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use std::collections::HashMap;
use crate::{Entry, EntryKind, EntryLink, Error, Version};
/// Represents partially loaded tree.
///
/// Some kind of "view" into the array representation of the MMR tree.
/// With only some of the leaves/nodes pre-loaded / pre-generated.
/// Exact amount of the loaded data can be calculated by the constructing party,
/// depending on the length of the tree and maximum amount of operations that are going
/// to happen after construction. `Tree` should not be used as self-contained data structure,
/// since it's internal state can grow indefinitely after serial operations.
/// Intended use of this `Tree` is to instantiate it based on partially loaded data (see example
/// how to pick right nodes from the array representation of MMR Tree), perform several operations
/// (append-s/delete-s) and then drop it.
pub struct Tree<V: Version> {
stored: HashMap<u32, Entry<V>>,
// This can grow indefinitely if `Tree` is misused as a self-contained data structure
generated: Vec<Entry<V>>,
// number of persistent(!) tree entries
stored_count: u32,
root: EntryLink,
}
impl<V: Version> Tree<V> {
/// Resolve link originated from this tree
pub fn resolve_link(&self, link: EntryLink) -> Result<IndexedNode<V>, Error> {
match link {
EntryLink::Generated(index) => self.generated.get(index as usize),
EntryLink::Stored(index) => self.stored.get(&index),
}
.map(|node| IndexedNode { node, link })
.ok_or(Error::ExpectedInMemory(link))
}
fn push(&mut self, data: Entry<V>) -> EntryLink {
let idx = self.stored_count;
self.stored_count += 1;
self.stored.insert(idx, data);
EntryLink::Stored(idx)
}
fn push_generated(&mut self, data: Entry<V>) -> EntryLink {
self.generated.push(data);
EntryLink::Generated(self.generated.len() as u32 - 1)
}
/// Populate tree with plain list of the leaves/nodes. For now, only for tests,
/// since this `Tree` structure is for partially loaded tree (but it might change)
#[cfg(test)]
pub fn populate(loaded: Vec<Entry<V>>, root: EntryLink) -> Self {
let mut result = Tree::invalid();
result.stored_count = loaded.len() as u32;
for (idx, item) in loaded.into_iter().enumerate() {
result.stored.insert(idx as u32, item);
}
result.root = root;
result
}
// Empty tree with invalid root
fn invalid() -> Self {
Tree {
root: EntryLink::Generated(0),
generated: Default::default(),
stored: Default::default(),
stored_count: 0,
}
}
/// New view into the the tree array representation
///
/// `length` is total length of the array representation (is generally not a sum of
/// peaks.len + extra.len)
/// `peaks` is peaks of the mmr tree
/// `extra` is some extra nodes that calculated to be required during next one or more
/// operations on the tree.
///
/// # Panics
///
/// Will panic if `peaks` is empty.
pub fn new(length: u32, peaks: Vec<(u32, Entry<V>)>, extra: Vec<(u32, Entry<V>)>) -> Self {
assert!(!peaks.is_empty());
let mut result = Tree::invalid();
result.stored_count = length;
let mut root = EntryLink::Stored(peaks[0].0);
for (gen, (idx, node)) in peaks.into_iter().enumerate() {
result.stored.insert(idx, node);
if gen != 0 {
let next_generated = combine_nodes(
result
.resolve_link(root)
.expect("Inserted before, cannot fail; qed"),
result
.resolve_link(EntryLink::Stored(idx))
.expect("Inserted before, cannot fail; qed"),
);
root = result.push_generated(next_generated);
}
}
for (idx, node) in extra {
result.stored.insert(idx, node);
}
result.root = root;
result
}
fn get_peaks(&self, root: EntryLink, target: &mut Vec<EntryLink>) -> Result<(), Error> {
let (left_child_link, right_child_link) = {
let root = self.resolve_link(root)?;
if root.node.complete() {
target.push(root.link);
return Ok(());
}
(root.left()?, root.right()?)
