# ESP HTTPS OTA 升级

[English]

## 概述

`esp_https_ota` 是现有 OTA（空中升级）API 的抽象层，其中提供了简化的 API，能够通过 HTTPS 升级固件。

>     esp_err_t do_firmware_upgrade()
>     {
>         esp_http_client_config_t config = {
>             .url = CONFIG_FIRMWARE_UPGRADE_URL,
>             .cert_pem = (char *)server_cert_pem_start,
>         };
>         esp_https_ota_config_t ota_config = {
>             .http_config = &config,
>         };
>         esp_err_t ret = esp_https_ota(&ota_config);
>         if (ret == ESP_OK) {
>             esp_restart();
>         } else {
>             return ESP_FAIL;
>         }
>         return ESP_OK;
>     }

## 服务器验证

验证服务器时，应将 PEM 格式的根证书提供给 `esp_http_client_config_t::cert_pem` 成员。如需了解有关服务器验证的更多信息，请参阅 TLS 服务器验证。

备注

应使用服务器端点的 根 证书应用于验证，而不能使用证书链中的任何中间证书，因为根证书有效期最长，且通常长时间维持不变。用户还可以通过 `esp_http_client_config_t::crt_bundle_attach` 成员使用 `ESP x509 证书包` 功能进行验证，其中涵盖了大多数受信任的根证书。

## 通过 HTTPS 下载部分镜像

要使用部分镜像下载功能，请启用 `esp_https_ota_config_t` 中的 `partial_http_download` 配置。启用此配置后，固件镜像将通过多个指定大小的 HTTP 请求进行下载。将 `max_http_request_size` 设置为所需值，即可指定每个请求的最大内容长度。

在从 AWS S3 等服务获取镜像时，这一选项非常有用。在启用该选项时，可以将 mbedTLS Rx 的 buffer 大小（即 CONFIG_MBEDTLS_SSL_IN_CONTENT_LEN）设置为较小的值。不启用此配置时，无法将其设置为较小值。

mbedTLS Rx buffer 的默认大小为 16 KB，但如果将 `partial_http_download` 的 `max_http_request_size` 设置为 4 KB，便能将 mbedTLS Rx 的 buffer 减小到 4 KB。使用这一配置方式预计可以节省约 12 KB 内存。

## 签名验证

要进一步提升安全性，还可以验证 OTA 固件镜像的签名。更多内容请参考 没有安全启动的安全 OTA 升级。

## 使用预加密固件进行 OTA 升级

预加密固件完全独立于 flash 加密 方案，主要原因如下：

> - flash 加密方案推荐各个设备使用在内部生成的唯一加密密钥，因此在 OTA 更新服务器上预加密固件并不可行。

> - flash 加密方案依赖 flash 偏移，会基于不同的 flash 偏移量生成不同的密文，因此根据分区槽（如 `ota_0`、`ota_1` 等）来管理不同的 OTA 更新镜像较为困难。

> - 即使设备未启用 flash 加密，仍可能要求进行 OTA 的固件镜像保持加密。

无论底层传输安全性如何，预加密固件的分发都能确保固件镜像在从服务器到设备的**传输过程中**保持加密状态。首先，预加密软件层在设备上通过网络接收并解密固件，然后使用平台 flash 加密（如果已启用）重新加密内容，最后写入 flash。

### 设计

- 该方案需首先生成一个唯一的 RSA-3072 公钥—私钥对。公钥保留在 OTA 更新服务器上，用于加密，而私钥作为设备的一部分，例如内嵌于固件中，用于解密。

- 预加密固件使用 AES-GCM 密钥进行加密，并将该密钥（及其配置参数）作为标头附加到镜像中。

- 此外，AES-GCM 密钥使用 RSA 公钥进行加密，生成的镜像会托管到 OTA 更新服务器上。

- 在设备端，首先使用可用的 RSA 私钥解密镜像标头，从而获取 AES-GCM 密钥。

- 最后，使用 AES-GCM 密钥（和配置参数）解密镜像内容，并将其写入 flash。

整个工作流程由外部组件 esp_encrypted_image 管理，并通过解密回调 (`esp_https_ota_config_t::decrypt_cb`) 机制插入到 OTA 更新框架中。

