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/>.

//! Parachains finality module.
//!
//! This module needs to be deployed with GRANDPA module, which is syncing relay
//! chain blocks. The main entry point of this module is `submit_parachain_heads`, which
//! accepts storage proof of some parachain `Heads` entries from bridged relay chain.
//! It requires corresponding relay headers to be already synced.

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

use bp_polkadot_core::parachains::{ParaHash, ParaHead, ParaId, ParachainHeadsProof};
use codec::{Decode, Encode};
use frame_support::RuntimeDebug;
use scale_info::TypeInfo;
use sp_runtime::traits::Header as HeaderT;
use sp_std::vec::Vec;

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

#[cfg(test)]
mod mock;

/// Block hash of the bridged relay chain.
pub type RelayBlockHash = bp_polkadot_core::Hash;
/// Block number of the bridged relay chain.
pub type RelayBlockNumber = bp_polkadot_core::BlockNumber;
/// Hasher of the bridged relay chain.
pub type RelayBlockHasher = bp_polkadot_core::Hasher;

/// Best known parachain head as it is stored in the runtime storage.
#[derive(Decode, Encode, PartialEq, RuntimeDebug, TypeInfo)]
pub struct BestParaHead {
	/// Number of relay block where this head has been updated.
	pub at_relay_block_number: RelayBlockNumber,
	/// Hash of parachain head.
	pub head_hash: ParaHash,
	/// Current ring buffer position for this parachain.
	pub next_imported_hash_position: u32,
}

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

	#[pallet::error]
	pub enum Error<T, I = ()> {
		/// Relay chain block is unknown to us.
		UnknownRelayChainBlock,
		/// Invalid storage proof has been passed.
		InvalidStorageProof,
	}

	#[pallet::config]
	#[pallet::disable_frame_system_supertrait_check]
	pub trait Config<I: 'static = ()>:
		pallet_bridge_grandpa::Config<Self::BridgesGrandpaPalletInstance>
	{
		/// Instance of bridges GRANDPA pallet that this pallet is linked to.
		///
		/// The GRANDPA pallet instance must be configured to import headers of relay chain that
		/// we're interested in.
		type BridgesGrandpaPalletInstance: 'static;

		/// Maximal number of single parachain heads to keep in the storage.
		///
		/// The setting is there to prevent growing the on-chain state indefinitely. Note
		/// the setting does not relate to parachain block numbers - we will simply keep as much
		/// items in the storage, so it doesn't guarantee any fixed timeframe for heads.
		#[pallet::constant]
		type HeadsToKeep: Get<u32>;
	}

	/// Best parachain heads.
	#[pallet::storage]
	pub type BestParaHeads<T: Config<I>, I: 'static = ()> =
		StorageMap<_, Blake2_128Concat, ParaId, BestParaHead>;

	/// Parachain heads which have been imported into the pallet.
	#[pallet::storage]
	pub type ImportedParaHeads<T: Config<I>, I: 'static = ()> =
		StorageDoubleMap<_, Blake2_128Concat, ParaId, Blake2_128Concat, ParaHash, ParaHead>;

	/// A ring buffer of imported parachain head hashes. Ordered by the insertion time.
	#[pallet::storage]
	pub(super) type ImportedParaHashes<T: Config<I>, I: 'static = ()> =
		StorageDoubleMap<_, Blake2_128Concat, ParaId, Twox64Concat, u32, ParaHash>;

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

	#[pallet::call]
	impl<T: Config<I>, I: 'static> Pallet<T, I>
	where
		<T as pallet_bridge_grandpa::Config<T::BridgesGrandpaPalletInstance>>::BridgedChain:
			bp_runtime::Chain<
				BlockNumber = RelayBlockNumber,
				Hash = RelayBlockHash,
				Hasher = RelayBlockHasher,
			>,
	{
		/// Submit proof of one or several parachain heads.
		///
		/// The proof is supposed to be proof of some `Heads` entries from the
		/// `polkadot-runtime-parachains::paras` pallet instance, deployed at the bridged chain.
		/// The proof is supposed to be crafted at the `relay_header_hash` that must already be
		/// imported by corresponding GRANDPA pallet at this chain.
		#[pallet::weight(0)] // TODO: https://github.com/paritytech/parity-bridges-common/issues/1391
		pub fn submit_parachain_heads(
			_origin: OriginFor<T>,
			relay_block_hash: RelayBlockHash,
			parachains: Vec<ParaId>,
			parachain_heads_proof: ParachainHeadsProof,
		) -> DispatchResult {
			// we'll need relay chain header to verify that parachains heads are always increasing.
			let relay_block = pallet_bridge_grandpa::ImportedHeaders::<
				T,
				T::BridgesGrandpaPalletInstance,
			>::get(relay_block_hash)
			.ok_or(Error::<T, I>::UnknownRelayChainBlock)?;
			let relay_block_number = *relay_block.number();

