dcs2-raft 0.1.0

An extensible distributed control system framework made in rust with no-std support.
Documentation
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use std::cmp::{max, min};
use std::fmt::{Debug, Write};
use std::slice::Iter;
use log::{debug, error};

use serde::de::DeserializeOwned;

use dcs::communication::messages::{UpdateClusterVec, COORDINATION_MESSAGE_OPCODE, Header, IdentificableMessage, Package, PackageBuilder};
use dcs::heapless;
use dcs::nodes::SystemNodeId;
use dcs::properties::MEASUREMENTS_MAX_COUNT;
use dcs::rules::measurements::{Measurement, SystemState};
use dcs::rules::strategy::Rule;

use crate::server::{LogData, Merge, NoOp};

use super::*;

pub type Term = u16;
pub type LogIndex = u32;

pub const LOG_LEN: usize = CLUSTER_NODE_COUNT * MEASUREMENTS_MAX_COUNT / 3;

#[derive(Eq, PartialEq, Debug, Clone, Serialize, Deserialize)]
pub struct Log<T: LogData> {
    vec: heapless::Vec<LogEntry<T>, LOG_LEN>,
    index_shift: u32,
}

impl<T: LogData> Default for Log<T> {
    fn default() -> Self {
        Self {
            vec: Default::default(),
            index_shift: 1,
        }
    }
}

impl<T: LogData> Log<T> {
    pub fn new() -> Log<T> {
        Self {
            vec: Default::default(),
            index_shift: 1,
        }
    }
    pub fn noop() -> Log<T> {
        Self::new()
    }

    pub fn push(&mut self, data: LogEntry<T>) -> Result<(), LogEntry<T>> {
        self.vec.push(data)
    }

    pub fn insert(&mut self, idx: LogIndex, data: LogEntry<T>) {
        assert!(idx > 0);
        let idx: usize = self.shift_idx(idx);
        if idx < self.len() {
            self.vec[idx] = data
        } else {
            if self.vec.push(data).is_err() {
                error!("Couldn't append element to log: max capacity of {} reached.", self.vec.len())
            };
        }
    }

    pub fn is_snapshot(&self, idx: LogIndex) -> bool {
        idx <= self.index_shift
    }

    pub fn last_included_index(&self) -> u32 {
        self.index_shift
    }

    pub fn last_included_term(&self) -> Term {
        if self.index_shift > 1 {
            self.vec.first().unwrap().term
        } else {
            0
        }
    }

    pub fn snapshot(&mut self, idx: LogIndex) {
        assert!(idx > 0);
        if idx < 2 {
            return;
        }
        let snapshot_count = min(self.shift_idx(idx) as u32 + 1, self.len() as u32);
        let mut data_accum = None::<T>;
        let mut term_accum = Term::default();
        let mut rule_accum = None;
        let mut config_change_accum = None;
        for _ in 0..snapshot_count {
            let entry = self.vec.remove(0);
            data_accum = match (data_accum, entry.data) {
                (Some(acc), Some(d)) => Some(acc.merge(d)),
                (acc, d) => acc.or(d),
            };
            term_accum = max(entry.term, term_accum);
            config_change_accum = entry.config_change.or(config_change_accum);
            rule_accum = entry.rule.or(rule_accum);
        }
        self.vec.insert(0, LogEntry::new(term_accum, data_accum, config_change_accum, rule_accum));
        self.index_shift += snapshot_count.checked_sub(1).unwrap_or_default();
    }

    pub fn install_snapshot(&mut self, last_included_index: LogIndex, entry: LogEntry<T>) {
        let snapshot_count = min(
            self.shift_idx(last_included_index) as u32 + 1,
            self.len() as u32,
        );
        for _ in 0..snapshot_count {
            self.vec.remove(0);
        }
        self.index_shift = last_included_index;
        self.vec.insert(0, entry);
    }

    pub fn capacity(&self) -> f32 {
        1.0 - (self.len() as f32 / LOG_LEN as f32)
    }

    fn shift_idx(&self, idx: LogIndex) -> usize {
        idx.checked_sub(self.index_shift).unwrap_or_default() as usize
    }

