consensus_core/

block_manager.rs

// Copyright (c) Mysten Labs, Inc.
// Modifications Copyright (c) 2024 IOTA Stiftung
// SPDX-License-Identifier: Apache-2.0

use std::{
    collections::{BTreeMap, BTreeSet, btree_map::Entry},
    sync::Arc,
    time::Instant,
};

use consensus_config::AuthorityIndex;
use iota_metrics::monitored_scope;
use itertools::Itertools as _;
use parking_lot::RwLock;
use tracing::{debug, trace, warn};

use crate::{
    Round,
    block::{BlockAPI, BlockRef, GENESIS_ROUND, VerifiedBlock},
    block_verifier::BlockVerifier,
    context::Context,
    dag_state::DagState,
};

#[derive(Clone)]
pub(crate) struct SuspendedBlock {
    block: VerifiedBlock,
    missing_ancestors: BTreeSet<BlockRef>,
    timestamp: Instant,
}

impl SuspendedBlock {
    pub(crate) fn new(block: VerifiedBlock, missing_ancestors: BTreeSet<BlockRef>) -> Self {
        Self {
            block,
            missing_ancestors,
            timestamp: Instant::now(),
        }
    }
}

/// Block manager suspends incoming blocks until they are connected to the
/// existing graph, returning newly connected blocks.
/// TODO: As it is possible to have Byzantine validators who produce Blocks
/// without valid causal history we need to make sure that BlockManager takes
/// care of that and avoid OOM (Out Of Memory) situations.
pub(crate) struct BlockManager {
    context: Arc<Context>,
    dag_state: Arc<RwLock<DagState>>,
    block_verifier: Arc<dyn BlockVerifier>,

    /// Keeps all the suspended blocks. A suspended block is a block that is
    /// missing part of its causal history and thus can't be immediately
    /// processed. A block will remain in this map until all its causal history
    /// has been successfully processed.
    suspended_blocks: BTreeMap<BlockRef, SuspendedBlock>,
    /// A map that keeps all the blocks that we are missing (keys) and the
    /// corresponding blocks that reference the missing blocks as ancestors
    /// and need them to get unsuspended. It is possible for a missing
    /// dependency (key) to be a suspended block, so the block has been
    /// already fetched but it self is still missing some of its ancestors to be
    /// processed.
    missing_ancestors: BTreeMap<BlockRef, BTreeSet<BlockRef>>,
    /// A map of currently missing blocks to the set of authorities expected
    /// to have them available locally. This set is approximated based on the
    /// block's author and the authors of its direct children.
    /// A block is considered missing if it appears in `missing_ancestors`
    /// and has not yet been accepted or fetched. Blocks already stored or
    /// present in `suspended_blocks` are excluded.
    missing_blocks: BTreeMap<BlockRef, BTreeSet<AuthorityIndex>>,
    /// A vector that holds a tuple of (lowest_round, highest_round) of received
    /// blocks per authority. This is used for metrics reporting purposes
    /// and resets during restarts.
    received_block_rounds: Vec<Option<(Round, Round)>>,
}

impl BlockManager {
    pub(crate) fn new(
        context: Arc<Context>,
        dag_state: Arc<RwLock<DagState>>,
        block_verifier: Arc<dyn BlockVerifier>,
    ) -> Self {
        let committee_size = context.committee.size();
        Self {
            context,
            dag_state,
            block_verifier,
            suspended_blocks: BTreeMap::new(),
            missing_ancestors: BTreeMap::new(),
            missing_blocks: BTreeMap::new(),
            received_block_rounds: vec![None; committee_size],
        }
    }

    /// Tries to accept the provided blocks assuming that all their causal
    /// history exists. The method returns all the blocks that have been
    /// successfully processed in round ascending order, that includes also
    /// previously suspended blocks that have now been able to get accepted.
    /// Method also returns a set with the missing ancestor blocks.
    #[tracing::instrument(skip_all)]
    pub(crate) fn try_accept_blocks(
        &mut self,
        blocks: Vec<VerifiedBlock>,
    ) -> (Vec<VerifiedBlock>, BTreeSet<BlockRef>) {
        let _s = monitored_scope("BlockManager::try_accept_blocks");
        self.try_accept_blocks_internal(blocks, false)
    }

    // Tries to accept blocks that have been committed. Returns all the blocks that
    // have been accepted, both from the ones provided and any children blocks.
    #[tracing::instrument(skip_all)]
    pub(crate) fn try_accept_committed_blocks(
        &mut self,
        blocks: Vec<VerifiedBlock>,
    ) -> Vec<VerifiedBlock> {
        // If GC is disabled then should not run any of this logic.
        if !self.dag_state.read().gc_enabled() {
            return Vec::new();
        }

        // Just accept the blocks
        let _s = monitored_scope("BlockManager::try_accept_committed_blocks");
        let (accepted_blocks, missing_blocks) = self.try_accept_blocks_internal(blocks, true);
        assert!(
            missing_blocks.is_empty(),
            "No missing blocks should be returned for committed blocks"
        );

        accepted_blocks
    }

    /// Attempts to accept the provided blocks. When `committed = true` then the
    /// blocks are considered to be committed via certified commits and
    /// are handled differently.
    fn try_accept_blocks_internal(
        &mut self,
        mut blocks: Vec<VerifiedBlock>,
        committed: bool,
    ) -> (Vec<VerifiedBlock>, BTreeSet<BlockRef>) {
        let _s = monitored_scope("BlockManager::try_accept_blocks_internal");

        blocks.sort_by_key(|b| b.round());
        debug!(
            "Trying to accept blocks: {}",
            blocks.iter().map(|b| b.reference().to_string()).join(",")
        );

        let mut accepted_blocks = vec![];
        let mut missing_blocks = BTreeSet::new();

        for block in blocks {
            self.update_block_received_metrics(&block);

            // Try to accept the input block.
            let block_ref = block.reference();

            let mut to_verify_timestamps_and_accept = vec![];
            if committed {
                match self.try_accept_one_committed_block(block) {
                    TryAcceptResult::Accepted(block) => {
                        // As this is a committed block, then it's already accepted and there is no
                        // need to verify its timestamps. Just add it to the
                        // accepted blocks list.
                        accepted_blocks.push(block);
                    }
                    TryAcceptResult::Processed => continue,
                    TryAcceptResult::Suspended(_) | TryAcceptResult::Skipped => {
                        panic!("Did not expect to suspend or skip a committed block: {block_ref:?}")
                    }
                };
            } else {
                match self.try_accept_one_block(block) {
                    TryAcceptResult::Accepted(block) => {
                        to_verify_timestamps_and_accept.push(block);
                    }
                    TryAcceptResult::Suspended(ancestors_to_fetch) => {
                        debug!(
                            "Missing ancestors to fetch for block {block_ref}: {}",
                            ancestors_to_fetch.iter().map(|b| b.to_string()).join(",")
                        );
                        missing_blocks.extend(ancestors_to_fetch);
                        continue;
                    }
                    TryAcceptResult::Processed | TryAcceptResult::Skipped => continue,
                };
            };

