CODEWITHSUNDEEP
c#unixxattr
Salaros
Salaros

Reputation: 1452

C# xattr file attributes

I'm creating a cross-platform software and I want to know if there is any (easy) way to read/write Unix (Mac OSX/Linux) extended file attributes in C#. I've just read about xattr namespaces, but I haven't found any information about C# implementation or bindings of this feature.

P.S. The only thing I found so far is python-xattr library, but I don't want to use it because:

Upvotes: 3

Views: 1015

Answers (3)

Stefan Steiger
Stefan Steiger

Reputation: 82296

You should use the syscalls in Mono.Unix.Native.Syscall.*attr*.
The nuget assembly is called Mono.Posix.NETStandard

Note that the name of the name-value pair is prefixed with a namespace.
According to man 7 xattr

Currently, the security, system, trusted, and user extended attribute classes are defined as described below. Additional classes may be added in the future.

public static void Test()
{
    string path = "/root/Desktop/CppSharp.txt";

    // Mono.Unix.Native.Syscall.getxattr()
    // Mono.Unix.Native.Syscall.fgetxattr()
    // Mono.Unix.Native.Syscall.lgetxattr()

    // Mono.Unix.Native.Syscall.setxattr()
    // Mono.Unix.Native.Syscall.fsetxattr()
    // Mono.Unix.Native.Syscall.lsetxattr

    // Mono.Unix.Native.Syscall.llistxattr()
    // Mono.Unix.Native.Syscall.flistxattr()
    // Mono.Unix.Native.Syscall.llistxattr()

    // Mono.Unix.Native.Syscall.removexattr()
    // Mono.Unix.Native.Syscall.fremovexattr()
    // Mono.Unix.Native.Syscall.lremovexattr()

    if (System.IO.File.Exists(path))
        System.Console.WriteLine("path exists");
    else
        System.Console.WriteLine("path doesn't exists");

    System.Text.Encoding enc = new System.Text.UTF8Encoding(false);
    string[] values = null;

    int setXattrSucceeded = Mono.Unix.Native.Syscall.setxattr(path, "user.foobar",
        enc.GetBytes("Hello World äöüÄÖÜ"), Mono.Unix.Native.XattrFlags.XATTR_CREATE);

    if (setXattrSucceeded == -1)
    {
        Mono.Unix.Native.Errno er = Mono.Unix.Native.Stdlib.GetLastError();
        string message = Mono.Unix.Native.Stdlib.strerror(er);
        // https://stackoverflow.com/questions/12662765/how-can-i-get-error-message-for-errno-value-c-language
        System.Console.WriteLine(message);
    } // End if (setXattrSucceeded == -1)

    byte[] data = null;
    long szLen = Mono.Unix.Native.Syscall.getxattr(path, "user.foobar", out data);

    string value = enc.GetString(data);
    System.Console.WriteLine(value);

    Mono.Unix.Native.Syscall.listxattr(path, System.Text.Encoding.UTF8, out values);
    System.Console.WriteLine(values);

    // https://man7.org/linux/man-pages/man2/getxattr.2.html
} // End Sub TestExtendedAttributes

Upvotes: 2

Salaros
Salaros

Reputation: 1452

The final solution might be the following, tell me what do you think?

FileAttrsManager is an abstract class, used to create 2 derived classes:

  • FileAttrsManagerDos: manages advanced attributes using DSOFile.dll*
  • FileAttrsManagerUnix: manages advanced attributes using IronPython* and python-xattr**

[ * ] http:\\www.microsoft.com/download/en/details.aspx?displaylang=en&id=8422
[ ** ] http:\\ironpython.codeplex.com
[ ** * ] http:\\pypi.python.org/pypi/xatt

Extended attributes operation (such as SetPropery(string key, object value) and GetProperty(string key) etc) will be managed in a static class (FileAttrsProvider) that initializes a FileAttrsManager object to one of two derived types i.e.:

public static class FileAttrProvider
{

    private static FileAttrReader _reader = null;

    public static void Initialize()
    {
        switch (Environment.OSVersion.Platform)
        {
            case PlatformID.MacOSX:
            case PlatformID.Unix:
                _reader = new FileAttrReaderUnix();
                break;
            case PlatformID.Win32NT:
                _reader = new FileAttrReaderDos();
                break;
        }
    }
}

While the derived type depends on the environment, the original type is used in order to ensure an automatic dispatch of all the methods call on _reader object).

Upvotes: 0

more
more

Reputation: 1

I think Mono.Unix.Native.Syscall.setxattr would be a better solution, which is in Mono.Posix module.

Upvotes: 0

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