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// Copyright (C) Parity Technologies (UK) Ltd.
// This file is part of Polkadot.
// Polkadot is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
// Polkadot is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with Polkadot. If not, see <http://www.gnu.org/licenses/>.
//! A pallet for any shared state that other pallets may want access to.
//!
//! To avoid cyclic dependencies, it is important that this pallet is not
//! dependent on any of the other pallets.
use alloc::{
collections::{btree_map::BTreeMap, vec_deque::VecDeque},
vec::Vec,
};
use frame_support::{pallet_prelude::*, traits::DisabledValidators};
use frame_system::pallet_prelude::BlockNumberFor;
use polkadot_primitives::{SessionIndex, ValidatorId, ValidatorIndex};
use sp_runtime::traits::AtLeast32BitUnsigned;
use rand::{seq::SliceRandom, SeedableRng};
use rand_chacha::ChaCha20Rng;
use crate::configuration::HostConfiguration;
pub use pallet::*;
// `SESSION_DELAY` is used to delay any changes to Paras registration or configurations.
// Wait until the session index is 2 larger then the current index to apply any changes,
// which guarantees that at least one full session has passed before any changes are applied.
pub(crate) const SESSION_DELAY: SessionIndex = 2;
#[cfg(test)]
mod tests;
/// Information about past relay-parents.
#[derive(Encode, Decode, Default, TypeInfo)]
pub struct AllowedRelayParentsTracker<Hash, BlockNumber> {
// The past relay parents, paired with state roots, that are viable to build upon.
//
// They are in ascending chronologic order, so the newest relay parents are at
// the back of the deque.
// (relay_parent, state_root)
buffer: VecDeque<(Hash, Hash)>,
// The number of the most recent relay-parent, if any.
// If the buffer is empty, this value has no meaning and may
// be nonsensical.
latest_number: BlockNumber,
}
impl<Hash: PartialEq + Copy, BlockNumber: AtLeast32BitUnsigned + Copy>
AllowedRelayParentsTracker<Hash, BlockNumber>
{
/// Add a new relay-parent to the allowed relay parents, along with info about the header.
/// Provide a maximum ancestry length for the buffer, which will cause old relay-parents to be
/// pruned.
pub(crate) fn update(
&mut self,
relay_parent: Hash,
state_root: Hash,
number: BlockNumber,
max_ancestry_len: u32,
) {
// + 1 for the most recent block, which is always allowed.
let buffer_size_limit = max_ancestry_len as usize + 1;
self.buffer.push_back((relay_parent, state_root));
self.latest_number = number;
while self.buffer.len() > buffer_size_limit {
let _ = self.buffer.pop_front();
// We only allow relay parents within the same sessions, the buffer
// gets cleared on session changes.
/// Attempt to acquire the state root and block number to be used when building
/// upon the given relay-parent.
///
/// This only succeeds if the relay-parent is one of the allowed relay-parents.
/// If a previous relay-parent number is passed, then this only passes if the new relay-parent
/// is more recent than the previous.
pub(crate) fn acquire_info(
&self,
prev: Option<BlockNumber>,
) -> Option<(Hash, BlockNumber)> {
let pos = self.buffer.iter().position(|(rp, _)| rp == &relay_parent)?;
let age = (self.buffer.len() - 1) - pos;
let number = self.latest_number - BlockNumber::from(age as u32);
if let Some(prev) = prev {
if prev > number {
return None
Some((self.buffer[pos].1, number))
/// Returns block number of the earliest block the buffer would contain if
/// `now` is pushed into it.
pub(crate) fn hypothetical_earliest_block_number(
now: BlockNumber,
) -> BlockNumber {
let allowed_ancestry_len = max_ancestry_len.min(self.buffer.len() as u32);
now - allowed_ancestry_len.into()
#[frame_support::pallet]
pub mod pallet {
use super::*;
#[pallet::pallet]
#[pallet::without_storage_info]
pub struct Pallet<T>(_);
#[pallet::config]
pub trait Config: frame_system::Config {
type DisabledValidators: frame_support::traits::DisabledValidators;
/// The current session index.
#[pallet::storage]
pub type CurrentSessionIndex<T: Config> = StorageValue<_, SessionIndex, ValueQuery>;
/// All the validators actively participating in parachain consensus.