    pub fn pop(&mut self) -> Option<LogEntry<T>> {
        self.vec.pop()
    }

    pub fn get(&self, idx: LogIndex) -> Option<&LogEntry<T>> {
        assert!(idx > 0);
        self.vec.get(self.shift_idx(idx))
    }

    pub fn len(&self) -> usize {
        self.vec.len()
    }

    pub fn last_index(&self) -> usize {
        (self.vec.len()  + self.index_shift as usize).checked_sub(1).unwrap_or_default()
    }

    pub fn is_empty(&self) -> bool {
        self.vec.is_empty()
    }

    pub fn last(&self) -> Option<&LogEntry<T>> {
        self.vec.last()
    }

    pub fn iter(&self) -> Iter<'_, LogEntry<T>> {
        self.vec.iter()
    }
}

impl<T: LogData, I: Iterator<Item = LogEntry<T>>> From<I> for Log<T> {
    fn from(value: I) -> Self {
        let mut log = Self::new();
        for i in value {
            log.push(i);
        }
        log
    }
}

impl<T: LogData> IntoIterator for Log<T> {
    type Item = LogEntry<T>;
    type IntoIter = IntoIter<T>;

    fn into_iter(self) -> Self::IntoIter {
        IntoIter {
            idx: 0,
            vec: self.vec,
        }
    }
}

pub struct IntoIter<T: LogData> {
    idx: usize,
    vec: heapless::Vec<LogEntry<T>, LOG_LEN>,
}

impl<T: LogData> Iterator for IntoIter<T> {
    type Item = LogEntry<T>;

    fn next(&mut self) -> Option<Self::Item> {
        let current = self.vec.get(self.idx);
        self.idx += 1;
        current.cloned()
    }
}

#[derive(Eq, PartialEq, Debug, Clone, Serialize, Deserialize)]
pub struct LogEntry<T: LogData> {
    pub term: Term,
    pub data: Option<T>,
    pub config_change: Option<UpdateClusterVec>,
    pub rule: Option<Rule>,
}

impl<T: LogData> LogEntry<T> {
    pub fn new(term: Term, data: Option<T>, config_change: Option<UpdateClusterVec>, rule: Option<Rule>, ) -> Self {
        Self {
            term,
            data,
            config_change,
            rule,
        }
    }
    pub fn with_data(term: Term, data: Option<T>) -> Self {
        Self {
            term,
            data,
            config_change: None,
            rule: None,
        }
    }

    pub fn with_rule(term: Term, rule: Rule) -> Self {
        Self {
            term,
            data: None,
            config_change: None,
            rule: Some(rule),
        }
    }

    pub fn with_config(term: Term, config_change: Option<UpdateClusterVec>) -> Self {
        Self {
            term,
            data: None,
            config_change,
            rule: None,
        }
    }
}

#[derive(Copy, Clone, Eq, PartialEq, Debug, Serialize, Deserialize)]
pub struct RequestVoteArgs {
    pub term: Term,
    pub prev_log_index: LogIndex,
    pub prev_log_term: Term,
}

#[derive(Eq, PartialEq, Debug, Clone, Serialize, Deserialize)]
pub struct AppendLogArgs<T: LogData> {
    pub term: Term,
    pub prev_log_index: LogIndex,
    pub prev_log_term: Term,
    pub entries: Log<T>,
    pub leader_commit: LogIndex,
}

#[derive(Eq, PartialEq, Debug, Clone, Serialize, Deserialize)]
pub enum RaftMessage<T>
where
    T: LogData,
{
    RequestVote(RequestVoteArgs),
    RequestVoteResponse(RequestVoteResponseResult),
    AppendLog(AppendLogArgs<T>),
    AppendLogResponse(AppendLogResponseResult),
    ReadRequest,
    ReadRequestReply(ReadRequestReplyArgs<T>),
    WriteRequest(WriteRequestArgs),
    WriteRequestReply(bool, Option<SystemNodeId>),
    ConfigChange(UpdateClusterVec),
    ConfigChangeACK(bool),
    InstallSnapshot(InstallSnapshotArgs<T>),
    InstallSnapshotResponse(Term),
}

