lighthouse/beacon_node/eth1/src/deposit_cache.rs

use crate::DepositLog;
use eth2_hashing::hash;
use ssz_derive::{Decode, Encode};
use std::cmp::Ordering;
use tree_hash::TreeHash;
use types::{Deposit, Hash256, DEPOSIT_TREE_DEPTH};

#[derive(Debug, PartialEq)]
pub enum Error {
    /// A deposit log was added when a prior deposit was not already in the cache.
    ///
    /// Logs have to be added with monotonically-increasing block numbers.
    NonConsecutive { log_index: u64, expected: usize },
    /// The eth1 event log data was unable to be parsed.
    LogParseError(String),
    /// There are insufficient deposits in the cache to fulfil the request.
    InsufficientDeposits {
        known_deposits: usize,
        requested: u64,
    },
    /// A log with the given index is already present in the cache and it does not match the one
    /// provided.
    DuplicateDistinctLog(u64),
    /// The deposit count must always be large enough to account for the requested deposit range.
    ///
    /// E.g., you cannot request deposit 10 when the deposit count is 9.
    DepositCountInvalid { deposit_count: u64, range_end: u64 },
    /// Error with the merkle tree for deposits.
    DepositTreeError(merkle_proof::MerkleTreeError),
    /// An unexpected condition was encountered.
    InternalError(String),
}

/// Emulates the eth1 deposit contract merkle tree.
pub struct DepositDataTree {
    tree: merkle_proof::MerkleTree,
    mix_in_length: usize,
    depth: usize,
}

impl DepositDataTree {
    /// Create a new Merkle tree from a list of leaves (`DepositData::tree_hash_root`) and a fixed depth.
    pub fn create(leaves: &[Hash256], mix_in_length: usize, depth: usize) -> Self {
        Self {
            tree: merkle_proof::MerkleTree::create(leaves, depth),
            mix_in_length,
            depth,
        }
    }

    /// Returns 32 bytes representing the "mix in length" for the merkle root of this tree.
    fn length_bytes(&self) -> Vec<u8> {
        int_to_bytes32(self.mix_in_length)
    }

    /// Retrieve the root hash of this Merkle tree with the length mixed in.
    pub fn root(&self) -> Hash256 {
        let mut preimage = [0; 64];
        preimage[0..32].copy_from_slice(&self.tree.hash()[..]);
        preimage[32..64].copy_from_slice(&self.length_bytes());
        Hash256::from_slice(&hash(&preimage))
    }

    /// Return the leaf at `index` and a Merkle proof of its inclusion.
    ///
    /// The Merkle proof is in "bottom-up" order, starting with a leaf node
    /// and moving up the tree. Its length will be exactly equal to `depth + 1`.
    pub fn generate_proof(&self, index: usize) -> (Hash256, Vec<Hash256>) {
        let (root, mut proof) = self.tree.generate_proof(index, self.depth);
        proof.push(Hash256::from_slice(&self.length_bytes()));
        (root, proof)
    }

    /// Add a deposit to the merkle tree.
    pub fn push_leaf(&mut self, leaf: Hash256) -> Result<(), Error> {
        self.tree
            .push_leaf(leaf, self.depth)
            .map_err(Error::DepositTreeError)?;
        self.mix_in_length += 1;
        Ok(())
    }
}

#[derive(Encode, Decode, Clone)]
pub struct SszDepositCache {
    logs: Vec<DepositLog>,
    leaves: Vec<Hash256>,
    deposit_contract_deploy_block: u64,
    deposit_roots: Vec<Hash256>,
}

impl SszDepositCache {
    pub fn from_deposit_cache(cache: &DepositCache) -> Self {
        Self {
            logs: cache.logs.clone(),
            leaves: cache.leaves.clone(),
            deposit_contract_deploy_block: cache.deposit_contract_deploy_block,
            deposit_roots: cache.deposit_roots.clone(),
        }
    }

    pub fn to_deposit_cache(&self) -> Result<DepositCache, String> {
        let deposit_tree =
            DepositDataTree::create(&self.leaves, self.leaves.len(), DEPOSIT_TREE_DEPTH);
        // Check for invalid SszDepositCache conditions
        if self.leaves.len() != self.logs.len() {
            return Err("Invalid SszDepositCache: logs and leaves should have equal length".into());
        }
        // `deposit_roots` also includes the zero root
        if self.leaves.len() + 1 != self.deposit_roots.len() {
            return Err(
                "Invalid SszDepositCache: deposit_roots length must be only one more than leaves"
                    .into(),
            );
        }
        Ok(DepositCache {
            logs: self.logs.clone(),
            leaves: self.leaves.clone(),
            deposit_contract_deploy_block: self.deposit_contract_deploy_block,
            deposit_tree,
            deposit_roots: self.deposit_roots.clone(),
        })
    }
}

