Aaru/Aaru.Filesystems/FAT/Xattr.cs

// /***************************************************************************
// Aaru Data Preservation Suite
// ----------------------------------------------------------------------------
//
// Filename       : Xattr.cs
// Author(s)      : Natalia Portillo <claunia@claunia.com>
//
// Component      : Microsoft FAT filesystem plugin.
//
// --[ Description ] ----------------------------------------------------------
//
//     Methods to handle Microsoft FAT extended attributes.
//
// --[ License ] --------------------------------------------------------------
//
//     This library is free software; you can redistribute it and/or modify
//     it under the terms of the GNU Lesser General Public License as
//     published by the Free Software Foundation; either version 2.1 of the
//     License, or (at your option) any later version.
//
//     This library 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
//     Lesser General Public License for more details.
//
//     You should have received a copy of the GNU Lesser General Public
//     License along with this library; if not, see <http://www.gnu.org/licenses/>.
//
// ----------------------------------------------------------------------------
// Copyright © 2011-2020 Natalia Portillo
// ****************************************************************************/

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using Aaru.CommonTypes.Structs;
using Aaru.Helpers;

namespace Aaru.Filesystems.FAT
{
    public partial class FAT
    {
        Dictionary<string, Dictionary<string, byte[]>> eaCache;

        /// <inheritdoc />
        public Errno ListXAttr(string path, out List<string> xattrs)
        {
            xattrs = null;

            if(!mounted)
                return Errno.AccessDenied;

            // No other xattr recognized yet
            if(cachedEaData is null &&
               !fat32)
                return Errno.NotSupported;

            if(path[0] == '/')
                path = path.Substring(1);

            if(eaCache.TryGetValue(path.ToLower(cultureInfo), out Dictionary<string, byte[]> eas))
            {
                xattrs = eas.Keys.ToList();

                return Errno.NoError;
            }

            Errno err = GetFileEntry(path, out CompleteDirectoryEntry entry);

            if(err != Errno.NoError ||
               entry is null)
                return err;

            xattrs = new List<string>();

            if(!fat32)
            {
                if(entry.Dirent.ea_handle == 0)
                    return Errno.NoError;

                eas = GetEas(entry.Dirent.ea_handle);
            }
            else
            {
                if(entry.Fat32Ea.start_cluster == 0)
                    return Errno.NoError;

                eas = GetEas(entry.Fat32Ea);
            }

            if(eas is null)
                return Errno.NoError;

            eaCache.Add(path.ToLower(cultureInfo), eas);
            xattrs = eas.Keys.ToList();

            return Errno.NoError;
        }

        /// <inheritdoc />
        public Errno GetXattr(string path, string xattr, ref byte[] buf)
        {
            if(!mounted)
                return Errno.AccessDenied;

            Errno err = ListXAttr(path, out List<string> xattrs);

            if(err != Errno.NoError)
                return err;

            if(path[0] == '/')
                path = path.Substring(1);

            if(!xattrs.Contains(xattr.ToLower(cultureInfo)))
                return Errno.NoSuchExtendedAttribute;

            if(!eaCache.TryGetValue(path.ToLower(cultureInfo), out Dictionary<string, byte[]> eas))
                return Errno.InvalidArgument;

            if(!eas.TryGetValue(xattr.ToLower(cultureInfo), out byte[] data))
                return Errno.InvalidArgument;

            buf = new byte[data.Length];
            data.CopyTo(buf, 0);

            return Errno.NoError;
        }

        Dictionary<string, byte[]> GetEas(DirectoryEntry entryFat32Ea)
        {
            var    eaMs                  = new MemoryStream();
            uint[] rootDirectoryClusters = GetClusters(entryFat32Ea.start_cluster);

            foreach(uint cluster in rootDirectoryClusters)
            {
                byte[] buffer =
                    image.ReadSectors(firstClusterSector + (cluster * sectorsPerCluster), sectorsPerCluster);

                eaMs.Write(buffer, 0, buffer.Length);
            }

            byte[] full = eaMs.ToArray();
            ushort size = BitConverter.ToUInt16(full, 0);
            byte[] eas  = new byte[size];
            Array.Copy(full, 0, eas, 0, size);

            full = null;
            eaMs.Close();

            return GetEas(eas);
        }

        Dictionary<string, byte[]> GetEas(ushort eaHandle)
        {
            int aIndex = eaHandle >> 7;

            // First 0x20 bytes are the magic number and unused words
            ushort a = BitConverter.ToUInt16(cachedEaData, (aIndex * 2) + 0x20);

            ushort b = BitConverter.ToUInt16(cachedEaData, (eaHandle * 2) + 0x200);

            uint eaCluster = (uint)(a + b);

            if(b == EA_UNUSED)
                return null;

            EaHeader header =
                Marshal.ByteArrayToStructureLittleEndian<EaHeader>(cachedEaData, (int)(eaCluster * bytesPerCluster),
                                                                   Marshal.SizeOf<EaHeader>());

            if(header.magic != 0x4145)
                return null;

            uint eaLen = BitConverter.ToUInt32(cachedEaData,
                                               (int)(eaCluster * bytesPerCluster) + Marshal.SizeOf<EaHeader>());

            byte[] eaData = new byte[eaLen];
            Array.Copy(cachedEaData, (int)(eaCluster * bytesPerCluster) + Marshal.SizeOf<EaHeader>(), eaData, 0, eaLen);

            return GetEas(eaData);
        }

        Dictionary<string, byte[]> GetEas(byte[] eaData)
        {
            if(eaData is null ||
               eaData.Length < 4)
                return null;

            Dictionary<string, byte[]> eas = new Dictionary<string, byte[]>();

            if(debug)
                eas.Add("com.microsoft.os2.fea", eaData);

            int pos = 4;

            while(pos < eaData.Length)
            {
                pos++; // Skip fEA
                byte   cbName  = eaData[pos++];
                ushort cbValue = BitConverter.ToUInt16(eaData, pos);
                pos += 2;

                string name = Encoding.ASCII.GetString(eaData, pos, cbName);
                pos += cbName;
                pos++;
                byte[] data = new byte[cbValue];

                Array.Copy(eaData, pos, data, 0, cbValue);
                pos += cbValue;

                // OS/2 System Attributes
                if(name[0] == '.')
                {
                    // This is WorkPlace System information so it's IBM
                    if(name == ".CLASSINFO")
                        name = "com.ibm.os2.classinfo";
                    else
                        name = "com.microsoft.os2" + name.ToLower();
                }

                eas.Add(name, data);
            }

            return eas;
        }

        void CacheEaData()
        {
            if(eaDirEntry.start_cluster == 0)
                return;

            var eaDataMs = new MemoryStream();

            foreach(byte[] buffer in GetClusters(eaDirEntry.start_cluster).
                Select(cluster => image.ReadSectors(firstClusterSector + (cluster * sectorsPerCluster),
                                                    sectorsPerCluster)))
                eaDataMs.Write(buffer, 0, buffer.Length);

            cachedEaData = eaDataMs.ToArray();
        }
    }
}