Fix awaiting queued handlers when cancelling a queued handler

src/Middleware/LimitConcurrentRequestsMiddleware.php

@@ -143,21 +143,39 @@ public function __invoke(ServerRequestInterface $request, $next)
         $queue[$id] = $deferred;
 
         $pending = &$this->pending;
-        return $this->await($deferred->promise()->then(function () use ($request, $next, $body, &$pending) {
+        $that = $this;
+        return $deferred->promise()->then(function () use ($request, $next, $body, &$pending, $that) {
             // invoke next request handler
             ++$pending;
-            $ret = $next($request);
+
+            try {
+                $response = $next($request);
+            } catch (\Exception $e) {
+                $that->processQueue();
+                throw $e;
+            } catch (\Throwable $e) { // @codeCoverageIgnoreStart
+                // handle Errors just like Exceptions (PHP 7+ only)
+                $that->processQueue();
+                throw $e; // @codeCoverageIgnoreEnd
+            }
 
             // resume readable stream and replay buffered events
             if ($body instanceof PauseBufferStream) {
                 $body->resumeImplicit();
             }
 
-            return $ret;
-        }));
+            // if the next handler returns a pending promise, we have to
+            // await its resolution before invoking next queued request
+            return $that->await(Promise\resolve($response));
+        });
     }
 
-    private function await(PromiseInterface $promise)
+    /**
+     * @internal
+     * @param PromiseInterface $promise
+     * @return PromiseInterface
+     */
+    public function await(PromiseInterface $promise)
     {
         $that = $this;
 

tests/Middleware/LimitConcurrentRequestsMiddlewareTest.php

@@ -296,6 +296,31 @@ public function testReceivesNextRequestAfterPreviousHandlerIsSettled()
         $middleware($request, $this->expectCallableOnceWith($request));
     }
 
+    public function testReceivesNextRequestWhichThrowsAfterPreviousHandlerIsSettled()
+    {
+        $request = new ServerRequest(
+            'POST',
+            'http://example.com/',
+            array(),
+            'hello'
+        );
+
+        $deferred = new Deferred();
+        $middleware = new LimitConcurrentRequestsMiddleware(1);
+        $middleware($request, function () use ($deferred) {
+            return $deferred->promise();
+        });
+
+        $second = $middleware($request, function () {
+            throw new \RuntimeException();
+        });
+
+        $this->assertTrue($second instanceof PromiseInterface);
+        $second->then(null, $this->expectCallableOnce());
+
+        $deferred->reject(new \RuntimeException());
+    }
+
     public function testPendingRequestCanBeCancelledAndForwardsCancellationToInnerPromise()
     {
         $request = new ServerRequest(
@@ -365,6 +390,50 @@ public function testReceivesNextRequestAfterPreviousHandlerIsCancelled()
         $middleware($request, $this->expectCallableOnceWith($request));
     }
 
+    public function testRejectsWhenQueuedPromiseIsCancelled()
+    {
+        $request = new ServerRequest(
+            'POST',
+            'http://example.com/',
+            array(),
+            'hello'
+        );
+
+        $deferred = new Deferred();
+        $middleware = new LimitConcurrentRequestsMiddleware(1);
+        $first = $middleware($request, function () use ($deferred) {
+            return $deferred->promise();
+        });
+
+        $second = $middleware($request, $this->expectCallableNever());
+
+        $this->assertTrue($second instanceof PromiseInterface);
+        $second->cancel();
+        $second->then(null, $this->expectCallableOnce());
+    }
+
+    public function testDoesNotInvokeNextHandlersWhenQueuedPromiseIsCancelled()
+    {
+        $request = new ServerRequest(
+            'POST',
+            'http://example.com/',
+            array(),
+            'hello'
+            );
+
+        $deferred = new Deferred();
+        $middleware = new LimitConcurrentRequestsMiddleware(1);
+        $first = $middleware($request, function () use ($deferred) {
+            return $deferred->promise();
+        });
+
+        $second = $middleware($request, $this->expectCallableNever());
+        /* $third = */ $middleware($request, $this->expectCallableNever());
+
+        $this->assertTrue($second instanceof PromiseInterface);
+        $second->cancel();
+    }
+
     public function testReceivesStreamingBodyChangesInstanceWithCustomBodyButSameDataWhenDequeued()
     {
         $stream = new ThroughStream();