            // If the block is accepted, try to unsuspend its children blocks if any.
            let unsuspended_blocks = self.try_unsuspend_children_blocks(block_ref);
            to_verify_timestamps_and_accept.extend(unsuspended_blocks);

            // Verify block timestamps
            let blocks_to_accept =
                self.verify_block_timestamps_and_accept(to_verify_timestamps_and_accept);
            accepted_blocks.extend(blocks_to_accept);
        }

        self.update_stats(missing_blocks.len() as u64);

        // Figure out the new missing blocks
        (accepted_blocks, missing_blocks)
    }

    fn try_accept_one_committed_block(&mut self, block: VerifiedBlock) -> TryAcceptResult {
        if self.dag_state.read().contains_block(&block.reference()) {
            return TryAcceptResult::Processed;
        }

        // Remove the block from missing and suspended blocks
        self.missing_blocks.remove(&block.reference());

        // If the block has been already fetched and parked as suspended block, then
        // remove it. Also find all the references of missing ancestors to
        // remove those as well. If we don't do that then it's possible once the missing
        // ancestor is fetched to cause a panic when trying to unsuspend this
        // children as it won't be found in the suspended blocks map.
        if let Some(suspended_block) = self.suspended_blocks.remove(&block.reference()) {
            suspended_block
                .missing_ancestors
                .iter()
                .for_each(|ancestor| {
                    if let Some(references) = self.missing_ancestors.get_mut(ancestor) {
                        references.remove(&block.reference());
                    }
                });
        }

        // Accept this block before any unsuspended children blocks
        self.dag_state.write().accept_blocks(vec![block.clone()]);

        TryAcceptResult::Accepted(block)
    }

    /// Tries to find the provided block_refs in DagState and BlockManager,
    /// and returns missing block refs.
    pub(crate) fn try_find_blocks(&mut self, block_refs: Vec<BlockRef>) -> BTreeSet<BlockRef> {
        let _s = monitored_scope("BlockManager::try_find_blocks");
        let gc_round = self.dag_state.read().gc_round();

        // No need to fetch blocks that are <= gc_round as they won't get processed
        // anyways and they'll get skipped. So keep only the ones above.
        let mut block_refs = block_refs
            .into_iter()
            .filter(|block_ref| block_ref.round > gc_round)
            .collect::<Vec<_>>();

        if block_refs.is_empty() {
            return BTreeSet::new();
        }

        block_refs.sort_by_key(|b| b.round);

        debug!(
            "Trying to find blocks: {}",
            block_refs.iter().map(|b| b.to_string()).join(",")
        );

        let mut missing_blocks = BTreeSet::new();

        for (found, block_ref) in self
            .dag_state
            .read()
            .contains_blocks(block_refs.clone())
            .into_iter()
            .zip(block_refs.iter())
        {
            if found || self.suspended_blocks.contains_key(block_ref) {
                continue;
            }
            // Fetches the block if it is not in dag state or suspended.
            missing_blocks.insert(*block_ref);
            if self
                .missing_blocks
                .insert(*block_ref, BTreeSet::from([block_ref.author]))
                .is_none()
            {
                // We want to report this as a missing ancestor even if there is no block that
                // is actually references it right now. That will allow us
                // to seamlessly GC the block later if needed.
                self.missing_ancestors.entry(*block_ref).or_default();

                let block_ref_hostname =
                    &self.context.committee.authority(block_ref.author).hostname;
                self.context
                    .metrics
                    .node_metrics
                    .block_manager_missing_blocks_by_authority
                    .with_label_values(&[block_ref_hostname])
                    .inc();
            }
        }

        let metrics = &self.context.metrics.node_metrics;
        metrics
            .missing_blocks_total
            .inc_by(missing_blocks.len() as u64);
        metrics
            .block_manager_missing_blocks
            .set(self.missing_blocks.len() as i64);

        missing_blocks
    }

    // TODO: remove once timestamping is refactored to the new approach.
    // Verifies each block's timestamp based on its ancestors, and persists in store
    // all the valid blocks that should be accepted. Method returns the accepted
    // and persisted blocks.
    fn verify_block_timestamps_and_accept(
        &mut self,
        unsuspended_blocks: impl IntoIterator<Item = VerifiedBlock>,
    ) -> Vec<VerifiedBlock> {
        let (gc_enabled, gc_round) = {
            let dag_state = self.dag_state.read();
            (dag_state.gc_enabled(), dag_state.gc_round())
        };
        // Try to verify the block and its children for timestamp, with ancestor blocks.
        let mut blocks_to_accept: BTreeMap<BlockRef, VerifiedBlock> = BTreeMap::new();
        let mut blocks_to_reject: BTreeMap<BlockRef, VerifiedBlock> = BTreeMap::new();
        {
            'block: for b in unsuspended_blocks {
                let ancestors = self.dag_state.read().get_blocks(b.ancestors());
                assert_eq!(b.ancestors().len(), ancestors.len());
                let mut ancestor_blocks = vec![];
                'ancestor: for (ancestor_ref, found) in
                    b.ancestors().iter().zip(ancestors.into_iter())
                {
                    if let Some(found_block) = found {
                        // This invariant should be guaranteed by DagState.
                        assert_eq!(ancestor_ref, &found_block.reference());
                        ancestor_blocks.push(Some(found_block));
                        continue 'ancestor;
                    }
                    // blocks_to_accept have not been added to DagState yet, but they
                    // can appear in ancestors.
                    if blocks_to_accept.contains_key(ancestor_ref) {
                        ancestor_blocks.push(Some(blocks_to_accept[ancestor_ref].clone()));
                        continue 'ancestor;
                    }
                    // If an ancestor is already rejected, reject this block as well.
                    if blocks_to_reject.contains_key(ancestor_ref) {
                        blocks_to_reject.insert(b.reference(), b);
                        continue 'block;
                    }

                    // When gc is enabled it's possible that we indeed won't find any ancestors that
                    // are passed gc_round. That's ok. We don't need to panic here.
                    // We do want to panic if gc_enabled we and have an ancestor that is > gc_round,
                    // or gc is disabled.
                    if gc_enabled
                        && ancestor_ref.round > GENESIS_ROUND
                        && ancestor_ref.round <= gc_round
                    {
                        debug!(
                            "Block {:?} has a missing ancestor: {:?} passed GC round {}",
                            b.reference(),
                            ancestor_ref,
                            gc_round
                        );
                        ancestor_blocks.push(None);
                    } else {
                        panic!(
                            "Unsuspended block {b:?} has a missing ancestor! Ancestor not found in DagState: {ancestor_ref:?}"
                        );
                    }
                }
                if let Err(e) =
                    self.block_verifier
                        .check_ancestors(&b, &ancestor_blocks, gc_enabled, gc_round)
                {
                    warn!("Block {:?} failed to verify ancestors: {}", b, e);
                    blocks_to_reject.insert(b.reference(), b);
                } else {
                    blocks_to_accept.insert(b.reference(), b);
                }
            }
        }

