chunked files are assembled into a part file on the target storage followed by an atomic rename operation.

lib/private/connector/sabre/file.php

@@ -223,9 +223,22 @@ class OC_Connector_Sabre_File extends OC_Connector_Sabre_Node implements Sabre_D
 		}
 
 		if ($chunk_handler->isComplete()) {
-			$newPath = $path . '/' . $info['name'];
-			$chunk_handler->file_assemble($newPath);
-			return OC_Connector_Sabre_Node::getETagPropertyForPath($newPath);
+
+			// we first assembly the target file as a part file
+			$partFile = $path . '/' . $info['name'] . '-' . $info['transferid'] . '.part';
+			$chunk_handler->file_assemble($partFile);
+
+			// here is the final atomic rename
+			$fs = $this->getFS();
+			$targetPath = $path . '/' . $info['name'];
+			$renameOkay = $fs->rename($partFile, $targetPath);
+			$fileExists = $fs->file_exists($targetPath);
+			if ($renameOkay === false || $fileExists === false) {
+				\OC_Log::write('webdav', '\OC\Files\Filesystem::rename() failed', \OC_Log::ERROR);
+				$fs->unlink($targetPath);
+				throw new Sabre_DAV_Exception();
+			}
+			return OC_Connector_Sabre_Node::getETagPropertyForPath($targetPath);
 		}
 
 		return null;