impl<T: LogData> Display for RaftMessage<T> {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        match self {
            RaftMessage::RequestVote(args) => {
                f.write_fmt(format_args!("RequestVote term: {}", args.term))
            }
            RaftMessage::RequestVoteResponse(args) => {
                let granted = if args.granted {"granted"} else {"rejected"};
                f.write_fmt(format_args!("RequestVoteResponse {}", granted))
            }
            RaftMessage::AppendLog(args) => {
                f.write_fmt(format_args!("AppendLog term: {} index: {}", args.term, args.prev_log_index + 1))
            }
            RaftMessage::AppendLogResponse(args) => {
                let granted = if args.success {"granted"} else {"rejected"};
                f.write_fmt(format_args!("AppendLogResponse {}", granted))
            }
            RaftMessage::ReadRequest => {
                f.write_fmt(format_args!("ReadRequest"))
            }
            RaftMessage::ReadRequestReply(args) => {
                let granted = if args.success {"granted"} else {"rejected"};
                f.write_fmt(format_args!("ReadRequestReply {}", granted))
            }
            RaftMessage::WriteRequest(args) => {
                let value = args.measurement.map(|m| m.value.to_string()).unwrap_or_default();
                let measurement_type = args.measurement.map(|m| m.typed.to_string()).unwrap_or_default();
                f.write_fmt(format_args!("WriteRequest value: {} type: {:?}", value, measurement_type))
            }
            RaftMessage::WriteRequestReply(success, _) => {
                let granted = if *success {"granted"} else {"rejected"};
                f.write_fmt(format_args!("WriteRequestReply {}", granted))
            }
            RaftMessage::ConfigChange(args) => {
                let prefix = f.write_str("ConfigChange new cluster: ");
                let cluster_ids = args.iter().map(|id| f.write_fmt(format_args!("{id} "))).collect();
                prefix.and(cluster_ids)
            }
            RaftMessage::ConfigChangeACK(success) => {
                let granted = if *success {"granted"} else {"rejected"};
                f.write_fmt(format_args!("ConfigChangeACK {}", granted))
            }
            RaftMessage::InstallSnapshot(args) => {
                f.write_fmt(format_args!("InstallSnapshot"))
            }
            RaftMessage::InstallSnapshotResponse(args) => {
                f.write_fmt(format_args!("ConfigChangeACK"))
            }
        }
    }
}

impl<T: Clone + Debug + Default + Serialize + DeserializeOwned + LogData> Default
    for RaftMessage<T>
{
    fn default() -> Self {
        RaftMessage::ReadRequest
    }
}

impl<T: LogData + Clone + Debug + Default + Serialize + DeserializeOwned> IdentificableMessage
    for RaftMessage<T>
{
    fn id() -> u8 {
        COORDINATION_MESSAGE_OPCODE
    }
}

pub struct RaftPackageBuilder<T: LogData> {
    to: Option<SystemNodeId>,
    from: Option<SystemNodeId>,
    body: Option<RaftMessage<T>>,
}

impl<T: LogData> Default for RaftPackageBuilder<T> {
    fn default() -> Self {
        Self {
            to: None,
            from: None,
            body: None,
        }
    }
}

impl<T: LogData> PackageBuilder for RaftPackageBuilder<T> {
    type NodeId = SystemNodeId;
    type Message = RaftMessage<T>;

    fn clean_copy(&self) -> Self {
        Self::default()
    }

    fn to(mut self, id: SystemNodeId) -> Self {
        self.to = Some(id);
        self
    }

    fn from(mut self, id: SystemNodeId) -> Self {
        self.from = Some(id);
        self
    }
    fn with_message(mut self, msg: RaftMessage<T>) -> Self {
        self.body = Some(msg);
        self
    }

    fn respond_to(self, package: Package<Self::NodeId, Self::Message>) -> Self {
        self.to(package.header.from)
    }

    fn build(self) -> Result<Package<Self::NodeId, Self::Message>, ()> {
        Ok(Package {
            header: Header {
                from: self.from.ok_or(())?,
                to: self.to.ok_or(())?,
            },
            body: self.body.ok_or(())?,
        })
    }
}

#[derive(Eq, PartialEq, Debug, Clone, Serialize, Deserialize)]
pub struct InstallSnapshotArgs<T: LogData> {
    pub term: Term,
    pub leader_id: SystemNodeId,
    pub last_included_index: LogIndex,
    pub last_included_term: Term,
    pub data: LogEntry<T>,
}

