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Add polyfills for RandomNumberGenerator.Fill(...) #73

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Add polyfills for RandomNumberGenerator.Fill(...) #73

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24 changes: 24 additions & 0 deletions PolyShim.Tests/NetCore21/RandomNumberGeneratorTests.cs
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using System;
using System.Security.Cryptography;
using FluentAssertions;
using Xunit;

namespace PolyShim.Tests.NetCore21;

public class RandomNumberGeneratorTests
{
[Fact]
public void Fill_Span_Test()
{
// Arrange
Span<byte> buffer = stackalloc byte[16];

// Act
RandomNumberGenerator.Fill(buffer);

// Assert
// Since cryptographic random data is non-deterministic,
// we can only verify that the buffer contains some non-zero bytes
buffer.ToArray().Should().Contain(b => b != 0);
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Copilot AI Feb 10, 2026

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The test uses stackalloc byte[16], which is not guaranteed to be zero-initialized; the assertion can pass even if RandomNumberGenerator.Fill(...) is a no-op because the stack buffer may already contain non-zero bytes. Initialize the span (e.g., call buffer.Clear() or use a new byte[16]) before invoking Fill so the test actually validates that bytes were written.

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}
}
25 changes: 25 additions & 0 deletions PolyShim/NetCore21/RandomNumberGenerator.cs
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#if (NETCOREAPP && !NETCOREAPP2_1_OR_GREATER) || (NETFRAMEWORK && NET45_OR_GREATER)
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@Tyrrrz Tyrrrz Feb 10, 2026

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This is missing net standard boundaries (up to 2.1)

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Copilot AI Feb 10, 2026

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The compilation guard here is inconsistent with the rest of the NetCore21/* polyfills (which generally include NETSTANDARD && !NETSTANDARD2_1_OR_GREATER and don’t special-case NETFRAMEWORK && NET45_OR_GREATER). As written, this polyfill won’t be included for netstandard2.0 consumers, and it’s unclear why it should be excluded for net35/net40 but not other NetCore21 polyfills. Consider aligning the #if condition with the pattern used in PolyShim/NetCore21/DateTime.cs / Random.cs so the API is polyfilled for the intended TFMs.

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#nullable enable
// ReSharper disable RedundantUsingDirective
// ReSharper disable CheckNamespace
// ReSharper disable InconsistentNaming
// ReSharper disable PartialTypeWithSinglePart

using System;
using System.Security.Cryptography;

internal static partial class PolyfillExtensions
{
extension(RandomNumberGenerator)
{
// https://learn.microsoft.com/dotnet/api/system.security.cryptography.randomnumbergenerator.fill
public static void Fill(Span<byte> data)
{
var buffer = new byte[data.Length];
using var rng = RandomNumberGenerator.Create();
rng.GetBytes(buffer);
buffer.CopyTo(data);
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Copilot AI Feb 10, 2026

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Fill(Span<byte>) always allocates a managed array and creates/disposes a RandomNumberGenerator, even when data.Length == 0. Adding a fast-path return for empty spans would avoid unnecessary allocations/crypto provider creation while preserving behavior.

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}
}
}
#endif
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