Consensus protocol upgrade to get the sending account of an inline action

[arhag]

Background

A contract may wish to simply notify another contract of some event (but not via require_recipient). Inline actions are a good way of doing this. However, if the sender does not wish to allow the receiver to bill the sender for any RAM, it must keep the authorization vector of the inline action empty. But this creates a spoofing problem. Another contract (or just a signed transaction) can send that action while pretending to be from some other contract.

If a contract could use an intrinsic to get the account that an inline action was sent from, it could know with certainty whether the message was authentic without relying on the authorization system that opens up the issue of RAM billing for the sender.

Consensus protocol upgrade feature

This protocol feature (codename: GET_SENDER) allows contracts to determine which account is the sender of an inline action.

New intrinsic get_sender

A new intrinsic account_name get_sender() should be added to the system_api. The C intrinsic for the WebAssembly side would have a signature such as uint64_t get_sender() where the return type is the uint64_t raw representation of the account name of the sender of the inline action. If the current action is not an inline action (for example the top-level actions of a transaction), then get_sender will return 0.

[arhag]

Resolved by #7111.