Throw EmptyPipelineException if passed continuation is invoked more t…

…han once

src/Next.php

@@ -9,6 +9,8 @@
 
 namespace Zend\Stratigility;
 
+use Zend\Stratigility\Middleware\RequestHandlerMiddleware;
+use Zend\Stratigility\Exception\EmptyPipelineException;
 use Psr\Http\Message\ResponseInterface;
 use Psr\Http\Message\ServerRequestInterface;
 use Psr\Http\Server\RequestHandlerInterface;
@@ -39,12 +41,15 @@ public function __construct(SplQueue $queue, RequestHandlerInterface $fallbackHa
     {
         $this->queue           = clone $queue;
         $this->fallbackHandler = $fallbackHandler;
+        $this->queue->push(
+            new RequestHandlerMiddleware($fallbackHandler),
+        );
     }
 
     public function handle(ServerRequestInterface $request) : ResponseInterface
     {
         if ($this->queue->isEmpty()) {
-            return $this->fallbackHandler->handle($request);
+            throw EmptyPipelineException::forClass(__CLASS__);
         }
 
         $middleware = $this->queue->dequeue();

test/NextTest.php

@@ -22,6 +22,7 @@
 use Zend\Diactoros\ServerRequest as Request;
 use Zend\Diactoros\Uri;
 use Zend\Stratigility\Next;
+use Zend\Stratigility\Exception\EmptyPipelineException;
 
 class NextTest extends TestCase
 {
@@ -214,4 +215,26 @@ public function testMiddlewareReturningResponseShortCircuitsProcess()
 
         $this->assertSame($response, $next->handle($this->request));
     }
+
+    public function testCallingContinuationMoreThanOnceRaisesException()
+    {
+        $this->expectException(EmptyPipelineException::class);
+        $fallBackHandler = $this->prophesize(RequestHandlerInterface::class);
+        $fallBackHandler
+            ->handle(Argument::any())
+            ->shouldBeCalledTimes(1);
+
+        // Middleware calling $handler->handle() twice. The first call will empty the
+        // middleware queue while the second call will raise the empty pipline exception.
+        $middleware = (new class () implements MiddlewareInterface {
+            public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface {
+                $handler->handle($request);
+                return $handler->handle($request);
+            }
+        });
+        $this->queue->push($middleware);
+
+        $next = new Next($this->queue, $fallBackHandler->reveal());
+        $next->handle($this->request);
+    }
 }