git.delta.rocks / unique-network / refs/commits / 313a9f3da734

1// Copyright 2019-2022 Unique Network (Gibraltar) Ltd.2// This file is part of Unique Network.34// Unique Network is free software: you can redistribute it and/or modify5// it under the terms of the GNU General Public License as published by6// the Free Software Foundation, either version 3 of the License, or7// (at your option) any later version.89// Unique Network is distributed in the hope that it will be useful,10// but WITHOUT ANY WARRANTY; without even the implied warranty of11// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the12// GNU General Public License for more details.1314// You should have received a copy of the GNU General Public License15// along with Unique Network. If not, see <http://www.gnu.org/licenses/>.1617// Original license:18// Copyright (C) 2021 Parity Technologies (UK) Ltd.19// SPDX-License-Identifier: Apache-2.02021// Licensed under the Apache License, Version 2.0 (the "License");22// you may not use this file except in compliance with the License.23// You may obtain a copy of the License at24//25// 	http://www.apache.org/licenses/LICENSE-2.026//27// Unless required by applicable law or agreed to in writing, software28// distributed under the License is distributed on an "AS IS" BASIS,29// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.30// See the License for the specific language governing permissions and31// limitations under the License.3233// todo:collator documentation34//! Collator Selection pallet.35//!36//! A pallet to manage collators in a parachain.37//!38//! ## Overview39//!40//! The Collator Selection pallet manages the collators of a parachain. **Collation is _not_ a41//! secure activity** and this pallet does not implement any game-theoretic mechanisms to meet BFT42//! safety assumptions of the chosen set.43//!44//! ## Terminology45//!46//! - Collator: A parachain block producer.47//! - Bond: An amount of `Balance` _reserved_ for candidate registration.48//! - Invulnerable: An account guaranteed to be in the collator set.49//!50//! ## Implementation51//!52//! The final `Collators` are aggregated from two individual lists:53//!54//! 1. [`Invulnerables`]: a set of collators appointed by governance. These accounts will always be55//!    collators.56//! 2. [`Candidates`]: these are *candidates to the collation task* and may or may not be elected as57//!    a final collator.58//!59//! The current implementation resolves congestion of [`Candidates`] in a first-come-first-serve60//! manner.61//!62//! Candidates will not be allowed to get kicked or leave_intent if the total number of candidates63//! fall below MinCandidates. This is for potential disaster recovery scenarios.64//!65//! ### Rewards66//!67//! The Collator Selection pallet maintains an on-chain account (the "Pot"). In each block, the68//! collator who authored it receives:69//!70//! - Half the value of the Pot.71//! - Half the value of the transaction fees within the block. The other half of the transaction72//!   fees are deposited into the Pot.73//!74//! To initiate rewards an ED needs to be transferred to the pot address.75//!76//! Note: Eventually the Pot distribution may be modified as discussed in77//! [this issue](https://github.com/paritytech/statemint/issues/21#issuecomment-810481073).7879#![cfg_attr(not(feature = "std"), no_std)]8081pub use pallet::*;8283#[cfg(test)]84mod mock;8586#[cfg(test)]87mod tests;8889#[cfg(feature = "runtime-benchmarks")]90mod benchmarking;91pub mod weights;9293#[frame_support::pallet]94pub mod pallet {95	pub use crate::weights::WeightInfo;96	use core::ops::Div;97	use frame_support::{98		dispatch::{DispatchClass, DispatchResultWithPostInfo},99		inherent::Vec,100		pallet_prelude::*,101		sp_runtime::{102			traits::{AccountIdConversion, CheckedSub, Saturating, Zero},103			RuntimeDebug,104		},105		traits::{106			Currency, EnsureOrigin, ExistenceRequirement::KeepAlive, ReservableCurrency,107			ValidatorRegistration,108		},109		BoundedVec, PalletId,110	};111	use frame_system::{pallet_prelude::*, Config as SystemConfig};112	