internal void Write(BitWriter writer)
{
writer.StartCrcCalculation();
writer.WriteStringAscii(Version.VersionString(), nullTerminated: false);
writer.WriteBytes(0, 0, 0, 0, 0);
if (Version == DwgVersionId.R14)
{
writer.WriteByte((byte)MaintenenceVersion);
}
else
{
writer.WriteByte(0);
}
writer.WriteByte(1);
writer.WriteInt(ImagePointer);
writer.WriteBytes(0, 0);
writer.WriteShort(CodePage);
writer.WriteInt(5); // 5 records
HeaderVariablesLocator.Write(writer);
ClassSectionLocator.Write(writer);
ObjectMapLocator.Write(writer);
UnknownSection_R13C3AndLaterLocator.Write(writer);
UnknownSection_PaddingLocator.Write(writer);
writer.WriteCrc(xorValue: 0x3CC4); // value for 5 records
writer.WriteBytes(HeaderSentinel);
}
internal void WriteSecondHeader(BitWriter writer, DwgHeaderVariables headerVariables, int pointer)
{
// write to memory the backtrack to fill in size and crc
using (var ms = new MemoryStream())
{
var tempWriter = new BitWriter(ms);
tempWriter.WriteBytes(SecondHeaderStartSentinel);
var sizeOffset = tempWriter.Position;
tempWriter.Write_RL(0); // size, filled in later
tempWriter.Write_BL(pointer);
tempWriter.WriteStringAscii(Version.VersionString(), nullTerminated: false);
tempWriter.WriteBytes(new byte[] { 0, 0, 0, 0, 0, 0 }); // 6 zero bytes
tempWriter.WriteBits(0x00000000, 4); // 4 zero bits
tempWriter.WriteBytes(new byte[] { 0, 0 }); // 2 unknown bytes
tempWriter.WriteBytes(SecondHeaderMidSentinel);
tempWriter.WriteByte(5); // record locator count
HeaderVariablesLocator.Write(tempWriter, writingSecondHeader: true);
ClassSectionLocator.Write(tempWriter, writingSecondHeader: true);
ObjectMapLocator.Write(tempWriter, writingSecondHeader: true);
UnknownSection_R13C3AndLaterLocator.Write(tempWriter, writingSecondHeader: true);
UnknownSection_PaddingLocator.Write(tempWriter, writingSecondHeader: true);
tempWriter.Write_BS(14);
headerVariables.NextAvailableHandle.WriteSecondHeader(tempWriter, 0);
headerVariables.BlockControlObjectHandle.WriteSecondHeader(tempWriter, 1);
headerVariables.LayerControlObjectHandle.WriteSecondHeader(tempWriter, 2);
headerVariables.StyleObjectControlHandle.WriteSecondHeader(tempWriter, 3);
headerVariables.LineTypeObjectControlHandle.WriteSecondHeader(tempWriter, 4);
headerVariables.ViewControlObjectHandle.WriteSecondHeader(tempWriter, 5);
headerVariables.UcsControlObjectHandle.WriteSecondHeader(tempWriter, 6);
headerVariables.ViewPortControlObjectHandle.WriteSecondHeader(tempWriter, 7);
headerVariables.AppIdControlObjectHandle.WriteSecondHeader(tempWriter, 8);
headerVariables.DimStyleControlObjectHandle.WriteSecondHeader(tempWriter, 9);
headerVariables.ViewPortEntityHeaderControlObjectHandle.WriteSecondHeader(tempWriter, 10);
headerVariables.NamedObjectsDictionaryHandle.WriteSecondHeader(tempWriter, 11);
headerVariables.MLineStyleDictionaryHandle.WriteSecondHeader(tempWriter, 12);
headerVariables.GroupDictionaryHandle.WriteSecondHeader(tempWriter, 13);
tempWriter.WriteByte(0); // unknown
tempWriter.AlignByte();
var crcOffset = tempWriter.Position;
tempWriter.WriteShort(0); // CRC, filled in later
if (Version == DwgVersionId.R14)
{
// unknown garbage bytes
tempWriter.WriteBytes(new byte[] { 0, 0, 0, 0, 0, 0, 0, 0 });
}
tempWriter.WriteBytes(SecondHeaderEndSentinel);
// get bytes of header
var secondHeaderBytes = tempWriter.AsBytes();
// fill in size
var sizeBytes = BitConverter.GetBytes(secondHeaderBytes.Length - SecondHeaderStartSentinel.Length - SecondHeaderEndSentinel.Length);
if (!BitConverter.IsLittleEndian)
{
Array.Reverse(sizeBytes);
}
Array.Copy(sizeBytes, 0, secondHeaderBytes, sizeOffset, sizeBytes.Length);
// fill in crc
var crc = BitReaderExtensions.ComputeCRC(secondHeaderBytes, sizeOffset, crcOffset - sizeOffset, DwgHeaderVariables.InitialCrcValue);
var crcBytes = BitConverter.GetBytes(crc);
if (!BitConverter.IsLittleEndian)
{
Array.Reverse(crcBytes);
}
