735 lines
25 KiB
Rust
735 lines
25 KiB
Rust
use std::convert::TryFrom;
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use std::mem::size_of;
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use crate::{Address, Hashable, Level, MerklePath, Position, Source};
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#[cfg(feature = "legacy-api")]
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use {std::collections::VecDeque, std::iter::repeat};
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/// Validation errors that can occur during reconstruction of a Merkle frontier from
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/// its constituent parts.
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#[derive(Clone, Debug, PartialEq, Eq)]
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pub enum FrontierError {
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/// An error representing that the number of ommers provided in frontier construction does not
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/// the expected length of the ommers list given the position.
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PositionMismatch { expected_ommers: u8 },
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/// An error representing that the position and/or list of ommers provided to frontier
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/// construction would result in a frontier that exceeds the maximum statically allowed depth
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/// of the tree. `depth` is the minimum tree depth that would be required in order for that
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/// tree to contain the position in question.
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MaxDepthExceeded { depth: u8 },
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}
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/// A [`NonEmptyFrontier`] is a reduced representation of a Merkle tree, containing a single leaf
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/// value, along with the vector of hashes produced by the reduction of previously appended leaf
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/// values that will be required when producing a witness for the current leaf.
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#[derive(Clone, Debug, PartialEq, Eq)]
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pub struct NonEmptyFrontier<H> {
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position: Position,
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leaf: H,
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ommers: Vec<H>,
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}
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impl<H> NonEmptyFrontier<H> {
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/// Constructs a new frontier with the specified value at position 0.
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pub fn new(leaf: H) -> Self {
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Self {
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position: 0.into(),
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leaf,
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ommers: vec![],
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}
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}
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/// Constructs a new frontier from its constituent parts.
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pub fn from_parts(position: Position, leaf: H, ommers: Vec<H>) -> Result<Self, FrontierError> {
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let expected_ommers = position.past_ommer_count();
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if ommers.len() == expected_ommers.into() {
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Ok(Self {
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position,
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leaf,
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ommers,
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})
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} else {
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Err(FrontierError::PositionMismatch { expected_ommers })
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}
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}
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/// Returns the position of the most recently appended leaf.
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pub fn position(&self) -> Position {
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self.position
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}
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/// Returns the leaf most recently appended to the frontier.
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pub fn leaf(&self) -> &H {
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&self.leaf
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}
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/// Returns the list of past hashes required to construct a witness for the
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/// leaf most recently appended to the frontier.
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pub fn ommers(&self) -> &[H] {
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&self.ommers
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}
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}
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impl<H: Hashable + Clone> NonEmptyFrontier<H> {
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/// Append a new leaf to the frontier, and recompute ommers by hashing together full subtrees
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/// until an empty ommer slot is found.
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pub fn append(&mut self, leaf: H) {
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let prior_position = self.position;
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let prior_leaf = self.leaf.clone();
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self.position += 1;
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self.leaf = leaf;
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if self.position.is_odd() {
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// if the new position is odd, the current leaf will directly become
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// an ommer at level 0, and there is no other mutation made to the tree.
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self.ommers.insert(0, prior_leaf);
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} else {
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// if the new position is even, then the current leaf will be hashed
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// with the first ommer, and so forth up the tree.
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let new_root_level = self.position.root_level();
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let mut carry = Some((prior_leaf, 0.into()));
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let mut new_ommers = Vec::with_capacity(self.position.past_ommer_count().into());
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for (addr, source) in prior_position.witness_addrs(new_root_level) {
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if let Source::Past(i) = source {
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if let Some((carry_ommer, carry_lvl)) = carry.as_ref() {
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if *carry_lvl == addr.level() {
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carry = Some((
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H::combine(addr.level(), &self.ommers[usize::from(i)], carry_ommer),
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addr.level() + 1,
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))
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} else {
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// insert the carry at the first empty slot; then the rest of the
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// ommers will remain unchanged
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new_ommers.push(carry_ommer.clone());
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new_ommers.push(self.ommers[usize::from(i)].clone());
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carry = None;
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}
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} else {
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// when there's no carry, just push on the ommer value
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new_ommers.push(self.ommers[usize::from(i)].clone());
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}
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}
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}
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// we carried value out, so we need to push on one more ommer.