use pallet_session::SessionManager;113	use sp_runtime::{114		Perbill,115		traits::{One, Convert},116	};117	use sp_staking::SessionIndex;118119	type BalanceOf<T> =120		<<T as Config>::Currency as Currency<<T as SystemConfig>::AccountId>>::Balance;121122	/// A convertor from collators id. Since this pallet does not have stash/controller, this is123	/// just identity.124	pub struct IdentityCollator;125	impl<T> sp_runtime::traits::Convert<T, Option<T>> for IdentityCollator {126		fn convert(t: T) -> Option<T> {127			Some(t)128		}129	}130131	/// Configure the pallet by specifying the parameters and types on which it depends.132	#[pallet::config]133	pub trait Config: frame_system::Config {134		/// Overarching event type.135		type RuntimeEvent: From<Event<Self>> + IsType<<Self as frame_system::Config>::RuntimeEvent>;136137		/// The currency mechanism.138		type Currency: ReservableCurrency<Self::AccountId>;139140		/// Origin that can dictate updating parameters of this pallet.141		type UpdateOrigin: EnsureOrigin<Self::RuntimeOrigin>;142143		/// Account Identifier that holds the chain's treasury.144		type TreasuryAccountId: Get<Self::AccountId>;145146		/// Account Identifier from which the internal Pot is generated.147		type PotId: Get<PalletId>;148149		/// Maximum number of candidates that we should have. This is enforced in code.150		///151		/// This does not take into account the invulnerables.152		type MaxCandidates: Get<u32>;153154		/// Minimum number of candidates that we should have. This is used for disaster recovery.155		///156		/// This does not take into account the invulnerables.157		type MinCandidates: Get<u32>;158159		/// Maximum number of invulnerables. This is enforced in code.160		type MaxInvulnerables: Get<u32>;161162		/// If kicked, how much of the collator's deposit will be slashed and sent to the slash destination.163		type SlashRatio: Get<Perbill>;164165		/// A stable ID for a validator.166		type ValidatorId: Member + Parameter;167168		/// A conversion from account ID to validator ID.169		///170		/// Its cost must be at most one storage read.171		type ValidatorIdOf: Convert<Self::AccountId, Option<Self::ValidatorId>>;172173		/// Validate a user is registered174		type ValidatorRegistration: ValidatorRegistration<Self::ValidatorId>;175176		/// The weight information of this pallet.177		type WeightInfo: WeightInfo;178	}179180	/// Basic information about a collation candidate.181	#[derive(182		PartialEq, Eq, Clone, Encode, Decode, RuntimeDebug, scale_info::TypeInfo, MaxEncodedLen,183	)]184	pub struct LicenseInfo<AccountId, Balance> {185		/// Account identifier.186		pub who: AccountId,187		/// Reserved deposit.188		pub deposit: Balance,189	}190191	#[pallet::pallet]192	#[pallet::generate_store(pub(super) trait Store)]193	pub struct Pallet<T>(_);194195	/// The invulnerable, fixed collators.196	#[pallet::storage]197	#[pallet::getter(fn invulnerables)]198	pub type Invulnerables<T: Config> =199		StorageValue<_, BoundedVec<T::AccountId, T::MaxInvulnerables>, ValueQuery>;200201	/// The (community) collation license holders.202	#[pallet::storage]203	#[pallet::getter(fn licenses)]204	pub type Licenses<T: Config> =205		StorageMap<_, Blake2_128Concat, T::AccountId, BalanceOf<T>, ValueQuery>;206207	/// The (community, limited) collation candidates.208	#[pallet::storage]209	#[pallet::getter(fn candidates)]210	pub type Candidates<T: Config> = StorageValue<211		_,212		BoundedVec<T::AccountId, T::MaxCandidates>, //LicenseInfo<T::AccountId, BalanceOf<T>>, T::MaxCandidates>, // license ID?213		ValueQuery,214	>;215216	/// Collator will be kicked if it does not produce a block within the threshold (does not apply to invulnerables).217	///218	/// Should be a multiple of session or things will get inconsistent. todo:collator reword?219	#[pallet::storage]220	#[pallet::getter(fn kick_threshold)]221	pub type KickThreshold<T: Config> = StorageValue<_, T::BlockNumber, ValueQuery>;222223	/// Last block authored by collator.224	#[pallet::storage]225	#[pallet::getter(fn last_authored_block)]226	pub type LastAuthoredBlock<T: Config> =227		