Why am I seeing ZgotmplZ in my Go HTML template output? - go

Question

When I'm calling a Go template function to output HTML, it displays ZgotmplZ.
Sample code:
http://play.golang.org/p/tfuJa_pFkm
package main
import (
"html/template"
"os"
)
func main() {
funcMap := template.FuncMap{
"printSelected": func(s string) string {
if s == "test" {
return `selected="selected"`
}
return ""
},
"safe": func(s string) template.HTML {
return template.HTML(s)
},
}
template.Must(template.New("Template").Funcs(funcMap).Parse(`
<option {{ printSelected "test" }} {{ printSelected "test" | safe }} >test</option>
`)).Execute(os.Stdout, nil)
}
Output:
<option ZgotmplZ ZgotmplZ >test</option>

Answer 1

"ZgotmplZ" is a special value that indicates that unsafe content reached a
CSS or URL context at runtime. The output of the example will be:
<img src="#ZgotmplZ">
You can add a safe and attr function to the template funcMap:
package main
import (
"html/template"
"os"
)
func main() {
funcMap := template.FuncMap{
"attr":func(s string) template.HTMLAttr{
return template.HTMLAttr(s)
},
"safe": func(s string) template.HTML {
return template.HTML(s)
},
}
template.Must(template.New("Template").Funcs(funcMap).Parse(`
<option {{ .attr |attr }} >test</option>
{{.html|safe}}
`)).Execute(os.Stdout, map[string]string{"attr":`selected="selected"`,"html":`<option selected="selected">option</option>`})
}
The output will look like:
<option selected="selected" >test</option>
<option selected="selected">option</option>
You may want to define some other functions which can convert string to template.CSS, template.JS, template.JSStr, template.URL etc.

Answer 2

I had similar problem with <img src="{{myfunction}}"> where myfunction return encoded image.
Finally I solved it when instead of string function return template.URL(mystring).

Answer 3

You are trying to output HTML in a place where template/html thinks is unsafe (for example, inside an HTML element, like this:
<option {{ printSelected }}>
I cannot find any way to convince it it is safe (including returning template.HTML instead of string); the only alternative I have found is to rewrite the template, in this example use a bool output instead:
<option {{ if printSelected }}selected{{ end }}>

Answer 4

package main
import (
"html/template"
"os"
)
type T struct {
HTML template.HTML
ATTR template.HTMLAttr
URL template.URL
JS template.JS
CSS template.CSS
}
func main() {
data := T{
HTML: `<div>test div</div>`,
ATTR: `selected="selected"`,
URL: `https://upload.wikimedia.org/wikipedia/commons/5/53/Google_%22G%22_Logo.svg`,
CSS: `font-size: 15px`,
JS: `console.log("hello world")`,
}
template.Must(template.New("Template").Parse(`
{{.HTML}}
<option {{.ATTR}} style="{{.CSS}}">test</option>
<script>{{.JS}}</script>
<img src="{{.URL}}">
`)).Execute(os.Stdout, data)
}
output
<div>test div</div>
<option selected="selected" style="font-size: 15px">test</option>
<script>console.log("hello world")</script>
<img src="https://upload.wikimedia.org/wikipedia/commons/5/53/Google_%22G%22_Logo.svg">
playground Example

Answer 5

easiest way:
import "html/template"
yourhref = template.URL(yourhref)

Answer 6

You should wrap the string in an HTMLAttr, which was designed for text that gets injected in between angle brackets. Per the documentation:
https://golang.org/pkg/html/template/#HTMLAttr
HTMLAttr encapsulates an HTML attribute from a trusted source, for example,  dir="ltr".
Use of this type presents a security risk: the encapsulated content should come from a trusted source, as it will be included verbatim in the template output.
type HTMLAttr string

Answer 7

I was trying to insert an image from frontmatter into my template but kept getting the same error. I solved it thus:
{{ if isset .Params "image" }}
{{ $myVar := print .Params.image }}
<img src="{{ $myVar }}">
{{ end }}
Notice that I first save the .Params.image as a variable, and then insert it as my src.