        // TODO: report blocks_to_reject to peers.
        for (block_ref, block) in blocks_to_reject {
            let hostname = self
                .context
                .committee
                .authority(block_ref.author)
                .hostname
                .clone();

            self.context
                .metrics
                .node_metrics
                .invalid_blocks
                .with_label_values(&[hostname.as_str(), "accept_block", "InvalidAncestors"])
                .inc();
            warn!("Invalid block {:?} is rejected", block);
        }

        let blocks_to_accept = blocks_to_accept.values().cloned().collect::<Vec<_>>();

        // Insert the accepted blocks into DAG state so future blocks including them as
        // ancestors do not get suspended.
        self.dag_state
            .write()
            .accept_blocks(blocks_to_accept.clone());

        blocks_to_accept
    }

    /// Tries to accept the provided block. To accept a block its ancestors must
    /// have been already successfully accepted. If block is accepted then
    /// Some result is returned. None is returned when either the block is
    /// suspended or the block has been already accepted before.
    fn try_accept_one_block(&mut self, block: VerifiedBlock) -> TryAcceptResult {
        let block_ref = block.reference();
        let mut missing_ancestors = BTreeSet::new();
        let mut ancestors_to_fetch = BTreeSet::new();
        let dag_state = self.dag_state.read();
        let gc_round = dag_state.gc_round();
        let gc_enabled = dag_state.gc_enabled();

        // If block has been already received and suspended, or already processed and
        // stored, or is a genesis block, then skip it.
        if self.suspended_blocks.contains_key(&block_ref) || dag_state.contains_block(&block_ref) {
            return TryAcceptResult::Processed;
        }

        // If the block is <= gc_round, then we simply skip its processing as there is
        // no meaning do any action on it or even store it.
        if gc_enabled && block.round() <= gc_round {
            let hostname = self
                .context
                .committee
                .authority(block.author())
                .hostname
                .as_str();
            self.context
                .metrics
                .node_metrics
                .block_manager_skipped_blocks
                .with_label_values(&[hostname])
                .inc();
            return TryAcceptResult::Skipped;
        }

        // Keep only the ancestors that are greater than the GC round to check for their
        // existence. Keep in mind that if GC is disabled then gc_round will be
        // 0 and all ancestors will be considered.
        let ancestors = if gc_enabled {
            block
                .ancestors()
                .iter()
                .filter(|ancestor| ancestor.round == GENESIS_ROUND || ancestor.round > gc_round)
                .cloned()
                .collect::<Vec<_>>()
        } else {
            block.ancestors().to_vec()
        };

        // make sure that we have all the required ancestors in store
        for (found, ancestor) in dag_state
            .contains_blocks(ancestors.clone())
            .into_iter()
            .zip(ancestors.iter())
        {
            if !found {
                missing_ancestors.insert(*ancestor);

                // mark the block as having missing ancestors
                self.missing_ancestors
                    .entry(*ancestor)
                    .or_default()
                    .insert(block_ref);

                let ancestor_hostname = &self.context.committee.authority(ancestor.author).hostname;
                self.context
                    .metrics
                    .node_metrics
                    .block_manager_missing_ancestors_by_authority
                    .with_label_values(&[ancestor_hostname])
                    .inc();

                // Add the ancestor to the missing blocks set only if it doesn't already exist
                // in the suspended blocks - meaning that we already have its
                // payload.
                if !self.suspended_blocks.contains_key(ancestor) {
                    // Fetches the block if it is not in dag state or suspended.
                    ancestors_to_fetch.insert(*ancestor);
                    // We also want to keep track of the authorities that have this block.
                    // This block could be already missing, so we just update the set  of
                    // authorities who have it.
                    let entry = self.missing_blocks.entry(*ancestor);
                    match entry {
                        Entry::Vacant(v) => {
                            v.insert(BTreeSet::from([ancestor.author, block_ref.author]));
                            self.context
                                .metrics
                                .node_metrics
                                .block_manager_missing_blocks_by_authority
                                .with_label_values(&[ancestor_hostname])
                                .inc();
                        }
                        Entry::Occupied(mut o) => {
                            o.get_mut().insert(block_ref.author);
                        }
                    }
                }
            }
        }

        // Remove the block ref from the `missing_blocks` - if exists - since we now
        // have received the block. The block might still get suspended, but we
        // won't report it as missing in order to not re-fetch.
        self.missing_blocks.remove(&block.reference());

        if !missing_ancestors.is_empty() {
            let hostname = self
                .context
                .committee
                .authority(block.author())
                .hostname
                .as_str();
            self.context
                .metrics
                .node_metrics
                .block_suspensions
                .with_label_values(&[hostname])
                .inc();
            self.suspended_blocks
                .insert(block_ref, SuspendedBlock::new(block, missing_ancestors));
            return TryAcceptResult::Suspended(ancestors_to_fetch);
        }

        TryAcceptResult::Accepted(block)
    }

    /// Given an accepted block `accepted_block` it attempts to accept all the
    /// suspended children blocks assuming such exist. All the unsuspended /
    /// accepted blocks are returned as a vector in causal order.
    fn try_unsuspend_children_blocks(&mut self, accepted_block: BlockRef) -> Vec<VerifiedBlock> {
        let mut unsuspended_blocks = vec![];
        let mut to_process_blocks = vec![accepted_block];

        while let Some(block_ref) = to_process_blocks.pop() {
            // And try to check if its direct children can be unsuspended
            if let Some(block_refs_with_missing_deps) = self.missing_ancestors.remove(&block_ref) {
                for r in block_refs_with_missing_deps {
                    // For each dependency try to unsuspend it. If that's successful then we add it
                    // to the queue so we can recursively try to unsuspend its
                    // children.
                    if let Some(block) = self.try_unsuspend_block(&r, &block_ref) {
                        to_process_blocks.push(block.block.reference());
                        unsuspended_blocks.push(block);
                    }
                }
            }
        }

        let now = Instant::now();

        // Report the unsuspended blocks
        for block in &unsuspended_blocks {
            let hostname = self
                .context
                .committee
                .authority(block.block.author())
                .hostname
                .as_str();
            self.context
                .metrics
                .node_metrics
                .block_unsuspensions
                .with_label_values(&[hostname])
                .inc();
            self.context
                .metrics
                .node_metrics
                .suspended_block_time
                .with_label_values(&[hostname])
                .observe(now.saturating_duration_since(block.timestamp).as_secs_f64());
        }

        unsuspended_blocks
            .into_iter()
            .map(|block| block.block)
            .collect()
    }

