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Fix DecalDat to work with real AC DAT files

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The DAT file reader had several bugs inherited from the old C++ reference
code, which targeted an older format version. Verified and fixed against
real client_portal.dat and client_cell_1.dat files:

- Fix header offset: BTree root is at 0x160, not 0x148 (file size field)
- Fix BTree entry size: 24 bytes (flags+id+offset+size+timestamp), not 12
- Fix sector-chain node reading: BTree nodes span multiple sectors via
  linked-list headers; must assemble node data across sector boundaries
- Fix DatStreamImpl.Read() BSTR handling: use Buffer.BlockCopy to match
  C++ SysAllocStringByteLen instead of Marshal.PtrToStringAnsi
- Fix DatStreamImpl.ReadBinary() pointer lifetime: inline fixed block to
  keep destination buffer pinned during Marshal.Copy
- Document LoadFilters() dependency on parameterized COM properties in
  IDecalCore.Configuration that need IDispatch to call correctly

Add smoke test project (13/13 tests pass against real DAT files).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
erik 2026-02-08 23:12:04 +01:00
parent c0d1135431
commit f0b6fedc9b
5 changed files with 356 additions and 56 deletions
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114
Managed/Decal.DecalDat/DatFile.cs
View file

@ -1,8 +1,11 @@
using System;
using System.IO;
using System.IO.MemoryMappedFiles;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
[assembly: InternalsVisibleTo("Decal.DecalDat.Tests")]
namespace Decal.DecalDat
{
/// <summary>
@ -11,17 +14,38 @@ namespace Decal.DecalDat
/// </summary>
internal sealed class DatFile : IDisposable
{
private const int FileCount = 62;
private const int FileCountOffset = 0x03E;
private const int RootDirPtrOffset = 0x148;
// DAT header layout (starting at 0x140):
// 0x140: "BT" magic (0x5442)
// 0x144: block/sector size
// 0x148: file size
// 0x14C: data set type (1=portal, 2=cell)
// 0x150: data subset
// 0x154: free head
// 0x158: free tail
// 0x15C: free count
// 0x160: BTree root directory offset
private const int RootDirPtrOffset = 0x160;
// Directory entry layout (packed):
// DWORD subdirs[62] = 248 bytes
// DWORD fileCount = 4 bytes
// FileEntry files[62] = 744 bytes (62 * 12)
// Total = 996 bytes
private const int SubdirsSize = FileCount * 4;
private const int FileEntrySize = 12; // 3 DWORDs: ID, Offset, Size
// BTree node data layout (within sector chain, after skipping sector headers):
// DWORD branches[62] = 248 bytes (child pointers; 0 = leaf)
// DWORD entryCount = 4 bytes
// FileEntry entries[62] = 1488 bytes (62 * 24)
// Total node data = 1740 bytes
//
// Nodes are stored in sector chains: each sector's first 4 bytes = next sector
// offset, with usable data in bytes [4..sectorSize-1].
//
// Each FileEntry (24 bytes):
// DWORD flags (+0)
// DWORD objectId (+4) — the file ID used for lookup
// DWORD fileOffset (+8) — sector offset to file data
// DWORD fileSize (+12) — size in bytes
// UINT64 timestamp (+16) — Windows FILETIME
private const int MaxEntries = 62;
private const int BranchCount = MaxEntries; // 62 child pointers
private const int BranchesSize = BranchCount * 4; // 248
private const int FileEntrySize = 24; // flags(4) + id(4) + offset(4) + size(4) + timestamp(8)
private const int MaxNodeDataSize = BranchesSize + 4 + MaxEntries * FileEntrySize; // 1740
private MemoryMappedFile _mmf;
private MemoryMappedViewAccessor _accessor;
@ -44,30 +68,76 @@ namespace Decal.DecalDat
return FindFile(rootDirOffset, fileId);
}
private DatFileEntry FindFile(uint dirOffset, uint fileId)
/// <summary>
/// Reads BTree node data from a sector chain into a contiguous byte array.
/// Each sector's first 4 bytes is the next-sector pointer; data follows.
/// </summary>
private byte[] ReadNodeData(uint sectorOffset)
{
// Read file count from directory
uint fileCount = _accessor.ReadUInt32(dirOffset + SubdirsSize);
var data = new byte[MaxNodeDataSize];
int dataPerSector = _sectorSize - 4;
int copied = 0;
uint currentSector = sectorOffset;
while (copied < MaxNodeDataSize && currentSector != 0 && currentSector < (uint)_fileLength)
{
int toCopy = Math.Min(dataPerSector, MaxNodeDataSize - copied);
// Bounds check: ensure we don't read past end of file
long readStart = currentSector + 4;
if (readStart + toCopy > _fileLength)
toCopy = (int)(_fileLength - readStart);
if (toCopy <= 0) break;
_accessor.ReadArray(readStart, data, copied, toCopy);
copied += toCopy;
if (copied < MaxNodeDataSize)
currentSector = _accessor.ReadUInt32(currentSector);
else
break;
}
return data;
}
private static uint ReadUInt32(byte[] data, int offset)
{
return BitConverter.ToUInt32(data, offset);
}
private DatFileEntry FindFile(uint sectorOffset, uint fileId)
{
if (sectorOffset >= (uint)_fileLength)
throw new FileNotFoundException($"BTree branch 0x{sectorOffset:X8} is out of bounds (file=0x{_fileLength:X})");
byte[] node = ReadNodeData(sectorOffset);
// Parse node: branches[62] (248 bytes) + entryCount (4 bytes) + entries
uint entryCount = ReadUInt32(node, BranchesSize);
if (entryCount > MaxEntries)
throw new InvalidDataException($"BTree node at 0x{sectorOffset:X8} has invalid entry count {entryCount}");
// Binary search through sorted file entries
int lo = 0, hi = (int)fileCount - 1;
int lo = 0, hi = (int)entryCount - 1;
while (lo <= hi)
{
int mid = (lo + hi) / 2;
long entryOffset = dirOffset + SubdirsSize + 4 + (mid * FileEntrySize);
uint entryId = _accessor.ReadUInt32(entryOffset);
int entryOffset = BranchesSize + 4 + (mid * FileEntrySize);
// Entry layout: flags(+0), objectId(+4), fileOffset(+8), fileSize(+12), timestamp(+16)
uint entryId = ReadUInt32(node, entryOffset + 4);
if (entryId == fileId)
{
uint offset = _accessor.ReadUInt32(entryOffset + 4);
uint size = _accessor.ReadUInt32(entryOffset + 8);
uint offset = ReadUInt32(node, entryOffset + 8);
uint size = ReadUInt32(node, entryOffset + 12);
return new DatFileEntry(this, offset, size);
}
else if (fileId < entryId)
{
// Recurse into left subdirectory
uint subdir = _accessor.ReadUInt32(dirOffset + (uint)(mid * 4));
// Recurse into left child branch
uint subdir = ReadUInt32(node, mid * 4);
if (subdir != 0)
{
try
@ -87,8 +157,8 @@ namespace Decal.DecalDat
}
}
// Check rightmost subdirectory
uint rightSubdir = _accessor.ReadUInt32(dirOffset + (uint)(lo * 4));
// Check rightmost child branch
uint rightSubdir = ReadUInt32(node, lo * 4);
if (rightSubdir != 0)
{
return FindFile(rightSubdir, fileId);

