gateway 정보 가져오기

// .pro
QT += network

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <net/if.h>
#include <linux/rtnetlink.h>
#include <unistd.h>
#include <arpa/inet.h>

 // 사용 부분 
    char gateway[20];
    memset(gateway, 0, sizeof(gateway));

    get_gatewayip(gateway, 20);
    memcpy(g_ODT.ENV.ODT_NETWORK.Gateway, gateway, 15);

int readNlSock(int sockFd, char *bufPtr, int seqNum, int pId)
{
    struct nlmsghdr *nlHdr;
    int readLen = 0, msgLen = 0;

    do
    {
        /* Recieve response from the kernel */
        if((readLen = recv(sockFd, bufPtr, BUFSIZE - msgLen, 0)) < 0)
        {
            g_Log.LogWrite((char *)"SOCK READ: ");가져오기
            return -1;
        }

        nlHdr = (struct nlmsghdr *)bufPtr;

        /* Check if the header is valid */
        if((NLMSG_OK(nlHdr, readLen) == 0) || (nlHdr->nlmsg_type == NLMSG_ERROR))
        {
            g_Log.LogWrite((char *)"Error in recieved packet");
            return -1;
        }

        /* Check if the its the last message */
        if(nlHdr->nlmsg_type == NLMSG_DONE)
        {
            break;
        }
        else
        {
            /* Else move the pointer to buffer appropriately */
            bufPtr += readLen;
            msgLen += readLen;
        }

        /* Check if its a multi part message */
        if((nlHdr->nlmsg_flags & NLM_F_MULTI) == 0)
        {
            /* return if its not */
            break;
        }
    } while((nlHdr->nlmsg_seq != (UINT32)seqNum) || (nlHdr->nlmsg_pid != (UINT32)pId));

    return msgLen;
}

/* parse the route info returned */
void parseRoutes(struct nlmsghdr *nlHdr, struct route_info *rtInfo)
{
    struct rtmsg *rtMsg;
    struct rtattr *rtAttr;
    int rtLen;

    rtMsg = (struct rtmsg *)NLMSG_DATA(nlHdr);

    /* If the route is not for AF_INET or does not belong to main routing table    then return. */
    if((rtMsg->rtm_family != AF_INET) || (rtMsg->rtm_table != RT_TABLE_MAIN))
        return;

    /* get the rtattr field */
    rtAttr = (struct rtattr *)RTM_RTA(rtMsg);
    rtLen = RTM_PAYLOAD(nlHdr);

    for(;RTA_OK(rtAttr,rtLen);rtAttr = RTA_NEXT(rtAttr,rtLen))
    {
        switch(rtAttr->rta_type)
        {
            case RTA_OIF:
            if_indextoname(*(int *)RTA_DATA(rtAttr), rtInfo->ifName);
            break;

            case RTA_GATEWAY:
            memcpy(&rtInfo->gateWay, RTA_DATA(rtAttr), sizeof(rtInfo->gateWay));
            break;

            case RTA_PREFSRC:
            memcpy(&rtInfo->srcAddr, RTA_DATA(rtAttr), sizeof(rtInfo->srcAddr));
            break;

            case RTA_DST:
            memcpy(&rtInfo->dstAddr, RTA_DATA(rtAttr), sizeof(rtInfo->dstAddr));
            break;
        }
    }

    return;
}

int get_gatewayip(char *gatewayip, socklen_t size)
{
    int found_gatewayip = 0;
    struct nlmsghdr *nlMsg;
    // struct rtmsg *rtMsg;
    struct route_info *rtInfo;
    char msgBuf[BUFSIZE]; // pretty large buffer
    int sock, len, msgSeq = 0;

    /* Create Socket */
    if((sock = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE)) < 0)
    {
        g_Log.LogWrite((char *)"Socket Creation: ");
        return(-1);
    }

    /* Initialize the buffer */
    memset(msgBuf, 0, BUFSIZE);

    /* point the header and the msg structure pointers into the buffer */
    nlMsg = (struct nlmsghdr *)msgBuf;
    // rtMsg = (struct rtmsg *)NLMSG_DATA(nlMsg);

    /* Fill in the nlmsg header*/
    nlMsg->nlmsg_len = NLMSG_LENGTH(sizeof(struct rtmsg)); // Length of message.
    nlMsg->nlmsg_type = RTM_GETROUTE; // Get the routes from kernel routing table .
    nlMsg->nlmsg_flags = NLM_F_DUMP | NLM_F_REQUEST; // The message is a request for dump.
    nlMsg->nlmsg_seq = msgSeq++; // Sequence of the message packet.
    nlMsg->nlmsg_pid = getpid(); // PID of process sending the request.

    /* Send the request */
    if(send(sock, nlMsg, nlMsg->nlmsg_len, 0) < 0)
    {
        g_Log.LogWrite((char *)"Write To Socket Failed...\n");
        return -1;
    }

    /* Read the response */
    if((len = readNlSock(sock, msgBuf, msgSeq, getpid())) < 0)
    {
        g_Log.LogWrite((char *)"Read From Socket Failed...\n");
        return -1;
    }

    /* Parse and print the response */
    rtInfo = (struct route_info *)malloc(sizeof(struct route_info));

    for(;NLMSG_OK(nlMsg,len);nlMsg = NLMSG_NEXT(nlMsg,len))
    {
        memset(rtInfo, 0, sizeof(struct route_info));
        parseRoutes(nlMsg, rtInfo);

        // Check if default gateway
        if (strstr((char *)inet_ntoa(rtInfo->dstAddr), "0.0.0.0"))
        {
            // copy it over
            inet_ntop(AF_INET, &rtInfo->gateWay, gatewayip, size);
            found_gatewayip = 1;
            break;
        }
    }

    free(rtInfo);
    close(sock);

    return found_gatewayip;
}