Collect stats on messages received by DF type

mode_s.c

@@ -2142,6 +2142,9 @@ void useModesMessage(struct modesMessage *mm) {
     struct aircraft *a;
 
     ++Modes.stats_current.messages_total;
+    if (mm->msgtype >= 0 && mm->msgtype < 32) {
+        ++Modes.stats_current.messages_by_df[mm->msgtype];
+    }
 
     // Track aircraft state
     a = trackUpdateFromMessage(mm);

net_io.c

@@ -1791,7 +1791,7 @@ static char * appendStatsJson(char *p,
                            ",\"tracks\":{\"all\":%u"
                            ",\"single_message\":%u"
                            ",\"unreliable\":%u}"
-                           ",\"messages\":%u}",
+                           ",\"messages\":%u",
                            st->cpr_surface,
                            st->cpr_airborne,
                            st->cpr_global_ok,
@@ -1814,6 +1814,14 @@ static char * appendStatsJson(char *p,
                            st->single_message_aircraft,
                            st->unreliable_aircraft,
                           st->messages_total);
+
+        for (i = 0; i < 32; ++i) {
+            if (i == 0)
+                p = safe_snprintf(p, end, ",\"messages_by_df\":[%u", st->messages_by_df[i]);
+            else
+                p = safe_snprintf(p, end, ",%u", st->messages_by_df[i]);
+        }
+        p = safe_snprintf(p, end, "]}");
     }
 
     return p;

stats.c

@@ -125,9 +125,14 @@ void display_stats(struct stats *st) {
             printf("    %8u accepted with %d-bit error repaired\n", st->remote_accepted[j], j);
     }
 
-    printf("%u total usable messages\n",
+    printf("%8u total usable messages\n",
            st->messages_total);
 
+    for (unsigned i = 0; i < 32; ++i) {
+        if (st->messages_by_df[i])
+            printf("  %8u DF%u messages\n", st->messages_by_df[i], i);
+    }
+
     printf("%8u surface position messages received\n"
            "%8u airborne position messages received\n"
            "%8u global CPR attempts with valid positions\n"
@@ -310,6 +315,8 @@ void add_stats(const struct stats *st1, const struct stats *st2, struct stats *t
 
     // total messages:
     target->messages_total = st1->messages_total + st2->messages_total;
+    for (i = 0; i < 32; ++i)
+        target->messages_by_df[i] = st1->messages_by_df[i] + st2->messages_by_df[i];
 
     // CPR decoding:
     target->cpr_surface = st1->cpr_surface + st2->cpr_surface;

stats.h

@@ -94,6 +94,8 @@ struct stats {
 
     // total messages:
     uint32_t messages_total;
+    // .. divided by DF
+    uint32_t messages_by_df[32];
 
     // CPR decoding:
     unsigned int cpr_surface;