Kick off the SDK based on Symfony's MCP SDK

src/Server/JsonRpcHandler.php

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+<?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;
+
+use Mcp\Exception\ExceptionInterface;
+use Mcp\Exception\HandlerNotFoundException;
+use Mcp\Exception\InvalidInputMessageException;
+use Mcp\Exception\NotFoundExceptionInterface;
+use Mcp\Message\Error;
+use Mcp\Message\Factory;
+use Mcp\Message\Notification;
+use Mcp\Message\Request;
+use Mcp\Message\Response;
+use Psr\Log\LoggerInterface;
+
+/**
+ * @final
+ *
+ * @author Christopher Hertel <mail@christopher-hertel.de>
+ */
+class JsonRpcHandler
+{
+    /**
+     * @var array<int, RequestHandlerInterface>
+     */
+    private readonly array $requestHandlers;
+
+    /**
+     * @var array<int, NotificationHandlerInterface>
+     */
+    private readonly array $notificationHandlers;
+
+    /**
+     * @param iterable<RequestHandlerInterface>      $requestHandlers
+     * @param iterable<NotificationHandlerInterface> $notificationHandlers
+     */
+    public function __construct(
+        private readonly Factory $messageFactory,
+        iterable $requestHandlers,
+        iterable $notificationHandlers,
+        private readonly LoggerInterface $logger,
+    ) {
+        $this->requestHandlers = $requestHandlers instanceof \Traversable ? iterator_to_array($requestHandlers) : $requestHandlers;
+        $this->notificationHandlers = $notificationHandlers instanceof \Traversable ? iterator_to_array($notificationHandlers) : $notificationHandlers;
+    }
+
+    /**
+     * @return iterable<string|null>
+     *
+     * @throws ExceptionInterface When a handler throws an exception during message processing
+     * @throws \JsonException     When JSON encoding of the response fails
+     */
+    public function process(string $input): iterable
+    {
+        $this->logger->info('Received message to process', ['message' => $input]);
+
+        try {
+            $messages = $this->messageFactory->create($input);
+        } catch (\JsonException $e) {
+            $this->logger->warning('Failed to decode json message', ['exception' => $e]);
+
+            yield $this->encodeResponse(Error::parseError($e->getMessage()));
+
+            return;
+        }
+
+        foreach ($messages as $message) {
+            if ($message instanceof InvalidInputMessageException) {
+                $this->logger->warning('Failed to create message', ['exception' => $message]);
+                yield $this->encodeResponse(Error::invalidRequest(0, $message->getMessage()));
+                continue;
+            }
+
+            $this->logger->info('Decoded incoming message', ['message' => $message]);
+
+            try {
+                yield $message instanceof Notification
+                    ? $this->handleNotification($message)
+                    : $this->encodeResponse($this->handleRequest($message));
+            } catch (\DomainException) {
+                yield null;
+            } catch (NotFoundExceptionInterface $e) {
+                $this->logger->warning(\sprintf('Failed to create response: %s', $e->getMessage()), ['exception' => $e]);
+
+                yield $this->encodeResponse(Error::methodNotFound($message->id, $e->getMessage()));
+            } catch (\InvalidArgumentException $e) {
+                $this->logger->warning(\sprintf('Invalid argument: %s', $e->getMessage()), ['exception' => $e]);
+
+                yield $this->encodeResponse(Error::invalidParams($message->id, $e->getMessage()));
+            } catch (\Throwable $e) {
+                $this->logger->critical(\sprintf('Uncaught exception: %s', $e->getMessage()), ['exception' => $e]);
+
+                yield $this->encodeResponse(Error::internalError($message->id, $e->getMessage()));
+            }
+        }
+    }
+
+    /**
+     * @throws \JsonException When JSON encoding fails
+     */
+    private function encodeResponse(Response|Error|null $response): ?string
+    {
+        if (null === $response) {
+            $this->logger->warning('Response is null');
+
+            return null;
+        }
+
+        $this->logger->info('Encoding response', ['response' => $response]);
+
+        if ($response instanceof Response && [] === $response->result) {
+            return json_encode($response, \JSON_THROW_ON_ERROR | \JSON_FORCE_OBJECT);
+        }
+
+        return json_encode($response, \JSON_THROW_ON_ERROR);
+    }
+
+    /**
+     * @return null
+     *
+     * @throws ExceptionInterface When a notification handler throws an exception
+     */
+    private function handleNotification(Notification $notification)
+    {
+        $handled = false;
+        foreach ($this->notificationHandlers as $handler) {
+            if ($handler->supports($notification)) {
+                $handler->handle($notification);
+                $handled = true;
+            }
+        }
+
+        if (!$handled) {
+            $this->logger->warning(\sprintf('No handler found for "%s".', $notification->method), ['notification' => $notification]);
+        }
+
+        return null;
+    }
+
+    /**
+     * @throws NotFoundExceptionInterface When no handler is found for the request method
+     * @throws ExceptionInterface         When a request handler throws an exception
+     */
+    private function handleRequest(Request $request): Response|Error
+    {
+        foreach ($this->requestHandlers as $handler) {
+            if ($handler->supports($request)) {
+                return $handler->createResponse($request);
+            }
+        }
+
+        throw new HandlerNotFoundException(\sprintf('No handler found for method "%s".', $request->method));
+    }
+}

