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Merge pull request #21 from zcash/always_rewind_unless_empty 

Rewinds are no longer blocked by existing witnesses.
This commit is contained in:
Kris Nuttycombe 2022-03-02 11:51:49 -07:00 committed by GitHub
parent dd57b430de e01885f6e2
commit 5707d6ac09
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GPG Key ID: 4AEE18F83AFDEB23
4 changed files with 101 additions and 98 deletions
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2
proptest-regressions/lib.txt
View File

@ -10,3 +10,5 @@ cc aa498d80d63c58720a913f2edcc6ba19da462f7a824f5be906e63c7ca1566076 # shrinks to
cc 7cebce1664b804d55e259c466ebcc140c4a3708f4ec49ed865d6009736b0a568 # shrinks to ops = [Append("d"), Checkpoint, Witness, Unwitness("d"), Rewind, Unwitness("d")] cc 7cebce1664b804d55e259c466ebcc140c4a3708f4ec49ed865d6009736b0a568 # shrinks to ops = [Append("d"), Checkpoint, Witness, Unwitness("d"), Rewind, Unwitness("d")]
cc 9078a200bceb14aa2f78743f545dab9719db29ddbbb5f1f67fae01805da90f4b # shrinks to ops = [Append("a"), Unwitness("a"), Checkpoint, Checkpoint, Rewind, Append("a"), Rewind, Append("a")] cc 9078a200bceb14aa2f78743f545dab9719db29ddbbb5f1f67fae01805da90f4b # shrinks to ops = [Append("a"), Unwitness("a"), Checkpoint, Checkpoint, Rewind, Append("a"), Rewind, Append("a")]
cc 20e43678bbf38f4c40fdd9e6f5bbc2b8eebcb1756b599f443f3268d6cf8e9d22 # shrinks to ops = [Append("o"), Checkpoint, Witness, Checkpoint, Unwitness("o"), Rewind, Rewind] cc 20e43678bbf38f4c40fdd9e6f5bbc2b8eebcb1756b599f443f3268d6cf8e9d22 # shrinks to ops = [Append("o"), Checkpoint, Witness, Checkpoint, Unwitness("o"), Rewind, Rewind]
cc 2b82b514115d3ddb4990853b0178e997632226be6b8f7c9cf07e94a3e9f41690 # shrinks to ops = [Checkpoint, Witness, Rewind, Unwitness(Position(0), "x"), Checkpoint, Rewind, Checkpoint, Unwitness(Position(0), "x"), Unwitness(Position(0), "x"), Witness, Unwitness(Position(0), "x"), Append("x"), Append("b"), Authpath(Position(0), "x"), Authpath(Position(0), "x"), Rewind, Rewind, Authpath(Position(0), "x"), Witness, Rewind, Witness, Rewind, Append("x"), Rewind, Authpath(Position(0), "x"), Checkpoint, Authpath(Position(0), "x"), Witness, Checkpoint, Witness, Checkpoint, Rewind, Unwitness(Position(0), "x"), Unwitness(Position(0), "x"), Rewind, Witness, Rewind, Authpath(Position(0), "x"), Unwitness(Position(0), "x"), Authpath(Position(0), "x"), Witness, Witness, Checkpoint, Rewind, Checkpoint]
cc 248258b4e2fd558b56611179f6c8493326a8a35bd3fd3ffb55634c14f6fe417a # shrinks to ops = [Append(SipHashable(0)), Checkpoint, Witness, Rewind, Rewind, Authpath(Position(0), SipHashable(0)), Authpath(Position(0), SipHashable(0)), Append(SipHashable(0)), Witness, Authpath(Position(0), SipHashable(0)), Unwitness(Position(0), SipHashable(0)), Unwitness(Position(0), SipHashable(0)), Authpath(Position(0), SipHashable(0)), Authpath(Position(0), SipHashable(0)), Unwitness(Position(0), SipHashable(0)), Witness, Rewind, Checkpoint, Authpath(Position(0), SipHashable(0)), Witness, Rewind, Authpath(Position(0), SipHashable(0)), Authpath(Position(0), SipHashable(0)), Unwitness(Position(0), SipHashable(0)), Rewind, Append(SipHashable(0)), Witness, Authpath(Position(1), SipHashable(0)), Witness, Witness, Unwitness(Position(3), SipHashable(0)), Append(SipHashable(0)), Checkpoint, Append(SipHashable(0)), Witness, Witness, Checkpoint, Unwitness(Position(5), SipHashable(0)), Unwitness(Position(1), SipHashable(0)), Append(SipHashable(0)), Checkpoint, Authpath(Position(2), SipHashable(0)), Witness, Append(SipHashable(0)), Unwitness(Position(6), SipHashable(0)), Authpath(Position(2), SipHashable(0)), Witness, Unwitness(Position(5), SipHashable(0)), Checkpoint, Rewind, Unwitness(Position(1), SipHashable(0)), Checkpoint, Rewind, Witness, Checkpoint, Unwitness(Position(5), SipHashable(0)), Authpath(Position(2), SipHashable(0)), Append(SipHashable(0)), Checkpoint, Append(SipHashable(0)), Checkpoint, Append(SipHashable(0)), Unwitness(Position(4), SipHashable(0)), Rewind, Append(SipHashable(7)), Checkpoint, Append(SipHashable(9)), Authpath(Position(5), SipHashable(0)), Checkpoint, Authpath(Position(10), SipHashable(7)), Rewind, Checkpoint, Rewind]

60
src/bridgetree.rs
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@ -1050,45 +1050,35 @@ impl<H: Hashable + Ord + Clone, const DEPTH: u8> Tree<H> for BridgeTree<H, DEPTH
} }
/// Rewinds the tree state to the previous checkpoint. This function will /// Rewinds the tree state to the previous checkpoint. This function will
/// fail and return false if there is no previous checkpoint or in the event /// return false and leave the tree unmodified if no checkpoints exist.
