Check if a file is real or a symbolic link

c#, symlink

Solution

I have some source code for symlinks posted on my blog that will allow you to:

- create symlinks

- check whether a path is a symlink

- retrieve the target of a symlink

It also contains NUnit test cases, that you may wish to extend.

The meaty bit is:

private static SafeFileHandle getFileHandle(string path)
{
    return CreateFile(path, genericReadAccess, shareModeAll, IntPtr.Zero, openExisting,
        fileFlagsForOpenReparsePointAndBackupSemantics, IntPtr.Zero);
}

public static string GetTarget(string path)
{
    SymbolicLinkReparseData reparseDataBuffer;

    using (SafeFileHandle fileHandle = getFileHandle(path))
    {
        if (fileHandle.IsInvalid)
        {
            Marshal.ThrowExceptionForHR(Marshal.GetHRForLastWin32Error());
        }

        int outBufferSize = Marshal.SizeOf(typeof(SymbolicLinkReparseData));
        IntPtr outBuffer = IntPtr.Zero;
        try
        {
            outBuffer = Marshal.AllocHGlobal(outBufferSize);
            int bytesReturned;
            bool success = DeviceIoControl(
                fileHandle.DangerousGetHandle(), ioctlCommandGetReparsePoint, IntPtr.Zero, 0,
                outBuffer, outBufferSize, out bytesReturned, IntPtr.Zero);

            fileHandle.Close();

            if (!success)
            {
                if (((uint)Marshal.GetHRForLastWin32Error()) == pathNotAReparsePointError)
                {
                    return null;
                }
                Marshal.ThrowExceptionForHR(Marshal.GetHRForLastWin32Error());
            }

            reparseDataBuffer = (SymbolicLinkReparseData)Marshal.PtrToStructure(
                outBuffer, typeof(SymbolicLinkReparseData));
        }
        finally
        {
            Marshal.FreeHGlobal(outBuffer);
        }
    }
    if (reparseDataBuffer.ReparseTag != symLinkTag)
    {
        return null;
    }

    string target = Encoding.Unicode.GetString(reparseDataBuffer.PathBuffer,
        reparseDataBuffer.PrintNameOffset, reparseDataBuffer.PrintNameLength);

    return target;
}

That is:

- Open the file with `CreateFile()`

- Call `DeviceIoControl()` to get the reparse point data (NOTE: it could be a junction point!)

- Check out the returned data structure to inspect. The reparse tag will tell you if it is a junction point or symbolic link. This may be all you want to do.

Problem

Original source

Related problems

• Find out whether a file is a symbolic link in PowerShell