darkfi/validator/

mod.rs

/* This file is part of DarkFi (https://dark.fi)
 *
 * Copyright (C) 2020-2026 Dyne.org foundation
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

use std::{collections::HashMap, sync::Arc};

use darkfi_sdk::{blockchain::compute_fee, crypto::MerkleTree};
use num_bigint::BigUint;
use sled_overlay::sled;
use smol::lock::RwLock;
use tracing::{debug, error, info, warn};

use crate::{
    blockchain::{
        block_store::{BlockDifficulty, BlockInfo, BlockRanks},
        Blockchain, BlockchainOverlay, HeaderHash,
    },
    error::TxVerifyFailed,
    tx::Transaction,
    zk::VerifyingKey,
    Error, Result,
};

/// DarkFi consensus module
pub mod consensus;
use consensus::{Consensus, Fork, Proposal};

/// DarkFi PoW module
pub mod pow;
use pow::PoWModule;

/// RandomX infrastructure
pub mod randomx_factory;
pub use randomx_factory::RandomXFactory;

/// Verification functions
pub mod verification;
use verification::{
    verify_block, verify_checkpoint_block, verify_genesis_block, verify_producer_transaction,
    verify_transaction, verify_transactions,
};

/// Fee calculation helpers
pub mod fees;

/// Helper utilities
pub mod utils;
use utils::{best_fork_index, block_rank, deploy_native_contracts};

/// Configuration for initializing [`Validator`]
#[derive(Clone)]
pub struct ValidatorConfig {
    /// Currently configured confirmation security threshold
    pub confirmation_threshold: usize,
    /// Currently configured max in-memory forks to maintain.
    pub max_forks: usize,
    /// Currently configured PoW target
    pub pow_target: u32,
    /// Optional fixed difficulty, for testing purposes
    pub pow_fixed_difficulty: Option<BigUint>,
    /// Genesis block
    pub genesis_block: BlockInfo,
    /// Flag to enable tx fee verification
    pub verify_fees: bool,
}

/// Atomic pointer to validator.
pub type ValidatorPtr = Arc<RwLock<Validator>>;

/// This struct represents a DarkFi validator node.
pub struct Validator {
    /// Canonical (confirmed) blockchain
    pub blockchain: Blockchain,
    /// Hot/Live data used by the consensus algorithm
    pub consensus: Consensus,
    /// Flag signalling if the node is synced
    pub synced: bool,
    /// Flag to enable tx fee verification
    pub verify_fees: bool,
}

impl Validator {
    pub async fn new(db: &sled::Db, config: &ValidatorConfig) -> Result<ValidatorPtr> {
        info!(target: "validator::new", "Initializing Validator");

        info!(target: "validator::new", "Initializing Blockchain");
        let blockchain = Blockchain::new(db)?;

        // Create an overlay over whole blockchain so we can write
        // stuff.
        let overlay = BlockchainOverlay::new(&blockchain)?;

        // Deploy native wasm contracts
        deploy_native_contracts(&overlay, config.pow_target).await?;

        // Update the contracts states monotree in case native
        // contracts zkas has changed.
        let diff = overlay.lock().unwrap().overlay.lock().unwrap().diff(&[])?;
        overlay.lock().unwrap().contracts.update_state_monotree(&diff)?;

        // Add genesis block if blockchain is empty
        if blockchain.genesis().is_err() {
            info!(target: "validator::new", "Appending genesis block");
            verify_genesis_block(&overlay, &[diff], &config.genesis_block, config.pow_target)
                .await?;
        };

        // Write the changes to the actual chain db
        overlay.lock().unwrap().overlay.lock().unwrap().apply()?;

        info!(target: "validator::new", "Initializing Consensus");
        let consensus = Consensus::new(
            blockchain.clone(),
            config.confirmation_threshold,
            config.max_forks,
            config.pow_target,
            config.pow_fixed_difficulty.clone(),
        )?;

        // Create the actual state
        let state = Arc::new(RwLock::new(Self {
            blockchain,
            consensus,
            synced: false,
            verify_fees: config.verify_fees,
        }));

        info!(target: "validator::new", "Finished initializing validator");
        Ok(state)
    }

