Remove `struct ndpi_id_struct` (#1427)

Remove the last uses of `struct ndpi_id_struct`.
That code is not really used and it has not been updated for a very long
time: see #1279 for details.

Correlation among flows is achieved via LRU caches.

This change allows to further reduce memory consumption (see also
91bb77a8).

At nDPI 4.0 (more precisly, at a6b10cf, 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):      235.27 KB
	Flow Memory (per flow):  688 B        <--------
```
i.e. memory usage per flow has been reduced by 77%.

Close #1279

1 files changed, 8 insertions, 41 deletions

diff --git a/example/reader_util.c b/example/reader_util.c
index d47b5a5ec..3340170ef 100644
--- a/example/reader_util.c
+++ b/example/reader_util.c
@@ -300,8 +300,6 @@ void ndpi_report_payload_stats() {
 
 void ndpi_free_flow_info_half(struct ndpi_flow_info *flow) {
   if(flow->ndpi_flow) { ndpi_flow_free(flow->ndpi_flow); flow->ndpi_flow = NULL; }
-  if(flow->src_id)    { ndpi_free(flow->src_id); flow->src_id = NULL; }
-  if(flow->dst_id)    { ndpi_free(flow->dst_id); flow->dst_id = NULL; }
 }
 
 /* ***************************************************** */
@@ -699,8 +697,6 @@ static struct ndpi_flow_info *get_ndpi_flow_info(struct ndpi_workflow * workflow
 						 struct ndpi_tcphdr **tcph,
 						 struct ndpi_udphdr **udph,
 						 u_int16_t *sport, u_int16_t *dport,
-						 struct ndpi_id_struct **src,
-						 struct ndpi_id_struct **dst,
 						 u_int8_t *proto,
 						 u_int8_t **payload,
 						 u_int16_t *payload_len,
@@ -878,30 +874,6 @@ static struct ndpi_flow_info *get_ndpi_flow_info(struct ndpi_workflow * workflow
       } else
 	memset(newflow->ndpi_flow, 0, SIZEOF_FLOW_STRUCT);
 
-      if((newflow->src_id = ndpi_malloc(SIZEOF_ID_STRUCT)) == NULL) {
-	LOG(NDPI_LOG_ERROR, "[NDPI] %s(3): not enough memory\n", __FUNCTION__);
-#ifdef DIRECTION_BINS
-	ndpi_free_bin(&newflow->payload_len_bin_src2dst), ndpi_free_bin(&newflow->payload_len_bin_dst2src);
-#else
-	ndpi_free_bin(&newflow->payload_len_bin);
-#endif
-	ndpi_free(newflow);
-	return(NULL);
-      } else
-	memset(newflow->src_id, 0, SIZEOF_ID_STRUCT);
-
-      if((newflow->dst_id = ndpi_malloc(SIZEOF_ID_STRUCT)) == NULL) {
-	LOG(NDPI_LOG_ERROR, "[NDPI] %s(4): not enough memory\n", __FUNCTION__);
-#ifdef DIRECTION_BINS
-	ndpi_free_bin(&newflow->payload_len_bin_src2dst), ndpi_free_bin(&newflow->payload_len_bin_dst2src);
-#else
-	ndpi_free_bin(&newflow->payload_len_bin);
-#endif
-	ndpi_free(newflow);
-	return(NULL);
-      } else
-	memset(newflow->dst_id, 0, SIZEOF_ID_STRUCT);
-
       ndpi_tsearch(newflow, &workflow->ndpi_flows_root[idx], ndpi_workflow_node_cmp); /* Add */
       workflow->stats.ndpi_flow_count++;
       if(*proto == IPPROTO_TCP)
@@ -911,8 +883,6 @@ static struct ndpi_flow_info *get_ndpi_flow_info(struct ndpi_workflow * workflow
       else
         workflow->stats.flow_count[2]++;
 
-      *src = newflow->src_id, *dst = newflow->dst_id;
-
       if(enable_flow_stats) {
         newflow->entropy = ndpi_calloc(1, sizeof(struct ndpi_entropy));
         newflow->last_entropy = ndpi_calloc(1, sizeof(struct ndpi_entropy));
