lib.rs

// Copyright 2021 Parity Technologies (UK) Ltd.
// This file is part of Parity Bridges Common.

// Parity Bridges Common 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.

// Parity Bridges Common 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 Parity Bridges Common.  If not, see <http://www.gnu.org/licenses/>.

//! Substrate GRANDPA Pallet
//!
//! This pallet is an on-chain GRANDPA light client for Substrate based chains.
//!
//! This pallet achieves this by trustlessly verifying GRANDPA finality proofs on-chain. Once
//! verified, finalized headers are stored in the pallet, thereby creating a sparse header chain.
//! This sparse header chain can be used as a source of truth for other higher-level applications.
//!
//! The pallet is responsible for tracking GRANDPA validator set hand-offs. We only import headers
//! with justifications signed by the current validator set we know of. The header is inspected for
//! a `ScheduledChanges` digest item, which is then used to update to next validator set.
//!
//! Since this pallet only tracks finalized headers it does not deal with forks. Forks can only
//! occur if the GRANDPA validator set on the bridged chain is either colluding or there is a severe
//! bug causing resulting in an equivocation. Such events are outside the scope of this pallet.
//! Shall the fork occur on the bridged chain governance intervention will be required to
//! re-initialize the bridge and track the right fork.

#![cfg_attr(not(feature = "std"), no_std)]
// Runtime-generated enums
#![allow(clippy::large_enum_variant)]

use bp_header_chain::{justification::GrandpaJustification, InitializationData};
use bp_runtime::{BlockNumberOf, Chain, HashOf, HasherOf, HeaderOf, OwnedBridgeModule};
use finality_grandpa::voter_set::VoterSet;
use frame_support::{ensure, fail};
use frame_system::ensure_signed;
use sp_finality_grandpa::{ConsensusLog, GRANDPA_ENGINE_ID};
use sp_runtime::traits::{Header as HeaderT, Zero};
use sp_std::{boxed::Box, convert::TryInto};

mod extension;
#[cfg(test)]
mod mock;

/// Module, containing weights for this pallet.
pub mod weights;

#[cfg(feature = "runtime-benchmarks")]
pub mod benchmarking;

// Re-export in crate namespace for `construct_runtime!`
pub use pallet::*;
pub use weights::WeightInfo;

/// The target that will be used when publishing logs related to this pallet.
const LOG_TARGET: &str = "runtime::bridge-grandpa";

/// Block number of the bridged chain.
pub type BridgedBlockNumber<T, I> = BlockNumberOf<<T as Config<I>>::BridgedChain>;
/// Block hash of the bridged chain.
pub type BridgedBlockHash<T, I> = HashOf<<T as Config<I>>::BridgedChain>;
/// Hasher of the bridged chain.
pub type BridgedBlockHasher<T, I> = HasherOf<<T as Config<I>>::BridgedChain>;
/// Header of the bridged chain.
pub type BridgedHeader<T, I> = HeaderOf<<T as Config<I>>::BridgedChain>;

#[frame_support::pallet]
pub mod pallet {
	use super::*;
	use bp_runtime::BasicOperatingMode;
	use frame_support::pallet_prelude::*;
	use frame_system::pallet_prelude::*;

	#[pallet::config]
	pub trait Config<I: 'static = ()>: frame_system::Config {
		/// The chain we are bridging to here.
		type BridgedChain: Chain;

		/// The upper bound on the number of requests allowed by the pallet.
		///
		/// A request refers to an action which writes a header to storage.
		///
		/// Once this bound is reached the pallet will not allow any dispatchables to be called
		/// until the request count has decreased.
		#[pallet::constant]
		type MaxRequests: Get<u32>;

		/// Maximal number of finalized headers to keep in the storage.
		///
		/// The setting is there to prevent growing the on-chain state indefinitely. Note
		/// the setting does not relate to block numbers - we will simply keep as much items
		/// in the storage, so it doesn't guarantee any fixed timeframe for finality headers.
		///
		/// Incautious change of this constant may lead to orphan entries in the runtime storage.
		#[pallet::constant]
		type HeadersToKeep: Get<u32>;