#[derive(Eq, PartialEq, Debug, Copy, Clone, Serialize, Deserialize)]
pub struct ReadRequestReplyArgs<T> {
    pub success: bool,
    pub data: Option<T>,
    pub redirect: Option<SystemNodeId>,
}

impl<T> ReadRequestReplyArgs<T> {
    pub fn fail(leader_id: Option<SystemNodeId>) -> Self {
        Self {
            success: false,
            data: None,
            redirect: leader_id,
        }
    }
}

#[derive(Eq, PartialEq, Debug, Copy, Clone, Serialize, Deserialize)]
pub struct RequestVoteResponseResult {
    pub term: Term,
    pub granted: bool,
}

#[derive(Eq, PartialEq, Debug, Copy, Clone, Serialize, Deserialize)]
pub struct AppendLogResponseResult {
    pub term: Term,
    pub success: bool,
}

#[derive(Eq, PartialEq, Debug, Copy, Clone, Serialize, Deserialize)]
pub struct WriteRequestArgs {
    pub measurement: Option<Measurement>,
    pub rule: Option<Rule>,
    pub id: SystemNodeId,
}

impl WriteRequestArgs {
    pub fn with_rule(id: SystemNodeId, rule: Rule) -> Self {
        Self {
            measurement: None,
            rule: Some(rule),
            id
        }
    }

    pub fn with_measurement(id: SystemNodeId, measurement: Measurement) -> Self {
        Self {
            measurement: Some(measurement),
            rule: None,
            id
        }
    }
}

#[cfg(test)]
mod log_tests {
    use crate::messages::{UpdateClusterVec, Log, LogEntry, Term, LOG_LEN};
    use crate::server::{Merge, NoOp};
    use dcs::nodes::SystemNodeId;
    use dcs::rules::measurements::{Measurement, SystemState};
    use serde::{Serialize, Serializer};
    use std::fmt::Debug;
    use dcs::rules::strategy::{Rule, RuleType};

    #[derive(Eq, PartialEq, Copy, Clone, Debug, Serialize)]
    struct TestLogData(usize);

    impl NoOp for TestLogData {
        fn noop() -> Self {
            Self(0)
        }
    }

    impl Merge for TestLogData {
        fn merge(self, rhs: Self) -> Self {
            Self(self.0 + rhs.0)
        }
    }

    impl From<(SystemNodeId, Measurement)> for TestLogData {
        fn from(value: (SystemNodeId, Measurement)) -> Self {
            unreachable!()
        }
    }

    impl Into<SystemState> for TestLogData {
        fn into(self) -> SystemState {
            unreachable!()
        }
    }

    #[test]
    pub fn new_log_is_empty() {
        let log = Log::<TestLogData>::new();
        assert!(log.is_empty())
    }

    #[test]
    pub fn can_insert() {
        let mut log = Log::<TestLogData>::new();
        let data = some_entry();
        log.push(data);

        assert!(!log.is_empty())
    }

    #[test]
    #[should_panic]
    pub fn zero_is_not_valid_index_when_getting() {
        let mut log = Log::<TestLogData>::new();
        log.push(some_entry()).expect("Failed push");

        let result = log.get(0);
    }

    #[test]
    #[should_panic]
    pub fn zero_is_not_valid_index_when_inserting() {
        let mut log = Log::<TestLogData>::new();
        log.insert(1, some_entry());

        let result = log.get(0);
    }

    #[test]
    pub fn one_is_the_first_index() {
        let mut log = Log::<TestLogData>::new();
        log.push(some_entry()).expect("Failed push");

        let result = log.get(1).cloned();
        assert_eq!(Some(some_entry()), result);
    }

    #[test]
    pub fn when_inserting_in_position_greater_than_length_then_is_the_same_as_pushing() {
        let mut log = Log::<TestLogData>::new();
        log.insert(32, some_entry());

        assert!(log.get(32).is_none());
        assert!(log.get(1).is_some());
    }

    #[test]
    pub fn when_inserting_in_existing_position_replaces_data() {
        let mut log = Log::<TestLogData>::new();
        log.push(entry(1));
        log.push(entry(2));
        log.push(entry(3));

        log.insert(2, entry(42));

        assert_eq!(&entry(3), log.get(3).unwrap());
        assert_eq!(&entry(42), log.get(2).unwrap());
        assert_eq!(&entry(1), log.get(1).unwrap());
    }

