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Merge pull request #62 from nuttycom/add_librustzcash_types 

Move `bridgetree::Frontier` to `incrementalmerkletree` and add `librustzcash` types.
This commit is contained in:
Kris Nuttycombe 2023-04-04 10:37:16 -06:00 committed by GitHub
parent 739441a892 ebbd2e3d2d
commit be81d67cef
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8 changed files with 1129 additions and 426 deletions
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3
bridgetree/CHANGELOG.md
View File

@ -14,8 +14,11 @@ and this project adheres to Rust's notion of
### Removed
- The `NonEmptyFrontier`, `Frontier`, and `FrontierError` types have
been moved to the `incrementalmerkletree` crate.
- The `testing` module has been removed in favor of depending on
`incrementalmerkletree::testing`.
- `serde` serialization and parsing are no longer supported.
## [bridgetree-v0.2.0] - 2022-05-10

1
bridgetree/Cargo.toml
View File

@ -15,7 +15,6 @@ rust-version = "1.60"
[dependencies]
incrementalmerkletree = { version = "0.3", path = "../incrementalmerkletree" }
serde = { version = "1", features = ["derive"] }
proptest = { version = "1.0.0", optional = true }
[dev-dependencies]

447
bridgetree/src/lib.rs
View File

@ -30,28 +30,14 @@
//! reset the state to.
//!
//! In this module, the term "ommer" is used as for the sibling of a parent node in a binary tree.
use serde::{Deserialize, Serialize};
pub use incrementalmerkletree::{
frontier::{Frontier, NonEmptyFrontier},
Address, Hashable, Level, Position, Retention, Source,
};
use std::collections::{BTreeMap, BTreeSet, VecDeque};
use std::convert::TryFrom;
use std::fmt::Debug;
use std::mem::size_of;
use std::ops::Range;
pub use incrementalmerkletree::{Address, Hashable, Level, Position, Retention};
/// Validation errors that can occur during reconstruction of a Merkle frontier from
/// its constituent parts.
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum FrontierError {
/// An error representing that the number of ommers provided in frontier construction does not
/// the expected length of the ommers list given the position.
PositionMismatch { expected_ommers: usize },
/// An error representing that the position and/or list of ommers provided to frontier
/// construction would result in a frontier that exceeds the maximum statically allowed depth
/// of the tree.
MaxDepthExceeded { depth: u8 },
}
/// Errors that can be discovered during checks that verify the compatibility of adjacent bridges.
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum ContinuityError {
@ -74,284 +60,6 @@ pub enum WitnessingError {
BridgeAddressInvalid(Address),
}
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
enum Source {
/// The sibling to the address can be derived from the incremental frontier
/// at the contained ommer index
Past(usize),
/// The sibling to the address must be obtained from values discovered by
/// the addition of more nodes to the tree
Future,
}
#[must_use = "iterators are lazy and do nothing unless consumed"]
struct WitnessAddrsIter {
root_level: Level,
current: Address,
ommer_count: usize,
}
/// Returns an iterator over the addresses of nodes required to create a witness for this
/// position, beginning with the sibling of the leaf at this position and ending with the
/// sibling of the ancestor of the leaf at this position that is required to compute a root at
/// the specified level.
fn witness_addrs(position: Position, root_level: Level) -> impl Iterator<Item = (Address, Source)> {
WitnessAddrsIter {
root_level,
current: Address::from(position),
ommer_count: 0,
}
}
impl Iterator for WitnessAddrsIter {
type Item = (Address, Source);
fn next(&mut self) -> Option<(Address, Source)> {
if self.current.level() < self.root_level {
let current = self.current;
let source = if current.is_right_child() {
Source::Past(self.ommer_count)
} else {
Source::Future
};
self.current = current.parent();
if matches!(source, Source::Past(_)) {
self.ommer_count += 1;
}
Some((current.sibling(), source))
} else {
None
}
}
}
/// A [`NonEmptyFrontier`] is a reduced representation of a Merkle tree, containing a single leaf
/// value, along with the vector of hashes produced by the reduction of previously appended leaf
/// values that will be required when producing a witness for the current leaf.
#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
pub struct NonEmptyFrontier<H> {
position: Position,
leaf: H,
ommers: Vec<H>,
}
impl<H> NonEmptyFrontier<H> {
/// Constructs a new frontier with the specified value at position 0.
pub fn new(leaf: H) -> Self {
Self {
position: 0.into(),
leaf,
ommers: vec![],
}
}
/// Constructs a new frontier from its constituent parts
pub fn from_parts(position: Position, leaf: H, ommers: Vec<H>) -> Result<Self, FrontierError> {
let expected_ommers = position.past_ommer_count();
if ommers.len() == expected_ommers {
Ok(Self {
position,
leaf,
ommers,
})
} else {
Err(FrontierError::PositionMismatch { expected_ommers })
}
}
/// Returns the position of the most recently appended leaf.
pub fn position(&self) -> Position {
self.position
}
/// Returns the leaf most recently appended to the frontier
pub fn leaf(&self) -> &H {
&self.leaf
}
/// Returns the list of past hashes required to construct a witness for the
/// leaf most recently appended to the frontier.
pub fn ommers(&self) -> &[H] {
&self.ommers
}
}