    /// Auxiliary function to compute provided transaction's required
    /// fee, against current best fork. The function takes a boolean
    /// called `verify_fee` to overwrite the nodes configured
    /// `verify_fees` flag.
    ///
    /// Note: Always remember to purge new trees from the database if
    /// not needed.
    pub async fn calculate_fee(&self, tx: &Transaction, verify_fee: bool) -> Result<u64> {
        // Grab the best fork to verify against
        let index = best_fork_index(&self.consensus.forks)?;
        let fork = self.consensus.forks[index].full_clone()?;

        // Map of ZK proof verifying keys for the transaction
        let mut vks: HashMap<[u8; 32], HashMap<String, VerifyingKey>> = HashMap::new();
        for call in &tx.calls {
            vks.insert(call.data.contract_id.to_bytes(), HashMap::new());
        }

        // Grab forks' next block height
        let next_block_height = fork.get_next_block_height()?;

        // Verify transaction to grab the gas used
        let verify_result = verify_transaction(
            &fork.overlay,
            next_block_height,
            self.consensus.module.target,
            tx,
            &mut MerkleTree::new(1),
            &mut vks,
            verify_fee,
        )
        .await?;

        Ok(compute_fee(&verify_result.total_gas_used()))
    }

    /// The node retrieves a transaction, validates its state
    /// transition agains best fork, and appends it to the pending txs
    /// store if its valid.
    ///
    /// Note: Always remember to purge new trees from the database if
    /// not needed.
    pub async fn append_tx(&mut self, tx: &Transaction, write: bool) -> Result<()> {
        let tx_hash = tx.hash();

        // Check if we have already seen this tx in the pending store
        if self.blockchain.transactions.contains_pending(&tx_hash)? {
            debug!(target: "validator::append_tx", "We have already seen pending tx: {tx_hash}");
            return Err(TxVerifyFailed::AlreadySeenTx(tx_hash.as_string()).into())
        }

        // Grab the best fork to verify against
        let index = best_fork_index(&self.consensus.forks)?;
        let fork = self.consensus.forks[index].full_clone()?;

        // Check if we have already seen this tx. This checks both the
        // fork cache and the actual database.
        if fork.overlay.lock().unwrap().transactions.contains(&tx_hash)? {
            debug!(target: "validator::append_tx", "We have already seen tx: {tx_hash}");
            return Err(TxVerifyFailed::AlreadySeenTx(tx_hash.as_string()).into())
        }

        // Verify state transition
        info!(target: "validator::append_tx", "Starting state transition validation for tx: {tx_hash}");
        // Map of ZK proof verifying keys for the transaction
        let mut vks: HashMap<[u8; 32], HashMap<String, VerifyingKey>> = HashMap::new();
        for call in &tx.calls {
            vks.insert(call.data.contract_id.to_bytes(), HashMap::new());
        }

        // Grab forks' next block height
        let next_block_height = fork.get_next_block_height()?;

        // Verify transaction
        verify_transaction(
            &fork.overlay,
            next_block_height,
            self.consensus.module.target,
            tx,
            &mut MerkleTree::new(1),
            &mut vks,
            self.verify_fees,
        )
        .await?;

        // Add transaction to pending txs store
        if write {
            self.blockchain.add_pending_txs(std::slice::from_ref(tx))?;
            info!(target: "validator::append_tx", "Appended tx {tx_hash} to pending txs store");
        }

        Ok(())
    }

    /// The node tries to append provided proposal to its consensus
    /// state.
    pub async fn append_proposal(&mut self, proposal: &Proposal) -> Result<()> {
        self.consensus.append_proposal(proposal, self.synced, self.verify_fees).await
    }

    /// The node checks if best fork can be confirmed.
    /// If proposals can be confirmed, node appends them to canonical,
    /// and resets the current forks.
    pub async fn confirmation(&mut self) -> Result<Vec<BlockInfo>> {
        info!(target: "validator::confirmation", "Performing confirmation check");

        // Grab best fork index that can be confirmed
        let confirmed_fork = self.consensus.confirmation().await?;
        if confirmed_fork.is_none() {
            info!(target: "validator::confirmation", "No proposals can be confirmed");
            return Ok(vec![])
        }

