Minimum C# code to extract from .CAB archives or InfoPath XSN files, in memory <p>Lately I've been trying to implement some functionality which extracts files from an InfoPath XSN file (a .CAB archive). After extensive searching around the internet, it seems that there is no native .NET API for this. All current solutions are centered around large libraries i.e. managed C++ which wrap up Cabinet.dll.</p> <p>All of this, sadly, falls foul of my companies "No third party libraries" policy.</p> <p>As of 2.0, .NET gained an attribute called UnmanagedFunctionPointer which allows source level callback declarations using __cdecl. Prior to this, __stdcall was the only show in town, unless you didn't mind fudging the IL, a practice also outlawed here. I immediately knew this would allow the implementation of a fairly small C# wrapper for Cabinet.dll, but I couldn't find an example of one anywhere.</p> <p>Does anyone know of a cleaner way than the below to do this with native code?</p> <p>My current solution (executes unmanaged code, but fully working, Tested on 32/64-bit):</p> <pre><code>[StructLayout(LayoutKind.Sequential)] public class CabinetInfo //Cabinet API: "FDCABINETINFO" { public int cbCabinet; public short cFolders; public short cFiles; public short setID; public short iCabinet; public int fReserve; public int hasprev; public int hasnext; } public class CabExtract : IDisposable { //If any of these classes end up with a different size to its C equivilent, we end up with crash and burn. [StructLayout(LayoutKind.Sequential)] private class CabError //Cabinet API: "ERF" { public int erfOper; public int erfType; public int fError; } [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)] private class FdiNotification //Cabinet API: "FDINOTIFICATION" { public int cb; public string psz1; public string psz2; public string psz3; public IntPtr userData; public IntPtr hf; public short date; public short time; public short attribs; public short setID; public short iCabinet; public short iFolder; public int fdie; } private enum FdiNotificationType { CabinetInfo, PartialFile, CopyFile, CloseFileInfo, NextCabinet, Enumerate } private class DecompressFile { public IntPtr Handle { get; set; } public string Name { get; set; } public bool Found { get; set; } public int Length { get; set; } public byte[] Data { get; set; } } [UnmanagedFunctionPointer(CallingConvention.Cdecl)] private delegate IntPtr FdiMemAllocDelegate(int numBytes); [UnmanagedFunctionPointer(CallingConvention.Cdecl)] private delegate void FdiMemFreeDelegate(IntPtr mem); [UnmanagedFunctionPointer(CallingConvention.Cdecl)] private delegate IntPtr FdiFileOpenDelegate(string fileName, int oflag, int pmode); [UnmanagedFunctionPointer(CallingConvention.Cdecl)] private delegate Int32 FdiFileReadDelegate(IntPtr hf, [In, Out] [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 2, ArraySubType = UnmanagedType.U1)] byte[] buffer, int cb); [UnmanagedFunctionPointer(CallingConvention.Cdecl)] private delegate Int32 FdiFileWriteDelegate(IntPtr hf, [In] [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 2, ArraySubType = UnmanagedType.U1)] byte[] buffer, int cb); [UnmanagedFunctionPointer(CallingConvention.Cdecl)] private delegate Int32 FdiFileCloseDelegate(IntPtr hf); [UnmanagedFunctionPointer(CallingConvention.Cdecl)] private delegate Int32 FdiFileSeekDelegate(IntPtr hf, int dist, int seektype); [UnmanagedFunctionPointer(CallingConvention.Cdecl)] private delegate IntPtr FdiNotifyDelegate( FdiNotificationType fdint, [In] [MarshalAs(UnmanagedType.LPStruct)] FdiNotification fdin); [DllImport("cabinet.