How to obtain the target of a symbolic link (or Reparse Point) using .Net?

Question

In .NET, I think I can determine if a file is a symbolic link by calling System.IO.File.GetAttributes(), and checking for the ReparsePoint bit. like so:

var a = System.IO.File.GetAttributes(fileName);
if ((a & FileAttributes.ReparsePoint) != 0)
{
    // it's a symlink
}

How can I obtain the target of the symbolic link, in this case?

ps: I know how to create a symbolic link. It requires P/Invoke:

[Interop.DllImport("kernel32.dll", EntryPoint="CreateSymbolicLinkW", CharSet=Interop.CharSet.Unicode)] 
public static extern int CreateSymbolicLink(string lpSymlinkFileName, string lpTargetFileName, int dwFlags);

score 17 · Answer 1 · answered Nov 02 '15 at 21:41

Based on the answer that mentioned GetFinalPathNameByHandle here is the C# code that does this (since all other answers were just pointers):

Usage

var path = NativeMethods.GetFinalPathName(@"c:\link");

Code:

public static class NativeMethods
{
    private static readonly IntPtr INVALID_HANDLE_VALUE = new IntPtr(-1);

    private const uint FILE_READ_EA = 0x0008;
    private const uint FILE_FLAG_BACKUP_SEMANTICS = 0x2000000;

    [DllImport("Kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
    static extern uint GetFinalPathNameByHandle(IntPtr hFile, [MarshalAs(UnmanagedType.LPTStr)] StringBuilder lpszFilePath, uint cchFilePath, uint dwFlags);

    [DllImport("kernel32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool CloseHandle(IntPtr hObject);

    [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    public static extern IntPtr CreateFile(
            [MarshalAs(UnmanagedType.LPTStr)] string filename,
            [MarshalAs(UnmanagedType.U4)] uint access,
            [MarshalAs(UnmanagedType.U4)] FileShare share,
            IntPtr securityAttributes, // optional SECURITY_ATTRIBUTES struct or IntPtr.Zero
            [MarshalAs(UnmanagedType.U4)] FileMode creationDisposition,
            [MarshalAs(UnmanagedType.U4)] uint flagsAndAttributes,
            IntPtr templateFile);

    public static string GetFinalPathName(string path)
    {
        var h = CreateFile(path, 
            FILE_READ_EA, 
            FileShare.ReadWrite | FileShare.Delete, 
            IntPtr.Zero, 
            FileMode.Open, 
            FILE_FLAG_BACKUP_SEMANTICS,
            IntPtr.Zero);
        if (h == INVALID_HANDLE_VALUE)
            throw new Win32Exception();

        try
        {
            var sb = new StringBuilder(1024);
            var res = GetFinalPathNameByHandle(h, sb, 1024, 0);
            if (res == 0)
                throw new Win32Exception();

            return sb.ToString();
        }
        finally
        {
            CloseHandle(h);
        }
    }
}

I think (but I have not tested) but you may be able to simplify your code using a .NET FileStream object then using `var h = yourStream.SafeFileHandle.DangerousGetHandle()`, when you close the stream you also release the handle so you don't need to call `CloseHandle(h)` on that variable. You could even make the function take in a `FileStream` instead of a string. — Scott Chamberlain, Nov 02 '15 at 22:03
@ScottChamberlain - the reasons why I did not use FileStream is a) I am not sure if it would pass through the attributes that are not defined in .NET and b) I am not sure if it would work for directories as well (CreateFile does work). Plus this should be faster (though I did not measure it). — Knaģis, Nov 03 '15 at 09:04
If you're like me, the next thing you'll want to know is this: https://stackoverflow.com/questions/31439011/getfinalpathnamebyhandle-without-prepended — datguy, Nov 09 '17 at 18:16
@datguy Are you aware that the paths prepended with `\\?\ ` are actually valid and usable? It also has some benefits (telling Windows to use the Unicode extensions where possible, bypassingthe `MAX_PATH_LENGTH` limit) By all means, strip it for aesthetic reasons, but it's a perfectly valid responsee — Basic, Feb 25 '19 at 18:53
`GetFinalPathNameByHandle` can fail on a volume that did not register with the volume manager, this includes Passmark OSFMount. — Dwedit, Apr 29 '22 at 20:06

score 10 · Accepted Answer · answered Feb 20 '10 at 14:27

10

You have to use DeviceIoControl() and send the FSCTL_GET_REPARSE_POINT control code. The P/Invoke and API usage details are quite gritty, but it Googles really well.

answered Feb 20 '10 at 14:27

Hans Passant

922,412
146
1,693
2,536

1

This led me to the source code for the Powershell Community Extensions (PSCX), which has good code for handling ReparsePoints. – Cheeso Feb 21 '10 at 16:12

score 10 · Answer 3 · answered Jan 18 '22 at 21:03

10

In .NET 6 you can use the property LinkTarget

bool IsLink(string path)
{
    var fi = new FileInfo(path);
    return fi.LinkTarget != null
}

answered Jan 18 '22 at 21:03

Marin

101
1
2

Mark Brackett · Answer 4 · 2019-04-30T12:49:42.590

5

Open the file using CreateFile, and then pass the handle to GetFinalPathNameByHandle.

edited Apr 30 '19 at 12:49

answered Feb 20 '10 at 14:27

Mark Brackett

84,552
17
108
152

1

@Cheeso: symlinks to files debuted in Vista, AFAIK. So, all of the file based symlink functins will have that same restriction. – Mark Brackett Feb 20 '10 at 17:24
2

Reparse points have been around since Win2k; it's only symbolic links to files that debuted in Vista. – Gabe Mar 12 '10 at 02:03
For some reason, I consistently get an Access Violation when calling this method... not sure why – Factor Mystic Jul 20 '14 at 18:32
Regarding Vista, anything is better. – IS4 Sep 03 '17 at 01:38
9 years later, the first link is broken. – Grault Apr 28 '19 at 00:16
1

@Grault - can't find (and don't remember) the Raymond Chen commentary, so updated link to the CreateFile function needed to open – Mark Brackett Apr 30 '19 at 12:50

How to obtain the target of a symbolic link (or Reparse Point) using .Net?

4 Answers4

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