+int
+udprelay(int fd, char *dir)
+{
+ struct {
+ Udphdr;
+ uchar data[8*1024];
+ } msg;
+ char addr[128], ldir[40];
+ int r, n, rfd, cfd;
+ uchar *p;
+
+ snprint(addr, sizeof(addr), "%s/udp!*!0", outside);
+ if((cfd = announce(addr, ldir)) < 0)
+ return -1;
+ if(write(cfd, "headers", 7) != 7)
+ return -1;
+ strcat(ldir, "/data");
+ if((rfd = open(ldir, ORDWR)) < 0)
+ return -1;
+ close(cfd);
+
+ if((r = rfork(RFMEM|RFPROC|RFNOWAIT)) <= 0)
+ return r;
+
+ if((cfd = listen(dir, ldir)) < 0)
+ return -1;
+ close(fd); /* close inside udp server */
+ if((fd = accept(cfd, ldir)) < 0)
+ return -1;
+
+ switch(rfork(RFMEM|RFPROC|RFNOWAIT)){
+ case -1:
+ return -1;
+ case 0:
+ while((r = read(fd, msg.data, sizeof(msg.data))) > 0){
+ if(r < 4)
+ continue;
+ p = msg.data;
+ if(p[0] | p[1] | p[2])
+ continue;
+ p += 3;
+ switch(*p++){
+ default:
+ continue;
+ case 0x01:
+ r -= 2+1+1+4+2;
+ if(r < 0)
+ continue;
+ v4tov6(msg.raddr, p);
+ p += 4;
+ break;
+ case 0x04:
+ r -= 2+1+1+16+2;
+ if(r < 0)
+ continue;
+ memmove(msg.raddr, p, 16);
+ p += 16;
+ break;
+ }
+ memmove(msg.rport, p, 2);
+ p += 2;
+ memmove(msg.data, p, r);
+ write(rfd, &msg, sizeof(Udphdr)+r);
+ }
+ break;
+ default:
+ while((r = read(rfd, &msg, sizeof(msg))) > 0){
+ r -= sizeof(Udphdr);
+ if(r < 0)
+ continue;
+ p = msg.data;
+ if(isv4(msg.raddr))
+ n = 2+1+1+4+2;
+ else
+ n = 2+1+1+16+2;
+ if(r+n > sizeof(msg.data))
+ r = sizeof(msg.data)-n;
+ memmove(p+n, p, r);
+ *p++ = 0;
+ *p++ = 0;
+ *p++ = 0;
+ if(isv4(msg.raddr)){
+ *p++ = 0x01;
+ v6tov4(p, msg.raddr);
+ p += 4;
+ } else {
+ *p++ = 0x04;
+ memmove(p, msg.raddr, 16);
+ p += 16;
+ }
+ memmove(p, msg.rport, 2);
+ r += n;
+ write(fd, msg.data, r);
+ }
+ }
+ return -1;
+}
+