c# - 为什么我不能使用 `WTSVirtualChannelQuery` 返回的句柄？

Question

试图利用 RDP 动态虚拟通道。我将WTSVirtualChannelQuerywith的结果传递WTSVirtualFileHandle给 a FileStream，但它会引发各种异常。为什么？

称呼：

public static FileStream Open(string channelName, WTS_CHANNEL_OPTION option = WTS_CHANNEL_OPTION.DYNAMIC)
{
    // Open
    SafeFileHandle pFile = null;
    using (var sfh = WTSVirtualChannelOpenEx(WTS_CURRENT_SESSION, channelName, option))
    {
        WtsAllocSafeHandle pBuffer = null;
        try
        {
            int cbReturned;
            if (!WTSVirtualChannelQuery(sfh, WTS_VIRTUAL_CLASS.FileHandle, out pBuffer, out cbReturned)
                || cbReturned < IntPtr.Size)
            {
                throw new Win32Exception();
            }
            pFile = new SafeFileHandle(Marshal.ReadIntPtr(pBuffer.DangerousGetHandle()), false);
        }
        finally
        {
            pBuffer?.Dispose();
        }
    }

    // create
    return new FileStream(pFile, FileAccess.ReadWrite, bufferSize: 32 * 1024 * 1024, isAsync: true);
}

例外：

System.ArgumentException: Handle does not support asynchronous operations.  The parameters to the FileStream constructor may need to be changed to indicate that the handle was opened synchronously (that is, it was not opened for overlapped I/O).
    at System.IO.FileStream..ctor(SafeFileHandle handle, FileAccess access, Int32 bufferSize, Boolean isAsync)

和

System.IO.IOException: The handle is invalid.
   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
   at System.IO.FileStream.VerifyHandleIsSync()
   at System.IO.FileStream..ctor(SafeFileHandle handle, FileAccess access, Int32 bufferSize, Boolean isAsync)

标签： c#remote-desktop

Answer 1

返回的句柄WTSVirtualChannelQuery似乎一WTSFreeMemory被调用就失效了。在调用DuplicateHandle之前调用WTSFreeMemory并使用重复的句柄。

public static FileStream Open(string channelName, WTS_CHANNEL_OPTION option = WTS_CHANNEL_OPTION.DYNAMIC)
{
    // Open
    SafeFileHandle pFile = null;
    using (var sfh = WTSVirtualChannelOpenEx(WTS_CURRENT_SESSION, channelName, option))
    {
        WtsAllocSafeHandle pBuffer = null;
        try
        {
            int cbReturned;
            if (!WTSVirtualChannelQuery(sfh, WTS_VIRTUAL_CLASS.FileHandle, out pBuffer, out cbReturned)
                || cbReturned < IntPtr.Size)
            {
                throw new Win32Exception();
            }
            var pWtsFile = Marshal.ReadIntPtr(pBuffer.DangerousGetHandle());
            if (!DuplicateHandle(
                GetCurrentProcess(), pWtsFile,
                GetCurrentProcess(), out pFile, 
                0, false, DUPLICATE_SAME_ACCESS))
            {
                throw new Win32Exception();
            }
        }
        finally
        {
            pBuffer?.Dispose();
        }
    }

    // create
    return new FileStream(pFile, FileAccess.ReadWrite, bufferSize: 32 * 1024 * 1024, isAsync: true);
}