[Client][Server] Add Roots support

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 All notable changes to `mcp/sdk` will be documented in this file.
 
+0.8.0
+-----
+
+* Add client-side `roots/list` handler (`ListRootsRequestHandler` + `RootsCallbackInterface`) and `Client::sendRootsListChanged()`, plus server-side `ClientGateway::listRoots()` / `supportsRoots()` and `ListRootsResult::fromArray()`.
+
 0.7.0
 -----
 

README.md

@@ -243,6 +243,15 @@ $client = Client::builder()
     ->build();
 ```
 
+- **Roots Support**: Expose `file://` workspace folders to the server
+```php
+$rootsHandler = new ListRootsRequestHandler($myCallback);
+$client = Client::builder()
+    ->setCapabilities(new ClientCapabilities(roots: true, rootsListChanged: true))
+    ->addRequestHandler($rootsHandler)
+    ->build();
+```
+
 - **Logging Notifications**: Receive server log messages
 ```php
 $loggingHandler = new LoggingNotificationHandler($myCallback);

docs/client.md

@@ -600,6 +600,51 @@ Only the `Accept` action carries content.
 See `examples/client/stdio_elicitation.php` for a runnable example against the
 elicitation demo server.
 
+### Roots
+
+Roots let the client expose a list of `file://` "workspace folders" that the server
+is allowed to operate on. Advertise the `roots` capability and register a handler
+that answers server `roots/list` requests:
+
+```php
+use Mcp\Client\Handler\Request\ListRootsRequestHandler;
+use Mcp\Client\Handler\Request\RootsCallbackInterface;
+use Mcp\Schema\ClientCapabilities;
+use Mcp\Schema\Request\ListRootsRequest;
+use Mcp\Schema\Result\ListRootsResult;
+use Mcp\Schema\Root;
+
+class WorkspaceRootsCallback implements RootsCallbackInterface
+{
+    public function __invoke(ListRootsRequest $request): ListRootsResult
+    {
+        return new ListRootsResult([
+            new Root('file:///home/user/projects/app', 'Application'),
+            new Root('file:///home/user/projects/library', 'Library'),
+        ]);
+    }
+}
+
+$client = Client::builder()
+    ->setCapabilities(new ClientCapabilities(roots: true, rootsListChanged: true))
+    ->addRequestHandler(new ListRootsRequestHandler(new WorkspaceRootsCallback))
+    ->build();
+```
+
+When the client's roots change, notify the server so it can request the updated
+list via `roots/list`. This requires advertising the `roots.listChanged`
+capability (`rootsListChanged: true` above); otherwise `sendRootsListChanged()`
+throws a `RuntimeException`. On a client that is not connected it throws a
+`ConnectionException`:
+
+```php
+$client->sendRootsListChanged();
+```
+
+See `examples/client/stdio_roots.php` for a runnable example: it calls the
+`inspect_workspace_roots` tool of the client-communication demo server, which
+answers by issuing the `roots/list` request back to the client.
+
 ## Error Handling
 
 The client throws exceptions for various error conditions:

