[Server] Fix result lists being sent as JSON objects

CHANGELOG.md

@@ -15,6 +15,7 @@ All notable changes to `mcp/sdk` will be documented in this file.
 * Fix `Psr16NotificationBus` subscribers missing the notifications published after the bus stayed quiet for longer than its TTL: the sequence counter no longer expires, and a subscriber whose cursor is ahead of a lost counter reads what the bus holds.
 * Fix `Session::save()` wiping the other keys of a session that the store failed to read, e.g. when `Psr16SessionStore` hits a cache error: it now returns `false` instead of writing the changed keys alone.
 * Fix `EnumCompletionProvider` and `ListCompletionProvider` offering all values for the prefix `"0"` instead of only the values that start with it.
+* Fix tools, prompts and resources sending `content`, `messages` and `contents` as a JSON object instead of an array when the handler returned a non-list array, e.g. the result of `array_filter()`. Named keys in nested results of mixed arrays no longer overwrite each other.
 * Add `Psr6SessionStore` and `Psr6NotificationBus`, which work like `Psr16SessionStore` and `Psr16NotificationBus` over a PSR-6 cache pool. `Builder::setDiscovery()` also accepts a PSR-6 pool as `$cache`.
 
 ### Client

phpstan-baseline.neon

@@ -1,7 +1,2 @@
 parameters:
 	ignoreErrors:
-		-
-			message: '#^Method Mcp\\Schema\\Result\\ReadResourceResult\:\:jsonSerialize\(\) should return array\{contents\: array\<Mcp\\Schema\\Content\\BlobResourceContents\|Mcp\\Schema\\Content\\TextResourceContents\>, ttlMs\?\: int, cacheScope\?\: string\} but returns array\{contents\: array\<Mcp\\Schema\\Content\\ResourceContents\>, ttlMs\?\: int\<0, max\>, cacheScope\?\: ''private''\|''public''\}\.$#'
-			identifier: return.type
-			count: 1
-			path: src/Schema/Result/ReadResourceResult.php

src/Capability/Formatter/PromptResultFormatter.php

@@ -74,12 +74,8 @@ public function format(mixed $promptGenerationResult): array
                     if ($item instanceof PromptMessage) {
                         $result[] = $item;
                     } else {
-                        foreach ($this->format($item) as $key => $message) {
-                            if (\is_int($key)) {
-                                $result[] = $message;
-                            } else {
-                                $result[$key] = $message;
-                            }
+                        foreach ($this->format($item) as $message) {
+                            $result[] = $message;
                         }
                     }
                 }

src/Capability/Formatter/ResourceResultFormatter.php

@@ -97,12 +97,8 @@ public function format(mixed $readResult, string $uri, ?string $mimeType = null,
                     } elseif ($item instanceof EmbeddedResource) {
                         $result[] = $item->resource;
                     } else {
-                        foreach ($this->format($item, $uri, $mimeType, $meta) as $key => $content) {
-                            if (\is_int($key)) {
-                                $result[] = $content;
-                            } else {
-                                $result[$key] = $content;
-                            }
+                        foreach ($this->format($item, $uri, $mimeType, $meta) as $content) {
+                            $result[] = $content;
                         }
                     }
                 }

src/Capability/Formatter/ToolResultFormatter.php

@@ -73,7 +73,9 @@ public function format(mixed $toolExecutionResult): array
                     if ($item instanceof Content) {
                         $result[] = $item;
                     } else {
-                        $result = array_merge($result, $this->format($item));
+                        foreach ($this->format($item) as $content) {
+                            $result[] = $content;
+                        }
                     }
                 }
 

src/Schema/Result/CallToolResult.php

@@ -130,7 +130,7 @@ public static function fromArray(array $data): self
 
     /**
      * @return array{
-     *     content: array<mixed>,
+     *     content: list<mixed>,
      *     isError: bool,
      *     structuredContent?: mixed,
      *     _meta?: array<string, mixed>,
@@ -139,7 +139,7 @@ public static function fromArray(array $data): self
     public function jsonSerialize(): array
     {
         $result = [
-            'content' => $this->content,
+            'content' => array_values($this->content),
             'isError' => $this->isError,
         ];
 

src/Schema/Result/GetPromptResult.php

@@ -69,14 +69,14 @@ public static function fromArray(array $data): self
 
     /**
      * @return array{
-     *     messages: array<PromptMessage>,
+     *     messages: list<PromptMessage>,
      *     description?: string,
      * }
      */
     public function jsonSerialize(): array
     {
         $result = [
-            'messages' => $this->messages,
+            'messages' => array_values($this->messages),
         ];
 
         if (null !== $this->description) {

src/Schema/Result/ReadResourceResult.php

@@ -79,14 +79,14 @@ public static function fromArray(array $data): self
 
     /**
      * @return array{
-     *     contents: array<BlobResourceContents|TextResourceContents>,
+     *     contents: list<ResourceContents>,
      *     ttlMs?: int,
      *     cacheScope?: string,
      * }
      */
     public function jsonSerialize(): array
     {
-        $data = ['contents' => $this->contents];
+        $data = ['contents' => array_values($this->contents)];
 
         // Only what this result actually decided; the wire codec fills the rest
         // from policy, and an absent member is the signal for it to do so.

tests/Unit/Capability/Formatter/PromptResultFormatterTest.php

@@ -24,7 +24,7 @@
 
 class PromptResultFormatterTest extends TestCase
 {
-    public function testMixedMessagesPreserveNestedKeysAndOrder(): void
+    public function testMixedMessagesAreFlattenedInOrder(): void
     {
         $first = new PromptMessage(Role::User, new TextContent('first'));
         $second = new PromptMessage(Role::Assistant, new TextContent('second'));
@@ -36,11 +36,7 @@ public function testMixedMessagesPreserveNestedKeysAndOrder(): void
             ['named' => $third, 5 => $second],
         ]);
 
