From 12859761b9d46b14e7f33c7433ddd3e991709a54 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=96mer=20Sinan=20A=C4=9Facan?= <omersa@google.com>
Date: Tue, 12 Mar 2024 21:26:51 +0000
Subject: [PATCH] [dart2wasm] Implement `_SecureRandom._getBytes`
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This only changes `_SecureRandom._getBytes` to make the rest of the code
work. Implementation is currently slow: for each random number
generation, it allocates one JS `Uint8Array`, and because we can't
directly read from a JS `Uint8Array` using `dart:js_interop`, a Dart
`Uint8List` wrapper for it. We can optimize separately.

Fixes #55031.

Fixes test lib/math/random_secure_test on browsers. The test keeps
failing in d8 as d8 doesn't define the `crypto` object.

Change-Id: I9d6bbd1bb576c0d0b7206cb2939ee65d987ec297
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/356040
Commit-Queue: Ömer Ağacan <omersa@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>
---
 sdk/lib/_internal/wasm/lib/math_patch.dart | 46 +++++++++++++++++++---
 1 file changed, 40 insertions(+), 6 deletions(-)

diff --git a/sdk/lib/_internal/wasm/lib/math_patch.dart b/sdk/lib/_internal/wasm/lib/math_patch.dart
index 29baa39409e..2da7af66ccd 100644
--- a/sdk/lib/_internal/wasm/lib/math_patch.dart
+++ b/sdk/lib/_internal/wasm/lib/math_patch.dart
@@ -2,9 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import "dart:_internal" show mix64, patch;
-
-import "dart:typed_data" show Uint32List;
+import "dart:_internal" show mix64, patch, unsafeCast;
+import "dart:_js_types" show JSUint8ArrayImpl;
+import "dart:js_interop";
 
 /// There are no parts of this patch library.
 
@@ -236,19 +236,53 @@ class _Random implements Random {
   }
 }
 
+@JS('crypto')
+external _JSCrypto get _jsCryptoGetter;
+
+final _JSCrypto _jsCrypto = _jsCryptoGetter;
+
+extension type _JSCrypto._(JSObject _jsCrypto) implements JSObject {}
+
+extension _JSCryptoGetRandomValues on _JSCrypto {
+  @JS('getRandomValues')
+  external void getRandomValues(JSUint8Array array);
+}
+
+@JS('Uint8Array')
+extension type _JSUint8Array(JSObject _) {
+  external factory _JSUint8Array.create(int length);
+}
+
 class _SecureRandom implements Random {
+  final JSUint8ArrayImpl _buffer = unsafeCast<JSUint8ArrayImpl>(
+      (_JSUint8Array.create(8) as JSUint8Array).toDart);
+
   _SecureRandom() {
     // Throw early in constructor if entropy source is not hooked up.
     _getBytes(1);
   }
 
-  // Return count bytes of entropy as a positive integer; count <= 8.
-  external static int _getBytes(int count);
+  // Return count bytes of entropy as an integer; count <= 8.
+  int _getBytes(int count) {
+    final JSUint8ArrayImpl bufferView =
+        JSUint8ArrayImpl.view(_buffer.buffer, 0, count);
+
+    final JSUint8Array bufferViewJS = bufferView.toJS;
+    _jsCrypto.getRandomValues(bufferViewJS);
+
+    int value = 0;
+    for (int i = 0; i < count; i += 1) {
+      value = (value << 8) | bufferView[i];
+    }
+
+    return value;
+  }
 
   int nextInt(int max) {
     RangeError.checkValueInInterval(
         max, 1, _POW2_32, "max", "Must be positive and <= 2^32");
-    final byteCount = ((max - 1).bitLength + 7) >> 3;
+    final byteCount =
+        ((max - 1).bitLength + 7) >> 3; // Divide number of bits by 8, round up.
     if (byteCount == 0) {
       return 0; // Not random if max == 1.
     }