fix(state): add support for the Deprecation link header

Author: aaa2000

src/State/Processor/AddLinkHeaderProcessor.php

@@ -52,7 +52,8 @@ public function process(mixed $data, Operation $operation, array $uriVariables =
         // We add our header here as Symfony does it only for the main Request and we want it to be done on errors (sub-request) as well
         $linksProvider = $request->attributes->get('_api_platform_links');
         if ($this->serializer && ($links = $linksProvider?->getLinks())) {
-            $response->headers->set('Link', $this->serializer->serialize($links));
+            $linkHeader = implode(',', array_filter([$this->serializer->serialize($links), $response->headers->get('Link')]));
+            $response->headers->set('Link', $linkHeader === '' ? null : $linkHeader);
         }
         $this->stopwatch?->stop('api_platform.processor.add_link_header');
 

tests/Fixtures/TestBundle/ApiResource/DeprecationHeader.php

@@ -0,0 +1,42 @@
+<?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\ApiProperty;
+use ApiPlatform\Metadata\ApiResource;
+use ApiPlatform\Metadata\GetCollection;
+
+#[ApiResource(
+    operations: [new GetCollection(provider: [self::class, 'provide'])],
+    deprecationReason: 'This API is deprecated ',
+    headers: [
+        'deprecation' => '@1688169599',
+        'sunset' => 'Sun, 30 Jun 2024 23:59:59 UTC',
+        'link' => '<https://developer.example.com/deprecation>; rel="deprecation"; type="text/html"',
+    ],
+)]
+class DeprecationHeader
+{
+    public function __construct(#[ApiProperty(identifier: true)] public int $id)
+    {
+    }
+
+    public static function provide(): iterable
+    {
+        return [
+            new self(1),
+            new self(2),
+        ];
+    }
+}

tests/Functional/DeprecationHeaderTest.php

@@ -0,0 +1,44 @@
+<?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\Symfony\Bundle\Test\ApiTestCase;
+use ApiPlatform\Tests\Fixtures\TestBundle\ApiResource\DeprecationHeader;
+use ApiPlatform\Tests\SetupClassResourcesTrait;
+
+final class DeprecationHeaderTest extends ApiTestCase
+{
+    use SetupClassResourcesTrait;
+
+    protected static ?bool $alwaysBootKernel = false;
+
+    /**
+     * @return class-string[]
+     */
+    public static function getResources(): array
+    {
+        return [DeprecationHeader::class];
+    }
+
+    public function testDeprecationHeader(): void
+    {
+        $response = self::createClient()->request('GET', '/deprecation_headers');
+
+        $headers = $response->getHeaders();
+
+        $this->assertContains('@1688169599', $headers['deprecation']);
+        $this->assertContains('Sun, 30 Jun 2024 23:59:59 UTC', $headers['sunset']);
+        $this->assertStringContainsString('<https://developer.example.com/deprecation>; rel="deprecation"; type="text/html"', $headers['link'][0]);
+    }
+}