A final(?) effort to reduce memory usage per flow (#1389)

Remove some unused fields and re-organize other ones.
In particular:
* Update the parameters of `ndpi_ssl_version2str()` function
* Zattoo, Thunder: these timestamps aren't really used.
* Ftp/mail: these protocols are dissected only over TCP.
* Attention must be paid to TLS.Bittorrent flows to avoid invalid
read/write to `flow->protos.bittorrent.hash` field.

This is the last(?) commit of a long series (see 22241a1d, 227e586e,
730c2360, a8ffcd8b) aiming to reduce library memory consumption.

Before, at nDPI 4.0 (more precisly, at a6b10cf7, because memory stats
were wrong until that commit):
```
nDPI Memory statistics:
	nDPI Memory (once):      221.15 KB
	Flow Memory (per flow):  2.94 KB
```
Now:
```
nDPI Memory statistics:
	nDPI Memory (once):      231.71 KB
	Flow Memory (per flow):  1008 B       <---------
```
i.e. memory usage per flow has been reduced by 66%, dropping below the
psychological threshold of 1 KB.

To further reduce this value, we probably need to look into #1279:
let's fight this battle another day.

1 files changed, 11 insertions, 7 deletions

diff --git a/src/lib/ndpi_main.c b/src/lib/ndpi_main.c
index ad70e59c6..7e1829b22 100644
--- a/src/lib/ndpi_main.c
+++ b/src/lib/ndpi_main.c
@@ -2377,8 +2377,6 @@ struct ndpi_detection_module_struct *ndpi_init_detection_module(ndpi_init_prefs
 
   ndpi_str->irc_timeout = NDPI_IRC_CONNECTION_TIMEOUT * ndpi_str->ticks_per_second;
   ndpi_str->gnutella_timeout = NDPI_GNUTELLA_CONNECTION_TIMEOUT * ndpi_str->ticks_per_second;
-  ndpi_str->thunder_timeout = NDPI_THUNDER_CONNECTION_TIMEOUT * ndpi_str->ticks_per_second;
-  ndpi_str->zattoo_connection_timeout = NDPI_ZATTOO_CONNECTION_TIMEOUT * ndpi_str->ticks_per_second;
   ndpi_str->jabber_stun_timeout = NDPI_JABBER_STUN_TIMEOUT * ndpi_str->ticks_per_second;
   ndpi_str->jabber_file_transfer_timeout = NDPI_JABBER_FT_TIMEOUT * ndpi_str->ticks_per_second;
 
@@ -4322,6 +4320,12 @@ void ndpi_free_flow_data(struct ndpi_flow_struct* flow) {
     if(flow->http.user_agent)
       ndpi_free(flow->http.user_agent);
 
+    if(flow->http.nat_ip)
+      ndpi_free(flow->http.nat_ip);
+
+    if(flow->http.detected_os)
+      ndpi_free(flow->http.detected_os);
+
     if(flow->kerberos_buf.pktbuf)
       ndpi_free(flow->kerberos_buf.pktbuf);
 
@@ -4918,12 +4922,12 @@ int ndpi_search_into_bittorrent_cache(struct ndpi_detection_module_struct *ndpi_
 				      struct ndpi_flow_struct *flow,
 				      /* Parameters below need to be in network byte order */
 				      u_int32_t saddr, u_int16_t sport, u_int32_t daddr, u_int16_t dport) {
-  if((!flow->bittorrent.bt_check_performed /* Do the check once */) && ndpi_struct->bittorrent_cache) {
+  if((!flow->bt_check_performed /* Do the check once */) && ndpi_struct->bittorrent_cache) {
     u_int16_t cached_proto;
     u_int8_t found = 0;
     u_int32_t key1, key2;
 
-    flow->bittorrent.bt_check_performed = 1;
+    flow->bt_check_performed = 1;
       
     /* Check cached communications */
     key1 = ndpi_bittorrent_hash_funct(saddr, sport), key2 = ndpi_bittorrent_hash_funct(daddr, dport);
@@ -7286,9 +7290,9 @@ u_int8_t ndpi_extra_dissection_possible(struct ndpi_detection_module_struct *ndp
   case NDPI_PROTOCOL_MAIL_POP:
   case NDPI_PROTOCOL_MAIL_IMAP:
   case NDPI_PROTOCOL_MAIL_SMTP:
-    if(flow->ftp_imap_pop_smtp.password[0] == '\0' &&
-       flow->ftp_imap_pop_smtp.auth_tls == 0 &&
-       flow->ftp_imap_pop_smtp.auth_done == 0)
+    if(flow->l4.tcp.ftp_imap_pop_smtp.password[0] == '\0' &&
+       flow->l4.tcp.ftp_imap_pop_smtp.auth_tls == 0 &&
+       flow->l4.tcp.ftp_imap_pop_smtp.auth_done == 0)
       return(1);
     break;