package main
 
import (
	"encoding/xml"
	"fmt"
	"net/http"
	"strconv"
)
 
type Tag struct {
	Key   string `xml:"name,attr,omitempty"`
	Value string `xml:",chardata"`
	L     string `xml:"l,attr,omitempty"`
}
 
type wrt100Result struct {
	XMLName struct{}    `xml:"root"`
	Id		int			`xml:"id"`
	Unit	string		`xml:"unit"`
	Access	[]string	`xml:"access>item"`
	Tags    []Tag		`xml:"tags>tag"`
}
 
func main() {
	http.HandleFunc("/wrt100", func(wr http.ResponseWriter, req *http.Request) {
		res := &wrt100Result{
			Id:123,
			Unit: "EugeneX",
			Access: []string{"member", "admin"},
			Tags: []Tag{
				{Key: "most", Value: "wanted", L: "13"},
				{Key: "lost", Value: "everything", L: "25"},
			},
		}
 
		for i, s := range []string{"Hw", "Rules", "Warp"} {
			res.Tags = append(res.Tags, Tag{
				L: strconv.Itoa(i + 1),
				Value: s,
			})
		}
 
 
		b, _ := xml.Marshal(res)
		wr.WriteHeader(200)
		fmt.Fprintln(wr, `<?xml version="1.0" encoding="UTF-8" ?>`)
		wr.Write(b)
	})
	http.ListenAndServe(":7000", nil)
}

Выводит вот такой вот XML

<?xml version="1.0" encoding="UTF-8" ?>
<root>
  <id>123</id>
  <unit>EugeneX</unit>
  <access>
    <item>member</item>
    <item>admin</item>
  </access>
  <tags>
    <tag name="most" l="13">wanted</tag>
    <tag name="lost" l="25">everything</tag>
    <tag l="1">Hw</tag>
    <tag l="2">Rules</tag>
    <tag l="3">Warp</tag>
  </tags>
</root>