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incrementalmerkletree
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Move frontier types from `bridgetree` to `incrementalmerkletree` 

These types are reusable outside of the context of the `bridgetree`
crate.
This commit is contained in:
Kris Nuttycombe 2023-02-15 17:03:19 -07:00
parent ff8095b7ed
commit 4e3c6a6378
5 changed files with 464 additions and 421 deletions
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2
bridgetree/CHANGELOG.md
View File

@ -14,6 +14,8 @@ and this project adheres to Rust's notion of
### Removed ### 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 - The `testing` module has been removed in favor of depending on
`incrementalmerkletree::testing`. `incrementalmerkletree::testing`.
- `serde` serialization and parsing are no longer supported. - `serde` serialization and parsing are no longer supported.

444
bridgetree/src/lib.rs
View File

@ -30,27 +30,14 @@
//! reset the state to. //! reset the state to.
//! //!
//! In this module, the term "ommer" is used as for the sibling of a parent node in a binary tree. //! In this module, the term "ommer" is used as for the sibling of a parent node in a binary tree.
pub use incrementalmerkletree::{
frontier::{Frontier, NonEmptyFrontier},
Address, Hashable, Level, Position, Retention, Source,
};
use std::collections::{BTreeMap, BTreeSet, VecDeque}; use std::collections::{BTreeMap, BTreeSet, VecDeque};
use std::convert::TryFrom;
use std::fmt::Debug; use std::fmt::Debug;
use std::mem::size_of;
use std::ops::Range; 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. /// Errors that can be discovered during checks that verify the compatibility of adjacent bridges.
#[derive(Clone, Debug, PartialEq, Eq)] #[derive(Clone, Debug, PartialEq, Eq)]
pub enum ContinuityError { pub enum ContinuityError {
@ -73,284 +60,6 @@ pub enum WitnessingError {
BridgeAddressInvalid(Address), 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)]
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)]
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 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 /// The witness for a particular leaf of a Merkle tree consists of the siblings of that leaf, plus
@ -581,19 +290,21 @@ impl<'a, H: Hashable + Ord + Clone + 'a> MerkleBridge<H> {
) -> Result<Vec<H>, WitnessingError> { ) -> Result<Vec<H>, WitnessingError> {
assert!(Some(prior_frontier.position()) == self.prior_position); assert!(Some(prior_frontier.position()) == self.prior_position);
prior_frontier.witness(depth, |addr| { prior_frontier
let r = addr.position_range(); .witness(depth, |addr| {
if self.frontier.position() < r.start { let r = addr.position_range();
Some(H::empty_root(addr.level())) if self.frontier.position() < r.start {
} else if r.contains(&self.frontier.position()) { Some(H::empty_root(addr.level()))
Some(self.frontier.root(Some(addr.level()))) } else if r.contains(&self.frontier.position()) {
} else { Some(self.frontier.root(Some(addr.level())))
// the frontier's position is after the end of the requested } else {
// range, so the requested value should exist in a stored // the frontier's position is after the end of the requested
// fragment // range, so the requested value should exist in a stored
self.ommers.get(&addr).cloned() // fragment
} self.ommers.get(&addr).cloned()
}) }
})
.map_err(WitnessingError::BridgeAddressInvalid)
} }
fn retain(&mut self, ommer_addrs: &BTreeSet<Address>) { fn retain(&mut self, ommer_addrs: &BTreeSet<Address>) {
@ -1229,8 +940,10 @@ impl<H: Hashable + Ord + Clone, const DEPTH: u8> BridgeTree<H, DEPTH> {
// Add the elements of the auth path to the set of addresses we should // Add the elements of the auth path to the set of addresses we should
// continue to track and retain information for // continue to track and retain information for
for (addr, source) in for (addr, source) in cur_bridge
witness_addrs(cur_bridge.frontier.position(), Level::from(DEPTH)) .frontier
.position()
.witness_addrs(Level::from(DEPTH))
{ {
if source == Source::Future { if source == Source::Future {
ommer_addrs.insert(addr); ommer_addrs.insert(addr);
@ -1283,24 +996,14 @@ mod tests {
use super::*; use super::*;
use incrementalmerkletree::{ use incrementalmerkletree::{
testing::{ testing::{
apply_operation, arb_operation, check_checkpoint_rewind, check_operations, self, apply_operation, arb_operation, check_checkpoint_rewind, check_operations,
check_remove_mark, check_rewind_remove_mark, check_root_hashes, check_witnesses, check_remove_mark, check_rewind_remove_mark, check_root_hashes, check_witnesses,
complete_tree::CompleteTree, CombinedTree, Frontier, SipHashable, Tree, complete_tree::CompleteTree, CombinedTree, SipHashable,
}, },
Hashable, Hashable,
}; };
impl<H: Hashable + Clone, const DEPTH: u8> Frontier<H> for super::Frontier<H, DEPTH> { impl<H: Hashable + Ord + Clone, const DEPTH: u8> testing::Tree<H, usize> for BridgeTree<H, DEPTH> {
fn append(&mut self, value: H) -> bool {
super::Frontier::append(self, value)
}
fn root(&self) -> H {
super::Frontier::root(self)
}
}
impl<H: Hashable + Ord + Clone, const DEPTH: u8> Tree<H, usize> for BridgeTree<H, DEPTH> {
fn append(&mut self, value: H, retention: Retention<usize>) -> bool { fn append(&mut self, value: H, retention: Retention<usize>) -> bool {
let appended = BridgeTree::append(self, value); let appended = BridgeTree::append(self, value);
if appended { if appended {
@ -1351,101 +1054,6 @@ 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] #[test]
fn tree_depth() { fn tree_depth() {
let mut tree = BridgeTree::<String, 3>::new(100, 0); let mut tree = BridgeTree::<String, 3>::new(100, 0);