        // Grab the actual best fork
        let confirmed_fork = confirmed_fork.unwrap();
        let fork = &mut self.consensus.forks[confirmed_fork];

        // Find the excess over confirmation threshold
        let excess = (fork.proposals.len() - self.consensus.confirmation_threshold) + 1;

        // Grab confirmed proposals and update fork's sequences
        let rest_proposals = fork.proposals.split_off(excess);
        let rest_diffs = fork.diffs.split_off(excess);
        let confirmed_proposals = fork.proposals.clone();
        let diffs = fork.diffs.clone();
        fork.proposals = rest_proposals;
        fork.diffs = rest_diffs;

        // Grab confirmed proposals blocks
        let confirmed_blocks =
            fork.overlay.lock().unwrap().get_blocks_by_hash(&confirmed_proposals)?;

        // Apply confirmed proposals diffs and update PoW module
        let mut module = self.consensus.module.clone();
        let mut confirmed_txs = vec![];
        let mut state_inverse_diffs_heights = vec![];
        let mut state_inverse_diffs = vec![];
        info!(target: "validator::confirmation", "Confirming proposals:");
        for (index, proposal) in confirmed_proposals.iter().enumerate() {
            info!(target: "validator::confirmation", "\t{proposal} ({}) - {}", confirmed_blocks[index].header.pow_data, confirmed_blocks[index].header.height);
            fork.overlay.lock().unwrap().overlay.lock().unwrap().apply_diff(&diffs[index])?;
            let next_difficulty = module.next_difficulty()?;
            module.append(&confirmed_blocks[index].header, &next_difficulty)?;
            confirmed_txs.extend_from_slice(&confirmed_blocks[index].txs);
            state_inverse_diffs_heights.push(confirmed_blocks[index].header.height);
            state_inverse_diffs.push(diffs[index].inverse());
        }
        self.consensus.module = module;

        // Store the block inverse diffs
        self.blockchain
            .blocks
            .insert_state_inverse_diff(&state_inverse_diffs_heights, &state_inverse_diffs)?;

        // Reset forks starting with the confirmed blocks
        self.consensus.reset_forks(&confirmed_proposals, &confirmed_fork, &confirmed_txs).await?;
        info!(target: "validator::confirmation", "Confirmation completed!");

        Ok(confirmed_blocks)
    }

    /// Apply provided set of [`BlockInfo`] without doing formal
    /// verification. A set of [`HeaderHash`] is also provided, to
    /// verify that the provided block hash matches the expected header
    /// one.
    ///
    /// Note: this function should only be used for blocks received
    /// using a checkpoint, since in that case we enforce the node to
    /// follow the sequence, assuming all its blocks are valid.
    /// Additionally, it will update any forks to a single empty one,
    /// holding the updated module. Always remember to purge new trees
    /// from the database if not needed.
    pub async fn add_checkpoint_blocks(
        &mut self,
        blocks: &[BlockInfo],
        headers: &[HeaderHash],
    ) -> Result<()> {
        // Check provided sequences are the same length
        if blocks.len() != headers.len() {
            return Err(Error::InvalidInputLengths)
        }

        debug!(target: "validator::add_checkpoint_blocks", "Instantiating BlockchainOverlay");
        let overlay = BlockchainOverlay::new(&self.blockchain)?;

        // Retrieve last block difficulty to access current ranks
        let last_difficulty = self.blockchain.last_block_difficulty()?;
        let mut current_targets_rank = last_difficulty.ranks.targets_rank;
        let mut current_hashes_rank = last_difficulty.ranks.hashes_rank;

        // Grab current PoW module to validate each block
        let mut module = self.consensus.module.clone();

        // Keep track of all blocks transactions to remove them from
        // pending txs store.
        let mut removed_txs = vec![];

        // Keep track of all block database state diffs and their
        // inverse.
        let mut diffs_heights = vec![];
        let mut diffs = vec![];
        let mut inverse_diffs = vec![];