impl<H: Hashable + Clone> NonEmptyFrontier<H> {
/// Append a new leaf to the frontier, and recompute recompute ommers by hashing together full
/// subtrees until an empty ommer slot is found.
pub fn append(&mut self, leaf: H) {
let prior_position = self.position;
let prior_leaf = self.leaf.clone();
self.position += 1;
self.leaf = leaf;
if self.position.is_odd() {
// if the new position is odd, the current leaf will directly become
// an ommer at level 0, and there is no other mutation made to the tree.
self.ommers.insert(0, prior_leaf);
} else {
// if the new position is even, then the current leaf will be hashed
// with the first ommer, and so forth up the tree.
let new_root_level = self.position.root_level();
let mut carry = Some((prior_leaf, 0.into()));
let mut new_ommers = Vec::with_capacity(self.position.past_ommer_count());
for (addr, source) in witness_addrs(prior_position, new_root_level) {
if let Source::Past(i) = source {
if let Some((carry_ommer, carry_lvl)) = carry.as_ref() {
if *carry_lvl == addr.level() {
carry = Some((
H::combine(addr.level(), &self.ommers[i], carry_ommer),
addr.level() + 1,
))
} else {
// insert the carry at the first empty slot; then the rest of the
// ommers will remain unchanged
new_ommers.push(carry_ommer.clone());
new_ommers.push(self.ommers[i].clone());
carry = None;
}
} else {
// when there's no carry, just push on the ommer value
new_ommers.push(self.ommers[i].clone());
}
}
}
// we carried value out, so we need to push on one more ommer.
if let Some((carry_ommer, _)) = carry {
new_ommers.push(carry_ommer);
}
self.ommers = new_ommers;
}
}
/// Generate the root of the Merkle tree by hashing against empty subtree roots.
pub fn root(&self, root_level: Option<Level>) -> H {
let max_level = root_level.unwrap_or_else(|| self.position.root_level());
witness_addrs(self.position, max_level)
.fold(
(self.leaf.clone(), Level::from(0)),
|(digest, complete_lvl), (addr, source)| {
// fold up from complete_lvl to addr.level() pairing with empty roots; if
// complete_lvl == addr.level() this is just the complete digest to this point
let digest = complete_lvl
.iter_to(addr.level())
.fold(digest, |d, l| H::combine(l, &d, &H::empty_root(l)));
let res_digest = match source {
Source::Past(i) => H::combine(addr.level(), &self.ommers[i], &digest),
Source::Future => {
H::combine(addr.level(), &digest, &H::empty_root(addr.level()))
}
};
(res_digest, addr.level() + 1)
},
)
.0
}
/// Constructs a witness for the leaf at the tip of this
/// frontier, given a source of node values that complement this frontier.
pub fn witness<F>(&self, depth: u8, bridge_value_at: F) -> Result<Vec<H>, WitnessingError>
where
F: Fn(Address) -> Option<H>,
{
// construct a complete trailing edge that includes the data from
// the following frontier not yet included in the trailing edge.
witness_addrs(self.position(), depth.into())
.map(|(addr, source)| match source {
Source::Past(i) => Ok(self.ommers[i].clone()),
Source::Future => {
bridge_value_at(addr).ok_or(WitnessingError::BridgeAddressInvalid(addr))
}
})
.collect::<Result<Vec<_>, _>>()
}
}
/// A possibly-empty Merkle frontier.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct Frontier<H, const DEPTH: u8> {
frontier: Option<NonEmptyFrontier<H>>,
}
impl<H, const DEPTH: u8> TryFrom<NonEmptyFrontier<H>> for Frontier<H, DEPTH> {
type Error = FrontierError;
fn try_from(f: NonEmptyFrontier<H>) -> Result<Self, FrontierError> {
if f.position.root_level() <= Level::from(DEPTH) {
Ok(Frontier { frontier: Some(f) })
} else {
Err(FrontierError::MaxDepthExceeded {
depth: f.position.root_level().into(),
})
}
}
}
impl<H, const DEPTH: u8> Frontier<H, DEPTH> {
/// Constructs a new empty frontier.
pub fn empty() -> Self {
Self { frontier: None }
}
/// Constructs a new frontier from its constituent parts.
///
/// Returns `None` if the new frontier would exceed the maximum
/// allowed depth or if the list of ommers provided is not consistent
/// with the position of the leaf.
pub fn from_parts(position: Position, leaf: H, ommers: Vec<H>) -> Result<Self, FrontierError> {
NonEmptyFrontier::from_parts(position, leaf, ommers).and_then(Self::try_from)
}
/// Return the wrapped NonEmptyFrontier reference, or None if
/// the frontier is empty.
pub fn value(&self) -> Option<&NonEmptyFrontier<H>> {
self.frontier.as_ref()
}
/// Returns the amount of memory dynamically allocated for ommer
/// values within the frontier.
pub fn dynamic_memory_usage(&self) -> usize {
self.frontier.as_ref().map_or(0, |f| {
size_of::<usize>() + (f.ommers.capacity() + 1) * size_of::<H>()
})
}
}
impl<H: Hashable + Clone, const DEPTH: u8> Frontier<H, DEPTH> {
/// Appends a new value to the frontier at the next available slot.
/// Returns true if successful and false if the frontier would exceed
/// the maximum allowed depth.
pub fn append(&mut self, value: H) -> bool {
if let Some(frontier) = self.frontier.as_mut() {
if frontier.position().is_complete_subtree(DEPTH.into()) {
false
} else {
frontier.append(value);
true
}
} else {
self.frontier = Some(NonEmptyFrontier::new(value));
true
}
}
/// Obtains the current root of this Merkle frontier by hashing
/// against empty nodes up to the maximum height of the pruned
/// tree that the frontier represents.
pub fn root(&self) -> H {
self.frontier
.as_ref()
.map_or(H::empty_root(DEPTH.into()), |frontier| {
frontier.root(Some(DEPTH.into()))
})
}
}
