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// This file is part of Substrate.
// Copyright (C) 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.
//! > Made with *Substrate*, for *Polkadot*.
//!
//! [![github]](https://github.com/paritytech/polkadot-sdk/tree/master/substrate/frame/fast-unstake) -
//! [![polkadot]](https://polkadot.network)
//!
//! [polkadot]: https://img.shields.io/badge/polkadot-E6007A?style=for-the-badge&logo=polkadot&logoColor=white
//! [github]: https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github
//!
//! # Fast Unstake Pallet
//!
//! A pallet to allow participants of the staking system (represented by [`Config::Staking`], being
//! [`StakingInterface`]) to unstake quicker, if and only if they meet the condition of not being
//! exposed to any slashes.
//!
//! ## Overview
//!
//! If a nominator is not exposed anywhere in the staking system, checked via
//! [`StakingInterface::is_exposed_in_era`] (i.e. "has not actively backed any validators in the
//! last [`StakingInterface::bonding_duration`] days"), then they can register themselves in this
//! pallet and unstake faster than having to wait an entire bonding duration.
//!
//! *Being exposed with validator* from the point of view of the staking system means earning
//! rewards with the validator, and also being at the risk of slashing with the validator. This is
//! equivalent to the "Active Nominator" role explained in
//! [here](https://polkadot.network/blog/staking-update-february-2022/).
//!
//! Stakers who are certain about NOT being exposed can register themselves with
//! [`Pallet::register_fast_unstake`]. This will chill, fully unbond the staker and place them
//! in the queue to be checked.
//!
//! A successful registration implies being fully unbonded and chilled in the staking system. These
//! effects persist even if the fast-unstake registration is retracted (see [`Pallet::deregister`]
//! and further).
//!
//! Once registered as a fast-unstaker, the staker will be queued and checked by the system. This
//! can take a variable number of blocks based on demand, but will almost certainly be "faster" (as
//! the name suggest) than waiting the standard bonding duration.
//!
//! A fast-unstaker is either in [`Queue`] or actively being checked, at which point it lives in
//! [`Head`]. Once in [`Head`], the request cannot be retracted anymore. But, once in [`Queue`], it
//! can, via [`Pallet::deregister`].
//!
//! A deposit equal to [`Config::Deposit`] is collected for this process, and is returned in case a
//! successful unstake occurs (`Event::Unstaked` signals that).
//!
//! Once processed, if successful, no additional fee for the checking process is taken, and the
//! staker is instantly unbonded.
//!
//! If unsuccessful, meaning that the staker was exposed, the aforementioned deposit will be slashed
//! for the amount of wasted work they have inflicted on the chain.
//!
//! All in all, this pallet is meant to provide an easy off-ramp for some stakers.
//!
//! ### Example
//!
//! 1. Fast-unstake with multiple participants in the queue.
#![doc = docify::embed!("src/tests.rs", successful_multi_queue)]
//!
//! 2. Fast unstake failing because a nominator is exposed.
#![doc = docify::embed!("src/tests.rs", exposed_nominator_cannot_unstake)]
//!
//! ## Pallet API
//!
//! See the [`pallet`] module for more information about the interfaces this pallet exposes,
//! including its configuration trait, dispatchables, storage items, events and errors.
//!
//! ## Low Level / Implementation Details
//!
//! This pallet works off the basis of `on_idle`, meaning that it provides no guarantee about when
//! it will succeed, if at all. Moreover, the queue implementation is unordered. In case of
//! congestion, no FIFO ordering is provided.
//!
//! A few important considerations can be concluded based on the `on_idle`-based implementation:
//!
//! * It is crucial for the weights of this pallet to be correct. The code inside
//! [`Pallet::on_idle`] MUST be able to measure itself and report the remaining weight correctly
//! after execution.
//!
//! * If the weight measurement is incorrect, it can lead to perpetual overweight (consequently
//! slow) blocks.
//!