			// now parse storage proof and read parachain heads
			pallet_bridge_grandpa::Pallet::<T, T::BridgesGrandpaPalletInstance>::parse_finalized_storage_proof(
				relay_block_hash,
				sp_trie::StorageProof::new(parachain_heads_proof),
				move |storage| {
					for parachain in parachains {
						// TODO: https://github.com/paritytech/parity-bridges-common/issues/1393
						let parachain_head = match Pallet::<T, I>::read_parachain_head(&storage, parachain) {
							Some(parachain_head) => parachain_head,
							None => {
								log::trace!(
									target: "runtime::bridge-parachains",
									"The head of parachain {:?} has been declared, but is missing from the proof",
									parachain,
								);
								continue;
							}
						};

						let _: Result<_, ()> = BestParaHeads::<T, I>::try_mutate(parachain, |stored_best_head| {
							*stored_best_head = Some(Pallet::<T, I>::update_parachain_head(
								parachain,
								stored_best_head.take(),
								relay_block_number,
								parachain_head,
							)?);
							Ok(())
						});
					}
				},
			)
			.map_err(|_| Error::<T, I>::InvalidStorageProof)?;

			// TODO: there may be parachains we are not interested in - so we only need to accept
			// intersection of `parachains-interesting-to-us` and `parachains`
			// https://github.com/paritytech/parity-bridges-common/issues/1392

			// TODO: if some parachain is no more interesting to us, we should start pruning its
			// heads
			// https://github.com/paritytech/parity-bridges-common/issues/1392

			Ok(())
		}
	}

	impl<T: Config<I>, I: 'static> Pallet<T, I> {
		/// Read parachain head from storage proof.
		fn read_parachain_head(
			storage: &bp_runtime::StorageProofChecker<RelayBlockHasher>,
			parachain: ParaId,
		) -> Option<ParaHead> {
			let parachain_head_key = storage_keys::parachain_head_key(parachain);
			let parachain_head = storage.read_value(parachain_head_key.0.as_ref()).ok()??;
			let parachain_head = ParaHead::decode(&mut &parachain_head[..]).ok()?;
			Some(parachain_head)
		}

		/// Try to update parachain head.
		fn update_parachain_head(
			parachain: ParaId,
			stored_best_head: Option<BestParaHead>,
			updated_at_relay_block_number: RelayBlockNumber,
			updated_head: ParaHead,
		) -> Result<BestParaHead, ()> {
			// check if head has been already updated at better relay chain block. Without this
			// check, we may import heads in random order
			let updated_head_hash = updated_head.hash();
			let next_imported_hash_position = match stored_best_head {
				Some(stored_best_head)
					if stored_best_head.at_relay_block_number <= updated_at_relay_block_number =>
				{
					// check if this head has already been imported before
					if updated_head_hash == stored_best_head.head_hash {
						log::trace!(
							target: "runtime::bridge-parachains",
							"The head of parachain {:?} can't be updated to {}, because it has been already updated\
							to the same value at previous relay chain block: {} < {}",
							parachain,
							updated_head_hash,
							stored_best_head.at_relay_block_number,
							updated_at_relay_block_number,
						);
						return Err(())
					}

					stored_best_head.next_imported_hash_position
				},
				None => 0,
				Some(stored_best_head) => {
					log::trace!(
						target: "runtime::bridge-parachains",
						"The head of parachain {:?} can't be updated to {}, because it has been already updated\
						to {} at better relay chain block: {} > {}",
						parachain,
						updated_head_hash,
						stored_best_head.head_hash,
						stored_best_head.at_relay_block_number,
						updated_at_relay_block_number,
					);
					return Err(())
				},
			};

