Enable gocritic equalFold and autofix issues

[silverwind]

Enable https://go-critic.com/overview.html#equalfold, which is marked experimental, so was not enabled by default and ran make lint-go-fix. Reasons why strings.EqualFold is preferred here.

[wxiaoguang]

I won't block it but IMO EqualFold is not a right approach if we only want to handle ASCII chars. Sometimes it is just abused.

func TestString(t *testing.T) {
	s1 := "K"
	s2 := "\u212A"
	assert.True(t, strings.EqualFold(s1, s2))
}

[silverwind]

I see it as a benefit that it handles unicode as well. More often than not you want unicode comparison, especially when dealing with user-submitted data.

[wxiaoguang]

Why it makes sense to use Unicode for HTTP headers or something else? Doesn't it break the standard if the headers are "folded" by unicode chars?

[wxiaoguang]

In short:

• If we'd like to check "if the string can pass", EqualFold relaxes the charsets, it might be abused or introduce security problems.
• If we'd like to check "if the string should not pass", EqualFold make the result more strict, in most cases it should be fine.

[silverwind]

Looks like there is a ASCII-only variant ascii.EqualFold:

https://pkg.go.dev/net/http/internal/ascii#EqualFold

Not sure if usable because its in internal namespace.

[wxiaoguang]

Looks like there is a ASCII-only variant ascii.EqualFold:

https://pkg.go.dev/net/http/internal/ascii#EqualFold

Yup, we need to implement one by ourself, something like "strcasecmp/stricmp" in C, or we can just call it util.AsciiEqualFold or util.StrEqualNoCase

[silverwind]

util.AsciiEqualFold sounds good, we can use it for all the header comparisons. Maybe even open a golang issue so that they make that function part of the public API.

[silverwind]

Related golang issue: golang/go#68736