From 02d3b53a6465a9942169cead607e3128fee17d2f Mon Sep 17 00:00:00 2001
From: Jon Shallow <supjps-libcoap@jpshallow.com>
Date: Tue, 27 Apr 2021 21:36:17 +0100
Subject: [PATCH] Observe: Make sure Observe option is not in non 2.xx response

https://tools.ietf.org/html/rfc7641#section-4.2 last paragraph.

Remove option if present in non 2.xx response.
---
 src/net.c      | 5 +++++
 src/resource.c | 3 +++
 2 files changed, 8 insertions(+)

diff --git a/src/net.c b/src/net.c
index c3c4ae15..8ec73f39 100644
--- a/src/net.c
+++ b/src/net.c
@@ -2830,6 +2830,11 @@ skip_handler:
       respond = no_response(pdu, response, session);
       if (respond != RESPONSE_DROP) {
         coap_mid_t mid = pdu->mid;
+        if (COAP_RESPONSE_CLASS(response->code) != 2) {
+          if (observe) {
+            coap_remove_option(response, COAP_OPTION_OBSERVE);
+          }
+        }
         if (COAP_RESPONSE_CLASS(response->code) > 2) {
           if (observe)
             coap_delete_observer(resource, session, &token);
diff --git a/src/resource.c b/src/resource.c
index 9ea29088..044828e0 100644
--- a/src/resource.c
+++ b/src/resource.c
@@ -931,6 +931,9 @@ coap_notify_observers(coap_context_t *context, coap_resource_t *r,
         h(r, obs->session, NULL, obs->query, response);
         /* Check if lg_xmit generated and update PDU code if so */
         coap_check_code_lg_xmit(obs->session, response, r, obs->query);
+        if (COAP_RESPONSE_CLASS(response->code) != 2) {
+          coap_remove_option(response, COAP_OPTION_OBSERVE);
+        }
         if (COAP_RESPONSE_CLASS(response->code) > 2) {
           coap_delete_observer(r, obs->session, &token);
         }