@@ -939,9 +909,9 @@ static struct ndpi_flow_info *get_ndpi_flow_info(struct ndpi_workflow * workflow
 	 && rflow->src_port == htons(*sport)
 	 && rflow->dst_port == htons(*dport)
 	 )
-	*src = rflow->dst_id, *dst = rflow->src_id, *src_to_dst_direction = 0, rflow->bidirectional = 1;
+	*src_to_dst_direction = 0, rflow->bidirectional = 1;
       else
-	*src = rflow->src_id, *dst = rflow->dst_id, *src_to_dst_direction = 1;
+	*src_to_dst_direction = 1;
     }
     else {
       if(rflow->src_ip == iph->saddr
@@ -949,9 +919,9 @@ static struct ndpi_flow_info *get_ndpi_flow_info(struct ndpi_workflow * workflow
 	 && rflow->src_port == htons(*sport)
 	 && rflow->dst_port == htons(*dport)
 	 )
-	*src = rflow->src_id, *dst = rflow->dst_id, *src_to_dst_direction = 1;
+	*src_to_dst_direction = 1;
       else
-	*src = rflow->dst_id, *dst = rflow->src_id, *src_to_dst_direction = 0, rflow->bidirectional = 1;
+	*src_to_dst_direction = 0, rflow->bidirectional = 1;
     }
     if(enable_flow_stats) {
       if(src_to_dst_direction) {
@@ -997,8 +967,6 @@ static struct ndpi_flow_info *get_ndpi_flow_info6(struct ndpi_workflow * workflo
 						  struct ndpi_tcphdr **tcph,
 						  struct ndpi_udphdr **udph,
 						  u_int16_t *sport, u_int16_t *dport,
-						  struct ndpi_id_struct **src,
-						  struct ndpi_id_struct **dst,
 						  u_int8_t *proto,
 						  u_int8_t **payload,
 						  u_int16_t *payload_len,
@@ -1024,7 +992,7 @@ static struct ndpi_flow_info *get_ndpi_flow_info6(struct ndpi_workflow * workflo
 			    &iph, iph6, ip_offset, ipsize,
 			    ip_len, l4ptr - (const u_int8_t *)iph6,
 			    tcph, udph, sport, dport,
-			    src, dst, proto, payload,
+			    proto, payload,
 			    payload_len, src_to_dst_direction, when));
 }
 
@@ -1347,7 +1315,6 @@ static struct ndpi_proto packet_processing(struct ndpi_workflow * workflow,
 					   pkt_timeval when,
 					   ndpi_risk *flow_risk,
 					   FILE * csv_fp) {
-  struct ndpi_id_struct *src, *dst;
   struct ndpi_flow_info *flow = NULL;
   struct ndpi_flow_struct *ndpi_flow = NULL;
   u_int8_t proto;
@@ -1369,13 +1336,13 @@ static struct ndpi_proto packet_processing(struct ndpi_workflow * workflow,
 			      ntohs(iph->tot_len) - (iph->ihl * 4),
 			      iph->ihl * 4,
 			      &tcph, &udph, &sport, &dport,
-			      &src, &dst, &proto,
+			      &proto,
 			      &payload, &payload_len, &src_to_dst_direction, when);
   else
     flow = get_ndpi_flow_info6(workflow, vlan_id,
 			       tunnel_type, iph6, ip_offset, ipsize,
 			       &tcph, &udph, &sport, &dport,
-			       &src, &dst, &proto,
+			       &proto,
 			       &payload, &payload_len, &src_to_dst_direction, when);
 
   if(flow != NULL) {
@@ -1563,7 +1530,7 @@ static struct ndpi_proto packet_processing(struct ndpi_workflow * workflow,
 
     flow->detected_protocol = ndpi_detection_process_packet(workflow->ndpi_struct, ndpi_flow,
 							    iph ? (uint8_t *)iph : (uint8_t *)iph6,
-							    ipsize, time_ms, src, dst);
+							    ipsize, time_ms);
 
     if(enough_packets || (flow->detected_protocol.app_protocol != NDPI_PROTOCOL_UNKNOWN)) {
       if((!enough_packets)