Create units with ancient parents

README.md

@@ -60,7 +60,7 @@ More details are available [in the book][reference-link-implementation-details].
 - Import AlephBFT in your crate
   ```toml
   [dependencies]
-  aleph-bft = "^0.41"
+  aleph-bft = "^0.42"
   ```
 - The main entry point is the `run_session` function, which returns a Future that runs the
   consensus algorithm.

consensus/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "aleph-bft"
-version = "0.41.0"
+version = "0.42.0"
 edition = "2021"
 authors = ["Cardinal Cryptography"]
 categories = ["algorithms", "data-structures", "cryptography", "database"]

consensus/src/creation/collector.rs

@@ -0,0 +1,342 @@
+use crate::{units::Unit, Hasher, NodeCount, NodeIndex, NodeMap, Round};
+use anyhow::Result;
+use thiserror::Error;
+
+#[derive(Eq, Error, Debug, PartialEq)]
+pub enum ConstraintError {
+    #[error("Not enough parents.")]
+    NotEnoughParents,
+    #[error("Missing own parent.")]
+    MissingOwnParent,
+}
+
+#[derive(Clone)]
+pub struct UnitsCollector<H: Hasher> {
+    candidates: NodeMap<(H::Hash, Round)>,
+    for_round: Round,
+    direct_parents: NodeCount,
+}
+
+impl<H: Hasher> UnitsCollector<H> {
+    pub fn new_initial(n_members: NodeCount) -> Self {
+        UnitsCollector {
+            candidates: NodeMap::with_size(n_members),
+            for_round: 1,
+            direct_parents: NodeCount(0),
+        }
+    }
+
+    pub fn from_previous(previous: &UnitsCollector<H>) -> Self {
+        UnitsCollector {
+            candidates: previous.candidates.clone(),
+            for_round: previous.for_round + 1,
+            direct_parents: NodeCount(0),
+        }
+    }
+
+    pub fn add_unit<U: Unit<Hasher = H>>(&mut self, unit: &U) {
+        let node_id = unit.creator();
+        let hash = unit.hash();
+        let round = unit.round();
+
+        if round >= self.for_round {
+            return;
+        }
+
+        let to_insert = match self.candidates.get(node_id) {
+            None => Some((hash, round)),
+            Some((_, r)) if *r < round => Some((hash, round)),
+            _ => None,
+        };
+
+        if let Some(data) = to_insert {
+            self.candidates.insert(node_id, data);
+            if round == self.for_round - 1 {
+                self.direct_parents += NodeCount(1);
+            }
+        }
+    }
+
+    pub fn prospective_parents(
+        &self,
+        node_id: NodeIndex,
+    ) -> Result<&NodeMap<(H::Hash, Round)>, ConstraintError> {
+        if self.direct_parents < self.candidates.size().consensus_threshold() {
+            return Err(ConstraintError::NotEnoughParents);
+        }
+        match self.candidates.get(node_id) {
+            Some((_, r)) if *r == self.for_round - 1 => Ok(&self.candidates),
+            _ => Err(ConstraintError::MissingOwnParent),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{
+        creation::collector::{ConstraintError, UnitsCollector},
+        units::{random_full_parent_units_up_to, Unit},
+        NodeCount, NodeIndex,
+    };
+    use aleph_bft_mock::Hasher64;
+
+    #[test]
+    fn initial_fails_without_parents() {
+        let n_members = NodeCount(4);
+        let units_collector = UnitsCollector::<Hasher64>::new_initial(n_members);
+
+        let err = units_collector
+            .prospective_parents(NodeIndex(0))
+            .expect_err("should fail without parents");
+        assert_eq!(err, ConstraintError::NotEnoughParents);
+    }
+
+    #[test]
+    fn initial_fails_with_too_few_parents() {
+        let n_members = NodeCount(4);
+        let mut units_collector = UnitsCollector::new_initial(n_members);
+        let units = random_full_parent_units_up_to(0, n_members, 43);
+        units_collector.add_unit(&units[0][0]);
+
+        let err = units_collector
+            .prospective_parents(NodeIndex(0))
+            .expect_err("should fail without parents");
+        assert_eq!(err, ConstraintError::NotEnoughParents);
+    }
+
+    #[test]
+    fn initial_fails_without_own_parent() {
+        let n_members = NodeCount(4);
+        let mut units_collector = UnitsCollector::new_initial(n_members);
+        let units = random_full_parent_units_up_to(0, n_members, 43);
+        for unit in units[0].iter().skip(1) {
+            units_collector.add_unit(unit);
+        }
+
+        let err = units_collector
+            .prospective_parents(NodeIndex(0))
+            .expect_err("should fail without parents");