    #[test]
    #[should_panic]
    pub fn zero_is_not_valid_index_for_snapshot() {
        let mut log = Log::<TestLogData>::new();
        log.snapshot(0);
    }

    #[test]
    pub fn can_calculate_log_capacity() {
        let mut log = Log::<TestLogData>::new();
        log.push(entry(1));
        log.push(entry(2));
        log.push(entry(3));

        assert!((1.0 - (3.0 / LOG_LEN as f32) - log.capacity()).abs() < 0.0001);
    }

    #[test]
    pub fn snapshot_empty_log_leaves_everything_untouched() {
        let mut log = Log::<TestLogData>::new();
        log.snapshot(1);

        log.push(entry(1));
        log.push(entry(2));
        log.push(entry(3));

        assert_eq!(&entry(3), log.get(3).unwrap());
        assert_eq!(&entry(2), log.get(2).unwrap());
        assert_eq!(&entry(1), log.get(1).unwrap());
    }

    #[test]
    pub fn snapshot_log_with_one_element_leaves_everything_untouched() {
        let mut log = Log::<TestLogData>::new();
        log.push(entry(1));

        log.snapshot(1);

        log.push(entry(2));
        log.push(entry(3));
        assert_eq!(&entry(3), log.get(3).unwrap());
        assert_eq!(&entry(2), log.get(2).unwrap());
        assert_eq!(&entry(1), log.get(1).unwrap());
    }

    #[test]
    pub fn can_get_value_not_snapshotted() {
        let mut log = Log::<TestLogData>::new();
        log.push(entry(1));
        log.push(entry(2));
        log.push(entry(3));

        log.snapshot(2);

        assert_eq!(&entry(3), log.get(3).unwrap());
    }

    #[test]
    pub fn all_snapshotted_values_are_the_same() {
        let mut log = Log::<TestLogData>::new();
        log.push(entry(1));
        log.push(entry(2));
        log.push(entry(3));

        log.snapshot(3);

        assert_eq!(log.get(1).unwrap(), log.get(2).unwrap());
        assert_eq!(log.get(2).unwrap(), log.get(3).unwrap());
    }

    #[test]
    pub fn can_check_if_entry_was_snapshotted() {
        let mut log = Log::<TestLogData>::new();
        log.push(entry(1));
        log.push(entry(2));
        log.push(entry(3));

        log.snapshot(2);

        assert!(log.is_snapshot(2));
        assert!(!log.is_snapshot(3));
    }

    #[test]
    pub fn can_get_last_included_index() {
        let mut log = Log::<TestLogData>::new();
        log.push(entry(1));
        log.push(entry(2));
        log.push(entry(3));

        log.snapshot(2);

        assert_eq!(2, log.last_included_index());
    }

    #[test]
    pub fn can_get_last_included_index_after_multiple_snapshots() {
        let mut log = Log::<TestLogData>::new();
        log.push(entry(1));
        log.push(entry(2));
        log.push(entry(3));

        log.snapshot(3);

        log.push(entry(4));
        log.push(entry(5));
        log.push(entry(6));

        log.snapshot(6);

        assert_eq!(6, log.last_included_index());
        assert_eq!(&entry(21), log.get(6).unwrap());
    }

    #[test]
    pub fn snapshot_is_the_merge_of_entries_up_to_idx() {
        let mut log = Log::<TestLogData>::new();
        log.push(entry(1));
        log.push(entry(2));
        log.push(entry(3));

        log.snapshot(3);

        assert_eq!(&entry(6), log.get(1).unwrap());
    }

    #[test]
    pub fn different_indices_generate_different_snapshot_data() {
        let mut log = Log::<TestLogData>::new();
        log.push(entry(1));
        log.push(entry(2));
        log.push(entry(3));

        let mut log2 = log.clone();
        log.snapshot(3);
        log2.snapshot(2);

        assert_ne!(log.get(1), log2.get(1));
        assert_eq!(&entry(6), log.get(1).unwrap());
        assert_eq!(&entry(3), log2.get(1).unwrap());
    }

