lib\Drupa\guzzle_example\GuzzleExample.php

<?php

/**
 * @file
 * Contains lib\Drupal\guzzle_example\GuzzleExample
 */

namespace Drupal\guzzle_example;

use GuzzleHttp\Client;

/**
 * My GuzzleExample
 */
class GuzzleExample {

  /**
   * @var \GuzzleHttp\Client
   *   The Guzzle HTTP client.
   */
  var $client;

  /**
   * Creates a new GuzzleExample.
   *
   * @param \GuzzleHttp\Client $client
   *   The Guzzle client.
   */
  public function __construct(Client $client) {
    $this->client = $client;
  }

  /**
   * Factory method.
   * @return $this
   */
  public static function create() {
    return new static(new Client());
  }

  /**
   * Finds the host IP address by calling the httpbin web service.
   *
   * @return string
   *   The current hosts IP address.
   */
  public function getHostIP() {
    $response = $this->client->get('http://httpbin.org/get');
    $json = $response->json();
    return $json['origin'];
  }

}