Fix some files are recognized as SVG incorrectly, make the diff UI unable to work

[stuzer05]

SVG file displaying is broken, meanwhile also breaks other diff files (such as php html templates) from displaying in the diff ui

Every commit here does not display SVGs, and also showcaases broken php html template display
https://try.gitea.io/stuzer05/test-preview/commits/branch/master

So I removed "smart" svg detection at all

Closes #19733

[wxiaoguang]

SVG file displaying is broken

It should work (I manually constructed those files, one side is valid while other side is invalid)

• https://try.gitea.io/wxiaoguang/test/commit/1f2a63ed813050e652637548bfab447d090e97e6
• https://try.gitea.io/wxiaoguang/test/commit/6c8f25fdf666bc853fea32eb869742906275e5cc

meanwhile also breaks other diff files (such as php html templates) from displaying in the diff ui

What's the root problem of the breaking? eg: how the detection goes wrong?

---

Maybe a case is like this:

view-source:https://try.gitea.io/stuzer05/test-preview/raw/commit/e2f752e123151fea55959571d56d57462025f0f6/test.blade.php

<!-- BEGIN: filter namings -->
<div>
            <!-- prettier-ignore -->
            <svg xmlns="http://www.w3.org/2000/svg" width="10" height="10" viewBox="0 0 10 10">
                <path fill="#8E8E93" fill-rule="evenodd" d="M9.816 8.981L7.08 6.243c.49-.67.753-1.479.75-2.309C7.819 1.767 6.067.013 3.9 0 2.864-.005 1.868.406 1.135 1.14.403 1.872-.006 2.868 0 3.905.01 6.072 1.762 7.828 3.93 7.84c.833.004 1.645-.262 2.315-.758l.003-.002 2.735 2.736c.148.156.368.218.576.165.207-.054.37-.216.423-.424.054-.207-.01-.428-.165-.576zm-5.89-1.925C2.193 7.046.79 5.642.783 3.909c-.005-.83.322-1.626.908-2.213.586-.587 1.383-.915 2.212-.912 1.733.01 3.135 1.414 3.143 3.147.004.83-.323 1.626-.909 2.213-.586.587-1.382.915-2.211.912z"/>
            </svg>
</div>

[stuzer05]

What's the root problem of the breaking? eg: how the detection goes wrong?

The initial problem is php files containing svg are not displaying as gitea returns svg mime type for them. The svg regex cause this issue
https://try.gitea.io/stuzer05/test-preview/commit/f97b3784f8c8efc222128f6dffd4e5abb5fda462

Example of the current regex used https://regex101.com/r/m1bCCP/1

And also on latest firefox (110.0.1) this is what I see

[wxiaoguang]

The initial problem is php files containing svg are not displaying as gitea returns svg mime type for them. The svg regex cause this issue

Yup, so I guess the detection should be improved, instead of removed?

[stuzer05]

Yup, so I guess the detection should be improved, instead of removed?

There's so many cases when browser won't display an svg (e.g. https://try.gitea.io/stuzer05/test-preview/raw/commit/72f4584ea11cf8579f57d1ab909a6d7d349bc4e7/test%20%28copy%201%29.svg), I think it's better to remove this smart parsing. It's just unreliable

[wxiaoguang]

If remove the smart detection, will it make the SVG files won't be shown as image in the diff view?

[stuzer05]

If remove the smart detection, will it make the SVG files won't be shown as image in the diff view?

Yeah. I think http.DetectContentType(data) does not detect svgs for a reason

[wxiaoguang]

Have you tried that? According to Golang's issue tracker:

https://github.com/golang/go/issues/15888#issuecomment-237295881

http.DetectContentType is documented to be an implementation of https://mimesniff.spec.whatwg.org/ and that mimesniff spec doesn't define svg.
And as you found, mime.TypeByExtension has ".svg" in its built-in table:
https://github.com/golang/go/blob/release-branch.go1.6/src/mime/type.go#L35
So I don't think there's anything to do here.

---

I will take a look at this problem , and fix some more SVG related problems.

[stuzer05]

Have you tried that? According to Golang's issue tracker:

https://github.com/golang/go/issues/15888#issuecomment-237295881

http.DetectContentType is documented to be an implementation of https://mimesniff.spec.whatwg.org/ and that mimesniff spec doesn't define svg.
And as you found, mime.TypeByExtension has ".svg" in its built-in table:
https://github.com/golang/go/blob/release-branch.go1.6/src/mime/type.go#L35
So I don't think there's anything to do here.

I will take a look at this problem , and fix some more SVG related problems.

No, I didn't check that. Maybe we can detect svg by file extension alone. That should actually cover most cases. Embedded svgs shouldn't really be detected (e.g. in html) as we don't want to display html content in diff preview

[stuzer05]

Have you tried that? According to Golang's issue tracker:

https://github.com/golang/go/issues/15888#issuecomment-237295881

http.DetectContentType is documented to be an implementation of https://mimesniff.spec.whatwg.org/ and that mimesniff spec doesn't define svg.
And as you found, mime.TypeByExtension has ".svg" in its built-in table:
https://github.com/golang/go/blob/release-branch.go1.6/src/mime/type.go#L35
So I don't think there's anything to do here.

I will take a look at this problem , and fix some more SVG related problems.

Thank you! Maybe if you could make svg regex not match anything between html comments, except spaces and \n, that would resolve the initial bug. As of right now the bug is caused by the last html comment near <svg tag https://regex101.com/r/m1bCCP/1

[wxiaoguang]

The problem is that the detector fails on this test:

	assert.False(t, DetectContentType([]byte(`
<!-- comment1 -->
<div>
	<!-- comment2 -->
	<svg></svg>
</div>
`)).IsSvgImage())

the regexp was quite tricky before.

[wxiaoguang]

I proposed a new PR for SVG/ImageDiff fix: Fix various ImageDiff/SVG bugs #23312