imgtool: Extend functionality with getpubhash and output to file

[bence-balogh]

• Added getpubhash: It returns the sha256 hash of the public key. It can be useful if MCUBOOT_HW_KEY is set and only the hash has to be written to the device.
• Added functionality to getpub and getpubhash to print to a file instead of stdout.
• Added functionality to getpub and getpubhash to print the output as a raw value.

[davidvincze]

Could you explain it to me? Thanks! :)
Is it possible that it's not necessary if the the default file=sys.stdout is removed for the "emit functions" ?

[bence-balogh]

The sys.stdout does not have the close method implemented and would throw an error when the with (open...'s scope ends. This way we add an empty method to prevent this error and there's no need for additional checks whether the file is sys.stdout or a regular file.

[davidvincze]

I've tried it without the sys.stdout.close = lambda: None line and it worked fine. Isn't it that with the is not sys.stdout check it's avoided?

[bence-balogh]

You are right, my reasoning was not correct. 😬
sys.stdout does have a close() method but once it's called, the print() will no longer work until the sys.stdout's open() is called again.
So a print() after the close() would cause a crash if this sys.stdout.close = lambda: None is removed so as a workaround its close() is overridden.

[bence-balogh]

Removed this solution from the latest patchset because it'd change the global state and it's not that clear either.

[davidvincze]

Thanks for the update.
Another solution could have been to use the open()/close() methods directly, without with.

[davidvincze]

Please rebase your PR, Zephyr build was broken, but it's been fixed by: #1755

[davidvincze]

#nitpick
MCUboot tends the follow Python's PEP8 style guide. I didn't want to comment on some minor warnings because you just followed the existing "patterns", but now new types of errors have been introduced in the scripts/imgtool/keys/general.py file. May I ask you to solve these?

imgtool/keys/general.py:12:80: E501 line too long (94 > 79 characters)
imgtool/keys/general.py:14:33: E272 multiple spaces before keyword
imgtool/keys/general.py:15:80: E501 line too long (94 > 79 characters)
imgtool/keys/general.py:17:80: E501 line too long (96 > 79 characters)
imgtool/keys/general.py:19:80: E501 line too long (88 > 79 characters)
imgtool/keys/general.py:34:80: E501 line too long (88 > 79 characters)
imgtool/keys/general.py:38:80: E501 line too long (96 > 79 characters)
imgtool/keys/general.py:45:80: E501 line too long (93 > 79 characters)
imgtool/keys/general.py:49:80: E501 line too long (101 > 79 characters)
imgtool/keys/general.py:54:34: E272 multiple spaces before keyword
imgtool/keys/general.py:70:80: E501 line too long (88 > 79 characters)
imgtool/keys/general.py:78:33: E272 multiple spaces before keyword

You can check these using either the pycodestyle or flake8 tools: https://realpython.com/python-pep8/#linters