From c88f10bac2b9d0ea056d5a4e40db959969dc6e61 Mon Sep 17 00:00:00 2001
From: automated-signal <37887102+automated-signal@users.noreply.github.com>
Date: Tue, 22 Feb 2022 18:39:03 -0800
Subject: [PATCH] Improve conversion between typed arrays

Co-authored-by: Fedor Indutny <79877362+indutny-signal@users.noreply.github.com>
---
 ts/Crypto.ts                    | 7 ++++++-
 ts/test-electron/Crypto_test.ts | 6 ++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/ts/Crypto.ts b/ts/Crypto.ts
index ab4c0d1c9..3a4008d46 100644
--- a/ts/Crypto.ts
+++ b/ts/Crypto.ts
@@ -35,7 +35,12 @@ export type EncryptedAttachment = {
 
 // Generate a number between zero and 16383
 export function generateRegistrationId(): number {
-  const id = new Uint16Array(getRandomBytes(2))[0];
+  const bytes = getRandomBytes(2);
+  const id = new Uint16Array(
+    bytes.buffer,
+    bytes.byteOffset,
+    bytes.byteLength / 2
+  )[0];
 
   // eslint-disable-next-line no-bitwise
   return id & 0x3fff;
diff --git a/ts/test-electron/Crypto_test.ts b/ts/test-electron/Crypto_test.ts
index 79162fafc..8c6d1f464 100644
--- a/ts/test-electron/Crypto_test.ts
+++ b/ts/test-electron/Crypto_test.ts
@@ -165,12 +165,18 @@ describe('Crypto', () => {
 
   describe('generateRegistrationId', () => {
     it('generates an integer between 0 and 16383 (inclusive)', () => {
+      let max = 0;
       for (let i = 0; i < 100; i += 1) {
         const id = generateRegistrationId();
         assert.isAtLeast(id, 0);
         assert.isAtMost(id, 16383);
         assert(Number.isInteger(id));
+
+        max = Math.max(max, id);
       }
+
+      // Probability of this being false is ~ 10^{-181}
+      assert.isAtLeast(max, 0x100);
     });
   });