package main
import (
"fmt"
"html/template"
"log"
"net"
"net/http"
)
const (
listenAddr = ":8080" // server port
ulaPrefix = "fdcb:7de3:a12a:0::" // fixed ULA /96 prefix
)
// pageTemplate is served for both GET (empty result) and POST (with result).
var pageTemplate = template.Must(template.New("page").Parse(`
IPv4 → IPv6‑Mapper
IPv4 → IPv6‑Mapper
{{if .IPv6}}
IPv6‑Adresse: {{.IPv6}}
{{end}}
{{if .Error}}
Fehler: {{.Error}}
{{end}}
Präfix: ` + ulaPrefix + ` (feste /96‑Zuordnung)
`))
// viewData transports data into the page template.
type viewData struct {
IPv4 string
IPv6 string
Error string
}
func main() {
http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
// Empty page on root
renderPage(w, viewData{})
})
http.HandleFunc("/convert", func(w http.ResponseWriter, r *http.Request) {
if err := r.ParseForm(); err != nil {
renderPage(w, viewData{Error: "Ungültiges Formular"})
return
}
ipv4Str := r.FormValue("ipv4")
ipv6, err := embedIPv4(ipv4Str)
data := viewData{IPv4: ipv4Str}
if err != nil {
data.Error = err.Error()
} else {
data.IPv6 = ipv6
}
renderPage(w, data)
})
log.Printf("Server läuft auf http://localhost%s …", listenAddr)
log.Fatal(http.ListenAndServe(listenAddr, nil))
}
// embedIPv4 converts an IPv4 dotted string into the ulaPrefix‑based IPv6 address.
func embedIPv4(ipv4 string) (string, error) {
ip := net.ParseIP(ipv4).To4()
if ip == nil {
return "", fmt.Errorf("'%s' ist keine gültige IPv4‑Adresse", ipv4)
}
first := uint16(ip[0])<<8 | uint16(ip[1]) // High 16 bits
second := uint16(ip[2])<<8 | uint16(ip[3]) // Low 16 bits
return fmt.Sprintf("%s%x:%x", ulaPrefix, first, second), nil
}
func renderPage(w http.ResponseWriter, d viewData) {
w.Header().Set("Content-Type", "text/html; charset=utf-8")
if err := pageTemplate.Execute(w, d); err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
}
}