Update readme/projectID detection

Bigtable/README.md

@@ -31,11 +31,26 @@ $ composer require google/cloud
 This component supports both REST over HTTP/1.1 and gRPC. In order to take advantage of the benefits offered by gRPC (such as streaming methods)
 please see our [gRPC installation guide](https://cloud.google.com/php/grpc).
 
+### Notable Client Differences
+
+The handwritten client offered by this package differs from the others in `google-cloud-php` in that it more directly wraps our generated clients.
+This means some of the idioms and configuration options you are used to may differ slightly. The most notable differences are outlined below:
+
+- A key file is now provided through the `credentials` configuration option as opposed to either `keyFile` or `keyFilePath`.
+- There is now more granular control over retry logic. Please see [the `bigtable_client_config.json` file](https://github.com/googleapis/google-cloud-php/blob/master/Bigtable/src/V2/resources/bigtable_client_config.json)
+  for an example of the configuration which can be passed into the client at construction time.
+- Exceptions triggered at the network level utilize the base class `Google\ApiCore\ApiException` as opposed to `Google\Cloud\Core\ServiceException`.
+- The `authHttpHandler` and `httpHandler` client configuration options are now provided through `$credentialsConfig['authHttpHandler']`
+  and `$transportConfig['httpHandler']`, respectively. Additionally, please note the `httpHandler` should now return an implementation of [Guzzle's `PromiseInterface`](https://github.com/guzzle/promises/blob/master/src/PromiseInterface.php).
+
 ### Authentication
 
 Please see our [Authentication guide](https://github.com/GoogleCloudPlatform/google-cloud-php/blob/master/AUTHENTICATION.md) for more information
 on authenticating your client. Once authenticated, you'll be ready to start making requests.
 
+When going through the authentication guide, please take note that the handwritten client for this package will more closely follow the conventions
+outlined for the generated clients.
+
 ### Sample
 
 ```php

Bigtable/src/BigtableClient.php

@@ -22,7 +22,7 @@
 use Google\ApiCore\ValidationException;
 use Google\Auth\FetchAuthTokenInterface;
 use Google\Cloud\Bigtable\V2\BigtableClient as GapicClient;
-use Google\Cloud\Core\ClientTrait;
+use Google\Cloud\Core\ArrayTrait;
 
 /**
  * Google Cloud Bigtable is Google's NoSQL Big Data database service.
@@ -38,7 +38,7 @@
  */
 class BigtableClient
 {
-    use ClientTrait;
+    use ArrayTrait;
 
     const VERSION = '0.5.3';
 
@@ -47,6 +47,11 @@ class BigtableClient
      */
     private $gapicClient;
 
+    /**
+     * @var string
+     */
+    private $projectId;
+
     /**
      * Create a Bigtable client.
      *
@@ -93,23 +98,26 @@ class BigtableClient
      *               'grpc' => [...],
      *               'rest' => [...]
      *           ];
-     *           See {@see Google\ApiCore\Transport\GrpcTransport} and
-     *           {@see Google\ApiCore\Transport\RestTransport} for
-     *           the supported options.
+     *           See the `build` method on {@see Google\ApiCore\Transport\GrpcTransport}
+     *           and {@see Google\ApiCore\Transport\RestTransport} for the
+     *           supported options.
      * }
      * @throws ValidationException
      */
     public function __construct(array $config = [])
     {
         if (!isset($config['transportConfig']['grpc']['stubOpts'])) {
-            // Workaround for large messages.
-            $config['transportConfig']['grpc']['stubOpts'] = [
-                'grpc.max_send_message_length' => -1,
-                'grpc.max_receive_message_length' => -1
-            ];
+            $config['transportConfig']['grpc']['stubOpts'] = [];
         }
 
-        $this->projectId = $this->detectProjectId($config);
+        // Workaround for large messages.
+        $config['transportConfig']['grpc']['stubOpts'] += [
+            'grpc.max_send_message_length' => -1,
+            'grpc.max_receive_message_length' => -1
+        ];
+
+        $this->projectId = $this->pluck('projectId', $config, false)
+            ?: $this->detectProjectId();
         $this->gapicClient = new GapicClient($config);
     }
 
@@ -141,4 +149,27 @@ public function table($instanceId, $tableId, array $options = [])
             $options
         );
     }
+
+    /**
+     * Attempts to detect the project ID.
+     *
+     * @todo Add better support for detecting the project ID (check keyFile/GCE metadata server).
+     * @return string
+     * @throws ValidationException If a project ID cannot be detected.
+     */
+    private function detectProjectId()
+    {
+        if (getenv('GOOGLE_CLOUD_PROJECT')) {
+            return getenv('GOOGLE_CLOUD_PROJECT');
+        }
+
+        if (getenv('GCLOUD_PROJECT')) {
+            return getenv('GCLOUD_PROJECT');
+        }
+
+        throw new ValidationException(
+            'No project ID was provided, ' .
+            'and we were unable to detect a default project ID.'
+        );
+    }
 }