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Editorial Team
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Asked: 2026-05-14T00:44:38+00:00

In one of the example servers given at golang.org: package main import ( flag

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In one of the example servers given at golang.org: 

package main

import (
    "flag"
    "http"
    "io"
    "log"
    "template"
)

var addr = flag.String("addr", ":1718", "http service address") // Q=17, R=18
var fmap = template.FormatterMap{
    "html": template.HTMLFormatter,
    "url+html": UrlHtmlFormatter,
}
var templ = template.MustParse(templateStr, fmap)

func main() {
    flag.Parse()
    http.Handle("/", http.HandlerFunc(QR))
    err := http.ListenAndServe(*addr, nil)
    if err != nil {
        log.Exit("ListenAndServe:", err)
    }
}

func QR(c *http.Conn, req *http.Request) {
    templ.Execute(req.FormValue("s"), c)
}

func UrlHtmlFormatter(w io.Writer, v interface{}, fmt string) {
    template.HTMLEscape(w, []byte(http.URLEscape(v.(string))))
}


const templateStr = `
<html>
<head>
<title>QR Link Generator</title>
</head>
<body>
{.section @}
<img src="http://chart.apis.google.com/chart?chs=300x300&cht=qr&choe=UTF- 8&chl={@|url+html}"
/>
<br>
{@|html}
<br>
<br>
{.end}
<form action="/" name=f method="GET"><input maxLength=1024 size=70
name=s value="" title="Text to QR Encode"><input type=submit
value="Show QR" name=qr>
</form>
</body>
</html>
`

Why is template.HTMLEscape(w, []byte(http.URLEscape(v.(string)))) contained within UrlHtmlFormatter? Why can’t it be directly linked to "url+html"?

Also, how could I change func QR to accept parameter values? What I’d like for it to do is accept a command-line flag in place of req *http.Request … Thanks in advance…

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1 Answer

  1. Editorial Team

    The signature for function template.HTMLEscape is:

    func(w io.Writer, s []byte)

    The type declaration for template.FormatterMap is:

    type FormatterMap map[string]func(io.Writer, interface{}, string)

    Therefore, the signature for a FormatterMap map element value function is:

    func(io.Writer, interface{}, string)

    The UrlHtmlFormatter function is a wrapper to give the HTMLEscape function the FormatterMap map element value function signature.

    func UrlHtmlFormatter(w io.Writer, v interface{}, fmt string) {
    template.HTMLEscape(w, []byte(http.URLEscape(v.(string))))
}
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