fix(app_update): avoid erasing an extra sector than the actual requir…

…ed size

OTA update used to fail if `firmware_size == partition_size`, because the code was trying to
erase one additional sector beyond the space reserved for the firmware partition.

This commit fixes the problem and OTA update can work if the firmware
size exactly matches the allocated partition size.

Closes espressif#12460

components/app_update/esp_ota_ops.c

@@ -199,13 +199,18 @@ esp_err_t esp_ota_write(esp_ota_handle_t handle, const void *data, size_t size)
         return ESP_ERR_INVALID_ARG;
     }
 
+    if (size == 0) {
+        ESP_LOGD(TAG, "write data size is 0");
+        return ESP_OK;
+    }
+
     // find ota handle in linked list
     for (it = LIST_FIRST(&s_ota_ops_entries_head); it != NULL; it = LIST_NEXT(it, entries)) {
         if (it->handle == handle) {
             if (it->need_erase) {
                 // must erase the partition before writing to it
-                uint32_t first_sector = it->wrote_size / SPI_FLASH_SEC_SIZE;
-                uint32_t last_sector = (it->wrote_size + size) / SPI_FLASH_SEC_SIZE;
+                uint32_t first_sector = it->wrote_size / SPI_FLASH_SEC_SIZE; // first affected sector
+                uint32_t last_sector = (it->wrote_size + size - 1) / SPI_FLASH_SEC_SIZE; // last affected sector
 
                 ret = ESP_OK;
                 if ((it->wrote_size % SPI_FLASH_SEC_SIZE) == 0) {

components/app_update/include/esp_ota_ops.h

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2015-2021 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2015-2023 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -111,7 +111,7 @@ esp_err_t esp_ota_begin(const esp_partition_t* partition, size_t image_size, esp
  * @param size    Size of data buffer in bytes.
  *
  * @return
- *    - ESP_OK: Data was written to flash successfully.
+ *    - ESP_OK: Data was written to flash successfully, or size = 0
  *    - ESP_ERR_INVALID_ARG: handle is invalid.
  *    - ESP_ERR_OTA_VALIDATE_FAILED: First byte of image contains invalid app image magic byte.
  *    - ESP_ERR_FLASH_OP_TIMEOUT or ESP_ERR_FLASH_OP_FAIL: Flash write failed.