/// The information required to "update" witnesses from one state of a Merkle tree to another.
///
/// The witness for a particular leaf of a Merkle tree consists of the siblings of that leaf, plus
@ -366,7 +74,7 @@ impl<H: Hashable + Clone, const DEPTH: u8> Frontier<H, DEPTH> {
/// [`MerkleBridge`] values have a semigroup, such that the sum (`fuse`d) value of two successive
/// bridges, along with a [`NonEmptyFrontier`] with its tip at the prior position of the first bridge
/// being fused, can be used to produce a witness for the leaf at the tip of the prior frontier.
#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct MerkleBridge<H> {
/// The position of the final leaf in the frontier of the bridge that this bridge is the
/// successor of, or None if this is the first bridge in a tree.
@ -582,19 +290,21 @@ impl<'a, H: Hashable + Clone + Ord + 'a> MerkleBridge<H> {
) -> Result<Vec<H>, WitnessingError> {
assert!(Some(prior_frontier.position()) == self.prior_position);
prior_frontier.witness(depth, |addr| {
let r = addr.position_range();
if self.frontier.position() < r.start {
Some(H::empty_root(addr.level()))
} else if r.contains(&self.frontier.position()) {
Some(self.frontier.root(Some(addr.level())))
} else {
// the frontier's position is after the end of the requested
// range, so the requested value should exist in a stored
// fragment
self.ommers.get(&addr).cloned()
}
})
prior_frontier
.witness(depth, |addr| {
let r = addr.position_range();
if self.frontier.position() < r.start {
Some(H::empty_root(addr.level()))
} else if r.contains(&self.frontier.position()) {
Some(self.frontier.root(Some(addr.level())))
} else {
// the frontier's position is after the end of the requested
// range, so the requested value should exist in a stored
// fragment
self.ommers.get(&addr).cloned()
}
})
.map_err(WitnessingError::BridgeAddressInvalid)
}
fn retain(&mut self, ommer_addrs: &BTreeSet<Address>) {
@ -612,7 +322,7 @@ impl<'a, H: Hashable + Clone + Ord + 'a> MerkleBridge<H> {
/// crosses [`MerkleBridge`] boundaries, and so it is not sufficient to just truncate the list of
/// bridges; instead, we use [`Checkpoint`] values to be able to rapidly restore the cache to its
/// previous state.
#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct Checkpoint<C> {
/// The unique identifier for this checkpoint.
id: C,
@ -712,7 +422,7 @@ impl<C> Checkpoint<C> {
/// A sparse representation of a Merkle tree with linear appending of leaves that contains enough
/// information to produce a witness for any `mark`ed leaf.
#[derive(Clone, PartialEq, Eq, Serialize, Deserialize)]
#[derive(Clone, PartialEq, Eq)]
pub struct BridgeTree<H, C, const DEPTH: u8> {
/// The ordered list of Merkle bridges representing the history
/// of the tree. There will be one bridge for each saved leaf.
@ -825,8 +535,12 @@ impl<H, C, const DEPTH: u8> BridgeTree<H, C, DEPTH> {
impl<H: Hashable + Clone + Ord, C: Clone + Ord, const DEPTH: u8> BridgeTree<H, C, DEPTH> {
/// Construct a new BridgeTree that will start recording changes from the state of
/// the specified frontier.
pub fn from_frontier(max_checkpoints: usize, frontier: NonEmptyFrontier<H>) -> Self {
Self {
pub fn from_frontier(
max_checkpoints: usize,
frontier: NonEmptyFrontier<H>,
checkpoint_id: C,
) -> Self {
let mut bridge = Self {
prior_bridges: vec![],
current_bridge: Some(MerkleBridge::from_parts(
None,
@ -837,7 +551,9 @@ impl<H: Hashable + Clone + Ord, C: Clone + Ord, const DEPTH: u8> BridgeTree<H, C
saved: BTreeMap::new(),
checkpoints: VecDeque::new(),
max_checkpoints,
}
};
bridge.checkpoint(checkpoint_id);
bridge
}
/// Construct a new BridgeTree from its constituent parts, checking for internal
@ -1229,8 +945,10 @@ impl<H: Hashable + Clone + Ord, C: Clone + Ord, const DEPTH: u8> BridgeTree<H, C
// Add the elements of the auth path to the set of addresses we should
// continue to track and retain information for
for (addr, source) in
witness_addrs(cur_bridge.frontier.position(), Level::from(DEPTH))
for (addr, source) in cur_bridge
.frontier
.position()
.witness_addrs(Level::from(DEPTH))
{
if source == Source::Future {
ommer_addrs.insert(addr);
@ -1343,101 +1061,6 @@ mod tests {
}
}
#[test]
fn position_witness_addrs() {
use Source::*;
let path_elem = |l, i, s| (Address::from_parts(Level::from(l), i), s);
assert_eq!(
vec![path_elem(0, 1, Future), path_elem(1, 1, Future)],
witness_addrs(Position::from(0), Level::from(2)).collect::<Vec<_>>()
);
assert_eq!(
vec![path_elem(0, 3, Future), path_elem(1, 0, Past(0))],
witness_addrs(Position::from(2), Level::from(2)).collect::<Vec<_>>()
);
assert_eq!(
vec![
path_elem(0, 2, Past(0)),
path_elem(1, 0, Past(1)),
path_elem(2, 1, Future)
],
witness_addrs(Position::from(3), Level::from(3)).collect::<Vec<_>>()
);
assert_eq!(
vec![
path_elem(0, 5, Future),
path_elem(1, 3, Future),
path_elem(2, 0, Past(0)),
path_elem(3, 1, Future)
],
witness_addrs(Position::from(4), Level::from(4)).collect::<Vec<_>>()
);
assert_eq!(
vec![
path_elem(0, 7, Future),
path_elem(1, 2, Past(0)),
path_elem(2, 0, Past(1)),
path_elem(3, 1, Future)
],
witness_addrs(Position::from(6), Level::from(4)).collect::<Vec<_>>()
);
}
#[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 frontier_witness() {
let mut frontier = NonEmptyFrontier::<String>::new("a".to_string());
for c in 'b'..'h' {
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 tree_depth() {
let mut tree = BridgeTree::<String, usize, 3>::new(100, 0);

