Add GZIP models

SabreTools.Models/GZIP/Archive.cs

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+namespace SabreTools.Models.GZIP
+{
+    /// <see href="https://www.ietf.org/rfc/rfc1952.txt"/> 
+    public sealed class Archive
+    {
+        /// <summary>
+        /// Header including optional fields
+        /// </summary>
+        public Header? Header;
+
+        // Compressed blocks live here
+
+        /// <summary>
+        /// Trailer
+        /// </summary>
+        public Trailer? Trailer;
+    }
+}

SabreTools.Models/GZIP/Constants.cs

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+namespace SabreTools.Models.GZIP
+{
+    /// <see href="https://www.ietf.org/rfc/rfc1952.txt"/> 
+    public static class Constants
+    {
+        public const byte ID1 = 0x1F;
+
+        public const byte ID2 = 0x8B;
+    }
+}

SabreTools.Models/GZIP/Enums.cs

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+using System;
+
+namespace SabreTools.Models.GZIP
+{
+    /// <see href="https://www.ietf.org/rfc/rfc1952.txt"/> 
+    public enum CompressionMethod : byte
+    {
+        RESERVED0 = 0,
+        RESERVED1 = 1,
+        RESERVED2 = 2,
+        RESERVED3 = 3,
+        RESERVED4 = 4,
+        RESERVED5 = 5,
+        RESERVED6 = 6,
+        RESERVED7 = 7,
+
+        Deflate = 8,
+    }
+
+    /// <see href="https://www.ietf.org/rfc/rfc1952.txt"/> 
+    [Flags]
+    public enum ExtraFlags : byte
+    {
+        /// <summary>
+        /// Compressor used maximum compression, slowest algorithm
+        /// </summary>
+        MaximumCompression = 0x02,
+
+        /// <summary>
+        /// Compressor used fastest algorithm
+        /// </summary>
+        FastestAlgorithm = 0x04,
+    }
+
+    /// <see href="https://www.ietf.org/rfc/rfc1952.txt"/> 
+    [Flags]
+    public enum Flags : byte
+    {
+        /// <summary>
+        /// The file is probably ASCII text
+        /// </summary>
+        FTEXT = 0x01,
+
+        /// <summary>
+        /// CRC-16 for the gzip header is present
+        /// </summary>
+        FHCRC = 0x02,
+
+        /// <summary>
+        /// Optional extra fields are present
+        /// </summary>
+        FEXTRA = 0x04,
+
+        /// <summary>
+        /// Original filename is present
+        /// </summary>
+        FNAME = 0x08,
+
+        /// <summary>
+        /// Zero-terminated file comment is present
+        /// </summary>
+        FCOMMENT = 0x10,
+
+        RESERVED5 = 0x20,
+        RESERVED6 = 0x40,
+        RESERVED7 = 0x80,
+    }
+
+    /// <see href="https://www.ietf.org/rfc/rfc1952.txt"/> 
+    public enum OperatingSystem : byte
+    {
+        /// <summary>
+        /// FAT filesystem (MS-DOS, OS/2, NT/Win32)
+        /// </summary>
+        FAT = 0,
+
+        /// <summary>
+        /// Amiga
+        /// </summary>
+        Amiga = 1,
+
+        /// <summary>
+        /// VMS (or OpenVMS)
+        /// </summary>
+        VMS = 2,
+
+        /// <summary>
+        /// Unix
+        /// </summary>
+        Unix = 3,
+
+        /// <summary>
+        /// VM/CMS
+        /// </summary>
+        VMCMS = 4,
+
+        /// <summary>
+        /// Atari TOS
+        /// </summary>
+        AtariTOS = 5,
+
+        /// <summary>
+        /// HPFS filesystem (OS/2, NT)
+        /// </summary>
+        HPFS = 6,
+
+        /// <summary>
+        /// Macintosh
+        /// </summary>
+        Macintosh = 7,
+
+        /// <summary>
+        /// Z-System
+        /// </summary>
+        ZSystem = 8,
+
+        /// <summary>
+        /// CP/M
+        /// </summary>
+        CPM = 9,
+
+        /// <summary>
+        /// TOPS-20
+        /// </summary>
+        TOPS20 = 10,
+
+        /// <summary>
+        /// NTFS filesystem (NT)
+        /// </summary>
+        NTFS = 11,
+
+        /// <summary>
+        /// QDOS
+        /// </summary>
+        QDOS = 12,
+
+        /// <summary>
+        /// Acorn RISCOS
+        /// </summary>
+        AcornRISCOS = 13,
+
+        /// <summary>
+        /// unknown
+        /// </summary>
+        Unknown = 255,
+    }
+}