StorageMap<_, Twox64Concat, T::AccountId, T::BlockNumber, ValueQuery>;228229	/// Desired number of candidates.230	///231	/// This should ideally always be less than [`Config::MaxCandidates`] for weights to be correct.232	#[pallet::storage]233	#[pallet::getter(fn desired_candidates)]234	pub type DesiredCandidates<T> = StorageValue<_, u32, ValueQuery>;235236	/// Fixed amount to deposit to become a collator.237	///238	/// When a collator calls `leave_intent` they immediately receive the deposit back.239	#[pallet::storage]240	#[pallet::getter(fn license_bond)]241	pub type LicenseBond<T> = StorageValue<_, BalanceOf<T>, ValueQuery>;242243	#[pallet::genesis_config]244	pub struct GenesisConfig<T: Config> {245		pub invulnerables: Vec<T::AccountId>,246		pub license_bond: BalanceOf<T>,247		pub kick_threshold: T::BlockNumber,248		pub desired_candidates: u32,249	}250251	#[cfg(feature = "std")]252	impl<T: Config> Default for GenesisConfig<T> {253		fn default() -> Self {254			Self {255				invulnerables: Default::default(),256				license_bond: Default::default(),257				kick_threshold: T::BlockNumber::one(),258				desired_candidates: Default::default(),259			}260		}261	}262263	#[pallet::genesis_build]264	impl<T: Config> GenesisBuild<T> for GenesisConfig<T> {265		fn build(&self) {266			let duplicate_invulnerables = self267				.invulnerables268				.iter()269				.collect::<std::collections::BTreeSet<_>>();270			assert!(271				duplicate_invulnerables.len() == self.invulnerables.len(),272				"duplicate invulnerables in genesis."273			);274275			let bounded_invulnerables =276				BoundedVec::<_, T::MaxInvulnerables>::try_from(self.invulnerables.clone())277					.expect("genesis invulnerables are more than T::MaxInvulnerables");278			assert!(279				T::MaxCandidates::get() >= self.desired_candidates,280				"genesis desired_candidates are more than T::MaxCandidates",281			);282283			<DesiredCandidates<T>>::put(&self.desired_candidates);284			<LicenseBond<T>>::put(&self.license_bond);285			<KickThreshold<T>>::put(&self.kick_threshold);286			<Invulnerables<T>>::put(bounded_invulnerables);287		}288	}289290	#[pallet::event]291	#[pallet::generate_deposit(pub(super) fn deposit_event)]292	pub enum Event<T: Config> {293		NewDesiredCandidates {294			desired_candidates: u32,295		},296		NewLicenseBond {297			bond_amount: BalanceOf<T>,298		},299		NewKickThreshold {300			length_in_blocks: T::BlockNumber,301		},302		InvulnerableAdded {303			invulnerable: T::AccountId,304		},305		InvulnerableRemoved {306			invulnerable: T::AccountId,307		},308		LicenseObtained {309			account_id: T::AccountId,310			deposit: BalanceOf<T>,311		},312		LicenseForfeited {313			account_id: T::AccountId,314			deposit_returned: BalanceOf<T>,315		},316		CandidateAdded {317			account_id: T::AccountId,318		},319		CandidateRemoved {320			account_id: T::AccountId,321		},322	}323324	// Errors inform users that something went wrong.325	#[pallet::error]326	pub enum Error<T> {327		/// Too many candidates328		TooManyCandidates,329		/// Too few candidates330		TooFewCandidates,331		/// Unknown error332		Unknown,333		/// Permission issue334		Permission,335		/// User already holds license to collate336		AlreadyLicenseHolder,337		/// User does not hold a license to collate338		NoLicense,339		/// User is already a candidate340		AlreadyCandidate,341		/// User is not a candidate342		NotCandidate,343		/// Too many invulnerables344		TooManyInvulnerables,345		/// Too few invulnerables346		TooFewInvulnerables,347		/// User is already an Invulnerable348		AlreadyInvulnerable,349		/// User is not an Invulnerable350		NotInvulnerable,351		/// Account has no associated validator ID352		NoAssociatedValidatorId,353		/// Validator ID is not yet registered354		ValidatorNotRegistered,355	}356357	#[pallet::hooks]358	impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {}359360	#[pallet::call]361	impl<T: Config> Pallet<T> {362		/// Add a collator to the list of invulnerable (fixed) collators.363		#[pallet::weight(T::WeightInfo::set_invulnerables(1 as u32))] // todo:collator weight364		pub fn add_invulnerable(365			origin: OriginFor<T>,366			new: T::AccountId,367		) -> DispatchResultWithPostInfo {368			T::UpdateOrigin::ensure_origin(origin)?;369370			// check if the new invulnerable has associated validator keys before it is added371			let validator_key = T::ValidatorIdOf::convert(new.clone())372				.ok_or(Error::<T>::NoAssociatedValidatorId)?;373			ensure!