LinuxC编程获取网关

LinuxC编程获取网关
#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>
#define BUFSIZE 8192
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_pi d != pId));
return msgLen;
}
/* For printing the routes. */
void printRoute(struct route_info *rtInfo)
{
char tempBuf[512];
/* Print Destination address */
if(rtInfo->dstAddr != 0)
strcpy(tempBuf,(char*)inet_ntoa(rtInfo->dstAddr));
else
sprintf(tempBuf,"*.*.*.*\t");
fprintf(stdout,"%s\t", tempBuf);
/* Print Gateway address */
if(rtInfo->gateWay != 0)
strcpy(tempBuf,(char*)inet_ntoa(rtInfo->gateWay));
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)
strcpy(tempBuf,(char*)inet_ntoa(rtInfo->srcAddr));
else
sprintf(tempBuf,"*.*.*.*\t");
fprintf(stdout,"%s\n", tempBuf);
}
/* For parsing the route info returned */
void parseRoutes(struct nlmsghdr *nlHdr,struct route_info * rtInfo,char*gateway)
{
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 != R T_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
if(strstr((char*)inet_ntoa(rtInfo->dstAddr),"0.0.0.0")) sprintf(gateway,(char*)inet_ntoa(rtInfo->gateWay));
//printRoute(rtInfo);
free(tempBuf);
return;
}
int get_gateway(char*gateway)
{
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_RO UTE))< 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,le n)){
memset(rtInfo, 0,sizeof(struct route_info)); parseRoutes(nlMsg, rtInfo,gateway);
}
free(rtInfo);
close(sock);
return 0;
}
int main()
{
char gateway[255]={0};
get_gateway(gateway);
printf("Gateway:%s\n", gateway);
}。