/// witness data would be destroyed in the process.
fn rewind(&mut self) -> bool { fn rewind(&mut self) -> bool {
match self.checkpoints.pop() { match self.checkpoints.pop() {
Some(mut c) => { Some(mut c) => {
if self.saved.values().any(|saved_idx| { // drop witnessed values at and above the checkpoint height;
c.bridges_len == 0 // we will re-witness if necessary.
|| (!c.is_witnessed && *saved_idx >= c.bridges_len - 1) self.saved
|| (c.is_witnessed && *saved_idx >= c.bridges_len) .retain(|_, saved_idx| *saved_idx + 1 < c.bridges_len);
}) { self.bridges.truncate(c.bridges_len);
// there is a witnessed value at a later position, or the self.saved.append(&mut c.forgotten);
// current position was witnessed since the checkpoint was
// created, so we restore the removed checkpoint and return
// failure
self.checkpoints.push(c);
false
} else {
self.bridges.truncate(c.bridges_len);
self.saved.append(&mut c.forgotten);
let was_duplicate_checkpoint = self let was_duplicate_checkpoint = self
.checkpoints .checkpoints
.last() .last()
.iter() .iter()
.any(|c0| c0.bridges_len == c.bridges_len); .any(|c0| c0.bridges_len == c.bridges_len);
let len = self.bridges.len(); let len = self.bridges.len();
if c.is_witnessed { if c.is_witnessed {
// if the checkpointed state was witnessed, we need to // if the checkpointed state was witnessed, we need to
// restore the witness, as the successor bridge will have // restore the witness, as the successor bridge will have
// been removed by truncation. // been removed by truncation.
self.witness(); self.witness();
} else if len > 0 && was_duplicate_checkpoint { } else if len > 0 && was_duplicate_checkpoint {
// if the checkpoint was a duplicate, we need to create // if the checkpoint was a duplicate, we need to create
// a successor so that future appends do not mutate the // a successor so that future appends do not mutate the
// state at the tip. // state at the tip.
self.bridges.push(self.bridges[len - 1].successor(false)); self.bridges.push(self.bridges[len - 1].successor(false));
}
true
} }
true
} }
None => false, None => false,
} }
@ -1198,11 +1188,11 @@ mod tests {
t.witness(); t.witness();
t.append(&"b".to_string()); t.append(&"b".to_string());
t.append(&"c".to_string()); t.append(&"c".to_string());
assert!(!t.rewind(), "Rewind is expected to fail.");
assert!( assert!(
t.drop_oldest_checkpoint(), t.drop_oldest_checkpoint(),
"Checkpoint drop is expected to succeed" "Checkpoint drop is expected to succeed"
); );
assert!(!t.rewind(), "Rewind is expected to fail.");
} }
#[test] #[test]

104
src/lib.rs
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@ -270,12 +270,7 @@ pub trait Tree<H>: Frontier<H> {
/// that checkpoint record. If there are multiple checkpoints at a given /// that checkpoint record. If there are multiple checkpoints at a given
/// tree state, the tree state will not be altered until all checkpoints /// tree state, the tree state will not be altered until all checkpoints
/// at that tree state have been removed using `rewind`. This function /// at that tree state have been removed using `rewind`. This function
/// will fail and return false if there is no previous checkpoint or in /// return false and leave the tree unmodified if no checkpoints exist.
/// the event witness data would be destroyed in the process.