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if let Some((carry_ommer, _)) = carry {
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new_ommers.push(carry_ommer);
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}
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self.ommers = new_ommers;
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}
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}
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/// Generate the root of the Merkle tree by hashing against empty subtree roots.
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pub fn root(&self, root_level: Option<Level>) -> H {
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let max_level = root_level.unwrap_or_else(|| self.position.root_level());
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self.position
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.witness_addrs(max_level)
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.fold(
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(self.leaf.clone(), Level::from(0)),
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|(digest, complete_lvl), (addr, source)| {
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// fold up from complete_lvl to addr.level() pairing with empty roots; if
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// complete_lvl == addr.level() this is just the complete digest to this point
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let digest = complete_lvl
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.iter_to(addr.level())
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.fold(digest, |d, l| H::combine(l, &d, &H::empty_root(l)));
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let res_digest = match source {
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Source::Past(i) => {
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H::combine(addr.level(), &self.ommers[usize::from(i)], &digest)
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}
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Source::Future => {
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H::combine(addr.level(), &digest, &H::empty_root(addr.level()))
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}
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};
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(res_digest, addr.level() + 1)
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},
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)
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.0
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}
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/// Constructs a witness for the leaf at the tip of this frontier, given a source of node
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/// values that complement this frontier.
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///
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/// If the `complement_nodes` function returns `None` when the value is requested at a given
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/// tree address, the address at which the failure occurs will be returned as an error.
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pub fn witness<F>(&self, depth: u8, complement_nodes: F) -> Result<Vec<H>, Address>
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where
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F: Fn(Address) -> Option<H>,
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{
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// construct a complete trailing edge that includes the data from
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// the following frontier not yet included in the trailing edge.
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self.position()
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.witness_addrs(depth.into())
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.map(|(addr, source)| match source {
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Source::Past(i) => Ok(self.ommers[usize::from(i)].clone()),
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Source::Future => complement_nodes(addr).ok_or(addr),
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})
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.collect::<Result<Vec<_>, _>>()
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}
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}
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/// A possibly-empty Merkle frontier.
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#[derive(Debug, Clone, PartialEq, Eq)]
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pub struct Frontier<H, const DEPTH: u8> {
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frontier: Option<NonEmptyFrontier<H>>,
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}
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impl<H, const DEPTH: u8> TryFrom<NonEmptyFrontier<H>> for Frontier<H, DEPTH> {
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type Error = FrontierError;
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fn try_from(f: NonEmptyFrontier<H>) -> Result<Self, FrontierError> {
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if f.position.root_level() <= Level::from(DEPTH) {
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Ok(Frontier { frontier: Some(f) })
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} else {
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Err(FrontierError::MaxDepthExceeded {
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depth: f.position.root_level().into(),
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})
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}
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}
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}
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impl<H, const DEPTH: u8> Frontier<H, DEPTH> {
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/// Constructs a new empty frontier.
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pub fn empty() -> Self {
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Self { frontier: None }
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}
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/// Constructs a new frontier from its constituent parts.
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///
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/// Returns `None` if the new frontier would exceed the maximum
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/// allowed depth or if the list of ommers provided is not consistent
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/// with the position of the leaf.
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pub fn from_parts(position: Position, leaf: H, ommers: Vec<H>) -> Result<Self, FrontierError> {
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NonEmptyFrontier::from_parts(position, leaf, ommers).and_then(Self::try_from)
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}
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/// Return the wrapped NonEmptyFrontier reference, or None if
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/// the frontier is empty.
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pub fn value(&self) -> Option<&NonEmptyFrontier<H>> {
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self.frontier.as_ref()
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}
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/// Returns the amount of memory dynamically allocated for ommer
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/// values within the frontier.
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pub fn dynamic_memory_usage(&self) -> usize {
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self.frontier.as_ref().map_or(0, |f| {
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size_of::<usize>() + (f.ommers.capacity() + 1) * size_of::<H>()
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})
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}
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}
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impl<H: Hashable + Clone, const DEPTH: u8> Frontier<H, DEPTH> {
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/// Appends a new value to the frontier at the next available slot.
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/// Returns true if successful and false if the frontier would exceed
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/// the maximum allowed depth.
