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#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <ifaddrs.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
static void die(const char *str)
{
fprintf(stderr, "%s\n", str);
exit(1);
}
static int is_same_subnet(struct sockaddr_in *a, struct sockaddr_in *b,
struct sockaddr_in *mask)
{
if (a->sin_family != b->sin_family)
return 0;
return ((a->sin_addr.s_addr & mask->sin_addr.s_addr)
== (b->sin_addr.s_addr & mask->sin_addr.s_addr));
}
static int get_bcast_addr(const char *iface, struct sockaddr_in *src,
struct sockaddr_in *bcast)
{
struct ifaddrs *ifaddr, *ifa;
int ret = 0;
if (getifaddrs(&ifaddr) == -1)
die("getifaddrs");
for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
if (ifa->ifa_addr == NULL
|| ifa->ifa_addr->sa_family != AF_INET
|| (strcmp(iface, ifa->ifa_name) != 0))
continue;
/* dont forward broadcast from our own subnet(s) */
if (is_same_subnet((struct sockaddr_in *)ifa->ifa_addr, src,
(struct sockaddr_in *)ifa->ifa_netmask))
continue;
memcpy(bcast, ifa->ifa_ifu.ifu_broadaddr,
sizeof(struct sockaddr_in));
ret = sizeof(struct sockaddr_in);
break;
}
freeifaddrs(ifaddr);
return ret;
}
static int run_proxy(const char *iface, int port)
{
struct sockaddr_in src, dst;
char buf[256];
int fd, n = 1;
socklen_t addrlen;
fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (fd < 0)
die("socket");
memset(&src, 0, sizeof(src));
src.sin_family = AF_INET;
src.sin_port = htons(port);
src.sin_addr.s_addr = htonl(INADDR_ANY);
if (bind(fd, (struct sockaddr *)&src, sizeof(src)) < 0)
die("bind");
setsockopt(fd, SOL_SOCKET, SO_BROADCAST, &n, sizeof(n));
while (1) {
n = recvfrom(fd, buf, sizeof(buf), 0, (struct sockaddr *)&src,
&addrlen);
if (n < 0)
die("recvfrom");
if (get_bcast_addr(iface, &src, &dst)) {
dst.sin_port = htons(port);
sendto(fd, buf, n, 0, (struct sockaddr *) &dst,
sizeof(dst));
}
}
return 0;
}
int main(int argc, char *argv[])
{
int port = 9;
const char *iface = NULL;
if (argc > 1)
iface = argv[1];
return run_proxy(iface, port);
}
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