Add PhpFlickr::setUserAgent() and send User Agent to API

Flickr is soon to make the User Agent header required for all
API requests.

Refs: #59

README.md

@@ -216,6 +216,15 @@ This method doesn't allow for setting any photo metadata,
 but you can do the replacement asynchronously
 (in which case a 'ticket ID' will be returned).
 
+## User Agent
+
+If you are using PhpFlickr in an application, it is a good idea to set a custom user agent.
+This can be done with the following:
+
+```php
+$flickr->setUserAgent('MyVendor-MyApp/1.0.0');
+```
+
 ## Proxy server
 
 PhpFlickr can be used with a proxy server

src/PhpFlickr.php

@@ -37,6 +37,9 @@
 
 class PhpFlickr
 {
+    /** PhpFlickr version. */
+    public const VERSION = '5.1.0';
+
     /** @param string */
     protected $api_key;
 
@@ -71,6 +74,9 @@ class PhpFlickr
     /** @var TokenStorageInterface */
     protected $oauthTokenStorage;
 
+    /** @var string The User Agent string to send to the Flickr API. */
+    protected $userAgent;
+
     /**
      * @param string $apiKey
      * @param string|null $secret
@@ -79,6 +85,7 @@ public function __construct(string $apiKey, string $secret = null)
     {
         $this->api_key = $apiKey;
         $this->secret = $secret;
+        $this->userAgent = 'PhpFlickr/' . self::VERSION . ' https://github.com/samwilson/phpflickr';
     }
 
     /**
@@ -157,6 +164,24 @@ protected function cache($request, $response)
         return false;
     }
 
+    /**
+     * Set the User Agent string that will be sent to Flickr.
+     * Should be of the form `product/product-version comment`.
+     * @param string $userAgent
+     */
+    public function setUserAgent(string $userAgent): void
+    {
+        $this->userAgent = $userAgent;
+    }
+
+    /**
+     * Get the User Agent string.
+     */
+    public function getUserAgent(): string
+    {
+        return $this->userAgent;
+    }
+
     /**
      * Send a POST request to the Flickr API.
      * @param string $command The API endpoint to call.
@@ -178,7 +203,10 @@ public function request($command, $args = array(), $nocache = false)
         if (!($this->response) || $nocache) {
             $args = array_filter($args);
             $oauthService = $this->getOauthService();
-            $this->response = $oauthService->requestJson($command, 'POST', $args);
+            $extraHeaders = [
+                'User-Agent' => $this->getUserAgent(),
+            ];
+            $this->response = $oauthService->requestJson($command, 'POST', $args, $extraHeaders);
             if (!$nocache) {
                 $this->cache($request, $this->response);
             }

src/Uploader.php

@@ -111,6 +111,7 @@ protected function sendFile($filename, $params)
         curl_setopt($curl, CURLOPT_POST, true);
         curl_setopt($curl, CURLOPT_POSTFIELDS, $args);
         curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
+        curl_setopt($curl, CURLOPT_USERAGENT, $this->flickr->getUserAgent());
         $response = curl_exec($curl);
         $this->response = $response;
         curl_close($curl);