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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,113 @@ | ||
| import { createPromise, IResolvablePromise } from '@secret-agent/commons/utils'; | ||
| import Log from '@secret-agent/commons/Logger'; | ||
| import { ConnectionOptions } from 'tls'; | ||
| import moment from 'moment'; | ||
| import net from 'net'; | ||
| import DnsOverTlsSocket from './DnsOverTlsSocket'; | ||
| import RequestSession from '../handlers/RequestSession'; | ||
|
|
||
| const { log } = Log(module); | ||
|
|
||
| export class Dns { | ||
| public socket: DnsOverTlsSocket; | ||
| public dnsEntries = new Map<string, IResolvablePromise<IDnsEntry>>(); | ||
| private readonly dnsServer: ConnectionOptions; | ||
|
|
||
| constructor(readonly requestSession?: RequestSession) { | ||
| this.dnsServer = requestSession?.delegate?.dnsOverTlsConnectOptions; | ||
| } | ||
|
|
||
| public async lookupIp(host: string, retries = 3) { | ||
| if (!this.dnsServer || host === 'localhost' || net.isIP(host)) return host; | ||
|
|
||
| try { | ||
| // get cached (or in process resolver) | ||
| const cachedRecord = await this.getNextCachedARecord(host); | ||
| if (cachedRecord) return cachedRecord.ip; | ||
| } catch (error) { | ||
| if (retries === 0) throw error; | ||
| // if the cache lookup failed, likely because another lookup failed... try again | ||
| return this.lookupIp(host, retries - 1); | ||
| } | ||
|
|
||
| // if not found in cache, perform dns lookup | ||
| try { | ||
| const dnsEntry = await this.lookupDnsEntry(host); | ||
| return this.nextIp(dnsEntry); | ||
| } catch (error) { | ||
| log.error('DnsLookup.Error', { | ||
| sessionId: this.requestSession.sessionId, | ||
| error, | ||
| }); | ||
| // fallback to host | ||
| return host; | ||
| } | ||
| } | ||
|
|
||
| public close() { | ||
| this.socket?.close(); | ||
| } | ||
|
|
||
| private async lookupDnsEntry(host: string) { | ||
| const existing = this.dnsEntries.get(host); | ||
| if (existing && !existing.isResolved) return existing.promise; | ||
|
|
||
| try { | ||
| const dnsEntry = createPromise<IDnsEntry>(); | ||
| this.dnsEntries.set(host, dnsEntry); | ||
|
|
||
| if (!this.socket?.isActive) { | ||
| this.socket = new DnsOverTlsSocket( | ||
| this.dnsServer, | ||
| this.requestSession, | ||
| () => (this.socket = null), | ||
| ); | ||
| } | ||
|
|
||
| const response = await this.socket.lookupARecords(host); | ||
|
|
||
| const entry = <IDnsEntry>{ | ||
| aRecords: response.answers | ||
| .filter(x => x.type === 'A') // gives non-query records sometimes | ||
| .map(x => ({ | ||
| ip: x.data, | ||
| expiry: moment() | ||
| .add(x.ttl, 'seconds') | ||
| .toDate(), | ||
| })), | ||
| }; | ||
| dnsEntry.resolve(entry); | ||
| return entry; | ||
| } catch (error) { | ||
| this.dnsEntries.get(host)?.reject(error); | ||
| this.dnsEntries.delete(host); | ||
| throw error; | ||
| } | ||
| } | ||
|
|
||
| private nextIp(dnsEntry: IDnsEntry) { | ||
| // implement rotating | ||
| for (let i = 0; i < dnsEntry.aRecords.length; i += 1) { | ||
| const record = dnsEntry.aRecords[i]; | ||
| if (record.expiry > new Date()) { | ||
| // move record to back | ||
| dnsEntry.aRecords.splice(i, 1); | ||
| dnsEntry.aRecords.push(record); | ||
| return record; | ||
| } | ||
| } | ||
| return null; | ||
| } | ||
|
|
||
| private async getNextCachedARecord(name: string) { | ||
| const cached = await this.dnsEntries.get(name)?.promise; | ||
| if (cached?.aRecords?.length) { | ||
| return this.nextIp(cached); | ||
| } | ||
| return null; | ||
| } | ||
| } | ||
|
|
||
| interface IDnsEntry { | ||
| aRecords: { ip: string; expiry: Date }[]; | ||
| } |
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