const LRUCache = require('lru-cache') const dns = require('dns') const defaultOptions = exports.defaultOptions = { family: undefined, hints: dns.ADDRCONFIG, all: false, verbatim: undefined, } const lookupCache = exports.lookupCache = new LRUCache({ max: 50 }) // this is a factory so that each request can have its own opts (i.e. ttl) // while still sharing the cache across all requests exports.getLookup = (dnsOptions) => { return (hostname, options, callback) => { if (typeof options === 'function') { callback = options options = null } else if (typeof options === 'number') { options = { family: options } } options = { ...defaultOptions, ...options } const key = JSON.stringify({ hostname, family: options.family, hints: options.hints, all: options.all, verbatim: options.verbatim, }) if (lookupCache.has(key)) { const [address, family] = lookupCache.get(key) process.nextTick(callback, null, address, family) return } dnsOptions.lookup(hostname, options, (err, address, family) => { if (err) { return callback(err) } lookupCache.set(key, [address, family], { ttl: dnsOptions.ttl }) return callback(null, address, family) }) } }