examples/client/stdio_roots.php

@@ -0,0 +1,85 @@
+<?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.
+ */
+
+/**
+ * STDIO Roots Example.
+ *
+ * This example demonstrates the "roots" client capability:
+ * - The client advertises the `roots` capability during initialization.
+ * - It answers server `roots/list` requests via a RootsCallbackInterface,
+ *   exposing a couple of `file://` workspace folders.
+ * - Calling the server's `inspect_workspace_roots` tool makes the server issue
+ *   a `roots/list` request, so the handler below actually runs.
+ * - It notifies the server when its list of roots changes.
+ *
+ * Usage: php examples/client/stdio_roots.php
+ */
+
+require_once __DIR__.'/../../vendor/autoload.php';
+
+use Mcp\Client;
+use Mcp\Client\Handler\Request\ListRootsRequestHandler;
+use Mcp\Client\Handler\Request\RootsCallbackInterface;
+use Mcp\Client\Transport\StdioTransport;
+use Mcp\Schema\ClientCapabilities;
+use Mcp\Schema\Content\TextContent;
+use Mcp\Schema\Request\ListRootsRequest;
+use Mcp\Schema\Result\ListRootsResult;
+use Mcp\Schema\Root;
+
+$rootsRequestHandler = new ListRootsRequestHandler(new class implements RootsCallbackInterface {
+    public function __invoke(ListRootsRequest $request): ListRootsResult
+    {
+        echo "[ROOTS] Server requested the client's list of roots\n";
+
+        return new ListRootsResult([
+            new Root('file:///home/user/projects/app', 'Application'),
+            new Root('file:///home/user/projects/library', 'Library'),
+        ]);
+    }
+});
+
+$client = Client::builder()
+    ->setClientInfo('STDIO Roots Test', '1.0.0')
+    ->setInitTimeout(30)
+    ->setRequestTimeout(120)
+    ->setCapabilities(new ClientCapabilities(roots: true, rootsListChanged: true))
+    ->addRequestHandler($rootsRequestHandler)
+    ->build();
+
+$transport = new StdioTransport(
+    command: 'php',
+    args: [__DIR__.'/../server/client-communication/server.php'],
+);
+
+echo "Connecting to MCP server...\n";
+$client->connect($transport);
+
+$serverInfo = $client->getServerInfo();
+echo 'Connected to: '.($serverInfo->name ?? 'unknown')."\n\n";
+
+// The server tool asks the client for its roots, which triggers the handler above.
+echo "Calling 'inspect_workspace_roots'...\n";
+$result = $client->callTool(name: 'inspect_workspace_roots');
+
+echo "\nResult:\n";
+foreach ($result->content as $content) {
+    if ($content instanceof TextContent) {
+        echo $content->text."\n";
+    }
+}
+
+// Whenever the client's workspace folders change, notify the server so it can
+// request an updated list via roots/list.
+echo "\nNotifying the server that the roots list changed...\n";
+$client->sendRootsListChanged();
+
+$client->disconnect();

examples/server/client-communication/ClientAwareService.php

@@ -25,6 +25,42 @@ public function __construct(
         $this->logger->info('SamplingTool instantiated for sampling example.');
     }
 
+    /**
+     * Ask the client which workspace folders the server is allowed to operate on.
+     *
+     * Demonstrates the server side of the "roots" client capability: the tool
+     * issues a roots/list request that the client answers from its own handler.
+     *
+     * @return array{status: string, message: string, roots?: list<array{uri: string, name: string|null}>}
+     */
+    #[McpTool(name: 'inspect_workspace_roots', description: 'Ask the client for its workspace roots via a roots/list request.')]
+    public function inspectWorkspaceRoots(RequestContext $context): array
+    {
+        $clientGateway = $context->getClientGateway();
+
+        if (!$clientGateway->supportsRoots()) {
+            return [
+                'status' => 'unsupported',
+                'message' => 'Client does not expose roots. Advertise the "roots" capability and register a ListRootsRequestHandler to let the server discover your workspace folders.',
+            ];
+        }
+
+        $result = $clientGateway->listRoots();
+
+        $roots = [];
+        foreach ($result->roots as $root) {
+            $roots[] = ['uri' => $root->uri, 'name' => $root->name];
+        }
+
+        $clientGateway->log(LoggingLevel::Info, \sprintf('Client exposed %d root(s).', \count($roots)));
+
+        return [
+            'status' => 'ok',
+            'message' => \sprintf('Client exposed %d root(s).', \count($roots)),
+            'roots' => $roots,
+        ];
+    }
+
     /**
      * @return array{incident: string, recommended_actions: string, model: string}
      */

src/Client.php

@@ -17,11 +17,13 @@
 use Mcp\Client\Transport\TransportInterface;
 use Mcp\Exception\ConnectionException;
 use Mcp\Exception\RequestException;
+use Mcp\Exception\RuntimeException;
 use Mcp\Schema\Enum\LoggingLevel;
 use Mcp\Schema\Implementation;
 use Mcp\Schema\JsonRpc\Error;
 use Mcp\Schema\JsonRpc\Request;
 use Mcp\Schema\JsonRpc\Response;
+use Mcp\Schema\Notification\RootsListChangedNotification;
 use Mcp\Schema\PromptReference;
 use Mcp\Schema\Request\CallToolRequest;
 use Mcp\Schema\Request\CompletionCompleteRequest;
@@ -244,6 +246,27 @@ public function setLoggingLevel(LoggingLevel $level): void
         $this->sendRequest($request);
     }
 
