C# using SendMessage, problem with WM_COPYDATA

Question

I\'ve been spending a few days (or more) trying to get this to work.

The application at hand is FTPRush, and I know there is a cmd line application call

Answer 1

My Definitions have

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = false)]
public static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, ref COPYDATASTRUCT lParam);

public struct COPYDATASTRUCT {
  public int cbData;
  public IntPtr dwData;
  [MarshalAs(UnmanagedType.LPStr)] public string lpData;
}

var cds = new Win32.COPYDATASTRUCT {
                                           dwData = new IntPtr(3),
                                           cbData = str.Length + 1,
                                           lpData = str
                                         };
Win32.SendMessage(ftprush, Win32.WM_COPYDATA, IntPtr.Zero, ref cds);

Of course, make sure that str is null terminated "\0"

Alternatively a definition given by PInvoke.NET is

[DllImport("user32.dll", CharSet = CharSet.Auto)]
static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, IntPtr wParam, StringBuilder lParam);
//If you use '[Out] StringBuilder', initialize the string builder with proper length first.

Answer 2

Between the 2 answers above I cobbled together a working example. Bryce Wagner's class works, so I added a method to use SendMessageTimeout to send the data. it's a static method, so you just call it to send data. This isn't really my work, just gluing together and sharing back.

    [StructLayout(LayoutKind.Sequential)]
    public struct CopyData: IDisposable {
        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = false)]
        static extern IntPtr SendMessageTimeout(IntPtr hWnd, uint Msg, IntPtr wParam, ref CopyData target,
                                                SendMessageTimeoutFlags fuFlags, uint uTimeout, out UIntPtr lpdwResult);

        [Flags]
        enum SendMessageTimeoutFlags: uint {
            SMTO_NORMAL             = 0x0,
            SMTO_BLOCK              = 0x1,
            SMTO_ABORTIFHUNG        = 0x2,
            SMTO_NOTIMEOUTIFNOTHUNG = 0x8
        }
        const uint WM_COPYDATA = 0x4A;

        public IntPtr dwData;
        public int cbData;
        public IntPtr lpData;

        public void Dispose() {
            if (lpData != IntPtr.Zero) {
                Marshal.FreeCoTaskMem(lpData);
                lpData = IntPtr.Zero;
                cbData = 0;
            }
        }
        public string AsAnsiString {
            get { return Marshal.PtrToStringAnsi(lpData, cbData); }
        }
        public string AsUnicodeString {
            get { return Marshal.PtrToStringUni(lpData); }
        }
        public static CopyData CreateForString(int dwData, string value, bool Unicode = false) {
            var result = new CopyData();
            result.dwData = (IntPtr) dwData;
            result.lpData = Unicode ? Marshal.StringToCoTaskMemUni(value) : Marshal.StringToCoTaskMemAnsi(value);
            result.cbData = value.Length + 1;
            return result;
        }

        public static UIntPtr Send(IntPtr targetHandle, int dwData, string value, uint timeoutMs = 1000, bool Unicode = false) {
            var cds = CopyData.CreateForString(dwData, value, Unicode);
            UIntPtr result;
            SendMessageTimeout(targetHandle, WM_COPYDATA, IntPtr.Zero, ref cds, SendMessageTimeoutFlags.SMTO_NORMAL, timeoutMs, out result);
            cds.Dispose();
            return result;
        }
    }

To use it:

CopyData.Send(targetHandle, 1234, "This is a test");

That uses the default 1 second timeout.

Answer 3

The order of arguments in the COPYDATASTRUCT are critically important, and Bob Vale's answer has them in the wrong order. http://msdn.microsoft.com/en-us/library/windows/desktop/ms649010(v=vs.85).aspx It should be in this order:

[StructLayout(LayoutKind.Sequential)]
public struct COPYDATASTRUCT
{
    public IntPtr dwData;
    public int cbData;
    public IntPtr lpData;
}

I haven't gotten the MarshalAs(UnmanagedType.LPStr)] public string lpData to work either. I've only gotten it to work by doing the marshalling myself:

[StructLayout(LayoutKind.Sequential)]
public struct COPYDATASTRUCT : IDisposable
{
    public IntPtr dwData;
    public int cbData;
    public IntPtr lpData;

    /// <summary>
    /// Only dispose COPYDATASTRUCT if you were the one who allocated it
    /// </summary>
    public void Dispose()
    {
        if (lpData != IntPtr.Zero)
        {
            Marshal.FreeCoTaskMem(lpData);
            lpData = IntPtr.Zero;
            cbData = 0;
        }
    }
    public string AsAnsiString { get { return Marshal.PtrToStringAnsi(lpData, cbData); } }
    public string AsUnicodeString { get { return Marshal.PtrToStringUni(lpData); } }
    public static COPYDATASTRUCT CreateForString(int dwData, string value, bool Unicode = false)
    {
        var result = new COPYDATASTRUCT();
        result.dwData = (IntPtr)dwData;
        result.lpData = Unicode ? Marshal.StringToCoTaskMemUni(value) : Marshal.StringToCoTaskMemAnsi(value);
        result.cbData = value.Length + 1;
        return result;
    }
}