Added listeners for ProblemDetailsMiddleware

Author: svycka

src/ProblemDetailsMiddleware.php

@@ -23,6 +23,11 @@
  */
 class ProblemDetailsMiddleware implements MiddlewareInterface
 {
+    /**
+     * @var callable[]
+     */
+    private $listeners = [];
+
     /**
      * @var ProblemDetailsResponseFactory
      */
@@ -52,13 +57,38 @@ public function process(ServerRequestInterface $request, DelegateInterface $dele
             }
         } catch (Throwable $e) {
             $response = $this->responseFactory->createResponseFromThrowable($request, $e);
+            $this->triggerListeners($e, $request, $response);
         } finally {
             restore_error_handler();
         }
 
         return $response;
     }
 
+    /**
+     * Attach an error listener.
+     *
+     * Each listener receives the following three arguments:
+     *
+     * - Throwable $error
+     * - ServerRequestInterface $request
+     * - ResponseInterface $response
+     *
+     * These instances are all immutable, and the return values of
+     * listeners are ignored; use listeners for reporting purposes
+     * only.
+     *
+     * @param callable $listener
+     */
+    public function attachListener(callable $listener)
+    {
+        if (\in_array($listener, $this->listeners, true)) {
+            return;
+        }
+
+        $this->listeners[] = $listener;
+    }
+
     /**
      * Can the middleware act as an error handler?
      *
@@ -98,4 +128,19 @@ private function createErrorHandler() : callable
             throw new ErrorException($errstr, 0, $errno, $errfile, $errline);
         };
     }
+
+    /**
+     * Trigger all error listeners.
+     *
+     * @param Throwable $error
+     * @param ServerRequestInterface $request
+     * @param ResponseInterface $response
+     * @return void
+     */
+    private function triggerListeners($error, ServerRequestInterface $request, ResponseInterface $response) : void
+    {
+        array_walk($this->listeners, function ($listener) use ($error, $request, $response) {
+            $listener($error, $request, $response);
+        });
+    }
 }

test/ProblemDetailsMiddlewareTest.php

@@ -148,4 +148,37 @@ public function testRethrowsCaughtExceptionIfUnableToNegotiateAcceptHeader() : v
         $this->expectExceptionCode(507);
         $middleware->process($this->request->reveal(), $delegate->reveal());
     }
+
+    /**
+     * @dataProvider acceptHeaders
+     */
+    public function testErrorHandlingTriggersListeners(string $accept) : void
+    {
+        $this->request->getHeaderLine('Accept')->willReturn($accept);
+
+        $exception = new TestAsset\RuntimeException('Thrown!', 507);
+
+        $delegate  = $this->prophesize(DelegateInterface::class);
+        $delegate
+            ->{HANDLER_METHOD}(Argument::that([$this->request, 'reveal']))
+            ->willThrow($exception);
+
+        $expected = $this->prophesize(ResponseInterface::class)->reveal();
+        $this->responseFactory
+            ->createResponseFromThrowable($this->request->reveal(), $exception)
+            ->willReturn($expected);
+
+        $listener = function ($error, $request, $response) use ($exception, $expected) {
+            $this->assertSame($exception, $error, 'Listener did not receive same exception as was raised');
+            $this->assertSame($this->request->reveal(), $request, 'Listener did not receive same request');
+            $this->assertSame($expected, $response, 'Listener did not receive same response');
+        };
+        $listener2 = clone $listener;
+        $this->middleware->attachListener($listener);
+        $this->middleware->attachListener($listener2);
+
+        $result = $this->middleware->process($this->request->reveal(), $delegate->reveal());
+
+        $this->assertSame($expected, $result);
+    }
 }