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// This file is part of Substrate.
// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//! BEEFY + MMR utilities.
//!
//! While BEEFY can be used completely independently as an additional consensus gadget,
//! it is designed around a main use case of bridging standalone networks together.
//! For that use case it's common to use some aggregated data structure (like MMR) to be
//! used in conjunction with BEEFY, to be able to efficiently prove any past blockchain data.
//!
//! This module contains primitives used by Polkadot implementation of the BEEFY+MMR bridge,
//! but we imagine they will be useful for other chains that either want to bridge with Polkadot
//! or are completely standalone, but heavily inspired by Polkadot.
use crate::{ecdsa_crypto::AuthorityId, ConsensusLog, MmrRootHash, BEEFY_ENGINE_ID};
use alloc::vec::Vec;
use codec::{Decode, Encode, MaxEncodedLen};
use scale_info::TypeInfo;
use sp_runtime::{
generic::OpaqueDigestItemId,
traits::{Block, Header},
};
/// A provider for extra data that gets added to the Mmr leaf
pub trait BeefyDataProvider<ExtraData> {
/// Return a vector of bytes, ideally should be a merkle root hash
fn extra_data() -> ExtraData;
}
/// A default implementation for runtimes.
impl BeefyDataProvider<Vec<u8>> for () {
fn extra_data() -> Vec<u8> {
Vec::new()
}
}
/// A standard leaf that gets added every block to the MMR constructed by Substrate's `pallet_mmr`.
#[derive(Debug, PartialEq, Eq, Clone, Encode, Decode, TypeInfo)]
pub struct MmrLeaf<BlockNumber, Hash, MerkleRoot, ExtraData> {
/// Version of the leaf format.
///
/// Can be used to enable future format migrations and compatibility.
/// See [`MmrLeafVersion`] documentation for details.
pub version: MmrLeafVersion,
/// Current block parent number and hash.
pub parent_number_and_hash: (BlockNumber, Hash),
/// A merkle root of the next BEEFY authority set.
pub beefy_next_authority_set: BeefyNextAuthoritySet<MerkleRoot>,
/// Arbitrary extra leaf data to be used by downstream pallets to include custom data in the
/// [`MmrLeaf`]
pub leaf_extra: ExtraData,
}
/// An MMR leaf versioning scheme.
///
/// Version is a single byte that consists of two components:
/// - `major` - 3 bits
/// - `minor` - 5 bits
///
/// Any change in encoding that adds new items to the structure is considered non-breaking, hence
/// only requires an update of `minor` version. Any backward incompatible change (i.e. decoding to a
/// previous leaf format fails) should be indicated with `major` version bump.
///
/// Given that adding new struct elements in SCALE is backward compatible (i.e. old format can be
/// still decoded, the new fields will simply be ignored). We expect the major version to be bumped
/// very rarely (hopefully never).
#[derive(Debug, Default, PartialEq, Eq, Clone, Encode, Decode, TypeInfo)]
pub struct MmrLeafVersion(u8);
impl MmrLeafVersion {
/// Create new version object from `major` and `minor` components.
///
/// Panics if any of the component occupies more than 4 bits.
pub fn new(major: u8, minor: u8) -> Self {
if major > 0b111 || minor > 0b11111 {
panic!("Version components are too big.");
}
let version = (major << 5) + minor;
Self(version)
}
/// Split the version into `major` and `minor` sub-components.
pub fn split(&self) -> (u8, u8) {
let major = self.0 >> 5;
let minor = self.0 & 0b11111;
(major, minor)
}
}
/// Details of a BEEFY authority set.
#[derive(Debug, Default, PartialEq, Eq, Clone, Encode, Decode, TypeInfo, MaxEncodedLen)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct BeefyAuthoritySet<AuthoritySetCommitment> {
/// Id of the set.
///
/// Id is required to correlate BEEFY signed commitments with the validator set.
/// Light Client can easily verify that the commitment witness it is getting is
/// produced by the latest validator set.
pub id: crate::ValidatorSetId,
/// Number of validators in the set.
///
/// Some BEEFY Light Clients may use an interactive protocol to verify only a subset
/// of signatures. We put set length here, so that these clients can verify the minimal
/// number of required signatures.
pub len: u32,
/// Commitment(s) to BEEFY AuthorityIds.
///
/// This is used by Light Clients to confirm that the commitments are signed by the correct
/// validator set. Light Clients using interactive protocol, might verify only subset of
/// signatures, hence don't require the full list here (will receive inclusion proofs).
///
/// This could be Merkle Root Hash built from BEEFY ECDSA public keys and/or
/// polynomial commitment to the polynomial interpolating BLS public keys
/// which is used by APK proof based light clients to verify the validity
/// of aggregated BLS keys using APK proofs.
