Fallback to dns.resolve4/6 on getaddrinfo failure

ts/util/dns.ts

@@ -0,0 +1,62 @@
+// Copyright 2023 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { lookup as nativeLookup, resolve4, resolve6 } from 'dns';
+import type { LookupOneOptions } from 'dns';
+
+import * as log from '../logging/log';
+import * as Errors from '../types/errors';
+import { strictAssert } from './assert';
+
+export function lookupWithFallback(
+  hostname: string,
+  opts: LookupOneOptions,
+  callback: (
+    err: NodeJS.ErrnoException | null,
+    address: string,
+    family: number
+  ) => void
+): void {
+  // Node.js support various signatures, but we only support one.
+  strictAssert(typeof opts === 'object', 'missing options');
+  strictAssert(Boolean(opts.all) !== true, 'options.all is not supported');
+  strictAssert(typeof callback === 'function', 'missing callback');
+
+  nativeLookup(hostname, opts, (err, ...nativeArgs) => {
+    if (!err) {
+      return callback(err, ...nativeArgs);
+    }
+
+    const family = opts.family === 6 ? 6 : 4;
+
+    log.error(
+      `lookup: failed for ${hostname}, error: ${Errors.toLogFormat(err)}. ` +
+        `Retrying with c-ares (IPv${family})`
+    );
+    const onRecords = (
+      fallbackErr: NodeJS.ErrnoException | null,
+      records: Array<string>
+    ): void => {
+      if (fallbackErr) {
+        return callback(fallbackErr, '', 0);
+      }
+
+      if (!Array.isArray(records) || records.length === 0) {
+        return callback(
+          new Error(`No DNS records returned for: ${hostname}`),
+          '',
+          0
+        );
+      }
+
+      const index = Math.floor(Math.random() * records.length);
+      callback(null, records[index], family);
+    };
+
+    if (family === 4) {
+      resolve4(hostname, onRecords);
+    } else {
+      resolve6(hostname, onRecords);
+    }
+  });
+}