			// insert updated best parachain head
			let head_hash_to_prune =
				ImportedParaHashes::<T, I>::try_get(parachain, next_imported_hash_position);
			let updated_best_para_head = BestParaHead {
				at_relay_block_number: updated_at_relay_block_number,
				head_hash: updated_head_hash,
				next_imported_hash_position: (next_imported_hash_position + 1) %
					T::HeadsToKeep::get(),
			};
			ImportedParaHashes::<T, I>::insert(
				parachain,
				next_imported_hash_position,
				updated_head_hash,
			);
			ImportedParaHeads::<T, I>::insert(parachain, updated_head_hash, updated_head);

			// remove old head
			if let Ok(head_hash_to_prune) = head_hash_to_prune {
				log::trace!(
					target: "runtime::bridge-parachains",
					"Pruning old head of parachain {:?}: {}",
					parachain,
					head_hash_to_prune,
				);
				ImportedParaHeads::<T, I>::remove(parachain, head_hash_to_prune);
			}

			Ok(updated_best_para_head)
		}
	}
}

pub mod storage_keys {
	use super::*;
	use bp_runtime::storage_map_final_key;
	use frame_support::Twox64Concat;
	use sp_core::storage::StorageKey;

	/// Storage key of the parachain head in the runtime storage of relay chain.
	pub fn parachain_head_key(parachain: ParaId) -> StorageKey {
		storage_map_final_key::<Twox64Concat>("Paras", "Heads", &parachain.encode())
	}
}

#[cfg(test)]
mod tests {
	use super::*;
	use crate::mock::{run_test, test_relay_header, Origin, TestRuntime};

	use bp_test_utils::{authority_list, make_default_justification};
	use frame_support::{assert_noop, assert_ok, traits::OnInitialize};
	use sp_trie::{
		record_all_keys, trie_types::TrieDBMutV1, LayoutV1, MemoryDB, Recorder, TrieMut,
	};

	type BridgesGrandpaPalletInstance = pallet_bridge_grandpa::Instance1;

	fn initialize(state_root: RelayBlockHash) {
		pallet_bridge_grandpa::Pallet::<TestRuntime, BridgesGrandpaPalletInstance>::initialize(
			Origin::root(),
			bp_header_chain::InitializationData {
				header: Box::new(test_relay_header(0, state_root)),
				authority_list: authority_list(),
				set_id: 1,
				is_halted: false,
			},
		)
		.unwrap();
	}

	fn proceed(num: RelayBlockNumber, state_root: RelayBlockHash) {
		pallet_bridge_grandpa::Pallet::<TestRuntime, BridgesGrandpaPalletInstance>::on_initialize(
			0,
		);

		let header = test_relay_header(num, state_root);
		let justification = make_default_justification(&header);
		assert_ok!(
			pallet_bridge_grandpa::Pallet::<TestRuntime, BridgesGrandpaPalletInstance>::submit_finality_proof(
				Origin::signed(1),
				Box::new(header),
				justification,
			)
		);
	}

	fn prepare_parachain_heads_proof(
		heads: Vec<(ParaId, ParaHead)>,
	) -> (RelayBlockHash, ParachainHeadsProof) {
		let mut root = Default::default();
		let mut mdb = MemoryDB::default();
		{
			let mut trie = TrieDBMutV1::<RelayBlockHasher>::new(&mut mdb, &mut root);
			for (parachain, head) in heads {
				let storage_key = storage_keys::parachain_head_key(parachain);
				trie.insert(&storage_key.0, &head.encode())
					.map_err(|_| "TrieMut::insert has failed")
					.expect("TrieMut::insert should not fail in tests");
			}
		}

		// generate storage proof to be delivered to This chain
		let mut proof_recorder = Recorder::<RelayBlockHash>::new();
		record_all_keys::<LayoutV1<RelayBlockHasher>, _>(&mdb, &root, &mut proof_recorder)
			.map_err(|_| "record_all_keys has failed")
			.expect("record_all_keys should not fail in benchmarks");
		let storage_proof = proof_recorder.drain().into_iter().map(|n| n.data.to_vec()).collect();

