fix(mcp): fix ignored output format

src/Mcp/State/StructuredContentProcessor.php

@@ -54,7 +54,11 @@ public function process(mixed $data, Operation $operation, array $uriVariables =
         $request = $context['request'] ?? null;
         $context['original_data'] = $result;
         $class = $operation->getClass();
-        $includeStructuredContent = $operation instanceof McpTool || $operation instanceof McpResource ? $operation->getStructuredContent() ?? true : false;
+        $isMcpOperation = $operation instanceof McpTool || $operation instanceof McpResource;
+        $includeStructuredContent = $isMcpOperation ? $operation->getStructuredContent() ?? true : false;
+        // Only an HttpOperation carries formats, and the base Operation type does not
+        // declare getOutputFormats().
+        $outputFormats = $isMcpOperation ? $operation->getOutputFormats() ?? [] : [];
         $structuredContent = null;
 
         if ($request && $this->serializer instanceof NormalizerInterface && $this->serializer instanceof EncoderInterface) {
@@ -63,7 +67,7 @@ public function process(mixed $data, Operation $operation, array $uriVariables =
                 'operation' => $operation,
             ]);
             $serializerContext['uri_variables'] = $uriVariables;
-            $format = $request->getRequestFormat('') ?: 'jsonld';
+            $format = $outputFormats ? array_key_first($outputFormats) : ($request->getRequestFormat('') ?: 'jsonld');
             $normalized = $this->serializer->normalize($result, $format, $serializerContext);
             $result = $this->serializer->encode($normalized, $format, $serializerContext);
 

src/Metadata/Resource/Factory/FormatsResourceMetadataCollectionFactory.php

@@ -75,9 +75,22 @@ public function create(string $resourceClass): ResourceMetadataCollection
                 $mcpFormats = [$this->mcpFormat => $this->formats[$this->mcpFormat]];
                 $newMcp = [];
                 foreach ($mcp as $key => $operation) {
-                    if (($operation instanceof McpTool || $operation instanceof McpResource) && null === $operation->getFormats() && null === $operation->getInputFormats() && null === $operation->getOutputFormats()) {
-                        $operation = $operation->withInputFormats($mcpFormats)->withOutputFormats($mcpFormats);
+                    if (!$operation instanceof McpTool && !$operation instanceof McpResource) {
+                        $newMcp[$key] = $operation;
+                        continue;
                     }
+
+                    // Same normalization as HTTP operations get in normalize(), with the
+                    // MCP format standing in for the resource-level defaults: without it a
+                    // format declared as a list (["json"]) would never be resolved against
+                    // api_platform.formats and would stay as [0 => "json"].
+                    if ($operation->getFormats()) {
+                        $operation = $operation->withFormats($this->normalizeFormats($operation->getFormats()));
+                    }
+
+                    $operation = $operation->withInputFormats($operation->getInputFormats() ? $this->normalizeFormats($operation->getInputFormats()) : $operation->getFormats() ?? $mcpFormats);
+                    $operation = $operation->withOutputFormats($operation->getOutputFormats() ? $this->normalizeFormats($operation->getOutputFormats()) : $operation->getFormats() ?? $mcpFormats);
+
                     $newMcp[$key] = $operation;
                 }
                 $resourceMetadataCollection[$index] = $resourceMetadataCollection[$index]->withMcp($newMcp);

tests/Fixtures/TestBundle/ApiResource/McpFormatListTool.php

@@ -0,0 +1,52 @@
+<?php
+
+/*
+ * This file is part of the API Platform project.
+ *
+ * (c) Kévin Dunglas <dunglas@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace ApiPlatform\Tests\Fixtures\TestBundle\ApiResource;
+
+use ApiPlatform\Metadata\McpTool;
+
+/**
+ * Reproducer fixture: a tool declaring its format as a LIST rather than a map.
+ *
+ * `['json']` means "reuse the already configured `json` format", and every HTTP operation
+ * gets it resolved to `['json' => ['application/json']]` by normalizeFormats(). MCP
+ * operations used to skip that normalization entirely, leaving `[0 => 'json']`.
+ */
+#[McpTool(
+    name: 'format_message_list',
+    description: 'Echo a message, with the output format declared as a list',
+    outputFormats: ['json'],
+    processor: [McpFormatListTool::class, 'process'],
+)]
+class McpFormatListTool
+{
+    public function __construct(
+        private string $message = '',
+    ) {
+    }
+
+    public function getMessage(): string
+    {
+        return $this->message;
+    }
+
+    public function setMessage(string $message): void
+    {
+        $this->message = $message;
+    }
+
+    public static function process($data): mixed
+    {
+        return $data;
+    }
+}

