sp_mmr_primitives/

utils.rs

// 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.

//! Merkle Mountain Range utilities.

use codec::Encode;
use mmr_lib::helper;

#[cfg(not(feature = "std"))]
use alloc::vec::Vec;
use sp_runtime::traits::{CheckedAdd, CheckedSub, Header, One};

use crate::{Error, LeafIndex, NodeIndex};

/// Get the first block with MMR.
pub fn first_mmr_block_num<H: Header>(
	best_block_num: H::Number,
	mmr_leaf_count: LeafIndex,
) -> Result<H::Number, Error> {
	let mmr_blocks_count = mmr_leaf_count.try_into().map_err(|_| {
		Error::InvalidNumericOp
			.log_debug("The number of leaves couldn't be converted to a block number.")
	})?;
	best_block_num
		.checked_sub(&mmr_blocks_count)
		.and_then(|last_non_mmr_block| last_non_mmr_block.checked_add(&One::one()))
		.ok_or_else(|| {
			Error::InvalidNumericOp
				.log_debug("The best block should be greater than the number of mmr blocks.")
		})
}

/// Convert a block number into a leaf index.
pub fn block_num_to_leaf_index<H: Header>(
	block_num: H::Number,
	first_mmr_block_num: H::Number,
) -> Result<LeafIndex, Error> {
	let leaf_idx = block_num.checked_sub(&first_mmr_block_num).ok_or_else(|| {
		Error::InvalidNumericOp
			.log_debug("The provided block should be greater than the first mmr block.")
	})?;

	leaf_idx.try_into().map_err(|_| {
		Error::InvalidNumericOp.log_debug("Couldn't convert the leaf index to `LeafIndex`.")
	})
}

/// MMR nodes & size -related utilities.
pub struct NodesUtils {
	no_of_leaves: LeafIndex,
}

impl NodesUtils {
	/// Create new instance of MMR nodes utilities for given number of leaves.
	pub fn new(no_of_leaves: LeafIndex) -> Self {
		Self { no_of_leaves }
	}

	/// Calculate number of peaks in the MMR.
	pub fn number_of_peaks(&self) -> NodeIndex {
		self.number_of_leaves().count_ones() as NodeIndex
	}

	/// Return the number of leaves in the MMR.
	pub fn number_of_leaves(&self) -> LeafIndex {
		self.no_of_leaves
	}

	/// Calculate the total size of MMR (number of nodes).
	pub fn size(&self) -> NodeIndex {
		2 * self.no_of_leaves - self.number_of_peaks()
	}

	/// Calculate `LeafIndex` for the leaf that added `node_index` to the MMR.
	pub fn leaf_index_that_added_node(node_index: NodeIndex) -> LeafIndex {
		let rightmost_leaf_pos = Self::rightmost_leaf_node_index_from_pos(node_index);
		Self::leaf_node_index_to_leaf_index(rightmost_leaf_pos)
	}

	/// Translate a _leaf_ `NodeIndex` to its `LeafIndex`.
	fn leaf_node_index_to_leaf_index(pos: NodeIndex) -> LeafIndex {
		if pos == 0 {
			return 0
		}
		let peaks = helper::get_peaks(pos);
		(pos + peaks.len() as u64) >> 1
	}

	/// Translate a `LeafIndex` to its _leaf_ `NodeIndex`.
	pub fn leaf_index_to_leaf_node_index(leaf_index: NodeIndex) -> LeafIndex {
		helper::leaf_index_to_pos(leaf_index)
	}

	/// Starting from any node position get position of rightmost leaf; this is the leaf
	/// responsible for the addition of node `pos`.
	fn rightmost_leaf_node_index_from_pos(pos: NodeIndex) -> NodeIndex {
		pos - (helper::pos_height_in_tree(pos) as u64)
	}