/// Mirrors the merkle tree of deposits in the eth1 deposit contract.
///
/// Provides `Deposit` objects with merkle proofs included.
pub struct DepositCache {
    logs: Vec<DepositLog>,
    leaves: Vec<Hash256>,
    deposit_contract_deploy_block: u64,
    /// An incremental merkle tree which represents the current state of the
    /// deposit contract tree.
    deposit_tree: DepositDataTree,
    /// Vector of deposit roots. `deposit_roots[i]` denotes `deposit_root` at
    /// `deposit_index` `i`.
    deposit_roots: Vec<Hash256>,
}

impl Default for DepositCache {
    fn default() -> Self {
        let deposit_tree = DepositDataTree::create(&[], 0, DEPOSIT_TREE_DEPTH);
        let deposit_roots = vec![deposit_tree.root()];
        DepositCache {
            logs: Vec::new(),
            leaves: Vec::new(),
            deposit_contract_deploy_block: 1,
            deposit_tree,
            deposit_roots,
        }
    }
}

impl DepositCache {
    /// Create new `DepositCache` given block number at which deposit
    /// contract was deployed.
    pub fn new(deposit_contract_deploy_block: u64) -> Self {
        DepositCache {
            deposit_contract_deploy_block,
            ..Self::default()
        }
    }

    /// Returns the number of deposits available in the cache.
    pub fn len(&self) -> usize {
        self.logs.len()
    }

    /// True if the cache does not store any blocks.
    pub fn is_empty(&self) -> bool {
        self.logs.is_empty()
    }

    /// Returns the block number for the most recent deposit in the cache.
    pub fn latest_block_number(&self) -> Option<u64> {
        self.logs.last().map(|log| log.block_number)
    }

    /// Returns an iterator over all the logs in `self`.
    pub fn iter(&self) -> impl Iterator<Item = &DepositLog> {
        self.logs.iter()
    }

    /// Returns the i'th deposit log.
    pub fn get(&self, i: usize) -> Option<&DepositLog> {
        self.logs.get(i)
    }

    /// Adds `log` to self.
    ///
    /// This function enforces that `logs` are imported one-by-one with no gaps between
    /// `log.index`, starting at `log.index == 0`.
    ///
    /// ## Errors
    ///
    /// - If a log with index `log.index - 1` is not already present in `self` (ignored when empty).
    /// - If a log with `log.index` is already known, but the given `log` is distinct to it.
    pub fn insert_log(&mut self, log: DepositLog) -> Result<(), Error> {
        match log.index.cmp(&(self.logs.len() as u64)) {
            Ordering::Equal => {
                let deposit = Hash256::from_slice(&log.deposit_data.tree_hash_root());
                self.leaves.push(deposit);
                self.logs.push(log);
                self.deposit_tree.push_leaf(deposit)?;
                self.deposit_roots.push(self.deposit_tree.root());
                Ok(())
            }
            Ordering::Less => {
                if self.logs[log.index as usize] == log {
                    Ok(())
                } else {
                    Err(Error::DuplicateDistinctLog(log.index))
                }
            }
            Ordering::Greater => Err(Error::NonConsecutive {
                log_index: log.index,
                expected: self.logs.len(),
            }),
        }
    }