    /// Attempts to unsuspend a block by checking its ancestors and removing the
    /// `accepted_dependency` by its local set. If there is no missing
    /// dependency then this block can be unsuspended immediately and is removed
    /// from the `suspended_blocks` map.
    fn try_unsuspend_block(
        &mut self,
        block_ref: &BlockRef,
        accepted_dependency: &BlockRef,
    ) -> Option<SuspendedBlock> {
        let block = self
            .suspended_blocks
            .get_mut(block_ref)
            .expect("Block should be in suspended map");

        assert!(
            block.missing_ancestors.remove(accepted_dependency),
            "Block reference {} should be present in missing dependencies of {:?}",
            block_ref,
            block.block
        );

        if block.missing_ancestors.is_empty() {
            // we have no missing dependency, so we unsuspend the block and return it
            return self.suspended_blocks.remove(block_ref);
        }
        None
    }

    /// Tries to unsuspend any blocks for the latest gc round. If gc round
    /// hasn't changed then no blocks will be unsuspended due to
    /// this action.
    pub(crate) fn try_unsuspend_blocks_for_latest_gc_round(&mut self) {
        let _s = monitored_scope("BlockManager::try_unsuspend_blocks_for_latest_gc_round");
        let (gc_enabled, gc_round) = {
            let dag_state = self.dag_state.read();
            (dag_state.gc_enabled(), dag_state.gc_round())
        };
        let mut blocks_unsuspended_below_gc_round = 0;
        let mut blocks_gc_ed = 0;

        if !gc_enabled {
            trace!("GC is disabled, no blocks will attempt to get unsuspended.");
            return;
        }

        while let Some((block_ref, _children_refs)) = self.missing_ancestors.first_key_value() {
            // If the first block in the missing ancestors is higher than the gc_round, then
            // we can't unsuspend it yet. So we just put it back
            // and we terminate the iteration as any next entry will be of equal or higher
            // round anyways.
            if block_ref.round > gc_round {
                return;
            }

            blocks_gc_ed += 1;

            let hostname = self
                .context
                .committee
                .authority(block_ref.author)
                .hostname
                .as_str();
            self.context
                .metrics
                .node_metrics
                .block_manager_gced_blocks
                .with_label_values(&[hostname])
                .inc();

            assert!(
                !self.suspended_blocks.contains_key(block_ref),
                "Block should not be suspended, as we are causally GC'ing and no suspended block should exist for a missing ancestor."
            );

            // Also remove it from the missing list - we don't want to keep looking for it.
            self.missing_blocks.remove(block_ref);

            // Find all the children blocks that have a dependency on this one and try to
            // unsuspend them
            let unsuspended_blocks = self.try_unsuspend_children_blocks(*block_ref);

            unsuspended_blocks.iter().for_each(|block| {
                if block.round() <= gc_round {
                    blocks_unsuspended_below_gc_round += 1;
                }
            });

            // Now validate their timestamps and accept them
            let accepted_blocks = self.verify_block_timestamps_and_accept(unsuspended_blocks);
            for block in accepted_blocks {
                let hostname = self
                    .context
                    .committee
                    .authority(block.author())
                    .hostname
                    .as_str();
                self.context
                    .metrics
                    .node_metrics
                    .block_manager_gc_unsuspended_blocks
                    .with_label_values(&[hostname])
                    .inc();
            }
        }

        debug!(
            "Total {} blocks unsuspended and total blocks {} gc'ed <= gc_round {}",
            blocks_unsuspended_below_gc_round, blocks_gc_ed, gc_round
        );
    }

    /// Returns all the blocks that are currently missing and needed in order to
    /// accept suspended blocks. For each block reference it returns the set of
    /// authorities who have this block.
    pub(crate) fn missing_blocks(&self) -> BTreeMap<BlockRef, BTreeSet<AuthorityIndex>> {
        self.missing_blocks.clone()
    }

    /// Returns all the block refs that are currently missing.
    #[cfg(test)]
    pub(crate) fn missing_block_refs(&self) -> BTreeSet<BlockRef> {
        self.missing_blocks.keys().cloned().collect()
    }

    fn update_stats(&mut self, missing_blocks: u64) {
        let metrics = &self.context.metrics.node_metrics;
        metrics.missing_blocks_total.inc_by(missing_blocks);
        metrics
            .block_manager_suspended_blocks
            .set(self.suspended_blocks.len() as i64);
        metrics
            .block_manager_missing_ancestors
            .set(self.missing_ancestors.len() as i64);
        metrics
            .block_manager_missing_blocks
            .set(self.missing_blocks.len() as i64);
    }

    fn update_block_received_metrics(&mut self, block: &VerifiedBlock) {
        let (min_round, max_round) =
            if let Some((curr_min, curr_max)) = self.received_block_rounds[block.author()] {
                (curr_min.min(block.round()), curr_max.max(block.round()))
            } else {
                (block.round(), block.round())
            };
        self.received_block_rounds[block.author()] = Some((min_round, max_round));

        let hostname = &self.context.committee.authority(block.author()).hostname;
        self.context
            .metrics
            .node_metrics
            .lowest_verified_authority_round
            .with_label_values(&[hostname])
            .set(min_round.into());
        self.context
            .metrics
            .node_metrics
            .highest_verified_authority_round
            .with_label_values(&[hostname])
            .set(max_round.into());
    }

    /// Checks if block manager is empty.
    #[cfg(test)]
    pub(crate) fn is_empty(&self) -> bool {
        self.suspended_blocks.is_empty()
            && self.missing_ancestors.is_empty()
            && self.missing_blocks.is_empty()
    }

    /// Returns all the suspended blocks whose causal history we miss hence we
    /// can't accept them yet.
    #[cfg(test)]
    fn suspended_blocks_refs(&self) -> BTreeSet<BlockRef> {
        self.suspended_blocks.keys().cloned().collect()
    }
}

// Result of trying to accept one block.
enum TryAcceptResult {
    // The block is accepted. Wraps the block itself.
    Accepted(VerifiedBlock),
    // The block is suspended. Wraps ancestors to be fetched.
    Suspended(BTreeSet<BlockRef>),
    // The block has been processed before and already exists in BlockManager (and is suspended)
    // or in DagState (so has been already accepted). No further processing has been done at
    // this point.
    Processed,
    // When a received block is <= gc_round, then we simply skip its processing as there is no
    // meaning do any action on it or even store it.
    Skipped,
}