Array.Copy(crcBytes, 0, secondHeaderBytes, crcOffset, crcBytes.Length);
// write to the real writer
writer.WriteBytes(secondHeaderBytes);
}
}
internal void ValidateSecondHeader(BitReader parentReader, DwgHeaderVariables headerVariables)
{
var reader = parentReader.FromOffset(SecondHeaderPointer);
reader.ValidateSentinel(SecondHeaderStartSentinel);
var sectionStart = reader.Offset;
reader.StartCrcCheck();
var reportedSectionSize = reader.Read_RL();
var expectedLocation = reader.Read_BL();
if (expectedLocation != sectionStart - SecondHeaderStartSentinel.Length)
{
throw new DwgReadException("Reported second header location incorrect.");
}
var version = DwgVersionIdExtensions.VersionIdFromString(reader.ReadStringAscii(6));
if (version != Version)
{
throw new DwgReadException("Inconsistent reported version.");
}
reader.ReadBytes(6);
reader.Read_B();
reader.Read_B();
reader.Read_B();
reader.Read_B();
reader.ReadBytes(2);
reader.ValidateBytes(SecondHeaderMidSentinel);
var recordLocatorCount = reader.ReadByte();
for (int i = 0; i < recordLocatorCount; i++)
{
var id = reader.ReadByte();
var pointer = reader.Read_BL();
var length = reader.Read_BL();
if (pointer != 0)
{
switch (i)
{
case 0:
HeaderVariablesLocator.ValidateLocator(id, pointer, length);
break;
case 1:
ClassSectionLocator.ValidateLocator(id, pointer, length);
break;
case 2:
ObjectMapLocator.ValidateLocator(id, pointer, length);
break;
case 3:
UnknownSection_R13C3AndLaterLocator.ValidateLocator(id, pointer, length);
break;
case 4:
UnknownSection_PaddingLocator.ValidateLocator(id, pointer, length);
break;
}
}
}
var handleRecordCount = reader.Read_BS();
for (int i = 0; i < handleRecordCount; i++)
{
var byteCount = reader.Read_RC();
var id = reader.Read_RC();
var handle = DwgHandleReference.ReadSecondHeader(reader, byteCount);
if (byteCount > 0)
{
if (id != i)
{
throw new DwgReadException("Invalid record handle ID.");
}
var actualHandle = -1;
switch (i)
{
case 0:
actualHandle = headerVariables.NextAvailableHandle.HandleOrOffset;
break;
case 1:
actualHandle = headerVariables.BlockControlObjectHandle.HandleOrOffset;
break;
case 2:
actualHandle = headerVariables.LayerControlObjectHandle.HandleOrOffset;
break;
case 3:
actualHandle = headerVariables.StyleObjectControlHandle.HandleOrOffset;
break;
case 4:
actualHandle = headerVariables.LineTypeObjectControlHandle.HandleOrOffset;
break;
case 5:
actualHandle = headerVariables.ViewControlObjectHandle.HandleOrOffset;
break;
case 6:
actualHandle = headerVariables.UcsControlObjectHandle.HandleOrOffset;
break;
case 7:
actualHandle = headerVariables.ViewPortControlObjectHandle.HandleOrOffset;
break;
case 8:
actualHandle = headerVariables.AppIdControlObjectHandle.HandleOrOffset;
break;
case 9:
actualHandle = headerVariables.DimStyleControlObjectHandle.HandleOrOffset;
break;
case 10:
actualHandle = headerVariables.ViewPortEntityHeaderControlObjectHandle.HandleOrOffset;
break;
case 11:
actualHandle = headerVariables.NamedObjectsDictionaryHandle.HandleOrOffset;
break;
case 12:
actualHandle = headerVariables.MLineStyleDictionaryHandle.HandleOrOffset;
break;
case 13:
actualHandle = headerVariables.GroupDictionaryHandle.HandleOrOffset;
break;
}
if (actualHandle > 0)
{
if (handle != actualHandle)
{
throw new DwgReadException($"Invalid record handle ID at location {i}. Expected: {handle}, Actual: {actualHandle}");
}
}
}
}
reader.ReadByte();
reader.ValidateCrc(initialValue: DwgHeaderVariables.InitialCrcValue);
var junkByteCount = Math.Max(0, reportedSectionSize - (reader.Offset - sectionStart));
reader.SkipBytes(junkByteCount);
reader.ValidateSentinel(SecondHeaderEndSentinel);
var computedSectionSize = reader.Offset - sectionStart - SecondHeaderEndSentinel.Length;
if (computedSectionSize != reportedSectionSize)
{
throw new DwgReadException($"Reported and actual second header sizes differ. Expected: {reportedSectionSize}, Actual: {computedSectionSize}");
}
}