Attachments: support for incrementalMac and chunkSize

Co-authored-by: Scott Nonnenberg <scott@signal.org>

ts/util/DigestingPassThrough.ts

@@ -0,0 +1,52 @@
+// Copyright 2024 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { Transform } from 'stream';
+
+import { DigestingWritable } from '@signalapp/libsignal-client/dist/incremental_mac';
+
+import type { ChunkSizeChoice } from '@signalapp/libsignal-client/dist/incremental_mac';
+
+type CallbackType = (error?: Error | null) => void;
+
+export class DigestingPassThrough extends Transform {
+  private digester: DigestingWritable;
+
+  constructor(key: Buffer, sizeChoice: ChunkSizeChoice) {
+    super();
+    this.digester = new DigestingWritable(key, sizeChoice);
+
+    // We handle errors coming from write/end
+    this.digester.on('error', () => {
+      /* noop */
+    });
+  }
+
+  getFinalDigest(): Buffer {
+    return this.digester.getFinalDigest();
+  }
+
+  public override _transform(
+    data: Buffer,
+    enc: BufferEncoding,
+    callback: CallbackType
+  ): void {
+    this.push(data);
+    this.digester.write(data, enc, err => {
+      if (err) {
+        return callback(err);
+      }
+      callback();
+    });
+  }
+
+  public override _final(callback: CallbackType): void {
+    this.digester.end((err?: Error) => {
+      if (err) {
+        return callback(err);
+      }
+
+      callback();
+    });
+  }
+}