Rework how hostname/SNI info is saved (#1330)

Looking at `struct ndpi_flow_struct` the two bigger fields are
`host_server_name[240]` (mainly for HTTP hostnames and DNS domains) and
`protos.tls_quic.client_requested_server_name[256]`
(for TLS/QUIC SNIs).

This commit aims to reduce `struct ndpi_flow_struct` size, according to
two simple observations:
 1) maximum one of these two fields is used for each flow. So it seems safe
to merge them;
 2) even if hostnames/SNIs might be very long, in practice they are rarely
longer than a fews tens of bytes. So, using a (single) large buffer is a
waste of memory for all kinds of flows. If we need to truncate the name,
we keep the *last* characters, easing domain matching.

Analyzing some real traffic, it seems safe to assume that the vast
majority of hostnames/SNIs is shorter than 80 bytes.

Hostnames/SNIs are always converted to lowercase.

Attention was given so as to be sure that unit-tests outputs are not
affected by this change.

Because of a bug, TLS/QUIC SNI were always truncated to 64 bytes (the
*first* 64 ones): as a consequence, there were some "Suspicious DGA
domain name" and "TLS Certificate Mismatch" false positives.

1 files changed, 3 insertions, 7 deletions

diff --git a/example/reader_util.c b/example/reader_util.c
index 3a161d684..d5638d183 100644
--- a/example/reader_util.c
+++ b/example/reader_util.c
@@ -1105,8 +1105,7 @@ void process_ndpi_collected_info(struct ndpi_workflow * workflow, struct ndpi_fl
   }
   /* MDNS */
   else if(is_ndpi_proto(flow, NDPI_PROTOCOL_MDNS)) {
-    char *name = (char*)flow->ndpi_flow->host_server_name; /* Trick to avoid warning(s) */
-    snprintf(flow->info, sizeof(flow->info), "%s", name);
+    snprintf(flow->info, sizeof(flow->info), "%s", flow->ndpi_flow->host_server_name);
   }
   /* UBNTAC2 */
   else if(is_ndpi_proto(flow, NDPI_PROTOCOL_UBNTAC2)) {
@@ -1161,8 +1160,8 @@ void process_ndpi_collected_info(struct ndpi_workflow * workflow, struct ndpi_fl
     if(flow->ndpi_flow->protos.telnet.password[0] != '\0')
       flow->telnet.password = ndpi_strdup(flow->ndpi_flow->protos.telnet.password);
   } else if(is_ndpi_proto(flow, NDPI_PROTOCOL_SSH)) {
-    snprintf(flow->ssh_tls.client_requested_server_name,
-	     sizeof(flow->ssh_tls.client_requested_server_name), "%s",
+    snprintf(flow->host_server_name,
+	     sizeof(flow->host_server_name), "%s",
 	     flow->ndpi_flow->protos.ssh.client_signature);
     snprintf(flow->ssh_tls.server_info, sizeof(flow->ssh_tls.server_info), "%s",
 	     flow->ndpi_flow->protos.ssh.server_signature);
@@ -1178,9 +1177,6 @@ void process_ndpi_collected_info(struct ndpi_workflow * workflow, struct ndpi_fl
 	  || (flow->ndpi_flow->protos.tls_quic.ja3_client[0] != '\0')
 	  ) {
     flow->ssh_tls.ssl_version = flow->ndpi_flow->protos.tls_quic.ssl_version;
-    snprintf(flow->ssh_tls.client_requested_server_name,
-	     sizeof(flow->ssh_tls.client_requested_server_name), "%s",
-	     flow->ndpi_flow->protos.tls_quic.client_requested_server_name);
 
     snprintf(flow->http.user_agent, sizeof(flow->http.user_agent), "%s", flow->ndpi_flow->http.user_agent ? flow->ndpi_flow->http.user_agent : "");