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)]

pub use storage_types::StoredAuthoritySet;

use bp_header_chain::{
	justification::GrandpaJustification, AuthoritySet, ChainWithGrandpa, GrandpaConsensusLogReader,
	HeaderChain, InitializationData, StoredHeaderData, StoredHeaderDataBuilder,
	StoredHeaderGrandpaInfo,
};
use bp_runtime::{BlockNumberOf, HashOf, HasherOf, HeaderId, HeaderOf, OwnedBridgeModule};
use frame_support::{dispatch::PostDispatchInfo, ensure, DefaultNoBound};
use sp_runtime::{
	traits::{Header as HeaderT, Zero},
	SaturatedConversion,
};
use sp_std::{boxed::Box, convert::TryInto, prelude::*};

mod call_ext;
#[cfg(test)]
mod mock;
mod storage_types;

/// 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 call_ext::*;
pub use pallet::*;
pub use weights::WeightInfo;

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

/// Bridged chain from the pallet configuration.
pub type BridgedChain<T, I> = <T as Config<I>>::BridgedChain;
/// 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>;
/// Block id of the bridged chain.
pub type BridgedBlockId<T, I> = HeaderId<BridgedBlockHash<T, I>, BridgedBlockNumber<T, I>>;
/// 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>;
/// Header data of the bridged chain that is stored at this chain by this pallet.
pub type BridgedStoredHeaderData<T, I> =
	StoredHeaderData<BridgedBlockNumber<T, I>, BridgedBlockHash<T, I>>;

#[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 overarching event type.
		type RuntimeEvent: From<Event<Self, I>>
			+ IsType<<Self as frame_system::Config>::RuntimeEvent>;

		/// The chain we are bridging to here.
		type BridgedChain: ChainWithGrandpa;

		/// Maximal number of "free" mandatory header transactions per block.
		///
		/// To be able to track the bridged chain, the pallet requires all headers that are
		/// changing GRANDPA authorities set at the bridged chain (we call them mandatory).
		/// So it is a common good deed to submit mandatory headers to the pallet. However, if the
		/// bridged chain gets compromised, its validators may generate as many mandatory headers
		/// as they want. And they may fill the whole block (at this chain) for free. This constants
		/// limits number of calls that we may refund in a single block. All calls above this
		/// limit are accepted, but are not refunded.
		#[pallet::constant]
		type MaxFreeMandatoryHeadersPerBlock: 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]
	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: BlockNumberFor<T>) -> Weight {
			FreeMandatoryHeadersRemaining::<T, I>::put(T::MaxFreeMandatoryHeadersPerBlock::get());
			Weight::zero()
		}

		fn on_finalize(_n: BlockNumberFor<T>) {
			FreeMandatoryHeadersRemaining::<T, I>::kill();
		}
	}

	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.
		///
		/// The call fails if:
		///
		/// - the pallet is halted;
		///
		/// - the pallet knows better header than the `finality_target`;
		///
		/// - verification is not optimized or invalid;
		///
		/// - header contains forced authorities set change or change with non-zero delay.
		#[pallet::call_index(0)]
		#[pallet::weight(<T::WeightInfo as WeightInfo>::submit_finality_proof(
			justification.commit.precommits.len().saturated_into(),
			justification.votes_ancestries.len().saturated_into(),
		))]
		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)?;
			ensure_signed(origin)?;

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

			SubmitFinalityProofHelper::<T, I>::check_obsolete(number)?;

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

			let maybe_new_authority_set =