DTLS: Detect connection issues

Supports upstream reconnection attempt detections.

src/coap_gnutls.c

@@ -2052,6 +2052,8 @@ coap_dgram_write(gnutls_transport_ptr_t context, const void *send_buffer,
                     result, send_buffer_length);
       errno = keep_errno;
       if (result < 0) {
+        if (errno == ENOTCONN || errno == ECONNREFUSED)
+          c_session->dtls_event = COAP_EVENT_DTLS_ERROR;
         return -1;
       } else {
         result = 0;

src/coap_mbedtls.c

@@ -251,6 +251,8 @@ coap_dgram_write(void *ctx, const unsigned char *send_buffer,
                     result, send_buffer_length);
       errno = keep_errno;
       if (result < 0) {
+        if (errno == ENOTCONN || errno == ECONNREFUSED)
+          c_session->dtls_event = COAP_EVENT_DTLS_ERROR;
         return -1;
       } else {
         result = 0;

src/coap_openssl.c

@@ -636,8 +636,11 @@ coap_dgram_write(BIO *a, const char *in, int inl) {
           (const uint8_t *)in,
           inl);
     BIO_clear_retry_flags(a);
-    if (ret <= 0)
+    if (ret <= 0) {
+      if (ret < 0 && (errno == ENOTCONN || errno == ECONNREFUSED))
+        data->session->dtls_event = COAP_EVENT_DTLS_ERROR;
       BIO_set_retry_write(a);
+    }
   } else {
     BIO_clear_retry_flags(a);
     ret = -1;

src/coap_tinydtls.c

@@ -365,6 +365,7 @@ dtls_send_to_peer(struct dtls_context_t *dtls_context,
   coap_context_t *coap_context = t_context ? t_context->coap_context : NULL;
   coap_session_t *coap_session;
   coap_address_t remote_addr;
+  int ret;
 
   assert(coap_context);
   get_session_addr(dtls_session, &remote_addr);
@@ -373,8 +374,10 @@ dtls_send_to_peer(struct dtls_context_t *dtls_context,
     coap_log_warn("dtls_send_to_peer: cannot find local interface\n");
     return -3;
   }
-  return (int)coap_session->sock.lfunc[COAP_LAYER_TLS].l_write(coap_session,
-         data, len);
+  ret = (int)coap_session->sock.lfunc[COAP_LAYER_TLS].l_write(coap_session, data, len);
+  if (ret == -1 && (errno == ENOTCONN || errno == ECONNREFUSED))
+    coap_session->dtls_event = COAP_EVENT_DTLS_ERROR;
+  return ret;
 }
 
 static int

src/coap_wolfssl.c

@@ -559,6 +559,9 @@ coap_dgram_write(WOLFSSL *ssl, char *in, int inl, void *ctx) {
     if (ret > 0) {
       coap_ticks(&now);
       w_env->last_timeout = now;
+    } else if (ret < 0) {
+      if (errno == ENOTCONN || errno == ECONNREFUSED)
+        data->session->dtls_event = COAP_EVENT_DTLS_ERROR;
     }
   } else {
     ret = -1;
@@ -2218,6 +2221,7 @@ coap_dtls_free_session(coap_session_t *session) {
       coap_handle_event_lkd(session->context, COAP_EVENT_DTLS_CLOSED, session);
   }
   coap_dtls_free_wolfssl_env(w_env);
+  session->tls = NULL;
 }
 
 ssize_t