feat: add response metadata to V16 GAPIC Clients (#1013)

* feat!: refactor response metadata for V16

* this change should ensure that the response metadata is null when the request fails

* fixes from PR review

* add missing import

src/Google/Ads/GoogleAds/Lib/V16/GoogleAdsGapicClientTrait.php

@@ -43,6 +43,7 @@ trait GoogleAdsGapicClientTrait
     private $linkedCustomerId = null;
     private $unaryMiddlewares = [];
     private $streamingMiddlewares = [];
+    private ?GoogleAdsResponseMetadata $responseMetadata = null;
 
     /**
      * @see GapicClientTrait::modifyClientOptions()
@@ -103,7 +104,7 @@ protected function modifyUnaryCallable(callable &$callable)
     {
         $callable = $this->addFixedHeaderMiddleware($callable);
         $callable = new UnaryGoogleAdsExceptionMiddleware($callable);
-        $callable = new UnaryGoogleAdsResponseMetadataCallable($callable);
+        $callable = new UnaryGoogleAdsResponseMetadataCallable($callable, $this);
         foreach ($this->unaryMiddlewares as $unaryMiddleware) {
             /** @var GoogleAdsMiddlewareAbstract $unaryMiddleware */
             $callable = $unaryMiddleware->withNextHandler($callable);
@@ -123,4 +124,14 @@ protected function modifyStreamingCallable(callable &$callable)
             $callable = $streamingMiddleware->withNextHandler($callable);
         }
     }
+
+    public function getResponseMetadata(): ?GoogleAdsResponseMetadata
+    {
+        return $this->responseMetadata;
+    }
+
+    public function setResponseMetadata(?GoogleAdsResponseMetadata $responseMetadata): void
+    {
+        $this->responseMetadata = $responseMetadata;
+    }
 }

src/Google/Ads/GoogleAds/Lib/V16/UnaryGoogleAdsResponseMetadataCallable.php

@@ -21,6 +21,8 @@
 use Google\Ads\GoogleAds\Lib\GoogleAdsMiddlewareAbstract;
 use Google\ApiCore\Call;
 use Google\ApiCore\Middleware\ResponseMetadataMiddleware;
+use GuzzleHttp\Promise\Promise;
+use GuzzleHttp\Promise\PromiseInterface;
 
 /**
  * Callable for returning `GoogleAdsResponseMetadata` from unary calls to the API.
@@ -29,24 +31,48 @@ class UnaryGoogleAdsResponseMetadataCallable extends GoogleAdsMiddlewareAbstract
 {
     use GoogleAdsMetadataTrait;
 
+    private $adsClient;
+
+    public function __construct(callable $nextHandler = null, $adsClient = null)
+    {
+        $this->adsClient = $adsClient;
+        parent::__construct($nextHandler);
+    }
     /**
      * @param Call $call the current request
      * @param array $options the optional parameters
-     * @return array|\GuzzleHttp\Promise\PromiseInterface the two-member array of
+     * @return array|PromiseInterface the two-member array of
      *     response and metadata if `withResponseMetadata` is specified as an option;
      *     Or else, the `Promise` interface of the next handler
      */
     public function __invoke(Call $call, array $options)
     {
-        if (!empty($options['withResponseMetadata'])) {
-            $next = new ResponseMetadataMiddleware($this->getNextHandler());
-            return $next($call, $options)->then(function ($responseList) {
-                list($response, $metadata) = $responseList;
-                return [$response, new GoogleAdsResponseMetadata($metadata)];
-            });
-        } else {
-            $next = $this->getNextHandler();
-            return $next($call, $options);
+        $next = $this->getNextHandler();
+        if (empty($options['withResponseMetadata'])) {
+            // Bypass this middleware if the option is not set.
+            return $next($call, $options)->then(
+                function ($response) {
+                    // Reset the metadata to null.
+                    $this->adsClient->setResponseMetadata(null);
+                    return $response;
+                }
+            );
         }
+
+        $metadataReceiver = new Promise();
+        $options['metadataCallback'] = function ($metadata) use ($metadataReceiver) {
+            $metadataReceiver->resolve($metadata);
+        };
+        return $next($call, $options)->then(
+            function ($response) use ($metadataReceiver) {
+                $metadata = null;
+                if ($metadataReceiver->getState() === PromiseInterface::FULFILLED) {
+                    $metadata = new GoogleAdsResponseMetadata($metadataReceiver->wait());
+                }
+                $this->adsClient->setResponseMetadata($metadata);
+
+                return $response;
+            }
+        );
     }
 }