Add Middleware handlers to StreamableHttpTransport (#218)

src/Server/Transport/Http/MiddlewareRequestHandler.php

@@ -0,0 +1,47 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Server\Transport\Http;
+
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use Psr\Http\Server\MiddlewareInterface;
+use Psr\Http\Server\RequestHandlerInterface;
+
+/**
+ * A request handler that processes a middleware pipeline before dispatching
+ * the request to the core transport handler.
+ *
+ * @author Volodymyr Panivko <sveneld300@gmail.com>
+ *
+ * @internal
+ */
+class MiddlewareRequestHandler implements RequestHandlerInterface
+{
+    /**
+     * @param list<MiddlewareInterface> $middleware
+     */
+    public function __construct(
+        private array $middleware,
+        private \Closure $application,
+    ) {
+    }
+
+    public function handle(ServerRequestInterface $request): ResponseInterface
+    {
+        $middleware = array_shift($this->middleware);
+        if (null === $middleware) {
+            return ($this->application)($request);
+        }
+
+        return $middleware->process($request, $this);
+    }
+}