bp_header_chain/

lib.rs

// Copyright (C) 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/>.

//! Defines traits which represent a common interface for Substrate pallets which want to
//! incorporate bridge functionality.

#![warn(missing_docs)]
#![cfg_attr(not(feature = "std"), no_std)]

use crate::justification::{
	GrandpaJustification, JustificationVerificationContext, JustificationVerificationError,
};
use bp_runtime::{
	BasicOperatingMode, BlockNumberOf, Chain, HashOf, HasherOf, HeaderOf, RawStorageProof,
	StorageProofChecker, StorageProofError, UnderlyingChainProvider,
};
use codec::{Codec, Decode, DecodeWithMemTracking, Encode, EncodeLike, MaxEncodedLen};
use core::{clone::Clone, cmp::Eq, default::Default, fmt::Debug};
use frame_support::PalletError;
use scale_info::TypeInfo;
use serde::{Deserialize, Serialize};
use sp_consensus_grandpa::{
	AuthorityList, ConsensusLog, ScheduledChange, SetId, GRANDPA_ENGINE_ID,
};
use sp_runtime::{traits::Header as HeaderT, Digest, SaturatedConversion};
use sp_std::{boxed::Box, vec::Vec};

pub use call_info::{BridgeGrandpaCall, BridgeGrandpaCallOf, SubmitFinalityProofInfo};

mod call_info;

pub mod justification;
pub mod storage_keys;

/// Header chain error.
#[derive(
	Clone, Decode, DecodeWithMemTracking, Encode, Eq, PartialEq, PalletError, Debug, TypeInfo,
)]
pub enum HeaderChainError {
	/// Header with given hash is missing from the chain.
	UnknownHeader,
	/// Error generated by the `storage_proof` module.
	StorageProof(StorageProofError),
}

/// Header data that we're storing on-chain.
///
/// Even though we may store full header, our applications (XCM) only use couple of header
/// fields. Extracting those values makes on-chain storage and PoV smaller, which is good.
#[derive(Clone, Decode, Encode, Eq, MaxEncodedLen, PartialEq, Debug, TypeInfo)]
pub struct StoredHeaderData<Number, Hash> {
	/// Header number.
	pub number: Number,
	/// Header state root.
	pub state_root: Hash,
}

/// Stored header data builder.
pub trait StoredHeaderDataBuilder<Number, Hash> {
	/// Build header data from self.
	fn build(&self) -> StoredHeaderData<Number, Hash>;
}

impl<H: HeaderT> StoredHeaderDataBuilder<H::Number, H::Hash> for H {
	fn build(&self) -> StoredHeaderData<H::Number, H::Hash> {
		StoredHeaderData { number: *self.number(), state_root: *self.state_root() }
	}
}

/// Substrate header chain, abstracted from the way it is stored.
pub trait HeaderChain<C: Chain> {
	/// Returns state (storage) root of given finalized header.
	fn finalized_header_state_root(header_hash: HashOf<C>) -> Option<HashOf<C>>;

	/// Get storage proof checker using finalized header.
	fn verify_storage_proof(
		header_hash: HashOf<C>,
		storage_proof: RawStorageProof,
	) -> Result<StorageProofChecker<HasherOf<C>>, HeaderChainError> {
		let state_root = Self::finalized_header_state_root(header_hash)
			.ok_or(HeaderChainError::UnknownHeader)?;
		StorageProofChecker::new(state_root, storage_proof).map_err(HeaderChainError::StorageProof)
	}
}

/// A type that can be used as a parameter in a dispatchable function.
///
/// When using `decl_module` all arguments for call functions must implement this trait.
pub trait Parameter: Codec + EncodeLike + Clone + Eq + Debug + TypeInfo {}
impl<T> Parameter for T where T: Codec + EncodeLike + Clone + Eq + Debug + TypeInfo {}

/// A GRANDPA Authority List and ID.
#[derive(Default, Encode, Eq, Decode, DecodeWithMemTracking, Debug, PartialEq, Clone, TypeInfo)]
#[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
pub struct AuthoritySet {
	/// List of GRANDPA authorities for the current round.
	pub authorities: AuthorityList,
	/// Monotonic identifier of the current GRANDPA authority set.
	pub set_id: SetId,
}

impl AuthoritySet {
	/// Create a new GRANDPA Authority Set.
	pub fn new(authorities: AuthorityList, set_id: SetId) -> Self {
		Self { authorities, set_id }
	}
}

