esp32/ota: Implement ESP-IDF OTA functionality.

[ekondayan]

UPDATE: The test completed successfully on NodeMCU ESP32 by ai-thinker with ESP-IDF v4.0, v4.1, v4.2, v4.3

Implemented new functions in esp32.Partition:

• mark_app_invalid_rollback_and_reboot()

• check_rollback_is_possible()

• app_description()

• app_state()

• ota_begin()

• ota_write()

• ota_write_with_offset() for ESP-IDF version >= 4.2

• ota_end()

• ota_abort() for ESP-IDF version >= 4.3

• create tests

• update documentation

For many commercial products, Over The Air updates are a very important and critical part. It must be reliable and should not brick the device. Writing a good OTA from scratch is a daunting task. For that reason the use of well tested and proven reliable libraries is much more preferable than the ones developed in the house.

USECASE

I'm developing an industrial device where the OTA is an essential part of it. Since only a few functions from esp-idf are
implemented (enough for hobby project but not enough for commercial project), I ended up duplicating the esp-idf ota functionality in python.
The result was a module with a questionable quality. I tried to predict all the possible places where it could crash, but my gut was
telling me that I could be missing something. So I decided to implement more of the the OTA functions from esp-idf and to use them in my OTA module.
I've rewritten my OTA module and replaced the redundant code with the implemented functions from esp-idf. This allowed me to reduced the size of the module significantly, increase the robustness of the code and on top of that now the code got much simpler and easier to maintain.
The total increase in size of the compiled app image is 2432 bytes.

IMPLEMENTATION

Extend the esp32.Partition class where all the OTA related functions are
prefixed with "ota_" and app related functions are prefixed with "app_".

Example:
from esp32 import Partition
app_part = Partition(Partition.RUNNING)
app_part.app_description()
app_part.app_state()
handle = app_part.ota_begin()
app_part.ota_end(handle)

New functions:
Partition.mark_app_invalid_rollback_and_reboot(cls)
Partition.check_rollback_is_possible(cls)
Partition.app_description(self)
Partition.app_state(self)
Partition.ota_begin(self, image_size = 0)
Partition.ota_write(self, handle_in, data_in)
Partition.ota_write_with_offset(self, handle_in, data_in, offset)
Partition.ota_end(self, handle_in)
Partition.ota_abort(self, handle_in) only for ESP-IDF version >= 4.3

BENEFITS

• no code duplication
• reduced code size
• cleaner and easier to maintain code
• esp-idf handles encrypted flash
• use a reliable and well tested library written by the creators of ESP32
• more robust OTA procedure
• better performance

CONS

• None :) (maybe the 2432 bytes overhead in the final compiled app image)

[ekondayan]

Anybody?
Is there any chance of this getting mainstream?

[projectgus]

This is an automated heads-up that we've just merged a Pull Request
that removes the STATIC macro from MicroPython's C API.

See #13763

A search suggests this PR might apply the STATIC macro to some C code. If it
does, then next time you rebase the PR (or merge from master) then you should
please replace all the STATIC keywords with static.

Although this is an automated message, feel free to @-reply to me directly if
you have any questions about this.