package main
import (
"fmt"
"html/template"
"log"
"net"
"net/http"
"os"
"strings"
)
const (
listenAddr = ":8080" // TCP port for the web UI
defaultPrefix = "fdcb:7de3:a12a:0::" // fallback when ULA_PREFIX is unset
defaultIP = "172.16.0.0"
)
var (
ulaPrefix string // effective /96 prefix (always ending in "::")
pageTemplate *template.Template // populated in init()
pageIP string
)
// viewData feeds data into the HTML template.
type viewData struct {
IPv4 string
IPv6 string
Error string
}
func main() {
initPrefixAndTemplate()
http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
renderPage(w, viewData{}) // empty form
})
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 (Präfix: %s)", listenAddr, ulaPrefix)
log.Fatal(http.ListenAndServe(listenAddr, nil))
}
// initPrefixAndTemplate reads the environment variable and prepares the HTML template.
func initPrefixAndTemplate() {
ulaPrefix = os.Getenv("ULA_PREFIX")
if ulaPrefix == "" {
ulaPrefix = defaultPrefix
}
pageIP = os.Getenv("IPv4")
if pageIP == "" {
pageIP = defaultIP
}
// Ensure the prefix ends with exactly two colons (::) so that we can append hex words.
if !strings.HasSuffix(ulaPrefix, "::") {
if strings.HasSuffix(ulaPrefix, ":") {
ulaPrefix += ":"
} else {
ulaPrefix += "::"
}
}
html := fmt.Sprintf(`
IPv4 → IPv6‑Mapper
IPv4 → IPv6-Mapper
{{if .IPv6}}
IPv6-Adresse: {{.IPv6}}
{{end}}
{{if .Error}}
Fehler: {{.Error}}
{{end}}
Präfix: %s (/96‑Zuordnung)
`, pageIP, ulaPrefix)
pageTemplate = template.Must(template.New("page").Parse(html))
}
// embedIPv4 converts a dotted IPv4 string into the chosen ULA /96 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)
}
hi := uint16(ip[0])<<8 | uint16(ip[1]) // high 16 bits (octets 0–1)
lo := uint16(ip[2])<<8 | uint16(ip[3]) // low 16 bits (octets 2–3)
return fmt.Sprintf("%s%x:%x", ulaPrefix, hi, lo), 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)
}
}