From f00be554cc65e5cdbcc5b6f07d454d82f70223a1 Mon Sep 17 00:00:00 2001
From: Olaf Bergmann <bergmann@tzi.org>
Date: Tue, 15 Sep 2020 10:10:11 +0200
Subject: [PATCH] net.c: Fix fail_cnt reset on empty ACK

coap_touch_observer() must be called on empty ACKs before leaving the
dispatch function.

Fixes #550 [1]

[1] https://github.com/obgm/libcoap/issues/550
---
 src/net.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/net.c b/src/net.c
index 20d0226b..ccbf0157 100644
--- a/src/net.c
+++ b/src/net.c
@@ -2647,9 +2647,6 @@ coap_dispatch(coap_context_t *context, coap_session_t *session,
           /* Flush out any entries on session->delayqueue */
           coap_session_connected(session);
       }
-      if (pdu->code == 0)
-        goto cleanup;
-
       /* if sent code was >= 64 the message might have been a
        * notification. Then, we must flag the observer to be alive
        * by setting obs->fail_cnt = 0. */
@@ -2658,6 +2655,11 @@ coap_dispatch(coap_context_t *context, coap_session_t *session,
         { sent->pdu->token_length, sent->pdu->token };
         coap_touch_observer(context, sent->session, &token);
       }
+
+      /* an empty ACK needs no further handling */
+      if (pdu->code == 0)
+        goto cleanup;
+
       break;
 
     case COAP_MESSAGE_RST: