dozr13344 2014-01-29 06:25
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将模板直接渲染成HTML

I've recently swapped out datastores and as a side-effect have had to change a struct field from template.HTML to string to be compatible with the marshaller/DB driver. This field, RenderedDesc, contains rendered HTML as passed through russross/blackfriday.

Previously I could just pass the whole struct into the template "as is" and call {{ .RenderedDesc }} in the template.

Because it's now a string, I've added a filter to convert it back on template render:

templates.go

func RenderUnsafe(s string) template.HTML {
    return template.HTML(s)
}

template.FuncMap{
        ...
        "unsafe": RenderUnsafe,
    }

_content.tmpl

...
<div class="detail">

    {{ .RenderedDesc | unsafe }}

</div>
...

Is there a better way to achieve this without having to use a filter at the template level? Short of re-writing marshalling logic from my DB driver (not on the cards) it looks like this is the simplest way to "store" strings but render raw HTML.

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  • duankousong9637 2014-01-29 07:44
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    IMHO, the right way to do this is using a filter, like you are already doing. There are more ways to achieve the same, one of them is using tags and converting the struct in to a map[string]Interface{}. Because map fields can be reached in the same way that structs, your templates will remain unmodified.

    Show me the code (playground):

    package main

import (
    "html/template"
    "os"
    "reflect"
)

var templates = template.Must(template.New("tmp").Parse(`
    <html>
        <head>
        </head>
        <body>
            <h1>Hello</h1>
            <div class="content">
                Usafe Content = {{.Content}}
                Safe Content  = {{.Safe}}
                Bool          = {{.Bool}}
                Num           = {{.Num}}
                Nested.Num    = {{.Nested.Num}}
                Nested.Bool   = {{.Nested.Bool}}
            </div>
        </body>
    </html>
`))

func asUnsafeMap(any interface{}) map[string]interface{} {
    v := reflect.ValueOf(any)
    if v.Kind() != reflect.Struct {
        panic("asUnsafeMap invoked with a non struct parameter")
    }
    m := map[string]interface{}{}
    for i := 0; i < v.NumField(); i++ {
        value := v.Field(i)
        if !value.CanInterface() {
            continue
        }
        ftype := v.Type().Field(i)
        if ftype.Tag.Get("unsafe") == "html" {
            m[ftype.Name] = template.HTML(value.String())
        } else {
            m[ftype.Name] = value.Interface()
        }
    }
    return m
}

func main() {
    templates.ExecuteTemplate(os.Stdout, "tmp", asUnsafeMap(struct {
        Content string `unsafe:"html"`
        Safe    string
        Bool    bool
        Num     int
        Nested  struct {
            Num  int
            Bool bool
        }
    }{
        Content: "<h2>Lol</h2>",
        Safe:    "<h2>Lol</h2>",
        Bool:    true,
        Num:     10,
        Nested: struct {
            Num  int
            Bool bool
        }{
            Num:  9,
            Bool: true,
        },
    }))
}

    Output:

    <html>
    <head>
    </head>
    <body>
        <h1>Hello</h1>
        <div class="content">
            Usafe Content = <h2>Lol</h2>
            Safe Content  = &lt;h2&gt;Lol&lt;/h2&gt;
            Bool          = true
            Num           = 10
            Nested.Num    = 9
            Nested.Bool   = true
        </div>
    </body>
</html>

    Note: the previous code doesn't work with nested structures, but it will be easy to add support for them. Also, every field tagged as unsafe will be treated as string.

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