protected override HeaderDetails ReadHeader()

in src/managed/DiffGen/archives/CpioArchives/NewAsciiCpioArchive.cs [33:115]
68 lines of code
11 McCabe index (conditional complexity)

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

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

            if (magic.CompareTo(NewAsciiMagic) == 0)
            {
                subtype = "ascii.new";
            }
            else if (magic.CompareTo(NewcAsciiMagic) == 0)
            {
                subtype = "ascii.newc";
            }
            else
            {
                throw new FormatException($"Found \"{magic}\" instead of expected new ascii header \"{NewAsciiMagic}\" or newc header \"{NewcAsciiMagic}\"");
            }

            var ino = AsciiData.FromHexadecimalData(rawHeaderData, 6, 8);
            var mode = AsciiData.FromHexadecimalData(rawHeaderData, 14, 8);
            var uid = AsciiData.FromHexadecimalData(rawHeaderData, 22, 8);
            var gid = AsciiData.FromHexadecimalData(rawHeaderData, 30, 8);
            var nlink = AsciiData.FromHexadecimalData(rawHeaderData, 38, 8);
            var mtime = AsciiData.FromHexadecimalData(rawHeaderData, 46, 8);
            var filesize = AsciiData.FromHexadecimalData(rawHeaderData, 54, 8);
            var devMajor = AsciiData.FromHexadecimalData(rawHeaderData, 62, 8);
            var devMinor = AsciiData.FromHexadecimalData(rawHeaderData, 70, 8);
            var rdevMajor = AsciiData.FromHexadecimalData(rawHeaderData, 78, 8);
            var rdevMinor = AsciiData.FromHexadecimalData(rawHeaderData, 86, 8);
            var namesize = AsciiData.FromHexadecimalData(rawHeaderData, 94, 8);
            var check = AsciiData.FromHexadecimalData(rawHeaderData, 102, 8);

            // CPIO appends an extra NUL character if the namesize is odd
            int rawNameSize = (int)namesize;
            if ((rawNameSize & 1) == 1)
            {
                rawNameSize++;
            }

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

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

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

            UInt64 allDataSize = (UInt64)allData.Count;

            UInt64 paddingNeeded = BinaryData.GetPaddingNeeded(allDataSize, 4);

            if (paddingNeeded != 0)
            {
                byte[] padding = new byte[paddingNeeded];
                if (paddingNeeded != (UInt64)reader.Read(padding, 0, (int)paddingNeeded))
                {
                    throw new FormatException("Couldn't read padding for header.");
                }

                allData.AddRange(padding);
                allDataSize += paddingNeeded;
            }

            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);
        }