/// Data required for initializing the GRANDPA bridge pallet.
///
/// The bridge needs to know where to start its sync from, and this provides that initial context.
#[derive(
	Default,
	Encode,
	Decode,
	DecodeWithMemTracking,
	Debug,
	PartialEq,
	Eq,
	Clone,
	TypeInfo,
	Serialize,
	Deserialize,
)]
pub struct InitializationData<H: HeaderT> {
	/// The header from which we should start syncing.
	pub header: Box<H>,
	/// The initial authorities of the pallet.
	pub authority_list: AuthorityList,
	/// The ID of the initial authority set.
	pub set_id: SetId,
	/// Pallet operating mode.
	pub operating_mode: BasicOperatingMode,
}

/// Abstract finality proof that is justifying block finality.
pub trait FinalityProof<Hash, Number>: Clone + Send + Sync + Debug {
	/// Return hash of header that this proof is generated for.
	fn target_header_hash(&self) -> Hash;

	/// Return number of header that this proof is generated for.
	fn target_header_number(&self) -> Number;
}

/// A trait that provides helper methods for querying the consensus log.
pub trait ConsensusLogReader {
	/// Returns true if digest contains item that schedules authorities set change.
	fn schedules_authorities_change(digest: &Digest) -> bool;
}

/// A struct that provides helper methods for querying the GRANDPA consensus log.
pub struct GrandpaConsensusLogReader<Number>(sp_std::marker::PhantomData<Number>);

impl<Number: Codec> GrandpaConsensusLogReader<Number> {
	/// Find and return scheduled (regular) change digest item.
	pub fn find_scheduled_change(digest: &Digest) -> Option<ScheduledChange<Number>> {
		use sp_runtime::generic::OpaqueDigestItemId;
		let id = OpaqueDigestItemId::Consensus(&GRANDPA_ENGINE_ID);

		let filter_log = |log: ConsensusLog<Number>| match log {
			ConsensusLog::ScheduledChange(change) => Some(change),
			_ => None,
		};

		// find the first consensus digest with the right ID which converts to
		// the right kind of consensus log.
		digest.convert_first(|l| l.try_to(id).and_then(filter_log))
	}

	/// Find and return forced change digest item. Or light client can't do anything
	/// with forced changes, so we can't accept header with the forced change digest.
	pub fn find_forced_change(digest: &Digest) -> Option<(Number, ScheduledChange<Number>)> {
		// find the first consensus digest with the right ID which converts to
		// the right kind of consensus log.
		digest
			.convert_first(|log| log.consensus_try_to(&GRANDPA_ENGINE_ID))
			.and_then(|log| match log {
				ConsensusLog::ForcedChange(delay, change) => Some((delay, change)),
				_ => None,
			})
	}
}

impl<Number: Codec> ConsensusLogReader for GrandpaConsensusLogReader<Number> {
	fn schedules_authorities_change(digest: &Digest) -> bool {
		GrandpaConsensusLogReader::<Number>::find_scheduled_change(digest).is_some()
	}
}

/// The finality-related info associated to a header.
#[derive(Encode, Decode, DecodeWithMemTracking, Debug, PartialEq, Clone, TypeInfo)]
pub struct HeaderFinalityInfo<FinalityProof, FinalityVerificationContext> {
	/// The header finality proof.
	pub finality_proof: FinalityProof,
	/// The new verification context introduced by the header.
	pub new_verification_context: Option<FinalityVerificationContext>,
}

/// Grandpa-related info associated to a header. This info can be saved to events.
pub type StoredHeaderGrandpaInfo<Header> =
	HeaderFinalityInfo<GrandpaJustification<Header>, AuthoritySet>;

/// Processed Grandpa-related info associated to a header.
pub type HeaderGrandpaInfo<Header> =
	HeaderFinalityInfo<GrandpaJustification<Header>, JustificationVerificationContext>;

impl<Header: HeaderT> TryFrom<StoredHeaderGrandpaInfo<Header>> for HeaderGrandpaInfo<Header> {
	type Error = JustificationVerificationError;

	fn try_from(grandpa_info: StoredHeaderGrandpaInfo<Header>) -> Result<Self, Self::Error> {
		Ok(Self {
			finality_proof: grandpa_info.finality_proof,
			new_verification_context: match grandpa_info.new_verification_context {
				Some(authority_set) => Some(authority_set.try_into()?),
				None => None,
			},
		})
	}
}

/// Helper trait for finding equivocations in finality proofs.
pub trait FindEquivocations<FinalityProof, FinalityVerificationContext, EquivocationProof> {
	/// The type returned when encountering an error while looking for equivocations.
	type Error: Debug;

	/// Find equivocations.
	fn find_equivocations(
		verification_context: &FinalityVerificationContext,
		synced_proof: &FinalityProof,
		source_proofs: &[FinalityProof],
	) -> Result<Vec<EquivocationProof>, Self::Error>;
}