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pub fn append(&mut self, value: H) -> bool {
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if let Some(frontier) = self.frontier.as_mut() {
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if frontier.position().is_complete_subtree(DEPTH.into()) {
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false
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} else {
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frontier.append(value);
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true
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}
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} else {
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self.frontier = Some(NonEmptyFrontier::new(value));
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true
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}
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}
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/// Obtains the current root of this Merkle frontier by hashing
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/// against empty nodes up to the maximum height of the pruned
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/// tree that the frontier represents.
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pub fn root(&self) -> H {
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self.frontier
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.as_ref()
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.map_or(H::empty_root(DEPTH.into()), |frontier| {
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frontier.root(Some(DEPTH.into()))
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})
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}
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/// Constructs a Merkle path that is suitable as a witness for the leaf at the tip of this
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/// frontier by using empty roots for the right-hand ommers. This is generally only useful
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/// for testing, so is not exposed in the public API.
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///
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/// Returns `Ok(Some(MerklePath))` if successful, `Ok(None)` if the frontier is empty,
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/// or an error containing the address of the failure.
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pub fn witness<F>(&self, complement_nodes: F) -> Result<Option<MerklePath<H, DEPTH>>, Address>
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where
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F: Fn(Address) -> Option<H>,
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{
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self.frontier
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.as_ref()
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.map(|f| {
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f.witness(DEPTH, complement_nodes).map(|path_elems| {
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MerklePath::from_parts(path_elems, f.position())
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.expect("Path length should be equal to frontier depth.")
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})
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})
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.transpose()
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}
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}
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#[cfg(feature = "legacy-api")]
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pub struct PathFiller<H> {
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queue: VecDeque<H>,
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}
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#[cfg(feature = "legacy-api")]
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impl<H: Hashable> PathFiller<H> {
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pub fn empty() -> Self {
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PathFiller {
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queue: VecDeque::new(),
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}
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}
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pub fn new(queue: VecDeque<H>) -> Self {
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Self { queue }
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}
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pub fn next(&mut self, level: Level) -> H {
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self.queue
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.pop_front()
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.unwrap_or_else(|| H::empty_root(level))
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}
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}
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/// A Merkle tree of note commitments.
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#[derive(Clone, Debug, PartialEq, Eq)]
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#[cfg(feature = "legacy-api")]
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pub struct CommitmentTree<H, const DEPTH: u8> {
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pub(crate) left: Option<H>,
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pub(crate) right: Option<H>,
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pub(crate) parents: Vec<Option<H>>,
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}
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#[cfg(feature = "legacy-api")]
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impl<H, const DEPTH: u8> CommitmentTree<H, DEPTH> {
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/// Creates an empty tree.
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pub fn empty() -> Self {
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CommitmentTree {
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left: None,
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right: None,
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parents: vec![],
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}
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}
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#[allow(clippy::result_unit_err)]
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pub fn from_parts(
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left: Option<H>,
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right: Option<H>,
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parents: Vec<Option<H>>,
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) -> Result<Self, ()> {
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if parents.len() < usize::from(DEPTH) {
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Ok(CommitmentTree {
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left,
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right,
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parents,
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})
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} else {
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Err(())
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}
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}
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pub fn left(&self) -> &Option<H> {
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&self.left
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}
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pub fn right(&self) -> &Option<H> {
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&self.right
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}
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pub fn parents(&self) -> &Vec<Option<H>> {
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&self.parents
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}
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/// Returns the number of leaf nodes in the tree.
