[Client] Fill elicitation defaults when accepting

CHANGELOG.md

@@ -17,6 +17,8 @@ All notable changes to `mcp/sdk` will be documented in this file.
 * [BC Break] Validate a tool result's `structuredContent` against the tool's `outputSchema`, which the specification requires the server to honour. A mismatch is answered with a `CallToolResult` carrying `isError: true` instead of the non-conforming value, matching the TypeScript, Python and Java SDKs. Skipped when the tool declares no `outputSchema`, when the result carries no `structuredContent`, and when the result is already an error.
 * Stop the server `Protocol` from logging full JSON-RPC payloads (tool arguments, client replies) at info level: info records now carry only the method and id, the raw message is logged at debug level.
 * Add `PassthroughMiddleware` to opt `StreamableHttpTransport` out of its default middleware without the warning an empty `$middleware` list logs.
+* Add `ElicitationSchema::getDefaults()`, returning the declared `default` of each field to accept a form elicitation with.
+* [BC Break] `AbstractSchemaDefinition` declares an abstract `getDefault()`, which a custom schema definition has to implement.
 
 0.8.0
 -----

src/Schema/Elicitation/AbstractSchemaDefinition.php

@@ -60,6 +60,11 @@ protected function buildBaseJson(string $type): array
         return $data;
     }
 
+    /**
+     * The value the field is pre-filled with, or null when it declares none.
+     */
+    abstract public function getDefault(): mixed;
+
     /**
      * @return array<string, mixed>
      */

src/Schema/Elicitation/BooleanSchemaDefinition.php

@@ -49,6 +49,11 @@ public static function fromArray(array $data): self
         );
     }
 
+    public function getDefault(): ?bool
+    {
+        return $this->default;
+    }
+
     /**
      * @return array{
      *     type: string,

src/Schema/Elicitation/ElicitationSchema.php

@@ -133,6 +133,24 @@ private static function resolveArrayType(array $data): AbstractSchemaDefinition
         throw new InvalidArgumentException('Array type must have "items" with either "enum" or "anyOf".');
     }
 
+    /**
+     * The declared default of each field that has one, keyed by field name.
+     *
+     * @return array<string, mixed>
+     */
+    public function getDefaults(): array
+    {
+        $defaults = [];
+
+        foreach ($this->properties as $name => $property) {
+            if (null !== $default = $property->getDefault()) {
+                $defaults[$name] = $default;
+            }
+        }
+
+        return $defaults;
+    }
+
     /**
      * @return array{
      *     type: string,

src/Schema/Elicitation/EnumSchemaDefinition.php

@@ -83,6 +83,11 @@ enumNames: $data['enumNames'] ?? null,
         );
     }
 
+    public function getDefault(): ?string
+    {
+        return $this->default;
+    }
+
     /**
      * @return array{
      *     type: string,

src/Schema/Elicitation/MultiSelectEnumSchemaDefinition.php

@@ -99,6 +99,14 @@ enum: $data['items']['enum'],
         );
     }
 
+    /**
+     * @return string[]|null
+     */
+    public function getDefault(): ?array
+    {
+        return $this->default;
+    }
+
     /**
      * @return array<string, mixed>
      */

src/Schema/Elicitation/NumberSchemaDefinition.php

@@ -84,6 +84,11 @@ public static function fromArray(array $data): self
         );
     }
 
+    public function getDefault(): int|float|null
+    {
+        return $this->default;
+    }
+
     /**
      * @return array{
      *     type: string,

src/Schema/Elicitation/StringSchemaDefinition.php

@@ -83,6 +83,11 @@ public static function fromArray(array $data): self
         );
     }
 
+    public function getDefault(): ?string
+    {
+        return $this->default;
+    }
+
     /**
      * @return array{
      *     type: string,

src/Schema/Elicitation/TitledEnumSchemaDefinition.php

@@ -81,6 +81,11 @@ public static function fromArray(array $data): self
         );
     }
 
+    public function getDefault(): ?string
+    {
+        return $this->default;
+    }
+
     /**
      * @return array<string, mixed>
      */

src/Schema/Elicitation/TitledMultiSelectEnumSchemaDefinition.php

@@ -104,6 +104,14 @@ public static function fromArray(array $data): self
         );
     }
 