12
incrementalmerkletree/CHANGELOG.md
View File

@ -7,6 +7,17 @@ and this project adheres to Rust's notion of
## [Unreleased]
### Added
- `incrementalmerkletree::frontier` Types that model the state at the rightmost
node of a Merkle tree that is filled sequentially from the left. These have
been migrated here from the `bridgetree` crate as they are useful outside
of the context of the `bridgetree` data structures. Additional legacy types
used for this modeling have been moved here from the `librustzcash` crate;
these migrated types are available under a `legacy-api` feature flag.
- `incrementalmerkletree::witness` Types migrated from `librustzcash` under
the `legacy-api` feature flag related to constructing witnesses for leaves
of a Merkle tree.
## [0.3.1] - 2023-02-28
### Fixed
@ -57,6 +68,7 @@ is not another good use case for polymorphism over tree implementations.
- `Position::max_altitude`
- `Position::ommer_altitudes`
- `impl Sub<u8> for Altitude`
- `serde` serialization and parsing are no longer supported.
## [0.3.0] - 2022-05-10

2
incrementalmerkletree/Cargo.toml
View File

@ -15,11 +15,11 @@ rust-version = "1.60"
[dependencies]
either = "1.8"
serde = { version = "1", features = ["derive"] }
proptest = { version = "1.0.0", optional = true }
[dev-dependencies]
proptest = "1.0.0"
[features]
legacy-api = []
test-dependencies = ["proptest"]