///
/// In the case that this method returns `false`, the user should have
/// explicitly called `remove_witness` for each witnessed leaf marked
/// since the last checkpoint.
fn rewind(&mut self) -> bool; fn rewind(&mut self) -> bool;
/// Start a recording of append operations performed on a tree. /// Start a recording of append operations performed on a tree.
@ -371,7 +366,6 @@ pub(crate) mod tests {
t.checkpoint(); t.checkpoint();
t.witness(); t.witness();
t.append(&"a".to_string()); t.append(&"a".to_string());
assert!(!t.rewind());
t.append(&"a".to_string()); t.append(&"a".to_string());
t.append(&"a".to_string()); t.append(&"a".to_string());
assert_eq!(t.root(), "aaaa____________"); assert_eq!(t.root(), "aaaa____________");
@ -599,17 +593,19 @@ pub(crate) mod tests {
pub(crate) fn check_checkpoint_rewind<T: Tree<String>, F: Fn(usize) -> T>(new_tree: F) { pub(crate) fn check_checkpoint_rewind<T: Tree<String>, F: Fn(usize) -> T>(new_tree: F) {
let mut t = new_tree(100); let mut t = new_tree(100);
t.append(&"a".to_string());
t.checkpoint();
t.append(&"b".to_string());
t.witness();
assert!(!t.rewind()); assert!(!t.rewind());
let mut t = new_tree(100);
t.checkpoint();
assert!(t.rewind());
let mut t = new_tree(100); let mut t = new_tree(100);
t.append(&"a".to_string()); t.append(&"a".to_string());
t.checkpoint(); t.checkpoint();
t.append(&"b".to_string());
t.witness(); t.witness();
assert!(!t.rewind()); assert!(t.rewind());
assert_eq!(Some((Position::from(0), "a".to_string())), t.current_leaf());
let mut t = new_tree(100); let mut t = new_tree(100);
t.append(&"a".to_string()); t.append(&"a".to_string());
@ -622,7 +618,8 @@ pub(crate) mod tests {
t.checkpoint(); t.checkpoint();
t.witness(); t.witness();
t.append(&"a".to_string()); t.append(&"a".to_string());
assert!(!t.rewind()); assert!(t.rewind());
assert_eq!(Some((Position::from(0), "a".to_string())), t.current_leaf());
let mut t = new_tree(100); let mut t = new_tree(100);
t.append(&"a".to_string()); t.append(&"a".to_string());
@ -636,6 +633,20 @@ pub(crate) mod tests {
} }
pub(crate) fn check_rewind_remove_witness<T: Tree<String>, F: Fn(usize) -> T>(new_tree: F) { pub(crate) fn check_rewind_remove_witness<T: Tree<String>, F: Fn(usize) -> T>(new_tree: F) {
let mut tree = new_tree(100);
tree.append(&"e".to_string());
tree.witness();
tree.checkpoint();
assert!(tree.rewind());
assert!(tree.remove_witness(0usize.into(), &"e".to_string()));
let mut tree = new_tree(100);
tree.append(&"e".to_string());
tree.checkpoint();
tree.witness();
assert!(tree.rewind());
assert!(!tree.remove_witness(0usize.into(), &"e".to_string()));
let mut tree = new_tree(100); let mut tree = new_tree(100);
tree.append(&"e".to_string()); tree.append(&"e".to_string());
tree.witness(); tree.witness();
@ -657,7 +668,7 @@ pub(crate) mod tests {
assert!(!tree.remove_witness(0usize.into(), &"a".to_string())); assert!(!tree.remove_witness(0usize.into(), &"a".to_string()));
tree.checkpoint(); tree.checkpoint();
assert!(tree.witness().is_some()); assert!(tree.witness().is_some());
assert!(!tree.rewind()); assert!(tree.rewind());
let mut tree = new_tree(100); let mut tree = new_tree(100);
tree.append(&"a".to_string()); tree.append(&"a".to_string());
@ -671,50 +682,69 @@ pub(crate) mod tests {
// test framework itself previously did not correctly handle // test framework itself previously did not correctly handle
// chain state restoration. // chain state restoration.