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "FDICreate", CharSet = CharSet.Ansi)] private static extern IntPtr FdiCreate( FdiMemAllocDelegate fnMemAlloc, FdiMemFreeDelegate fnMemFree, FdiFileOpenDelegate fnFileOpen, FdiFileReadDelegate fnFileRead, FdiFileWriteDelegate fnFileWrite, FdiFileCloseDelegate fnFileClose, FdiFileSeekDelegate fnFileSeek, int cpuType, [MarshalAs(UnmanagedType.LPStruct)] CabError erf); [DllImport("cabinet.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "FDIIsCabinet", CharSet = CharSet.Ansi)] private static extern bool FdiIsCabinet( IntPtr hfdi, IntPtr hf, [MarshalAs(UnmanagedType.LPStruct)] CabinetInfo cabInfo); [DllImport("cabinet.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "FDIDestroy", CharSet = CharSet.Ansi)] private static extern bool FdiDestroy(IntPtr hfdi); [DllImport("cabinet.dll", CallingConvention = CallingConvention.Cdecl, EntryPoint = "FDICopy", CharSet = CharSet.Ansi)] private static extern bool FdiCopy( IntPtr hfdi, string cabinetName, string cabinetPath, int flags, FdiNotifyDelegate fnNotify, IntPtr fnDecrypt, IntPtr userData); private readonly FdiFileCloseDelegate _fileCloseDelegate; private readonly FdiFileOpenDelegate _fileOpenDelegate; private readonly FdiFileReadDelegate _fileReadDelegate; private readonly FdiFileSeekDelegate _fileSeekDelegate; private readonly FdiFileWriteDelegate _fileWriteDelegate; private readonly FdiMemAllocDelegate _femAllocDelegate; private readonly FdiMemFreeDelegate _memFreeDelegate; private readonly CabError _erf; private readonly List&lt;DecompressFile&gt; _decompressFiles; private readonly byte[] _inputData; private IntPtr _hfdi; private bool _disposed; private const int CpuTypeUnknown = -1; public CabExtract(byte[] inputData) { _fileReadDelegate = FileRead; _fileOpenDelegate = InputFileOpen; _femAllocDelegate = MemAlloc; _fileSeekDelegate = FileSeek; _memFreeDelegate = MemFree; _fileWriteDelegate = FileWrite; _fileCloseDelegate = InputFileClose; _inputData = inputData; _decompressFiles = new List&lt;DecompressFile&gt;(); _erf = new CabError(); _hfdi = IntPtr.Zero; } private static IntPtr FdiCreate( FdiMemAllocDelegate fnMemAlloc, FdiMemFreeDelegate fnMemFree, FdiFileOpenDelegate fnFileOpen, FdiFileReadDelegate fnFileRead, FdiFileWriteDelegate fnFileWrite, FdiFileCloseDelegate fnFileClose, FdiFileSeekDelegate fnFileSeek, CabError erf) { return FdiCreate(fnMemAlloc, fnMemFree, fnFileOpen, fnFileRead, fnFileWrite, fnFileClose, fnFileSeek, CpuTypeUnknown, erf); } private static bool FdiCopy( IntPtr hfdi, FdiNotifyDelegate fnNotify) { return FdiCopy(hfdi, "&lt;notused&gt;", "&lt;notused&gt;", 0, fnNotify, IntPtr.Zero, IntPtr.Zero); } private IntPtr FdiContext { get { if (_hfdi == IntPtr.Zero) { _hfdi = FdiCreate(_femAllocDelegate, _memFreeDelegate, _fileOpenDelegate, _fileReadDelegate, _fileWriteDelegate, _fileCloseDelegate, _fileSeekDelegate, _erf); if (_hfdi == IntPtr.Zero) throw new ApplicationException("Failed to create FDI context."); } return _hfdi; } } public void Dispose() { Dispose(true); } private void Dispose(bool disposing) { if (!