CORS: add an optional custom function to validate the origin

[dahu33]

The CORS middleware is great and works very well if the list of allowed origins is static. However, in many use cases, this list need to be dynamic (for example, if coming from the database). This is a non-breaking change that makes the CORS middleware accepting an optional custom function to validate the origin.

PS: the diff looks weird for some unknown reason but the code change is minimal (mostly indentation).

Thanks!

[codecov]

Codecov Report

Merging #1651 (e6f24aa) into master (17a5fca) will increase coverage by 0.15%.
The diff coverage is 90.90%.

@@            Coverage Diff             @@
##           master    #1651      +/-   ##
==========================================
+ Coverage   84.72%   84.88%   +0.15%     
==========================================
  Files          29       29              
  Lines        1938     1945       +7     
==========================================
+ Hits         1642     1651       +9     
+ Misses        188      187       -1     
+ Partials      108      107       -1     

Impacted Files	Coverage Δ
middleware/cors.go	89.15% <90.90%> (+3.63%)	⬆️

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[shoenseiwaso]

Codecov appears broken, it's saying coverage was reduced by 284 lines in files completely unrelated to the change. See also this 3 line README.md change with a similar code coverage result. Echo maintainers, let us know if we've missed something here!

[pafuent]

LGTM

[dahu33]

@pafuent thank you very much for the review! @lammel, @vishr, any chance this could merged (I cannot merge myself) and land in the next release?

[lammel]

The use case looks valid to me.
I also do not see any breaking changes. Tests look ok, if you can think of further useful tests.

Would you mind providing a PR with a code example in https://github.com/labstack/echox too.
That would complete the change and help others with an example.

[dahu33]

@lammel thanks the review. I have implemented your feedback and opened a PR here labstack/echox#164 to document the feature. Could you please have a look?

[lammel]

Seems I was too eager merging another CORS related issue first.
Could you rebase please, will merge it than.

[dahu33]

Seems I was too eager merging another CORS related issue first.
Could you rebase please, will merge it than.

Done! The diff looks weird for some reason but the code change is the same as before.

[lammel]

Merged. Thanks @dahu33 !