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pub fn size(&self) -> usize {
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self.parents.iter().enumerate().fold(
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match (self.left.as_ref(), self.right.as_ref()) {
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(None, None) => 0,
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(Some(_), None) => 1,
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(Some(_), Some(_)) => 2,
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(None, Some(_)) => unreachable!(),
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},
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|acc, (i, p)| {
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// Treat occupation of parents array as a binary number
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// (right-shifted by 1)
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acc + if p.is_some() { 1 << (i + 1) } else { 0 }
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},
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)
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}
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pub(crate) fn is_complete(&self, depth: u8) -> bool {
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if depth == 0 {
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self.left.is_some() && self.right.is_none() && self.parents.is_empty()
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} else {
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self.left.is_some()
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&& self.right.is_some()
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&& self
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.parents
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.iter()
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.chain(repeat(&None))
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.take((depth - 1).into())
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.all(|p| p.is_some())
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}
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}
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}
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#[cfg(feature = "legacy-api")]
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impl<H: Hashable + Clone, const DEPTH: u8> CommitmentTree<H, DEPTH> {
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pub fn from_frontier(frontier: &Frontier<H, DEPTH>) -> Self {
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frontier.value().map_or_else(Self::empty, |f| {
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let mut ommers_iter = f.ommers().iter().cloned();
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let (left, right) = if f.position().is_odd() {
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(
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ommers_iter
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.next()
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.expect("An ommer must exist if the frontier position is odd"),
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Some(f.leaf().clone()),
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)
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} else {
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(f.leaf().clone(), None)
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};
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Self {
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left: Some(left),
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right,
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parents: (1u8..DEPTH)
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.into_iter()
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.map(|i| {
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if u64::from(f.position()) & (1 << i) == 0 {
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None
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} else {
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ommers_iter.next()
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}
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})
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.collect(),
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}
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})
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}
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pub fn to_frontier(&self) -> Frontier<H, DEPTH> {
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if self.size() == 0 {
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Frontier::empty()
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} else {
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let ommers_iter = self.parents.iter().filter_map(|v| v.as_ref()).cloned();
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let (leaf, ommers) = match (self.left.as_ref(), self.right.as_ref()) {
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(Some(a), None) => (a.clone(), ommers_iter.collect()),
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(Some(a), Some(b)) => (
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b.clone(),
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Some(a.clone()).into_iter().chain(ommers_iter).collect(),
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),
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_ => unreachable!(),
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};
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// If a frontier cannot be successfully constructed from the
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// parts of a commitment tree, it is a programming error.
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Frontier::from_parts((self.size() - 1).try_into().unwrap(), leaf, ommers)
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.expect("Frontier should be constructable from CommitmentTree.")
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}
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}
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/// Adds a leaf node to the tree.
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///
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/// Returns an error if the tree is full.
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#[allow(clippy::result_unit_err)]
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pub fn append(&mut self, node: H) -> Result<(), ()> {
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if self.is_complete(DEPTH) {
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// Tree is full
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return Err(());
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}
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match (&self.left, &self.right) {
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(None, _) => self.left = Some(node),
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(_, None) => self.right = Some(node),
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(Some(l), Some(r)) => {
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let mut combined = H::combine(0.into(), l, r);
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self.left = Some(node);
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self.right = None;
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for i in 0..DEPTH {
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let i_usize = usize::from(i);
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if i_usize < self.parents.len() {
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if let Some(p) = &self.parents[i_usize] {
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combined = H::combine((i + 1).into(), p, &combined);
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self.parents[i_usize] = None;
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} else {
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self.parents[i_usize] = Some(combined);
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break;
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}
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} else {
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self.parents.push(Some(combined));
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break;
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}
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}
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}
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}
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Ok(())
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}
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/// Returns the current root of the tree.
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pub fn root(&self) -> H {
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self.root_at_depth(DEPTH, PathFiller::empty())
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}
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pub fn root_at_depth(&self, depth: u8, mut filler: PathFiller<H>) -> H {
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assert!(depth > 0);
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// 1) Hash left and right leaves together.
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// - Empty leaves are used as needed.
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// - Note that `filler.next` is side-effecting and so cannot be factored out.
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let leaf_root = H::combine(
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0.into(),
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&self
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.left
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.as_ref()
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.map_or_else(|| filler.next(0.into()), |n| n.clone()),
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&self
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.right
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.as_ref()
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.map_or_else(|| filler.next(0.into()), |n| n.clone()),
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);
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// 2) Extend the parents to the desired depth with None values, then hash from leaf to
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// root. Roots of the empty subtrees are used as needed.
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self.parents
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.iter()
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.chain(repeat(&None))
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.take((depth - 1).into())
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.zip(0u8..)