/// Substrate-based chain that is using direct GRANDPA finality.
///
/// Keep in mind that parachains are relying on relay chain GRANDPA, so they should not implement
/// this trait.
pub trait ChainWithGrandpa: Chain {
	/// Name of the bridge GRANDPA pallet (used in `construct_runtime` macro call) that is deployed
	/// at some other chain to bridge with this `ChainWithGrandpa`.
	///
	/// We assume that all chains that are bridging with this `ChainWithGrandpa` are using
	/// the same name.
	const WITH_CHAIN_GRANDPA_PALLET_NAME: &'static str;

	/// Max number of GRANDPA authorities at the chain.
	///
	/// This is a strict constant. If bridged chain will have more authorities than that,
	/// the GRANDPA bridge pallet may halt.
	const MAX_AUTHORITIES_COUNT: u32;

	/// Max reasonable number of headers in `votes_ancestries` vector of the GRANDPA justification.
	///
	/// This isn't a strict limit. The relay may submit justifications with more headers in its
	/// ancestry and the pallet will accept such justification. The limit is only used to compute
	/// maximal refund amount and submitting justifications which exceed the limit, may be costly
	/// to submitter.
	const REASONABLE_HEADERS_IN_JUSTIFICATION_ANCESTRY: u32;

	/// Maximal size of the mandatory chain header. Mandatory header is the header that enacts new
	/// GRANDPA authorities set (so it has large digest inside).
	///
	/// This isn't a strict limit. The relay may submit larger headers and the pallet will accept
	/// the call. The limit is only used to compute maximal refund amount and doing calls which
	/// exceed the limit, may be costly to submitter.
	const MAX_MANDATORY_HEADER_SIZE: u32;

	/// Average size of the chain header. We don't expect to see there headers that change GRANDPA
	/// authorities set (GRANDPA will probably be able to finalize at least one additional header
	/// per session on non test chains), so this is average size of headers that aren't changing the
	/// set.
	///
	/// This isn't a strict limit. The relay may submit justifications with larger headers and the
	/// pallet will accept the call. However, if the total size of all `submit_finality_proof`
	/// arguments exceeds the maximal size, computed using this average size, relayer will only get
	/// partial refund.
	///
	/// We expect some headers on production chains that are above this size. But they are rare and
	/// if rellayer cares about its profitability, we expect it'll select other headers for
	/// submission.
	const AVERAGE_HEADER_SIZE: u32;
}

impl<T> ChainWithGrandpa for T
where
	T: Chain + UnderlyingChainProvider,
	T::Chain: ChainWithGrandpa,
{
	const WITH_CHAIN_GRANDPA_PALLET_NAME: &'static str =
		<T::Chain as ChainWithGrandpa>::WITH_CHAIN_GRANDPA_PALLET_NAME;
	const MAX_AUTHORITIES_COUNT: u32 = <T::Chain as ChainWithGrandpa>::MAX_AUTHORITIES_COUNT;
	const REASONABLE_HEADERS_IN_JUSTIFICATION_ANCESTRY: u32 =
		<T::Chain as ChainWithGrandpa>::REASONABLE_HEADERS_IN_JUSTIFICATION_ANCESTRY;
	const MAX_MANDATORY_HEADER_SIZE: u32 =
		<T::Chain as ChainWithGrandpa>::MAX_MANDATORY_HEADER_SIZE;
	const AVERAGE_HEADER_SIZE: u32 = <T::Chain as ChainWithGrandpa>::AVERAGE_HEADER_SIZE;
}

/// Result of checking maximal expected submit finality proof call weight and size.
#[derive(Debug)]
pub struct SubmitFinalityProofCallExtras {
	/// If true, the call weight is larger than what we have assumed.
	///
	/// We have some assumptions about headers and justifications of the bridged chain.
	/// We know that if our assumptions are correct, then the call must not have the
	/// weight above some limit. The fee paid for weight above that limit, is never refunded.
	pub is_weight_limit_exceeded: bool,
	/// Extra size (in bytes) that we assume are included in the call.
	///
	/// We have some assumptions about headers and justifications of the bridged chain.
	/// We know that if our assumptions are correct, then the call must not have the
	/// weight above some limit. The fee paid for bytes above that limit, is never refunded.
	pub extra_size: u32,
	/// A flag that is true if the header is the mandatory header that enacts new
	/// authorities set.
	pub is_mandatory_finality_target: bool,
}

/// Checks whether the given `header` and its finality `proof` fit the maximal expected
/// call limits (size and weight). The submission may be refunded sometimes (see pallet
/// configuration for details), but it should fit some limits. If the call has some extra
/// weight and/or size included, though, we won't refund it or refund will be partial.
pub fn submit_finality_proof_limits_extras<C: ChainWithGrandpa>(
	header: &C::Header,
	proof: &justification::GrandpaJustification<C::Header>,
) -> SubmitFinalityProofCallExtras {
	// the `submit_finality_proof` call will reject justifications with invalid, duplicate,
	// unknown and extra signatures. It'll also reject justifications with less than necessary
	// signatures. So we do not care about extra weight because of additional signatures here.
	let precommits_len = proof.commit.precommits.len().saturated_into();
	let required_precommits = precommits_len;