693
incrementalmerkletree/src/frontier.rs Normal file
View File

@ -0,0 +1,693 @@
use std::convert::TryFrom;
use std::mem::size_of;
use crate::{Address, Hashable, Level, Position, Source};
#[cfg(feature = "legacy-api")]
use {std::collections::VecDeque, std::iter::repeat};
/// Validation errors that can occur during reconstruction of a Merkle frontier from
/// its constituent parts.
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum FrontierError {
/// An error representing that the number of ommers provided in frontier construction does not
/// the expected length of the ommers list given the position.
PositionMismatch { expected_ommers: usize },
/// An error representing that the position and/or list of ommers provided to frontier
/// construction would result in a frontier that exceeds the maximum statically allowed depth
/// of the tree. `depth` is the minimum tree depth that would be required in order for that
/// tree to contain the position in question.
MaxDepthExceeded { depth: u8 },
}
/// A [`NonEmptyFrontier`] is a reduced representation of a Merkle tree, containing a single leaf
/// value, along with the vector of hashes produced by the reduction of previously appended leaf
/// values that will be required when producing a witness for the current leaf.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct NonEmptyFrontier<H> {
position: Position,
leaf: H,
ommers: Vec<H>,
}
impl<H> NonEmptyFrontier<H> {
/// Constructs a new frontier with the specified value at position 0.
pub fn new(leaf: H) -> Self {
Self {
position: 0.into(),
leaf,
ommers: vec![],
}
}
/// Constructs a new frontier from its constituent parts.
pub fn from_parts(position: Position, leaf: H, ommers: Vec<H>) -> Result<Self, FrontierError> {
let expected_ommers = position.past_ommer_count();
if ommers.len() == expected_ommers {
Ok(Self {
position,
leaf,
ommers,
})
} else {
Err(FrontierError::PositionMismatch { expected_ommers })
}
}
/// Returns the position of the most recently appended leaf.
pub fn position(&self) -> Position {
self.position
}
/// Returns the leaf most recently appended to the frontier.
pub fn leaf(&self) -> &H {
&self.leaf
}
/// Returns the list of past hashes required to construct a witness for the
/// leaf most recently appended to the frontier.
pub fn ommers(&self) -> &[H] {
&self.ommers
}
}
impl<H: Hashable + Clone> NonEmptyFrontier<H> {
/// Append a new leaf to the frontier, and recompute ommers by hashing together full subtrees
/// until an empty ommer slot is found.
pub fn append(&mut self, leaf: H) {
let prior_position = self.position;
let prior_leaf = self.leaf.clone();
self.position += 1;
self.leaf = leaf;
if self.position.is_odd() {
// if the new position is odd, the current leaf will directly become
// an ommer at level 0, and there is no other mutation made to the tree.
self.ommers.insert(0, prior_leaf);
} else {
// if the new position is even, then the current leaf will be hashed
// with the first ommer, and so forth up the tree.
let new_root_level = self.position.root_level();
let mut carry = Some((prior_leaf, 0.into()));
let mut new_ommers = Vec::with_capacity(self.position.past_ommer_count());
for (addr, source) in prior_position.witness_addrs(new_root_level) {
if let Source::Past(i) = source {
if let Some((carry_ommer, carry_lvl)) = carry.as_ref() {
if *carry_lvl == addr.level() {
carry = Some((
H::combine(addr.level(), &self.ommers[i], carry_ommer),
addr.level() + 1,
))
} else {
// insert the carry at the first empty slot; then the rest of the
// ommers will remain unchanged
new_ommers.push(carry_ommer.clone());
new_ommers.push(self.ommers[i].clone());
carry = None;
}
} else {
// when there's no carry, just push on the ommer value
new_ommers.push(self.ommers[i].clone());
}
}
}
// we carried value out, so we need to push on one more ommer.
if let Some((carry_ommer, _)) = carry {
new_ommers.push(carry_ommer);
}
self.ommers = new_ommers;
}
}
/// Generate the root of the Merkle tree by hashing against empty subtree roots.
pub fn root(&self, root_level: Option<Level>) -> H {
let max_level = root_level.unwrap_or_else(|| self.position.root_level());
self.position
.witness_addrs(max_level)
.fold(
(self.leaf.clone(), Level::from(0)),
|(digest, complete_lvl), (addr, source)| {
// fold up from complete_lvl to addr.level() pairing with empty roots; if
// complete_lvl == addr.level() this is just the complete digest to this point
let digest = complete_lvl
.iter_to(addr.level())
.fold(digest, |d, l| H::combine(l, &d, &H::empty_root(l)));
let res_digest = match source {
Source::Past(i) => H::combine(addr.level(), &self.ommers[i], &digest),
Source::Future => {
H::combine(addr.level(), &digest, &H::empty_root(addr.level()))
}
};
(res_digest, addr.level() + 1)
},
)
.0
}
/// Constructs a witness for the leaf at the tip of this frontier, given a source of node
/// values that complement this frontier.
///
/// If the `complement_nodes` function returns `None` when the value is requested at a given
/// tree address, the address at which the failure occurs will be returned as an error.
pub fn witness<F>(&self, depth: u8, complement_nodes: F) -> Result<Vec<H>, Address>
where
F: Fn(Address) -> Option<H>,
{
// construct a complete trailing edge that includes the data from
// the following frontier not yet included in the trailing edge.
self.position()
.witness_addrs(depth.into())
.map(|(addr, source)| match source {
Source::Past(i) => Ok(self.ommers[i].clone()),
Source::Future => complement_nodes(addr).ok_or(addr),
})
.collect::<Result<Vec<_>, _>>()
}
}
/// A possibly-empty Merkle frontier.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Frontier<H, const DEPTH: u8> {
frontier: Option<NonEmptyFrontier<H>>,
}
impl<H, const DEPTH: u8> TryFrom<NonEmptyFrontier<H>> for Frontier<H, DEPTH> {
type Error = FrontierError;
fn try_from(f: NonEmptyFrontier<H>) -> Result<Self, FrontierError> {
if f.position.root_level() <= Level::from(DEPTH) {
Ok(Frontier { frontier: Some(f) })
} else {
Err(FrontierError::MaxDepthExceeded {
depth: f.position.root_level().into(),
})
}
}
}
impl<H, const DEPTH: u8> Frontier<H, DEPTH> {
/// Constructs a new empty frontier.
pub fn empty() -> Self {
Self { frontier: None }
}
/// Constructs a new frontier from its constituent parts.
///
/// Returns `None` if the new frontier would exceed the maximum
/// allowed depth or if the list of ommers provided is not consistent
/// with the position of the leaf.
pub fn from_parts(position: Position, leaf: H, ommers: Vec<H>) -> Result<Self, FrontierError> {
