Fix #1787: Add support for optional filesystem to the static middleware

[lukasdietrich]

This PR is related to #1787.

By supporting http.Filesystem we also provide support for the new fs.FS while maintaining compatibility with versions prior to go1.16.

[codecov]

Codecov Report

Merging #1797 (eb51091) into master (6f9b71c) will decrease coverage by 0.02%.
The diff coverage is 81.25%.

@@            Coverage Diff             @@
##           master    #1797      +/-   ##
==========================================
- Coverage   89.56%   89.54%   -0.03%     
==========================================
  Files          32       32              
  Lines        2646     2659      +13     
==========================================
+ Hits         2370     2381      +11     
  Misses        178      178              
- Partials       98      100       +2     

Impacted Files	Coverage Δ
middleware/static.go	70.00% <81.25%> (+2.83%)	⬆️

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[aldas]

NB: you might want to try static tests with config.Filesystem = http.FS(os.DirFS(".")) and probably add tests for embed fs (with build tag // +build go1.16)

I think the change may not be that simple as Open in os/fs packages does some extra file name validation and messes up some logic we rely on static middleware.

[lukasdietrich]

@aldas Thank you for your super quick codereview!

NB: you might want to try static tests with config.Filesystem = http.FS(os.DirFS(".")) and probably add tests for embed fs (with build tag // +build go1.16)

Great idea to use build tags! Go did not let me use embed.FS, because go1.15 is specified in go.mod, I did however add some testcases using testing/testfs and os.DirFS(...).

I think the change may not be that simple as Open in os/fs packages does some extra file name validation and messes up some logic we rely on static middleware.

Which validation exactly do you mean? What I saw so far is that fs.FS as well as http.Filesystem expects forward slashes instead of the system file separator.

regarding to filepath.Clean vs path.Clean there is subtle difference in their behavior #1718 (comment)

Well I am glad you caught that one! I reverted back to filepath.Clean and then convert to filepath.ToSlash to comply with the http.FileSystem. Do you think that is a sufficient solution?

[aldas]

well I was just tinkering around and saw your PR. I tried solve same thing ( couple of days ago ) by going fs.FS route and did not switch from c.File() to http.ServeContent and saw that changes just pile up with some of them being "different" path validation in Open. Using http.Filesystem is nice move.
That go.mod problem I think will be fixed in next Go patch version but this does not need to block accepting this PR.

[aldas]

Looks good to me