lorawan: add callback for descriptor changes

allow the application to decide whether to keep going with the fuota
process by setting a callback that exposes the descriptor field
whenever `FragSessionSetupReq` is sent to the device.

Signed-off-by: Kiara Navarro <sophiekovalevsky@fedoraproject.org>

include/zephyr/lorawan/lorawan.h

@@ -217,6 +217,27 @@ typedef uint8_t (*lorawan_battery_level_cb_t)(void);
  */
 typedef void (*lorawan_dr_changed_cb_t)(enum lorawan_datarate dr);
 
+/**
+ * @brief Defines the user's descriptor callback handler function signature.
+ *
+ * The use of this callback is optional. When Fragmented Data Block Transport
+ * is enabled, the application will be notified with the descriptor field present on
+ * the FragSessionSetupReq command.
+ *
+ * @param descriptor Descriptor value given on the FragSessionSetupReq command.
+ *
+ * The meaning of Descriptor is application dependent. When doing a FUOTA
+ * with a binary image, it may represent the version of the firmware
+ * transported.
+ *
+ * @return 0 if successful. This represents, in the case that the descriptor is the firmware
+ * version, that the end-device is able to receive binary firmware. Otherwise, a negative error code
+ * (errno.h) indicating the reason for failure. Any negative error code will result in setting
+ * the Wrong Descriptor status bit mask when sending FragSessionSetupAns to the Network Server.
+ *
+ */
+typedef int (*transport_descriptor_cb)(uint32_t descriptor);
+
 /**
  * @brief Register a battery level callback function.
  *
@@ -439,6 +460,17 @@ int lorawan_clock_sync_get(uint32_t *gps_time);
 
 #ifdef CONFIG_LORAWAN_FRAG_TRANSPORT
 
+/**
+ * @brief Register a handle descriptor callback function.
+ *
+ * Provide to the fragmentation transport service a function to be called
+ * whenever a FragSessionSetupReq is received and Descriptor field should be
+ * handled.
+ *
+ * @param transport_descriptor_cb Callback for notification.
+ */
+void lorawan_frag_transport_register_descriptor_callback(transport_descriptor_cb cb);
+
 /**
  * @brief Run Fragmented Data Block Transport service
  *

subsys/lorawan/services/frag_transport.c

@@ -101,6 +101,9 @@ static struct frag_transport_context ctx;
 /* Callback for notification of finished firmware transfer */
 static void (*finished_cb)(void);
 
+/* Callback to handle descriptor field */
+static transport_descriptor_cb descriptor_cb;
+
 static void frag_transport_package_callback(uint8_t port, uint8_t flags, int16_t rssi, int8_t snr,
 					    uint8_t len, const uint8_t *rx_buf)
 {
@@ -207,7 +210,14 @@ static void frag_transport_package_callback(uint8_t port, uint8_t flags, int16_t
 			}
 #endif
 
-			/* Descriptor not used: Ignore Wrong Descriptor error */
+			if (descriptor_cb != NULL) {
+				int rc = descriptor_cb(ctx.descriptor);
+
+				if (rc < 0) {
+					/* Wrong Descriptor */
+					status |= BIT(3);
+				}
+			}
 
 			if ((status & 0x1F) == 0) {
 #ifdef CONFIG_LORAWAN_FRAG_TRANSPORT_DECODER_SEMTECH
@@ -314,6 +324,11 @@ static void frag_transport_package_callback(uint8_t port, uint8_t flags, int16_t
 	}
 }
 
+void lorawan_frag_transport_register_descriptor_callback(transport_descriptor_cb cb)
+{
+	descriptor_cb = cb;
+}
+
 static struct lorawan_downlink_cb downlink_cb = {
 	.port = (uint8_t)LORAWAN_PORT_FRAG_TRANSPORT,
 	.cb = frag_transport_package_callback,