IrDA and getsockopt Using IRLMP_ENUMDEVICES

Article
05/31/2018

The Windows Sockets getsockopt function is used to run a discovery. Before a connection can be initiated, a device address must be obtained by performing a discovery operation. An extension to the Winsock getsockopt call returns a list of all currently visible IrDA devices. A device address returned from this list is copied into a SOCKADDR_IRDA structure to be used by the connect function call.

To initiate a discovery

Performing a getsockopt function call with the IRLMP_ENUMDEVICES option causes a single discovery to be run on each idle adapter. The list of discovered devices and cached devices (on active adapters) will be returned immediately. The following code demonstrates this:

#include <windows.h>
#include <af_irda.h>

#pragma comment(lib, "ws2_32.lib")

#define DEVICE_LIST_LEN    10

void main()
{
    SOCKADDR_IRDA     DestSockAddr = { AF_IRDA, 0, 0, 0, 0, "SampleIrDAService" };

    unsigned char    DevListBuff[sizeof(DEVICELIST) -
             sizeof(IRDA_DEVICE_INFO) +
             (sizeof(IRDA_DEVICE_INFO) * DEVICE_LIST_LEN)];
    int        DevListLen    = sizeof(DevListBuff);
    PDEVICELIST    pDevList    = (PDEVICELIST) &amp;DevListBuff;
  int i;

    pDevList->numDevice = 0;

    // Sock is not in connected state
    if (getsockopt(Sock, SOL_IRLMP, IRLMP_ENUMDEVICES,
                   (char *) pDevList, &amp;DevListLen) == SOCKET_ERROR)
    {
    // WSAGetLastError 
    }

    if (pDevList->numDevice == 0)
    {
        // no devices discovered or cached
        // not a bad idea to run a couple of times
    }
    else
    {
        // one per discovered device
        for (i = 0; i < (int) pDevList->numDevice; i++)
        {
        // typedef struct _IRDA_DEVICE_INFO
        // {
                //    u_char    irdaDeviceID[4];
                //    char    irdaDeviceName[22];
                //    u_char    irdaDeviceHints1;
                //     u_char    irdaDeviceHints2;
                //    u_char    irdaCharSet;
        // } _IRDA_DEVICE_INFO;

            // pDevList->Device[i]. see _IRDA_DEVICE_INFO for fields
            // display the device names and let the user select one
        }
    }

    // assume the user selected the first device [0]
    memcpy(&amp;DestSockAddr.irdaDeviceID[0], &amp;pDevList->Device[0].irdaDeviceID[0], 4);

    if (connect(Sock, (const struct sockaddr *) &amp;DestSockAddr,
                sizeof(SOCKADDR_IRDA)) == SOCKET_ERROR)
    {
        // WSAGetLastError
    }
}

To run a lazy discovery

It is also possible to run a lazy discovery — the application will not be notified until the discovered device list changes from the last discovery run by the stack.

IrDA and getsockopt Using IRLMP_ENUMDEVICES

Additional resources