        // Validate and insert each block
        for (index, block) in blocks.iter().enumerate() {
            // Verify block
            match verify_checkpoint_block(&overlay, &diffs, block, &headers[index], module.target)
                .await
            {
                Ok(()) => { /* Do nothing */ }
                // Skip already existing block
                Err(Error::BlockAlreadyExists(_)) => continue,
                Err(e) => {
                    error!(target: "validator::add_checkpoint_blocks", "Erroneous block found in set: {e}");
                    return Err(Error::BlockIsInvalid(block.hash().as_string()))
                }
            };

            // Calculate block rank
            let (next_difficulty, target_distance_sq, hash_distance_sq) =
                block_rank(&mut module, block)?;

            // Update current ranks
            current_targets_rank += target_distance_sq.clone();
            current_hashes_rank += hash_distance_sq.clone();

            // Generate block difficulty and update PoW module
            let cumulative_difficulty =
                module.cumulative_difficulty.clone() + next_difficulty.clone();
            let ranks = BlockRanks::new(
                target_distance_sq,
                current_targets_rank.clone(),
                hash_distance_sq,
                current_hashes_rank.clone(),
            );
            let block_difficulty = BlockDifficulty::new(
                block.header.height,
                block.header.timestamp,
                next_difficulty,
                cumulative_difficulty,
                ranks,
            );
            module.append_difficulty(&overlay, &block.header, block_difficulty)?;

            // Store block transactions
            for tx in &block.txs {
                removed_txs.push(tx.clone());
            }

            // Store block database state diff and its inverse
            diffs_heights.push(block.header.height);
            let diff = overlay.lock().unwrap().overlay.lock().unwrap().diff(&diffs)?;
            inverse_diffs.push(diff.inverse());
            diffs.push(diff);
        }

        debug!(target: "validator::add_checkpoint_blocks", "Applying overlay changes");
        overlay.lock().unwrap().overlay.lock().unwrap().apply()?;

        // Store the block diffs
        self.blockchain.blocks.insert_state_inverse_diff(&diffs_heights, &inverse_diffs)?;

        // Remove blocks transactions from pending txs store
        self.blockchain.remove_pending_txs(&removed_txs)?;

        // Update PoW module
        self.consensus.module = module.clone();

        // Update forks
        self.consensus.forks = vec![Fork::new(self.blockchain.clone(), module).await?];

        Ok(())
    }

    /// Validate a set of [`BlockInfo`] in sequence and apply them if
    /// all are valid.
    ///
    /// Note: this function should only be used in tests when we don't
    /// want to perform consensus logic and always remember to purge
    /// new trees from the database if not needed.
    pub async fn add_test_blocks(&mut self, blocks: &[BlockInfo]) -> Result<()> {
        debug!(target: "validator::add_test_blocks", "Instantiating BlockchainOverlay");
        let overlay = BlockchainOverlay::new(&self.blockchain)?;

        // Retrieve last block
        let mut previous = &overlay.lock().unwrap().last_block()?;

        // Retrieve last block difficulty to access current ranks
        let last_difficulty = self.blockchain.last_block_difficulty()?;
        let mut current_targets_rank = last_difficulty.ranks.targets_rank;
        let mut current_hashes_rank = last_difficulty.ranks.hashes_rank;

        // Grab current PoW module to validate each block
        let mut module = self.consensus.module.clone();

        // Keep track of all blocks transactions to remove them from
        // pending txs store.
        let mut removed_txs = vec![];

        // Keep track of all block database state diffs and their
        // inverse.
        let mut diffs_heights = vec![];
        let mut diffs = vec![];
        let mut inverse_diffs = vec![];

        // Validate and insert each block
        for block in blocks {
            // Verify block
            match verify_block(
                &overlay,
                &diffs,
                &mut module,
                block,
                previous,
                true,
                self.verify_fees,
            )
            .await
            {
                Ok(()) => { /* Do nothing */ }
                // Skip already existing block
                Err(Error::BlockAlreadyExists(_)) => {
                    previous = block;
                    continue
                }
                Err(e) => {
                    error!(target: "validator::add_test_blocks", "Erroneous block found in set: {e}");
                    return Err(Error::BlockIsInvalid(block.hash().as_string()))
                }
            };