#[cfg(test)]
mod tests {
    use std::{collections::BTreeSet, sync::Arc};

    use consensus_config::AuthorityIndex;
    use parking_lot::RwLock;
    use rand::{SeedableRng, prelude::StdRng, seq::SliceRandom};
    use rstest::rstest;

    use crate::{
        CommitDigest, Round,
        block::{BlockAPI, BlockDigest, BlockRef, SignedBlock, VerifiedBlock},
        block_manager::BlockManager,
        block_verifier::{BlockVerifier, NoopBlockVerifier},
        commit::TrustedCommit,
        context::Context,
        dag_state::DagState,
        error::{ConsensusError, ConsensusResult},
        storage::mem_store::MemStore,
        test_dag_builder::DagBuilder,
        test_dag_parser::parse_dag,
    };

    #[tokio::test]
    async fn suspend_blocks_with_missing_ancestors() {
        // GIVEN
        let (context, _key_pairs) = Context::new_for_test(4);
        let context = Arc::new(context);
        let store = Arc::new(MemStore::new());
        let dag_state = Arc::new(RwLock::new(DagState::new(context.clone(), store.clone())));

        let mut block_manager =
            BlockManager::new(context.clone(), dag_state, Arc::new(NoopBlockVerifier));

        // create a DAG
        let mut dag_builder = DagBuilder::new(context.clone());
        dag_builder
            .layers(1..=2) // 2 rounds
            .authorities(vec![
                AuthorityIndex::new_for_test(0),
                AuthorityIndex::new_for_test(2),
            ]) // Create equivocating blocks for 2 authorities
            .equivocate(3)
            .build();

        // Take only the blocks of round 2 and try to accept them
        let round_2_blocks = dag_builder
            .blocks
            .into_iter()
            .filter_map(|(_, block)| (block.round() == 2).then_some(block))
            .collect::<Vec<VerifiedBlock>>();

        // WHEN
        let (accepted_blocks, missing) = block_manager.try_accept_blocks(round_2_blocks.clone());

        // THEN
        assert!(accepted_blocks.is_empty());

        // AND the returned missing ancestors should be the same as the provided block
        // ancestors
        let missing_block_refs = round_2_blocks.first().unwrap().ancestors();
        let missing_block_refs = missing_block_refs.iter().cloned().collect::<BTreeSet<_>>();
        assert_eq!(missing, missing_block_refs);

        // AND the missing blocks are the parents of the round 2 blocks. Since this is a
        // fully connected DAG taking the ancestors of the first element
        // suffices.
        assert_eq!(block_manager.missing_block_refs(), missing_block_refs);

        // AND suspended blocks should return the round_2_blocks
        assert_eq!(
            block_manager.suspended_blocks_refs(),
            round_2_blocks
                .into_iter()
                .map(|block| block.reference())
                .collect::<BTreeSet<_>>()
        );

        // AND each missing block should be known to all authorities
        let known_by_manager = block_manager
            .missing_blocks()
            .iter()
            .next()
            .expect("We should expect at least two elements there")
            .1
            .clone();
        assert_eq!(
            known_by_manager,
            context
                .committee
                .authorities()
                .map(|(a, _)| a)
                .collect::<BTreeSet<_>>()
        );
    }

    #[tokio::test]
    async fn try_accept_block_returns_missing_blocks() {
        let (context, _key_pairs) = Context::new_for_test(4);
        let context = Arc::new(context);
        let store = Arc::new(MemStore::new());
        let dag_state = Arc::new(RwLock::new(DagState::new(context.clone(), store.clone())));

        let mut block_manager =
            BlockManager::new(context.clone(), dag_state, Arc::new(NoopBlockVerifier));

        // create a DAG
        let mut dag_builder = DagBuilder::new(context.clone());
        dag_builder
            .layers(1..=4) // 4 rounds
            .authorities(vec![
                AuthorityIndex::new_for_test(0),
                AuthorityIndex::new_for_test(2),
            ]) // Create equivocating blocks for 2 authorities
            .equivocate(3) // Use 3 equivocations blocks per authority
            .build();

        // Take the blocks from round 4 up to 2 (included). Only the first block of each
        // round should return missing ancestors when try to accept
        for (_, block) in dag_builder
            .blocks
            .into_iter()
            .rev()
            .take_while(|(_, block)| block.round() >= 2)
        {
            // WHEN
            let (accepted_blocks, missing) = block_manager.try_accept_blocks(vec![block.clone()]);

            // THEN
            assert!(accepted_blocks.is_empty());

            let block_ancestors = block.ancestors().iter().cloned().collect::<BTreeSet<_>>();
            assert_eq!(missing, block_ancestors);
        }
    }

    #[tokio::test]
    async fn accept_blocks_with_complete_causal_history() {
        // GIVEN
        let (context, _key_pairs) = Context::new_for_test(4);
        let context = Arc::new(context);
        let store = Arc::new(MemStore::new());
        let dag_state = Arc::new(RwLock::new(DagState::new(context.clone(), store.clone())));

        let mut block_manager =
            BlockManager::new(context.clone(), dag_state, Arc::new(NoopBlockVerifier));

        // create a DAG of 2 rounds
        let mut dag_builder = DagBuilder::new(context.clone());
        dag_builder.layers(1..=2).build();

        let all_blocks = dag_builder.blocks.values().cloned().collect::<Vec<_>>();

        // WHEN
        let (accepted_blocks, missing) = block_manager.try_accept_blocks(all_blocks.clone());

        // THEN
        assert_eq!(accepted_blocks.len(), 8);
        assert_eq!(
            accepted_blocks,
            all_blocks
                .iter()
                .filter(|block| block.round() > 0)
                .cloned()
                .collect::<Vec<VerifiedBlock>>()
        );
        assert!(missing.is_empty());
        assert!(block_manager.is_empty());

        // WHEN trying to accept same blocks again, then none will be returned as those
        // have been already accepted
        let (accepted_blocks, _) = block_manager.try_accept_blocks(all_blocks);
        assert!(accepted_blocks.is_empty());
    }

    /// Tests that the block manager accepts blocks when some or all of their
    /// causal history is below or equal to the GC round.
    #[tokio::test]
    async fn accept_blocks_with_causal_history_below_gc_round() {
        // GIVEN
        let (mut context, _key_pairs) = Context::new_for_test(4);

        // We set the gc depth to 4
        context
            .protocol_config
            .set_consensus_gc_depth_for_testing(4);
        let context = Arc::new(context);
        let store = Arc::new(MemStore::new());
        let dag_state = Arc::new(RwLock::new(DagState::new(context.clone(), store.clone())));

