Attribute Macro pbc_contract_codegen::callback

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#[callback]

Expand description

Public callback contract annotation

OPTIONAL HOOK: This is an optional hook, only required if the contract needs callback functionality.

Annotated function is a callback from an event sent by this contract. Unlike actions, callbacks must specify their shortname explicitly.

If the annotated function panics the contract state will be rolled back to the state before the callback.

Must have a signature of the following format:

#[callback(shortname = 0x13)]
pub fn callback_internal_name(
  contract_context: ContractContext,
  callback_context: CallbackContext,
  state: ContractState,
  // ... Invocation RPC arguments
) -> (ContractState, Vec<EventGroup>)

with following constraints:

ContractState must be the type annotated with state, and must have an pbc_traits::ReadWriteState implementation.
Additional arguments are must have pbc_traits::ReadRPC and pbc_traits::WriteRPC implementations. These are treated as invocation arguments, and are included in the ABI.

The callback receives the previous state, along with two context objects, and the declared arguments. The CallbackContext object contains the execution status of all the events sent by the original transaction. Just like actions, callbacks must return the new state, along with a vector of EventGroup; a list of interactions with other contracts.

§Shortname

In addition to the readable name the callback needs a shortname, a small unique identifier. This shortname must be set using the shortname = <shortname> attribute. This has to be a u32 and gets encoded as LEB128 (up to 5 bytes). These bytes are then encoded as lowercase zero-padded hex.