update

Author: zhiyuanliang-ms

src/ConfigurationClientManager.ts

@@ -8,6 +8,7 @@ import { AzureAppConfigurationOptions, MaxRetries, MaxRetryDelayInMs } from "./A
 import { isBrowser, isWebWorker } from "./requestTracing/utils.js";
 import * as RequestTracing from "./requestTracing/constants.js";
 import { shuffleList } from "./common/utils.js";
+import { Resolver   } from "dns/promises";
 
 const TCP_ORIGIN_KEY_NAME = "_origin._tcp";
 const ALT_KEY_NAME = "_alt";
@@ -148,7 +149,7 @@ export class ConfigurationClientManager {
         try {
             result = await this.#querySrvTargetHost(host);
         } catch (error) {
-            console.warn(`Failed to build fallback clients, ${error.message}`);
+            console.warn(`Failed to build fallback clients. ${error.message}`);
             return; // swallow the error when srv query fails
         }
 
@@ -173,24 +174,32 @@ export class ConfigurationClientManager {
     }
 
     /**
-     * Queries SRV records for the given host and returns the target hosts.
+     * Query SRV records and return target hosts.
      */
     async #querySrvTargetHost(host: string): Promise<string[]> {
         const results: string[] = [];
 
         try {
             // https://nodejs.org/api/dns.html#dnspromisesresolvesrvhostname
-            const resolver = new this.#dns.Resolver({timeout: DNS_RESOLVER_TIMEOUT, tries: DNS_RESOLVER_TRIES});
+            const resolver = new Resolver({timeout: DNS_RESOLVER_TIMEOUT, tries: DNS_RESOLVER_TRIES});
             // On success, resolveSrv() returns an array of SrvRecord
             // On failure, resolveSrv() throws an error with code 'ENOTFOUND'.
-            const originRecords = await resolver.resolveSrv(`${TCP_ORIGIN_KEY_NAME}.${host}`); // look up SRV records for the origin host
+            const originRecords = await resolver.resolveSrv(`${TCP_ORIGIN_KEY_NAME}.${host}`); // Look up SRV records for the origin host
+            if (originRecords.length === 0) {
+                return results;
+            }
+
+            // Add the first origin record to results
             const originHost = originRecords[0].name;
-            results.push(originHost); // add the first origin record to results
+            results.push(originHost);
 
             let index = 0;
             while (index < MAX_ALTNATIVE_SRV_COUNT) {
-                const currentAlt = `${ALT_KEY_NAME}${index}`; // look up SRV records for alternate hosts
+                const currentAlt = `${ALT_KEY_NAME}${index}`; // Look up SRV records for alternate hosts
                 const altRecords = await resolver.resolveSrv(`${currentAlt}.${TCP_KEY_NAME}.${originHost}`);
+                if (altRecords.length === 0) {
+                    break;
+                }
 
                 altRecords.forEach(record => {
                     const altHost = record.name;
@@ -202,8 +211,7 @@ export class ConfigurationClientManager {
             }
         } catch (err) {
             if (err.code === "ENOTFOUND") {
-                // No more SRV records found, return results.
-                return results;
+                return results; // No more SRV records found, return results
             } else {
                 throw new Error(`Failed to lookup SRV records: ${err.message}`);
             }