Storage wrapper should work theoratically, whatever 
Seems like you are right about read signals. I found before and after read event in here core/lib/private/Files/View.php at 2a6722494dcecf175597d524093ceeeef10d47ae · owncloud/core · GitHub . You can listen this event to achieve your purpose. Your listener should something like that security/lib/Hooks.php at master · owncloud-archive/security · GitHub. You will listen “file.beforeread” and “file.afterread” events, these events are supplying path as an argument.