备注

该支持方案基于 RSA-3072，必须使用平台安全功能保护设备端的私钥。

## OTA 系统事件

ESP HTTPS OTA 过程中可能发生各种系统事件。当特定事件发生时，会由 事件循环库 触发处理程序。此处理程序必须使用 `esp_event_handler_register()` 注册。这有助于 ESP HTTPS OTA 进行事件处理。

`esp_https_ota_event_t` 中包含了使用 ESP HTTPS OTA 升级时可能发生的所有事件。

### 事件处理程序示例

>     /* 用于捕获系统事件的事件处理程序 */
>     static void event_handler(void* arg, esp_event_base_t event_base,
>                             int32_t event_id, void* event_data)
>     {
>         if (event_base == ESP_HTTPS_OTA_EVENT) {
>             switch (event_id) {
>                 case ESP_HTTPS_OTA_START:
>                     ESP_LOGI(TAG, "OTA started");
>                     break;
>                 case ESP_HTTPS_OTA_CONNECTED:
>                     ESP_LOGI(TAG, "Connected to server");
>                     break;
>                 case ESP_HTTPS_OTA_GET_IMG_DESC:
>                     ESP_LOGI(TAG, "Reading Image Description");
>                     break;
>                 case ESP_HTTPS_OTA_VERIFY_CHIP_ID:
>                     ESP_LOGI(TAG, "Verifying chip id of new image: %d", *(esp_chip_id_t *)event_data);
>                     break;
>                 case ESP_HTTPS_OTA_DECRYPT_CB:
>                     ESP_LOGI(TAG, "Callback to decrypt function");
>                     break;
>                 case ESP_HTTPS_OTA_WRITE_FLASH:
>                     ESP_LOGD(TAG, "Writing to flash: %d written", *(int *)event_data);
>                     break;
>                 case ESP_HTTPS_OTA_UPDATE_BOOT_PARTITION:
>                     ESP_LOGI(TAG, "Boot partition updated. Next Partition: %d", *(esp_partition_subtype_t *)event_data);
>                     break;
>                 case ESP_HTTPS_OTA_FINISH:
>                     ESP_LOGI(TAG, "OTA finish");
>                     break;
>                 case ESP_HTTPS_OTA_ABORT:
>                     ESP_LOGI(TAG, "OTA abort");
>                     break;
>             }
>         }
>     }

系统事件循环中，不同 ESP HTTPS OTA 事件的预期数据类型如下所示：

> - ESP_HTTPS_OTA_START : `NULL`

> - ESP_HTTPS_OTA_CONNECTED : `NULL`

> - ESP_HTTPS_OTA_GET_IMG_DESC : `NULL`

> - ESP_HTTPS_OTA_VERIFY_CHIP_ID : `esp_chip_id_t`

> - ESP_HTTPS_OTA_DECRYPT_CB : `NULL`

> - ESP_HTTPS_OTA_WRITE_FLASH : `int`

> - ESP_HTTPS_OTA_UPDATE_BOOT_PARTITION : `esp_partition_subtype_t`

> - ESP_HTTPS_OTA_FINISH : `NULL`

> - ESP_HTTPS_OTA_ABORT : `NULL`

## 应用示例

- system/ota/pre_encrypted_ota 演示了如何使用 esp_encrypted_img 组件的 API 和工具进行带预加密二进制文件的 OTA 更新，确保固件在网络通道上的机密性，但不保证其真实性。要进行带预加密固件的 OTA 升级，请在组件 menuconfig 中启用 CONFIG_ESP_HTTPS_OTA_DECRYPT_CB。