src/Server/NotificationHandler/BaseNotificationHandler.php

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+<?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\NotificationHandler;
+
+use Mcp\Message\Notification;
+use Mcp\Server\NotificationHandlerInterface;
+
+/**
+ * @author Christopher Hertel <mail@christopher-hertel.de>
+ */
+abstract class BaseNotificationHandler implements NotificationHandlerInterface
+{
+    public function supports(Notification $message): bool
+    {
+        return $message->method === \sprintf('notifications/%s', $this->supportedNotification());
+    }
+
+    abstract protected function supportedNotification(): string;
+}

src/Server/NotificationHandler/InitializedHandler.php

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+<?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\NotificationHandler;
+
+use Mcp\Message\Notification;
+
+/**
+ * @author Christopher Hertel <mail@christopher-hertel.de>
+ */
+final class InitializedHandler extends BaseNotificationHandler
+{
+    protected function supportedNotification(): string
+    {
+        return 'initialized';
+    }
+
+    public function handle(Notification $notification): void
+    {
+    }
+}

src/Server/NotificationHandlerInterface.php

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+<?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;
+
+use Mcp\Exception\ExceptionInterface;
+use Mcp\Message\Notification;
+
+/**
+ * @author Christopher Hertel <mail@christopher-hertel.de>
+ */
+interface NotificationHandlerInterface
+{
+    public function supports(Notification $message): bool;
+
+    /**
+     * @throws ExceptionInterface When the handler encounters an error processing the notification
+     */
+    public function handle(Notification $notification): void;
+}

src/Server/RequestHandler/BaseRequestHandler.php

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+<?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\RequestHandler;
+
+use Mcp\Message\Request;
+use Mcp\Server\RequestHandlerInterface;
+
+/**
+ * @author Christopher Hertel <mail@christopher-hertel.de>
+ */
+abstract class BaseRequestHandler implements RequestHandlerInterface
+{
+    public function supports(Request $message): bool
+    {
+        return $message->method === $this->supportedMethod();
+    }
+
+    abstract protected function supportedMethod(): string;
+}

src/Server/RequestHandler/InitializeHandler.php

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+<?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\RequestHandler;
+
+use Mcp\Message\Request;
+use Mcp\Message\Response;
+
+/**
+ * @author Christopher Hertel <mail@christopher-hertel.de>
+ */
+final class InitializeHandler extends BaseRequestHandler
+{
+    public function __construct(
+        private readonly string $name = 'app',
+        private readonly string $version = 'dev',
+    ) {
+    }
+
+    public function createResponse(Request $message): Response
+    {
+        return new Response($message->id, [
+            'protocolVersion' => '2025-03-26',
+            'capabilities' => [
+                'prompts' => ['listChanged' => false],
+                'tools' => ['listChanged' => false],
+                'resources' => ['listChanged' => false, 'subscribe' => false],
+            ],
+            'serverInfo' => ['name' => $this->name, 'version' => $this->version],
+        ]);
+    }
+
+    protected function supportedMethod(): string
+    {
+        return 'initialize';
+    }
+}

src/Server/RequestHandler/PingHandler.php

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+<?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\RequestHandler;
+
+use Mcp\Message\Request;
+use Mcp\Message\Response;
+
+/**
+ * @author Christopher Hertel <mail@christopher-hertel.de>
+ */
+final class PingHandler extends BaseRequestHandler
+{
+    public function createResponse(Request $message): Response
+    {
+        return new Response($message->id, []);
+    }
+
+    protected function supportedMethod(): string
+    {
+        return 'ping';
+    }
+}

