Use DoH for query fallback

ts/test-node/util/dns_test.ts

@@ -0,0 +1,67 @@
+// Copyright 2023 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { assert } from 'chai';
+import * as sinon from 'sinon';
+
+import { DNSCache } from '../../util/dns';
+import { SECOND } from '../../util/durations';
+
+const NOW = 1680726906000;
+
+describe('dns/DNSCache', () => {
+  let sandbox: sinon.SinonSandbox;
+  let cache: DNSCache;
+  beforeEach(() => {
+    sandbox = sinon.createSandbox();
+    cache = new DNSCache();
+  });
+
+  afterEach(() => {
+    sandbox.restore();
+  });
+
+  it('should cache records and pick a random one', () => {
+    sandbox.useFakeTimers({
+      now: NOW,
+    });
+
+    const result = cache.setAndPick('signal.org', 4, [
+      {
+        data: '10.0.0.1',
+        expiresAt: NOW + SECOND,
+      },
+      {
+        data: '10.0.0.2',
+        expiresAt: NOW + SECOND,
+      },
+    ]);
+
+    assert.oneOf(result, ['10.0.0.1', '10.0.0.2']);
+  });
+
+  it('should invalidate cache after expiration', () => {
+    const clock = sandbox.useFakeTimers({
+      now: NOW,
+    });
+
+    cache.setAndPick('signal.org', 4, [
+      {
+        data: '10.0.0.1',
+        expiresAt: NOW + SECOND,
+      },
+      {
+        data: '10.0.0.2',
+        expiresAt: NOW + 2 * SECOND,
+      },
+    ]);
+
+    assert.oneOf(cache.get('signal.org', 4), ['10.0.0.1', '10.0.0.2']);
+
+    clock.tick(SECOND);
+    assert.strictEqual(cache.get('signal.org', 4), '10.0.0.2');
+
+    clock.tick(SECOND);
+    assert.strictEqual(cache.get('signal.org', 4), undefined);
+  });
+});