const dns = require('dns'), Logger = require('./Logger'), util = require('util'), dnsLookupAsync = util.promisify(dns.lookup), dnsResolveAsync = util.promisify(dns.resolve), punycode = require('punycode'); class DnsResolver { /** * @param {Logger} logger */ constructor(logger) { this.logger = logger; } isIp(host) { return !!host.match(/\d+\.\d+\.\d+\.\d+/); } /** * Response port will only be present if srv record was involved. * @param {string} host * @param {string=} srvRecordPrefix * @returns {Promise<{address:string, port:number=}>} */ async resolve(host, srvRecordPrefix) { this.logger.debug("DNS Lookup: " + host); if(this.isIp(host)) { this.logger.debug("Raw IP Address: " + host); return {address: host}; } const asciiForm = punycode.toASCII(host); if (asciiForm !== host) { this.logger.debug("Encoded punycode: " + host + " -> " + asciiForm); host = asciiForm; } if (srvRecordPrefix) { this.logger.debug("SRV Resolve: " + srvRecordPrefix + '.' + host); let records; try { records = await dnsResolveAsync(srvRecordPrefix + '.' + host, 'SRV'); if (records.length >= 1) { this.logger.debug("Found SRV Records: ", records); const record = records[0]; const srvPort = record.port; const srvHost = record.name; if (srvHost === host) { throw new Error('Loop in DNS SRV records'); } return { port: srvPort, ...await this.resolve(srvHost, srvRecordPrefix) }; } this.logger.debug("No SRV Record"); } catch (e) { this.logger.debug(e); } } this.logger.debug("Standard Resolve: " + host); const dnsResult = await dnsLookupAsync(host); // For some reason, this sometimes returns a string address rather than an object. // I haven't been able to reproduce, but it's been reported on the issue tracker. let address; if (typeof dnsResult === 'string') { address = dnsResult; } else { address = dnsResult.address; } this.logger.debug("Found address: " + address); return {address: address}; } } module.exports = DnsResolver;