Go text/template Form handling, with custom FuncMap - function returning blank string outputs garbag-CodePudding

Using Go html/template functionality, with custom FuncMap. The custom function I've defined "isChecked(checkName string, form url.Values)" returns the string "checked" if the checkbox with checkName exists in the form, and a blank string if it does not. It works fine, but the curious thing is on the completed HTML for an un-checked checkbox, I am seeing the string "ZgotmplZ" where there should be no string at all. Here is the main.go program that sets up the FuncMap:

package main

import (
    "fmt"
    "html/template"
    "log"
    "net/http"
    "net/url"
)

var tpl *template.Template

func init() {
    tpl = template.Must(template.New("").Funcs(fm).ParseFiles("templates/check-box.html"))
}

var fm = template.FuncMap{
    "isChecked": isChecked,
}

func isChecked(checkName string, form url.Values) string {
    if form.Has(checkName) {
        return "checked"
    }
    return ""
}

func checkboxHandler(w http.ResponseWriter, r *http.Request) {
    err := r.ParseForm()
    if err != nil {
        log.Fatalln(err)
    }

    err = tpl.ExecuteTemplate(w, "check-box.html", r.Form)
    if err != nil {
        log.Fatalln(err)
    }
}

func main() {
    http.HandleFunc("/checkbox/", checkboxHandler)

    err := http.ListenAndServe(":8080", nil)
}

Here is the template:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Checkbox Control</title>
</head>
<body>

    <h1>Go html/template Form Handling - Checkbox</h1>

    <div>
    Form Data: {{.}}
    </div>

    <form action="/checkbox/" method="POST">

        <div>
            <label for="checkbox">Check Box</label>
            <input type="checkbox" name="check1" id="checkbox" value="check1" {{isChecked "check1" .}}>Check 1
            <input type="checkbox" name="check2" id="checkbox" value="check2" {{isChecked "check2" .}}>Check 2
            <input type="checkbox" name="check3" id="checkbox" value="check3" {{isChecked "check3" .}}>Check 3
        </div>

        <div>
            <button type="submit">Submit</button>
        </div>

    </form>

</body>
</html>

The result of submitting the form and checking the checkboxes is good. But when I examine source, I get this funny string "ZgotmplZ" for checkboxes that are not checked (in other words, it seems the custom function in the FuncMap is not returning a blank string for un-checked checkboxes):

        <div>
            <label for="checkbox">Check Box</label>
            <input type="checkbox" name="check1" id="checkbox" value="check1" checked>Check 1
            <input type="checkbox" name="check2" id="checkbox" value="check2" ZgotmplZ>Check 2
            <input type="checkbox" name="check3" id="checkbox" value="check3" ZgotmplZ>Check 3
        </div>

Also wondering if anyone has other suggestions on how to propate checkbox "checked" states to an html template.

Thanks!

CodePudding user response：

The template emits ZgotmplZ because it does not like an empty string in an attribute context. Fix by doing the following.

Return bool from isChecked:

func isChecked(checkName string, form url.Values) bool {
     return form.Has(checkName) 
}

Use an if action in the template:

{{if isChecked "check1" .}}checked{{end}}