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, 1 insertions, 4 deletions

diff --git a/src/lib/protocols/whoisdas.c b/src/lib/protocols/whoisdas.c
index 7321626d2..6f6f2a06b 100644
--- a/src/lib/protocols/whoisdas.c
+++ b/src/lib/protocols/whoisdas.c
@@ -41,10 +41,7 @@ void ndpi_search_whois_das(struct ndpi_detection_module_struct *ndpi_struct, str
       ndpi_set_detected_protocol(ndpi_struct, flow, NDPI_PROTOCOL_WHOIS_DAS, NDPI_PROTOCOL_UNKNOWN);
 
       if((dport == 43) || (dport == 4343)) { /* Request */
-        u_int hostname_len = ndpi_min(sizeof(flow->host_server_name) - 1, (long unsigned int)packet->payload_packet_len - 2); /* Skip \r\n */
-
-        memcpy(flow->host_server_name, &packet->payload[0], hostname_len);
-        flow->host_server_name[hostname_len] = '\0';
+        ndpi_hostname_sni_set(flow, &packet->payload[0], packet->payload_packet_len - 2); /* Skip \r\n */
         NDPI_LOG_INFO(ndpi_struct, "[WHOIS/DAS] %s\n", flow->host_server_name);
       }
       return;