    /// Returns a list of `Deposit` objects, within the given deposit index `range`.
    ///
    /// The `deposit_count` is used to generate the proofs for the `Deposits`. For example, if we
    /// have 100 proofs, but the eth2 chain only acknowledges 50 of them, we must produce our
    /// proofs with respect to a tree size of 50.
    ///
    ///
    /// ## Errors
    ///
    /// - If `deposit_count` is larger than `end`.
    /// - There are not sufficient deposits in the tree to generate the proof.
    pub fn get_deposits(
        &self,
        start: u64,
        end: u64,
        deposit_count: u64,
        tree_depth: usize,
    ) -> Result<(Hash256, Vec<Deposit>), Error> {
        if deposit_count < end {
            // It's invalid to ask for more deposits than should exist.
            Err(Error::DepositCountInvalid {
                deposit_count,
                range_end: end,
            })
        } else if end > self.logs.len() as u64 {
            // The range of requested deposits exceeds the deposits stored locally.
            Err(Error::InsufficientDeposits {
                requested: end,
                known_deposits: self.logs.len(),
            })
        } else if deposit_count > self.leaves.len() as u64 {
            // There are not `deposit_count` known deposit roots, so we can't build the merkle tree
            // to prove into.
            Err(Error::InsufficientDeposits {
                requested: deposit_count,
                known_deposits: self.logs.len(),
            })
        } else {
            let leaves = self
                .leaves
                .get(0..deposit_count as usize)
                .ok_or_else(|| Error::InternalError("Unable to get known leaves".into()))?;

            // Note: there is likely a more optimal solution than recreating the `DepositDataTree`
            // each time this function is called.
            //
            // Perhaps a base merkle tree could be maintained that contains all deposits up to the
            // last finalized eth1 deposit count. Then, that tree could be cloned and extended for
            // each of these calls.

            let tree = DepositDataTree::create(leaves, deposit_count as usize, tree_depth);

            let deposits = self
                .logs
                .get(start as usize..end as usize)
                .ok_or_else(|| Error::InternalError("Unable to get known log".into()))?
                .iter()
                .map(|deposit_log| {
                    let (_leaf, proof) = tree.generate_proof(deposit_log.index as usize);

                    Deposit {
                        proof: proof.into(),
                        data: deposit_log.deposit_data.clone(),
                    }
                })
                .collect();

            Ok((tree.root(), deposits))
        }
    }

    /// Gets the deposit count at block height = block_number.
    ///
    /// Fetches the `DepositLog` that was emitted at or just before `block_number`
    /// and returns the deposit count as `index + 1`.
    ///
    /// Returns `None` if block number queried is 0 or less than deposit_contract_deployed block.
    pub fn get_deposit_count_from_cache(&self, block_number: u64) -> Option<u64> {
        // Contract cannot be deployed in 0'th block
        if block_number == 0 {
            return None;
        }
        if block_number < self.deposit_contract_deploy_block {
            return None;
        }
        // Return 0 if block_num queried is before first deposit
        if let Some(first_deposit) = self.logs.first() {
            if first_deposit.block_number > block_number {
                return Some(0);
            }
        }
        let index = self
            .logs
            .binary_search_by(|deposit| deposit.block_number.cmp(&block_number));
        match index {
            Ok(index) => self.logs.get(index).map(|x| x.index + 1),
            Err(next) => Some(
                self.logs
                    .get(next.saturating_sub(1))
                    .map_or(0, |x| x.index + 1),
            ),
        }
    }

    /// Gets the deposit root at block height = block_number.
    ///
    /// Fetches the `deposit_count` on or just before the queried `block_number`
    /// and queries the `deposit_roots` map to get the corresponding `deposit_root`.
    pub fn get_deposit_root_from_cache(&self, block_number: u64) -> Option<Hash256> {
        let index = self.get_deposit_count_from_cache(block_number)?;
        Some(*self.deposit_roots.get(index as usize)?)
    }
}

/// Returns `int` as little-endian bytes with a length of 32.
fn int_to_bytes32(int: usize) -> Vec<u8> {
    let mut vec = int.to_le_bytes().to_vec();
    vec.resize(32, 0);
    vec
}

#[cfg(test)]
pub mod tests {
    use super::*;
    use crate::deposit_log::tests::EXAMPLE_LOG;
    use crate::http::Log;

    pub const TREE_DEPTH: usize = 32;

    fn example_log() -> DepositLog {
        let log = Log {
            block_number: 42,
            data: EXAMPLE_LOG.to_vec(),
        };
        DepositLog::from_log(&log).expect("should decode log")
    }

