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#include <asm/types.h>
#include <netinet/ether.h>
#include <netinet/in.h>
#include <net/if.h>
#include <stdio.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>

#define BUFSIZE 8192
// ADDED BY BOB
char gateway[255];

struct route_info{
u_int dstAddr;
u_int srcAddr;
u_int gateWay;
char ifName[IF_NAMESIZE];
};

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){
perror("SOCK READ: ");
return -1;
}

nlHdr = (struct nlmsghdr *)bufPtr;

/* Check if the header is valid */
if((NLMSG_OK(nlHdr, readLen) == 0) || (nlHdr->nlmsg_type == NLMSG_ERROR))
{
perror("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 != seqNum) || (nlHdr->nlmsg_pid != pId));
return msgLen;
}

/* For printing the routes. */
void printRoute(struct route_info *rtInfo)
{
char tempBuf[512];

/* Print Destination address */
if(rtInfo->dstAddr != 0) {
struct in_addr addr;
addr.s_addr = rtInfo->dstAddr;
strcpy(tempBuf, (char *)inet_ntoa(addr));
}else {
sprintf(tempBuf,"*.*.*.*\t");
}
fprintf(stdout,"%s\t", tempBuf);

/* Print Gateway address */
if(rtInfo->gateWay != 0) {
struct in_addr addr;
addr.s_addr = rtInfo->gateWay;
strcpy(tempBuf, (char *)inet_ntoa(addr));
}else{
sprintf(tempBuf,"*.*.*.*\t");
}
fprintf(stdout,"%s\t", tempBuf);

/* Print Interface Name*/
fprintf(stdout,"%s\t", rtInfo->ifName);

/* Print Source address */
if(rtInfo->srcAddr != 0) {
struct in_addr addr;
addr.s_addr = rtInfo->srcAddr;
strcpy(tempBuf, (char *)inet_ntoa(addr));
}else{
sprintf(tempBuf,"*.*.*.*\t");
}
fprintf(stdout,"%s\n", tempBuf);
}

void printGateway()
{
printf("%s\n", gateway);
}

/* For parsing the route info returned */
void parseRoutes(struct nlmsghdr *nlHdr, struct route_info *rtInfo)
{
struct rtmsg *rtMsg;
struct rtattr *rtAttr;
int rtLen;
char *tempBuf = NULL;

tempBuf = (char *)malloc(100);
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:
rtInfo->gateWay = *(u_int *)RTA_DATA(rtAttr);
break;
case RTA_PREFSRC:
rtInfo->srcAddr = *(u_int *)RTA_DATA(rtAttr);
break;
case RTA_DST:
rtInfo->dstAddr = *(u_int *)RTA_DATA(rtAttr);
break;
}
}
//printf("%s\n", (char *)inet_ntoa(rtInfo->dstAddr));
// ADDED BY BOB - ALSO COMMENTED printRoute
struct in_addr addr;
addr.s_addr = rtInfo->dstAddr;
if (strstr((char *)inet_ntoa(addr), "0.0.0.0")) {
    struct in_addr addr;
    addr.s_addr = rtInfo->gateWay;
    sprintf(gateway, (char *)inet_ntoa(addr));
}
//printRoute(rtInfo);
free(tempBuf);
return;
}

int main()
{
struct nlmsghdr *nlMsg;
struct rtmsg *rtMsg;
struct route_info *rtInfo;
char msgBuf[BUFSIZE];

int sock, len, msgSeq = 0;
char buff[1024];

/* Create Socket */
if((sock = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE)) < 0)
perror("Socket Creation: ");

/* 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){
printf("Write To Socket Failed...\n");
return -1;
}

/* Read the response */
if((len = readNlSock(sock, msgBuf, msgSeq, getpid())) < 0) {
printf("Read From Socket Failed...\n");
return -1;
}
/* Parse and print the response */
rtInfo = (struct route_info *)malloc(sizeof(struct route_info));
// ADDED BY BOB
/* THIS IS THE NETTSTAT -RL code I commented out the printing here and in parse routes */
//fprintf(stdout, "Destination\tGateway\tInterface\tSource\n");
for(;NLMSG_OK(nlMsg,len);nlMsg = NLMSG_NEXT(nlMsg,len)){
memset(rtInfo, 0, sizeof(struct route_info));
parseRoutes(nlMsg, rtInfo);
}
free(rtInfo);
close(sock);
// ADDED BY BOB
printGateway();
return 0;
}