tests/Fixtures/TestBundle/ApiResource/McpFormatTool.php

@@ -0,0 +1,54 @@
+<?php
+
+/*
+ * This file is part of the API Platform project.
+ *
+ * (c) Kévin Dunglas <dunglas@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace ApiPlatform\Tests\Fixtures\TestBundle\ApiResource;
+
+use ApiPlatform\Metadata\McpTool;
+
+/**
+ * Reproducer fixture: a tool that explicitly asks for the `json` format.
+ *
+ * `api_platform.mcp.format` is applied by FormatsResourceMetadataCollectionFactory as
+ * `$operation->withInputFormats(...)->withOutputFormats(...)`, i.e. the global option is
+ * implemented by writing the operation's own formats. Declaring them here therefore
+ * exercises the same code path as the global option, without touching the test app's
+ * shared configuration.
+ */
+#[McpTool(
+    name: 'format_message',
+    description: 'Echo a message, serialized with the format declared on the operation',
+    outputFormats: ['json' => ['application/json']],
+    processor: [McpFormatTool::class, 'process'],
+)]
+class McpFormatTool
+{
+    public function __construct(
+        private string $message = '',
+    ) {
+    }
+
+    public function getMessage(): string
+    {
+        return $this->message;
+    }
+
+    public function setMessage(string $message): void
+    {
+        $this->message = $message;
+    }
+
+    public static function process($data): mixed
+    {
+        return $data;
+    }
+}