		(root, storage_proof)
	}

	fn initial_best_head(parachain: u32) -> BestParaHead {
		BestParaHead {
			at_relay_block_number: 0,
			head_hash: head_data(parachain, 0).hash(),
			next_imported_hash_position: 1,
		}
	}

	fn head_data(parachain: u32, head_number: u32) -> ParaHead {
		ParaHead((parachain, head_number).encode())
	}

	fn head_hash(parachain: u32, head_number: u32) -> ParaHash {
		head_data(parachain, head_number).hash()
	}

	fn import_parachain_1_head(
		relay_chain_block: RelayBlockNumber,
		relay_state_root: RelayBlockHash,
		proof: ParachainHeadsProof,
	) -> sp_runtime::DispatchResult {
		Pallet::<TestRuntime>::submit_parachain_heads(
			Origin::signed(1),
			test_relay_header(relay_chain_block, relay_state_root).hash(),
			vec![ParaId(1)],
			proof,
		)
	}

	#[test]
	fn imports_initial_parachain_heads() {
		let (state_root, proof) = prepare_parachain_heads_proof(vec![
			(ParaId(1), head_data(1, 0)),
			(ParaId(3), head_data(3, 10)),
		]);
		run_test(|| {
			initialize(state_root);

			// we're trying to update heads of parachains 1, 2 and 3
			assert_ok!(Pallet::<TestRuntime>::submit_parachain_heads(
				Origin::signed(1),
				test_relay_header(0, state_root).hash(),
				vec![ParaId(1), ParaId(2), ParaId(3)],
				proof,
			),);

			// but only 1 and 2 are updated, because proof is missing head of parachain#2
			assert_eq!(BestParaHeads::<TestRuntime>::get(ParaId(1)), Some(initial_best_head(1)));
			assert_eq!(BestParaHeads::<TestRuntime>::get(ParaId(2)), None);
			assert_eq!(
				BestParaHeads::<TestRuntime>::get(ParaId(3)),
				Some(BestParaHead {
					at_relay_block_number: 0,
					head_hash: head_data(3, 10).hash(),
					next_imported_hash_position: 1,
				})
			);

			assert_eq!(
				ImportedParaHeads::<TestRuntime>::get(ParaId(1), initial_best_head(1).head_hash),
				Some(head_data(1, 0))
			);
			assert_eq!(
				ImportedParaHeads::<TestRuntime>::get(ParaId(2), initial_best_head(2).head_hash),
				None
			);
			assert_eq!(
				ImportedParaHeads::<TestRuntime>::get(ParaId(3), head_hash(3, 10)),
				Some(head_data(3, 10))
			);
		});
	}

	#[test]
	fn imports_parachain_heads_is_able_to_progress() {
		let (state_root_5, proof_5) =
			prepare_parachain_heads_proof(vec![(ParaId(1), head_data(1, 5))]);
		let (state_root_10, proof_10) =
			prepare_parachain_heads_proof(vec![(ParaId(1), head_data(1, 10))]);
		run_test(|| {
			// start with relay block #0 and import head#5 of parachain#1
			initialize(state_root_5);
			assert_ok!(import_parachain_1_head(0, state_root_5, proof_5));
			assert_eq!(
				BestParaHeads::<TestRuntime>::get(ParaId(1)),
				Some(BestParaHead {
					at_relay_block_number: 0,
					head_hash: head_data(1, 5).hash(),
					next_imported_hash_position: 1,
				})
			);
			assert_eq!(
				ImportedParaHeads::<TestRuntime>::get(ParaId(1), head_data(1, 5).hash()),
				Some(head_data(1, 5))
			);
			assert_eq!(
				ImportedParaHeads::<TestRuntime>::get(ParaId(1), head_data(1, 10).hash()),
				None
			);

			// import head#10 of parachain#1 at relay block #1
			proceed(1, state_root_10);
			assert_ok!(import_parachain_1_head(1, state_root_10, proof_10));
			assert_eq!(
				BestParaHeads::<TestRuntime>::get(ParaId(1)),
				Some(BestParaHead {
					at_relay_block_number: 1,
					head_hash: head_data(1, 10).hash(),
					next_imported_hash_position: 2,
				})
			);
			assert_eq!(
				ImportedParaHeads::<TestRuntime>::get(ParaId(1), head_data(1, 5).hash()),
				Some(head_data(1, 5))
			);
			assert_eq!(
				ImportedParaHeads::<TestRuntime>::get(ParaId(1), head_data(1, 10).hash()),
				Some(head_data(1, 10))
			);
		});
	}

