fix(s3): ignore prefixes with repeating delimiters

Signed-off-by: Kent Delante <kent@delante.me>

Amazon's hosted S3 service allows repeating delimiters in keys
(e.g. 'path/to//file.txt' or 'path/to///file.txt') and we get
repeating directories in the filecache as a result (based on the
previous examples we get 'path/to/to/file.txt' or
'path/to/to/to/file.txt'). This ignores it and its contents for S3 external storage.

Author: leftybournes

apps/files_external/lib/Lib/Storage/AmazonS3.php

@@ -645,6 +645,12 @@ public function getDirectoryContent(string $directory): \Traversable {
 			// sub folders
 			if (is_array($result['CommonPrefixes'])) {
 				foreach ($result['CommonPrefixes'] as $prefix) {
+					if (preg_match('/\/{2,}$/', $prefix['Prefix'])) {
+						$this->logger->warning('Detected a repeating delimiter in prefix \'' . $prefix['Prefix']
+											   . '\'. This is unsupported and its contents have been ignored.');
+						continue;
+					}
+
 					$dir = $this->getDirectoryMetaData($prefix['Prefix']);
 					if ($dir) {
 						yield $dir;