upd_proxy: allow dropping of nth packet

In dtls v1.3 sequence number are encrypted so we can't use them to selct packet
to discard

udp_proxy.c

@@ -74,6 +74,8 @@ struct sockaddr_in proxy, server; /* proxy address and server address */
 int serverLen = sizeof(server); /* server address len */
 int dropPacket = 0; /* dropping packet interval */
 int delayPacket = 0; /* delay packet interval */
+int dropNth = 0;
+int dropPacketNo = 0;
 int dropSpecific = 0; /* specific seq to drop in epoch */
 int dropSpecificSeq = 0; /* specific seq to drop */
 int dropSpecificEpoch = 0; /* specific epoch to drop in */
@@ -408,6 +410,11 @@ static void Msg(evutil_socket_t fd, short which, void* arg)
  return;
  }
 
+ if (dropNth && dropPacketNo == msgCount) {
+ printf("*** but dropping the %d packet\n", msgCount);
+ return;
+ }
+
  /* should we delay the current packet */
  if (delayPacket && (msgCount % delayPacket) == 0) {
  printf("*** but delaying this packet\n");
@@ -566,6 +573,11 @@ static void newClient(evutil_socket_t fd, short which, void* arg)
  }
  event_add(srvEvent, NULL);
 
+ if (dropNth && dropPacketNo == 0) {
+ printf("*** but dropping this packet\n");
+ return;
+ }
+
  /* send along initial client message */
  ret = send(ctx->serverFd, msg, msgLen, 0);
  if (ret < 0) {
@@ -583,6 +595,7 @@ static void Usage(void)
  printf("-p <num> Proxy port to 'listen' on\n");
  printf("-s <server:port> Server address in dotted decimal:port\n");
  printf("-d <num> Drop every <num> packet, default 0\n");
+ printf("-f <num> Drop the <num> packet, default none\n");
  printf("-x <epoch>:<num> "
  "Drop specifically packet with sequence <num> from <epoch>\n");
  printf("-y <num> Delay every <num> packet, default 0\n");
@@ -605,7 +618,7 @@ int main(int argc, char** argv)
  short port = -1;
  char* serverString = NULL;
 
- while ( (ch = GetOpt(argc, argv, "?Dap:s:d:y:x:b:R:S:r:")) != -1) {
+ while ( (ch = GetOpt(argc, argv, "?Dap:s:d:y:x:b:R:S:r:f:")) != -1) {
  switch (ch) {
  case '?' :
  Usage();
@@ -673,6 +686,10 @@ int main(int argc, char** argv)
  }
  break;
 
+ case 'f':
+ dropNth = 1;
+ dropPacketNo = atoi(myoptarg);
+ break;
  default:
  Usage();
  exit(MY_EX_USAGE);