Fix reading empty files from objectstorage

Since we try to do range requests this will fail hard.
However since empty files are not that interesting to read anyways we
just read from an emptry memory stream.

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

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

@@ -404,12 +404,12 @@ class AmazonS3 extends \OC\Files\Storage\Common {
 	 */
 	private function getContentLength($path) {
 		if (isset($this->filesCache[$path])) {
-			return $this->filesCache[$path]['ContentLength'];
+			return (int)$this->filesCache[$path]['ContentLength'];
 		}
 
 		$result = $this->headObject($path);
 		if (isset($result['ContentLength'])) {
-			return $result['ContentLength'];
+			return (int)$result['ContentLength'];
 		}
 
 		return 0;
@@ -506,6 +506,12 @@ class AmazonS3 extends \OC\Files\Storage\Common {
 		switch ($mode) {
 			case 'r':
 			case 'rb':
+				// Don't try to fetch empty files
+				$stat = $this->stat($path);
+				if (is_array($stat) && isset($stat['size']) && $stat['size'] === 0) {
+					return fopen('php://memory', $mode);
+				}
+
 				try {
 					return $this->readObject($path);
 				} catch (S3Exception $e) {

lib/private/Files/ObjectStore/ObjectStoreStorage.php

@@ -286,6 +286,11 @@ class ObjectStoreStorage extends \OC\Files\Storage\Common {
 			case 'rb':
 				$stat = $this->stat($path);
 				if (is_array($stat)) {
+					// Reading 0 sized files is a waste of time
+					if (isset($stat['size']) && $stat['size'] === 0) {
+						return fopen('php://memory', $mode);
+					}
+
 					try {
 						return $this->objectStore->readObject($this->getURN($stat['fileid']));
 					} catch (NotFoundException $e) {