	// the weight check is simple - we assume that there are no more than the `limit`
	// headers in the ancestry proof
	let votes_ancestries_len: u32 = proof.votes_ancestries.len().saturated_into();
	let is_weight_limit_exceeded =
		votes_ancestries_len > C::REASONABLE_HEADERS_IN_JUSTIFICATION_ANCESTRY;

	// check if the `finality_target` is a mandatory header. If so, we are ready to refund larger
	// size
	let is_mandatory_finality_target =
		GrandpaConsensusLogReader::<BlockNumberOf<C>>::find_scheduled_change(header.digest())
			.is_some();

	// we can estimate extra call size easily, without any additional significant overhead
	let actual_call_size: u32 =
		header.encoded_size().saturating_add(proof.encoded_size()).saturated_into();
	let max_expected_call_size = max_expected_submit_finality_proof_arguments_size::<C>(
		is_mandatory_finality_target,
		required_precommits,
	);
	let extra_size = actual_call_size.saturating_sub(max_expected_call_size);

	SubmitFinalityProofCallExtras {
		is_weight_limit_exceeded,
		extra_size,
		is_mandatory_finality_target,
	}
}

/// Returns maximal expected size of `submit_finality_proof` call arguments.
pub fn max_expected_submit_finality_proof_arguments_size<C: ChainWithGrandpa>(
	is_mandatory_finality_target: bool,
	precommits: u32,
) -> u32 {
	let max_expected_justification_size =
		GrandpaJustification::<HeaderOf<C>>::max_reasonable_size::<C>(precommits);

	// call arguments are header and justification
	let max_expected_finality_target_size = if is_mandatory_finality_target {
		C::MAX_MANDATORY_HEADER_SIZE
	} else {
		C::AVERAGE_HEADER_SIZE
	};
	max_expected_finality_target_size.saturating_add(max_expected_justification_size)
}

#[cfg(test)]
mod tests {
	use super::*;
	use bp_runtime::ChainId;
	use frame_support::weights::Weight;
	use sp_runtime::{
		testing::H256, traits::BlakeTwo256, DigestItem, MultiSignature, StateVersion,
	};

	struct TestChain;

	impl Chain for TestChain {
		const ID: ChainId = *b"test";

		type BlockNumber = u32;
		type Hash = H256;
		type Hasher = BlakeTwo256;
		type Header = sp_runtime::generic::Header<u32, BlakeTwo256>;
		type AccountId = u64;
		type Balance = u64;
		type Nonce = u64;
		type Signature = MultiSignature;

		const STATE_VERSION: StateVersion = StateVersion::V1;

		fn max_extrinsic_size() -> u32 {
			0
		}
		fn max_extrinsic_weight() -> Weight {
			Weight::zero()
		}
	}

	impl ChainWithGrandpa for TestChain {
		const WITH_CHAIN_GRANDPA_PALLET_NAME: &'static str = "Test";
		const MAX_AUTHORITIES_COUNT: u32 = 128;
		const REASONABLE_HEADERS_IN_JUSTIFICATION_ANCESTRY: u32 = 2;
		const MAX_MANDATORY_HEADER_SIZE: u32 = 100_000;
		const AVERAGE_HEADER_SIZE: u32 = 1_024;
	}

	#[test]
	fn max_expected_submit_finality_proof_arguments_size_respects_mandatory_argument() {
		assert!(
			max_expected_submit_finality_proof_arguments_size::<TestChain>(true, 100) >
				max_expected_submit_finality_proof_arguments_size::<TestChain>(false, 100),
		);
	}

	#[test]
	fn find_scheduled_change_works() {
		let scheduled_change = ScheduledChange { next_authorities: vec![], delay: 0 };

		// first
		let mut digest = Digest::default();
		digest.push(DigestItem::Consensus(
			GRANDPA_ENGINE_ID,
			ConsensusLog::ScheduledChange(scheduled_change.clone()).encode(),
		));
		assert_eq!(
			GrandpaConsensusLogReader::find_scheduled_change(&digest),
			Some(scheduled_change.clone())
		);

		// not first
		let mut digest = Digest::default();
		digest.push(DigestItem::Consensus(
			GRANDPA_ENGINE_ID,
			ConsensusLog::<u64>::OnDisabled(0).encode(),
		));
		digest.push(DigestItem::Consensus(
			GRANDPA_ENGINE_ID,
			ConsensusLog::ScheduledChange(scheduled_change.clone()).encode(),
		));
		assert_eq!(
			GrandpaConsensusLogReader::find_scheduled_change(&digest),
			Some(scheduled_change.clone())
		);
	}
}