    #[test]
    pub fn the_snapshot_term_is_the_greater_term_of_all_entries() {
        let mut log = Log::<TestLogData>::new();
        log.push(entry_with_term(0, 0));
        log.push(entry_with_term(1, 0));
        log.push(entry_with_term(2, 0));

        log.snapshot(3);

        assert_eq!(&entry_with_term(2, 0), log.get(1).unwrap());
    }

    #[test]
    pub fn different_indices_generate_different_snapshot_term() {
        let mut log = Log::<TestLogData>::new();
        log.push(entry_with_term(0, 1));
        log.push(entry_with_term(1, 2));
        log.push(entry_with_term(2, 3));

        let mut log2 = log.clone();
        log.snapshot(3);
        log2.snapshot(2);

        assert_eq!(&entry_with_term(2, 6), log.get(1).unwrap());
        assert_eq!(&entry_with_term(1, 3), log2.get(1).unwrap());
    }

    #[test]
    pub fn the_snapshot_change_request_is_the_latest_change_req() {
        let mut log = Log::<TestLogData>::new();
        log.push(config_change(&[1]));
        log.push(config_change(&[1, 2]));
        log.push(config_change(&[1, 2, 3]));

        log.snapshot(3);

        assert_eq!(&config_change(&[1, 2, 3]), log.get(1).unwrap());
    }

    fn update_cluster_vector(slice: Vec<u32>) -> Option<UpdateClusterVec> {
        let mut cluster = UpdateClusterVec::new();
        for elem in slice {
            cluster.push(SystemNodeId::from(elem));
        }
        Some(cluster)
    }

    #[test]
    pub fn entries_with_data_config_change_and_rule() {
        let mut log = Log::<TestLogData>::new();
        log.push(LogEntry::new(0, Some(TestLogData::noop()), update_cluster_vector(vec!(1, 2)), Some(rule(1))));
        log.push(LogEntry::new(1, Some(TestLogData(2)), None, None));
        log.push(LogEntry::new(2, None, update_cluster_vector(vec!(1, 2, 3)), Some(rule(2))));
        log.push(LogEntry::new(3, None, None, None));

        log.snapshot(4);

        let expected_snapshot = LogEntry::new(
            3,
            Some(TestLogData(2)),
            update_cluster_vector(vec!(1, 2, 3)),
            Some(rule(2)),
        );
        assert_eq!(&expected_snapshot, log.get(1).unwrap());
    }

    fn config_change(config: &[u32]) -> LogEntry<TestLogData> {
        LogEntry::with_config(0, update_cluster_vector(config.to_vec()))
    }

    #[test]
    pub fn snapshot_several_times() {
        let mut log = Log::<TestLogData>::new();
        log.push(LogEntry::new(1, Some(TestLogData::noop()), update_cluster_vector(vec!(1, 2)), None));
        log.push(LogEntry::new(2, Some(TestLogData(2)), None, None));
        log.push(LogEntry::new(3, None, update_cluster_vector(vec!(1, 2, 3)), None));
        log.push(LogEntry::new(4, None, None, None));

        log.snapshot(4);

        log.push(LogEntry::new(5, Some(TestLogData(3)), None, None));
        log.push(LogEntry::new(6, None, update_cluster_vector(vec!(1, 2, 3, 4)), None));
        log.push(LogEntry::new(7, None, None, None));
        log.push(LogEntry::new(8, Some(TestLogData(5)), None, None));

        log.snapshot(7);

        let expected_data = Some(TestLogData(5));
        let expected_config = update_cluster_vector(vec!(1, 2, 3, 4));
        let expected_snapshot = LogEntry::new(7, expected_data, expected_config, None);
        assert_eq!(&expected_snapshot, log.get(1).unwrap());
        assert_eq!(
            &LogEntry::new(8, Some(TestLogData(5)), None, None),
            log.get(8).unwrap()
        );
    }

    #[test]
    pub fn snapshot_log_increases_capacity() {
        let mut log = Log::<TestLogData>::new();
        log.push(entry(1));
        log.push(entry(2));
        log.push(entry(3));

        let initial_capacity = log.capacity();

        log.snapshot(2);

        let final_capacity = log.capacity();
        assert!(initial_capacity < final_capacity);
    }

