Abstractly something on layer 7 of the OSI model shouldn't care exactly how the data is being routed, but the security considerations of using TOR breaks the ab

Abstractly something on layer 7 of the OSI model shouldn't care exactly how the data is being routed, but the security considerations of using TOR breaks the abstraction. A naïve client could be made to leak identifying information through any number of side-channels. Since the lower layers can't have a whitelist of acceptable applications to connect to .onion addresses, the applications themselves must voluntarily refrain from connecting. This is like the prevailing wisdom to check malloc's return value, not storing passwords in the database, not rolling your own crypto, etc. except that in this case it actually got included in the standard. Unfortunately like all those other things, there's nothing that actually prevents a programmer from breaking the rules.