+    /**
+     * @return string[]|null
+     */
+    public function getDefault(): ?array
+    {
+        return $this->default;
+    }
+
     /**
      * @return array<string, mixed>
      */

tests/Conformance/client.php

@@ -52,10 +52,9 @@
     ->setLogger($logger);
 
 /**
- * Accepts every elicitation with an empty payload.
+ * Accepts every form elicitation with its declared defaults.
  *
- * Enough for the scenarios here, which check that the client asked and echoed
- * correctly rather than what a user would have typed.
+ * A url-mode elicitation has no schema to fill, so it is declined.
  */
 $acceptElicitation = new class($logger) implements RequestHandlerInterface {
     public function __construct(private readonly Psr\Log\LoggerInterface $logger)
@@ -69,9 +68,16 @@ public function supports(Request $request): bool
 
     public function handle(Request $request): Response
     {
-        $this->logger->info('Received elicitation request, accepting with empty content');
+        if (!$request instanceof ElicitRequest || null === $request->requestedSchema) {
+            $this->logger->info('Received elicitation request without a schema, declining');
 
-        return new Response($request->getId(), new ElicitResult(ElicitAction::Accept, []));
+            return new Response($request->getId(), new ElicitResult(ElicitAction::Decline));
+        }
+
+        $content = $request->requestedSchema->getDefaults();
+        $this->logger->info(sprintf('Received elicitation request, accepting with %d defaults', count($content)));
+
+        return new Response($request->getId(), new ElicitResult(ElicitAction::Accept, $content));
     }
 };
 

tests/Unit/Schema/Elicitation/ElicitationSchemaTest.php

@@ -67,6 +67,58 @@ public function testConstructorWithMultipleTypes(): void
         $this->assertInstanceOf(EnumSchemaDefinition::class, $schema->properties['rating']);
     }
 
+    public function testGetDefaults(): void
+    {
+        $schema = ElicitationSchema::fromArray([
+            'type' => 'object',
+            'properties' => [
+                'name' => ['type' => 'string', 'title' => 'Name', 'default' => 'Ada'],
+                'age' => ['type' => 'integer', 'title' => 'Age', 'default' => 0],
+                'score' => ['type' => 'number', 'title' => 'Score', 'default' => 95.5],
+                'color' => ['type' => 'string', 'title' => 'Color', 'enum' => ['red', 'blue'], 'default' => 'blue'],
+                'plan' => [
+                    'type' => 'string',
+                    'title' => 'Plan',
+                    'oneOf' => [
+                        ['const' => 'free', 'title' => 'Free'],
+                        ['const' => 'pro', 'title' => 'Pro'],
+                    ],
+                    'default' => 'pro',
+                ],
+                'subscribe' => ['type' => 'boolean', 'title' => 'Subscribe', 'default' => false],
+                'tags' => [
+                    'type' => 'array',
+                    'title' => 'Tags',
+                    'items' => ['type' => 'string', 'enum' => ['php', 'mcp']],
+                    'default' => ['php'],
+                ],
+                'channels' => [
+                    'type' => 'array',
+                    'title' => 'Channels',
+                    'items' => [
+                        'anyOf' => [
+                            ['const' => 'mail', 'title' => 'Mail'],
+                            ['const' => 'sms', 'title' => 'SMS'],
+                        ],
+                    ],
+                    'default' => ['mail', 'sms'],
+                ],
+                'withoutDefault' => ['type' => 'string', 'title' => 'Without default'],
+            ],
+        ]);
+
+        $this->assertSame([
+            'name' => 'Ada',
+            'age' => 0,
+            'score' => 95.5,
+            'color' => 'blue',
+            'plan' => 'pro',
+            'subscribe' => false,
+            'tags' => ['php'],
+            'channels' => ['mail', 'sms'],
+        ], $schema->getDefaults());
+    }
+
     public function testConstructorWithEmptyProperties(): void
     {
         $this->expectException(InvalidArgumentException::class);