cuprate/consensus/src/context/weight.rs

//! # Block Weights
//!
//! This module contains calculations for block weights, including calculating block weight
//! limits, effective medians and long term block weights.
//!
//! For more information please see the [block weights chapter](https://cuprate.github.io/monero-book/consensus_rules/blocks/weight_limit.html)
//! in the Monero Book.
//!
use std::{
    cmp::{max, min},
    collections::VecDeque,
    ops::Range,
};

use rayon::prelude::*;
use tower::ServiceExt;
use tracing::instrument;

use crate::{
    helper::{median, rayon_spawn_async},
    ConsensusError, Database, DatabaseRequest, DatabaseResponse, HardFork,
};

#[cfg(test)]
pub(super) mod tests;

const PENALTY_FREE_ZONE_1: usize = 20000;
const PENALTY_FREE_ZONE_2: usize = 60000;
const PENALTY_FREE_ZONE_5: usize = 300000;

const SHORT_TERM_WINDOW: u64 = 100;
const LONG_TERM_WINDOW: u64 = 100000;

/// Returns the penalty free zone
///
/// https://cuprate.github.io/monero-book/consensus_rules/blocks/weight_limit.html#penalty-free-zone
pub fn penalty_free_zone(hf: &HardFork) -> usize {
    if hf == &HardFork::V1 {
        PENALTY_FREE_ZONE_1
    } else if hf.in_range(&HardFork::V2, &HardFork::V5) {
        PENALTY_FREE_ZONE_2
    } else {
        PENALTY_FREE_ZONE_5
    }
}

/// Configuration for the block weight cache.
///
#[derive(Debug, Clone)]
pub struct BlockWeightsCacheConfig {
    short_term_window: u64,
    long_term_window: u64,
}

impl BlockWeightsCacheConfig {
    pub const fn new(short_term_window: u64, long_term_window: u64) -> BlockWeightsCacheConfig {
        BlockWeightsCacheConfig {
            short_term_window,
            long_term_window,
        }
    }

    pub fn main_net() -> BlockWeightsCacheConfig {
        BlockWeightsCacheConfig {
            short_term_window: SHORT_TERM_WINDOW,
            long_term_window: LONG_TERM_WINDOW,
        }
    }
}

/// A cache used to calculate block weight limits, the effective median and
/// long term block weights.
///
/// These calculations require a lot of data from the database so by caching
/// this data it reduces the load on the database.
#[derive(Clone)]
pub struct BlockWeightsCache {
    short_term_block_weights: VecDeque<usize>,
    long_term_weights: VecDeque<usize>,
    /// The height of the top block.
    tip_height: u64,

    config: BlockWeightsCacheConfig,
}

impl BlockWeightsCache {
    /// Initialize the [`BlockWeightsCache`] at the the given chain height.
    #[instrument(name = "init_weight_cache", level = "info", skip(database, config))]
    pub async fn init_from_chain_height<D: Database + Clone>(
        chain_height: u64,
        config: BlockWeightsCacheConfig,
        database: D,
    ) -> Result<Self, ConsensusError> {
        tracing::info!("Initializing weight cache this may take a while.");

        let long_term_weights: VecDeque<usize> = get_long_term_weight_in_range(
            chain_height.saturating_sub(config.long_term_window)..chain_height,
            database.clone(),
        )
        .await?
        .into();

        let short_term_block_weights: VecDeque<usize> = get_blocks_weight_in_range(
            chain_height.saturating_sub(config.short_term_window)..chain_height,
            database,
        )
        .await?
        .into();

        tracing::info!("Initialized block weight cache, chain-height: {:?}, long term weights length: {:?}, short term weights length: {:?}", chain_height, long_term_weights.len(), short_term_block_weights.len());

        Ok(BlockWeightsCache {
            short_term_block_weights,
            long_term_weights,
            tip_height: chain_height - 1,
            config,
        })
    }

    /// Add a new block to the cache.
    ///
    /// The block_height **MUST** be one more than the last height the cache has
    /// seen.
    pub fn new_block(&mut self, block_height: u64, block_weight: usize, long_term_weight: usize) {
        assert_eq!(self.tip_height + 1, block_height);
        self.tip_height += 1;
        tracing::debug!(
            "Adding new block's {} weights to block cache, weight: {}, long term weight: {}",
            self.tip_height,
            block_weight,
            long_term_weight
        );

        self.long_term_weights.push_back(long_term_weight);
        if u64::try_from(self.long_term_weights.len()).unwrap() > self.config.long_term_window {
            self.long_term_weights.pop_front();
        }

        self.short_term_block_weights.push_back(block_weight);
        if u64::try_from(self.short_term_block_weights.len()).unwrap()
            > self.config.short_term_window
        {
            self.short_term_block_weights.pop_front();
        }
    }

