ArjHeader.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using SharpCompress.Common.Zip.Headers;
using SharpCompress.Crypto;

namespace SharpCompress.Common.Arj.Headers;

public enum ArjHeaderType
{
    MainHeader,
    LocalHeader,
}

public abstract partial class ArjHeader
{
    private const ushort ARJ_MAGIC = 0xEA60;

    public ArjHeader(ArjHeaderType type)
    {
        ArjHeaderType = type;
    }

    public ArjHeaderType ArjHeaderType { get; }
    public byte Flags { get; set; }
    public FileType FileType { get; set; }

    public abstract ArjHeader? Read(Stream reader);

    // Async methods moved to ArjHeader.Async.cs

    public byte[] ReadHeader(Stream stream)
    {
        // check for magic bytes
        var magic = new byte[2];
        if (stream.Read(magic) != 2)
        {
            return Array.Empty<byte>();
        }

        if (!CheckMagicBytes(magic))
        {
            throw new InvalidFormatException("Not an ARJ file (wrong magic bytes)");
        }

        // read header_size
        byte[] headerBytes = new byte[2];
        stream.Read(headerBytes, 0, 2);
        var headerSize = (ushort)(headerBytes[0] | headerBytes[1] << 8);
        if (headerSize < 1)
        {
            return Array.Empty<byte>();
        }

        var body = new byte[headerSize];
        var read = stream.Read(body, 0, headerSize);
        if (read < headerSize)
        {
            return Array.Empty<byte>();
        }

        byte[] crc = new byte[4];
        read = stream.Read(crc, 0, 4);
        var checksum = Crc32Stream.Compute(body);
        // Compute the hash value
        if (checksum != BitConverter.ToUInt32(crc, 0))
        {
            throw new InvalidFormatException("Header checksum is invalid");
        }
        return body;
    }

    // ReadHeaderAsync moved to ArjHeader.Async.cs

    protected List<byte[]> ReadExtendedHeaders(Stream reader)
    {
        List<byte[]> extendedHeader = new List<byte[]>();
        byte[] buffer = new byte[2];

        while (true)
        {
            int bytesRead = reader.Read(buffer, 0, 2);
            if (bytesRead < 2)
            {
                throw new IncompleteArchiveException(
                    "Unexpected end of stream while reading extended header size."
                );
            }

            var extHeaderSize = (ushort)(buffer[0] | (buffer[1] << 8));
            if (extHeaderSize == 0)
            {
                return extendedHeader;
            }

            byte[] header = new byte[extHeaderSize];
            bytesRead = reader.Read(header, 0, extHeaderSize);
            if (bytesRead < extHeaderSize)
            {
                throw new IncompleteArchiveException(
                    "Unexpected end of stream while reading extended header data."
                );
            }

            byte[] crc = new byte[4];
            bytesRead = reader.Read(crc, 0, 4);
            if (bytesRead < 4)
            {
                throw new IncompleteArchiveException(
                    "Unexpected end of stream while reading extended header CRC."
                );
            }

            var checksum = Crc32Stream.Compute(header);
            if (checksum != BitConverter.ToUInt32(crc, 0))
            {
                throw new InvalidFormatException("Extended header checksum is invalid");
            }

            extendedHeader.Add(header);
        }
    }

    // Flag helpers
    public bool IsGabled => (Flags & 0x01) != 0;
    public bool IsAnsiPage => (Flags & 0x02) != 0;
    public bool IsVolume => (Flags & 0x04) != 0;
    public bool IsArjProtected => (Flags & 0x08) != 0;
    public bool IsPathSym => (Flags & 0x10) != 0;
    public bool IsBackup => (Flags & 0x20) != 0;
    public bool IsSecured => (Flags & 0x40) != 0;
    public bool IsAltName => (Flags & 0x80) != 0;

    public static FileType FileTypeFromByte(byte value)
    {
#if LEGACY_DOTNET
        return Enum.IsDefined(typeof(FileType), value) ? (FileType)value : Headers.FileType.Unknown;
#else
        return Enum.IsDefined((FileType)value) ? (FileType)value : Headers.FileType.Unknown;
#endif
    }

    public static bool IsArchive(Stream stream)
    {
        var bytes = new byte[2];
        if (stream.Read(bytes, 0, 2) != 2)
        {
            return false;
        }

        return CheckMagicBytes(bytes);
    }

    protected static bool CheckMagicBytes(byte[] headerBytes)
    {
        var magicValue = (ushort)(headerBytes[0] | headerBytes[1] << 8);
        return magicValue == ARJ_MAGIC;
    }
}