ArjLocalHeader.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace SharpCompress.Common.Arj.Headers;

public partial class ArjLocalHeader : ArjHeader
{
    public ArchiveEncoding ArchiveEncoding { get; }
    public long DataStartPosition { get; protected set; }

    public byte ArchiverVersionNumber { get; set; }
    public byte MinVersionToExtract { get; set; }
    public HostOS HostOS { get; set; }
    public CompressionMethod CompressionMethod { get; set; }
    public DosDateTime DateTimeModified { get; set; } = new DosDateTime(0);
    public long CompressedSize { get; set; }
    public long OriginalSize { get; set; }
    public long OriginalCrc32 { get; set; }
    public int FileSpecPosition { get; set; }
    public int FileAccessMode { get; set; }
    public byte FirstChapter { get; set; }
    public byte LastChapter { get; set; }
    public long ExtendedFilePosition { get; set; }
    public DosDateTime? DateTimeAccessed { get; set; }
    public DosDateTime? DateTimeCreated { get; set; }
    public long OriginalSizeEvenForVolumes { get; set; }
    public string Name { get; set; } = string.Empty;
    public string Comment { get; set; } = string.Empty;

    private const byte StdHdrSize = 30;
    private const byte R9HdrSize = 46;

    public ArjLocalHeader(ArchiveEncoding archiveEncoding)
        : base(ArjHeaderType.LocalHeader)
    {
        ArchiveEncoding =
            archiveEncoding ?? throw new ArgumentNullException(nameof(archiveEncoding));
    }

    public override ArjHeader? Read(Stream reader)
    {
        var body = ReadHeader(reader);
        if (body.Length > 0)
        {
            ReadExtendedHeaders(reader);
            var header = LoadFrom(body);
            header.DataStartPosition = reader.Position;
            return header;
        }
        return null;
    }

    // ReadAsync moved to ArjLocalHeader.Async.cs

    public ArjLocalHeader LoadFrom(byte[] headerBytes)
    {
        int offset = 0;

        int ReadInt16()
        {
            if (offset + 1 >= headerBytes.Length)
            {
                throw new IncompleteArchiveException("Unexpected end of stream.");
            }
            var v = headerBytes[offset] & 0xFF | (headerBytes[offset + 1] & 0xFF) << 8;
            offset += 2;
            return v;
        }
        long ReadInt32()
        {
            if (offset + 3 >= headerBytes.Length)
            {
                throw new IncompleteArchiveException("Unexpected end of stream.");
            }
            long v =
                headerBytes[offset] & 0xFF
                | (headerBytes[offset + 1] & 0xFF) << 8
                | (headerBytes[offset + 2] & 0xFF) << 16
                | (headerBytes[offset + 3] & 0xFF) << 24;
            offset += 4;
            return v;
        }

        byte headerSize = headerBytes[offset++];
        ArchiverVersionNumber = headerBytes[offset++];
        MinVersionToExtract = headerBytes[offset++];
        HostOS hostOS = (HostOS)headerBytes[offset++];
        Flags = headerBytes[offset++];
        CompressionMethod = CompressionMethodFromByte(headerBytes[offset++]);
        FileType = FileTypeFromByte(headerBytes[offset++]);

        offset++; // Skip 1 byte

        var rawTimestamp = ReadInt32();
        DateTimeModified = rawTimestamp != 0 ? new DosDateTime(rawTimestamp) : new DosDateTime(0);

        CompressedSize = ReadInt32();
        OriginalSize = ReadInt32();
        OriginalCrc32 = ReadInt32();
        FileSpecPosition = ReadInt16();
        FileAccessMode = ReadInt16();

        FirstChapter = headerBytes[offset++];
        LastChapter = headerBytes[offset++];

        ExtendedFilePosition = 0;
        OriginalSizeEvenForVolumes = 0;

        if (headerSize > StdHdrSize)
        {
            ExtendedFilePosition = ReadInt32();

            if (headerSize >= R9HdrSize)
            {
                rawTimestamp = ReadInt32();
                DateTimeAccessed = rawTimestamp != 0 ? new DosDateTime(rawTimestamp) : null;
                rawTimestamp = ReadInt32();
                DateTimeCreated = rawTimestamp != 0 ? new DosDateTime(rawTimestamp) : null;
                OriginalSizeEvenForVolumes = ReadInt32();
            }
        }

        Name = Encoding.ASCII.GetString(
            headerBytes,
            offset,
            Array.IndexOf(headerBytes, (byte)0, offset) - offset
        );
        offset += Name.Length + 1;

        Comment = Encoding.ASCII.GetString(
            headerBytes,
            offset,
            Array.IndexOf(headerBytes, (byte)0, offset) - offset
        );
        offset += Comment.Length + 1;

        return this;
    }

    public static CompressionMethod CompressionMethodFromByte(byte value)
    {
        return value switch
        {
            0 => CompressionMethod.Stored,
            1 => CompressionMethod.CompressedMost,
            2 => CompressionMethod.Compressed,
            3 => CompressionMethod.CompressedFaster,
            4 => CompressionMethod.CompressedFastest,
            8 => CompressionMethod.NoDataNoCrc,
            9 => CompressionMethod.NoData,
            _ => CompressionMethod.Unknown,
        };
    }
}