FreeBSD下查询路由

我们的程序参数中有一个需要查询路由ipv4的地址，程序把ipv4地址使用RTM_GET发送到系统内核，内核在路由表中查询这个ipv4地址的路由信息，然后把路由信息返回。
例如：
freebsd % reqroute 206.168.112.219
dest: 0.0.0.0
gateway: 12.106.32.1
netmask: 0.0.0.0
可以运行在freebsd上，也可以运行在macos10.4/5/6上。

#include <stdio.h>
#include <stdlib.h>
#include <net/route.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <net/if_dl.h>
#include <sys/un.h>
#include <netinet/in.h>
#include <string.h>

#define BUFLEN   (sizeof(struct rt_msghdr) + 512)
                      /* sizeof(struct sockaddr_in6) * 8 = 192 */
#define SEQ      9999

void get_rtaddrs(int addrs, struct sockaddr  *sa, struct sockaddr  **rti_info);
const char * sock_masktop(struct sockaddr *sa, socklen_t salen);
char *sock_ntop_host(const struct sockaddr *sa, socklen_t salen);

int main(int argc, char **argv){
 int     sockfd;
 char   *buf;
 pid_t   pid;
 size_t n;
 struct rt_msghdr *rtm;
 struct sockaddr *sa, *rti_info[RTAX_MAX];
 struct sockaddr_in *sin;

 if (argc != 2){
  printf("usage: reqroute <IPaddress>");
  exit(0);
 }

 sockfd = socket(AF_ROUTE, SOCK_RAW, 0); /* need superuser privileges */

 buf = calloc(1, BUFLEN);     /* and initialized to 0 */

 rtm = (struct rt_msghdr *) buf;
 rtm->rtm_msglen = sizeof(struct rt_msghdr) + sizeof(struct sockaddr_in);
 rtm->rtm_version = RTM_VERSION;
 rtm->rtm_type = RTM_GET;
 rtm->rtm_addrs = RTA_DST;
 rtm->rtm_pid = pid = getpid();
 rtm->rtm_seq = SEQ;/*compared with reply to get correct value*/

 sin = (struct sockaddr_in *) (rtm + 1);
 sin->sin_len = sizeof(struct sockaddr_in);
 sin->sin_family = AF_INET;
 inet_pton(AF_INET, argv[1], &sin->sin_addr);

 write(sockfd, rtm, rtm->rtm_msglen);

 /*Since other processes may have routing sockets open, and since
  the kernel passes a copy of all routing messages to all routing
  sockets, we must check the message type, sequence number, and
  process ID to verify that the message received is the one we are waiting for.
 */
 do {
  n = read(sockfd, rtm, BUFLEN);
 } while (rtm->rtm_type != RTM_GET || rtm->rtm_seq != SEQ ||
  rtm->rtm_pid != pid);
 rtm = (struct rt_msghdr *) buf;
 sa = (struct sockaddr *) (rtm + 1);
 get_rtaddrs(rtm->rtm_addrs, sa, rti_info);
 if ( (sa = rti_info[RTAX_DST]) != NULL){
  printf("dest: %s/n", sock_ntop_host(sa, sa->sa_len));
 }

 if ( (sa = rti_info[RTAX_GATEWAY]) != NULL){
  printf("gateway: %s/n", sock_ntop_host(sa, sa->sa_len));
 }

 if ( (sa = rti_info[RTAX_NETMASK]) != NULL){
  printf("netmask: %s/n", sock_masktop(sa, sa->sa_len));
 }

 if ( (sa = rti_info[RTAX_GENMASK]) != NULL){
  printf("genmask: %s/n", sock_masktop(sa, sa->sa_len));
 }

 exit(0);
}

/*
 * Round up 'a' to next multiple of 'size', which must be a power of 2
 */
#define ROUNDUP(a, size) (((a) & ((size)-1)) ? (1 + ((a) | ((size)-1))) : (a))
/*
 * Step to next socket address structure;
 * if sa_len is 0, assume it is sizeof(u_long).
 */
#define NEXT_SA(ap) ap = (struct sockaddr  *) /
    ((caddr_t) ap + (ap->sa_len ? ROUNDUP(ap->sa_len, sizeof (u_long)) : /
                                       sizeof(u_long)))

void get_rtaddrs(int addrs, struct sockaddr  *sa, struct sockaddr  **rti_info){
 int     i;

 for (i = 0; i < RTAX_MAX; i++) {
  if (addrs & (1 << i)) {
   rti_info[i] = sa;
   NEXT_SA(sa);
  }else{
   rti_info[i] = NULL;
  }
 }
}

const char * sock_masktop(struct sockaddr *sa, socklen_t salen){
 static char str[INET6_ADDRSTRLEN];
 unsigned char *ptr = &sa->sa_data[2];

 if (sa->sa_len == 0){
  return ("0.0.0.0");
 }else if (sa->sa_len == 5){
  snprintf(str, sizeof(str), "%d.0.0.0", *ptr);
 }else if (sa->sa_len == 6){
  snprintf(str, sizeof(str), "%d.%d.0.0", *ptr, *(ptr + 1));
 }else if (sa->sa_len == 7){
  snprintf(str, sizeof(str), "%d.%d.%d.0", *ptr, *(ptr + 1),
   *(ptr + 2));
 }else if (sa->sa_len == 8){
  snprintf(str, sizeof(str), "%d.%d.%d.%d",
   *ptr, *(ptr + 1), *(ptr + 2), *(ptr + 3));
 }else{
  snprintf(str, sizeof(str), "(unknown mask, len = %d, family = %d)",
   sa->sa_len, sa->sa_family);
 }
 return (str);
}

char *sock_ntop_host(const struct sockaddr *sa, socklen_t salen){
 static char str[128]; /* Unix domain is largest */

 switch (sa->sa_family) {
  case AF_INET: {
   struct sockaddr_in *sin = (struct sockaddr_in *) sa;

   if (!inet_ntop(AF_INET, &sin->sin_addr, str, sizeof(str))){
    return(NULL);
   }
   return(str);
  } 
  case AF_INET6: {
   struct sockaddr_in6 *sin6 = (struct sockaddr_in6 *) sa;

   if (!inet_ntop(AF_INET6, &sin6->sin6_addr, str, sizeof(str))){
    return(NULL);
   }
   return(str);
  }

  case AF_UNIX: {
   struct sockaddr_un *unp = (struct sockaddr_un *) sa;

   /* OK to have no pathname bound to the socket: happens on
      every connect() unless client calls bind() first. */
   if (!unp->sun_path[0]){
    strcpy(str, "(no pathname bound)");
   }else{
    snprintf(str, sizeof(str), "%s", unp->sun_path);
   }
   return(str);
  } 

  case AF_LINK: {
   struct sockaddr_dl *sdl = (struct sockaddr_dl *) sa;

   if (sdl->sdl_nlen > 0){
    snprintf(str, sizeof(str), "%*s",
      sdl->sdl_nlen, &sdl->sdl_data[0]);
   }else{
    char ifname[128] = {0};
    if_indextoname(sdl->sdl_index,ifname);
    snprintf(str, sizeof(str), "AF_LINK, index=%d,%s", sdl->sdl_index,ifname);
   }
   return(str);
  }

  default:
   snprintf(str, sizeof(str), "sock_ntop_host: unknown AF_xxx: %d, len %d",
      sa->sa_family, salen);
   return(str);
 }
 return (NULL);
}