//! * The amount of weight that `on_idle` consumes is a direct function of [`ErasToCheckPerBlock`].
//!
//! * Thus, a correct value of [`ErasToCheckPerBlock`] (which can be set via [`Pallet::control`])
//! should be chosen, such that a reasonable amount of weight is used `on_idle`. If
//! [`ErasToCheckPerBlock`] is too large, `on_idle` will always conclude that it has not enough
//! weight to proceed, and will early-return. Nonetheless, this should also be *safe* as long as
//! the benchmarking/weights are *accurate*.
//!
//! * See the inline code-comments on `do_on_idle` (private) for more details.
//!
//! * For further safety, in case of any unforeseen errors, the pallet will emit
//! [`Event::InternalError`] and set [`ErasToCheckPerBlock`] back to 0, which essentially means
//! the pallet will halt/disable itself.
#![cfg_attr(not(feature = "std"), no_std)]
extern crate alloc;
pub use pallet::*;
#[cfg(test)]
mod mock;
#[cfg(test)]
mod tests;
// NOTE: enable benchmarking in tests as well.
#[cfg(feature = "runtime-benchmarks")]
mod benchmarking;
pub mod migrations;
pub mod types;
pub mod weights;
// some extra imports for docs to link properly.
#[cfg(doc)]
pub use frame_support::traits::Hooks;
#[cfg(doc)]
pub use sp_staking::StakingInterface;
/// The logging target of this pallet.
pub const LOG_TARGET: &'static str = "runtime::fast-unstake";
#[macro_export]
macro_rules! log {
($level:tt, $patter:expr $(, $values:expr)* $(,)?) => {
log::$level!(
target: crate::LOG_TARGET,
concat!("[{:?}] 💨 ", $patter), frame_system::Pallet::<T>::block_number() $(, $values)*
)
};
}
#[frame_support::pallet]
pub mod pallet {
use super::*;
use crate::types::*;
use alloc::vec::Vec;
use frame_support::{
pallet_prelude::*,
traits::{Defensive, ReservableCurrency, StorageVersion},
};
use frame_system::pallet_prelude::*;
use sp_runtime::{traits::Zero, DispatchResult};
use sp_staking::{EraIndex, StakingInterface};
pub use weights::WeightInfo;
#[cfg(feature = "try-runtime")]
use sp_runtime::TryRuntimeError;
const STORAGE_VERSION: StorageVersion = StorageVersion::new(1);
#[pallet::pallet]
#[pallet::storage_version(STORAGE_VERSION)]
pub struct Pallet<T>(_);
#[pallet::config]
pub trait Config: frame_system::Config {
/// The overarching event type.
type RuntimeEvent: From<Event<Self>>
+ IsType<<Self as frame_system::Config>::RuntimeEvent>
+ TryInto<Event<Self>>;
/// The currency used for deposits.
type Currency: ReservableCurrency<Self::AccountId>;
/// Deposit to take for unstaking, to make sure we're able to slash the it in order to cover
/// the costs of resources on unsuccessful unstake.
#[pallet::constant]
type Deposit: Get<BalanceOf<Self>>;
/// The origin that can control this pallet, in other words invoke [`Pallet::control`].
type ControlOrigin: frame_support::traits::EnsureOrigin<Self::RuntimeOrigin>;
/// Batch size.
///
/// This many stashes are processed in each unstake request.
type BatchSize: Get<u32>;
/// The access to staking functionality.
type Staking: StakingInterface<Balance = BalanceOf<Self>, AccountId = Self::AccountId>;
/// Maximum value for `ErasToCheckPerBlock`, checked in [`Pallet::control`].
///
/// This should be slightly bigger than the actual value in order to have accurate
/// benchmarks.
type MaxErasToCheckPerBlock: Get<u32>;
/// The weight information of this pallet.
type WeightInfo: WeightInfo;
}
/// The current "head of the queue" being unstaked.
///
/// The head in itself can be a batch of up to [`Config::BatchSize`] stakers.
