Deserialise seq of bytes into bitlist only if last byte is non null

[franck44]

What was wrong?

A sequence of bytes ending with 0x00 cannot be a serialisation of a bitlist. As a consequence it should not be possible to deserialise such sequence into a bitlist. The current implementation allows that.

Issue #109

How the issue was uncovered?

This issue was uncovered as part of the formal verification of the Eth2.0 specs using Dafny: issue 4

How was it fixed?

Deserialise into bitlist code; add a test to check that the last byte is not null. If it is raise an exception.

Tests: two tests provided with illegal input for deserialising into biltists and check that the exception is actually raised.

Cute Animal Picture

[franck44]

@ralexstokes @pipermerriam I am not sure how to fix the latest lint error. I don't see any error message apart from a command invocation error. Is the reformatter failing for some reason?

[pipermerriam]

Looks like the linting error is related to the black code formatter that we use. If you run make lint-roll from the root of the project it should run the code formatter and clean this up for you.

[ralexstokes]

separately i think we do want to ensure that deserializing with extra input raises an error, but this is separate from this PR. i'll move to an issue

[franck44]

Looks like the linting error is related to the black code formatter that we use. If you run make lint-roll from the root of the project it should run the code formatter and clean this up for you.

@pipermerriam Re formatting with black, I have installed and reformatted the files, but still get an error when I run make lint-roll:

franck:~/development/franck44-py-ssz [master]$ black tests/sedes/test_bitlist_serializer.py
All done! ✨ 🍰 ✨
1 file left unchanged.
franck:~/development/franck44-py-ssz [master]$ make lint-roll
isort --recursive ssz tests
/Library/Developer/CommandLineTools/usr/bin/make lint
tox -elint
lint develop-inst-noop: /Users/franck/development/franck44-py-ssz
lint installed: appdirs==1.4.4,attrs==19.3.0,black==19.3b0,click==7.1.2,cytoolz==0.10.1,entrypoints==0.3,eth-hash==0.2.0,eth-typing==2.2.1,eth-utils==1.9.0,flake8==3.7.8,isort==4.3.21,lru-dict==1.1.6,mccabe==0.6.1,pycodestyle==2.5.0,pyflakes==2.1.1,pyrsistent==0.16.0,six==1.14.0,-e git+git@github.com:franck44/py-ssz.git@cda99a64d68ced1ee8c051f4acd87244de5f62b5#egg=ssz,toml==0.10.1,toolz==0.10.0
lint run-test-pre: PYTHONHASHSEED='2896134891'
lint run-test: commands[0] | flake8 /Users/franck/development/franck44-py-ssz/ssz /Users/franck/development/franck44-py-ssz/tests /Users/franck/development/franck44-py-ssz/scripts
lint run-test: commands[1] | black --check /Users/franck/development/franck44-py-ssz/ssz /Users/franck/development/franck44-py-ssz/tests /Users/franck/development/franck44-py-ssz/scripts
would reformat /Users/franck/development/franck44-py-ssz/tests/sedes/test_bitlist_serializer.py
All done! 💥 💔 💥
1 file would be reformatted, 64 files would be left unchanged.
ERROR: InvocationError for command /Users/franck/development/franck44-py-ssz/.tox/lint/bin/black --check ssz tests scripts (exited with code 1)

Any idea what can go wrong? I am not a Python/PyCharm regular user :-(

[franck44]

@pipermerriam I fixed the lint problem. I think I had not properly completed the setup (activate the venv) and may have used different version of black on my MacOS box/PyCharm.

[ralexstokes]

@franck44 sorry about that! make lint-roll in this case only prints the linting errors, it does not go fix them for you