NonEmptyFrontier::from_parts(position, leaf, ommers).and_then(Self::try_from)
}
/// Return the wrapped NonEmptyFrontier reference, or None if
/// the frontier is empty.
pub fn value(&self) -> Option<&NonEmptyFrontier<H>> {
self.frontier.as_ref()
}
/// Returns the amount of memory dynamically allocated for ommer
/// values within the frontier.
pub fn dynamic_memory_usage(&self) -> usize {
self.frontier.as_ref().map_or(0, |f| {
size_of::<usize>() + (f.ommers.capacity() + 1) * size_of::<H>()
})
}
}
impl<H: Hashable + Clone, const DEPTH: u8> Frontier<H, DEPTH> {
/// Appends a new value to the frontier at the next available slot.
/// Returns true if successful and false if the frontier would exceed
/// the maximum allowed depth.
pub fn append(&mut self, value: H) -> bool {
if let Some(frontier) = self.frontier.as_mut() {
if frontier.position().is_complete_subtree(DEPTH.into()) {
false
} else {
frontier.append(value);
true
}
} else {
self.frontier = Some(NonEmptyFrontier::new(value));
true
}
}
/// Obtains the current root of this Merkle frontier by hashing
/// against empty nodes up to the maximum height of the pruned
/// tree that the frontier represents.
pub fn root(&self) -> H {
self.frontier
.as_ref()
.map_or(H::empty_root(DEPTH.into()), |frontier| {
frontier.root(Some(DEPTH.into()))
})
}
}
#[cfg(feature = "legacy-api")]
pub struct PathFiller<H> {
queue: VecDeque<H>,
}
#[cfg(feature = "legacy-api")]
impl<H: Hashable> PathFiller<H> {
pub fn empty() -> Self {
PathFiller {
queue: VecDeque::new(),
}
}
pub fn new(queue: VecDeque<H>) -> Self {
Self { queue }
}
pub fn next(&mut self, level: Level) -> H {
self.queue
.pop_front()
.unwrap_or_else(|| H::empty_root(level))
}
}
/// A Merkle tree of note commitments.
#[derive(Clone, Debug, PartialEq, Eq)]
#[cfg(feature = "legacy-api")]
pub struct CommitmentTree<H, const DEPTH: u8> {
pub(crate) left: Option<H>,
pub(crate) right: Option<H>,
pub(crate) parents: Vec<Option<H>>,
}
#[cfg(feature = "legacy-api")]
impl<H, const DEPTH: u8> CommitmentTree<H, DEPTH> {
/// Creates an empty tree.
pub fn empty() -> Self {
CommitmentTree {
left: None,
right: None,
parents: vec![],
}
}
#[allow(clippy::result_unit_err)]
pub fn from_parts(
left: Option<H>,
right: Option<H>,
parents: Vec<Option<H>>,
) -> Result<Self, ()> {
if parents.len() < usize::from(DEPTH) {
Ok(CommitmentTree {
left,
right,
parents,
})
} else {
Err(())
}
}
pub fn left(&self) -> &Option<H> {
&self.left
}
pub fn right(&self) -> &Option<H> {
&self.right
}
pub fn parents(&self) -> &Vec<Option<H>> {
&self.parents
}
/// Returns the number of leaf nodes in the tree.
pub fn size(&self) -> usize {
self.parents.iter().enumerate().fold(
match (self.left.as_ref(), self.right.as_ref()) {
(None, None) => 0,
(Some(_), None) => 1,
(Some(_), Some(_)) => 2,
(None, Some(_)) => unreachable!(),
},
|acc, (i, p)| {
// Treat occupation of parents array as a binary number
// (right-shifted by 1)
acc + if p.is_some() { 1 << (i + 1) } else { 0 }
},
)
}
pub(crate) fn is_complete(&self, depth: u8) -> bool {
if depth == 0 {
self.left.is_some() && self.right.is_none() && self.parents.is_empty()
} else {
self.left.is_some()
&& self.right.is_some()
&& self
.parents
.iter()
.chain(repeat(&None))
.take((depth - 1).into())
.all(|p| p.is_some())
}
}
}
#[cfg(feature = "legacy-api")]
impl<H: Hashable + Clone, const DEPTH: u8> CommitmentTree<H, DEPTH> {
pub fn from_frontier(frontier: &Frontier<H, DEPTH>) -> Self {
frontier.value().map_or_else(Self::empty, |f| {
let mut ommers_iter = f.ommers().iter().cloned();
let (left, right) = if f.position().is_odd() {
(
ommers_iter
.next()
.expect("An ommer must exist if the frontier position is odd"),
Some(f.leaf().clone()),
)
} else {
(f.leaf().clone(), None)
};
let upos: usize = f.position().into();
Self {
left: Some(left),
right,
parents: (1u8..DEPTH)
.into_iter()
.map(|i| {
if upos & (1 << i) == 0 {
None
} else {
ommers_iter.next()
}
})
.collect(),
}
})
}
pub fn to_frontier(&self) -> Frontier<H, DEPTH> {
if self.size() == 0 {
Frontier::empty()
} else {
let ommers_iter = self.parents.iter().filter_map(|v| v.as_ref()).cloned();
let (leaf, ommers) = match (self.left.as_ref(), self.right.as_ref()) {
(Some(a), None) => (a.clone(), ommers_iter.collect()),
(Some(a), Some(b)) => (
b.clone(),
Some(a.clone()).into_iter().chain(ommers_iter).collect(),
),
_ => unreachable!(),
};
// If a frontier cannot be successfully constructed from the
// parts of a commitment tree, it is a programming error.
Frontier::from_parts((self.size() - 1).into(), leaf, ommers)
.expect("Frontier should be constructable from CommitmentTree.")
}
}
/// Adds a leaf node to the tree.
///
/// Returns an error if the tree is full.
#[allow(clippy::result_unit_err)]
pub fn append(&mut self, node: H) -> Result<(), ()> {
if self.is_complete(DEPTH) {
// Tree is full
return Err(());
}
match (&self.left, &self.right) {
(None, _) => self.left = Some(node),
(_, None) => self.right = Some(node),
(Some(l), Some(r)) => {
let mut combined = H::combine(0.into(), l, r);
self.left = Some(node);
self.right = None;
for i in 0..DEPTH {
let i_usize = usize::from(i);
if i_usize < self.parents.len() {
if let Some(p) = &self.parents[i_usize] {
combined = H::combine((i + 1).into(), p, &combined);
self.parents[i_usize] = None;
} else {
self.parents[i_usize] = Some(combined);
break;
}
} else {
self.parents.push(Some(combined));
break;
}
}
}
}
Ok(())
}
/// Returns the current root of the tree.
pub fn root(&self) -> H {
self.root_at_depth(DEPTH, PathFiller::empty())
}
pub fn root_at_depth(&self, depth: u8, mut filler: PathFiller<H>) -> H {
assert!(depth > 0);
// 1) Hash left and right leaves together.
// - Empty leaves are used as needed.
// - Note that `filler.next` is side-effecting and so cannot be factored out.
let leaf_root = H::combine(
0.into(),
&self
.left
.as_ref()
.map_or_else(|| filler.next(0.into()), |n| n.clone()),
&self
.right
.as_ref()
.map_or_else(|| filler.next(0.into()), |n| n.clone()),
);
// 2) Extend the parents to the desired depth with None values, then hash from leaf to
// root. Roots of the empty subtrees are used as needed.
self.parents
.iter()
.chain(repeat(&None))
.take((depth - 1).into())
.enumerate()
.fold(leaf_root, |root, (i, p)| {
let level = Level::from(i as u8 + 1);
match p {
Some(node) => H::combine(level, node, &root),
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 frontier_witness() {
let mut frontier = NonEmptyFrontier::<String>::new("a".to_string());
for c in 'b'..'h' {
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]
#[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);
}
}
}