#[pallet::storage]
pub type Head<T: Config> = StorageValue<_, UnstakeRequest<T>, OptionQuery>;
/// The map of all accounts wishing to be unstaked.
///
/// Keeps track of `AccountId` wishing to unstake and it's corresponding deposit.
// Hasher: Twox safe since `AccountId` is a secure hash.
#[pallet::storage]
pub type Queue<T: Config> = CountedStorageMap<_, Twox64Concat, T::AccountId, BalanceOf<T>>;
/// Number of eras to check per block.
///
/// If set to 0, this pallet does absolutely nothing. Cannot be set to more than
/// [`Config::MaxErasToCheckPerBlock`].
///
/// Based on the amount of weight available at [`Pallet::on_idle`], up to this many eras are
/// checked. The checking is represented by updating [`UnstakeRequest::checked`], which is
/// stored in [`Head`].
#[pallet::storage]
pub type ErasToCheckPerBlock<T: Config> = StorageValue<_, u32, ValueQuery>;
#[pallet::event]
#[pallet::generate_deposit(pub(super) fn deposit_event)]
pub enum Event<T: Config> {
/// A staker was unstaked.
Unstaked { stash: T::AccountId, result: DispatchResult },
/// A staker was slashed for requesting fast-unstake whilst being exposed.
Slashed { stash: T::AccountId, amount: BalanceOf<T> },
/// A batch was partially checked for the given eras, but the process did not finish.
BatchChecked { eras: Vec<EraIndex> },
/// A batch of a given size was terminated.
///
/// This is always follows by a number of `Unstaked` or `Slashed` events, marking the end
/// of the batch. A new batch will be created upon next block.
BatchFinished { size: u32 },
/// An internal error happened. Operations will be paused now.
InternalError,
}
#[pallet::error]
#[cfg_attr(test, derive(PartialEq))]
pub enum Error<T> {
/// The provided Controller account was not found.
///
/// This means that the given account is not bonded.
NotController,
/// The bonded account has already been queued.
AlreadyQueued,
/// The bonded account has active unlocking chunks.
NotFullyBonded,
/// The provided un-staker is not in the `Queue`.
NotQueued,
/// The provided un-staker is already in Head, and cannot deregister.
AlreadyHead,
/// The call is not allowed at this point because the pallet is not active.
CallNotAllowed,
}
#[pallet::hooks]
impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {
fn on_idle(_: BlockNumberFor<T>, remaining_weight: Weight) -> Weight {
if remaining_weight.any_lt(T::DbWeight::get().reads(2)) {
return Weight::from_parts(0, 0)
}
Self::do_on_idle(remaining_weight)
}
fn integrity_test() {
// Ensure that the value of `ErasToCheckPerBlock` is less or equal to
// `T::MaxErasToCheckPerBlock`.
assert!(
ErasToCheckPerBlock::<T>::get() <= T::MaxErasToCheckPerBlock::get(),
"the value of `ErasToCheckPerBlock` is greater than `T::MaxErasToCheckPerBlock`",
);
}
#[cfg(feature = "try-runtime")]
fn try_state(_n: BlockNumberFor<T>) -> Result<(), TryRuntimeError> {
// ensure that the value of `ErasToCheckPerBlock` is less than
// `T::MaxErasToCheckPerBlock`.
ensure!(
ErasToCheckPerBlock::<T>::get() <= T::MaxErasToCheckPerBlock::get(),
"the value of `ErasToCheckPerBlock` is greater than `T::MaxErasToCheckPerBlock`",
);
Ok(())
}
}
#[pallet::call]
impl<T: Config> Pallet<T> {
/// Register oneself for fast-unstake.
///
/// ## Dispatch Origin
///
/// The dispatch origin of this call must be *signed* by whoever is permitted to call
/// unbond funds by the staking system. See [`Config::Staking`].
