fix: support authority overrides in the DNS resolver

Author: George Kampitakis

packages/grpc-js/src/resolver-dns.ts

@@ -21,6 +21,7 @@ import {
   registerDefaultScheme,
 } from './resolver';
 import * as dns from 'dns';
+import * as dnsPromises from 'dns/promises';
 import * as util from 'util';
 import { extractAndSelectServiceConfig, ServiceConfig } from './service-config';
 import { Status } from './constants';
@@ -48,7 +49,6 @@ export const DEFAULT_PORT = 443;
 const DEFAULT_MIN_TIME_BETWEEN_RESOLUTIONS_MS = 30_000;
 
 const resolveTxtPromise = util.promisify(dns.resolveTxt);
-const dnsLookupPromise = util.promisify(dns.lookup);
 
 /**
  * Resolver implementation that handles DNS names and IP addresses.
@@ -63,7 +63,7 @@ class DnsResolver implements Resolver {
    * Failures are handled by the backoff timer.
    */
   private readonly minTimeBetweenResolutionsMs: number;
-  private pendingLookupPromise: Promise<dns.LookupAddress[]> | null = null;
+  private pendingLookupPromise: Promise<string[]> | null = null;
   private pendingTxtPromise: Promise<string[][]> | null = null;
   private latestLookupResult: Endpoint[] | null = null;
   private latestServiceConfig: ServiceConfig | null = null;
@@ -76,12 +76,17 @@ class DnsResolver implements Resolver {
   private isNextResolutionTimerRunning = false;
   private isServiceConfigEnabled = true;
   private returnedIpResult = false;
+  private resolver = new dnsPromises.Resolver();
+
   constructor(
     private target: GrpcUri,
     private listener: ResolverListener,
     channelOptions: ChannelOptions
   ) {
     trace('Resolver constructed for target ' + uriToString(target));
+    if (target.authority) {
+      this.resolver.setServers([target.authority]);
+    }
     const hostPort = splitHostPort(target.path);
     if (hostPort === null) {
       this.ipResult = null;
@@ -189,7 +194,7 @@ class DnsResolver implements Resolver {
        * because when looking up a single family, dns.lookup outputs an error
        * if the name exists but there are no records for that family, and that
        * error is indistinguishable from other kinds of errors */
-      this.pendingLookupPromise = dnsLookupPromise(hostname, { all: true });
+      this.pendingLookupPromise = this.resolver.resolve(hostname);
       this.pendingLookupPromise.then(
         addressList => {
           if (this.pendingLookupPromise === null) {
@@ -199,7 +204,7 @@ class DnsResolver implements Resolver {
           this.backoff.reset();
           this.backoff.stop();
           const subchannelAddresses: TcpSubchannelAddress[] = addressList.map(
-            addr => ({ host: addr.address, port: +this.port! })
+            addr => ({ host: addr, port: +this.port! })
           );
           this.latestLookupResult = subchannelAddresses.map(address => ({
             addresses: [address],