Fix f-2752 client connack failure return codes

Author: embhorn

src/mqtt_client.c

@@ -1867,6 +1867,14 @@ int MqttClient_Connect(MqttClient *client, MqttConnect *mc_connect)
     /* reset state */
     mc_connect->stat.write = MQTT_MSG_BEGIN;
 
+    /* CONNACK was received and decoded, but the broker refused the
+     * connection. The specific reason is in mc_connect->ack.return_code
+     * (MqttConnectAckReturnCodes for v3.1.1, MqttReasonCodes for v5). */
+    if (rc == MQTT_CODE_SUCCESS &&
+            mc_connect->ack.return_code != MQTT_CONNECT_ACK_CODE_ACCEPTED) {
+        rc = MQTT_TRACE_ERROR(MQTT_CODE_ERROR_CONNECT_REFUSED);
+    }
+
     return rc;
 }
 
@@ -3055,6 +3063,8 @@ const char* MqttClient_ReturnCodeToString(int return_code)
             return "Error (System resource failed)";
         case MQTT_CODE_ERROR_NOT_FOUND:
             return "Error (Not found)";
+        case MQTT_CODE_ERROR_CONNECT_REFUSED:
+            return "Error (Broker refused connection)";
 #if defined(ENABLE_MQTT_CURL)
         case MQTT_CODE_ERROR_CURL:
             return "Error (libcurl)";

wolfmqtt/mqtt_client.h

@@ -290,7 +290,11 @@ WOLFMQTT_API int MqttClient_SetPropertyCallback(
  *  \param      client      Pointer to MqttClient structure
  *  \param      connect     Pointer to MqttConnect structure initialized
                             with connect parameters
- *  \return     MQTT_CODE_SUCCESS or MQTT_CODE_ERROR_*
+ *  \return     MQTT_CODE_SUCCESS if the broker accepted the connection,
+                MQTT_CODE_ERROR_CONNECT_REFUSED if the broker returned a
+                non-zero CONNACK return_code (check
+                connect->ack.return_code for the specific reason), or
+                another MQTT_CODE_ERROR_* for transport/protocol failures
                 (see enum MqttPacketResponseCodes)
  */
 WOLFMQTT_API int MqttClient_Connect(

wolfmqtt/mqtt_types.h

@@ -203,6 +203,9 @@ enum MqttPacketResponseCodes {
                                  * a network, memory, TLS, or system error. */
 #endif
     MQTT_CODE_ERROR_PROPERTY_MISMATCH = -17,
+    MQTT_CODE_ERROR_CONNECT_REFUSED = -18, /* Broker rejected the CONNECT;
+                                              see MqttConnect.ack.return_code
+                                              for the specific reason. */
 
     MQTT_CODE_CONTINUE = -101,
     MQTT_CODE_STDIN_WAKE = -102,