- system/ota/advanced_https_ota 演示了如何在 ESP32-S2 上使用 esp_https_ota 组件的 API 来使用 HTTPS OTA 更新功能。关于该示例适用的芯片，请参考 system/ota/advanced_https_ota/README.md。

- system/ota/simple_ota_example 演示了如何使用 esp_https_ota 组件的 API，通过特定的网络接口，如以太网或 Wi-Fi Station，在 ESP32-S2 上进行固件升级。关于该示例适用的芯片，请参考 system/ota/simple_ota_example/README.md。

## API 参考

### Header File

- components/esp_https_ota/include/esp_https_ota.h

- This header file can be included with:

  >     #include "esp_https_ota.h"

- This header file is a part of the API provided by the `esp_https_ota` component. To declare that your component depends on `esp_https_ota`, add the following to your CMakeLists.txt:

  >     REQUIRES esp_https_ota

  > or

  >     PRIV_REQUIRES esp_https_ota

### Functions

esp_err_t esp_https_ota(const esp_https_ota_config_t *ota_config)

  HTTPS OTA Firmware upgrade.

  This function allocates HTTPS OTA Firmware upgrade context, establishes HTTPS connection, reads image data from HTTP stream and writes it to OTA partition and finishes HTTPS OTA Firmware upgrade operation. This API supports URL redirection, but if CA cert of URLs differ then it should be appended to `cert_pem` member of `ota_config->http_config`.

  备注

  This API handles the entire OTA operation, so if this API is being used then no other APIs from `esp_https_ota` component should be called. If more information and control is needed during the HTTPS OTA process, then one can use `esp_https_ota_begin` and subsequent APIs. If this API returns successfully, esp_restart() must be called to boot from the new firmware image.

  参数:

    ota_config -- [in] pointer to esp_https_ota_config_t structure.

  返回:

    - ESP_OK: OTA data updated, next reboot will use specified partition.

    - ESP_FAIL: For generic failure.

    - ESP_ERR_INVALID_ARG: Invalid argument

    - ESP_ERR_OTA_VALIDATE_FAILED: Invalid app image

    - ESP_ERR_NO_MEM: Cannot allocate memory for OTA operation.

    - ESP_ERR_FLASH_OP_TIMEOUT or ESP_ERR_FLASH_OP_FAIL: Flash write failed.

    - For other return codes, refer OTA documentation in esp-idf's app_update component.

esp_err_t esp_https_ota_begin(const esp_https_ota_config_t *ota_config, esp_https_ota_handle_t *handle)

  Start HTTPS OTA Firmware upgrade.

  This function initializes ESP HTTPS OTA context and establishes HTTPS connection. This function must be invoked first. If this function returns successfully, then `esp_https_ota_perform` should be called to continue with the OTA process and there should be a call to `esp_https_ota_finish` on completion of OTA operation or on failure in subsequent operations. This API supports URL redirection, but if CA cert of URLs differ then it should be appended to `cert_pem` member of `http_config`, which is a part of `ota_config`. In case of error, this API explicitly sets `handle` to NULL.

  备注

  This API is blocking, so setting `is_async` member of `http_config` structure will result in an error.

  参数:

    - ota_config -- [in] pointer to esp_https_ota_config_t structure

    - handle -- [out] pointer to an allocated data of type `esp_https_ota_handle_t` which will be initialised in this function

  返回:

    - ESP_OK: HTTPS OTA Firmware upgrade context initialised and HTTPS connection established

    - ESP_FAIL: For generic failure.

    - ESP_ERR_INVALID_ARG: Invalid argument (missing/incorrect config, certificate, etc.)

    - For other return codes, refer documentation in app_update component and esp_http_client component in esp-idf.

esp_err_t esp_https_ota_perform(esp_https_ota_handle_t https_ota_handle)

  Read image data from HTTP stream and write it to OTA partition.

