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.