            // Calculate block rank
            let (next_difficulty, target_distance_sq, hash_distance_sq) =
                block_rank(&mut module, block)?;

            // Update current ranks
            current_targets_rank += target_distance_sq.clone();
            current_hashes_rank += hash_distance_sq.clone();

            // Generate block difficulty and update PoW module
            let cumulative_difficulty =
                module.cumulative_difficulty.clone() + next_difficulty.clone();
            let ranks = BlockRanks::new(
                target_distance_sq,
                current_targets_rank.clone(),
                hash_distance_sq,
                current_hashes_rank.clone(),
            );
            let block_difficulty = BlockDifficulty::new(
                block.header.height,
                block.header.timestamp,
                next_difficulty,
                cumulative_difficulty,
                ranks,
            );
            module.append_difficulty(&overlay, &block.header, block_difficulty)?;

            // Store block transactions
            for tx in &block.txs {
                removed_txs.push(tx.clone());
            }

            // Store block database state diff and its inverse
            diffs_heights.push(block.header.height);
            let diff = overlay.lock().unwrap().overlay.lock().unwrap().diff(&diffs)?;
            inverse_diffs.push(diff.inverse());
            diffs.push(diff);

            // Use last inserted block as next iteration previous
            previous = block;
        }

        debug!(target: "validator::add_test_blocks", "Applying overlay changes");
        overlay.lock().unwrap().overlay.lock().unwrap().apply()?;

        // Store the block diffs
        self.blockchain.blocks.insert_state_inverse_diff(&diffs_heights, &inverse_diffs)?;

        // Remove blocks transactions from pending txs store
        self.blockchain.remove_pending_txs(&removed_txs)?;

        // Update PoW module
        self.consensus.module = module;

        Ok(())
    }

    /// Validate a set of [`Transaction`] in sequence and apply them if
    /// all are valid. In case any of the transactions fail, they will
    /// be returned to the caller. The function takes a boolean called
    /// `write` which tells it to actually write the state transitions
    /// to the database, and a boolean called `verify_fees` to
    /// overwrite the nodes configured `verify_fees` flag.
    ///
    /// Returns the total gas used and total paid fees for the given
    /// transactions.
    ///
    /// Note: This function should only be used in tests and always
    /// remember to purge new trees from the database if not needed.
    pub async fn add_test_transactions(
        &self,
        txs: &[Transaction],
        verifying_block_height: u32,
        block_target: u32,
        write: bool,
        verify_fees: bool,
    ) -> Result<(u64, u64)> {
        debug!(target: "validator::add_transactions", "Instantiating BlockchainOverlay");
        let overlay = BlockchainOverlay::new(&self.blockchain)?;

        // Verify all transactions and get erroneous ones
        let verify_result = verify_transactions(
            &overlay,
            verifying_block_height,
            block_target,
            txs,
            &mut MerkleTree::new(1),
            verify_fees,
        )
        .await;

        let lock = overlay.lock().unwrap();
        let mut overlay = lock.overlay.lock().unwrap();

        let gas_values = verify_result?;

        if !write {
            debug!(target: "validator::add_transactions", "Skipping apply of state updates because write=false");
            return Ok(gas_values)
        }

        debug!(target: "validator::add_transactions", "Applying overlay changes");
        overlay.apply()?;
        Ok(gas_values)
    }

    /// Validate a producer `Transaction` and apply it if valid. In
    /// case the transactions fail, ir will be returned to the caller.
    /// The function takes a boolean called `write` which tells it to
    /// actually write the state transitions to the database.
    ///
    /// Note: This function should only be used in tests and always
    /// remember to purge new trees from the database if not needed.
    pub async fn add_test_producer_transaction(
        &self,
        tx: &Transaction,
        verifying_block_height: u32,
        block_target: u32,
        write: bool,
    ) -> Result<()> {
        debug!(target: "validator::add_test_producer_transaction", "Instantiating BlockchainOverlay");
        let overlay = BlockchainOverlay::new(&self.blockchain)?;