src/Server/RequestHandler/PromptGetHandler.php

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+<?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\RequestHandler;
+
+use Mcp\Capability\Prompt\PromptGet;
+use Mcp\Capability\Prompt\PromptGetterInterface;
+use Mcp\Exception\ExceptionInterface;
+use Mcp\Exception\InvalidArgumentException;
+use Mcp\Message\Error;
+use Mcp\Message\Request;
+use Mcp\Message\Response;
+
+/**
+ * @author Tobias Nyholm <tobias.nyholm@gmail.com>
+ */
+final class PromptGetHandler extends BaseRequestHandler
+{
+    public function __construct(
+        private readonly PromptGetterInterface $getter,
+    ) {
+    }
+
+    public function createResponse(Request $message): Response|Error
+    {
+        $name = $message->params['name'];
+        $arguments = $message->params['arguments'] ?? [];
+
+        try {
+            $result = $this->getter->get(new PromptGet(uniqid('', true), $name, $arguments));
+        } catch (ExceptionInterface) {
+            return Error::internalError($message->id, 'Error while handling prompt');
+        }
+
+        $messages = [];
+        foreach ($result->messages as $resultMessage) {
+            $content = match ($resultMessage->type) {
+                'text' => [
+                    'type' => 'text',
+                    'text' => $resultMessage->result,
+                ],
+                'image', 'audio' => [
+                    'type' => $resultMessage->type,
+                    'data' => $resultMessage->result,
+                    'mimeType' => $resultMessage->mimeType,
+                ],
+                'resource' => [
+                    'type' => 'resource',
+                    'resource' => [
+                        'uri' => $resultMessage->uri,
+                        'mimeType' => $resultMessage->mimeType,
+                        'text' => $resultMessage->result,
+                    ],
+                ],
+                // TODO better exception
+                default => throw new InvalidArgumentException('Unsupported PromptGet result type: '.$resultMessage->type),
+            };
+
+            $messages[] = [
+                'role' => $resultMessage->role,
+                'content' => $content,
+            ];
+        }
+
+        return new Response($message->id, [
+            'description' => $result->description,
+            'messages' => $messages,
+        ]);
+    }
+
+    protected function supportedMethod(): string
+    {
+        return 'prompts/get';
+    }
+}

src/Server/RequestHandler/PromptListHandler.php

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+<?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\RequestHandler;
+
+use Mcp\Capability\Prompt\CollectionInterface;
+use Mcp\Message\Request;
+use Mcp\Message\Response;
+
+/**
+ * @author Tobias Nyholm <tobias.nyholm@gmail.com>
+ */
+final class PromptListHandler extends BaseRequestHandler
+{
+    public function __construct(
+        private readonly CollectionInterface $collection,
+        private readonly int $pageSize = 20,
+    ) {
+    }
+
+    public function createResponse(Request $message): Response
+    {
+        $nextCursor = null;
+        $prompts = [];
+
+        $metadataList = $this->collection->getMetadata(
+            $this->pageSize,
+            $message->params['cursor'] ?? null
+        );
+
+        foreach ($metadataList as $metadata) {
+            $nextCursor = $metadata->getName();
+            $result = [
+                'name' => $metadata->getName(),
+            ];
+
+            $description = $metadata->getDescription();
+            if (null !== $description) {
+                $result['description'] = $description;
+            }
+
+            $arguments = [];
+            foreach ($metadata->getArguments() as $data) {
+                $argument = [
+                    'name' => $data['name'],
+                    'required' => $data['required'] ?? false,
+                ];
+
+                if (isset($data['description'])) {
+                    $argument['description'] = $data['description'];
+                }
+                $arguments[] = $argument;
+            }
+
+            if ([] !== $arguments) {
+                $result['arguments'] = $arguments;
+            }
+
+            $prompts[] = $result;
+        }
+
+        $result = [
+            'prompts' => $prompts,
+        ];
+
+        if (null !== $nextCursor && \count($prompts) === $this->pageSize) {
+            $result['nextCursor'] = $nextCursor;
+        }
+
+        return new Response($message->id, $result);
+    }
+
+    protected function supportedMethod(): string
+    {
+        return 'prompts/list';
+    }
+}