35
Managed/Decal.DecalDat/DatServiceImpl.cs
View file

@ -55,22 +55,25 @@ namespace Decal.DecalDat
private void LoadFilters()
{
try
{
var config = _decalCore.Configuration;
if (config == null) return;
// Look up "FileFilters" collection in Decal configuration
// The C++ code iterates an IDecalEnum to read filter definitions
// Each filter has: Prefix (string), Cache (bool), ComClass (CLSID)
//
// For now, register the known built-in filters that ship with Decal.
// When Decal.Core is implemented, this will read from live config.
}
catch
{
// Config may not be available yet
}
// The C++ original calls:
// m_pDecal->get_Configuration(L"FileFilters", GUID_NULL, &pEnum)
// then iterates the IDecalEnum reading:
// pEnum->get_ComClass(&clsid)
// pEnum->get_Property(L"Prefix", &vPrefix) // protocol name, e.g. "portal"
// pEnum->get_Property(L"Cache", &vCache) // 0 or 1
//
// However, IDecalCore.Configuration and IDecalEnum.Property are
// parameterized COM properties that the decompiler flattened to
// simple getters. They need to be called via IDispatch to pass
// the category name / property name arguments.
//
// Filters are registered externally (by plugins/installer in the
// registry under HKLM\SOFTWARE\Decal\FileFilters\{CLSID}) and
// will be loaded once Decal.Core exposes the Configuration enum.
//
// DecalDat still works without filters — callers get raw IDatStream
// objects. Filters are an optional layer that parses the stream into
// typed objects (e.g., spell tables, character data).
}
public void BeforePlugins()

33
Managed/Decal.DecalDat/DatStreamImpl.cs
View file

@ -38,8 +38,14 @@ namespace Decal.DecalDat
var buf = new byte[Bytes];
_file.Read(buf, 0, Bytes);
// Copy to unmanaged buffer starting at ref Buffer
Marshal.Copy(buf, 0, GetBufferPtr(ref Buffer), Bytes);
// Pin the destination buffer for the duration of the copy
unsafe
{
fixed (byte* p = &Buffer)
{
Marshal.Copy(buf, 0, new IntPtr(p), Bytes);
}
}
}
public string Read(int Bytes)
@ -49,22 +55,13 @@ namespace Decal.DecalDat
var buf = new byte[Bytes];
int read = _file.Read(buf, 0, Bytes);
// Return as binary BSTR (same as SysAllocStringByteLen in C++)
unsafe
{
fixed (byte* p = buf)
{
return Marshal.PtrToStringAnsi(new IntPtr(p), read);
}
}
}
private static unsafe IntPtr GetBufferPtr(ref byte buffer)
{
fixed (byte* p = &buffer)
{
return new IntPtr(p);
}
// Match C++ SysAllocStringByteLen: pack raw bytes into WCHAR pairs.
// When the CLR marshals this string to BSTR, the raw bytes are preserved
// byte-for-byte (each char = 2 raw bytes, little-endian).
int charCount = (read + 1) / 2;
var chars = new char[charCount];
Buffer.BlockCopy(buf, 0, chars, 0, read);
return new string(chars, 0, charCount);
}
}
}