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.fold(leaf_root, |root, (p, i)| {
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let level = Level::from(i + 1);
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match p {
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Some(node) => H::combine(level, node, &root),
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None => H::combine(level, &root, &filler.next(level)),
|
|
}
|
|
})
|
|
}
|
|
}
|
|
|
|
#[cfg(feature = "test-dependencies")]
|
|
pub mod testing {
|
|
use core::fmt::Debug;
|
|
use proptest::prelude::*;
|
|
use std::collections::hash_map::DefaultHasher;
|
|
use std::hash::Hasher;
|
|
|
|
use crate::{Hashable, Level};
|
|
|
|
impl<H: Hashable + Clone, const DEPTH: u8> crate::testing::Frontier<H>
|
|
for super::Frontier<H, DEPTH>
|
|
{
|
|
fn append(&mut self, value: H) -> bool {
|
|
super::Frontier::append(self, value)
|
|
}
|
|
|
|
fn root(&self) -> H {
|
|
super::Frontier::root(self)
|
|
}
|
|
}
|
|
|
|
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
|
|
pub struct TestNode(pub u64);
|
|
|
|
impl Hashable for TestNode {
|
|
fn empty_leaf() -> Self {
|
|
Self(0)
|
|
}
|
|
|
|
fn combine(level: Level, a: &Self, b: &Self) -> Self {
|
|
let mut hasher = DefaultHasher::new();
|
|
hasher.write_u8(level.into());
|
|
hasher.write_u64(a.0);
|
|
hasher.write_u64(b.0);
|
|
Self(hasher.finish())
|
|
}
|
|
}
|
|
|
|
prop_compose! {
|
|
pub fn arb_test_node()(i in any::<u64>()) -> TestNode {
|
|
TestNode(i)
|
|
}
|
|
}
|
|
|
|
#[cfg(feature = "legacy-api")]
|
|
use {crate::frontier::CommitmentTree, proptest::collection::vec};
|
|
|
|
#[cfg(feature = "legacy-api")]
|
|
pub fn arb_commitment_tree<
|
|
H: Hashable + Clone + Debug,
|
|
T: Strategy<Value = H>,
|
|
const DEPTH: u8,
|
|
>(
|
|
min_size: usize,
|
|
arb_node: T,
|
|
) -> impl Strategy<Value = CommitmentTree<H, DEPTH>> {
|
|
assert!((1 << DEPTH) >= min_size + 100);
|
|
vec(arb_node, min_size..(min_size + 100)).prop_map(move |v| {
|
|
let mut tree = CommitmentTree::empty();
|
|
for node in v.into_iter() {
|
|
tree.append(node).unwrap();
|
|
}
|
|
tree.parents.resize_with((DEPTH - 1).into(), || None);
|
|
tree
|
|
})
|
|
}
|
|
}
|
|
|
|
#[cfg(test)]
|
|
mod tests {
|
|
|
|
use super::*;
|
|
|
|
#[cfg(feature = "legacy-api")]
|
|
use {
|
|
super::testing::{arb_commitment_tree, arb_test_node, TestNode},
|
|
proptest::prelude::*,
|
|
};
|
|
|
|
#[test]
|
|
fn nonempty_frontier_root() {
|
|
let mut frontier = NonEmptyFrontier::new("a".to_string());
|
|
assert_eq!(frontier.root(None), "a");
|
|
|
|
frontier.append("b".to_string());
|
|
assert_eq!(frontier.root(None), "ab");
|
|
|
|
frontier.append("c".to_string());
|
|
assert_eq!(frontier.root(None), "abc_");
|
|
}
|
|
|
|
#[test]
|
|
fn frontier_from_parts() {
|
|
assert!(super::Frontier::<(), 1>::from_parts(0.into(), (), vec![]).is_ok());
|
|
assert!(super::Frontier::<(), 1>::from_parts(1.into(), (), vec![()]).is_ok());
|
|
assert!(super::Frontier::<(), 1>::from_parts(0.into(), (), vec![()]).is_err());
|
|
}
|
|
|
|
#[test]
|
|
fn frontier_root() {
|
|
let mut frontier: super::Frontier<String, 4> = super::Frontier::empty();
|
|
assert_eq!(frontier.root().len(), 16);
|
|
assert_eq!(frontier.root(), "________________");
|
|