        // Verify transaction
        let mut erroneous_txs = vec![];
        if let Err(e) = verify_producer_transaction(
            &overlay,
            verifying_block_height,
            block_target,
            tx,
            &mut MerkleTree::new(1),
        )
        .await
        {
            warn!(target: "validator::add_test_producer_transaction", "Transaction verification failed: {e}");
            erroneous_txs.push(tx.clone());
        }

        let lock = overlay.lock().unwrap();
        let mut overlay = lock.overlay.lock().unwrap();
        if !erroneous_txs.is_empty() {
            warn!(target: "validator::add_test_producer_transaction", "Erroneous transactions found in set");
            return Err(TxVerifyFailed::ErroneousTxs(erroneous_txs).into())
        }

        if !write {
            debug!(target: "validator::add_test_producer_transaction", "Skipping apply of state updates because write=false");
            return Ok(())
        }

        debug!(target: "validator::add_test_producer_transaction", "Applying overlay changes");
        overlay.apply()?;
        Ok(())
    }

    /// Retrieve all existing blocks and try to apply them
    /// to an in memory overlay to verify their correctness.
    /// Be careful as this will try to load everything in memory.
    ///
    /// Note: Always remember to purge new trees from the database if
    /// not needed.
    pub async fn validate_blockchain(
        &self,
        pow_target: u32,
        pow_fixed_difficulty: Option<BigUint>,
    ) -> Result<()> {
        // An empty blockchain is considered valid
        let mut blocks_count = self.blockchain.len() as u32;
        info!(target: "validator::validate_blockchain", "Validating {blocks_count} blocks...");
        if blocks_count == 0 {
            info!(target: "validator::validate_blockchain", "Blockchain validated successfully!");
            return Ok(())
        }

        // Create an in memory blockchain overlay
        let sled_db = sled::Config::new().temporary(true).open()?;
        let blockchain = Blockchain::new(&sled_db)?;
        let overlay = BlockchainOverlay::new(&blockchain)?;

        // Set previous
        let mut previous = self.blockchain.genesis_block()?;

        // Deploy native wasm contracts
        deploy_native_contracts(&overlay, pow_target).await?;

        // Update the contracts states monotree
        let diff = overlay.lock().unwrap().overlay.lock().unwrap().diff(&[])?;
        overlay.lock().unwrap().contracts.update_state_monotree(&diff)?;

        // Validate genesis block
        verify_genesis_block(&overlay, &[diff], &previous, pow_target).await?;
        info!(target: "validator::validate_blockchain", "Genesis block validated successfully!");

        // Write the changes to the in memory db
        overlay.lock().unwrap().overlay.lock().unwrap().apply()?;

        // Create a PoW module to validate each block
        let mut module = PoWModule::new(blockchain, pow_target, pow_fixed_difficulty, Some(0))?;

        // Keep track of all block database state diffs
        let mut diffs = vec![];

        // Validate and insert each block
        info!(target: "validator::validate_blockchain", "Validating rest blocks...");
        blocks_count -= 1;
        let mut index = 1;
        while index <= blocks_count {
            // Grab block
            let block = self.blockchain.get_blocks_by_heights(&[index])?[0].clone();

            // Verify block
            if let Err(e) = verify_block(
                &overlay,
                &diffs,
                &mut module,
                &block,
                &previous,
                false,
                self.verify_fees,
            )
            .await
            {
                error!(target: "validator::validate_blockchain", "Erroneous block found in set: {e}");
                return Err(Error::BlockIsInvalid(block.hash().as_string()))
            };

            // Update PoW module
            module.append(&block.header, &module.next_difficulty()?)?;

            // Store block database state diff
            let diff = overlay.lock().unwrap().overlay.lock().unwrap().diff(&diffs)?;
            diffs.push(diff);

            // Use last inserted block as next iteration previous
            previous = block;

            info!(target: "validator::validate_blockchain", "Block {index}/{blocks_count} validated successfully!");
            index += 1;
        }

        info!(target: "validator::validate_blockchain", "Blockchain validated successfully!");
        Ok(())
    }

    /// Auxiliary function to grab current mining RandomX key,
    /// based on next block height.
    /// If no forks exist, returns the canonical key.
    pub async fn current_mining_randomx_key(&self) -> Result<HeaderHash> {
        self.consensus.current_mining_randomx_key().await
    }