        // We "fake" the commit for round 10, so we can test the GC round 6
        // (commit_round - gc_depth = 10 - 4 = 6)
        let last_commit = TrustedCommit::new_for_test(
            10,
            CommitDigest::MIN,
            context.clock.timestamp_utc_ms(),
            BlockRef::new(10, AuthorityIndex::new_for_test(0), BlockDigest::MIN),
            vec![],
        );
        dag_state.write().set_last_commit(last_commit);
        assert_eq!(
            dag_state.read().gc_round(),
            6,
            "GC round should have moved to round 6"
        );

        let mut block_manager =
            BlockManager::new(context.clone(), dag_state, Arc::new(NoopBlockVerifier));

        // create a DAG of 10 rounds with some weak links for the blocks of round 9
        let dag_str = "DAG {
            Round 0 : { 4 },
            Round 1 : { * },
            Round 2 : { * },
            Round 3 : { * },
            Round 4 : { * },
            Round 5 : { * },
            Round 6 : { * },
            Round 7 : {
                A -> [*],
                B -> [*],
                C -> [*],
            }
            Round 8 : {
                A -> [*],
                B -> [*],
                C -> [*],
            },
            Round 9 : {
                A -> [A8, B8, C8, D6],
                B -> [A8, B8, C8, D6],
                C -> [A8, B8, C8, D6],
                D -> [A8, B8, C8, D6],
            },
            Round 10 : { * },
        }";

        let (_, dag_builder) = parse_dag(dag_str).expect("Invalid dag");

        // Now take all the blocks for round 7 & 8 , which are above the gc_round = 6.
        // All those blocks should eventually be returned as accepted. Pay attention
        // that without GC none of those blocks should get accepted.
        let blocks_ranges = vec![7..=8 as Round, 9..=10 as Round];

        for rounds_range in blocks_ranges {
            let all_blocks = dag_builder
                .blocks
                .values()
                .filter(|block| rounds_range.contains(&block.round()))
                .cloned()
                .collect::<Vec<_>>();

            // WHEN
            let mut reversed_blocks = all_blocks.clone();
            reversed_blocks.sort_by_key(|b| std::cmp::Reverse(b.reference()));
            let (mut accepted_blocks, missing) = block_manager.try_accept_blocks(reversed_blocks);
            accepted_blocks.sort_by_key(|a| a.reference());

            // THEN
            assert_eq!(accepted_blocks, all_blocks.to_vec());
            assert!(missing.is_empty());
            assert!(block_manager.is_empty());

            let (accepted_blocks, _) = block_manager.try_accept_blocks(all_blocks);
            assert!(accepted_blocks.is_empty());
        }
    }

    /// Blocks that are attempted to be accepted but are <= gc_round they will
    /// be skipped for processing. Nothing should be stored or trigger any
    /// unsuspension etc.
    #[tokio::test]
    async fn skip_accepting_blocks_below_gc_round() {
        // GIVEN
        let (mut context, _key_pairs) = Context::new_for_test(4);
        // We set the gc depth to 4
        context
            .protocol_config
            .set_consensus_gc_depth_for_testing(4);
        let context = Arc::new(context);
        let store = Arc::new(MemStore::new());
        let dag_state = Arc::new(RwLock::new(DagState::new(context.clone(), store.clone())));

        // We "fake" the commit for round 10, so we can test the GC round 6
        // (commit_round - gc_depth = 10 - 4 = 6)
        let last_commit = TrustedCommit::new_for_test(
            10,
            CommitDigest::MIN,
            context.clock.timestamp_utc_ms(),
            BlockRef::new(10, AuthorityIndex::new_for_test(0), BlockDigest::MIN),
            vec![],
        );
        dag_state.write().set_last_commit(last_commit);
        assert_eq!(
            dag_state.read().gc_round(),
            6,
            "GC round should have moved to round 6"
        );

        let mut block_manager =
            BlockManager::new(context.clone(), dag_state, Arc::new(NoopBlockVerifier));

        // create a DAG of 6 rounds
        let mut dag_builder = DagBuilder::new(context.clone());
        dag_builder.layers(1..=6).build();

        let all_blocks = dag_builder.blocks.values().cloned().collect::<Vec<_>>();

        // WHEN
        let (accepted_blocks, missing) = block_manager.try_accept_blocks(all_blocks.clone());

        // THEN
        assert!(accepted_blocks.is_empty());
        assert!(missing.is_empty());
        assert!(block_manager.is_empty());
    }

    /// The test generate blocks for a well connected DAG and feed them to block
    /// manager in random order. In the end all the blocks should be
    /// uniquely suspended and no missing blocks should exist. The test will run
    /// for both gc_enabled/disabled. When gc is enabeld we set a high
    /// gc_depth value so in practice gc_round will be 0, but we'll be able to
    /// test in the common case that this work exactly the same way as when
    /// gc is disabled.
    #[rstest]
    #[tokio::test]
    async fn accept_blocks_unsuspend_children_blocks(#[values(false, true)] gc_enabled: bool) {
        // GIVEN
        let (mut context, _key_pairs) = Context::new_for_test(4);

        if gc_enabled {
            context
                .protocol_config
                .set_consensus_gc_depth_for_testing(10);
        }
        let context = Arc::new(context);

        // create a DAG of rounds 1 ~ 3
        let mut dag_builder = DagBuilder::new(context.clone());
        dag_builder.layers(1..=3).build();

        let mut all_blocks = dag_builder.blocks.values().cloned().collect::<Vec<_>>();

        // Now randomize the sequence of sending the blocks to block manager. In the end
        // all the blocks should be uniquely suspended and no missing blocks
        // should exist.
        for seed in 0..100u8 {
            all_blocks.shuffle(&mut StdRng::from_seed([seed; 32]));

            let store = Arc::new(MemStore::new());
            let dag_state = Arc::new(RwLock::new(DagState::new(context.clone(), store.clone())));

            let mut block_manager =
                BlockManager::new(context.clone(), dag_state, Arc::new(NoopBlockVerifier));

            // WHEN
            let mut all_accepted_blocks = vec![];
            for block in &all_blocks {
                let (accepted_blocks, _) = block_manager.try_accept_blocks(vec![block.clone()]);

                all_accepted_blocks.extend(accepted_blocks);
            }

            // THEN
            all_accepted_blocks.sort_by_key(|b| b.reference());
            all_blocks.sort_by_key(|b| b.reference());

            assert_eq!(
                all_accepted_blocks, all_blocks,
                "Failed acceptance sequence for seed {seed}"
            );
            assert!(block_manager.is_empty());
        }
    }

    /// Tests that `missing_blocks()` correctly infers the authorities
    /// referencing each missing block based on accepted blocks in the DAG.
    #[tokio::test]
    async fn authorities_that_know_missing_blocks() {
        let (context, _key_pairs) = Context::new_for_test(4);

        let context = Arc::new(context);