    /// Returns the median long term weight over the last [`LONG_TERM_WINDOW`] blocks, or custom amount of blocks in the config.
    pub async fn median_long_term_weight(&self) -> usize {
        let mut sorted_long_term_weights: Vec<usize> = self.long_term_weights.clone().into();

        // Move this out of the async runtime as this can take a bit.
        let sorted_long_term_weights = rayon_spawn_async(|| {
            sorted_long_term_weights.par_sort_unstable();
            sorted_long_term_weights
        })
        .await;

        median(&sorted_long_term_weights)
    }

    pub fn median_short_term_weight(&self) -> usize {
        let mut sorted_short_term_block_weights: Vec<usize> =
            self.short_term_block_weights.clone().into();
        sorted_short_term_block_weights.sort_unstable();
        median(&sorted_short_term_block_weights)
    }

    /// Returns the effective median weight, used for block reward calculations and to calculate
    /// the block weight limit.
    ///
    /// See: https://cuprate.github.io/monero-book/consensus_rules/blocks/weight_limit.html#calculating-effective-median-weight
    pub async fn effective_median_block_weight(&self, hf: &HardFork) -> usize {
        calculate_effective_median_block_weight(
            hf,
            self.median_short_term_weight(),
            self.median_long_term_weight().await,
        )
    }

    /// Returns the median weight used to calculate block reward punishment.
    ///
    /// https://cuprate.github.io/monero-book/consensus_rules/blocks/reward.html#calculating-block-reward
    pub async fn median_for_block_reward(&self, hf: &HardFork) -> usize {
        if hf.in_range(&HardFork::V1, &HardFork::V12) {
            self.median_short_term_weight()
        } else {
            self.effective_median_block_weight(hf).await
        }
        .max(penalty_free_zone(hf))
    }
}

fn calculate_effective_median_block_weight(
    hf: &HardFork,
    median_short_term_weight: usize,
    median_long_term_weight: usize,
) -> usize {
    if hf.in_range(&HardFork::V1, &HardFork::V10) {
        return median_short_term_weight.max(penalty_free_zone(hf));
    }

    let long_term_median = median_long_term_weight.max(PENALTY_FREE_ZONE_5);
    let short_term_median = median_short_term_weight;
    let effective_median = if hf.in_range(&HardFork::V10, &HardFork::V15) {
        min(
            max(PENALTY_FREE_ZONE_5, short_term_median),
            50 * long_term_median,
        )
    } else {
        min(
            max(long_term_median, short_term_median),
            50 * long_term_median,
        )
    };

    effective_median.max(penalty_free_zone(hf))
}

pub fn calculate_block_long_term_weight(
    hf: &HardFork,
    block_weight: usize,
    long_term_median: usize,
) -> usize {
    if hf.in_range(&HardFork::V1, &HardFork::V10) {
        return block_weight;
    }

    let long_term_median = max(penalty_free_zone(hf), long_term_median);

    let (short_term_constraint, adjusted_block_weight) =
        if hf.in_range(&HardFork::V10, &HardFork::V15) {
            let stc = long_term_median + long_term_median * 2 / 5;
            (stc, block_weight)
        } else {
            let stc = long_term_median + long_term_median * 7 / 10;
            (stc, max(block_weight, long_term_median * 10 / 17))
        };

    min(short_term_constraint, adjusted_block_weight)
}

#[instrument(name = "get_block_weights", skip(database))]
async fn get_blocks_weight_in_range<D: Database + Clone>(
    range: Range<u64>,
    database: D,
) -> Result<Vec<usize>, ConsensusError> {
    tracing::info!("getting block weights.");

    let DatabaseResponse::BlockExtendedHeaderInRange(ext_headers) = database
        .oneshot(DatabaseRequest::BlockExtendedHeaderInRange(range))
        .await?
    else {
        panic!("Database sent incorrect response!")
    };

    Ok(ext_headers
        .into_iter()
        .map(|info| info.block_weight)
        .collect())
}

#[instrument(name = "get_long_term_weights", skip(database), level = "info")]
async fn get_long_term_weight_in_range<D: Database + Clone>(
    range: Range<u64>,
    database: D,
) -> Result<Vec<usize>, ConsensusError> {
    tracing::info!("getting block long term weights.");

    let DatabaseResponse::BlockExtendedHeaderInRange(ext_headers) = database
        .oneshot(DatabaseRequest::BlockExtendedHeaderInRange(range))
        .await?
    else {
        panic!("Database sent incorrect response!")
    };

    Ok(ext_headers
        .into_iter()
        .map(|info| info.long_term_weight)
        .collect())
}