App-Installer-For-Windows-8.x-Reset/PriFileFormat/ComStreamWrapper.cs

using System;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.InteropServices.ComTypes;

namespace PriFileFormat
{
	public class ComStreamWrapper: Stream
	{
		private IStream comStream;
		public ComStreamWrapper (IStream stream)
		{
			if (stream == null)
				throw new ArgumentNullException ("stream");
			comStream = stream;
		}
		public override bool CanRead
		{
			get { return true; }
		}
		public override bool CanSeek
		{
			get { return true; }
		}
		public override bool CanWrite
		{
			get { return true; }
		}
		public override long Length
		{
			get
			{
				System.Runtime.InteropServices.ComTypes.STATSTG stat;
				comStream.Stat (out stat, 1); // STATFLAG_NONAME = 1
				return stat.cbSize;
			}
		}
		public override long Position
		{
			get
			{
				IntPtr posPtr = Marshal.AllocHGlobal (sizeof (long));
				try
				{
					// SEEK_CUR = 1
					comStream.Seek (0, 1, posPtr);
					return Marshal.ReadInt64 (posPtr);
				}
				finally
				{
					Marshal.FreeHGlobal (posPtr);
				}
			}
			set
			{
				// SEEK_SET = 0
				comStream.Seek (value, 0, IntPtr.Zero);
			}
		}
		public override void Flush ()
		{
			comStream.Commit (0); // STGC_DEFAULT = 0
		}
		public override int Read (byte [] buffer, int offset, int count)
		{
			if (offset != 0)
				throw new NotSupportedException ("Offset != 0 not supported in this wrapper.");

			IntPtr bytesRead = Marshal.AllocHGlobal (sizeof (int));
			try
			{
				comStream.Read (buffer, count, bytesRead);
				return Marshal.ReadInt32 (bytesRead);
			}
			finally
			{
				Marshal.FreeHGlobal (bytesRead);
			}
		}
		public override void Write (byte [] buffer, int offset, int count)
		{
			if (offset != 0)
				throw new NotSupportedException ("Offset != 0 not supported in this wrapper.");

			IntPtr bytesWritten = Marshal.AllocHGlobal (sizeof (int));
			try
			{
				comStream.Write (buffer, count, bytesWritten);
			}
			finally
			{
				Marshal.FreeHGlobal (bytesWritten);
			}
		}
		public override long Seek (long offset, SeekOrigin origin)
		{
			int originInt = 0;
			switch (origin)
			{
				case SeekOrigin.Begin: originInt = 0; break; // STREAM_SEEK_SET
				case SeekOrigin.Current: originInt = 1; break; // STREAM_SEEK_CUR
				case SeekOrigin.End: originInt = 2; break; // STREAM_SEEK_END
			}

			IntPtr posPtr = Marshal.AllocHGlobal (sizeof (long));
			try
			{
				comStream.Seek (offset, originInt, posPtr);
				return Marshal.ReadInt64 (posPtr);
			}
			finally
			{
				Marshal.FreeHGlobal (posPtr);
			}
		}
		public override void SetLength (long value)
		{
			comStream.SetSize (value);
		}
		~ComStreamWrapper () { comStream = null;}
	}
}