(374				T::ValidatorRegistration::is_registered(&validator_key),375				Error::<T>::ValidatorNotRegistered376			);377			// ensure!(!Self::invulnerables().contains(&new), Error::<T>::AlreadyInvulnerable);378			if Self::invulnerables().contains(&new) {379				return Ok(().into());380			}381382			// todo:collator check license holders, release moneys, promotion!383			// force_release_license? Error::<T>::lreadyLicenseHolder?384385			<Invulnerables<T>>::try_append(new.clone())386				.map_err(|_| Error::<T>::TooManyInvulnerables)?;387			Self::deposit_event(Event::InvulnerableAdded { invulnerable: new });388			Ok(().into())389		}390391		/// Remove a collator from the list of invulnerable (fixed) collators.392		#[pallet::weight(T::WeightInfo::set_invulnerables(1))] // todo:collator weight393		pub fn remove_invulnerable(394			origin: OriginFor<T>,395			who: T::AccountId,396		) -> DispatchResultWithPostInfo {397			T::UpdateOrigin::ensure_origin(origin)?;398399			// let index = Self::invulnerables().into_iter().position(|r| r == who).ok_or(Error::<T>::NotInvulnerable)?;400			<Invulnerables<T>>::try_mutate(|invulnerables| -> DispatchResult {401				if invulnerables.len() <= 1 {402					return Err(Error::<T>::TooFewInvulnerables.into());403				}404405				let index = invulnerables406					.into_iter()407					.position(|r| *r == who)408					.ok_or(Error::<T>::NotInvulnerable)?;409				invulnerables.remove(index);410				Ok(())411			})?;412			/*let bounded_invulnerables = BoundedVec::<_, T::MaxInvulnerables>::try_from(new)413				.map_err(|_| Error::<T>::TooManyInvulnerables)?;414415			<Invulnerables<T>>::put(&bounded_invulnerables);*/416			Self::deposit_event(Event::InvulnerableRemoved { invulnerable: who });417			Ok(().into())418		}419420		/// Set the ideal number of collators (not including the invulnerables).421		/// If lowering this number, then the number of running collators could be higher than this figure.422		/// Aside from that edge case, there should be no other way to have more collators than the desired number.423		#[pallet::weight(T::WeightInfo::set_desired_candidates())]424		pub fn set_desired_candidates(425			origin: OriginFor<T>,426			max: u32,427		) -> DispatchResultWithPostInfo {428			T::UpdateOrigin::ensure_origin(origin)?;429			// we trust origin calls, this is just a for more accurate benchmarking430			if max > T::MaxCandidates::get() {431				log::warn!("max > T::MaxCandidates; you might need to run benchmarks again");432			}433			<DesiredCandidates<T>>::put(&max);434			Self::deposit_event(Event::NewDesiredCandidates {435				desired_candidates: max,436			});437			Ok(().into())438		}439440		/// Set the candidacy bond amount.441		#[pallet::weight(T::WeightInfo::set_license_bond())]442		pub fn set_license_bond(443			origin: OriginFor<T>,444			bond: BalanceOf<T>,445		) -> DispatchResultWithPostInfo {446			T::UpdateOrigin::ensure_origin(origin)?;447			<LicenseBond<T>>::put(&bond);448			Self::deposit_event(Event::NewLicenseBond { bond_amount: bond });449			Ok(().into())450		}451452		/// Set the length of the kick threshold.453		/// Note that if the length is not a multiple of the session period, it might get inconsistent.454		#[pallet::weight(T::WeightInfo::set_license_bond())] // todo:collator weight455		pub fn set_kick_threshold(456			origin: OriginFor<T>,457			kick_threshold: T::BlockNumber,458		) -> DispatchResultWithPostInfo {459			T::UpdateOrigin::ensure_origin(origin)?;460			// todo:collator insert something to guarantee consistency?461			<KickThreshold<T>>::put(kick_threshold);462			Self::deposit_event(Event::NewKickThreshold {463				length_in_blocks: kick_threshold,464			});465			Ok(().into())466		}467468		/// Purchase a license on block collation for this account.469		/// It does not make it a collator candidate, use `onboard` afterward. The account must470		/// (a) already have registered session keys and (b) be able to reserve the `LicenseBond`.471		///472		/// This call is not available to `Invulnerable` collators.473		#[pallet::weight(T::WeightInfo::register_as_candidate(T::MaxCandidates::get()))] // todo:collator weight474		pub fn get_license(origin: OriginFor<T>) -> DispatchResultWithPostInfo {475			// register_as_candidate476			let who = ensure_signed(origin)?;477478			if Licenses::<T>::contains_key(&who) {479				return Ok(().into());480			}481482			ensure!