net: fota_download: Add event for failed connection attempt

The errnos -ECONNREFUSED and -ECONNABORTED are most likely to
happen during connection establishment, and in particular because
of issues with the TLS handshake.

This patch attempts to distinguish between general errors from the
download_client and errors arrising from the connection establishment.

Signed-off-by: Jan Tore Guggedal <[email protected]>

doc/nrf/releases_and_maturity/releases/release-notes-changelog.rst

@@ -730,7 +730,10 @@ Libraries for networking
 
 * :ref:`lib_fota_download` library:
 
-  * Added the functions :c:func:`fota_download` and :c:func:`fota_download_any` that can accept a security tag list and security tag count as arguments instead of a single security tag.
+  * Added:
+
+    * The functions :c:func:`fota_download` and :c:func:`fota_download_any` that can accept a security tag list and security tag count as arguments instead of a single security tag.
+    * :c:enumerator:`FOTA_DOWNLOAD_ERROR_CAUSE_CONNECT_FAILED` as a potential error cause in  :c:enumerator:`FOTA_DOWNLOAD_EVT_ERROR` events.
 
 Libraries for NFC
 -----------------

include/net/fota_download.h

@@ -71,6 +71,10 @@ enum fota_download_evt_id {
 enum fota_download_error_cause {
 	/** No error, used when event ID is not FOTA_DOWNLOAD_EVT_ERROR. */
 	FOTA_DOWNLOAD_ERROR_CAUSE_NO_ERROR,
+	/** Connecting to the FOTA server failed. A possible reason could be wrong
+	 *  TLS credentials. A retry is unlikely to help with the same credentials.
+	 */
+	FOTA_DOWNLOAD_ERROR_CAUSE_CONNECT_FAILED,
 	/** Downloading the update failed. The download may be retried. */
 	FOTA_DOWNLOAD_ERROR_CAUSE_DOWNLOAD_FAILED,
 	/** The update is invalid and was rejected. Retry will not help. */

subsys/net/lib/fota_download/src/fota_download.c

@@ -280,6 +280,11 @@ static int download_client_callback(const struct download_client_evt *event)
 			/* Fall through and return 0 below to tell
 			 * download_client to retry
 			 */
+		} else if ((event->error == -ECONNABORTED) || (event->error == -ECONNREFUSED)) {
+			LOG_ERR("Download client failed to connect to server");
+			set_error_state(FOTA_DOWNLOAD_ERROR_CAUSE_CONNECT_FAILED);
+
+			goto error_and_close;
 		} else {
 			LOG_ERR("Download client error");
 			err = dfu_target_done(false);