};
self.get_peaks(left_child_link, target)?;
self.get_peaks(right_child_link, target)?;
Ok(())
}
/// Append one leaf to the tree.
///
/// Returns links to actual nodes that has to be persisted as the result of the append.
/// If completed without error, at least one link to the appended
/// node (with metadata provided in `new_leaf`) will be returned.
pub fn append_leaf(&mut self, new_leaf: V::NodeData) -> Result<Vec<EntryLink>, Error> {
let root = self.root;
let new_leaf_link = self.push(Entry::new_leaf(new_leaf));
let mut appended = vec![new_leaf_link];
let mut peaks = Vec::new();
self.get_peaks(root, &mut peaks)?;
let mut merge_stack = vec![new_leaf_link];
// Scan the peaks right-to-left, merging together equal-sized adjacent
// complete subtrees. After this, merge_stack only contains peaks of
// unequal-sized subtrees.
while let Some(next_peak) = peaks.pop() {
let next_merge = merge_stack
.pop()
.expect("there should be at least one, initial or re-pushed");
if let Some(stored) = {
let peak = self.resolve_link(next_peak)?;
let m = self.resolve_link(next_merge)?;
if peak.node.leaf_count() == m.node.leaf_count() {
Some(combine_nodes(peak, m))
} else {
None
}
} {
let link = self.push(stored);
merge_stack.push(link);
appended.push(link);
continue;
} else {
merge_stack.push(next_merge);
merge_stack.push(next_peak);
}
}
let mut new_root = merge_stack
.pop()
.expect("Loop above cannot reduce the merge_stack");
// Scan the peaks left-to-right, producing new generated nodes that
// connect the subtrees
while let Some(next_child) = merge_stack.pop() {
new_root = self.push_generated(combine_nodes(
self.resolve_link(new_root)?,
self.resolve_link(next_child)?,
))
}
self.root = new_root;
Ok(appended)
}
#[cfg(test)]
fn for_children<F: Fn(EntryLink, EntryLink)>(&self, node: EntryLink, f: F) {
let (left, right) = {
let link = self
.resolve_link(node)
.expect("Failed to resolve link in test");
(
link.left().expect("Failed to find node in test"),
link.right().expect("Failed to find node in test"),
)
};
f(left, right);
}
fn pop(&mut self) {
self.stored.remove(&(self.stored_count - 1));
self.stored_count -= 1;
}
/// Truncate one leaf from the end of the tree.
///
/// Returns actual number of nodes that should be removed by the caller
/// from the end of the array representation.
pub fn truncate_leaf(&mut self) -> Result<u32, Error> {
let root = {
let (leaves, root_left_child) = {
let n = self.resolve_link(self.root)?;
(n.node.leaf_count(), n.node.left()?)
};
if leaves & 1 != 0 {
self.pop();
self.root = root_left_child;
return Ok(1);
} else {
self.resolve_link(self.root)?
}
};
let mut peaks = vec![root.left()?];
let mut subtree_root_link = root.right()?;
let mut truncated = 1;
loop {
let left_link = self.resolve_link(subtree_root_link)?.node;
if let EntryKind::Node(left, right) = left_link.kind {
peaks.push(left);
subtree_root_link = right;
truncated += 1;
} else {
if root.node.complete() {
truncated += 1;
}
break;
}
}
let mut new_root = *peaks.get(0).expect("At lest 1 elements in peaks");
for next_peak in peaks.into_iter().skip(1) {
new_root = self.push_generated(combine_nodes(
self.resolve_link(new_root)?,
self.resolve_link(next_peak)?,
));
}
for _ in 0..truncated {
self.pop();
}
self.root = new_root;
Ok(truncated)
}
/// Length of array representation of the tree.
pub fn len(&self) -> u32 {
self.stored_count
}
/// Link to the root node
pub fn root(&self) -> EntryLink {
self.root
}
/// Reference to the root node.
pub fn root_node(&self) -> Result<IndexedNode<V>, Error> {
self.resolve_link(self.root)
}
/// If this tree is empty.
pub fn is_empty(&self) -> bool {
self.stored_count == 0
}
}
/// Reference to the node with link attached.
