ESP HTTPS OTA 升级
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-C2 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-C2 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
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 onesp_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 ofota_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 useesp_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 toesp_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 tocert_pem
member ofhttp_config
, which is a part ofota_config
. In case of error, this API explicitly setshandle
to NULL.备注
This API is blocking, so setting
is_async
member ofhttp_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 ifesp_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.
-
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
-
const esp_http_client_config_t *http_config
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
-
enumerator ESP_HTTPS_OTA_START