C# IStream implemenation of IStream

Question

First of all this is no duplicate of this Does a wrapper class for a COM interop IStream already exist? because I need the implemenation in the other direction. I need to create an IStream implemenation from IO.Stream to IStream. But before I start to try to do that, wanted to ask if anyone knows an already existing implemenation or any articles about that. I could not find anything in the .net framework and google just gave me results of implemenations from IStream to IO.Stream. So does anyone has a nice tip for me? I really don't know how to start because the first member(Clone -> Creates a new stream object that references the same bytes as the original stream but provides a separate seek pointer to those bytes) makes me troubles. I've got no idea how to do that based on a IO.Stream.

Bots

Answer 1

Finally, I've done it by myself (feel free to copy and modify it):

[ComImport]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
[Guid("0000000c-0000-0000-C000-000000000046")]
public interface IStream
{
    [PreserveSig]
    HResult Read([MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)] [Out] byte[] pv, int cb, IntPtr pcbRead);

    [PreserveSig]
    HResult Write([MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1)] byte[] pv, int cb, IntPtr pcbWritten);

    [PreserveSig]
    HResult Seek(long dlibMove, int dwOrigin, IntPtr plibNewPosition);

    [PreserveSig]
    HResult SetSize(long libNewSize);

    HResult CopyTo(IStream pstm, long cb, IntPtr pcbRead, IntPtr pcbWritten);

    [PreserveSig]
    HResult Commit(int grfCommitFlags);

    [PreserveSig]
    HResult Revert();

    [PreserveSig]
    HResult LockRegion(long libOffset, long cb, int dwLockType);

    [PreserveSig]
    HResult UnlockRegion(long libOffset, long cb, int dwLockType);

    [PreserveSig]
    HResult Stat(out comtypes.STATSTG pstatstg, int grfStatFlag);

    [PreserveSig]
    HResult Clone(out IStream ppstm);
}

    /// <summary>
    /// see http://msdn.microsoft.com/en-us/library/windows/desktop/ms752876(v=vs.85).aspx
    /// </summary>
    public class ComStream : Stream, IStream
    {
        private Stream _stream;

        public ComStream(Stream stream)
            : this(stream, true)
        {
        }

        internal ComStream(Stream stream, bool sync)
        {
            if (stream == null)
                throw new ArgumentNullException("stream");

            if (sync)
            {
                stream = Stream.Synchronized(stream);
            }
            _stream = stream;
        }

        HResult IStream.Clone(out IStream ppstm)
        {
            //ComStream newstream = new ComStream(_stream, false);
            //ppstm = newstream;
            ppstm = null;
            return HResult.E_NOTIMPL;
        }

        HResult IStream.Commit(int grfCommitFlags)
        {
            return HResult.E_NOTIMPL;
        }

        HResult IStream.CopyTo(IStream pstm, long cb, IntPtr pcbRead, IntPtr pcbWritten)
        {
            return HResult.E_NOTIMPL;
        }

        HResult IStream.LockRegion(long libOffset, long cb, int dwLockType)
        {
            return HResult.E_NOTIMPL;
        }

        HResult IStream.Read(byte[] pv, int cb, IntPtr pcbRead)
        {
            if (!CanRead)
                throw new InvalidOperationException("Stream not readable");

            int read = Read(pv, 0, cb);
            if (pcbRead != IntPtr.Zero)
                Marshal.WriteInt64(pcbRead, read);
            return HResult.S_OK;
        }

        HResult IStream.Revert()
        {
            return HResult.E_NOTIMPL;
        }

        HResult IStream.Seek(long dlibMove, int dwOrigin, IntPtr plibNewPosition)
        {
            SeekOrigin origin = (SeekOrigin)dwOrigin; //hope that the SeekOrigin enumeration won't change
            long pos = Seek(dlibMove, origin);
            if (plibNewPosition != IntPtr.Zero)
                Marshal.WriteInt64(plibNewPosition, pos);
            return HResult.S_OK;
        }

        HResult IStream.SetSize(long libNewSize)
        {
            return HResult.E_NOTIMPL;
        }

        HResult IStream.Stat(out comtypes.STATSTG pstatstg, int grfStatFlag)
        {
            pstatstg = new comtypes.STATSTG();
            pstatstg.cbSize = Length;
            return HResult.S_OK;
        }

        HResult IStream.UnlockRegion(long libOffset, long cb, int dwLockType)
        {
            return HResult.E_NOTIMPL;
        }

        HResult IStream.Write(byte[] pv, int cb, IntPtr pcbWritten)
        {
            if (!CanWrite)
                throw new InvalidOperationException("Stream is not writeable.");

            Write(pv, 0, cb);
            if (pcbWritten != null)
                Marshal.WriteInt32(pcbWritten, cb);
            return HResult.S_OK;
        }

        public override bool CanRead
        {
            get { return _stream.CanRead; }
        }

        public override bool CanSeek
        {
            get { return _stream.CanSeek; }
        }

        public override bool CanWrite
        {
            get { return _stream.CanWrite; }
        }

        public override void Flush()
        {
            _stream.Flush();
        }

        public override long Length
        {
            get { return _stream.Length; }
        }

        public override long Position
        {
            get
            {
                return _stream.Position;
            }
            set
            {
                _stream.Position = value;
            }
        }

        public override int Read(byte[] buffer, int offset, int count)
        {
            return _stream.Read(buffer, offset, count);
        }

        public override long Seek(long offset, SeekOrigin origin)
        {
            return _stream.Seek(offset, origin);
        }

        public override void SetLength(long value)
        {
            _stream.SetLength(value);
        }

        public override void Write(byte[] buffer, int offset, int count)
        {
            _stream.Write(buffer, offset, count);
        }

        protected override void Dispose(bool disposing)
        {
            if (_stream != null)
            {
                _stream.Dispose();
                _stream = null;
            }
        }
    }

Bots

the COM client will end up calling ::Release() on the IUnknown COM-interface/CCW, but there is no way to hook that up to .Dispose() ? – Moulding

Does not work as-is, even if it appears to: System.IO.Stream.Read() is allowed to return early and tell it has not read all the bytes, but just one or more. IStream::Read() always read all the requested bytes unless the end of stream is reached. Different, incompatible contracts: you must add a read loop in your implementation of IStream.Read() and read / fill the buffer until either you got all the requested bytes, or there is no more to read. – Superload