Differential updates

ts/updater/util.ts

@@ -0,0 +1,45 @@
+// Copyright 2022 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { createReadStream } from 'fs';
+import { createHash } from 'crypto';
+
+import * as Errors from '../types/errors';
+
+export type CheckIntegrityResultType = Readonly<
+  | {
+      ok: true;
+      error?: void;
+    }
+  | {
+      ok: false;
+      error: string;
+    }
+>;
+
+export async function checkIntegrity(
+  fileName: string,
+  sha512: string
+): Promise<CheckIntegrityResultType> {
+  try {
+    const hash = createHash('sha512');
+    for await (const chunk of createReadStream(fileName)) {
+      hash.update(chunk);
+    }
+
+    const actualSHA512 = hash.digest('base64');
+    if (sha512 === actualSHA512) {
+      return { ok: true };
+    }
+
+    return {
+      ok: false,
+      error: `Integrity check failure: expected ${sha512}, got ${actualSHA512}`,
+    };
+  } catch (error) {
+    return {
+      ok: false,
+      error: Errors.toLogFormat(error),
+    };
+  }
+}