6
incrementalmerkletree/CHANGELOG.md
View File

@ -7,6 +7,12 @@ and this project adheres to Rust's notion of
## [Unreleased] ## [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.
## [0.3.1] - 2023-02-28 ## [0.3.1] - 2023-02-28
### Fixed ### Fixed

322
incrementalmerkletree/src/frontier.rs Normal file
View File

@ -0,0 +1,322 @@
use std::convert::TryFrom;
use std::mem::size_of;
use crate::{Address, Hashable, Level, Position, Source};
/// 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 },
}
/// 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 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 = "test-dependencies")]
pub mod testing {
use crate::Hashable;
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)
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[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)
);
}
}

111
incrementalmerkletree/src/lib.rs
View File

@ -6,6 +6,8 @@ use std::convert::{TryFrom, TryInto};
use std::num::TryFromIntError; use std::num::TryFromIntError;
use std::ops::{Add, AddAssign, Range, Sub}; use std::ops::{Add, AddAssign, Range, Sub};
pub mod frontier;
#[cfg(feature = "test-dependencies")] #[cfg(feature = "test-dependencies")]
pub mod testing; pub mod testing;
@ -42,6 +44,47 @@ 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. /// A type representing the position of a leaf in a Merkle tree.
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)] #[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
#[repr(transparent)] #[repr(transparent)]
@ -73,6 +116,18 @@ impl Position {
pub fn is_complete_subtree(&self, root_level: Level) -> bool { pub fn is_complete_subtree(&self, root_level: Level) -> bool {
!(0..(root_level.0)).any(|l| self.0 & (1 << l) == 0) !(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 { impl From<Position> for usize {
@ -419,7 +474,7 @@ pub trait Hashable: Sized + core::fmt::Debug {
#[cfg(test)] #[cfg(test)]
pub(crate) mod tests { pub(crate) mod tests {
use super::{Address, Level, Position}; use super::{Address, Level, Position, Source};
use core::ops::Range; use core::ops::Range;
use either::Either; use either::Either;
@ -458,7 +513,57 @@ pub(crate) mod tests {
} }
#[test] #[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); let addr = |l, i| Address::from_parts(Level(l), i);
assert_eq!(addr(0, 0), addr(0, 0).current_incomplete()); assert_eq!(addr(0, 0), addr(0, 0).current_incomplete());
assert_eq!(addr(1, 0), addr(0, 1).current_incomplete()); assert_eq!(addr(1, 0), addr(0, 1).current_incomplete());
@ -467,7 +572,7 @@ pub(crate) mod tests {
} }
#[test] #[test]
fn next_incomplete_parent() { fn address_next_incomplete_parent() {
let addr = |l, i| Address::from_parts(Level(l), i); 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, 0).next_incomplete_parent());
assert_eq!(addr(1, 0), addr(0, 1).next_incomplete_parent()); assert_eq!(addr(1, 0), addr(0, 1).next_incomplete_parent());