-        $this->assertSame([0, 'named', 1, 2], array_keys($result));
-        $this->assertSame($first, $result[0]);
-        $this->assertSame($third, $result['named']);
-        $this->assertSame($first, $result[1]);
-        $this->assertSame($second, $result[2]);
+        $this->assertSame([$first, $second, $first, $third, $second], $result);
     }
 
     public function testFormatPromptMessage(): void

tests/Unit/Capability/Formatter/ResourceResultFormatterTest.php

@@ -17,7 +17,7 @@
 
 class ResourceResultFormatterTest extends TestCase
 {
-    public function testMixedResourcesPreserveNestedKeysAndOrder(): void
+    public function testMixedResourcesAreFlattenedInOrder(): void
     {
         $first = new TextResourceContents('file://test', 'text/plain', 'first');
         $second = new TextResourceContents('file://test', 'text/plain', 'second');
@@ -29,11 +29,7 @@ public function testMixedResourcesPreserveNestedKeysAndOrder(): void
             ['named' => $third, 5 => $second],
         ], 'file://test');
 
-        $this->assertSame([0, 'named', 1, 2], array_keys($result));
-        $this->assertSame($first, $result[0]);
-        $this->assertSame($third, $result['named']);
-        $this->assertSame($first, $result[1]);
-        $this->assertSame($second, $result[2]);
+        $this->assertSame([$first, $second, $first, $third, $second], $result);
     }
 
     public function testFormatStringResult(): void

tests/Unit/Capability/Formatter/ToolResultFormatterTest.php

@@ -17,6 +17,21 @@
 
 class ToolResultFormatterTest extends TestCase
 {
+    public function testMixedContentIsFlattenedInOrder(): void
+    {
+        $first = new TextContent('first');
+        $second = new TextContent('second');
+        $third = new TextContent('third');
+
+        $result = (new ToolResultFormatter())->format([
+            $first,
+            ['named' => $second, 8 => $first],
+            ['named' => $third, 5 => $second],
+        ]);
+
+        $this->assertSame([$first, $second, $first, $third, $second], $result);
+    }
+
     public function testFormatStringResult(): void
     {
         $result = (new ToolResultFormatter())->format('hello');

tests/Unit/Schema/Result/CallToolResultTest.php

@@ -18,10 +18,26 @@
 use Mcp\Schema\Content\ResourceLink;
 use Mcp\Schema\Content\TextContent;
 use Mcp\Schema\Result\CallToolResult;
+use PHPUnit\Framework\Attributes\TestWith;
 use PHPUnit\Framework\TestCase;
 
 final class CallToolResultTest extends TestCase
 {
+    /**
+     * @param array{int|string, int|string} $keys
+     */
+    #[TestWith([['first', 'second']])]
+    #[TestWith([[1, 3]])]
+    public function testContentSerializesAsListForNonListKeys(array $keys): void
+    {
+        $first = new TextContent('first');
+        $second = new TextContent('second');
+
+        $result = new CallToolResult([$keys[0] => $first, $keys[1] => $second]);
+
+        $this->assertSame([$first, $second], $result->jsonSerialize()['content']);
+    }
+
     public function testFromArrayDeserializesResourceLinkContent(): void
     {
         $result = CallToolResult::fromArray([

tests/Unit/Schema/Result/GetPromptResultTest.php

@@ -0,0 +1,37 @@
+<?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\Tests\Unit\Schema\Result;
+
+use Mcp\Schema\Content\PromptMessage;
+use Mcp\Schema\Content\TextContent;
+use Mcp\Schema\Enum\Role;
+use Mcp\Schema\Result\GetPromptResult;
+use PHPUnit\Framework\Attributes\TestWith;
+use PHPUnit\Framework\TestCase;
+
+final class GetPromptResultTest extends TestCase
+{
+    /**
+     * @param array{int|string, int|string} $keys
+     */
+    #[TestWith([['first', 'second']])]
+    #[TestWith([[1, 3]])]
+    public function testMessagesSerializeAsListForNonListKeys(array $keys): void
+    {
+        $first = new PromptMessage(Role::User, new TextContent('first'));
+        $second = new PromptMessage(Role::Assistant, new TextContent('second'));
+
+        $result = new GetPromptResult([$keys[0] => $first, $keys[1] => $second]);
+
+        $this->assertSame([$first, $second], $result->jsonSerialize()['messages']);
+    }
+}

tests/Unit/Schema/Result/ReadResourceResultTest.php

@@ -0,0 +1,35 @@
+<?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\Tests\Unit\Schema\Result;
+
+use Mcp\Schema\Content\TextResourceContents;
+use Mcp\Schema\Result\ReadResourceResult;
+use PHPUnit\Framework\Attributes\TestWith;
+use PHPUnit\Framework\TestCase;
+
+final class ReadResourceResultTest extends TestCase
+{
+    /**
+     * @param array{int|string, int|string} $keys
+     */
+    #[TestWith([['first', 'second']])]
+    #[TestWith([[1, 3]])]
+    public function testContentsSerializeAsListForNonListKeys(array $keys): void
+    {
+        $first = new TextResourceContents('file://test', 'text/plain', 'first');
+        $second = new TextResourceContents('file://test', 'text/plain', 'second');
+
+        $result = new ReadResourceResult([$keys[0] => $first, $keys[1] => $second]);
+
+        $this->assertSame([$first, $second], $result->jsonSerialize()['contents']);
+    }
+}