internal static DwgFileHeader Parse(BitReader reader)
{
reader.StartCrcCheck();
var versionString = reader.ReadStringAscii(6);
var version = DwgVersionIdExtensions.VersionIdFromString(versionString);
var unknown1 = reader.ReadBytes(6);
var maintVer = 0;
if (version == DwgVersionId.R14)
{
maintVer = unknown1[5];
}
var marker = reader.ReadByte();
if (marker != 1)
{
throw new DwgReadException("Expected value of 1 at offset 13.");
}
var imagePointer = reader.ReadInt();
var unknown2 = reader.ReadBytes(2);
var codePage = reader.ReadShort();
var header = new DwgFileHeader(version, maintVer, imagePointer, codePage);
var recordLocatorCount = reader.ReadInt();
for (int i = 0; i < recordLocatorCount; i++)
{
var locator = DwgSectionLocator.Parse(reader);
switch (i)
{
case 0:
header.HeaderVariablesLocator = locator;
break;
case 1:
header.ClassSectionLocator = locator;
break;
case 2:
header.ObjectMapLocator = locator;
break;
case 3:
header.UnknownSection_R13C3AndLaterLocator = locator;
break;
case 4:
header.UnknownSection_PaddingLocator = locator;
break;
}
}
ushort crcXorValue;
switch (recordLocatorCount)
{
case 0:
case 1:
case 2:
crcXorValue = 0;
break;
case 3:
crcXorValue = 0xAD98;
break;
case 4:
crcXorValue = 0x8101;
break;
case 5:
crcXorValue = 0x3CC4;
break;
case 6:
crcXorValue = 0x8461;
break;
default:
throw new DwgReadException("Unsupported record locator count.");
}
reader.ValidateCrc(xorValue: crcXorValue);
reader.ValidateSentinel(HeaderSentinel);
return(header);
}
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}");
}
}
