Question

I have a problem retrieving the information of printer ports. I already use XcvData function to add, configure and delete ports, but I can not get the following to run as I expect it to:

public PrinterNativeMethods.PORT_DATA_1 GetPortData1FromPort(string serverName, string portName)
{
    IntPtr printerHandle;
    PrinterNativeMethods.PRINTER_DEFAULTS defaults = new PrinterNativeMethods.PRINTER_DEFAULTS
    {
        DesiredAccess = PrinterNativeMethods.PrinterAccess.ServerAdmin
    };

    string connection = string.Format(@"{0},XcvPort {1}", serverName, portName);

    PrinterNativeMethods.OpenPrinter(connection, out printerHandle, ref defaults);

    PrinterNativeMethods.CONFIG_INFO_DATA_1 configData = new PrinterNativeMethods.CONFIG_INFO_DATA_1
    {
        dwVersion = 1,
    };

    uint size = (uint)Marshal.SizeOf(configData);

    IntPtr pointer = Marshal.AllocHGlobal((int)size);
    Marshal.StructureToPtr(configData, pointer, true);

    PrinterNativeMethods.PORT_DATA_1 portData = new PrinterNativeMethods.PORT_DATA_1();
    uint portDataSize = (uint)Marshal.SizeOf(portData);
    IntPtr portDataHandle = Marshal.AllocHGlobal((int)portDataSize);

    try
    {
        uint outputNeeded;
        uint status;

        var retVal = PrinterNativeMethods.XcvData(printerHandle, "GetConfigInfo", pointer, size, out portDataHandle, portDataSize, out outputNeeded, out status);
        //portDataHandle now points to a different location!? Unmarshalling will fail:
        portData = (PrinterNativeMethods.PORT_DATA_1)Marshal.PtrToStructure(portDataHandle, typeof(PrinterNativeMethods.PORT_DATA_1));

    }
    finally
    {
        PrinterNativeMethods.ClosePrinter(printerHandle);
        Marshal.FreeHGlobal(pointer);
        Marshal.FreeHGlobal(portDataHandle);
    }

    return portData;
}

from PrinterNativeMethods:

    [DllImport("winspool.drv", SetLastError = true, CharSet = CharSet.Unicode)]
    internal static extern int XcvData(
        IntPtr handle,
        string dataName,
        IntPtr inputData,
        uint inputDataSize,
        out IntPtr outputData,
        uint outputDataSize,
        out uint outputNeededSize,
        out uint status);

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
    public struct PORT_DATA_1
    {
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 64)]
        public string sztPortName;

        public uint dwVersion;

        public uint dwProtocol;

        public uint cbSize;

        public uint dwReserved;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 49)]
        public string sztHostAddress;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 33h)]
        public string sztSNMPCommunity;

        public uint dwDoubleSpool;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 33)]
        public string sztQueue;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 16)]
        public string sztIPAddress;

        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 540)]
        public byte[] Reserved;

        public uint dwPortNumber;

        public uint dwSNMPEnabled;

        public uint dwSNMPDevIndex;
    }

Additional comment: I cannot use WMI or prnadmin.dll as an alternative.

Answer 1

The problem you are having is in the definition of your XcvData definition. The outputData parameter by MS’s definition is simply wanting a pointer to write data to, an IntPtr is a pointer, however by setting the parameter to out IntPtr you are making it a pointer to a pointer, this is why the address of your parameter appears to be changing. Changing the signature to the below will fix your problem.

[DllImport("winspool.drv", SetLastError = true, CharSet = CharSet.Unicode)]
internal static extern int XcvData(
    IntPtr handle,
    string dataName,
    IntPtr inputData,
    uint inputDataSize,
    IntPtr outputData,
    uint outputDataSize,
    out uint outputNeededSize,
    out uint status);

You can also avoid some unnecessary allocation/deallocation by changing things around a bit.

Change your method signature for XcvData to

[DllImport("winspool.drv", SetLastError = true, CharSet = CharSet.Unicode)]
internal static extern int XcvData(
    IntPtr handle,
    string dataName,
    IntPtr inputData,
    uint inputDataSize,
    ref PORT_DATA_1 outputData,
    uint outputDataSize,
    out uint outputNeededSize,
    out uint status);

Assuming that you will be using XcvData for more than just this single call you can make multiple references to it with slightly different signatures by setting the EntryPoint property on the DllImport Attribute.

[DllImport("winspool.drv", SetLastError = true, CharSet = CharSet.Unicode, EntryPoint="XcvData")]
internal static extern int XcvDataGetPortData1(
    IntPtr handle,
    string dataName,
    IntPtr inputData,
    uint inputDataSize,
    ref PORT_DATA_1 outputData,
    uint outputDataSize,
    out uint outputNeededSize,
    out uint status);

I have given this a quick test on my machine and can confirm that this will fix your problem.