|
|
frontier.append("a".to_string());
|
|
assert_eq!(frontier.root(), "a_______________");
|
|
|
|
frontier.append("b".to_string());
|
|
assert_eq!(frontier.root(), "ab______________");
|
|
|
|
frontier.append("c".to_string());
|
|
assert_eq!(frontier.root(), "abc_____________");
|
|
}
|
|
|
|
#[test]
|
|
fn nonempty_frontier_witness() {
|
|
let mut frontier = NonEmptyFrontier::<String>::new("a".to_string());
|
|
for c in 'b'..='g' {
|
|
frontier.append(c.to_string());
|
|
}
|
|
let bridge_value_at = |addr: Address| match <u8>::from(addr.level()) {
|
|
0 => Some("h".to_string()),
|
|
3 => Some("xxxxxxxx".to_string()),
|
|
_ => None,
|
|
};
|
|
|
|
assert_eq!(
|
|
Ok(["h", "ef", "abcd", "xxxxxxxx"]
|
|
.map(|v| v.to_string())
|
|
.to_vec()),
|
|
frontier.witness(4, bridge_value_at)
|
|
);
|
|
}
|
|
|
|
#[test]
|
|
fn frontier_witness() {
|
|
let mut frontier = Frontier::<String, 4>::empty();
|
|
for c in 'a'..='g' {
|
|
frontier.append(c.to_string());
|
|
}
|
|
|
|
assert_eq!(
|
|
frontier
|
|
.witness(|addr| Some(String::empty_root(addr.level())))
|
|
.map(|maybe_p| maybe_p.map(|p| p.path_elems().to_vec())),
|
|
Ok(Some(
|
|
["_", "ef", "abcd", "________"]
|
|
.map(|v| v.to_string())
|
|
.to_vec()
|
|
)),
|
|
);
|
|
}
|
|
|
|
#[test]
|
|
#[cfg(feature = "legacy-api")]
|
|
fn test_commitment_tree_complete() {
|
|
let mut t: CommitmentTree<TestNode, 6> = CommitmentTree::empty();
|
|
for n in 1u64..=32 {
|
|
t.append(TestNode(n)).unwrap();
|
|
// every tree of a power-of-two height is complete
|
|
let is_complete = n.count_ones() == 1;
|
|
let level = usize::BITS - 1 - n.leading_zeros(); //log2
|
|
assert_eq!(
|
|
is_complete,
|
|
t.is_complete(level.try_into().unwrap()),
|
|
"Tree {:?} {} complete at height {}",
|
|
t,
|
|
if is_complete {
|
|
"should be"
|
|
} else {
|
|
"should not be"
|
|
},
|
|
n
|
|
);
|
|
}
|
|
}
|
|
|
|
#[test]
|
|
#[cfg(feature = "legacy-api")]
|
|
fn test_commitment_tree_roundtrip() {
|
|
let ct = CommitmentTree {
|
|
left: Some("a".to_string()),
|
|
right: Some("b".to_string()),
|
|
parents: vec![
|
|
Some("c".to_string()),
|
|
Some("d".to_string()),
|
|
Some("e".to_string()),
|
|
Some("f".to_string()),
|
|
None,
|
|
None,
|
|
None,
|
|
],
|
|
};
|
|
|
|
let frontier: Frontier<String, 8> = ct.to_frontier();
|
|
let ct0 = CommitmentTree::from_frontier(&frontier);
|
|
assert_eq!(ct, ct0);
|
|
let frontier0: Frontier<String, 8> = ct0.to_frontier();
|
|
assert_eq!(frontier, frontier0);
|
|
}
|
|
|
|
#[cfg(feature = "legacy-api")]
|
|
proptest! {
|
|
#[test]
|
|
fn prop_commitment_tree_roundtrip(ct in arb_commitment_tree(32, arb_test_node())) {
|
|
let frontier: Frontier<TestNode, 8> = ct.to_frontier();
|
|
let ct0 = CommitmentTree::from_frontier(&frontier);
|
|
assert_eq!(ct, ct0);
|
|
let frontier0: Frontier<TestNode, 8> = ct0.to_frontier();
|
|
assert_eq!(frontier, frontier0);
|
|
}
|
|
|
|
#[test]
|
|
fn prop_commitment_tree_roundtrip_str(ct in arb_commitment_tree::<_, _, 8>(32, any::<char>().prop_map(|c| c.to_string()))) {
|
|
let frontier: Frontier<String, 8> = ct.to_frontier();
|
|
let ct0 = CommitmentTree::from_frontier(&frontier);
|
|
assert_eq!(ct, ct0);
|
|
let frontier0: Frontier<String, 8> = ct0.to_frontier();
|
|
assert_eq!(frontier, frontier0);
|
|
}
|
|
}
|
|
}
|