  This function reads image data from HTTP stream and writes it to OTA partition. This function must be called only if esp_https_ota_begin() returns successfully. This function must be called in a loop since it returns after every HTTP read operation thus giving you the flexibility to stop OTA operation midway.

  参数:

    https_ota_handle -- [in] pointer to esp_https_ota_handle_t structure

  返回:

    - ESP_ERR_HTTPS_OTA_IN_PROGRESS: OTA update is in progress, call this API again to continue.

    - ESP_OK: OTA update was successful

    - ESP_FAIL: OTA update failed

    - ESP_ERR_INVALID_ARG: Invalid argument

    - ESP_ERR_INVALID_VERSION: Invalid chip revision in image header

    - ESP_ERR_OTA_VALIDATE_FAILED: Invalid app image

    - ESP_ERR_NO_MEM: Cannot allocate memory for OTA operation.

    - ESP_ERR_FLASH_OP_TIMEOUT or ESP_ERR_FLASH_OP_FAIL: Flash write failed.

    - For other return codes, refer OTA documentation in esp-idf's app_update component.

bool esp_https_ota_is_complete_data_received(esp_https_ota_handle_t https_ota_handle)

  Checks if complete data was received or not.

  备注

  This API can be called just before esp_https_ota_finish() to validate if the complete image was indeed received.

  参数:

    https_ota_handle -- [in] pointer to esp_https_ota_handle_t structure

  返回:

    - false

    - true

esp_err_t esp_https_ota_finish(esp_https_ota_handle_t https_ota_handle)

  Clean-up HTTPS OTA Firmware upgrade and close HTTPS connection.

  This function closes the HTTP connection and frees the ESP HTTPS OTA context. This function switches the boot partition to the OTA partition containing the new firmware image.

  备注

  If this API returns successfully, esp_restart() must be called to boot from the new firmware image esp_https_ota_finish should not be called after calling esp_https_ota_abort

  参数:

    https_ota_handle -- [in] pointer to esp_https_ota_handle_t structure

  返回:

    - ESP_OK: Clean-up successful

    - ESP_ERR_INVALID_STATE

    - ESP_ERR_INVALID_ARG: Invalid argument

    - ESP_ERR_OTA_VALIDATE_FAILED: Invalid app image

esp_err_t esp_https_ota_abort(esp_https_ota_handle_t https_ota_handle)

  Clean-up HTTPS OTA Firmware upgrade and close HTTPS connection.

  This function closes the HTTP connection and frees the ESP HTTPS OTA context.

  备注

  esp_https_ota_abort should not be called after calling esp_https_ota_finish

  参数:

    https_ota_handle -- [in] pointer to esp_https_ota_handle_t structure

  返回:

    - ESP_OK: Clean-up successful

    - ESP_ERR_INVALID_STATE: Invalid ESP HTTPS OTA state

    - ESP_FAIL: OTA not started

    - ESP_ERR_NOT_FOUND: OTA handle not found

    - ESP_ERR_INVALID_ARG: Invalid argument

esp_err_t esp_https_ota_get_img_desc(esp_https_ota_handle_t https_ota_handle, esp_app_desc_t *new_app_info)

  Reads app description from image header. The app description provides information like the "Firmware version" of the image.

  备注

  This API can be called only after esp_https_ota_begin() and before esp_https_ota_perform(). Calling this API is not mandatory.

  参数:

    - https_ota_handle -- [in] pointer to esp_https_ota_handle_t structure

    - new_app_info -- [out] pointer to an allocated esp_app_desc_t structure

  返回:

    - ESP_ERR_INVALID_ARG: Invalid arguments

    - ESP_ERR_INVALID_STATE: Invalid state to call this API. esp_https_ota_begin() not called yet.

    - ESP_FAIL: Failed to read image descriptor

    - ESP_OK: Successfully read image descriptor

int esp_https_ota_get_image_len_read(esp_https_ota_handle_t https_ota_handle)

  This function returns OTA image data read so far.

