protected override HeaderDetails ReadHeader()

in src/managed/DiffGen/archives/CpioArchives/AsciiCpioArchive.cs [33:83]
41 lines of code
8 McCabe index (conditional complexity)

        protected override HeaderDetails ReadHeader(BinaryReader reader)
        {
            byte[] rawHeaderData = new byte[AsciiHeaderSize];
            if (reader.Read(rawHeaderData, 0, AsciiHeaderSize) != AsciiHeaderSize)
            {
                throw new FormatException("Not enough data for CPIO ascii header");
            }

            var magicBytes = new ReadOnlySpan<byte>(rawHeaderData, 0, 6);
            string magic = Encoding.ASCII.GetString(magicBytes);

            if ((magic.CompareTo(AsciiMagic) != 0) && (magic.CompareTo(AsciiMagic) != 0))
            {
                throw new FormatException($"Found \"{magic}\" instead of expected new ascii header \"{AsciiMagic}\"");
            }

            var dev = AsciiData.FromOctalData(rawHeaderData, 6, 6);
            var ino = AsciiData.FromOctalData(rawHeaderData, 12, 6);
            var mode = AsciiData.FromOctalData(rawHeaderData, 18, 6);
            var uid = AsciiData.FromOctalData(rawHeaderData, 24, 6);
            var gid = AsciiData.FromOctalData(rawHeaderData, 30, 6);
            var nlink = AsciiData.FromOctalData(rawHeaderData, 36, 6);
            var rdev = AsciiData.FromOctalData(rawHeaderData, 42, 6);
            var mtime = AsciiData.FromOctalData(rawHeaderData, 48, 11);
            var namesize = AsciiData.FromOctalData(rawHeaderData, 59, 6);
            var filesize = AsciiData.FromOctalData(rawHeaderData, 65, 11);

            byte[] rawName = new byte[namesize];
            if (namesize != (UInt64)reader.Read(rawName, 0, (int)namesize))
            {
                throw new FormatException("Not enough data for the name for CPIO ascii header");
            }

            var name = AsciiData.FromNulPaddedString(rawName, 0, (int)namesize);

            var allData = new List<byte>();
            allData.AddRange(rawHeaderData);
            allData.AddRange(rawName);

            int allDataSize = allData.Count;

            if ((name.CompareTo(TrailerFileName) == 0) && (filesize == 0) && (uid == 0))
            {
                TrailerDetected = true;
            }

            var chunkName = ChunkNames.MakeHeaderChunkName(name);
            var headerItem = ItemDefinition.FromByteSpan(allData.ToArray()).WithName(chunkName);

            return new HeaderDetails(headerItem, null, name, filesize);
        }