Ensures that path segregated middleware may provide an altered request

Discovered while backporting to the 2.X series. Essentially, a path
segregated middleware should still be able to pass a new request on to
the next layer. However, in doing so, the _path_ should be reset.

This patch updates the `PathMiddlewareDecoratorIntegrationTest` to
reflect this behavior, and updates the anonymous request handler created
by the `PathMiddlewareDecorator` to invoke the composed handler with the
runtime request after resetting its URI instance with the original path.

src/Middleware/PathMiddlewareDecorator.php

@@ -122,11 +122,20 @@ public function __construct(RequestHandlerInterface $handler, ServerRequestInter
             }
 
             /**
-             * Invokes the composed handler with the original server request.
+             * Invokes the composed handler with a request using the original URI.
+             *
+             * The decorated middleware may provide an altered response. However,
+             * we want to reset the path to the original path on invocation, as
+             * that is the part we originally modified, and is a part the decorated
+             * middleware should not modify.
+             *
+             * {@inheritDoc}
              */
             public function handle(ServerRequestInterface $request) : ResponseInterface
             {
-                return $this->handler->handle($this->originalRequest);
+                $uri = $request->getUri()
+                    ->withPath($this->originalRequest->getUri()->getPath());
+                return $this->handler->handle($request->withUri($uri));
             }
         };
     }

test/Middleware/PathMiddlewareDecoratorIntegrationTest.php

@@ -32,9 +32,39 @@ public function testPipelineComposingPathDecoratedMiddlewareExecutesAsExpected()
 
         $pipeline = new MiddlewarePipe();
 
-        $first = $this->createPassThroughMiddleware($request);
+        $first = $this->createPassThroughMiddleware(function ($received) use ($request) {
+            Assert::assertSame(
+                $request,
+                $received,
+                'First middleware did not receive original request, but should have'
+            );
+            return $request;
+        });
         $second = new PathMiddlewareDecorator('/foo', $this->createNestedPipeline($request));
-        $last = $this->createPassThroughMiddleware($request);
+        $last = $this->createPassThroughMiddleware(function ($received) use ($request) {
+            Assert::assertNotSame(
+                $request,
+                $received,
+                'Last middleware received original request, but should not have'
+            );
+
+            $originalUri = $request->getUri();
+            $receivedUri = $received->getUri();
+
+            Assert::assertNotSame(
+                $originalUri,
+                $receivedUri,
+                'Last middleware received original URI instance, but should not have'
+            );
+
+            Assert::assertSame(
+                $originalUri->getPath(),
+                $receivedUri->getPath(),
+                'Last middleware did not receive original URI path, but should have'
+            );
+
+            return $request;
+        });
 
         $pipeline->pipe($first);
         $pipeline->pipe($second);
@@ -51,6 +81,22 @@ public function testPipelineComposingPathDecoratedMiddlewareExecutesAsExpected()
         );
     }
 
+    public function createPassThroughMiddleware(callable $requestAssertion) : MiddlewareInterface
+    {
+        $middleware = $this->prophesize(MiddlewareInterface::class);
+        $middleware
+            ->process(
+                Argument::that($requestAssertion),
+                Argument::type(RequestHandlerInterface::class)
+            )
+            ->will(function ($args) {
+                $request = $args[0];
+                $next = $args[1];
+                return $next->handle($request);
+            });
+        return $middleware->reveal();
+    }
+
     public function createNestedPipeline(ServerRequestInterface $originalRequest) : MiddlewareInterface
     {
         $pipeline = new MiddlewarePipe();
@@ -111,27 +157,4 @@ public function createNestedPipeline(ServerRequestInterface $originalRequest) :
 
         return $pipeline;
     }
-
-    public function createPassThroughMiddleware(ServerRequestInterface $originalRequest) : MiddlewareInterface
-    {
-        $middleware = $this->prophesize(MiddlewareInterface::class);
-        $middleware
-            ->process(
-                Argument::that(function ($request) use ($originalRequest) {
-                    Assert::assertSame(
-                        $originalRequest,
-                        $request,
-                        'Non-segregated middleware did not receive original request, but should have'
-                    );
-                    return $request;
-                }),
-                Argument::type(RequestHandlerInterface::class)
-            )
-            ->will(function ($args) {
-                $request = $args[0];
-                $next = $args[1];
-                return $next->handle($request);
-            });
-        return $middleware->reveal();
-    }
 }