    #[test]
    fn insert_log_valid() {
        let mut tree = DepositCache::default();

        for i in 0..16 {
            let mut log = example_log();
            log.index = i;
            tree.insert_log(log).expect("should add consecutive logs")
        }
    }

    #[test]
    fn insert_log_invalid() {
        let mut tree = DepositCache::default();

        for i in 0..4 {
            let mut log = example_log();
            log.index = i;
            tree.insert_log(log).expect("should add consecutive logs")
        }

        // Add duplicate, when given is the same as the one known.
        let mut log = example_log();
        log.index = 3;
        assert!(tree.insert_log(log).is_ok());

        // Add duplicate, when given is different to the one known.
        let mut log = example_log();
        log.index = 3;
        log.block_number = 99;
        assert!(tree.insert_log(log).is_err());

        //  Skip inserting a log.
        let mut log = example_log();
        log.index = 5;
        assert!(tree.insert_log(log).is_err());
    }

    #[test]
    fn get_deposit_valid() {
        let n = 1_024;
        let mut tree = DepositCache::default();

        for i in 0..n {
            let mut log = example_log();
            log.index = i;
            log.block_number = i;
            log.deposit_data.withdrawal_credentials = Hash256::from_low_u64_be(i);
            tree.insert_log(log).expect("should add consecutive logs")
        }

        // Get 0 deposits, with max deposit count.
        let (_, deposits) = tree
            .get_deposits(0, 0, n, TREE_DEPTH)
            .expect("should get the full tree");
        assert_eq!(deposits.len(), 0, "should return no deposits");

        // Get 0 deposits, with 0 deposit count.
        let (_, deposits) = tree
            .get_deposits(0, 0, 0, TREE_DEPTH)
            .expect("should get the full tree");
        assert_eq!(deposits.len(), 0, "should return no deposits");

        // Get 0 deposits, with 0 deposit count, tree depth 0.
        let (_, deposits) = tree
            .get_deposits(0, 0, 0, 0)
            .expect("should get the full tree");
        assert_eq!(deposits.len(), 0, "should return no deposits");

        // Get all deposits, with max deposit count.
        let (full_root, deposits) = tree
            .get_deposits(0, n, n, TREE_DEPTH)
            .expect("should get the full tree");
        assert_eq!(deposits.len(), n as usize, "should return all deposits");

        // Get 4 deposits, with max deposit count.
        let (root, deposits) = tree
            .get_deposits(0, 4, n, TREE_DEPTH)
            .expect("should get the four from the full tree");
        assert_eq!(
            deposits.len(),
            4 as usize,
            "should get 4 deposits from full tree"
        );
        assert_eq!(
            root, full_root,
            "should still return full root when getting deposit subset"
        );

        // Get half of the deposits, with half deposit count.
        let half = n / 2;
        let (half_root, deposits) = tree
            .get_deposits(0, half, half, TREE_DEPTH)
            .expect("should get the half tree");
        assert_eq!(deposits.len(), half as usize, "should return half deposits");

        // Get 4 deposits, with half deposit count.
        let (root, deposits) = tree
            .get_deposits(0, 4, n / 2, TREE_DEPTH)
            .expect("should get the half tree");
        assert_eq!(
            deposits.len(),
            4 as usize,
            "should get 4 deposits from half tree"
        );
        assert_eq!(
            root, half_root,
            "should still return half root when getting deposit subset"
        );
        assert_ne!(
            full_root, half_root,
            "should get different root when pinning deposit count"
        );
    }

    #[test]
    fn get_deposit_invalid() {
        let n = 16;
        let mut tree = DepositCache::default();

        for i in 0..n {
            let mut log = example_log();
            log.index = i;
            log.block_number = i;
            log.deposit_data.withdrawal_credentials = Hash256::from_low_u64_be(i);
            tree.insert_log(log).expect("should add consecutive logs")
        }

        // Range too high.
        assert!(tree.get_deposits(0, n + 1, n, TREE_DEPTH).is_err());

        // Count too high.
        assert!(tree.get_deposits(0, n, n + 1, TREE_DEPTH).is_err());

        // Range higher than count.
        assert!(tree.get_deposits(0, 4, 2, TREE_DEPTH).is_err());
    }
}