  备注

  This API should be called only if `esp_https_ota_perform()` has been called at least once or if `esp_https_ota_get_img_desc` has been called before.

  参数:

    https_ota_handle -- [in] pointer to esp_https_ota_handle_t structure

  返回:

    - -1 On failure

    - total bytes read so far

int esp_https_ota_get_status_code(esp_https_ota_handle_t https_ota_handle)

  This function returns the HTTP status code of the last HTTP response.

  备注

  This API should be called only after esp_https_ota_begin() has been called. This can be used to check the HTTP status code of the OTA download process.

  参数:

    https_ota_handle -- [in] pointer to esp_https_ota_handle_t structure

  返回:

    - -1 On failure

    - HTTP status code

int esp_https_ota_get_image_size(esp_https_ota_handle_t https_ota_handle)

  This function returns OTA image total size.

  备注

  This API should be called after esp_https_ota_begin() has been already called. This can be used to create some sort of progress indication (in combination with esp_https_ota_get_image_len_read())

  参数:

    https_ota_handle -- [in] pointer to esp_https_ota_handle_t structure

  返回:

    - -1 On failure or chunked encoding

    - total bytes of image

### Structures

struct decrypt_cb_arg_t

  ESP HTTPS OTA decrypt callback args.

  Public Members

  const char *data_in

    Pointer to data to be decrypted

  size_t data_in_len

    Input data length

  char *data_out

    Pointer to data decrypted using callback, this will be freed after data is written to flash

  size_t data_out_len

    Output data length

struct esp_https_ota_config_t

  ESP HTTPS OTA configuration.

  Public Members

  const esp_http_client_config_t *http_config

    ESP HTTP client configuration

  http_client_init_cb_t http_client_init_cb

    Callback after ESP HTTP client is initialised

  bool bulk_flash_erase

    Erase entire flash partition during initialization. By default flash partition is erased during write operation and in chunk of 4K sector size

  bool partial_http_download

    Enable Firmware image to be downloaded over multiple HTTP requests

  int max_http_request_size

    Maximum request size for partial HTTP download

  uint32_t buffer_caps

    The memory capability to use when allocating the buffer for OTA update. Default capability is MALLOC_CAP_DEFAULT

  decrypt_cb_t decrypt_cb

    Callback for external decryption layer

  void *decrypt_user_ctx

    User context for external decryption layer

  uint16_t enc_img_header_size

    Header size of pre-encrypted ota image header

### Macros

ESP_ERR_HTTPS_OTA_BASE

ESP_ERR_HTTPS_OTA_IN_PROGRESS

### Type Definitions

typedef void *esp_https_ota_handle_t

typedef esp_err_t (*http_client_init_cb_t)(esp_http_client_handle_t)

typedef esp_err_t (*decrypt_cb_t)(decrypt_cb_arg_t *args, void *user_ctx)

### Enumerations

enum esp_https_ota_event_t

  Events generated by OTA process.

  Values:

  enumerator ESP_HTTPS_OTA_START

    OTA started

  enumerator ESP_HTTPS_OTA_CONNECTED

    Connected to server

  enumerator ESP_HTTPS_OTA_GET_IMG_DESC

    Read app description from image header

  enumerator ESP_HTTPS_OTA_VERIFY_CHIP_ID

    Verify chip id of new image

  enumerator ESP_HTTPS_OTA_DECRYPT_CB

    Callback to decrypt function

  enumerator ESP_HTTPS_OTA_WRITE_FLASH

    Flash write operation

  enumerator ESP_HTTPS_OTA_UPDATE_BOOT_PARTITION

    Boot partition update after successful ota update

  enumerator ESP_HTTPS_OTA_FINISH

    OTA finished

  enumerator ESP_HTTPS_OTA_ABORT

    OTA aborted

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