ADD: Get the response code from a failing connection.

This commit adds an event information "connect_return_code" that is written
when the client state is MQTT_STATE_INIT, and the connection fails.

This event info can then be written by the user app to find out the reason
of the fail connection.

Merges https://github.com/espressif/esp-mqtt/pull/100

include/mqtt_client.h

@@ -37,7 +37,7 @@ typedef struct esp_mqtt_client *esp_mqtt_client_handle_t;
  *
  */
 typedef enum {
-    MQTT_EVENT_ERROR = 0,
+    MQTT_EVENT_ERROR = 0,          /*!< on error event, additional context: error handle from esp_tls (if supported) */
     MQTT_EVENT_CONNECTED,          /*!< connected event, additional context: session_present flag */
     MQTT_EVENT_DISCONNECTED,       /*!< disconnected event */
     MQTT_EVENT_SUBSCRIBED,         /*!< subscribed event, additional context: msg_id */
@@ -57,8 +57,21 @@ typedef enum {
                                         and current data offset updating.
                                          */
     MQTT_EVENT_BEFORE_CONNECT,     /*!< The event occurs before connecting */
+    MQTT_EVENT_CONNECTION_REFUSED, /*!< The event occurs if connection is refused by the broker, additional context: connect_return_code */
 } esp_mqtt_event_id_t;
 
+/**
+ * MQTT connection error codes propagated via ERROR event
+ */
+typedef enum {
+    MQTT_CONNECTION_ACCEPTED = 0,                   /*!< Connection accepted  */
+    MQTT_CONNECTION_REFUSE_PROTOCOL,                /*!< MQTT connection refused reason: Wrong protocol */
+    MQTT_CONNECTION_REFUSE_ID_REJECTED,             /*!< MQTT connection refused reason: ID rejected */
+    MQTT_CONNECTION_REFUSE_SERVER_UNAVAILABLE,      /*!< MQTT connection refused reason: Server unavailable */
+    MQTT_CONNECTION_REFUSE_BAD_USERNAME,            /*!< MQTT connection refused reason: Wrong user */
+    MQTT_CONNECTION_REFUSE_NOT_AUTHORIZED           /*!< MQTT connection refused reason: Wrong username or password */
+} esp_mqtt_connect_return_code_t;
+
 typedef enum {
     MQTT_TRANSPORT_UNKNOWN = 0x0,
     MQTT_TRANSPORT_OVER_TCP,      /*!< MQTT over TCP, using scheme: ``mqtt`` */
@@ -83,6 +96,7 @@ typedef struct {
     int msg_id;                         /*!< MQTT messaged id of message */
     int session_present;                /*!< MQTT session_present flag for connection event */
     void* error_handle;                 /*!< esp-tls error handle referencing last error/flags captured in transports */
+    esp_mqtt_connect_return_code_t connect_return_code;     /*!< MQTT connection return code. Only written on a connection */
 } esp_mqtt_event_t;
 
 typedef esp_mqtt_event_t *esp_mqtt_event_handle_t;

lib/include/mqtt_msg.h

@@ -57,15 +57,6 @@ enum mqtt_message_type {
     MQTT_MSG_TYPE_DISCONNECT = 14
 };
 
-enum mqtt_connect_return_code {
-    CONNECTION_ACCEPTED = 0,
-    CONNECTION_REFUSE_PROTOCOL,
-    CONNECTION_REFUSE_ID_REJECTED,
-    CONNECTION_REFUSE_SERVER_UNAVAILABLE,
-    CONNECTION_REFUSE_BAD_USERNAME,
-    CONNECTION_REFUSE_NOT_AUTHORIZED
-};
-
 typedef struct mqtt_message {
     uint8_t *data;
     uint32_t length;

mqtt_client.c

@@ -317,27 +317,33 @@ static esp_err_t esp_mqtt_connect(esp_mqtt_client_handle_t client, int timeout_m
     }
     client->mqtt_state.in_buffer_read_len = 0;
     connect_rsp_code = mqtt_get_connect_return_code(client->mqtt_state.in_buffer);
-    switch (connect_rsp_code) {
+    if (connect_rsp_code == MQTT_CONNECTION_ACCEPTED) {
-    case CONNECTION_ACCEPTED:
         ESP_LOGD(TAG, "Connected");
         return ESP_OK;
-    case CONNECTION_REFUSE_PROTOCOL:
+    }
+    switch (connect_rsp_code) {
+    case MQTT_CONNECTION_REFUSE_PROTOCOL:
         ESP_LOGW(TAG, "Connection refused, bad protocol");
-        return ESP_FAIL;
+        break;
-    case CONNECTION_REFUSE_SERVER_UNAVAILABLE:
+    case MQTT_CONNECTION_REFUSE_SERVER_UNAVAILABLE:
         ESP_LOGW(TAG, "Connection refused, server unavailable");
-        return ESP_FAIL;
+        break;
-    case CONNECTION_REFUSE_BAD_USERNAME:
+    case MQTT_CONNECTION_REFUSE_BAD_USERNAME:
         ESP_LOGW(TAG, "Connection refused, bad username or password");
-        return ESP_FAIL;
+        break;
-    case CONNECTION_REFUSE_NOT_AUTHORIZED:
+    case MQTT_CONNECTION_REFUSE_NOT_AUTHORIZED:
         ESP_LOGW(TAG, "Connection refused, not authorized");
-        return ESP_FAIL;
+        break;
     default:
         ESP_LOGW(TAG, "Connection refused, Unknow reason");
-        return ESP_FAIL;
+        break;
     }
-    return ESP_OK;
+    /* propagate event with connection refused error */
+    client->event.event_id = MQTT_EVENT_CONNECTION_REFUSED;
+    client->event.connect_return_code = connect_rsp_code;
+    esp_mqtt_dispatch_event_with_msgid(client);
+
+    return ESP_FAIL;
 }
 
 static esp_err_t esp_mqtt_abort_connection(esp_mqtt_client_handle_t client)