something is working

node_modules/mongodb/src/sdam/srv_polling.ts

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+import * as dns from 'dns';
+import { clearTimeout, setTimeout } from 'timers';
+
+import { MongoRuntimeError } from '../error';
+import { Logger, LoggerOptions } from '../logger';
+import { TypedEventEmitter } from '../mongo_types';
+import { HostAddress } from '../utils';
+
+/**
+ * Determines whether a provided address matches the provided parent domain in order
+ * to avoid certain attack vectors.
+ *
+ * @param srvAddress - The address to check against a domain
+ * @param parentDomain - The domain to check the provided address against
+ * @returns Whether the provided address matches the parent domain
+ */
+function matchesParentDomain(srvAddress: string, parentDomain: string): boolean {
+  const regex = /^.*?\./;
+  const srv = `.${srvAddress.replace(regex, '')}`;
+  const parent = `.${parentDomain.replace(regex, '')}`;
+  return srv.endsWith(parent);
+}
+
+/**
+ * @internal
+ * @category Event
+ */
+export class SrvPollingEvent {
+  srvRecords: dns.SrvRecord[];
+  constructor(srvRecords: dns.SrvRecord[]) {
+    this.srvRecords = srvRecords;
+  }
+
+  hostnames(): Set<string> {
+    return new Set(this.srvRecords.map(r => HostAddress.fromSrvRecord(r).toString()));
+  }
+}
+
+/** @internal */
+export interface SrvPollerOptions extends LoggerOptions {
+  srvServiceName: string;
+  srvMaxHosts: number;
+  srvHost: string;
+  heartbeatFrequencyMS: number;
+}
+
+/** @internal */
+export type SrvPollerEvents = {
+  srvRecordDiscovery(event: SrvPollingEvent): void;
+};
+
+/** @internal */
+export class SrvPoller extends TypedEventEmitter<SrvPollerEvents> {
+  srvHost: string;
+  rescanSrvIntervalMS: number;
+  heartbeatFrequencyMS: number;
+  logger: Logger;
+  haMode: boolean;
+  generation: number;
+  srvMaxHosts: number;
+  srvServiceName: string;
+  _timeout?: NodeJS.Timeout;
+
+  /** @event */
+  static readonly SRV_RECORD_DISCOVERY = 'srvRecordDiscovery' as const;
+
+  constructor(options: SrvPollerOptions) {
+    super();
+
+    if (!options || !options.srvHost) {
+      throw new MongoRuntimeError('Options for SrvPoller must exist and include srvHost');
+    }
+
+    this.srvHost = options.srvHost;
+    this.srvMaxHosts = options.srvMaxHosts ?? 0;
+    this.srvServiceName = options.srvServiceName ?? 'mongodb';
+    this.rescanSrvIntervalMS = 60000;
+    this.heartbeatFrequencyMS = options.heartbeatFrequencyMS ?? 10000;
+    this.logger = new Logger('srvPoller', options);
+
+    this.haMode = false;
+    this.generation = 0;
+
+    this._timeout = undefined;
+  }
+
+  get srvAddress(): string {
+    return `_${this.srvServiceName}._tcp.${this.srvHost}`;
+  }
+
+  get intervalMS(): number {
+    return this.haMode ? this.heartbeatFrequencyMS : this.rescanSrvIntervalMS;
+  }
+
+  start(): void {
+    if (!this._timeout) {
+      this.schedule();
+    }
+  }
+
+  stop(): void {
+    if (this._timeout) {
+      clearTimeout(this._timeout);
+      this.generation += 1;
+      this._timeout = undefined;
+    }
+  }
+
+  schedule(): void {
+    if (this._timeout) {
+      clearTimeout(this._timeout);
+    }
+
+    this._timeout = setTimeout(() => this._poll(), this.intervalMS);
+  }
+
+  success(srvRecords: dns.SrvRecord[]): void {
+    this.haMode = false;
+    this.schedule();
+    this.emit(SrvPoller.SRV_RECORD_DISCOVERY, new SrvPollingEvent(srvRecords));
+  }
+
+  failure(message: string, obj?: NodeJS.ErrnoException): void {
+    this.logger.warn(message, obj);
+    this.haMode = true;
+    this.schedule();
+  }
+
+  parentDomainMismatch(srvRecord: dns.SrvRecord): void {
+    this.logger.warn(
+      `parent domain mismatch on SRV record (${srvRecord.name}:${srvRecord.port})`,
+      srvRecord
+    );
+  }
+
+  _poll(): void {
+    const generation = this.generation;
+    dns.resolveSrv(this.srvAddress, (err, srvRecords) => {
+      if (generation !== this.generation) {
+        return;
+      }
+
+      if (err) {
+        this.failure('DNS error', err);
+        return;
+      }
+
+      const finalAddresses: dns.SrvRecord[] = [];
+      for (const record of srvRecords) {
+        if (matchesParentDomain(record.name, this.srvHost)) {
+          finalAddresses.push(record);
+        } else {
+          this.parentDomainMismatch(record);
+        }
+      }
+
+      if (!finalAddresses.length) {
+        this.failure('No valid addresses found at host');
+        return;
+      }
+
+      this.success(finalAddresses);
+    });
+  }
+}