fix: maintain forwards compatibility with REST server streaming

src/RequestBuilder.php

@@ -65,6 +65,16 @@ public function __construct($baseUri, $restConfigPath)
         $this->restConfig = require($restConfigPath);
     }
 
+    /**
+     * @param string $path
+     * @return bool
+     */
+    public function pathExists($path)
+    {
+        list($interface, $method) = explode('/', $path);
+        return isset($this->restConfig['interfaces'][$interface][$method]);
+    }
+
     /**
      * @param string $path
      * @param Message $message

src/Transport/RestTransport.php

@@ -42,6 +42,7 @@
 use Google\Protobuf\Internal\Message;
 use GuzzleHttp\Exception\RequestException;
 use Psr\Http\Message\ResponseInterface;
+use BadMethodCallException;
 
 /**
  * A REST based transport implementation.
@@ -145,6 +146,7 @@ function (\Exception $ex) {
 
     /**
      * {@inheritdoc}
+     * @throws BadMethodCallException for forwards compatibility with older GAPIC clients
      */
     public function startServerStreamingCall(Call $call, array $options)
     {
@@ -153,6 +155,12 @@ public function startServerStreamingCall(Call $call, array $options)
             throw new \InvalidArgumentException('A message is required for ServerStreaming calls.');
         }
 
+        // Maintain forwards compatibility with older GAPIC clients not configured for REST server streaming
+        // @see https://github.com/googleapis/gax-php/issues/370
+        if (!$this->requestBuilder->pathExists($call->getMethod())) {
+            throw new BadMethodCallException('Streaming calls are not supported while using the REST transport');
+        }
+
         $headers = self::buildCommonHeaders($options);
         $callOptions = $this->getCallOptions($options);
         $request = $this->requestBuilder->build(

tests/Tests/Unit/Transport/RestTransportTest.php

@@ -73,6 +73,8 @@ private function getTransport(callable $httpHandler = null, $apiEndpoint = 'http
             ->getMock();
         $requestBuilder->method('build')
             ->willReturn($request);
+        $requestBuilder->method('pathExists')
+            ->willReturn(true);
 
         return new RestTransport(
             $requestBuilder,