chore: Improve SVG handling in link previews

Signed-off-by: Benjamin Frueh <benjamin.frueh@gmail.com>

Author: benjaminfrueh

lib/public/Collaboration/Reference/LinkReferenceProvider.php

@@ -193,7 +193,7 @@ private function fetchReference(Reference $reference): void {
 					$bodyStream = new LimitStream($stream, self::MAX_CONTENT_LENGTH, 0);
 					$content = $bodyStream->getContents();
 
-					if ($contentType === 'image/svg+xml' && stripos(html_entity_decode($content, ENT_XML1), 'XSL/Transform') !== false) {
+					if ($contentType === 'image/svg+xml' && $this->containsXslt($content)) {
 						return;
 					}
 
@@ -230,4 +230,30 @@ public function getCacheKey(string $referenceId): ?string {
 	public function getCacheKeyPublic(string $referenceId, string $sharingToken): ?string {
 		return null;
 	}
+
+	/**
+	 * Check if XML content contains XSLT transformations
+	 *
+	 * XSLT transformations in SVG files can cause memory exhaustion
+	 * in Chromium based browsers when rendered.
+	 */
+	private function containsXslt(string $xmlContent): bool {
+		set_error_handler(function (int $code, string $message): bool {
+			$this->logger->debug('Failed to parse XML content for XSLT check', ['error' => $message]);
+			return true;
+		});
+
+		$xml = simplexml_load_string($xmlContent);
+
+		restore_error_handler();
+
+		$namespaces = $xml ? $xml->getNamespaces(true) : [];
+		foreach ($namespaces as $namespace) {
+			if (stripos($namespace, 'XSL/Transform') !== false) {
+				return true;
+			}
+		}
+
+		return false;
+	}
 }