let ops = vec![ fn append(x: &str) -> Operation<String> {
Append("a".to_string()), Append(x.to_string())
Unwitness(0usize.into(), "a".to_string()), }
Checkpoint,
Witness, fn unwitness(pos: usize, x: &str) -> Operation<String> {
Rewind, Unwitness(Position::from(pos), x.to_string())
]; }
let ops = vec![append("x"), Checkpoint, Witness, Rewind, unwitness(0, "x")];
let result = check_operations(ops); let result = check_operations(ops);
assert!(matches!(result, Ok(())), "Test failed: {:?}", result); assert!(
matches!(result, Ok(())),
"Reference/Test mismatch: {:?}",
result
);
let ops = vec![ let ops = vec![
Append("s".to_string()), append("d"),
Witness,
Append("m".to_string()),
Checkpoint, Checkpoint,
Unwitness(0usize.into(), "s".to_string()), Witness,
unwitness(0, "d"),
Rewind, Rewind,
Unwitness(0usize.into(), "s".to_string()), unwitness(0, "d"),
]; ];
let result = check_operations(ops); let result = check_operations(ops);
assert!(matches!(result, Ok(())), "Test failed: {:?}", result); assert!(
matches!(result, Ok(())),
"Reference/Test mismatch: {:?}",
result
);
let ops = vec![ let ops = vec![
Append("d".to_string()), append("o"),
Checkpoint, Checkpoint,
Witness, Witness,
Unwitness(0usize.into(), "d".to_string()), Checkpoint,
unwitness(0, "o"),
Rewind,
Rewind, Rewind,
Unwitness(0usize.into(), "d".to_string()),
]; ];
let result = check_operations(ops); let result = check_operations(ops);
assert!(matches!(result, Ok(())), "Test failed: {:?}", result); assert!(
matches!(result, Ok(())),
"Reference/Test mismatch: {:?}",
result
);
let ops = vec![ let ops = vec![
Append("o".to_string()), append("s"),
Checkpoint,
Witness, Witness,
append("m"),
Checkpoint, Checkpoint,
Unwitness(0usize.into(), "o".to_string()), unwitness(0, "s"),
Rewind,
Rewind, Rewind,
unwitness(0, "s"),
unwitness(0, "m"),
]; ];
let result = check_operations(ops); let result = check_operations(ops);
assert!(matches!(result, Ok(())), "Test failed: {:?}", result); assert!(
matches!(result, Ok(())),
"Reference/Test mismatch: {:?}",
result
);
} }
// //

33
src/sample.rs
View File

@ -1,6 +1,5 @@
//! Sample implementation of the Tree interface.
use super::{Altitude, Frontier, Hashable, Position, Recording, Tree}; use super::{Altitude, Frontier, Hashable, Position, Recording, Tree};
/// Sample implementation of the Tree interface.
use std::convert::TryInto;
#[derive(Clone, Debug)] #[derive(Clone, Debug)]
pub struct TreeState<H: Hashable> { pub struct TreeState<H: Hashable> {
@ -144,7 +143,7 @@ impl<H: Hashable + PartialEq + Clone> TreeState<H> {
#[derive(Clone, Debug)] #[derive(Clone, Debug)]
pub struct CompleteTree<H: Hashable> { pub struct CompleteTree<H: Hashable> {
tree_state: TreeState<H>, tree_state: TreeState<H>,
checkpoints: Vec<(TreeState<H>, bool)>, checkpoints: Vec<TreeState<H>>,
max_checkpoints: usize, max_checkpoints: usize,
} }
@ -228,36 +227,18 @@ impl<H: Hashable + PartialEq + Clone> Tree<H> for CompleteTree<H> {
/// Marks the current tree state as a checkpoint if it is not already a /// Marks the current tree state as a checkpoint if it is not already a
/// checkpoint. /// checkpoint.
fn checkpoint(&mut self) { fn checkpoint(&mut self) {
let is_witnessed = self self.checkpoints.push(self.tree_state.clone());
.tree_state
.current_leaf()
.into_iter()
.any(|(p, l)| self.tree_state.is_witnessed(p, &l));
self.checkpoints
.push((self.tree_state.clone(), is_witnessed));
if self.checkpoints.len() > self.max_checkpoints { if self.checkpoints.len() > self.max_checkpoints {
self.drop_oldest_checkpoint(); self.drop_oldest_checkpoint();
} }
} }
/// Rewinds the tree state to the previous checkpoint. This function will /// Rewinds the tree state to the previous checkpoint. This function will
/// fail and return false if there is no previous checkpoint or in the event /// return false and leave the tree unmodified if no checkpoints exist.
/// witness data would be destroyed in the process.
fn rewind(&mut self) -> bool { fn rewind(&mut self) -> bool {
if let Some((checkpointed_state, is_witnessed)) = self.checkpoints.pop() { if let Some(checkpointed_state) = self.checkpoints.pop() {
// if there are any witnessed leaves in the current tree state self.tree_state = checkpointed_state;
// that would be removed, we don't rewind true
if self.tree_state.witnesses.iter().any(|&(pos, _)| {
let offset: usize = (pos + 1).try_into().unwrap();
offset > checkpointed_state.current_offset
|| (offset == checkpointed_state.current_offset && !is_witnessed)
}) {
self.checkpoints.push((checkpointed_state, is_witnessed));
false
} else {
self.tree_state = checkpointed_state;
true
}
} else { } else {
false false
} }