    /// Auxiliary function to grab best current fork full clone.
    pub async fn best_current_fork(&self) -> Result<Fork> {
        self.consensus.best_current_fork().await
    }

    /// Auxiliary function to retrieve current best fork next block
    /// height.
    pub async fn best_fork_next_block_height(&self) -> Result<u32> {
        let index = best_fork_index(&self.consensus.forks)?;
        let fork = &self.consensus.forks[index];
        let next_block_height = fork.get_next_block_height()?;

        Ok(next_block_height)
    }

    /// Auxiliary function to reset the validator blockchain and
    /// consensus states to the provided block height.
    pub async fn reset_to_height(&mut self, height: u32) -> Result<()> {
        info!(target: "validator::reset_to_height", "Resetting validator to height: {height}");
        // Reset our databasse to provided height
        self.blockchain.reset_to_height(height)?;

        // Reset consensus PoW module
        self.consensus.reset_pow_module().await?;

        // Purge current forks
        self.consensus.purge_forks().await?;

        info!(target: "validator::reset_to_height", "Validator reset successfully!");

        Ok(())
    }

    /// Auxiliary function to rebuild the block difficulties database
    /// based on current validator blockchain.
    /// Be careful as this will try to load everything in memory.
    pub async fn rebuild_block_difficulties(
        &self,
        pow_target: u32,
        pow_fixed_difficulty: Option<BigUint>,
    ) -> Result<()> {
        info!(target: "validator::rebuild_block_difficulties", "Rebuilding validator block difficulties...");
        // Clear the block difficulties tree
        self.blockchain.blocks.difficulty.clear()?;

        // An empty blockchain doesn't have difficulty records
        let mut blocks_count = self.blockchain.len() as u32;
        info!(target: "validator::rebuild_block_difficulties", "Rebuilding {blocks_count} block difficulties...");
        if blocks_count == 0 {
            info!(target: "validator::rebuild_block_difficulties", "Validator block difficulties rebuilt successfully!");
            return Ok(())
        }

        // Create a PoW module and an in memory overlay to compute each
        // block difficulty.
        let mut module =
            PoWModule::new(self.blockchain.clone(), pow_target, pow_fixed_difficulty, Some(0))?;

        // Grab genesis block difficulty to access current ranks
        let genesis_block = self.blockchain.genesis_block()?;
        let last_difficulty = BlockDifficulty::genesis(genesis_block.header.timestamp);
        let mut targets_rank = last_difficulty.ranks.targets_rank;
        let mut hashes_rank = last_difficulty.ranks.hashes_rank;

        // Grab each block to compute its difficulty
        blocks_count -= 1;
        let mut index = 1;
        while index <= blocks_count {
            // Grab block
            let block = self.blockchain.get_blocks_by_heights(&[index])?[0].clone();

            // Calculate block rank
            let (next_difficulty, target_distance_sq, hash_distance_sq) =
                block_rank(&mut module, &block)?;

            // Update chain ranks
            targets_rank += target_distance_sq.clone();
            hashes_rank += hash_distance_sq.clone();

            // Generate block difficulty and update PoW module
            let cumulative_difficulty =
                module.cumulative_difficulty.clone() + next_difficulty.clone();
            let ranks = BlockRanks::new(
                target_distance_sq,
                targets_rank.clone(),
                hash_distance_sq,
                hashes_rank.clone(),
            );
            let block_difficulty = BlockDifficulty::new(
                block.header.height,
                block.header.timestamp,
                next_difficulty,
                cumulative_difficulty,
                ranks,
            );
            module.append(&block.header, &block_difficulty.difficulty)?;

            // Add difficulty to database
            self.blockchain.blocks.insert_difficulty(&[block_difficulty])?;

            info!(target: "validator::rebuild_block_difficulties", "Block {index}/{blocks_count} difficulty added successfully!");
            index += 1;
        }

        // Flush the database
        self.blockchain.sled_db.flush()?;

        info!(target: "validator::rebuild_block_difficulties", "Validator block difficulties rebuilt successfully!");

        Ok(())
    }
}