src/Server/RequestHandler/ResourceListHandler.php

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+<?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\RequestHandler;
+
+use Mcp\Capability\Resource\CollectionInterface;
+use Mcp\Message\Request;
+use Mcp\Message\Response;
+
+/**
+ * @author Tobias Nyholm <tobias.nyholm@gmail.com>
+ */
+final class ResourceListHandler extends BaseRequestHandler
+{
+    public function __construct(
+        private readonly CollectionInterface $collection,
+        private readonly int $pageSize = 20,
+    ) {
+    }
+
+    public function createResponse(Request $message): Response
+    {
+        $nextCursor = null;
+        $resources = [];
+
+        $metadataList = $this->collection->getMetadata(
+            $this->pageSize,
+            $message->params['cursor'] ?? null
+        );
+
+        foreach ($metadataList as $metadata) {
+            $nextCursor = $metadata->getUri();
+            $result = [
+                'uri' => $metadata->getUri(),
+                'name' => $metadata->getName(),
+            ];
+
+            $description = $metadata->getDescription();
+            if (null !== $description) {
+                $result['description'] = $description;
+            }
+
+            $mimeType = $metadata->getMimeType();
+            if (null !== $mimeType) {
+                $result['mimeType'] = $mimeType;
+            }
+
+            $size = $metadata->getSize();
+            if (null !== $size) {
+                $result['size'] = $size;
+            }
+
+            $resources[] = $result;
+        }
+
+        $result = [
+            'resources' => $resources,
+        ];
+
+        if (null !== $nextCursor && \count($resources) === $this->pageSize) {
+            $result['nextCursor'] = $nextCursor;
+        }
+
+        return new Response($message->id, $result);
+    }
+
+    protected function supportedMethod(): string
+    {
+        return 'resources/list';
+    }
+}

src/Server/RequestHandler/ResourceReadHandler.php

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+<?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\RequestHandler;
+
+use Mcp\Capability\Resource\ResourceRead;
+use Mcp\Capability\Resource\ResourceReaderInterface;
+use Mcp\Exception\ExceptionInterface;
+use Mcp\Exception\ResourceNotFoundException;
+use Mcp\Message\Error;
+use Mcp\Message\Request;
+use Mcp\Message\Response;
+
+/**
+ * @author Tobias Nyholm <tobias.nyholm@gmail.com>
+ */
+final class ResourceReadHandler extends BaseRequestHandler
+{
+    public function __construct(
+        private readonly ResourceReaderInterface $reader,
+    ) {
+    }
+
+    public function createResponse(Request $message): Response|Error
+    {
+        $uri = $message->params['uri'];
+
+        try {
+            $result = $this->reader->read(new ResourceRead(uniqid('', true), $uri));
+        } catch (ResourceNotFoundException $e) {
+            return new Error($message->id, Error::RESOURCE_NOT_FOUND, $e->getMessage());
+        } catch (ExceptionInterface) {
+            return Error::internalError($message->id, 'Error while reading resource');
+        }
+
+        return new Response($message->id, [
+            'contents' => [
+                [
+                    'uri' => $result->uri,
+                    'mimeType' => $result->mimeType,
+                    $result->type => $result->result,
+                ],
+            ],
+        ]);
+    }
+
+    protected function supportedMethod(): string
+    {
+        return 'resources/read';
+    }
+}