    #[test]
    pub fn more_elements_in_snapshot_means_more_capacity_gained() {
        let mut log = Log::<TestLogData>::new();
        log.push(entry(1));
        log.push(entry(2));
        log.push(entry(3));

        let mut log2 = log.clone();

        log.snapshot(2);
        log2.snapshot(3);

        assert!(log.capacity() < log2.capacity());
    }

    #[test]
    pub fn if_no_snapshot_then_last_included_term_is_zero() {
        let mut log = Log::<TestLogData>::new();
        log.push(LogEntry::with_data(1, Some(TestLogData(1))));
        log.push(LogEntry::with_data(1, Some(TestLogData(2))));
        log.push(LogEntry::with_data(1, Some(TestLogData(3))));

        assert_eq!(0, log.last_included_term());
    }

    #[test]
    pub fn if_snapshot_then_last_included_term_is_given() {
        let mut log = Log::<TestLogData>::new();
        log.push(LogEntry::with_data(1, Some(TestLogData(1))));
        log.push(LogEntry::with_data(2, Some(TestLogData(2))));
        log.push(LogEntry::with_data(3, Some(TestLogData(3))));

        log.snapshot(3);

        assert_eq!(3, log.last_included_term());
    }

    #[test]
    pub fn install_snapshot() {
        let mut log = Log::<TestLogData>::new();
        log.push(LogEntry::with_data(1, Some(TestLogData(1))));
        log.push(LogEntry::with_data(2, Some(TestLogData(2))));
        log.push(LogEntry::with_data(3, Some(TestLogData(3))));

        log.install_snapshot(2, LogEntry::with_data(2, Some(TestLogData(3))));

        assert_eq!(2, log.len());
        assert!(log.is_snapshot(1));
        assert!(log.is_snapshot(2));
        assert!(!log.is_snapshot(3));
    }

    #[test]
    pub fn append_after_install_snapshot() {
        let mut log = Log::<TestLogData>::new();
        log.push(LogEntry::with_data(1, Some(TestLogData(1))));
        log.push(LogEntry::with_data(2, Some(TestLogData(2))));
        log.push(LogEntry::with_data(3, Some(TestLogData(3))));
        log.install_snapshot(2, LogEntry::with_data(2, Some(TestLogData(3))));

        log.push(LogEntry::with_data(4, Some(TestLogData(4))));

        assert_eq!(
            &LogEntry::with_data(4, Some(TestLogData(4))),
            log.get(4).unwrap()
        )
    }

    #[test]
    pub fn multiple_install_snapshot() {
        let mut log = Log::<TestLogData>::new();
        log.push(LogEntry::with_data(1, Some(TestLogData(1))));
        log.push(LogEntry::with_data(2, Some(TestLogData(2))));
        log.push(LogEntry::with_data(3, Some(TestLogData(3))));

        log.install_snapshot(2, LogEntry::with_data(2, Some(TestLogData(3))));

        log.push(LogEntry::with_data(4, Some(TestLogData(4))));
        log.push(LogEntry::with_data(5, Some(TestLogData(5))));
        log.push(LogEntry::with_data(6, Some(TestLogData(6))));

        log.install_snapshot(5, LogEntry::with_data(5, Some(TestLogData(15))));

        assert_eq!(
            &LogEntry::with_data(5, Some(TestLogData(15))),
            log.get(5).unwrap()
        );
        assert_eq!(
            &LogEntry::with_data(6, Some(TestLogData(6))),
            log.get(6).unwrap()
        )
    }

    fn some_entry() -> LogEntry<TestLogData> {
        entry(1)
    }

    fn entry(value: usize) -> LogEntry<TestLogData> {
        LogEntry::with_data(0, Some(TestLogData(value)))
    }

    fn rule(threshold: i32) -> Rule {
        Rule {
            name: RuleType::MeanOver,
            threshold,
        }
    }

    fn entry_with_term(term: u16, value: usize) -> LogEntry<TestLogData> {
        LogEntry::with_data(term as Term, Some(TestLogData(value)))
    }
}