/// Multiple commitments can be tupled together.
pub keyset_commitment: AuthoritySetCommitment,
}
/// Details of the next BEEFY authority set.
pub type BeefyNextAuthoritySet<MerkleRoot> = BeefyAuthoritySet<MerkleRoot>;
/// Extract the MMR root hash from a digest in the given header, if it exists.
pub fn find_mmr_root_digest<B: Block>(header: &B::Header) -> Option<MmrRootHash> {
let id = OpaqueDigestItemId::Consensus(&BEEFY_ENGINE_ID);
let filter = |log: ConsensusLog<AuthorityId>| match log {
ConsensusLog::MmrRoot(root) => Some(root),
_ => None,
};
header.digest().convert_first(|l| l.try_to(id).and_then(filter))
}
#[cfg(feature = "std")]
pub use mmr_root_provider::MmrRootProvider;
#[cfg(feature = "std")]
mod mmr_root_provider {
use super::*;
use crate::{known_payloads, payload::PayloadProvider, Payload};
use alloc::sync::Arc;
use core::marker::PhantomData;
use sp_api::ProvideRuntimeApi;
use sp_mmr_primitives::MmrApi;
use sp_runtime::traits::NumberFor;
/// A [`crate::Payload`] provider where payload is Merkle Mountain Range root hash.
///
/// Encoded payload contains a [`crate::MmrRootHash`] type (i.e. 32-bytes hash).
pub struct MmrRootProvider<B, R> {
runtime: Arc<R>,
_phantom: PhantomData<B>,
}
impl<B, R> Clone for MmrRootProvider<B, R> {
fn clone(&self) -> Self {
Self { runtime: self.runtime.clone(), _phantom: PhantomData }
}
}
impl<B, R> MmrRootProvider<B, R>
where
B: Block,
R: ProvideRuntimeApi<B>,
R::Api: MmrApi<B, MmrRootHash, NumberFor<B>>,
{
/// Create new BEEFY Payload provider with MMR Root as payload.
pub fn new(runtime: Arc<R>) -> Self {
Self { runtime, _phantom: PhantomData }
}
/// Simple wrapper that gets MMR root from header digests or from client state.
fn mmr_root_from_digest_or_runtime(&self, header: &B::Header) -> Option<MmrRootHash> {
find_mmr_root_digest::<B>(header).or_else(|| {
self.runtime.runtime_api().mmr_root(header.hash()).ok().and_then(|r| r.ok())
})
}
}
impl<B: Block, R> PayloadProvider<B> for MmrRootProvider<B, R>
where
B: Block,
R: ProvideRuntimeApi<B>,
R::Api: MmrApi<B, MmrRootHash, NumberFor<B>>,
{
fn payload(&self, header: &B::Header) -> Option<Payload> {
self.mmr_root_from_digest_or_runtime(header).map(|mmr_root| {
Payload::from_single_entry(known_payloads::MMR_ROOT_ID, mmr_root.encode())
})
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::H256;
use sp_runtime::{traits::BlakeTwo256, Digest, DigestItem, OpaqueExtrinsic};
#[test]
fn should_construct_version_correctly() {
let tests = vec![(0, 0, 0b00000000), (7, 2, 0b11100010), (7, 31, 0b11111111)];
for (major, minor, version) in tests {
let v = MmrLeafVersion::new(major, minor);
assert_eq!(v.encode(), vec![version], "Encoding does not match.");
assert_eq!(v.split(), (major, minor));
}
}
#[test]
#[should_panic]
fn should_panic_if_major_too_large() {
MmrLeafVersion::new(8, 0);
}
#[test]
#[should_panic]
fn should_panic_if_minor_too_large() {
MmrLeafVersion::new(0, 32);
}
#[test]
fn extract_mmr_root_digest() {
type Header = sp_runtime::generic::Header<u64, BlakeTwo256>;
type Block = sp_runtime::generic::Block<Header, OpaqueExtrinsic>;
let mut header = Header::new(
1u64,
Default::default(),
Default::default(),
Default::default(),
Digest::default(),
);
// verify empty digest shows nothing
assert!(find_mmr_root_digest::<Block>(&header).is_none());
let mmr_root_hash = H256::random();
header.digest_mut().push(DigestItem::Consensus(
BEEFY_ENGINE_ID,
ConsensusLog::<AuthorityId>::MmrRoot(mmr_root_hash).encode(),
));
// verify validator set is correctly extracted from digest
let extracted = find_mmr_root_digest::<Block>(&header);
assert_eq!(extracted, Some(mmr_root_hash));
}
}