fix: django-storage 1.14 complains about files being opened twice when copying

[fsbraun]

Description

While the root cause of the bug #1417 might be in django-storages 1.14, this quick-fix ensures that any ValueError raised opening a file for copying does not crash the file application with a server error.

Related resources

• 1417

• ...

Checklist

• [x] I have opened this pull request against master
• [x] I have added or modified the tests when changing logic
• [x] I have followed the conventional commits guidelines to add meaningful information into the changelog
• [x] I have read the contribution guidelines and I have joined #workgroup-pr-review on Slack to find a “pr review buddy” who is going to review my pull request.

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (ac3985d) 75.21% compared to head (a4cfe26) 75.22%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1418 +/- ## ======================================= Coverage 75.21% 75.22% ======================================= Files 75 75 Lines 3454 3455 +1 Branches 555 555 ======================================= + Hits 2598 2599 +1 Misses 691 691 Partials 165 165 ``` | [Files Changed](https://app.codecov.io/gh/django-cms/django-filer/pull/1418?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=django-cms) | Coverage Δ | | |---|---|---| | [filer/admin/folderadmin.py](https://app.codecov.io/gh/django-cms/django-filer/pull/1418?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=django-cms#diff-ZmlsZXIvYWRtaW4vZm9sZGVyYWRtaW4ucHk=) | `75.65% <100.00%> (ø)` | | | [filer/models/filemodels.py](https://app.codecov.io/gh/django-cms/django-filer/pull/1418?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=django-cms#diff-ZmlsZXIvbW9kZWxzL2ZpbGVtb2RlbHMucHk=) | `88.69% <100.00%> (+0.04%)` | :arrow_up: |

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[vinitkumar]

@fsbraun Is it possible to have a test with this patch?

[fsbraun]

@vinitkumar I know! I've been thinking about it, but I do not see a way of testing this without the specific implementation of django-storage's S3Storage on an AWS instance. I frankly believe that the underlying issue is between Django and django-storage, but it's hard to tell. Since thetry except block.

Any idea how to test this?

[vinitkumar]

@fsbraun I don't know. Seems hard to implement in the test. Have you tried testing this patch with a real s3 backend?

[fsbraun]

@vinitkumar I tested it on my staging setup with AWS: Without the fix, copying files fails and a copy of the first file remains in the source folder. After fixing it, copying works fine.

The fix also does not affect local file storage (which just runs seek(0) in case of a reopen).