src/Server/RequestHandler/ToolCallHandler.php

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+<?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\RequestHandler;
+
+use Mcp\Capability\Tool\ToolCall;
+use Mcp\Capability\Tool\ToolExecutorInterface;
+use Mcp\Exception\ExceptionInterface;
+use Mcp\Exception\InvalidArgumentException;
+use Mcp\Message\Error;
+use Mcp\Message\Request;
+use Mcp\Message\Response;
+
+/**
+ * @author Christopher Hertel <mail@christopher-hertel.de>
+ * @author Tobias Nyholm <tobias.nyholm@gmail.com>
+ */
+final class ToolCallHandler extends BaseRequestHandler
+{
+    public function __construct(
+        private readonly ToolExecutorInterface $toolExecutor,
+    ) {
+    }
+
+    public function createResponse(Request $message): Response|Error
+    {
+        $name = $message->params['name'];
+        $arguments = $message->params['arguments'] ?? [];
+
+        try {
+            $result = $this->toolExecutor->call(new ToolCall(uniqid('', true), $name, $arguments));
+        } catch (ExceptionInterface) {
+            return Error::internalError($message->id, 'Error while executing tool');
+        }
+
+        $content = match ($result->type) {
+            'text' => [
+                'type' => 'text',
+                'text' => $result->result,
+            ],
+            'image', 'audio' => [
+                'type' => $result->type,
+                'data' => $result->result,
+                'mimeType' => $result->mimeType,
+            ],
+            'resource' => [
+                'type' => 'resource',
+                'resource' => [
+                    'uri' => $result->uri,
+                    'mimeType' => $result->mimeType,
+                    'text' => $result->result,
+                ],
+            ],
+            // TODO better exception
+            default => throw new InvalidArgumentException('Unsupported tool result type: '.$result->type),
+        };
+
+        return new Response($message->id, [
+            'content' => [$content], // TODO: allow multiple `ToolCallResult`s in the future
+            'isError' => $result->isError,
+        ]);
+    }
+
+    protected function supportedMethod(): string
+    {
+        return 'tools/call';
+    }
+}

src/Server/RequestHandler/ToolListHandler.php

@@ -0,0 +1,68 @@
+<?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\RequestHandler;
+
+use Mcp\Capability\Tool\CollectionInterface;
+use Mcp\Message\Request;
+use Mcp\Message\Response;
+
+/**
+ * @author Christopher Hertel <mail@christopher-hertel.de>
+ * @author Tobias Nyholm <tobias.nyholm@gmail.com>
+ */
+final class ToolListHandler extends BaseRequestHandler
+{
+    public function __construct(
+        private readonly CollectionInterface $collection,
+        private readonly int $pageSize = 20,
+    ) {
+    }
+
+    public function createResponse(Request $message): Response
+    {
+        $nextCursor = null;
+        $tools = [];
+
+        $metadataList = $this->collection->getMetadata(
+            $this->pageSize,
+            $message->params['cursor'] ?? null
+        );
+
+        foreach ($metadataList as $tool) {
+            $nextCursor = $tool->getName();
+            $inputSchema = $tool->getInputSchema();
+            $tools[] = [
+                'name' => $tool->getName(),
+                'description' => $tool->getDescription(),
+                'inputSchema' => [] === $inputSchema ? [
+                    'type' => 'object',
+                    '$schema' => 'http://json-schema.org/draft-07/schema#',
+                ] : $inputSchema,
+            ];
+        }
+
+        $result = [
+            'tools' => $tools,
+        ];
+
+        if (null !== $nextCursor && \count($tools) === $this->pageSize) {
+            $result['nextCursor'] = $nextCursor;
+        }
+
+        return new Response($message->id, $result);
+    }
+
+    protected function supportedMethod(): string
+    {
+        return 'tools/list';
+    }
+}

src/Server/RequestHandlerInterface.php

@@ -0,0 +1,30 @@
+<?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;
+
+use Mcp\Exception\ExceptionInterface;
+use Mcp\Message\Error;
+use Mcp\Message\Request;
+use Mcp\Message\Response;
+
+/**
+ * @author Christopher Hertel <mail@christopher-hertel.de>
+ */
+interface RequestHandlerInterface
+{
+    public function supports(Request $message): bool;
+
+    /**
+     * @throws ExceptionInterface When the handler encounters an error processing the request
+     */
+    public function createResponse(Request $message): Response|Error;
+}

src/Server/Transport/Sse/Store/CachePoolStore.php

@@ -0,0 +1,65 @@
+<?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\Sse\Store;
+
+use Mcp\Server\Transport\Sse\StoreInterface;
+use Psr\Cache\CacheItemPoolInterface;
+use Symfony\Component\Uid\Uuid;
+
+/**
+ * @author Christopher Hertel <mail@christopher-hertel.de>
+ */
+final class CachePoolStore implements StoreInterface
+{
+    public function __construct(
+        private readonly CacheItemPoolInterface $cachePool,
+    ) {
+    }
+
+    public function push(Uuid $id, string $message): void
+    {
+        $item = $this->cachePool->getItem($this->getCacheKey($id));
+
+        $messages = $item->isHit() ? $item->get() : [];
+        $messages[] = $message;
+        $item->set($messages);
+
+        $this->cachePool->save($item);
+    }
+
+    public function pop(Uuid $id): ?string
+    {
+        $item = $this->cachePool->getItem($this->getCacheKey($id));
+
+        if (!$item->isHit()) {
+            return null;
+        }
+
+        $messages = $item->get();
+        $message = array_shift($messages);
+
+        $item->set($messages);
+        $this->cachePool->save($item);
+
+        return $message;
+    }
+
+    public function remove(Uuid $id): void
+    {
+        $this->cachePool->deleteItem($this->getCacheKey($id));
+    }
+
+    private function getCacheKey(Uuid $id): string
+    {
+        return 'message_'.$id->toRfc4122();
+    }
+}