///
/// ## Details
///
/// The stash associated with the origin must have no ongoing unlocking chunks. If
/// successful, this will fully unbond and chill the stash. Then, it will enqueue the stash
/// to be checked in further blocks.
///
/// If by the time this is called, the stash is actually eligible for fast-unstake, then
/// they are guaranteed to remain eligible, because the call will chill them as well.
///
/// If the check works, the entire staking data is removed, i.e. the stash is fully
/// unstaked.
///
/// If the check fails, the stash remains chilled and waiting for being unbonded as in with
/// the normal staking system, but they lose part of their unbonding chunks due to consuming
/// the chain's resources.
///
/// ## Events
///
/// Some events from the staking and currency system might be emitted.
#[pallet::call_index(0)]
#[pallet::weight(<T as Config>::WeightInfo::register_fast_unstake())]
pub fn register_fast_unstake(origin: OriginFor<T>) -> DispatchResult {
let ctrl = ensure_signed(origin)?;
ensure!(ErasToCheckPerBlock::<T>::get() != 0, Error::<T>::CallNotAllowed);
let stash_account =
T::Staking::stash_by_ctrl(&ctrl).map_err(|_| Error::<T>::NotController)?;
ensure!(!Queue::<T>::contains_key(&stash_account), Error::<T>::AlreadyQueued);
ensure!(!Self::is_head(&stash_account), Error::<T>::AlreadyHead);
ensure!(!T::Staking::is_unbonding(&stash_account)?, Error::<T>::NotFullyBonded);
// chill and fully unstake.
T::Staking::chill(&stash_account)?;
T::Staking::fully_unbond(&stash_account)?;
T::Currency::reserve(&stash_account, T::Deposit::get())?;
// enqueue them.
Queue::<T>::insert(stash_account, T::Deposit::get());
Ok(())
}
/// Deregister oneself from the fast-unstake.
///
/// ## Dispatch Origin
///
/// The dispatch origin of this call must be *signed* by whoever is permitted to call
/// unbond funds by the staking system. See [`Config::Staking`].
///
/// ## Details
///
/// This is useful if one is registered, they are still waiting, and they change their mind.
///
/// Note that the associated stash is still fully unbonded and chilled as a consequence of
/// calling [`Pallet::register_fast_unstake`]. Therefore, this should probably be followed
/// by a call to `rebond` in the staking system.
///
/// ## Events
///
/// Some events from the staking and currency system might be emitted.
#[pallet::call_index(1)]
#[pallet::weight(<T as Config>::WeightInfo::deregister())]
pub fn deregister(origin: OriginFor<T>) -> DispatchResult {
let ctrl = ensure_signed(origin)?;
ensure!(ErasToCheckPerBlock::<T>::get() != 0, Error::<T>::CallNotAllowed);
let stash_account =
T::Staking::stash_by_ctrl(&ctrl).map_err(|_| Error::<T>::NotController)?;
ensure!(Queue::<T>::contains_key(&stash_account), Error::<T>::NotQueued);
ensure!(!Self::is_head(&stash_account), Error::<T>::AlreadyHead);
let deposit = Queue::<T>::take(stash_account.clone());
if let Some(deposit) = deposit.defensive() {
let remaining = T::Currency::unreserve(&stash_account, deposit);
if !remaining.is_zero() {
Self::halt("not enough balance to unreserve");
}
}
Ok(())
}
/// Control the operation of this pallet.
///
/// ## Dispatch Origin
///
/// The dispatch origin of this call must be [`Config::ControlOrigin`].
///
/// ## Details
///
/// Can set the number of eras to check per block, and potentially other admin work.
///
/// ## Events
///
/// No events are emitted from this dispatch.
