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// Copyright (C) 2024 Vaughn Nugent
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.
using System;
using System.Runtime.InteropServices;
using VNLib.Utils.Native;
using VNLib.Utils.Extensions;
namespace VNLib.Utils.Cryptography.Noscrypt.Random
{
/// <summary>
/// A wrapper class for an unmanaged random source that conforms to the <see cref="IRandomSource"/> interface
/// </summary>
public class UnmanagedRandomSource : VnDisposeable, IRandomSource
{
/// <summary>
/// The explicit name of the unmanaged random function to get random bytes
/// </summary>
public const string RngFunctionName = "GetRandomBytes";
unsafe delegate void UnmanagedRandomSourceDelegate(byte* buffer, int size);
private readonly bool OwnsHandle;
private readonly SafeLibraryHandle _library;
private readonly UnmanagedRandomSourceDelegate _getRandomBytes;
/// <summary>
/// Loads the unmanaged random source from the given library
/// and attempts to get the random bytes method <see cref="RngFunctionName"/>
/// </summary>
/// <param name="path"></param>
/// <param name="search"></param>
/// <returns>The wrapped library that conforms to the <see cref="IRandomSource"/></returns>
public static UnmanagedRandomSource LoadLibrary(string path, DllImportSearchPath search)
{
//Try to load the library
SafeLibraryHandle lib = SafeLibraryHandle.LoadLibrary(path, search);
try
{
return new UnmanagedRandomSource(lib, true);
}
catch
{
//release lib
lib.Dispose();
throw;
}
}
/// <summary>
/// Creates the unmanaged random source from the given library
/// </summary>
/// <param name="lib">The library handle to wrap</param>
/// <exception cref="ObjectDisposedException"></exception>
/// <exception cref="EntryPointNotFoundException"></exception>
public UnmanagedRandomSource(SafeLibraryHandle lib, bool ownsHandle)
{
lib.ThrowIfClosed();
_library = lib;
//get the method delegate
_getRandomBytes = lib.DangerousGetFunction<UnmanagedRandomSourceDelegate>(RngFunctionName);
OwnsHandle = ownsHandle;
}
///<inheritdoc/>
public unsafe void GetRandomBytes(Span<byte> buffer)
{
_library.ThrowIfClosed();
//Fix buffer and call unmanaged method
fixed (byte* ptr = &MemoryMarshal.GetReference(buffer))
{
_getRandomBytes(ptr, buffer.Length);
}
}
///<inheritdoc/>
protected override void Free()
{
if (OwnsHandle)
{
_library.Dispose();
}
}
}
}
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