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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using System.Runtime.InteropServices;
using System.Buffers;
using System.Text;
internal static partial class Interop
{
internal static partial class Sys
{
/// <summary>
/// Takes a path to a symbolic link and attempts to place the link target path into the buffer. If the buffer is too
/// small, the path will be truncated. No matter what, the buffer will not be null terminated.
/// </summary>
/// <param name="path">The path to the symlink</param>
/// <param name="buffer">The buffer to hold the output path</param>
/// <param name="bufferSize">The size of the buffer</param>
/// <returns>
/// Returns the number of bytes placed into the buffer on success; bufferSize if the buffer is too small; and -1 on error.
/// </returns>
[DllImport(Libraries.SystemNative, EntryPoint = "SystemNative_ReadLink", SetLastError = true)]
private static extern unsafe int ReadLink(string path, byte[] buffer, int bufferSize);
/// <summary>
/// Takes a path to a symbolic link and returns the link target path.
/// </summary>
/// <param name="path">The path to the symlink</param>
/// <returns>
/// Returns the link to the target path on success; and null otherwise.
/// </returns>
public static string ReadLink(string path)
{
int bufferSize = 256;
do
{
byte[] buffer = ArrayPool<byte>.Shared.Rent(bufferSize);
try
{
int resultLength = Interop.Sys.ReadLink(path, buffer, buffer.Length);
if (resultLength < 0)
{
// error
return null;
}
else if (resultLength < buffer.Length)
{
// success
return Encoding.UTF8.GetString(buffer, 0, resultLength);
}
}
finally
{
ArrayPool<byte>.Shared.Return(buffer);
}
// buffer was too small, loop around again and try with a larger buffer.
bufferSize *= 2;
} while (true);
}
}
}
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