@multiformats/dns/dist/src/utils/cache.js

Resolve DNS queries with browser fallback

import hashlru from 'hashlru';
import { RecordType } from '../index.js';
import { DEFAULT_TTL, toDNSResponse } from './to-dns-response.js';
/**
 * Time Aware Least Recent Used Cache
 *
 * @see https://arxiv.org/pdf/1801.00390
 */
class CachedAnswers {
    lru;
    constructor(maxSize) {
        this.lru = hashlru(maxSize);
    }
    get(fqdn, types) {
        let foundAllAnswers = true;
        const answers = [];
        for (const type of types) {
            const cached = this.getAnswers(fqdn, type);
            if (cached.length === 0) {
                foundAllAnswers = false;
                break;
            }
            answers.push(...cached);
        }
        if (foundAllAnswers) {
            return toDNSResponse({ answers });
        }
    }
    getAnswers(domain, type) {
        const key = `${domain.toLowerCase()}-${type}`;
        const answers = this.lru.get(key);
        if (answers != null) {
            const cachedAnswers = answers
                .filter((entry) => {
                return entry.expires > Date.now();
            })
                .map(({ expires, value }) => ({
                ...value,
                TTL: Math.round((expires - Date.now()) / 1000),
                type: RecordType[value.type]
            }));
            if (cachedAnswers.length === 0) {
                this.lru.remove(key);
            }
            // @ts-expect-error hashlru stringifies stored types which turns enums
            // into strings, we convert back into enums above but tsc doesn't know
            return cachedAnswers;
        }
        return [];
    }
    add(domain, answer) {
        const key = `${domain.toLowerCase()}-${answer.type}`;
        const answers = this.lru.get(key) ?? [];
        answers.push({
            expires: Date.now() + ((answer.TTL ?? DEFAULT_TTL) * 1000),
            value: answer
        });
        this.lru.set(key, answers);
    }
    remove(domain, type) {
        const key = `${domain.toLowerCase()}-${type}`;
        this.lru.remove(key);
    }
    clear() {
        this.lru.clear();
    }
}
/**
 * Avoid sending multiple queries for the same hostname by caching results
 */
export function cache(size) {
    return new CachedAnswers(size);
}
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