        // create a DAG of rounds 1 ~ 3
        let mut dag_builder = DagBuilder::new(context.clone());
        dag_builder.layers(1..=3).build();

        let all_blocks = dag_builder.blocks.values().cloned().collect::<Vec<_>>();

        let blocks_round_2 = all_blocks
            .iter()
            .filter(|block| block.round() == 2)
            .cloned()
            .collect::<Vec<_>>();

        let blocks_round_1 = all_blocks
            .iter()
            .filter(|block| block.round() == 1)
            .map(|block| block.reference())
            .collect::<BTreeSet<_>>();

        let store = Arc::new(MemStore::new());
        let dag_state = Arc::new(RwLock::new(DagState::new(context.clone(), store.clone())));

        let mut block_manager =
            BlockManager::new(context.clone(), dag_state, Arc::new(NoopBlockVerifier));

        let (_, missing_blocks) = block_manager.try_accept_blocks(vec![blocks_round_2[0].clone()]);
        // Blocks from round 1 are all missing, since the DAG is fully connected
        assert_eq!(missing_blocks, blocks_round_1);

        let missing_blocks_with_authorities = block_manager.missing_blocks();

        let block_round_1_authority_0 = all_blocks
            .iter()
            .filter(|block| block.round() == 1 && block.author() == AuthorityIndex::new_for_test(0))
            .map(|block| block.reference())
            .next()
            .unwrap();
        let block_round_1_authority_1 = all_blocks
            .iter()
            .filter(|block| block.round() == 1 && block.author() == AuthorityIndex::new_for_test(1))
            .map(|block| block.reference())
            .next()
            .unwrap();
        assert_eq!(
            missing_blocks_with_authorities[&block_round_1_authority_0],
            BTreeSet::from([AuthorityIndex::new_for_test(0)])
        );
        assert_eq!(
            missing_blocks_with_authorities[&block_round_1_authority_1],
            BTreeSet::from([
                AuthorityIndex::new_for_test(0),
                AuthorityIndex::new_for_test(1)
            ])
        );

        // Add a new block from round 2 from authority 1, which updates the set of
        // authorities that are aware of the missing blocks
        block_manager.try_accept_blocks(vec![blocks_round_2[1].clone()]);
        let missing_blocks_with_authorities = block_manager.missing_blocks();
        assert_eq!(
            missing_blocks_with_authorities[&block_round_1_authority_0],
            BTreeSet::from([
                AuthorityIndex::new_for_test(0),
                AuthorityIndex::new_for_test(1)
            ])
        );
    }

    #[rstest]
    #[tokio::test]
    async fn unsuspend_blocks_for_latest_gc_round(#[values(5, 10, 14)] gc_depth: u32) {
        telemetry_subscribers::init_for_testing();
        // GIVEN
        let (mut context, _key_pairs) = Context::new_for_test(4);

        if gc_depth > 0 {
            context
                .protocol_config
                .set_consensus_gc_depth_for_testing(gc_depth);
        }
        let context = Arc::new(context);

        // create a DAG of rounds 1 ~ gc_depth * 2
        let mut dag_builder = DagBuilder::new(context.clone());
        dag_builder.layers(1..=gc_depth * 2).build();

        // Pay attention that we start from round 2. Round 1 will always be missing so
        // no matter what we do we can't unsuspend it unless gc_round has
        // advanced to round >= 1.
        let mut all_blocks = dag_builder
            .blocks
            .values()
            .filter(|block| block.round() > 1)
            .cloned()
            .collect::<Vec<_>>();

        // Now randomize the sequence of sending the blocks to block manager. In the end
        // all the blocks should be uniquely suspended and no missing blocks
        // should exist.
        for seed in 0..100u8 {
            all_blocks.shuffle(&mut StdRng::from_seed([seed; 32]));

            let store = Arc::new(MemStore::new());
            let dag_state = Arc::new(RwLock::new(DagState::new(context.clone(), store.clone())));

            let mut block_manager = BlockManager::new(
                context.clone(),
                dag_state.clone(),
                Arc::new(NoopBlockVerifier),
            );

            // WHEN
            for block in &all_blocks {
                let (accepted_blocks, _) = block_manager.try_accept_blocks(vec![block.clone()]);
                assert!(accepted_blocks.is_empty());
            }
            assert!(!block_manager.is_empty());

            // AND also call the try_to_find method with some non existing block refs. Those
            // should be cleaned up as well once GC kicks in.
            let non_existing_refs = (1..=3)
                .map(|round| {
                    BlockRef::new(round, AuthorityIndex::new_for_test(0), BlockDigest::MIN)
                })
                .collect::<Vec<_>>();
            assert_eq!(block_manager.try_find_blocks(non_existing_refs).len(), 3);

            // AND
            // Trigger a commit which will advance GC round
            let last_commit = TrustedCommit::new_for_test(
                gc_depth * 2,
                CommitDigest::MIN,
                context.clock.timestamp_utc_ms(),
                BlockRef::new(
                    gc_depth * 2,
                    AuthorityIndex::new_for_test(0),
                    BlockDigest::MIN,
                ),
                vec![],
            );
            dag_state.write().set_last_commit(last_commit);

            // AND
            block_manager.try_unsuspend_blocks_for_latest_gc_round();

            // THEN
            assert!(block_manager.is_empty());

            // AND ensure that all have been accepted to the DAG
            for block in &all_blocks {
                assert!(dag_state.read().contains_block(&block.reference()));
            }
        }
    }

    #[rstest]
    #[tokio::test]
    async fn try_accept_committed_blocks() {
        // GIVEN
        let (mut context, _key_pairs) = Context::new_for_test(4);
        // We set the gc depth to 4
        context
            .protocol_config
            .set_consensus_gc_depth_for_testing(4);
        let context = Arc::new(context);
        let store = Arc::new(MemStore::new());
        let dag_state = Arc::new(RwLock::new(DagState::new(context.clone(), store.clone())));

        // We "fake" the commit for round 6, so GC round moves to (commit_round -
        // gc_depth = 6 - 4 = 2)
        let last_commit = TrustedCommit::new_for_test(
            10,
            CommitDigest::MIN,
            context.clock.timestamp_utc_ms(),
            BlockRef::new(6, AuthorityIndex::new_for_test(0), BlockDigest::MIN),
            vec![],
        );
        dag_state.write().set_last_commit(last_commit);
        assert_eq!(
            dag_state.read().gc_round(),
            2,
            "GC round should have moved to round 2"
        );

        let mut block_manager =
            BlockManager::new(context.clone(), dag_state, Arc::new(NoopBlockVerifier));

        // create a DAG of 12 rounds
        let mut dag_builder = DagBuilder::new(context.clone());
        dag_builder.layers(1..=12).build();

        // Now try to accept via the normal acceptance block path the blocks of rounds 7
        // ~ 12. None of them should be accepted
        let blocks = dag_builder.blocks(7..=12);
        let (accepted_blocks, missing) = block_manager.try_accept_blocks(blocks.clone());
        assert!(accepted_blocks.is_empty());
        assert_eq!(missing.len(), 4);