/// Indices are into the broader validator set.
pub type ActiveValidatorIndices<T: Config> = StorageValue<_, Vec<ValidatorIndex>, ValueQuery>;
/// The parachain attestation keys of the validators actively participating in parachain
/// consensus. This should be the same length as `ActiveValidatorIndices`.
pub type ActiveValidatorKeys<T: Config> = StorageValue<_, Vec<ValidatorId>, ValueQuery>;
/// All allowed relay-parents.
pub(crate) type AllowedRelayParents<T: Config> =
StorageValue<_, AllowedRelayParentsTracker<T::Hash, BlockNumberFor<T>>, ValueQuery>;
#[pallet::call]
impl<T: Config> Pallet<T> {}
impl<T: Config> Pallet<T> {
/// Called by the initializer to initialize the configuration pallet.
pub(crate) fn initializer_initialize(_now: BlockNumberFor<T>) -> Weight {
Weight::zero()
/// Called by the initializer to finalize the configuration pallet.
pub(crate) fn initializer_finalize() {}
/// Called by the initializer to note that a new session has started.
/// Returns the list of outgoing paras from the actions queue.
pub(crate) fn initializer_on_new_session(
session_index: SessionIndex,
random_seed: [u8; 32],
new_config: &HostConfiguration<BlockNumberFor<T>>,
all_validators: Vec<ValidatorId>,
) -> Vec<ValidatorId> {
// Drop allowed relay parents buffer on a session change.
// During the initialization of the next block we always add its parent
// to the tracker.
// With asynchronous backing candidates built on top of relay
// parent `R` are still restricted by the runtime to be backed
// by the group assigned at `number(R) + 1`, which is guaranteed
// to be in the current session.
AllowedRelayParents::<T>::mutate(|tracker| tracker.buffer.clear());
CurrentSessionIndex::<T>::set(session_index);
let mut rng: ChaCha20Rng = SeedableRng::from_seed(random_seed);
let mut shuffled_indices: Vec<_> = (0..all_validators.len())
.enumerate()
.map(|(i, _)| ValidatorIndex(i as _))
.collect();
shuffled_indices.shuffle(&mut rng);
if let Some(max) = new_config.max_validators {
shuffled_indices.truncate(max as usize);
let active_validator_keys =
crate::util::take_active_subset(&shuffled_indices, &all_validators);
ActiveValidatorIndices::<T>::set(shuffled_indices);
ActiveValidatorKeys::<T>::set(active_validator_keys.clone());
active_validator_keys
/// Return the session index that should be used for any future scheduled changes.
pub fn scheduled_session() -> SessionIndex {
CurrentSessionIndex::<T>::get().saturating_add(SESSION_DELAY)
/// Fetches disabled validators list from session pallet.
/// CAVEAT: this might produce incorrect results on session boundaries
pub fn disabled_validators() -> Vec<ValidatorIndex> {
let shuffled_indices = ActiveValidatorIndices::<T>::get();
// mapping from raw validator index to `ValidatorIndex`
// this computation is the same within a session, but should be cheap
let reverse_index = shuffled_indices
.iter()
.map(|(i, v)| (v.0, ValidatorIndex(i as u32)))
.collect::<BTreeMap<u32, ValidatorIndex>>();
// we might have disabled validators who are not parachain validators
T::DisabledValidators::disabled_validators()
.filter_map(|v| reverse_index.get(v).cloned())
.collect()
/// Test function for setting the current session index.
#[cfg(any(feature = "std", feature = "runtime-benchmarks", test))]
pub fn set_session_index(index: SessionIndex) {
CurrentSessionIndex::<T>::set(index);
pub fn set_active_validators_ascending(active: Vec<ValidatorId>) {
ActiveValidatorIndices::<T>::set(
(0..active.len()).map(|i| ValidatorIndex(i as _)).collect(),
);
ActiveValidatorKeys::<T>::set(active);
pub(crate) fn set_active_validators_with_indices(
indices: Vec<ValidatorIndex>,
keys: Vec<ValidatorId>,
assert_eq!(indices.len(), keys.len());
ActiveValidatorIndices::<T>::set(indices);
ActiveValidatorKeys::<T>::set(keys);
pub(crate) fn add_allowed_relay_parent(
relay_parent: T::Hash,
state_root: T::Hash,
number: BlockNumberFor<T>,
AllowedRelayParents::<T>::mutate(|tracker| {
tracker.update(relay_parent, state_root, number, max_ancestry_len)
})