+        assert_eq!(err, ConstraintError::MissingOwnParent);
+    }
+
+    #[test]
+    fn initial_successfully_computes_minimal_parents() {
+        let n_members = NodeCount(4);
+        let mut units_collector = UnitsCollector::new_initial(n_members);
+        let units = random_full_parent_units_up_to(0, n_members, 43);
+        for unit in units[0].iter().take(3) {
+            units_collector.add_unit(unit);
+        }
+
+        let parents = units_collector
+            .prospective_parents(NodeIndex(0))
+            .expect("we should be able to retrieve parents");
+        assert_eq!(parents.item_count(), 3);
+
+        let new_units: Vec<_> = units[0]
+            .iter()
+            .take(3)
+            .map(|unit| (unit.hash(), unit.round()))
+            .collect();
+        let selected_parents: Vec<_> = parents.values().cloned().collect();
+        assert_eq!(new_units, selected_parents);
+    }
+
+    #[test]
+    fn initial_successfully_computes_full_parents() {
+        let n_members = NodeCount(4);
+        let mut units_collector = UnitsCollector::new_initial(n_members);
+        let units = random_full_parent_units_up_to(0, n_members, 43);
+        for unit in &units[0] {
+            units_collector.add_unit(unit);
+        }
+
+        let parents = units_collector
+            .prospective_parents(NodeIndex(0))
+            .expect("we should be able to retrieve parents");
+        assert_eq!(parents.item_count(), 4);
+
+        let new_units: Vec<_> = units[0]
+            .iter()
+            .map(|unit| (unit.hash(), unit.round()))
+            .collect();
+        let selected_parents: Vec<_> = parents.values().cloned().collect();
+        assert_eq!(new_units, selected_parents);
+    }
+
+    #[test]
+    fn following_fails_without_parents() {
+        let n_members = NodeCount(4);
+        let initial_units_collector = UnitsCollector::<Hasher64>::new_initial(n_members);
+        let units_collector = UnitsCollector::from_previous(&initial_units_collector);
+
+        let err = units_collector
+            .prospective_parents(NodeIndex(0))
+            .expect_err("should fail without parents");
+        assert_eq!(err, ConstraintError::NotEnoughParents);
+    }
+
+    #[test]
+    fn following_fails_with_too_few_parents() {
+        let n_members = NodeCount(4);
+        let initial_units_collector = UnitsCollector::<Hasher64>::new_initial(n_members);
+        let mut units_collector = UnitsCollector::from_previous(&initial_units_collector);
+        let units = random_full_parent_units_up_to(1, n_members, 43);
+        units_collector.add_unit(&units[1][0]);
+
+        let err = units_collector
+            .prospective_parents(NodeIndex(0))
+            .expect_err("should fail without parents");
+        assert_eq!(err, ConstraintError::NotEnoughParents);
+    }
+
+    #[test]
+    fn following_fails_with_too_old_parents() {
+        let n_members = NodeCount(4);
+        let initial_units_collector = UnitsCollector::<Hasher64>::new_initial(n_members);
+        let mut units_collector = UnitsCollector::from_previous(&initial_units_collector);
+        let units = random_full_parent_units_up_to(0, n_members, 43);
+        for unit in &units[0] {
+            units_collector.add_unit(unit);
+        }
+
+        let err = units_collector
+            .prospective_parents(NodeIndex(0))
+            .expect_err("should fail without parents");
+        assert_eq!(err, ConstraintError::NotEnoughParents);
+    }
+
+    #[test]
+    fn following_fails_without_own_parent() {
+        let n_members = NodeCount(4);
+        let initial_units_collector = UnitsCollector::<Hasher64>::new_initial(n_members);
+        let mut units_collector = UnitsCollector::from_previous(&initial_units_collector);
+        let units = random_full_parent_units_up_to(1, n_members, 43);
+        for unit in units[1].iter().skip(1) {
+            units_collector.add_unit(unit);
+        }
+
+        let err = units_collector
+            .prospective_parents(NodeIndex(0))
+            .expect_err("should fail without parents");
+        assert_eq!(err, ConstraintError::MissingOwnParent);
+    }
+
+    #[test]
+    fn following_fails_with_too_old_own_parent() {
+        let n_members = NodeCount(4);
+        let initial_units_collector = UnitsCollector::<Hasher64>::new_initial(n_members);
+        let mut units_collector = UnitsCollector::from_previous(&initial_units_collector);
+        let units = random_full_parent_units_up_to(1, n_members, 43);