#[derive(Debug)]
pub struct IndexedNode<'a, V: Version> {
node: &'a Entry<V>,
link: EntryLink,
}
impl<'a, V: Version> IndexedNode<'a, V> {
fn left(&self) -> Result<EntryLink, Error> {
self.node.left().map_err(|e| e.augment(self.link))
}
fn right(&self) -> Result<EntryLink, Error> {
self.node.right().map_err(|e| e.augment(self.link))
}
/// Reference to the entry struct.
pub fn node(&self) -> &Entry<V> {
self.node
}
/// Reference to the entry metadata.
pub fn data(&self) -> &V::NodeData {
&self.node.data
}
/// Actual link by what this node was resolved.
pub fn link(&self) -> EntryLink {
self.link
}
}
fn combine_nodes<'a, V: Version>(left: IndexedNode<'a, V>, right: IndexedNode<'a, V>) -> Entry<V> {
Entry {
kind: EntryKind::Node(left.link, right.link),
data: V::combine(&left.node.data, &right.node.data),
}
}
#[cfg(test)]
mod tests {
use super::{Entry, EntryKind, EntryLink, Tree};
use crate::{node_data, NodeData, Version, V2};
use assert_matches::assert_matches;
use proptest::prelude::*;
fn leaf(height: u32) -> node_data::V2 {
node_data::V2 {
v1: NodeData {
consensus_branch_id: 1,
subtree_commitment: [0u8; 32],
start_time: 0,
end_time: 0,
start_target: 0,
end_target: 0,
start_sapling_root: [0u8; 32],
end_sapling_root: [0u8; 32],
subtree_total_work: 0.into(),
start_height: height as u64,
end_height: height as u64,
sapling_tx: 7,
},
start_orchard_root: [0u8; 32],
end_orchard_root: [0u8; 32],
orchard_tx: 42,
}
}
fn initial() -> Tree<V2> {
let node1 = Entry::new_leaf(leaf(1));
let node2 = Entry::new_leaf(leaf(2));
let node3 = Entry {
data: V2::combine(&node1.data, &node2.data),
kind: EntryKind::Leaf,
};
Tree::populate(vec![node1, node2, node3], EntryLink::Stored(2))
}
// returns tree with specified number of leafs and it's root
fn generated(length: u32) -> Tree<V2> {
assert!(length >= 3);
let mut tree = initial();
for i in 2..length {
tree.append_leaf(leaf(i + 1)).expect("Failed to append");
}
tree
}
#[test]
fn discrete_append() {
let mut tree = initial();
// ** APPEND 3 **
let appended = tree.append_leaf(leaf(3)).expect("Failed to append");
let new_root = tree.root_node().expect("Failed to resolve root").node;
// initial tree: (2)
// / \
// (0) (1)
//
// new tree:
// (4g)
// / \
// (2) \
// / \ \
// (0) (1) (3)
//
// so only (3) is added as real leaf
// while new root, (4g) is generated one
assert_eq!(new_root.data.v1.end_height, 3);
assert_eq!(appended.len(), 1);
// ** APPEND 4 **
let appended = tree.append_leaf(leaf(4)).expect("Failed to append");
let new_root = tree.root_node().expect("Failed to resolve root").node;
// intermediate tree:
// (4g)
// / \
// (2) \
// / \ \
// (0) (1) (3)
//
// new tree:
// ( 6 )
// / \
// (2) (5)
// / \ / \
// (0) (1) (3) (4)
//
// so (4), (5), (6) are added as real leaves
// and new root, (6) is stored one
assert_eq!(new_root.data.v1.end_height, 4);
assert_eq!(appended.len(), 3);
assert_matches!(tree.root(), EntryLink::Stored(6));
// ** APPEND 5 **
let appended = tree.append_leaf(leaf(5)).expect("Failed to append");
let new_root = tree.root_node().expect("Failed to resolve root").node;
