Make finalization part of the stream

ts/test-node/util/finalStream_test.ts

@@ -0,0 +1,40 @@
+// Copyright 2024 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { assert } from 'chai';
+import { Readable } from 'node:stream';
+import { pipeline } from 'node:stream/promises';
+
+import { finalStream } from '../../util/finalStream';
+
+describe('finalStream', () => {
+  it('should invoke callback before pipeline resolves', async () => {
+    let called = false;
+    await pipeline(
+      Readable.from(['abc']),
+      finalStream(async () => {
+        // Forcing next tick
+        await Promise.resolve();
+
+        called = true;
+      })
+    );
+
+    assert.isTrue(called);
+  });
+
+  it('should propagate errors from callback', async () => {
+    await assert.isRejected(
+      pipeline(
+        Readable.from(['abc']),
+        finalStream(async () => {
+          // Forcing next tick
+          await Promise.resolve();
+
+          throw new Error('failure');
+        })
+      ),
+      'failure'
+    );
+  });
+});