@sap/xssec/src/cache/ResponseReplica.js

XS Advanced Container Security API for node.js

class ResponseReplica {
    cache; // cache containing this replica
    key; // cache key of this replica
    request; // callback for fetching response data
    data; // last response data
    lastRefresh; // UNIX timestamp of last refresh
    expirationTime; // time in milliseconds that needs to pass after creation for the replica to count as expired
    pendingRequest; // promise for ongoing update of response or undefined

    constructor(cache, key, request) {
        Object.assign(this, { cache, key, request });
        this.data = null;
        this.expirationTime = cache.expirationTime;
    }

    /**
     * Returns the remaining time until expiration.
     * @returns time until expiration or 0 if no data available or data expired
     */
    get remainingTime() {
        if (!this.hasData || this.lastRefresh == null) {
            return 0;
        }

        const elapsedTime = Date.now() - this.lastRefresh;
        return Math.max(0, this.expirationTime - elapsedTime);
    }

    /** Returns whether the replica already has response data. **/
    hasData() {
        return this.data != null;
    }

    /** Returns whether the replica is expired. **/
    isExpired() {
        return this.remainingTime <= 0;
    }

    /**
     * Returns if the replica is considered stale given the refresh period. Stale replicas should be refreshed but may still be used before expiration.
     * @param refreshPeriod time period (in ms) before expiration time in which the replica should count as stale (but not yet as expired)
     * @returns true if the replica is already expired or will expire within the given refresh period.
     */
    isStale(refreshPeriod) {
        return this.expired || this.remainingTime <= refreshPeriod;
    }

    /**
     * Triggers a refresh of this replica. Multiple calls will still result in only one refresh at a time.
     * @param {string} correlationId 
     */
    refresh(correlationId) {
        this.pendingRequest ??= this.#fetchResponse(correlationId);

        return this.pendingRequest;
    }

    /** Fetches new data from the request. */
    async #fetchResponse(correlationId) {
        try {
            this.data = await this.request(correlationId);
        } finally {
            this.pendingRequest = null;
        }

        this.lastRefresh = Date.now();
    }
}

module.exports = ResponseReplica;