Remove `struct ndpi_packet_struct` from `struct ndpi_flow_struct` (#1319)

There are no real reasons to embed `struct ndpi_packet_struct` (i.e. "packet")
in `struct ndpi_flow_struct` (i.e. "flow"). In other words, we can avoid
saving dissection information of "current packet" into the "flow" state,
i.e. in the flow management table.

The nDPI detection module processes only one packet at the time, so it is
safe to save packet dissection information in `struct ndpi_detection_module_struct`,
reusing always the same "packet" instance and saving a huge amount of memory.
Bottom line: we need only one copy of "packet" (for detection module),
not one for each "flow".

It is not clear how/why "packet" ended up in "flow" in the first place.
It has been there since the beginning of the GIT history, but in the original
OpenDPI code `struct ipoque_packet_struct` was embedded in
`struct ipoque_detection_module_struct`, i.e. there was the same exact
situation this commit wants to achieve.

Most of the changes in this PR are some boilerplate to update something
like "flow->packet" into something like "module->packet" throughout the code.
Some attention has been paid to update `ndpi_init_packet()` since we need
to reset some "packet" fields before starting to process another packet.

There has been one important change, though, in ndpi_detection_giveup().
Nothing changed for the applications/users, but this function can't access
"packet" anymore.
The reason is that this function can be called "asynchronously" with respect
to the data processing, i.e in context where there is no valid notion of
"current packet"; for example ndpiReader calls it after having processed all
the traffic, iterating the entire session table.

Mining LRU stuff seems a bit odd (even before this patch): probably we need
to rethink it, as a follow-up.

1 files changed, 9 insertions, 6 deletions

diff --git a/src/lib/protocols/starcraft.c b/src/lib/protocols/starcraft.c
index 9419b7a5b..c26b76a0a 100644
--- a/src/lib/protocols/starcraft.c
+++ b/src/lib/protocols/starcraft.c
@@ -49,10 +49,12 @@ u_int8_t sc2_match_logon_ip(struct ndpi_packet_struct* packet)
 */
 u_int8_t ndpi_check_starcraft_tcp(struct ndpi_detection_module_struct* ndpi_struct, struct ndpi_flow_struct* flow)
 {
-  if (sc2_match_logon_ip(&flow->packet)
-      && flow->packet.tcp->dest == htons(1119)	//bnetgame port
-      && (ndpi_match_strprefix(flow->packet.payload, flow->packet.payload_packet_len, "\x4a\x00\x00\x0a\x66\x02\x0a\xed\x2d\x66") 
-	  || ndpi_match_strprefix(flow->packet.payload, flow->packet.payload_packet_len, "\x49\x00\x00\x0a\x66\x02\x0a\xed\x2d\x66")))
+  struct ndpi_packet_struct* packet = &ndpi_struct->packet;
+
+  if (sc2_match_logon_ip(packet)
+      && packet->tcp->dest == htons(1119)	//bnetgame port
+      && (ndpi_match_strprefix(packet->payload, packet->payload_packet_len, "\x4a\x00\x00\x0a\x66\x02\x0a\xed\x2d\x66") 
+	  || ndpi_match_strprefix(packet->payload, packet->payload_packet_len, "\x49\x00\x00\x0a\x66\x02\x0a\xed\x2d\x66")))
     return 1;
   else
     return -1;
@@ -66,7 +68,7 @@ u_int8_t ndpi_check_starcraft_tcp(struct ndpi_detection_module_struct* ndpi_stru
 */
 u_int8_t ndpi_check_starcraft_udp(struct ndpi_detection_module_struct* ndpi_struct, struct ndpi_flow_struct* flow)
 {
-  struct ndpi_packet_struct* packet = &flow->packet;
+  struct ndpi_packet_struct* packet = &ndpi_struct->packet;
 
   /* First off, filter out any traffic not using port 1119, removing the chance of any false positive if we assume that non allowed protocols don't use the port */
   if (packet->udp->source != htons(1119) && packet->udp->dest != htons(1119))
@@ -114,9 +116,10 @@ u_int8_t ndpi_check_starcraft_udp(struct ndpi_detection_module_struct* ndpi_stru
 
 void ndpi_search_starcraft(struct ndpi_detection_module_struct* ndpi_struct, struct ndpi_flow_struct* flow)
 {
+  struct ndpi_packet_struct* packet = &ndpi_struct->packet;
+
   NDPI_LOG_DBG(ndpi_struct, "search Starcraft\n");
   if (flow->detected_protocol_stack[0] != NDPI_PROTOCOL_STARCRAFT) {
-    struct ndpi_packet_struct* packet = &flow->packet;
     int8_t result = 0;
 
     if (packet->udp != NULL) {