From c148fdca846d4f5e465104ab0773bb4ab5a612c0 Mon Sep 17 00:00:00 2001
From: Oliver Jowett <oliver.jowett@flightaware.com>
Date: Thu, 29 Jul 2021 19:04:51 +0800
Subject: [PATCH] Distinguish "unknown format" from "didn't even try to decode"
 when decoding Comm-B messages

---
 comm_b.c   | 5 +++--
 dump1090.h | 1 +
 mode_s.c   | 2 ++
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/comm_b.c b/comm_b.c
index e7e57a7..1da2397 100644
--- a/comm_b.c
+++ b/comm_b.c
@@ -47,12 +47,11 @@ static CommBDecoderFn comm_b_decoders[] = {
 
 void decodeCommB(struct modesMessage *mm)
 {
-    mm->commb_format = COMMB_UNKNOWN;
-
     // If DR or UM are set, this message is _probably_ noise
     // as nothing really seems to use the multisite broadcast stuff?
     // Also skip anything that had errors corrected
     if (mm->DR != 0 || mm->UM != 0 || mm->correctedbits > 0) {
+        mm->commb_format = COMMB_NOT_DECODED;
         return;
     }
 
@@ -79,6 +78,8 @@ void decodeCommB(struct modesMessage *mm)
             // decode it
             bestDecoder(mm, true);
         }
+    } else {
+        mm->commb_format = COMMB_UNKNOWN;
     }
 }
 
diff --git a/dump1090.h b/dump1090.h
index 31d48e2..3864f43 100644
--- a/dump1090.h
+++ b/dump1090.h
@@ -202,6 +202,7 @@ typedef enum {
 typedef enum {
     COMMB_UNKNOWN,
     COMMB_AMBIGUOUS,
+    COMMB_NOT_DECODED,
     COMMB_EMPTY_RESPONSE,
     COMMB_DATALINK_CAPS,
     COMMB_GICB_CAPS,
diff --git a/mode_s.c b/mode_s.c
index f1c9ce0..5f7b666 100644
--- a/mode_s.c
+++ b/mode_s.c
@@ -1681,6 +1681,8 @@ static const char *commb_format_to_string(commb_format_t format) {
         return "empty response";
     case COMMB_AMBIGUOUS:
         return "ambiguous format";
+    case COMMB_NOT_DECODED:
+        return "not decoded";
     case COMMB_DATALINK_CAPS:
         return "BDS1,0 Datalink capabilities";
     case COMMB_GICB_CAPS: