Whitelist tags exempt from escaping using Go's html/template

Pass a []byte into a template as the body of a message post on a forum-style web app. In the template, call a method to convert to string and along the way, switch out all newlines for line breaks:

<p>{{.BodyString}}</p>

...

func (p *Post) BodyString() string {
    nl := regexp.MustCompile(`\n`)
    return nl.ReplaceAllString(string(p.Body), `<br>`)
}

What you'll end up with:

paragraphs <br> <br>in <br> <br>this <br> <br>post

I don't want to pass the entire post in with HTML(p.Body), as it represents third party data from potentially untrustworthy sources. Is there a way to whitelist only some tags for formatting purposes using the vanilla Go1 template package?

I do think you want to parse the HTML. The HTML parser in exp/html was deemed incomplete and so removed from Go 1, although the exp tree is still in the Go source tree and can be accessed by weekly tag, for example. I don't know exactly what is incomplete. I used it for a simple task once and it met my needs.

Also of course, check the dashboard and see related SO post, https://stackoverflow.com/questions/9986329/any-smart-method-to-get-exp-html-back-after-go1/, mostly for the recomendation of http://code.google.com/p/go-html-transform/

I'm affraid the template package cannot help with this too much. If you want to remove specific (black-listed) tags (resp. the sub-tree enclosed by such tags) or allow to pass only specific tags (white-listed) then I think probably nothing less than parsing and rewriting the html AST can be a good solution. That said, one can see here and there some crazy REs trying to do the same, but I don't consider that a "good solution" and I doubt they can be a "correct" solution in the general case of a specs conforming HTML, including several legal irregularities, as it is probably ruled out of a regular grammar category problem.