udpproxy.c

   1 #define _GNU_SOURCE
   2
   3 #include <stdio.h>
   4 #include <stdlib.h>
   5 #include <string.h>
   6 #include <time.h>
   7 #include <errno.h>
   8 #include <sys/socket.h>
   9 #include <netdb.h>
  10 #include <unistd.h>
  11 #include <stdlib.h>
  12 #include <fcntl.h>
  13 #include <sys/types.h>
  14 #include <sys/time.h>
  15 #include <arpa/inet.h>
  16 #include <netinet/in.h>
  17
  18 static void get_address(const char *host, struct in_addr *addr)
  19 {
  20        if (inet_pton(AF_INET, host, addr) <= 0) {
  21                struct hostent *hp;
  22                hp = gethostbyname(host);
  23                if (!hp) {
  24                        fprintf(stderr,"unknown host %s\n", host);
  25                        exit(1);
  26                }
  27                memcpy(addr, hp->h_addr, hp->h_length);
  28        }
  29 }
  30
  31 /*
  32   open a socket of the specified type, port and address for incoming data
  33 */
  34 int open_socket_in(int port)
  35 {
  36         struct sockaddr_in sock;
  37         int res;
  38         int one=1;
  39
  40         memset(&sock,0,sizeof(sock));
  41
  42 #ifdef HAVE_SOCK_SIN_LEN
  43         sock.sin_len = sizeof(sock);
  44 #endif
  45         sock.sin_port = htons(port);
  46         sock.sin_family = AF_INET;
  47
  48         res = socket(AF_INET, SOCK_DGRAM, 0);
  49         if (res == -1) {
  50                 fprintf(stderr, "socket failed\n"); return -1;
  51                 return -1;
  52         }
  53
  54         setsockopt(res,SOL_SOCKET,SO_REUSEADDR,(char *)&one,sizeof(one));
  55
  56         if (bind(res, (struct sockaddr *)&sock, sizeof(sock)) < 0) {
  57                 return(-1);
  58         }
  59
  60         return res;
  61 }
  62
  63 static void main_loop(int sock, const char *host1, const char *host2)
  64 {
  65         unsigned char buf[10240];
  66         struct in_addr addr1, addr2;
  67
  68         get_address(host1, &addr1);
  69         get_address(host2, &addr2);
  70
  71         while (1) {
  72                 fd_set fds;
  73                 int ret;
  74                 struct in_addr *addr;
  75
  76                 FD_ZERO(&fds);
  77                 FD_SET(sock, &fds);
  78
  79                 ret = select(sock, &fds, NULL, NULL, NULL);
  80                 if (ret == -1 && errno == EINTR) continue;
  81                 if (ret <= 0) break;
  82
  83                 if (FD_ISSET(sock, &fds)) {
  84                         static struct sockaddr_in from;
  85                         static socklen_t fromlen = sizeof(from);
  86                         int n = recvfrom(sock, buf, sizeof(buf), 0,
  87                                          (struct sockaddr *)&from, &fromlen);
  88                         if (n <= 0) break;
  89
  90                         if (from.sin_addr.s_addr == addr1.s_addr) {
  91                                 addr = &addr2;
  92                         } else if (from.sin_addr.s_addr == addr2.s_addr) {
  93                                 addr = &addr1;
  94                         } else {
  95                                 printf("Unexpected packet from %s\n", inet_ntoa(from.sin_addr));
  96                                 continue;
  97                         }
  98
  99                         from.sin_addr = *addr;
 100                         ret = sendto(sock, buf, n, 0, (struct sockaddr *)&from, sizeof(from));
 101                         if (ret != n) {
 102                                 printf("Failed to send %d bytes to %s - %d\n",
 103                                        n, inet_ntoa(*addr), ret);
 104                         }
 105                 }
 106         }
 107 }
 108
 109 int main(int argc, char *argv[])
 110 {
 111         int listen_port;
 112         char *host1, *host2;
 113         int sock_in;
 114
 115         if (argc < 4) {
 116                 printf("Usage: udpproxy <port> <host1> <host2>\n");
 117                 exit(1);
 118         }
 119
 120         listen_port = atoi(argv[1]);
 121         host1 = argv[2];
 122         host2 = argv[3];
 123
 124         sock_in = open_socket_in(listen_port);
 125         if (sock_in == -1) {
 126                 fprintf(stderr,"sock on port %d failed - %s\n",
 127                         listen_port, strerror(errno));
 128                 exit(1);
 129         }
 130
 131         main_loop(sock_in, host1, host2);
 132
 133         return 0;
 134 }