Do not close given file

[christian-intra2net]

Correct for excessive closing of file handles

When creating the last PR (#39), I closed too much. I did not take into account that closing an OleFileIO also closes the file handle it was given in the constructor. If the caller of OfficeFile wanted to continue working the the file handle (which is her right), she was presented with "ValueError: seek of closed file".

Correct this here and create unittest to prevent this from happening again.
And since we are looking at file handles: also seek to 0 before checking for isOleFile()

[codecov-io]

Codecov Report

Merging #40 into master will decrease coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #40      +/-   ##
==========================================
- Coverage   86.68%   86.64%   -0.04%     
==========================================
  Files          13       13              
  Lines        1179     1168      -11     
==========================================
- Hits         1022     1012      -10     
+ Misses        157      156       -1

Impacted Files	Coverage Δ
msoffcrypto/format/ooxml.py	78.78% <ø> (-1.02%)	⬇️
msoffcrypto/__init__.py	79.16% <100%> (+0.9%)	⬆️
msoffcrypto/format/doc97.py	88.08% <100%> (+0.26%)	⬆️
msoffcrypto/format/xls97.py	87.8% <100%> (-0.15%)	⬇️
msoffcrypto/format/ppt97.py	98.88% <100%> (-0.01%)	⬇️

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[nolze]

Thanks for fixes and tests! Just merged.
By the way, your previous PR reminded me that there should have been OfficeFile.close().

Another possible way I'm considering as an option for the next major release is to redesign APIs boldly and make it more functional:

with open("sample.docx", "rb") as f:
    if msoffcrypto.is_encrypted(f):
        # msoffcrypto.test_key(f, password="1234")
        decrypted = msoffcrypto.decrypt(f, password="1234")

[christian-intra2net]

Thanks for the merge and sorry I implemented the excessive close in the first place.

For the OfficeFile.close() it would have to be a class, right?

Your api idea sounds good and feasible. However, I grew up with object oriented programming, so I would actually prefer if OfficeFile were a real class (not just a function that looks like a class). Then you could also easily make it a context manager that manages the file handle itself:

with OfficeFile("sample.docx") as ofile:
  if ofile.is_encrypted():
    ofile.test_key(password="1234")
    decrypted = ofile.decrypt(password="1234")

(However, it does not have to be a class to do that, a context manager could also be just another function)

@contextlib.contextmanager
def create_office_file(filename)
    with open(filename, 'rb') as file_handle:
       yield OfficeFile(file_handle)

with create_office_file("sample.docx") as ofile:
    ....

[nolze]

A recent acknowledgement of the effort on Twitter. @christian-intra2net https://twitter.com/Malwageddon/status/1132006186008621060