Improved attachment retrieval and added test cases

tests/OnlineTests/ObjectRetrieverCacheTest.php

@@ -51,4 +51,34 @@ class ObjectRetrieverCacheTest extends \PHPUnit\Framework\TestCase {
         $this->assertEquals($object2->getRevision(), $object3->getRevision());
     }
 
+    public function testAttachmentCacheInRuntimeStorage() {
+        $cacheStorage = new VolatileRuntimeStorage;
+        $logger = new InMemoryLogger;
+
+        $coid = new IRI('coid://cloudobjects.io/Test');
+        $cacheId = (string)$coid.'#file.txt';
+
+        $retriever = new ObjectRetriever([
+            'cache_storage' => $cacheStorage,
+            'logger' => $logger
+        ]);
+
+        $content1 = $retriever->getAttachment($coid, 'file.txt');
+
+        $this->assertEquals('Test file content', trim($content1));
+        $this->assertNotNull($cacheStorage->fetch($retriever->getCacheKey($cacheId)));
+        $this->assertStringContainsString('from Core API', $logger->getLastLogMessage());
+
+        // Reinitialize retriever with same cache storage to verify that cache is used
+        $retriever = new ObjectRetriever([
+            'cache_storage' => $cacheStorage,
+            'logger' => $logger
+        ]);
+
+        $content2 = $retriever->getAttachment($coid, 'file.txt');
+
+        $this->assertEquals('Test file content', trim($content2));
+        $this->assertStringContainsString('from object cache', $logger->getLastLogMessage());
+    }
+
 }