134
incrementalmerkletree/src/lib.rs
View File

@ -1,12 +1,16 @@
//! Common types and utilities used in incremental Merkle tree implementations.
use either::Either;
use serde::{Deserialize, Serialize};
use std::cmp::Ordering;
use std::convert::{TryFrom, TryInto};
use std::num::TryFromIntError;
use std::ops::{Add, AddAssign, Range, Sub};
pub mod frontier;
#[cfg(feature = "legacy-api")]
pub mod witness;
#[cfg(feature = "test-dependencies")]
pub mod testing;
@ -43,8 +47,49 @@ impl<C> Retention<C> {
}
}
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum Source {
/// The sibling to the address can be derived from the incremental frontier
/// at the contained ommer index
Past(usize),
/// The sibling to the address must be obtained from values discovered by
/// the addition of more nodes to the tree
Future,
}
#[must_use = "iterators are lazy and do nothing unless consumed"]
struct WitnessAddrsIter {
root_level: Level,
current: Address,
ommer_count: usize,
}
impl Iterator for WitnessAddrsIter {
type Item = (Address, Source);
fn next(&mut self) -> Option<(Address, Source)> {
if self.current.level() < self.root_level {
let current = self.current;
let source = if current.is_right_child() {
Source::Past(self.ommer_count)
} else {
Source::Future
};
self.current = current.parent();
if matches!(source, Source::Past(_)) {
self.ommer_count += 1;
}
Some((current.sibling(), source))
} else {
None
}
}
}
/// A type representing the position of a leaf in a Merkle tree.
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize, Deserialize)]
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(transparent)]
pub struct Position(usize);
@ -74,6 +119,18 @@ impl Position {
pub fn is_complete_subtree(&self, root_level: Level) -> bool {
!(0..(root_level.0)).any(|l| self.0 & (1 << l) == 0)
}
/// Returns an iterator over the addresses of nodes required to create a witness for this
/// position, beginning with the sibling of the leaf at this position and ending with the
/// sibling of the ancestor of the leaf at this position that is required to compute a root at
/// the specified level.
pub fn witness_addrs(&self, root_level: Level) -> impl Iterator<Item = (Address, Source)> {
WitnessAddrsIter {
root_level,
current: Address::from(*self),
ommer_count: 0,
}
}
}
impl From<Position> for usize {
@ -128,7 +185,7 @@ impl TryFrom<u64> for Position {
/// nodes at level `0` are leaves, nodes at level `1` are parents of nodes at
/// level `0`, and so forth. This type is capable of representing levels in
/// trees containing up to 2^255 leaves.
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize, Deserialize)]
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(transparent)]
pub struct Level(u8);
@ -165,6 +222,13 @@ impl From<Level> for usize {
}
}
impl TryFrom<usize> for Level {
type Error = TryFromIntError;
fn try_from(sz: usize) -> Result<Self, Self::Error> {
<u8>::try_from(sz).map(Self)
}
}
impl Sub<u8> for Level {
type Output = Self;
fn sub(self, value: u8) -> Self {
@ -178,7 +242,7 @@ impl Sub<u8> for Level {
/// The address of an internal node of the Merkle tree.
/// When `level == 0`, the index has the same value as the
/// position.
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Serialize, Deserialize)]
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Address {
level: Level,
index: usize,
@ -225,11 +289,7 @@ impl Address {
pub fn sibling(&self) -> Address {
Address {
level: self.level,
index: if self.index & 0x1 == 0 {
self.index + 1
} else {
self.index - 1
},
index: self.index ^ 1,
}
}
@ -420,7 +480,7 @@ pub trait Hashable: Sized + core::fmt::Debug {
#[cfg(test)]
pub(crate) mod tests {
use super::{Address, Level, Position};
use super::{Address, Level, Position, Source};
use core::ops::Range;
use either::Either;
@ -459,7 +519,57 @@ pub(crate) mod tests {
}
#[test]
fn current_incomplete() {
fn position_witness_addrs() {
use Source::*;
let path_elem = |l, i, s| (Address::from_parts(Level::from(l), i), s);
assert_eq!(
vec![path_elem(0, 1, Future), path_elem(1, 1, Future)],
Position::from(0)
.witness_addrs(Level::from(2))
.collect::<Vec<_>>()
);
assert_eq!(
vec![path_elem(0, 3, Future), path_elem(1, 0, Past(0))],
Position::from(2)
.witness_addrs(Level::from(2))
.collect::<Vec<_>>()
);
assert_eq!(
vec![
path_elem(0, 2, Past(0)),
path_elem(1, 0, Past(1)),
path_elem(2, 1, Future)
],
Position::from(3)
.witness_addrs(Level::from(3))
.collect::<Vec<_>>()
);
assert_eq!(
vec![
path_elem(0, 5, Future),
path_elem(1, 3, Future),
path_elem(2, 0, Past(0)),
path_elem(3, 1, Future)
],
Position::from(4)
.witness_addrs(Level::from(4))
.collect::<Vec<_>>()
);
assert_eq!(
vec![
path_elem(0, 7, Future),
path_elem(1, 2, Past(0)),
path_elem(2, 0, Past(1)),
path_elem(3, 1, Future)
],
Position::from(6)
.witness_addrs(Level::from(4))
.collect::<Vec<_>>()
);
}
#[test]
fn address_current_incomplete() {
let addr = |l, i| Address::from_parts(Level(l), i);
assert_eq!(addr(0, 0), addr(0, 0).current_incomplete());
assert_eq!(addr(1, 0), addr(0, 1).current_incomplete());
@ -468,7 +578,7 @@ pub(crate) mod tests {
}
#[test]
fn next_incomplete_parent() {
fn address_next_incomplete_parent() {
let addr = |l, i| Address::from_parts(Level(l), i);
assert_eq!(addr(1, 0), addr(0, 0).next_incomplete_parent());
assert_eq!(addr(1, 0), addr(0, 1).next_incomplete_parent());

