Pass ErrorHandler to the RouteHandler.

src/App.php

@@ -101,8 +101,10 @@ public function __construct(...$middleware)
         if ($needsAccessLog instanceof Container) {
             \array_unshift($handlers, $needsAccessLog->getAccessLogHandler());
         }
-
-        $this->router = new RouteHandler($container);
+        $errorHandler = \array_reduce($handlers, function ($carry, $handler) {
+            return $carry ?? ($handler instanceof ErrorHandler ? $handler : null);
+        });
+        $this->router = new RouteHandler($container, $errorHandler);
         $handlers[] = $this->router;
         $this->handler = new MiddlewareHandler($handlers);
         $this->sapi = \PHP_SAPI === 'cli' ? new ReactiveHandler($container->getEnv('X_LISTEN')) : new SapiHandler();

src/Io/RouteHandler.php

@@ -30,10 +30,10 @@ class RouteHandler
     /** @var Container */
     private $container;
 
-    public function __construct(Container $container = null)
+    public function __construct(Container $container = null, ErrorHandler $errorHandler = null)
     {
         $this->routeCollector = new RouteCollector(new RouteParser(), new RouteGenerator());
-        $this->errorHandler = new ErrorHandler();
+        $this->errorHandler = $errorHandler ?? new ErrorHandler();
         $this->container = $container ?? new Container();
     }
 

tests/AppTest.php

@@ -1649,6 +1649,32 @@ public function testInvokeWithMatchingRouteReturnsInternalServerErrorResponseWhe
         $this->assertStringContainsString("<p>Expected request handler to return <code>Psr\Http\Message\ResponseInterface</code> but got <code>null</code>.</p>\n", (string) $response->getBody());
     }
 
+    public function testRouteHandlerUsesErrorHandlerPassedFromApp(): void
+    {
+        $errorHandler = $this->createMock(ErrorHandler::class);
+        $errorHandler->expects($this->once())
+                     ->method('requestNotFound')
+                     ->willReturn(Response::json(['error' => 'Not Found'])->withStatus(404));
+        $errorHandler->method('__invoke')
+                     ->will(
+                         $this->returnCallback(
+                             function (ServerRequestInterface $request, callable $next) {
+                                 return $next($request);
+                             }
+                         )
+                     );
+        $app = $this->createAppWithoutLogger($errorHandler);
+
+        $request = new ServerRequest('GET', 'http://localhost/invalid');
+
+        $response = $app($request);
+        assert($response instanceof ResponseInterface);
+
+        $this->assertEquals(404, $response->getStatusCode());
+        $this->assertEquals('application/json', $response->getHeaderLine('Content-Type'));
+        $this->assertStringMatchesFormat("{%a}", (string) $response->getBody());
+    }
+
     private function createAppWithoutLogger(callable ...$middleware): App
     {
         $app = new App(...$middleware);