// intermediate tree:
// ( 6 )
// / \
// (2) (5)
// / \ / \
// (0) (1) (3) (4)
//
// new tree:
// ( 8g )
// / \
// ( 6 ) \
// / \ \
// (2) (5) \
// / \ / \ \
// (0) (1) (3) (4) (7)
//
// so (7) is added as real leaf
// and new root, (8g) is generated one
assert_eq!(new_root.data.v1.end_height, 5);
assert_eq!(appended.len(), 1);
assert_matches!(tree.root(), EntryLink::Generated(_));
tree.for_children(tree.root(), |l, r| {
assert_matches!(l, EntryLink::Stored(6));
assert_matches!(r, EntryLink::Stored(7));
});
// *** APPEND #6 ***
let appended = tree.append_leaf(leaf(6)).expect("Failed to append");
let new_root = tree.root_node().expect("Failed to resolve root").node;
// intermediate tree:
// ( 8g )
// / \
// ( 6 ) \
// / \ \
// (2) (5) \
// / \ / \ \
// (0) (1) (3) (4) (7)
//
// new tree:
// (---10g--)
// / \
// ( 6 ) \
// / \ \
// (2) (5) (9)
// / \ / \ / \
// (0) (1) (3) (4) (7) (8)
//
// so (7) is added as real leaf
// and new root, (10g) is generated one
assert_eq!(new_root.data.v1.end_height, 6);
assert_eq!(appended.len(), 2);
assert_matches!(tree.root(), EntryLink::Generated(_));
tree.for_children(tree.root(), |l, r| {
assert_matches!(l, EntryLink::Stored(6));
assert_matches!(r, EntryLink::Stored(9));
});
// *** APPEND #7 ***
let appended = tree.append_leaf(leaf(7)).expect("Failed to append");
let new_root = tree.root_node().expect("Failed to resolve root").node;
// intermediate tree:
// (---8g---)
// / \
// ( 6 ) \
// / \ \
// (2) (5) (9)
// / \ / \ / \
// (0) (1) (3) (4) (7) (8)
//
// new tree:
// (---12g--)
// / \
// (---11g---) \
// / \ \
// ( 6 ) \ \
// / \ \ \
// (2) (5) (9) \
// / \ / \ / \ \
// (0) (1) (3) (4) (7) (8) (10)
//
// so (10) is added as real leaf
// and new root, (12g) is generated one
assert_eq!(new_root.data.v1.end_height, 7);
assert_eq!(appended.len(), 1);
assert_matches!(tree.root(), EntryLink::Generated(_));
tree.for_children(tree.root(), |l, r| {
assert_matches!(l, EntryLink::Generated(_));
tree.for_children(l, |l, r| {
assert_matches!((l, r), (EntryLink::Stored(6), EntryLink::Stored(9)))
});
assert_matches!(r, EntryLink::Stored(10));
});
}
#[test]
fn truncate_simple() {
let mut tree = generated(9);
let total_truncated = tree.truncate_leaf().expect("Failed to truncate");
// initial tree:
//
// (-------16g------)
// / \
// (--------14-------) \
// / \ \
// ( 6 ) ( 13 ) \
// / \ / \ \
// (2) (5) (9) (12) \
// / \ / \ / \ / \ \
// (0) (1) (3) (4) (7) (8) (10) (11) (15)
//
// new tree:
// (--------14-------)
// / \
// ( 6 ) ( 13 )
// / \ / \
// (2) (5) (9) (12)
// / \ / \ / \ / \
// (0) (1) (3) (4) (7) (8) (10) (11)
//
// so (15) is truncated
// and new root, (14) is a stored one now
assert_matches!(tree.root(), EntryLink::Stored(14));
assert_eq!(total_truncated, 1);
assert_eq!(tree.len(), 15);
}
#[test]
fn truncate_generated() {
let mut tree = generated(10);
let deleted = tree.truncate_leaf().expect("Failed to truncate");
// initial tree:
//
// (--------18g--------)
// / \
// (--------14-------) \
// / \ \
// ( 6 ) ( 13 ) \
// / \ / \ \
// (2) (5) (9) (12) (17)
// / \ / \ / \ / \ / \