	#[test]
	fn does_nothing_when_already_imported_this_head_at_previous_relay_header() {
		let (state_root, proof) = prepare_parachain_heads_proof(vec![(ParaId(1), head_data(1, 0))]);
		run_test(|| {
			// import head#0 of parachain#1 at relay block#0
			initialize(state_root);
			assert_ok!(import_parachain_1_head(0, state_root, proof.clone()));
			assert_eq!(BestParaHeads::<TestRuntime>::get(ParaId(1)), Some(initial_best_head(1)));

			// try to import head#0 of parachain#1 at relay block#1
			// => call succeeds, but nothing is changed
			proceed(1, state_root);
			assert_ok!(import_parachain_1_head(1, state_root, proof));
			assert_eq!(BestParaHeads::<TestRuntime>::get(ParaId(1)), Some(initial_best_head(1)));
		});
	}

	#[test]
	fn does_nothing_when_already_imported_head_at_better_relay_header() {
		let (state_root_5, proof_5) =
			prepare_parachain_heads_proof(vec![(ParaId(1), head_data(1, 5))]);
		let (state_root_10, proof_10) =
			prepare_parachain_heads_proof(vec![(ParaId(1), head_data(1, 10))]);
		run_test(|| {
			// start with relay block #0
			initialize(state_root_5);

			// head#10 of parachain#1 at relay block#1
			proceed(1, state_root_10);
			assert_ok!(import_parachain_1_head(1, state_root_10, proof_10));
			assert_eq!(
				BestParaHeads::<TestRuntime>::get(ParaId(1)),
				Some(BestParaHead {
					at_relay_block_number: 1,
					head_hash: head_data(1, 10).hash(),
					next_imported_hash_position: 1,
				})
			);

			// now try to import head#1 at relay block#0
			// => nothing is changed, because better head has already been imported
			assert_ok!(import_parachain_1_head(0, state_root_5, proof_5));
			assert_eq!(
				BestParaHeads::<TestRuntime>::get(ParaId(1)),
				Some(BestParaHead {
					at_relay_block_number: 1,
					head_hash: head_data(1, 10).hash(),
					next_imported_hash_position: 1,
				})
			);
		});
	}

	#[test]
	fn prunes_old_heads() {
		run_test(|| {
			let heads_to_keep = crate::mock::HeadsToKeep::get();

			// import exactly `HeadsToKeep` headers
			for i in 0..heads_to_keep {
				let (state_root, proof) =
					prepare_parachain_heads_proof(vec![(ParaId(1), head_data(1, i))]);
				if i == 0 {
					initialize(state_root);
				} else {
					proceed(i, state_root);
				}
				assert_ok!(import_parachain_1_head(i, state_root, proof));
			}

			// nothing is pruned yet
			for i in 0..heads_to_keep {
				assert!(ImportedParaHeads::<TestRuntime>::get(ParaId(1), head_data(1, i).hash())
					.is_some());
			}

			// import next relay chain header and next parachain head
			let (state_root, proof) =
				prepare_parachain_heads_proof(vec![(ParaId(1), head_data(1, heads_to_keep))]);
			proceed(heads_to_keep, state_root);
			assert_ok!(import_parachain_1_head(heads_to_keep, state_root, proof));

			// and the head#0 is pruned
			assert!(
				ImportedParaHeads::<TestRuntime>::get(ParaId(1), head_data(1, 0).hash()).is_none()
			);
			for i in 1..=heads_to_keep {
				assert!(ImportedParaHeads::<TestRuntime>::get(ParaId(1), head_data(1, i).hash())
					.is_some());
			}
		});
	}

	#[test]
	fn fails_on_unknown_relay_chain_block() {
		let (state_root, proof) = prepare_parachain_heads_proof(vec![(ParaId(1), head_data(1, 5))]);
		run_test(|| {
			// start with relay block #0
			initialize(state_root);

			// try to import head#5 of parachain#1 at unknown relay chain block #1
			assert_noop!(
				import_parachain_1_head(1, state_root, proof),
				Error::<TestRuntime>::UnknownRelayChainBlock
			);
		});
	}

	#[test]
	fn fails_on_invalid_storage_proof() {
		let (_state_root, proof) =
			prepare_parachain_heads_proof(vec![(ParaId(1), head_data(1, 5))]);
		run_test(|| {
			// start with relay block #0
			initialize(Default::default());

			// try to import head#5 of parachain#1 at relay chain block #0
			assert_noop!(
				import_parachain_1_head(0, Default::default(), proof),
				Error::<TestRuntime>::InvalidStorageProof
			);
		});
	}
}