	/// Starting from any leaf index, get the sequence of positions of the nodes added
	/// to the mmr when this leaf was added (inclusive of the leaf's position itself).
	/// That is, all of these nodes are right children of their respective parents.
	pub fn right_branch_ending_in_leaf(leaf_index: LeafIndex) -> Vec<NodeIndex> {
		let pos = helper::leaf_index_to_pos(leaf_index);
		let num_parents = leaf_index.trailing_ones() as u64;
		return (pos..=pos + num_parents).collect()
	}

	/// Build offchain key from `parent_hash` of block that originally added node `pos` to MMR.
	///
	/// This combination makes the offchain (key,value) entry resilient to chain forks.
	pub fn node_temp_offchain_key<H: Header>(
		prefix: &[u8],
		pos: NodeIndex,
		parent_hash: H::Hash,
	) -> Vec<u8> {
		(prefix, pos, parent_hash).encode()
	}

	/// Build canonical offchain key for node `pos` in MMR.
	///
	/// Used for nodes added by now finalized blocks.
	/// Never read keys using `node_canon_offchain_key` unless you sure that
	/// there's no `node_offchain_key` key in the storage.
	pub fn node_canon_offchain_key(prefix: &[u8], pos: NodeIndex) -> alloc::vec::Vec<u8> {
		(prefix, pos).encode()
	}
}

#[cfg(test)]
mod tests {
	use super::*;
	use mmr_lib::helper::leaf_index_to_pos;

	#[test]
	fn should_calculate_node_index_from_leaf_index() {
		for index in 0..100000 {
			let pos = leaf_index_to_pos(index);
			assert_eq!(NodesUtils::leaf_node_index_to_leaf_index(pos), index);
		}
	}

	#[test]
	fn should_calculate_right_branch_correctly() {
		fn left_jump_sequence(leaf_index: LeafIndex) -> Vec<u64> {
			let pos = leaf_index_to_pos(leaf_index);
			let mut right_branch_ending_in_leaf = vec![pos];
			let mut next_pos = pos + 1;
			while mmr_lib::helper::pos_height_in_tree(next_pos) > 0 {
				right_branch_ending_in_leaf.push(next_pos);
				next_pos += 1;
			}
			right_branch_ending_in_leaf
		}

		for leaf_index in 0..100000 {
			let pos = mmr_lib::helper::leaf_index_to_pos(leaf_index);
			assert_eq!(NodesUtils::right_branch_ending_in_leaf(pos), left_jump_sequence(pos));
		}
	}

	#[test]
	fn should_calculate_rightmost_leaf_node_index_from_pos() {
		for pos in 0..100000 {
			let leaf_pos = NodesUtils::rightmost_leaf_node_index_from_pos(pos);
			let leaf_index = NodesUtils::leaf_node_index_to_leaf_index(leaf_pos);
			assert!(NodesUtils::right_branch_ending_in_leaf(leaf_index).contains(&pos));
		}
	}

	#[test]
	fn should_calculate_depth_correctly() {
		assert_eq!(
			vec![0, 1, 2, 3, 4, 9, 15, 21]
				.into_iter()
				.map(|n| NodesUtils::new(n).number_of_leaves())
				.collect::<Vec<_>>(),
			vec![0, 1, 2, 3, 4, 9, 15, 21]
		);
	}

	#[test]
	fn should_calculate_number_of_peaks_correctly() {
		assert_eq!(
			vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 21]
				.into_iter()
				.map(|n| NodesUtils::new(n).number_of_peaks())
				.collect::<Vec<_>>(),
			vec![0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4, 3]
		);
	}

	#[test]
	fn should_calculate_the_size_correctly() {
		let leaves = vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 21];
		let sizes = vec![0, 1, 3, 4, 7, 8, 10, 11, 15, 16, 18, 19, 22, 23, 25, 26, 39];
		assert_eq!(
			leaves
				.clone()
				.into_iter()
				.map(|n| NodesUtils::new(n).size())
				.collect::<Vec<_>>(),
			sizes.clone()
		);
	}
}