// (0) (1) (3) (4) (7) (8) (10) (11) (15) (16)
//
// new tree:
// (-------16g------)
// / \
// (--------14-------) \
// / \ \
// ( 6 ) ( 13 ) \
// / \ / \ \
// (2) (5) (9) (12) \
// / \ / \ / \ / \ \
// (0) (1) (3) (4) (7) (8) (10) (11) (15)
// new root is generated
assert_matches!(tree.root(), EntryLink::Generated(_));
tree.for_children(tree.root(), |left, right| {
assert_matches!(
(left, right),
(EntryLink::Stored(14), EntryLink::Stored(15))
)
});
// two stored nodes should leave us (leaf 16 and no longer needed node 17)
assert_eq!(deleted, 2);
assert_eq!(tree.len(), 16);
}
#[test]
fn tree_len() {
let mut tree = initial();
assert_eq!(tree.len(), 3);
for i in 0..2 {
tree.append_leaf(leaf(i + 3)).expect("Failed to append");
}
assert_eq!(tree.len(), 7);
tree.truncate_leaf().expect("Failed to truncate");
assert_eq!(tree.len(), 4);
}
#[test]
fn tree_len_long() {
let mut tree = initial();
assert_eq!(tree.len(), 3);
for i in 0..4094 {
tree.append_leaf(leaf(i + 3)).expect("Failed to append");
}
assert_eq!(tree.len(), 8191); // 4096*2-1 (full tree)
for _ in 0..2049 {
tree.truncate_leaf().expect("Failed to truncate");
}
assert_eq!(tree.len(), 4083); // 4095 - log2(4096)
}
proptest! {
#[test]
fn prop_there_and_back(number in 0u32..=1024) {
let mut tree = initial();
for i in 0..number {
tree.append_leaf(leaf(i+3)).expect("Failed to append");
}
for _ in 0..number {
tree.truncate_leaf().expect("Failed to truncate");
}
assert_matches!(tree.root(), EntryLink::Stored(2));
}
#[test]
fn prop_leaf_count(number in 3u32..=1024) {
let mut tree = initial();
for i in 1..(number-1) {
tree.append_leaf(leaf(i+2)).expect("Failed to append");
}
assert_eq!(tree.root_node().expect("no root").node.leaf_count(), number as u64);
}
#[test]
fn prop_parity(number in 3u32..=2048) {
let mut tree = initial();
for i in 1..(number-1) {
tree.append_leaf(leaf(i+2)).expect("Failed to append");
}
if number & (number - 1) == 0 {
assert_matches!(tree.root(), EntryLink::Stored(_));
} else {
assert_matches!(tree.root(), EntryLink::Generated(_));
}
}
#[test]
fn prop_parity_with_truncate(
add_and_delete in (0u32..=2048).prop_flat_map(
|add| (Just(add), 0..=add)
)
) {
let (add, delete) = add_and_delete;
// First we add `add` number of leaves, then delete `delete` number of leaves
// What is left should be consistent with generated-stored structure
let mut tree = initial();
for i in 0..add {
tree.append_leaf(leaf(i+3)).expect("Failed to append");
}
for _ in 0..delete {
tree.truncate_leaf().expect("Failed to truncate");
}
let total = add - delete + 2;
if total & (total - 1) == 0 {
assert_matches!(tree.root(), EntryLink::Stored(_));
} else {
assert_matches!(tree.root(), EntryLink::Generated(_));
}
}
#[test]
fn prop_stored_length(
add_and_delete in (0u32..=2048).prop_flat_map(
|add| (Just(add), 0..=add)
)
) {
let (add, delete) = add_and_delete;
let mut tree = initial();
for i in 0..add {
tree.append_leaf(leaf(i+3)).expect("Failed to append");
}
for _ in 0..delete {
tree.truncate_leaf().expect("Failed to truncate");
}
let total = add - delete + 2;
assert!(total * total > tree.len())
}
}
}