tests/Functional/McpFormatTest.php

@@ -0,0 +1,224 @@
+<?php
+
+/*
+ * This file is part of the API Platform project.
+ *
+ * (c) Kévin Dunglas <dunglas@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace ApiPlatform\Tests\Functional;
+
+use ApiPlatform\Metadata\Resource\Factory\ResourceMetadataCollectionFactoryInterface;
+use ApiPlatform\Symfony\Bundle\Test\ApiTestCase;
+use ApiPlatform\Tests\Fixtures\TestBundle\ApiResource\McpFormatListTool;
+use ApiPlatform\Tests\Fixtures\TestBundle\ApiResource\McpFormatTool;
+use ApiPlatform\Tests\RecreateSchemaTrait;
+use ApiPlatform\Tests\SetupClassResourcesTrait;
+use Symfony\AI\McpBundle\McpBundle;
+
+/**
+ * Reproducer: the format configured for an MCP operation has no effect on its output.
+ *
+ * `ApiPlatform\Mcp\State\StructuredContentProcessor::process()` serializes with
+ *
+ *     $format = $request->getRequestFormat('') ?: 'jsonld';
+ *
+ * and never reads `$operation->getOutputFormats()`, although `$operation` is in scope and
+ * `FormatsResourceMetadataCollectionFactory` has populated it. The MCP route carries no
+ * `_format` placeholder or default either, so `getRequestFormat()` is always empty and
+ * the expression is a constant `'jsonld'` on every call.
+ *
+ * This also covers `api_platform.mcp.format`: that option is implemented by writing the
+ * operation's own formats, so it travels through the very same getter.
+ */
+class McpFormatTest extends ApiTestCase
+{
+    use RecreateSchemaTrait;
+    use SetupClassResourcesTrait;
+
+    protected static ?bool $alwaysBootKernel = false;
+
+    /**
+     * @return class-string[]
+     */
+    public static function getResources(): array
+    {
+        return [McpFormatTool::class, McpFormatListTool::class];
+    }
+
+    public function testAFormatDeclaredAsAListIsResolved(): void
+    {
+        $this->skipUnlessMcpIsUsable();
+
+        $client = self::createClient();
+
+        /** @var ResourceMetadataCollectionFactoryInterface $factory */
+        $factory = self::getContainer()->get('api_platform.metadata.resource.metadata_collection_factory');
+
+        $outputFormats = null;
+        foreach ($factory->create(McpFormatListTool::class) as $resource) {
+            foreach ($resource->getMcp() ?? [] as $name => $operation) {
+                if ('format_message_list' === $name) {
+                    $outputFormats = $operation->getOutputFormats();
+                }
+            }
+        }
+
+        self::assertSame(
+            ['json' => ['application/json']],
+            $outputFormats,
+            'A list form such as ["json"] must be resolved against api_platform.formats, '.
+            'exactly as normalizeFormats() does for every HTTP operation.',
+        );
+
+        $sessionId = $this->initializeMcpSession($client);
+        $res = $this->callTool($client, $sessionId, 'format_message_list', ['message' => 'hello']);
+
+        self::assertResponseIsSuccessful();
+        $result = $res->toArray(false);
+        self::assertArrayNotHasKey('error', $result, 'MCP error: '.json_encode($result['error'] ?? null));
+        self::assertStringNotContainsString('@context', (string) ($result['result']['content'][0]['text'] ?? ''));
+    }
+
+    public function testTheOperationMetadataCarriesTheDeclaredFormat(): void
+    {
+        $this->skipUnlessMcpIsUsable();
+
+        self::createClient();
+
+        /** @var ResourceMetadataCollectionFactoryInterface $factory */
+        $factory = self::getContainer()->get('api_platform.metadata.resource.metadata_collection_factory');
+
+        $outputFormats = null;
+        foreach ($factory->create(McpFormatTool::class) as $resource) {
+            foreach ($resource->getMcp() ?? [] as $name => $operation) {
+                if ('format_message' === $name) {
+                    $outputFormats = $operation->getOutputFormats();
+                }
+            }
+        }
+
+        self::assertSame(
+            ['json' => ['application/json']],
+            $outputFormats,
+            'Precondition: the metadata layer honours the declared format.',
+        );
+    }
+
+    public function testTheOutputHonoursTheDeclaredFormat(): void
+    {
+        $this->skipUnlessMcpIsUsable();
+
+        $client = self::createClient();
+        $sessionId = $this->initializeMcpSession($client);
+
+        $res = $this->callTool($client, $sessionId, 'format_message', ['message' => 'hello']);
+
+        self::assertResponseIsSuccessful();
+        $result = $res->toArray(false);
+        self::assertArrayNotHasKey('error', $result, 'MCP error: '.json_encode($result['error'] ?? null));
+
+        $text = $result['result']['content'][0]['text'] ?? null;
+        self::assertNotNull($text);
+
+        self::assertStringNotContainsString(
+            '@context',
+            $text,
+            'The tool declares the "json" output format but the payload is JSON-LD: '.
+            'StructuredContentProcessor ignores $operation->getOutputFormats().',
+        );
+    }
+
+    public function testStructuredContentHonoursTheDeclaredFormatToo(): void
+    {
+        $this->skipUnlessMcpIsUsable();
+
+        $client = self::createClient();
+        $sessionId = $this->initializeMcpSession($client);
+
+        $res = $this->callTool($client, $sessionId, 'format_message', ['message' => 'hello']);
+
+        $structured = $res->toArray(false)['result']['structuredContent'] ?? [];
+
+        self::assertArrayNotHasKey(
+            '@context',
+            $structured,
+            'structuredContent carries the JSON-LD envelope as well: it is normalized with the same format.',
+        );
+    }
+
+    private function skipUnlessMcpIsUsable(): void
+    {
+        if (!class_exists(McpBundle::class)) {
+            $this->markTestSkipped('MCP bundle is not installed');
+        }
+
+        // The MongoDB test app loads routing_mongodb.yml, which — unlike every other
+        // environment — does not import routing_test.php and therefore has no /mcp
+        // route. McpTest skips for the same reason.
+        if ($this->isMongoDB()) {
+            $this->markTestSkipped('MCP is not supported with MongoDB');
+        }
+
+        try {
+            if (!class_exists('Http\Discovery\Psr17FactoryDiscovery')) {
+                $this->markTestSkipped('PSR-17 HTTP factory implementation not available (required for MCP)');
+            }
+
+            \Http\Discovery\Psr17FactoryDiscovery::findServerRequestFactory();
+        } catch (\Throwable) {
+            $this->markTestSkipped('PSR-17 HTTP factory implementation not available (required for MCP)');
+        }
+    }
+
+    private function initializeMcpSession($client): string
+    {
+        $res = $client->request('POST', '/mcp', [
+            'headers' => [
+                'Accept' => 'application/json, text/event-stream',
+                'Content-Type' => 'application/json',
+            ],
+            'json' => [
+                'jsonrpc' => '2.0',
+                'id' => 1,
+                'method' => 'initialize',
+                'params' => [
+                    'protocolVersion' => '2024-11-05',
+                    'clientInfo' => ['name' => 'ApiPlatform Test Suite', 'version' => '1.0'],
+                    'capabilities' => [],
+                ],
+            ],
+        ]);
+        self::assertResponseIsSuccessful();
+
+        return $res->getHeaders()['mcp-session-id'][0];
+    }
+
+    /**
+     * @param array<string, mixed> $arguments
+     */
+    private function callTool($client, string $sessionId, string $toolName, array $arguments = [])
+    {
+        return $client->request('POST', '/mcp', [
+            'headers' => [
+                'Accept' => 'application/json, text/event-stream',
+                'Content-Type' => 'application/json',
+                'mcp-session-id' => $sessionId,
+            ],
+            'json' => [
+                'jsonrpc' => '2.0',
+                'id' => 2,
+                'method' => 'tools/call',
+                'params' => [
+                    'name' => $toolName,
+                    'arguments' => $arguments,
+                ],
+            ],
+        ]);
+    }
+}