node: Move TypeScript source files into ts/ directory

This way, files that reference the non-compiled Native.js/.d.ts can
consistently refer to it as '../Native' without having to copy
anything around.

node/ts/zkgroup/internal/ByteArray.ts

@@ -0,0 +1,37 @@
+//
+// Copyright 2020-2021 Signal Messenger, LLC.
+// SPDX-License-Identifier: AGPL-3.0-only
+//
+
+import { SignalClientErrorBase } from '../../Errors';
+
+export default class ByteArray {
+  contents: Buffer;
+
+  constructor(contents: Buffer, checkValid: (contents: Buffer) => void) {
+    checkValid(contents);
+    this.contents = Buffer.from(contents);
+  }
+
+  protected static checkLength(
+    expectedLength: number
+  ): (contents: Buffer) => void {
+    return contents => {
+      if (contents.length !== expectedLength) {
+        throw new SignalClientErrorBase(
+          `Length of array supplied was ${contents.length} expected ${expectedLength}`,
+          undefined,
+          this.name
+        );
+      }
+    };
+  }
+
+  public getContents(): Buffer {
+    return this.contents;
+  }
+
+  public serialize(): Buffer {
+    return Buffer.from(this.contents);
+  }
+}