_disposed) { if (_hfdi != IntPtr.Zero) { FdiDestroy(_hfdi); _hfdi = IntPtr.Zero; } _disposed = true; } } private IntPtr NotifyCallback(FdiNotificationType fdint, FdiNotification fdin) { switch (fdint) { case FdiNotificationType.CopyFile: return OutputFileOpen(fdin); case FdiNotificationType.CloseFileInfo: return OutputFileClose(fdin); default: return IntPtr.Zero; } } private IntPtr InputFileOpen(string fileName, int oflag, int pmode) { var stream = new MemoryStream(_inputData); GCHandle gch = GCHandle.Alloc(stream); return (IntPtr)gch; } private int InputFileClose(IntPtr hf) { var stream = StreamFromHandle(hf); stream.Close(); ((GCHandle)(hf)).Free(); return 0; } private IntPtr OutputFileOpen(FdiNotification fdin) { var extractFile = _decompressFiles.Where(ef =&gt; ef.Name == fdin.psz1).SingleOrDefault(); if (extractFile != null) { var stream = new MemoryStream(); GCHandle gch = GCHandle.Alloc(stream); extractFile.Handle = (IntPtr)gch; return extractFile.Handle; } //Don't extract return IntPtr.Zero; } private IntPtr OutputFileClose(FdiNotification fdin) { var extractFile = _decompressFiles.Where(ef =&gt; ef.Handle == fdin.hf).Single(); var stream = StreamFromHandle(fdin.hf); extractFile.Found = true; extractFile.Length = (int)stream.Length; if (stream.Length &gt; 0) { extractFile.Data = new byte[stream.Length]; stream.Position = 0; stream.Read(extractFile.Data, 0, (int)stream.Length); } stream.Close(); return IntPtr.Zero; } private int FileRead(IntPtr hf, byte[] buffer, int cb) { var stream = StreamFromHandle(hf); return stream.Read(buffer, 0, cb); } private int FileWrite(IntPtr hf, byte[] buffer, int cb) { var stream = StreamFromHandle(hf); stream.Write(buffer, 0, cb); return cb; } private static Stream StreamFromHandle(IntPtr hf) { return (Stream)((GCHandle)hf).Target; } private IntPtr MemAlloc(int cb) { return Marshal.AllocHGlobal(cb); } private void MemFree(IntPtr mem) { Marshal.FreeHGlobal(mem); } private int FileSeek(IntPtr hf, int dist, int seektype) { var stream = StreamFromHandle(hf); return (int)stream.Seek(dist, (SeekOrigin)seektype); } public bool ExtractFile(string fileName, out byte[] outputData, out int outputLength) { if (_disposed) throw new ObjectDisposedException("CabExtract"); var fileToDecompress = new DecompressFile(); fileToDecompress.Found = false; fileToDecompress.Name = fileName; _decompressFiles.Add(fileToDecompress); FdiCopy(FdiContext, NotifyCallback); if (fileToDecompress.Found) { outputData = fileToDecompress.Data; outputLength = fileToDecompress.Length; _decompressFiles.Remove(fileToDecompress); return true; } outputData = null; outputLength = 0; return false; } public bool IsCabinetFile(out CabinetInfo cabinfo) { if (_disposed) throw new ObjectDisposedException("CabExtract"); var stream = new MemoryStream(_inputData); GCHandle gch = GCHandle.Alloc(stream); try { var info = new CabinetInfo(); var ret = FdiIsCabinet(FdiContext, (IntPtr)gch, info); cabinfo = info; return ret; } finally { stream.Close(); gch.Free(); } } public static bool IsCabinetFile(byte[] inputData, out CabinetInfo cabinfo) { using (var decomp = new CabExtract(inputData)) { return decomp.IsCabinetFile(out cabinfo); } } //In an ideal world, this would take a stream, but Cabinet.dll seems to want to open the input several times. public static bool ExtractFile(byte[] inputData, string fileName, out byte[] outputData, out int length) { using (var decomp = new CabExtract(inputData)) { return decomp.ExtractFile(fileName, out outputData, out length); } } //TODO: Add methods for enumerating/extracting multiple files } </code></pre>