#[pallet::call_index(2)]
#[pallet::weight(<T as Config>::WeightInfo::control())]
pub fn control(origin: OriginFor<T>, eras_to_check: EraIndex) -> DispatchResult {
let _ = T::ControlOrigin::ensure_origin(origin)?;
ensure!(eras_to_check <= T::MaxErasToCheckPerBlock::get(), Error::<T>::CallNotAllowed);
ErasToCheckPerBlock::<T>::put(eras_to_check);
Ok(())
}
}
impl<T: Config> Pallet<T> {
/// Returns `true` if `staker` is anywhere to be found in the `head`.
pub(crate) fn is_head(staker: &T::AccountId) -> bool {
Head::<T>::get().map_or(false, |UnstakeRequest { stashes, .. }| {
stashes.iter().any(|(stash, _)| stash == staker)
})
}
/// Halt the operations of this pallet.
pub(crate) fn halt(reason: &'static str) {
frame_support::defensive!(reason);
ErasToCheckPerBlock::<T>::put(0);
Self::deposit_event(Event::<T>::InternalError)
}
/// process up to `remaining_weight`.
///
/// Returns the actual weight consumed.
///
/// Written for readability in mind, not efficiency. For example:
///
/// 1. We assume this is only ever called once per `on_idle`. This is because we know that
/// in all use cases, even a single nominator cannot be unbonded in a single call. Multiple
/// calls to this function are thus not needed.
///
/// 2. We will only mark a staker as unstaked if at the beginning of a check cycle, they are
/// found out to have no eras to check. At the end of a check cycle, even if they are fully
/// checked, we don't finish the process.
pub(crate) fn do_on_idle(remaining_weight: Weight) -> Weight {
// any weight that is unaccounted for
let mut unaccounted_weight = Weight::from_parts(0, 0);
let eras_to_check_per_block = ErasToCheckPerBlock::<T>::get();
if eras_to_check_per_block.is_zero() {
return T::DbWeight::get().reads(1).saturating_add(unaccounted_weight)
}
// NOTE: here we're assuming that the number of validators has only ever increased,
// meaning that the number of exposures to check is either this per era, or less.
let validator_count = T::Staking::desired_validator_count();
let (next_batch_size, reads_from_queue) = Head::<T>::get()
.map_or((Queue::<T>::count().min(T::BatchSize::get()), true), |head| {
(head.stashes.len() as u32, false)
});
// determine the number of eras to check. This is based on both `ErasToCheckPerBlock`
// and `remaining_weight` passed on to us from the runtime executive.
let max_weight = |v, b| {
// NOTE: this potentially under-counts by up to `BatchSize` reads from the queue.
<T as Config>::WeightInfo::on_idle_check(v, b)
.max(<T as Config>::WeightInfo::on_idle_unstake(b))
.saturating_add(if reads_from_queue {
T::DbWeight::get().reads(next_batch_size.into())
} else {
Zero::zero()
})
};
if max_weight(validator_count, next_batch_size).any_gt(remaining_weight) {
log!(debug, "early exit because eras_to_check_per_block is zero");
return T::DbWeight::get().reads(3).saturating_add(unaccounted_weight)
}
if T::Staking::election_ongoing() {
// NOTE: we assume `ongoing` does not consume any weight.
// there is an ongoing election -- we better not do anything. Imagine someone is not
// exposed anywhere in the last era, and the snapshot for the election is already
// taken. In this time period, we don't want to accidentally unstake them.
return T::DbWeight::get().reads(4).saturating_add(unaccounted_weight)
}
let UnstakeRequest { stashes, mut checked } = match Head::<T>::take().or_else(|| {
// NOTE: there is no order guarantees in `Queue`.
let stashes: BoundedVec<_, T::BatchSize> = Queue::<T>::drain()
.take(T::BatchSize::get() as usize)
.collect::<Vec<_>>()
.try_into()
.expect("take ensures bound is met; qed");
unaccounted_weight.saturating_accrue(
T::DbWeight::get().reads_writes(stashes.len() as u64, stashes.len() as u64),
);
if stashes.is_empty() {
None
} else {
Some(UnstakeRequest { stashes, checked: Default::default() })
}
}) {
None => {
// There's no `Head` and nothing in the `Queue`, nothing to do here.