(483				!Self::invulnerables().contains(&who),484				Error::<T>::AlreadyInvulnerable485			);486487			let validator_key = T::ValidatorIdOf::convert(who.clone())488				.ok_or(Error::<T>::NoAssociatedValidatorId)?;489			ensure!(490				T::ValidatorRegistration::is_registered(&validator_key),491				Error::<T>::ValidatorNotRegistered492			);493494			let deposit = Self::license_bond();495			// First authored block is current block plus kick threshold to handle session delay496			/*let incoming = LicenseInfo {497				who: who.clone(),498				deposit,499			};*/500501			T::Currency::reserve(&who, deposit)?;502			Licenses::<T>::insert(who.clone(), deposit);503504			/*let current_count =505			<Licenses<T>>::try_mutate(|licenses| -> Result<usize, DispatchError> {506				if T::OriginPrivilegeCmp::cmp_privilege(&origin, &scheduled.origin) {507					return Err(BadOrigin.into());508				}509				if candidates.iter().any(|candidate| *candidate == who) {510					Err(Error::<T>::AlreadyLicenseHolder)?511				} else {512					T::Currency::reserve(&who, deposit)?;513					candidates514						.try_push(incoming)515						.map_err(|_| Error::<T>::TooManyCandidates)?;516					<LastAuthoredBlock<T>>::insert(517						who.clone(),518						frame_system::Pallet::<T>::block_number() + Self::kick_threshold(),519					);520					Ok(candidates.len())521				}522			})?;*/523524			Self::deposit_event(Event::LicenseObtained {525				account_id: who,526				deposit,527			});528			Ok(().into()) // Some(T::WeightInfo::register_as_candidate(current_count as u32)).into())529		}530531		/// Register this account as a candidate for collators for next sessions.532		/// The account must already hold a license, and cannot offboard immediately during a session.533		///534		/// This call is not available to `Invulnerable` collators.535		#[pallet::weight(T::WeightInfo::register_as_candidate(T::MaxCandidates::get()))] // todo:collator weight536		pub fn onboard(origin: OriginFor<T>) -> DispatchResultWithPostInfo {537			// register_as_candidate538			let who = ensure_signed(origin)?;539540			// ensure the user obtained the license.541			ensure!(Licenses::<T>::contains_key(&who), Error::<T>::NoLicense);542			// ensure we are below limit.543			let length = <Candidates<T>>::decode_len().unwrap_or_default();544			ensure!(545				(length as u32) < Self::desired_candidates(),546				Error::<T>::TooManyCandidates547			);548			// todo:collator really need it?549			ensure!(550				!Self::invulnerables().contains(&who),551				Error::<T>::AlreadyInvulnerable552			);553554			let deposit = Self::license_bond();555			// First authored block is current block plus kick threshold to handle session delay556			/*let incoming = LicenseInfo {557				who: who.clone(),558				deposit,559			};*/560561			let current_count =562				<Candidates<T>>::try_mutate(|candidates| -> Result<usize, DispatchError> {563					if candidates.iter().any(|candidate| *candidate == who) {564						Err(Error::<T>::AlreadyCandidate)?565					} else {566						T::Currency::reserve(&who, deposit)?;567						candidates568							.try_push(who.clone())569							.map_err(|_| Error::<T>::TooManyCandidates)?;570						<LastAuthoredBlock<T>>::insert(571							who.clone(),572							frame_system::Pallet::<T>::block_number() + Self::kick_threshold(),573						);574						Ok(candidates.len())575					}576				})?;577578			Self::deposit_event(Event::CandidateAdded { account_id: who });579			Ok(Some(T::WeightInfo::register_as_candidate(current_count as u32)).into())580		}581582		/// Deregister `origin` as a collator candidate. Note that the collator can only leave on583		/// session change. The license to `onboard` later at any other time will remain.584		///585		/// This call will fail if the total number of candidates would drop below `MinCandidates`. todo:collator maybe not586		#[pallet::weight(T::WeightInfo::leave_intent(T::MaxCandidates::get()))] // todo:collator weight587		pub fn offboard(origin: OriginFor<T>) -> DispatchResultWithPostInfo {588			// leave_intent589			let who = ensure_signed(origin)?;590			// todo:collator invulnerables and candidates should count against min candidates together591			ensure!(592				Self::candidates().len() as u32 > T::MinCandidates::get(),593				Error::<T>::TooFewCandidates594			);595			let current_count = Self::try_remove_candidate(&who)?;596597			Ok(Some(T::WeightInfo::leave_intent(current_count as u32)).into())598		}599600		/// Forfeit `origin`'s own license. The `LicenseBond` will be unreserved immediately.601		///602		/// This call is not available to `Invulnerable` collators.603		#[pallet::weight(T::WeightInfo::leave_intent(T::MaxCandidates::get()))] // todo:collator weight604		pub fn release_license(origin: OriginFor<T>) -> DispatchResultWithPostInfo {605			// leave_intent606			let who = ensure_signed(origin)?;607			// let current_count = Self::try_remove_candidate(&who, false)?;608			Self::try_release_license(&who, false)?;609610			Ok(().into())611		}612613		/// Force deregister `origin` as a collator candidate as a governing authority, and revoke its license.614		/// Note that the collator can only leave on session change.615		/// The `LicenseBond` will be unreserved and returned immediately.616		///617		/// This call is not available to `Invulnerable` collators.618		#[pallet::weight(T::WeightInfo::leave_intent(T::MaxCandidates::get()))] // todo:collator weight619		pub fn force_release_license(620			origin: OriginFor<T>,621			who: T::AccountId,622		) -> DispatchResultWithPostInfo {623			// leave_intent624			T::UpdateOrigin::ensure_origin(origin)?;625626			let current_count = Self::try_remove_candidate(&who)?;627			Self::try_release_license(&who, false)?;628629			Ok(Some(T::WeightInfo::leave_intent(current_count as u32)).into()) // todo:collator weight630		}631	}632633	impl<T: Config> Pallet<T> {634		/// Get a unique, inaccessible account id from the `PotId`.635		pub fn account_id() -> T::AccountId {636			T::PotId::get().into_account_truncating()637		}638639		/// Removes a candidate from the collator pool for the next session if they exist.640		fn try_remove_candidate(who: &T::AccountId) -> Result<usize, DispatchError> {641			let current_count =642				<Candidates<T>>::try_mutate(|candidates| -> Result<usize, DispatchError> {643					let index = candidates644						.iter()645						.position(|candidate| *candidate == *who)646						.ok_or(Error::<T>::NotCandidate)?;647					candidates.remove(index);648					<LastAuthoredBlock<T>>::remove(who.clone());649					Ok(candidates.len())650				})?;651			Self::deposit_event(Event::CandidateRemoved {652				account_id: who.clone(),653			});654			Ok(current_count)655		}656657		/// Removes a candidate if they exist and sends them back their deposit, optionally slashed.658		fn try_release_license(who: &T::AccountId, should_slash: bool) -> DispatchResult {659			let mut deposit_returned = BalanceOf::<T>::default();660			Licenses::<T>::try_mutate_exists(&who, |deposit| -> DispatchResult {661				if let Some(deposit) = deposit.take() {662					if should_slash {663						let slashed = T::SlashRatio::get() * deposit;664						let remaining = deposit - slashed;665666						let (imbalance, _) = T::Currency::slash_reserved(who, slashed);667						//T::Currency::unreserve(who, remaining);668						deposit_returned = remaining;669670						T::Currency::resolve_creating(&T::TreasuryAccountId::get(), imbalance);671					} else {672						//T::Currency::unreserve(who, deposit);673						deposit_returned = deposit;674					}675676					T::Currency::unreserve(who, deposit_returned);677					Ok(())678				} else {679					Err(Error::<T>::NoLicense.into())680				}681			