        // Now try to accept via the committed blocks path the blocks of rounds 3 ~ 6.
        // All of them should be accepted and also the blocks of rounds 7 ~ 12
        // should be unsuspended and accepted as well.
        let blocks = dag_builder.blocks(3..=6);

        // WHEN
        let mut accepted_blocks = block_manager.try_accept_committed_blocks(blocks);

        // THEN
        accepted_blocks.sort_by_key(|b| b.reference());

        let mut all_blocks = dag_builder.blocks(3..=12);
        all_blocks.sort_by_key(|b| b.reference());

        assert_eq!(accepted_blocks, all_blocks);
        assert!(block_manager.is_empty());
    }

    struct TestBlockVerifier {
        fail: BTreeSet<BlockRef>,
    }

    impl TestBlockVerifier {
        fn new(fail: BTreeSet<BlockRef>) -> Self {
            Self { fail }
        }
    }

    impl BlockVerifier for TestBlockVerifier {
        fn verify(&self, _block: &SignedBlock) -> ConsensusResult<()> {
            Ok(())
        }

        fn check_ancestors(
            &self,
            block: &VerifiedBlock,
            _ancestors: &[Option<VerifiedBlock>],
            _gc_enabled: bool,
            _gc_round: Round,
        ) -> ConsensusResult<()> {
            if self.fail.contains(&block.reference()) {
                Err(ConsensusError::InvalidBlockTimestamp {
                    max_timestamp_ms: 0,
                    block_timestamp_ms: block.timestamp_ms(),
                })
            } else {
                Ok(())
            }
        }
    }

    #[tokio::test]
    async fn reject_blocks_failing_verifications() {
        let (context, _key_pairs) = Context::new_for_test(4);
        let context = Arc::new(context);

        // create a DAG of rounds 1 ~ 5.
        let mut dag_builder = DagBuilder::new(context.clone());
        dag_builder.layers(1..=5).build();

        let all_blocks = dag_builder.blocks.values().cloned().collect::<Vec<_>>();

        // Create a test verifier that fails the blocks of round 3
        let test_verifier = TestBlockVerifier::new(
            all_blocks
                .iter()
                .filter(|block| block.round() == 3)
                .map(|block| block.reference())
                .collect(),
        );

        // Create BlockManager.
        let store = Arc::new(MemStore::new());
        let dag_state = Arc::new(RwLock::new(DagState::new(context.clone(), store.clone())));
        let mut block_manager =
            BlockManager::new(context.clone(), dag_state, Arc::new(test_verifier));

        // Try to accept blocks from round 2 ~ 5 into block manager. All of them should
        // be suspended.
        let (accepted_blocks, missing_refs) = block_manager.try_accept_blocks(
            all_blocks
                .iter()
                .filter(|block| block.round() > 1)
                .cloned()
                .collect(),
        );

        // Missing refs should all come from round 1.
        assert!(accepted_blocks.is_empty());
        assert_eq!(missing_refs.len(), 4);
        missing_refs.iter().for_each(|missing_ref| {
            assert_eq!(missing_ref.round, 1);
        });

        // Now add round 1 blocks into block manager.
        let (accepted_blocks, missing_refs) = block_manager.try_accept_blocks(
            all_blocks
                .iter()
                .filter(|block| block.round() == 1)
                .cloned()
                .collect(),
        );

        // Only round 1 and round 2 blocks should be accepted.
        assert_eq!(accepted_blocks.len(), 8);
        accepted_blocks.iter().for_each(|block| {
            assert!(block.round() <= 2);
        });
        assert!(missing_refs.is_empty());

        // Other blocks should be rejected and there should be no remaining suspended
        // block.
        assert!(block_manager.suspended_blocks_refs().is_empty());
    }

    #[tokio::test]
    async fn try_find_blocks() {
        // GIVEN
        let (context, _key_pairs) = Context::new_for_test(4);
        let context = Arc::new(context);
        let store = Arc::new(MemStore::new());
        let dag_state = Arc::new(RwLock::new(DagState::new(context.clone(), store.clone())));

        let mut block_manager =
            BlockManager::new(context.clone(), dag_state, Arc::new(NoopBlockVerifier));

        // create a DAG
        let mut dag_builder = DagBuilder::new(context.clone());
        dag_builder
            .layers(1..=2) // 2 rounds
            .authorities(vec![
                AuthorityIndex::new_for_test(0),
                AuthorityIndex::new_for_test(2),
            ]) // Create equivocating blocks for 2 authorities
            .equivocate(3)
            .build();

        // Take only the blocks of round 2 and try to accept them
        let round_2_blocks = dag_builder
            .blocks
            .iter()
            .filter_map(|(_, block)| (block.round() == 2).then_some(block.clone()))
            .collect::<Vec<VerifiedBlock>>();

        // All blocks should be missing
        let missing_block_refs_from_find =
            block_manager.try_find_blocks(round_2_blocks.iter().map(|b| b.reference()).collect());
        assert_eq!(missing_block_refs_from_find.len(), 10);
        assert!(
            missing_block_refs_from_find
                .iter()
                .all(|block_ref| block_ref.round == 2)
        );

        // Try accept blocks which will cause blocks to be suspended and added to
        // missing in block manager.
        let (accepted_blocks, missing) = block_manager.try_accept_blocks(round_2_blocks.clone());
        assert!(accepted_blocks.is_empty());

        let missing_block_refs = round_2_blocks.first().unwrap().ancestors();
        let missing_block_refs_from_accept =
            missing_block_refs.iter().cloned().collect::<BTreeSet<_>>();
        assert_eq!(missing, missing_block_refs_from_accept);
        assert_eq!(
            block_manager.missing_block_refs(),
            missing_block_refs_from_accept
        );

        // No blocks should be accepted and block manager should have made note
        // of the missing & suspended blocks.
        // Now we can check get the result of try find block with all of the blocks
        // from newly created but not accepted round 3.
        dag_builder.layer(3).build();

        let round_3_blocks = dag_builder
            .blocks
            .iter()
            .filter_map(|(_, block)| (block.round() == 3).then_some(block.reference()))
            .collect::<Vec<BlockRef>>();

        let missing_block_refs_from_find = block_manager.try_find_blocks(
            round_2_blocks
                .iter()
                .map(|b| b.reference())
                .chain(round_3_blocks.into_iter())
                .collect(),
        );

        assert_eq!(missing_block_refs_from_find.len(), 4);
        assert!(
            missing_block_refs_from_find
                .iter()
                .all(|block_ref| block_ref.round == 3)
        );
        assert_eq!(
            block_manager.missing_block_refs(),
            missing_block_refs_from_accept
                .into_iter()
                .chain(missing_block_refs_from_find.into_iter())
                .collect()
        );
    }
}