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// This file is part of Substrate.
// Copyright (C) 2019-2020 Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//! Common traits and types that are useful for describing offences for usage in environments
//! that use staking.
use sp_std::vec::Vec;
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use crate::SessionIndex;
/// The kind of an offence, is a byte string representing some kind identifier
/// e.g. `b"im-online:offlin"`, `b"babe:equivocatio"`
pub type Kind = [u8; 16];
/// Number of times the offence of this authority was already reported in the past.
///
/// Note that we don't buffer offence reporting, so every time we see a new offence
/// of the same kind, we will report past authorities again.
/// This counter keeps track of how many times the authority was already reported in the past,
/// so that we can slash it accordingly.
pub type OffenceCount = u32;
/// A trait implemented by an offence report.
///
/// This trait assumes that the offence is legitimate and was validated already.
///
/// Examples of offences include: a BABE equivocation or a GRANDPA unjustified vote.
pub trait Offence<Offender> {
/// Identifier which is unique for this kind of an offence.
const ID: Kind;
/// A type that represents a point in time on an abstract timescale.
///
/// See `Offence::time_slot` for details. The only requirement is that such timescale could be
/// represented by a single `u128` value.
type TimeSlot: Clone + codec::Codec + Ord;
/// The list of all offenders involved in this incident.
///
/// The list has no duplicates, so it is rather a set.
fn offenders(&self) -> Vec<Offender>;
/// The session index that is used for querying the validator set for the `slash_fraction`
/// function.
///
/// This is used for filtering historical sessions.
fn session_index(&self) -> SessionIndex;
/// Return a validator set count at the time when the offence took place.
fn validator_set_count(&self) -> u32;
/// A point in time when this offence happened.
///
/// This is used for looking up offences that happened at the "same time".
///
/// The timescale is abstract and doesn't have to be the same across different implementations
/// of this trait. The value doesn't represent absolute timescale though since it is interpreted
/// along with the `session_index`. Two offences are considered to happen at the same time iff
/// both `session_index` and `time_slot` are equal.
///
/// As an example, for GRANDPA timescale could be a round number and for BABE it could be a slot
/// number. Note that for GRANDPA the round number is reset each epoch.
fn time_slot(&self) -> Self::TimeSlot;
/// A slash fraction of the total exposure that should be slashed for this
/// particular offence kind for the given parameters that happened at a singular `TimeSlot`.
///
/// `offenders_count` - the count of unique offending authorities. It is >0.
/// `validator_set_count` - the cardinality of the validator set at the time of offence.
fn slash_fraction(
offenders_count: u32,
validator_set_count: u32,
) -> Perbill;
}
/// Errors that may happen on offence reports.
#[derive(PartialEq, sp_runtime::RuntimeDebug)]
pub enum OffenceError {
/// The report has already been sumbmitted.
DuplicateReport,
/// Other error has happened.
Other(u8),
}
impl sp_runtime::traits::Printable for OffenceError {
fn print(&self) {
"OffenceError".print();
match self {
Self::DuplicateReport => "DuplicateReport".print(),
Self::Other(e) => {
"Other".print();
e.print();
}
}
}
}
/// A trait for decoupling offence reporters from the actual handling of offence reports.
pub trait ReportOffence<Reporter, Offender, O: Offence<Offender>> {
/// Report an `offence` and reward given `reporters`.
fn report_offence(reporters: Vec<Reporter>, offence: O) -> Result<(), OffenceError>;
}
impl<Reporter, Offender, O: Offence<Offender>> ReportOffence<Reporter, Offender, O> for () {
fn report_offence(_reporters: Vec<Reporter>, _offence: O) -> Result<(), OffenceError> { Ok(()) }
}
/// A trait to take action on an offence.
///
/// Used to decouple the module that handles offences and
/// the one that should punish for those offences.
pub trait OnOffenceHandler<Reporter, Offender> {
/// A handler for an offence of a particular kind.
///
/// Note that this contains a list of all previous offenders
/// as well. The implementer should cater for a case, where
/// the same authorities were reported for the same offence
/// in the past (see `OffenceCount`).
///
/// The vector of `slash_fraction` contains `Perbill`s
/// the authorities should be slashed and is computed
/// according to the `OffenceCount` already. This is of the same length as `offenders.`
/// Zero is a valid value for a fraction.
///
/// The `session` parameter is the session index of the offence.
///
/// The receiver might decide to not accept this offence. In this case, the call site is
/// responsible for queuing the report and re-submitting again.
fn on_offence(
offenders: &[OffenceDetails<Reporter, Offender>],
slash_fraction: &[Perbill],
) -> Result<(), ()>;
/// Can an offence be reported now or not. This is an method to short-circuit a call into
/// `on_offence`. Ideally, a correct implementation should return `false` if `on_offence` will
/// return `Err`. Nonetheless, this is up to the implementation and this trait cannot guarantee
/// it.
fn can_report() -> bool;
}
impl<Reporter, Offender> OnOffenceHandler<Reporter, Offender> for () {
fn on_offence(
_offenders: &[OffenceDetails<Reporter, Offender>],
_slash_fraction: &[Perbill],
) -> Result<(), ()> { Ok(()) }
fn can_report() -> bool { true }
}
/// A details about an offending authority for a particular kind of offence.
#[derive(Clone, PartialEq, Eq, Encode, Decode, sp_runtime::RuntimeDebug)]
pub struct OffenceDetails<Reporter, Offender> {
/// The offending authority id
pub offender: Offender,
/// A list of reporters of offences of this authority ID. Possibly empty where there are no
/// particular reporters.
pub reporters: Vec<Reporter>,
}