src/Server/Transport/Sse/StoreInterface.php

@@ -0,0 +1,26 @@
+<?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\Sse;
+
+use Symfony\Component\Uid\Uuid;
+
+/**
+ * @author Christopher Hertel <mail@christopher-hertel.de>
+ */
+interface StoreInterface
+{
+    public function push(Uuid $id, string $message): void;
+
+    public function pop(Uuid $id): ?string;
+
+    public function remove(Uuid $id): void;
+}

src/Server/Transport/Sse/StreamTransport.php

@@ -0,0 +1,65 @@
+<?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\Sse;
+
+use Mcp\Server\TransportInterface;
+use Symfony\Component\Uid\Uuid;
+
+/**
+ * @author Christopher Hertel <mail@christopher-hertel.de>
+ */
+final class StreamTransport implements TransportInterface
+{
+    public function __construct(
+        private readonly string $messageEndpoint,
+        private readonly StoreInterface $store,
+        private readonly Uuid $id,
+    ) {
+    }
+
+    public function initialize(): void
+    {
+        ignore_user_abort(true);
+        $this->flushEvent('endpoint', $this->messageEndpoint);
+    }
+
+    public function isConnected(): bool
+    {
+        return 0 === connection_aborted();
+    }
+
+    public function receive(): \Generator
+    {
+        yield $this->store->pop($this->id);
+    }
+
+    public function send(string $data): void
+    {
+        $this->flushEvent('message', $data);
+    }
+
+    public function close(): void
+    {
+        $this->store->remove($this->id);
+    }
+
+    private function flushEvent(string $event, string $data): void
+    {
+        echo \sprintf('event: %s', $event).\PHP_EOL;
+        echo \sprintf('data: %s', $data).\PHP_EOL;
+        echo \PHP_EOL;
+        if (false !== ob_get_length()) {
+            ob_flush();
+        }
+        flush();
+    }
+}

src/Server/Transport/Stdio/SymfonyConsoleTransport.php

@@ -0,0 +1,65 @@
+<?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\Stdio;
+
+use Mcp\Server\TransportInterface;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Input\StreamableInputInterface;
+use Symfony\Component\Console\Output\OutputInterface;
+
+/**
+ * Heavily inspired by https://jolicode.com/blog/mcp-the-open-protocol-that-turns-llm-chatbots-into-intelligent-agents.
+ */
+final class SymfonyConsoleTransport implements TransportInterface
+{
+    private string $buffer = '';
+
+    public function __construct(
+        private readonly InputInterface $input,
+        private readonly OutputInterface $output,
+    ) {
+    }
+
+    public function initialize(): void
+    {
+    }
+
+    public function isConnected(): bool
+    {
+        return true;
+    }
+
+    public function receive(): \Generator
+    {
+        $stream = $this->input instanceof StreamableInputInterface ? $this->input->getStream() ?? \STDIN : \STDIN;
+        $line = fgets($stream);
+        if (false === $line) {
+            return;
+        }
+        $this->buffer .= \STDIN === $stream ? rtrim($line).\PHP_EOL : $line;
+        if (str_contains($this->buffer, \PHP_EOL)) {
+            $lines = explode(\PHP_EOL, $this->buffer);
+            $this->buffer = array_pop($lines);
+
+            yield from $lines;
+        }
+    }
+
+    public function send(string $data): void
+    {
+        $this->output->writeln($data);
+    }
+
+    public function close(): void
+    {
+    }
+}

src/Server/TransportInterface.php

@@ -0,0 +1,28 @@
+<?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;
+
+/**
+ * @author Christopher Hertel <mail@christopher-hertel.de>
+ */
+interface TransportInterface
+{
+    public function initialize(): void;
+
+    public function isConnected(): bool;
+
+    public function receive(): \Generator;
+
+    public function send(string $data): void;
+
+    public function close(): void;
+}