New attachment storage system

ts/util/trimPadding.ts

@@ -0,0 +1,26 @@
+// Copyright 2024 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { Transform } from 'node:stream';
+
+/**
+ * Truncates the stream to the target size.
+ */
+export function trimPadding(size: number): Transform {
+  let total = 0;
+  return new Transform({
+    transform(chunk, _encoding, callback) {
+      const chunkSize = chunk.byteLength;
+      const sizeLeft = size - total;
+      if (sizeLeft >= chunkSize) {
+        total += chunkSize;
+        callback(null, chunk);
+      } else if (sizeLeft > 0) {
+        total += sizeLeft;
+        callback(null, chunk.subarray(0, sizeLeft));
+      } else {
+        callback(null, null);
+      }
+    },
+  });
+}