})?;682			Self::deposit_event(Event::LicenseForfeited {683				account_id: who.clone(),684				deposit_returned,685			});686			Ok(())687		}688689		/// Assemble the current set of candidates and invulnerables into the next collator set.690		///691		/// This is done on the fly, as frequent as we are told to do so, as the session manager.692		pub fn assemble_collators(693			candidates: BoundedVec<T::AccountId, T::MaxCandidates>,694		) -> Vec<T::AccountId> {695			let mut collators = Self::invulnerables().to_vec();696			collators.extend(candidates);697			collators698		}699700		/// Kicks out candidates that did not produce a block in the kick threshold701		/// and **confiscates** their deposits to the treasury.702		pub fn kick_stale_candidates(703			candidates: BoundedVec<T::AccountId, T::MaxCandidates>, //LicenseInfo<T::AccountId, BalanceOf<T>>704		) -> BoundedVec<T::AccountId, T::MaxCandidates> {705			let now = frame_system::Pallet::<T>::block_number();706			let kick_threshold = Self::kick_threshold();707			candidates708				.into_iter()709				.filter_map(|c| {710					let last_block = <LastAuthoredBlock<T>>::get(c.clone());711					let since_last = now.saturating_sub(last_block);712					if since_last < kick_threshold ||713						Self::candidates().len() as u32 <= T::MinCandidates::get()714					{715						Some(c)716					} else {717						let outcome = Self::try_remove_candidate(&c);718						if let Err(why) = outcome {719							log::warn!("Failed to remove candidate {:?}", why);720							debug_assert!(false, "failed to remove candidate {:?}", why);721							return None;722						}723						let outcome = Self::try_release_license(&c, true);724						if let Err(why) = outcome {725							log::warn!("Failed to release license {:?}", why);726							debug_assert!(false, "failed to release license {:?}", why);727						}728						None729					}730				})731				.collect::<Vec<_>>()732				.try_into()733				.expect("filter_map operation can't result in a bounded vec larger than its original; qed")734		}735	}736737	/// Keep track of number of authored blocks per authority, uncles are counted as well since738	/// they're a valid proof of being online.739	impl<T: Config + pallet_authorship::Config>740		pallet_authorship::EventHandler<T::AccountId, T::BlockNumber> for Pallet<T>741	{742		fn note_author(author: T::AccountId) {743			let pot = Self::account_id();744			// assumes an ED will be sent to pot.745			let reward = T::Currency::free_balance(&pot)746				.checked_sub(&T::Currency::minimum_balance())747				.unwrap_or_else(Zero::zero)748				.div(2u32.into());749			// `reward` is half of pot account minus ED, this should never fail.750			let _success = T::Currency::transfer(&pot, &author, reward, KeepAlive);751			debug_assert!(_success.is_ok());752			<LastAuthoredBlock<T>>::insert(author, frame_system::Pallet::<T>::block_number());753754			frame_system::Pallet::<T>::register_extra_weight_unchecked(755				T::WeightInfo::note_author(),756				DispatchClass::Mandatory,757			);758		}759760		fn note_uncle(_author: T::AccountId, _age: T::BlockNumber) {761			//TODO can we ignore this?762		}763	}764765	/// Play the role of the session manager.766	impl<T: Config> SessionManager<T::AccountId> for Pallet<T> {767		fn new_session(index: SessionIndex) -> Option<Vec<T::AccountId>> {768			log::info!(769				"assembling new collators for new session {} at #{:?}",770				index,771				<frame_system::Pallet<T>>::block_number(),772			);773774			let candidates = Self::candidates();775			let candidates_len_before = candidates.len();776			let active_candidates = Self::kick_stale_candidates(candidates);777			let removed = candidates_len_before - active_candidates.len();778			let result = Self::assemble_collators(active_candidates);779780			frame_system::Pallet::<T>::register_extra_weight_unchecked(781				T::WeightInfo::new_session(candidates_len_before as u32, removed as u32),782				DispatchClass::Mandatory,783			);784			Some(result)785		}786		fn start_session(_: SessionIndex) {787			// we don't care.788		}789		fn end_session(_: SessionIndex) {790			// we don't care.791		}792	}793}