		/// Weights gathered through benchmarking.
		type WeightInfo: WeightInfo;
	}

	#[pallet::pallet]
	#[pallet::without_storage_info]
	pub struct Pallet<T, I = ()>(PhantomData<(T, I)>);

	#[pallet::hooks]
	impl<T: Config<I>, I: 'static> Hooks<BlockNumberFor<T>> for Pallet<T, I> {
		fn on_initialize(_n: T::BlockNumber) -> frame_support::weights::Weight {
			<RequestCount<T, I>>::mutate(|count| *count = count.saturating_sub(1));

			(0_u64)
				.saturating_add(T::DbWeight::get().reads(1))
				.saturating_add(T::DbWeight::get().writes(1))
		}
	}

	impl<T: Config<I>, I: 'static> OwnedBridgeModule<T> for Pallet<T, I> {
		const LOG_TARGET: &'static str = LOG_TARGET;
		type OwnerStorage = PalletOwner<T, I>;
		type OperatingMode = BasicOperatingMode;
		type OperatingModeStorage = PalletOperatingMode<T, I>;
	}

	#[pallet::call]
	impl<T: Config<I>, I: 'static> Pallet<T, I> {
		/// Verify a target header is finalized according to the given finality proof.
		///
		/// It will use the underlying storage pallet to fetch information about the current
		/// authorities and best finalized header in order to verify that the header is finalized.
		///
		/// If successful in verification, it will write the target header to the underlying storage
		/// pallet.
		#[pallet::weight(T::WeightInfo::submit_finality_proof(
			justification.commit.precommits.len().try_into().unwrap_or(u32::MAX),
			justification.votes_ancestries.len().try_into().unwrap_or(u32::MAX),
		))]
		pub fn submit_finality_proof(
			origin: OriginFor<T>,
			finality_target: Box<BridgedHeader<T, I>>,
			justification: GrandpaJustification<BridgedHeader<T, I>>,
		) -> DispatchResultWithPostInfo {
			Self::ensure_not_halted().map_err(Error::<T, I>::BridgeModule)?;
			let _ = ensure_signed(origin)?;

			ensure!(Self::request_count() < T::MaxRequests::get(), <Error<T, I>>::TooManyRequests);

			let (hash, number) = (finality_target.hash(), finality_target.number());
			log::trace!(
				target: LOG_TARGET,
				"Going to try and finalize header {:?}",
				finality_target
			);

			let best_finalized = BestFinalized::<T, I>::get();
			let best_finalized =
				best_finalized.and_then(|(_, hash)| ImportedHeaders::<T, I>::get(hash));
			let best_finalized = match best_finalized {
				Some(best_finalized) => best_finalized,
				None => {
					log::error!(
						target: LOG_TARGET,
						"Cannot finalize header {:?} because pallet is not yet initialized",
						finality_target,
					);
					fail!(<Error<T, I>>::NotInitialized);
				},
			};

			// We do a quick check here to ensure that our header chain is making progress and isn't
			// "travelling back in time" (which could be indicative of something bad, e.g a
			// hard-fork).
			ensure!(best_finalized.number() < number, <Error<T, I>>::OldHeader);

			let authority_set = <CurrentAuthoritySet<T, I>>::get();
			let set_id = authority_set.set_id;
			verify_justification::<T, I>(&justification, hash, *number, authority_set)?;

			let is_authorities_change_enacted =
				try_enact_authority_change::<T, I>(&finality_target, set_id)?;
			<RequestCount<T, I>>::mutate(|count| *count += 1);
			insert_header::<T, I>(*finality_target, hash);
			log::info!(
				target: LOG_TARGET,
				"Successfully imported finalized header with hash {:?}!",
				hash
			);

			// mandatory header is a header that changes authorities set. The pallet can't go
			// further without importing this header. So every bridge MUST import mandatory headers.
			//
			// We don't want to charge extra costs for mandatory operations. So relayer is not
			// paying fee for mandatory headers import transactions.
			let is_mandatory_header = is_authorities_change_enacted;