263
incrementalmerkletree/src/witness.rs Normal file
View File

@ -0,0 +1,263 @@
use std::convert::TryInto;
use std::iter::repeat;
use crate::{
frontier::{CommitmentTree, PathFiller},
Hashable, Level,
};
/// A path from a position in a particular commitment tree to the root of that tree.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct MerklePath<H, const DEPTH: u8> {
auth_path: Vec<(H, bool)>,
position: u64,
}
impl<H, const DEPTH: u8> MerklePath<H, DEPTH> {
/// Constructs a Merkle path directly from a path and position.
#[allow(clippy::result_unit_err)]
pub fn from_parts(auth_path: Vec<(H, bool)>, position: u64) -> Result<Self, ()> {
if auth_path.len() == usize::from(DEPTH) {
Ok(MerklePath {
auth_path,
position,
})
} else {
Err(())
}
}
pub fn auth_path(&self) -> &[(H, bool)] {
&self.auth_path
}
pub fn position(&self) -> u64 {
self.position
}
}
impl<H: Hashable, const DEPTH: u8> MerklePath<H, DEPTH> {
/// Returns the root of the tree corresponding to this path applied to `leaf`.
pub fn root(&self, leaf: H) -> H {
self.auth_path
.iter()
.enumerate()
.fold(leaf, |root, (i, (p, leaf_is_on_right))| {
let level = u8::try_from(i)
.expect("Parents list length may not exceed what is representable by an u8")
.into();
match leaf_is_on_right {
false => H::combine(level, &root, p),
true => H::combine(level, p, &root),
}
})
}
}
/// An updatable witness to a path from a position in a particular [`CommitmentTree`].
///
/// Appending the same commitments in the same order to both the original
/// [`CommitmentTree`] and this `IncrementalWitness` will result in a witness to the path
/// from the target position to the root of the updated tree.
///
/// # Examples
///
/// ```
/// use incrementalmerkletree::{
/// frontier::{CommitmentTree, testing::TestNode},
/// witness::IncrementalWitness,
/// };
///
/// let mut tree = CommitmentTree::<TestNode, 8>::empty();
///
/// tree.append(TestNode(0));
/// tree.append(TestNode(1));
/// let mut witness = IncrementalWitness::from_tree(tree.clone());
/// assert_eq!(witness.position(), 1);
/// assert_eq!(tree.root(), witness.root());
///
/// let next = TestNode(2);
/// tree.append(next.clone());
/// witness.append(next);
/// assert_eq!(tree.root(), witness.root());
/// ```
#[derive(Clone, Debug)]
pub struct IncrementalWitness<H, const DEPTH: u8> {
tree: CommitmentTree<H, DEPTH>,
filled: Vec<H>,
cursor_depth: u8,
cursor: Option<CommitmentTree<H, DEPTH>>,
}
impl<H, const DEPTH: u8> IncrementalWitness<H, DEPTH> {
/// Creates an `IncrementalWitness` for the most recent commitment added to the given
/// [`CommitmentTree`].
pub fn from_tree(tree: CommitmentTree<H, DEPTH>) -> Self {
IncrementalWitness {
tree,
filled: vec![],
cursor_depth: 0,
cursor: None,
}
}
pub fn from_parts(
tree: CommitmentTree<H, DEPTH>,
filled: Vec<H>,
cursor: Option<CommitmentTree<H, DEPTH>>,
) -> Self {
let mut witness = IncrementalWitness {
tree,
filled,
cursor_depth: 0,
cursor,
};
witness.cursor_depth = witness.next_depth();
witness
}
pub fn tree(&self) -> &CommitmentTree<H, DEPTH> {
&self.tree
}
pub fn filled(&self) -> &Vec<H> {
&self.filled
}
pub fn cursor(&self) -> &Option<CommitmentTree<H, DEPTH>> {
&self.cursor
}
/// Returns the position of the witnessed leaf node in the commitment tree.
pub fn position(&self) -> usize {
self.tree.size() - 1
}
/// Finds the next "depth" of an unfilled subtree.
fn next_depth(&self) -> u8 {
let mut skip: u8 = self
.filled
.len()
.try_into()
.expect("Merkle tree depths may not exceed the bounds of a u8");
if self.tree.left.is_none() {
if skip > 0 {
skip -= 1;
} else {
return 0;
}
}
if self.tree.right.is_none() {
if skip > 0 {
skip -= 1;
} else {
return 0;
}
}
let mut d = 1;
for p in &self.tree.parents {
if p.is_none() {
if skip > 0 {
skip -= 1;
} else {
return d;
}
}
d += 1;
}
d + skip
}
}
impl<H: Hashable + Clone, const DEPTH: u8> IncrementalWitness<H, DEPTH> {
fn filler(&self) -> PathFiller<H> {
let cursor_root = self
.cursor
.as_ref()
.map(|c| c.root_at_depth(self.cursor_depth, PathFiller::empty()));
PathFiller::new(self.filled.iter().cloned().chain(cursor_root).collect())
}
/// Tracks a leaf node that has been added to the underlying tree.
///
/// Returns an error if the tree is full.
#[allow(clippy::result_unit_err)]
pub fn append(&mut self, node: H) -> Result<(), ()> {
if let Some(mut cursor) = self.cursor.take() {
cursor.append(node).expect("cursor should not be full");
if cursor.is_complete(self.cursor_depth) {
self.filled
.push(cursor.root_at_depth(self.cursor_depth, PathFiller::empty()));
} else {
self.cursor = Some(cursor);
}
} else {
self.cursor_depth = self.next_depth();
if self.cursor_depth >= DEPTH {
// Tree is full
return Err(());
}
if self.cursor_depth == 0 {
self.filled.push(node);
} else {
let mut cursor = CommitmentTree::empty();
cursor.append(node).expect("cursor should not be full");
self.cursor = Some(cursor);
}
}
Ok(())
}
/// Returns the current root of the tree corresponding to the witness.
pub fn root(&self) -> H {
self.tree.root_at_depth(DEPTH, self.filler())
}
/// Returns the current witness, or None if the tree is empty.
pub fn path(&self) -> Option<MerklePath<H, DEPTH>> {
self.path_inner(DEPTH)
}
fn path_inner(&self, depth: u8) -> Option<MerklePath<H, DEPTH>> {
let mut filler = self.filler();
let mut auth_path = Vec::new();
if let Some(node) = &self.tree.left {
if self.tree.right.is_some() {
auth_path.push((node.clone(), true));
} else {
auth_path.push((filler.next(0.into()), false));
}
} else {
// Can't create an authentication path for the beginning of the tree
return None;
}
for (i, p) in self
.tree
.parents
.iter()
.chain(repeat(&None))
.take((depth - 1).into())
.enumerate()
{
auth_path.push(match p {
Some(node) => (node.clone(), true),
None => (filler.next(Level::from((i + 1) as u8)), false),
});
}
assert_eq!(auth_path.len(), usize::from(depth));
MerklePath::from_parts(auth_path, self.position() as u64).ok()
}
}