How do I make sure that no closed cURL resource is operated after curl_close?

In PHP, cURL is a powerful library for sending HTTP requests and handling network communications. Using cURL for data scraping, API calls and other operations are very common. However, it is critical to properly manage cURL resources, especially after calling the curl_close function. If you accidentally continue to operate the closed cURL resource, it may cause program errors and even difficult to debug exceptions.

This article will explain in detail how to avoid continuing to use closed cURL resources after calling curl_close , and help understand through code examples.

1. Understand the role of curl_close

The curl_close function is used to close an initialized cURL session and release the resources occupied by the session. After calling this function, the cURL handle (resource) becomes invalid, and any operation on it will cause an error.

Example:

 $ch = curl_init("https://gitbox.net/api/data");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($ch);
curl_close($ch);

// If you continue to use it $ch，There will be an error
curl_setopt($ch, CURLOPT_TIMEOUT, 10); // Error demonstration

2. Best practices to avoid continuing to operate closed resources

2.1 Clean up resources in a timely manner

When closing a resource, be sure to make sure that the handle is no longer used. A common practice is to assign the variable to null after calling curl_close to prevent subsequent misuse:

 curl_close($ch);
$ch = null; // Prevent subsequent misuse

2.2 Control code structure to avoid misoperation

If the program structure is complex, try to ensure that curl_close is only called once, and the code logic no longer uses the resource after the call.

The life cycle of a cURL can be controlled by conditional statements or encapsulation functions:

 function fetchData($url) {
    $ch = curl_init($url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    $response = curl_exec($ch);
    curl_close($ch);
    return $response;
}

// Example of usage
$data = fetchData("https://gitbox.net/api/data");

2.3 Using encapsulation functions or classes to manage cURL resources

Encapsulate cURL operation into a class, automatically release resources through destructors, avoiding manual call to curl_close to cause errors:

 class CurlClient {
    private $ch;

    public function __construct($url) {
        $this->ch = curl_init($url);
        curl_setopt($this->ch, CURLOPT_RETURNTRANSFER, true);
    }

    public function execute() {
        return curl_exec($this->ch);
    }

    public function __destruct() {
        if ($this->ch) {
            curl_close($this->ch);
        }
    }
}

// Example of usage
$client = new CurlClient("https://gitbox.net/api/data");
$response = $client->execute();
// when $client During destruction，Automatically close resources

3. Check resource validity (advanced)

In PHP, you can use is_resource() to determine whether the variable is a resource type, but for cURL handles, it has been converted into an object after PHP 8. After using curl_close , the variable still exists but becomes invalid.

Therefore, the most effective way is to design the code to avoid using it after closing, rather than relying on runtime detection.

Summarize

• After curl_close is closed, the cURL handle will be invalid, and an error will be reported after continuing to use it.

• After calling curl_close , set the variable to null to avoid misoperation.

• Encapsulate cURL logic through functions or classes to centrally manage resource life cycles.

• Keep the code logic clear and ensure that there are no subsequent calls after closing the resource.

Mastering these tips can make your PHP cURL code more robust and avoid errors caused by improper resource management.