SabreTools.Models/GZIP/ExtraFieldData.cs

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+namespace SabreTools.Models.GZIP
+{
+    /// <see href="https://www.ietf.org/rfc/rfc1952.txt"/> 
+    public sealed class ExtraFieldData
+    {
+        /// <summary>
+        /// SI1 and SI2 provide a subfield ID, typically two ASCII letters
+        /// with some mnemonic value.
+        /// </summary>
+        public byte SI1;
+
+        /// <summary>
+        /// SI1 and SI2 provide a subfield ID, typically two ASCII letters
+        /// with some mnemonic value.
+        /// </summary>
+        public byte SI2;
+
+        /// <summary>
+        /// LEN gives the length of the subfield data, excluding the 4
+        /// initial bytes.
+        /// </summary>
+        public ushort LEN;
+
+        public byte[]? Data;
+    }
+}

SabreTools.Models/GZIP/Header.cs

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+namespace SabreTools.Models.GZIP
+{
+    /// <see href="https://www.ietf.org/rfc/rfc1952.txt"/> 
+    public sealed class Header
+    {
+        /// <summary>
+        /// IDentification 1 (0x1F)
+        /// </summary>
+        public byte ID1;
+
+        /// <summary>
+        /// IDentification 2 (0x8B)
+        /// </summary>
+        public byte ID2;
+
+        /// <summary>
+        /// Compression Method
+        /// </summary>
+        public CompressionMethod CM;
+
+        /// <summary>
+        /// FLaGs
+        /// </summary>
+        public Flags FLG;
+
+        /// <summary>
+        /// Modification TIME
+        /// 
+        /// This gives the most recent modification time of the original
+        /// file being compressed.  The time is in Unix format, i.e.,
+        /// seconds since 00:00:00 GMT, Jan.  1, 1970.  (Note that this
+        /// may cause problems for MS-DOS and other systems that use
+        /// local rather than Universal time.)  If the compressed data
+        /// did not come from a file, MTIME is set to the time at which
+        /// compression started.  MTIME = 0 means no time stamp is
+        /// available.
+        /// </summary>
+        public uint MTIME;
+
+        /// <summary>
+        /// eXtra FLags
+        /// </summary>
+        public ExtraFlags XFL;
+
+        /// <summary>
+        /// Operating System
+        /// 
+        /// This identifies the type of file system on which compression
+        /// took place.  This may be useful in determining end-of-line
+        /// convention for text files.
+        /// </summary>
+        public OperatingSystem OS;
+
+        /// <summary>
+        /// eXtra LENgth
+        /// 
+        /// If FLG.FEXTRA is set, this gives the length of the optional
+        /// extra field.
+        /// </summary>
+        public ushort XLEN;
+
+        /// <summary>
+        /// Extra field
+        /// 
+        /// If the FLG.FEXTRA bit is set, an "extra field" is present in
+        /// the header, with total length XLEN bytes.  It consists of a
+        /// series of subfields, each of the form <see cref="ExtraFieldData"/>.
+        /// </summary>
+        public ExtraFieldData[]? ExtraField;
+
+        /// <summary>
+        /// Original filename before compression, zero-terminated
+        /// </summary>
+        public string? OriginalFileName;
+
+        /// <summary>
+        /// File comment, zero terminated
+        /// </summary>
+        public string? FileComment;
+
+        /// <summary>
+        ///  The CRC16 consists of the two least significant bytes of the
+        ///  CRC32 for all bytes of the gzip header up to and not including
+        ///  the CRC16.
+        /// </summary>
+        public ushort? CRC16;
+    }
+}

SabreTools.Models/GZIP/Trailer.cs

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+namespace SabreTools.Models.GZIP
+{
+    /// <see href="https://www.ietf.org/rfc/rfc1952.txt"/> 
+    public sealed class Trailer
+    {
+        /// <summary>
+        /// CRC-32
+        /// 
+        /// This contains a Cyclic Redundancy Check value of the
+        /// uncompressed data computed according to CRC-32 algorithm
+        /// used in the ISO 3309 standard and in section 8.1.1.6.2 of
+        /// ITU-T recommendation V.42.  (See http://www.iso.ch for
+        /// ordering ISO documents. See gopher://info.itu.ch for an
+        /// online version of ITU-T V.42.)
+        /// </summary>
+        public uint CRC32;
+
+        /// <summary>
+        /// Input SIZE
+        /// 
+        /// This contains the size of the original (uncompressed) input
+        /// data modulo 2^32.
+        /// </summary>
+        public uint ISIZE;
+    }
+}