Contract Interfaces

Terms

Contract State - data associated with a contract that can be retrieved by Applications and Delegates.
Delta - Represents a modification to some state - similar to a diff in source code
Parameters - Data that forms part of a contract along with the WebAssembly code
State Summary - A compact summary of a contract’s state that can be used to create a delta

Interface

Freenet contracts must implement the ContractInterface trait:

pub trait ContractInterface {
    // Required methods
    fn validate_state(
        parameters: Parameters<'static>,
        state: State<'static>,
        related: RelatedContracts<'static>,
    ) -> Result<ValidateResult, ContractError>;
    fn update_state(
        parameters: Parameters<'static>,
        state: State<'static>,
        data: Vec<UpdateData<'static>>,
    ) -> Result<UpdateModification<'static>, ContractError>;
    fn summarize_state(
        parameters: Parameters<'static>,
        state: State<'static>,
    ) -> Result<StateSummary<'static>, ContractError>;
    fn get_state_delta(
        parameters: Parameters<'static>,
        state: State<'static>,
        summary: StateSummary<'static>,
    ) -> Result<StateDelta<'static>, ContractError>;
}

Parameters, State, and StateDelta are all wrappers around simple [u8] byte arrays for maximum efficiency and flexibility.

Contract Interaction

In the (hopefully) near future we’ll be adding the ability for contracts to read each other’s state while validating and updating their own, see issue #167 for the latest on this.