ar­ately, as it comes as a built-in extension. However, ensure that the cURL extension is enabled in your PHP setup. You can confirm cURL func­tion­al­ity by creating a PHP file and running the following code within it:

phpinfo();

On the generated page, look for cURL support or similar in­form­a­tion to see if PHP cURL is enabled. If cURL is not active, you’ll need to edit the php.ini file. Therein, locate the ex­pres­sion ;extension=php_curl.dll for cURL in Windows or ;extension=curl for cURL in Linux. To activate the cURL extension, remove the semicolon ‘;’ preceding the line. Save the file, and for the changes to take effect, restart the web server.

Learn the most important basics of PHP pro­gram­ming in our PHP tutorial – essential for using cURL. To learn more about the ad­vant­ages and dis­ad­vant­ages of the PHP pro­gram­ming language, you can check out the com­par­is­ons between PHP vs Python and PHP vs JavaS­cript in the IONOS Digital Guide.

This is the syntax of PHP cURL

The syntax of PHP cURL consists of various functions and options to configure a cURL session, perform queries and work with the results.

Step 1: ini­tial­ise a cURL session

$curl = curl_init();

Step 2: set options

curl_setopt($curl, CURLOPT_URL, 'https://example.com/api'); // defines the URL
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true); // sets the result of the query as return value

Step 3: execute the cURL request

$response = curl_exec($curl);

Step 4: closing the cURL session

curl_close($curl);

What cURL functions exist in PHP?

A variety of PHP functions are available to create HTTP requests or upload files. It’s also possible to use PHP to retrieve in­form­a­tion from a MySQL database and send it as JSON via cURL.

Here are some of the most important cURL functions in PHP:

• curl_init: Ini­tial­ises a new cURL session and returns a cURL handle.
• curl_setopt: Sets options for the cURL session. Para­met­ers such as the URL, headers, or au­then­tic­a­tion methods are set here. You can also use PHP cURL to specify POST data to send to the server.
• curl_exec: Executes the cURL session and returns the response as a string.
• curl_close: Closes the cURL session and releases the resources.
• curl_setopt_array: Defines an array of cURL options in a single call.
• curl_getinfo: Returns in­form­a­tion about the last cURL session, such as the URL or HTTP status code.
• curl_error: Returns the error message from the last cURL request.
• curl_errno: Returns the error code of the last cURL request.
• curl_multi_init: Ini­tial­ises a multi-cURL handle that allows you to make multiple cURL requests at the same time.
• curl_multi_add_handle: Adds a cURL session to a multi-cURL handle.
• curl_multi_exec: Executes the multi-cURL requests.
• curl_multi_get­con­tent: Returns the content of the response for a given cURL session in the multi-cURL handle.

An example of the use of cURL in PHP

By creating your own PHP classes, you can make the code more modular, define reusable methods, and simplify the im­ple­ment­a­tion of PHP cURL in your ap­plic­a­tions.

Here’s an example of what a PHP class might look like in con­junc­tion with PHP cURL GET:

class MyCurlClient {
    private $curl;
    public function __construct() {
        $this->curl = curl_init();
        // Further configurations can be made here
    }
    public function sendRequest($url) {
        curl_setopt($this->curl, CURLOPT_URL, $url);
        curl_setopt($this->curl, CURLOPT_RETURNTRANSFER, true);
        
        $response = curl_exec($this->curl);
        return $response;
    }
    public function close() {
        curl_close($this->curl);
    }
}
// Using your own class
$myCurl = new MyCurlClient();
$response = $myCurl->sendRequest('https://example.com/api');
echo $response;
$data = json_decode($response, true);
// Output of the data with PHP operators
echo "Post ID: " . $data['id'] . "<br>";
echo "Title: " . $data['title'] . "<br>";
echo "Body: " . $data['body'] . "<br>";
$myCurl->close();

In this example, we created the My­Curl­Cli­ent class that handles a PHP cURL session in its con­struct­or. The sendRe­quest() method takes a URL, con­fig­ures the cURL options, and executes the HTTP GET request. The output strings are con­cat­en­ated using PHP operators. Finally, we use the close() function to end the cURL session.