+    /**
+     * Notify the server that the client's list of roots has changed.
+     *
+     * The server should react by requesting an updated list via roots/list.
+     *
+     * @throws RuntimeException    if the client did not advertise the `roots.listChanged` capability
+     * @throws ConnectionException if the client is not connected
+     */
+    public function sendRootsListChanged(): void
+    {
+        if (true !== $this->config->capabilities->rootsListChanged) {
+            throw new RuntimeException('Cannot send a "roots/list_changed" notification without advertising the "roots.listChanged" capability. Build the client with new ClientCapabilities(roots: true, rootsListChanged: true).');
+        }
+
+        if (!$this->isConnected()) {
+            throw new ConnectionException('Client is not connected. Call connect() first.');
+        }
+
+        $this->protocol->sendNotification(new RootsListChangedNotification());
+    }
+
     /**
      * Send a request to the server and wait for response.
      *

src/Client/Handler/Request/ListRootsRequestHandler.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\Client\Handler\Request;
+
+use Mcp\Exception\RootsException;
+use Mcp\Schema\JsonRpc\Error;
+use Mcp\Schema\JsonRpc\Request;
+use Mcp\Schema\JsonRpc\Response;
+use Mcp\Schema\Request\ListRootsRequest;
+use Mcp\Schema\Result\ListRootsResult;
+use Psr\Log\LoggerInterface;
+use Psr\Log\NullLogger;
+
+/**
+ * Handler for roots/list requests from the server.
+ *
+ * The MCP server may ask the client for the list of filesystem roots (its
+ * "workspace folders"). This handler wraps a user-provided callback that returns
+ * the roots the client wishes to expose.
+ *
+ * @implements RequestHandlerInterface<ListRootsResult>
+ *
+ * @author Johannes Wachter <johannes@sulu.io>
+ */
+class ListRootsRequestHandler implements RequestHandlerInterface
+{
+    public function __construct(
+        private readonly RootsCallbackInterface $callback,
+        private readonly LoggerInterface $logger = new NullLogger(),
+    ) {
+    }
+
+    public function supports(Request $request): bool
+    {
+        return $request instanceof ListRootsRequest;
+    }
+
+    /**
+     * @return Response<ListRootsResult>|Error
+     */
+    public function handle(Request $request): Response|Error
+    {
+        \assert($request instanceof ListRootsRequest);
+
+        try {
+            $result = $this->callback->__invoke($request);
+
+            return new Response($request->getId(), $result);
+        } catch (RootsException $e) {
+            $this->logger->error('Listing roots failed: '.$e->getMessage(), ['exception' => $e]);
+
+            return Error::forInternalError($e->getMessage(), $request->getId());
+        } catch (\Throwable $e) {
+            $this->logger->error('Unexpected error while listing roots', ['exception' => $e]);
+
+            return Error::forInternalError('Error while listing roots', $request->getId());
+        }
+    }
+}

src/Client/Handler/Request/RootsCallbackInterface.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\Client\Handler\Request;
+
+use Mcp\Schema\Request\ListRootsRequest;
+use Mcp\Schema\Result\ListRootsResult;
+
+/**
+ * Contract for callbacks used by ListRootsRequestHandler.
+ *
+ * Implementations return the list of filesystem roots the client exposes when
+ * requested by the server.
+ *
+ * @author Johannes Wachter <johannes@sulu.io>
+ */
+interface RootsCallbackInterface
+{
+    public function __invoke(ListRootsRequest $request): ListRootsResult;
+}

src/Exception/RootsException.php

@@ -0,0 +1,24 @@
+<?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\Exception;
+
+/**
+ * Exception thrown when listing roots fails.
+ *
+ * When thrown from a roots callback, this exception's message will be
+ * included in the error response sent back to the server.
+ *
+ * @author Johannes Wachter <johannes@sulu.io>
+ */
+final class RootsException extends \RuntimeException implements ExceptionInterface
+{
+}