Check singularity image already cached

[manabuishii]

If there is already exists singularity image under cache directory , singularity pull causes error.
To avoid error, check whether singularity image is exists or not.

[mr-c]

Thanks @manabuishii !

Should there be a command line option added to always download?

[manabuishii]

@mr-c Thanks !
Is --force-download good name for command line option ?

[codecov]

Codecov Report

Merging #101 (111d979) into main (eb89df4) will decrease coverage by 15.19%.
The diff coverage is 33.33%.

❗ Current head 111d979 differs from pull request most recent head 59c0cea. Consider uploading reports for the commit 59c0cea to get more accurate results

@@             Coverage Diff             @@
##             main     #101       +/-   ##
===========================================
- Coverage   40.92%   25.74%   -15.19%     
===========================================
  Files          30       16       -14     
  Lines       23519    19627     -3892     
  Branches     6656        0     -6656     
===========================================
- Hits         9625     5052     -4573     
- Misses      11820    14575     +2755     
+ Partials     2074        0     -2074     

Impacted Files	Coverage Δ
cwl_utils/image_puller.py	88.23% <33.33%> (+1.13%)	⬆️

... and 34 files with indirect coverage changes

[mr-c]

@mr-c Thanks !
Is --force-download good name for command line option ?

Yes!

[stevekm]

isn't a feature like this already implemented here?
https://github.com/common-workflow-language/cwltool/blob/ef7cb301a891adaee8255f4c0a28f1712fc54bd0/cwltool/singularity.py#L190-L191
it uses the CWL_SINGULARITY_CACHE env var, maybe that would be good to use for this update as well?

[jfennick]

I've just been affected by this issue, and I can confirm that the fix works. Can we revisit this PR?