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, 4 insertions, 7 deletions

diff --git a/src/lib/protocols/dhcp.c b/src/lib/protocols/dhcp.c
index d40bb5c35..23d358b74 100644
--- a/src/lib/protocols/dhcp.c
+++ b/src/lib/protocols/dhcp.c
@@ -159,17 +159,14 @@ void ndpi_search_dhcp_udp(struct ndpi_detection_module_struct *ndpi_struct, stru
             strncpy((char*)flow->protos.dhcp.class_ident, name, j);
             flow->protos.dhcp.class_ident[j] = '\0';
           } else if(id == 12 /* Host Name */) {
-            char *name = (char*)&dhcp->options[i+2];
-            int j = 0;
-	    
+            u_int8_t *name = &dhcp->options[i+2];
+
 #ifdef DHCP_DEBUG
             NDPI_LOG_DBG2(ndpi_struct, "[DHCP] '%.*s'\n",name,len);
 	      //	    while(j < len) { printf( "%c", name[j]); j++; }; printf("\n");
 #endif
-            j = ndpi_min(len, sizeof(flow->host_server_name)-1);
-            strncpy((char*)flow->host_server_name, name, j);
-            flow->host_server_name[j] = '\0';
-          }
+            ndpi_hostname_sni_set(flow, name, len);
+	  }
 
           i += len + 2;
         }