PHP: Error handling with cURL

PHP’s cURL functions are extremely useful for sending HTTP requests.

Some examples of its usefulness.

• Retrieving data from an external API.
• Sending data to an external web service.
• Checking to see if a HTTP resource exists.
• Crawling / scraping web pages (logging into other websites with PHP).

Although you can easily request external content via the function file_get_contents, cURL is much more useful in the sense that it allows us to detect and handle certain HTTP errors.

Let’s take the following example.

$url = 'http://example.com';
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$result = curl_exec($ch);
echo $result;

As you can see, we have setup a very simple GET request that returns the contents of a website called example.com.

Unfortunately, this code doesn’t take into account the fact that the cURL request could fail. As a result, the request might fail without providing us with any details about what happened.

Using curl_errno to detect cURL errors.

This is where the curl_errno function comes in handy.

The curl_errno function will return the number 0 (zero) if the request was successful. In other words, it will return a “falsey” value if no error occurs. This is because PHP sees 0 as a false value in a boolean context.

This allows us to figure out whether or not our cURL request resulted in an error.

Take a look at the following example.

$url = 'http://example.com';

$ch = curl_init($url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$result = curl_exec($ch);
if(curl_errno($ch)){
    echo 'Request Error:' . curl_error($ch);
}

If an error occurs, then our script will print out the result of the curl_error function.

Throwing Exceptions.

In certain situations, you might want to throw an exception if a cURL request fails.

For this example, let us pretend that we have an object function called get.

/**
 * Send a GET request to a URL.
 * 
 * @param string $url
 * @return string
 * @throws Exception If cURL request fails.
 */
public function get($url){
    $ch = curl_init($url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    $result = curl_exec($ch);
    if(curl_errno($ch)){
        throw new Exception(curl_error($ch));
    }
    return $result;
}

As you can see, the function above will attempt to send a GET request to a given URL.

If all goes well, the function will return the contents of the URL.

However, if the request fails and a cURL error exists, PHP will throw an Exception.

This allows us to handle the request like so.

try{
    $object->get('http://test.com');
} catch(Exception $e){
    //do something with the exception you caught
}

In the above piece of code, we are using a TRY-CATCH block.

If we do not want our application to continue after a failed HTTP request, we can omit the TRY-CATCH block and let our Exception Handler deal with it.