return T::DbWeight::get().reads(4)
},
Some(head) => head,
};
log!(
debug,
"checking {:?} stashes, eras_to_check_per_block = {:?}, checked {:?}, remaining_weight = {:?}",
stashes.len(),
eras_to_check_per_block,
checked,
remaining_weight,
);
// the range that we're allowed to check in this round.
let current_era = T::Staking::current_era();
let bonding_duration = T::Staking::bonding_duration();
// prune all the old eras that we don't care about. This will help us keep the bound
// of `checked`.
checked.retain(|e| *e >= current_era.saturating_sub(bonding_duration));
let unchecked_eras_to_check = {
// get the last available `bonding_duration` eras up to current era in reverse
// order.
let total_check_range = (current_era.saturating_sub(bonding_duration)..=
current_era)
.rev()
.collect::<Vec<_>>();
debug_assert!(
total_check_range.len() <= (bonding_duration + 1) as usize,
"{:?}",
total_check_range
);
// remove eras that have already been checked, take a maximum of
// eras_to_check_per_block.
total_check_range
.into_iter()
.filter(|e| !checked.contains(e))
.take(eras_to_check_per_block as usize)
.collect::<Vec<_>>()
};
log!(
debug,
"{} eras to check: {:?}",
unchecked_eras_to_check.len(),
unchecked_eras_to_check
);
let unstake_stash = |stash: T::AccountId, deposit| {
let result = T::Staking::force_unstake(stash.clone());
let remaining = T::Currency::unreserve(&stash, deposit);
if !remaining.is_zero() {
Self::halt("not enough balance to unreserve");
} else {
log!(debug, "unstaked {:?}, outcome: {:?}", stash, result);
Self::deposit_event(Event::<T>::Unstaked { stash, result });
}
};
let check_stash = |stash, deposit| {
let is_exposed = unchecked_eras_to_check
.iter()
.any(|e| T::Staking::is_exposed_in_era(&stash, e));
if is_exposed {
let _ = T::Currency::slash_reserved(&stash, deposit);
log!(info, "slashed {:?} by {:?}", stash, deposit);
Self::deposit_event(Event::<T>::Slashed { stash, amount: deposit });
false
} else {
true
}
};
if unchecked_eras_to_check.is_empty() {
// `stashes` are not exposed in any era now -- we can let go of them now.
let size = stashes.len() as u32;
stashes.into_iter().for_each(|(stash, deposit)| unstake_stash(stash, deposit));
Self::deposit_event(Event::<T>::BatchFinished { size });
<T as Config>::WeightInfo::on_idle_unstake(size).saturating_add(unaccounted_weight)
} else {
let pre_length = stashes.len();
let stashes: BoundedVec<(T::AccountId, BalanceOf<T>), T::BatchSize> = stashes
.into_iter()
.filter(|(stash, deposit)| check_stash(stash.clone(), *deposit))
.collect::<Vec<_>>()
.try_into()
.expect("filter can only lessen the length; still in bound; qed");
let post_length = stashes.len();
log!(
debug,
"checked {:?}, pre stashes: {:?}, post: {:?}",
unchecked_eras_to_check,
pre_length,
post_length,
);
match checked.try_extend(unchecked_eras_to_check.clone().into_iter()) {
Ok(_) =>
if stashes.is_empty() {
Self::deposit_event(Event::<T>::BatchFinished { size: 0 });
} else {
Head::<T>::put(UnstakeRequest { stashes, checked });
Self::deposit_event(Event::<T>::BatchChecked {
eras: unchecked_eras_to_check,
});
},
Err(_) => {
// don't put the head back in -- there is an internal error in the pallet.
Self::halt("checked is pruned via retain above")
},
}
<T as Config>::WeightInfo::on_idle_check(validator_count, pre_length as u32)
.saturating_add(unaccounted_weight)
}
}
}
}