+        for unit in units[1].iter().skip(1) {
+            units_collector.add_unit(unit);
+        }
+        units_collector.add_unit(&units[0][0]);
+
+        let err = units_collector
+            .prospective_parents(NodeIndex(0))
+            .expect_err("should fail without parents");
+        assert_eq!(err, ConstraintError::MissingOwnParent);
+    }
+
+    #[test]
+    fn following_successfully_computes_minimal_parents() {
+        let n_members = NodeCount(4);
+        let initial_units_collector = UnitsCollector::<Hasher64>::new_initial(n_members);
+        let mut units_collector = UnitsCollector::from_previous(&initial_units_collector);
+        let units = random_full_parent_units_up_to(1, n_members, 43);
+        for unit in units[1].iter().take(3) {
+            units_collector.add_unit(unit);
+        }
+
+        let parents = units_collector
+            .prospective_parents(NodeIndex(0))
+            .expect("we should be able to retrieve parents");
+        assert_eq!(parents.item_count(), 3);
+
+        let new_units: Vec<_> = units[1]
+            .iter()
+            .take(3)
+            .map(|unit| (unit.hash(), unit.round()))
+            .collect();
+        let selected_parents: Vec<_> = parents.values().cloned().collect();
+        assert_eq!(new_units, selected_parents);
+    }
+
+    #[test]
+    fn following_successfully_computes_minimal_parents_with_ancient() {
+        let n_members = NodeCount(4);
+        let initial_units_collector = UnitsCollector::<Hasher64>::new_initial(n_members);
+        let mut units_collector = UnitsCollector::from_previous(&initial_units_collector);
+        let units = random_full_parent_units_up_to(1, n_members, 43);
+        for unit in units[1].iter().take(3) {
+            units_collector.add_unit(unit);
+        }
+        units_collector.add_unit(&units[0][3]);
+
+        let parents = units_collector
+            .prospective_parents(NodeIndex(0))
+            .expect("we should be able to retrieve parents");
+        assert_eq!(parents.item_count(), 4);
+
+        let mut new_units: Vec<_> = units[1]
+            .iter()
+            .take(3)
+            .map(|unit| (unit.hash(), unit.round()))
+            .collect();
+        new_units.push((units[0][3].hash(), units[0][3].round()));
+        let selected_parents: Vec<_> = parents.values().cloned().collect();
+        assert_eq!(new_units, selected_parents);
+    }
+
+    #[test]
+    fn following_successfully_computes_full_parents() {
+        let n_members = NodeCount(4);
+        let initial_units_collector = UnitsCollector::<Hasher64>::new_initial(n_members);
+        let mut units_collector = UnitsCollector::from_previous(&initial_units_collector);
+        let units = random_full_parent_units_up_to(1, n_members, 43);
+        for unit in &units[1] {
+            units_collector.add_unit(unit);
+        }
+
+        let parents = units_collector
+            .prospective_parents(NodeIndex(0))
+            .expect("we should be able to retrieve parents");
+        assert_eq!(parents.item_count(), 4);
+
+        let new_units: Vec<_> = units[1]
+            .iter()
+            .map(|unit| (unit.hash(), unit.round()))
+            .collect();
+        let selected_parents: Vec<_> = parents.values().cloned().collect();
+        assert_eq!(new_units, selected_parents);
+    }
+
+    #[test]
+    fn following_inherits_units() {
+        let n_members = NodeCount(4);
+        let mut initial_units_collector = UnitsCollector::<Hasher64>::new_initial(n_members);
+        let units = random_full_parent_units_up_to(1, n_members, 43);
+        for unit in &units[0] {
+            initial_units_collector.add_unit(unit);
+        }
+        let mut units_collector = UnitsCollector::from_previous(&initial_units_collector);
+        for unit in units[1].iter().take(3) {
+            units_collector.add_unit(unit);
+        }
+
+        let parents = units_collector
+            .prospective_parents(NodeIndex(0))
+            .expect("we should be able to retrieve parents");
+        assert_eq!(parents.item_count(), 4);
+
+        let mut new_units: Vec<_> = units[1]
+            .iter()
+            .take(3)
+            .map(|unit| (unit.hash(), unit.round()))
+            .collect();
+        new_units.push((units[0][3].hash(), units[0][3].round()));
+        let selected_parents: Vec<_> = parents.values().cloned().collect();
+        assert_eq!(new_units, selected_parents);
+    }
+}