curl_close Error handling: How to deal with exceptions and warnings when calling?

cURL is a library of tools for sending HTTP requests to servers. In PHP, curl_init() initializes a cURL session, curl_setopt() sets relevant options, curl_exec() executes the request, and curl_close() is used to close the session.

 $ch = curl_init('https://gitbox.net');  // initialization cURL Session
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);  // Set return data
$response = curl_exec($ch);  // implement cURL ask
curl_close($ch);  // 关闭Session

The purpose of curl_close() is to release resources created by curl_init() . Generally, if all cURL operations go smoothly, curl_close() will not throw any exceptions or warnings.

2. Common curl_close() errors and warnings

When using curl_close() , you may encounter some common errors or warnings. Let's take a look at these issues and how to solve them.

2.1 Error: Uninitialized cURL session

In some cases, a warning appears if the cURL session has not been initialized when curl_close() is called. This problem usually occurs when we try to close a cURL session that has not been initialized with curl_init() .

Error example :

 curl_close($ch);  // 未initialization的 cURL Session

Solution :

Before calling curl_close() , make sure that the cURL session has been initialized correctly. You can avoid this error by checking whether the $ch variable is false :

 if ($ch !== false) {
    curl_close($ch);
}

2.2 Error: The cURL session has been closed

When curl_close() is called, PHP may throw a warning if the session has been closed. This usually happens when curl_close() is called multiple times or when the cURL session has been manually closed, try to close it again.

Error example :

 curl_close($ch);  // 第一次关闭Session
curl_close($ch);  // 再次关闭已经关闭的Session

Solution :

Make sure to call curl_close() only once, or use conditional judgment to avoid repeated closing:

 if (is_resource($ch)) {
    curl_close($ch);
}

2.3 Error: Wrong cURL resource type

The cURL session must be a valid resource type, and an error will also occur when calling curl_close() if the $ch variable is not a cURL resource.

Error example :

 $ch = null;  // Wrong cURL Session资源
curl_close($ch);  // Wrong资源类型

Solution :

Make sure $ch is a valid resource type. You can check it through the is_resource() function:

 if (is_resource($ch)) {
    curl_close($ch);
}

3. Error handling of cURL sessions

Although curl_close() itself is simple, cURL sessions may encounter errors. Before closing a session, it is usually necessary to check whether the session was successfully executed. If an error occurs in the request, you can get the details through curl_error() or curl_errno() .

Example of checking cURL error :

 $ch = curl_init('https://gitbox.net');  
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($ch);

if ($response === false) {
    echo 'cURL mistake: ' . curl_error($ch);
} else {
    echo 'Response content: ' . $response;
}

curl_close($ch);

Get cURL error information via curl_error() so that the problem can be quickly located when problems occur.

4. Use try-catch to catch exceptions

In PHP 7 and above, try-catch can be used to catch exceptions and handle errors. Although curl_close() itself does not throw exceptions, cURL requests can be encapsulated in a try-catch , thus catching any potential exceptions.

Exception handling example :

 try {
    $ch = curl_init('https://gitbox.net');
    if ($ch === false) {
        throw new Exception('无法initialization cURL Session');
    }
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    $response = curl_exec($ch);

    if ($response === false) {
        throw new Exception('cURL ask失败: ' . curl_error($ch));
    }

    echo $response;
} catch (Exception $e) {
    echo 'mistake信息: ' . $e->getMessage();
} finally {
    if (isset($ch) && is_resource($ch)) {
        curl_close($ch);
    }
}

Using try-catch ensures that the program can gracefully handle and close session resources even in the event of an error.

5. Summary

The curl_close() function is a very important function in PHP, which is used to close a cURL session and free resources. While it usually doesn't throw an error, we still need to deal with warnings and exceptions that may occur. By checking the validity of cURL resources, ensuring the session is initialized correctly, and using conditional statements and exception handling, we can avoid most curl_close() -related issues.