Can Guzzle handle asynchronous requests when scraping data?

Guzzle is a PHP HTTP client that simplifies making HTTP requests from PHP applications. It is commonly used for web scraping, consuming RESTful APIs, and general client-server interactions. Guzzle by itself is synchronous, meaning that each HTTP request will block further script execution until it is completed.

However, Guzzle does provide a way to send asynchronous requests using Promises (based on the Promises/A+ specification), which allows you to send non-blocking requests. This feature is particularly useful when you need to make multiple HTTP requests without waiting for each one to finish before starting the next.

The following is an example in PHP on how to make asynchronous requests using Guzzle:

require 'vendor/autoload.php';

use GuzzleHttp\Client;
use GuzzleHttp\Promise;

$client = new Client();

// Initiate each request but do not block
$promises = [
    'image' => $client->getAsync('http://httpbin.org/image'),
    'png'   => $client->getAsync('http://httpbin.org/image/png'),
    'jpeg'  => $client->getAsync('http://httpbin.org/image/jpeg'),
    'webp'  => $client->getAsync('http://httpbin.org/image/webp')
];

// Wait for the requests to complete, even if some of them fail
$results = Promise\unwrap($promises);

// You can access each result using the key provided to the promise
echo $results['image']->getBody();
echo $results['png']->getBody();
echo $results['jpeg']->getBody();
echo $results['webp']->getBody();

// Wait for the requests to complete, this time ignoring any exceptions
$results = Promise\settle($promises)->wait();

// Handle each result
foreach ($results as $key => $result) {
    if (isset($result['value'])) {
        echo "The response for {$key} was received.\n";
    }
    if (isset($result['reason'])) {
        echo "The request for {$key} failed.\n";
    }
}

In the example above, the getAsync method is used to send asynchronous requests. The unwrap function is then used to wait for all of the Promises to complete. Alternatively, the settle function waits for all of the Promises to complete but does not throw exceptions if any of the requests failed; instead, it provides the outcome of each operation, which can be either a success (value) or a failure (reason).

Using Guzzle's asynchronous requests can significantly improve the performance of your web scraping or data collection tasks when dealing with multiple HTTP requests by taking advantage of concurrent connections.