@lodestar/beacon-node/lib/chain/balancesCache.js

A Typescript implementation of the beacon chain

import { computeStartSlotAtEpoch } from "@lodestar/state-transition";
import { toRootHex } from "@lodestar/utils";
/** The number of validator balance sets that are cached within `CheckpointBalancesCache`. */
const MAX_BALANCE_CACHE_SIZE = 4;
/**
 * Cache EffectiveBalanceIncrements of checkpoint blocks
 */
export class CheckpointBalancesCache {
    items = [];
    /**
     * Inspect the given `state` and determine the root of the block at the first slot of
     * `state.current_epoch`. If there is not already some entry for the given block root, then
     * add the effective balances from the `state` to the cache.
     */
    processState(blockRootHex, state) {
        const epoch = state.epoch;
        const epochBoundarySlot = computeStartSlotAtEpoch(epoch);
        const epochBoundaryRoot = epochBoundarySlot === state.slot ? blockRootHex : toRootHex(state.getBlockRootAtSlot(epochBoundarySlot));
        const index = this.items.findIndex((item) => item.epoch === epoch && item.rootHex === epochBoundaryRoot);
        if (index === -1) {
            if (this.items.length === MAX_BALANCE_CACHE_SIZE) {
                this.items.shift();
            }
            // expect to reach this once per epoch
            this.items.push({ epoch, rootHex: epochBoundaryRoot, balances: state.getEffectiveBalanceIncrementsZeroInactive() });
        }
    }
    get(checkpoint) {
        const { rootHex, epoch } = checkpoint;
        return this.items.find((item) => item.epoch === epoch && item.rootHex === rootHex)?.balances;
    }
}
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