init

2025-05-09 07:28:10 +02:00
parent 5adf974949
commit 125135b755
4 changed files with 158 additions and 0 deletions
--- a/main.go
+++ b/main.go
@@ -0,0 +1,96 @@
+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(`<!DOCTYPE html>
+<html lang="de">
+<head>
+<meta charset="utf-8"/>
+<title>IPv4 → IPv6‑Mapper</title>
+<style>
+ body { font-family: system-ui, sans-serif; margin: 2rem; }
+ form { display:flex; gap:.5rem; }
+ input[type=text] { flex:1; padding:.4rem; font-size:1rem; }
+ button { padding:.5rem 1rem; font-size:1rem; cursor:pointer; }
+ #result { margin-top:1.5rem; font-weight:bold; }
+ .error { color:#b00; }
+</style>
+</head>
+<body>
+ <h1>IPv4 → IPv6‑Mapper</h1>
+ <form action="/convert" method="post">
+  <input type="text" name="ipv4" placeholder="172.29.0.0" value="{{.IPv4}}" required />
+  <button type="submit">Umrechnen</button>
+ </form>
+ {{if .IPv6}}
+   <div id="result">IPv6‑Adresse: <code>{{.IPv6}}</code></div>
+ {{end}}
+ {{if .Error}}
+   <div class="error">Fehler: {{.Error}}</div>
+ {{end}}
+ <p>Präfix: <code>` + ulaPrefix + `</code> &nbsp; (feste /96‑Zuordnung)</p>
+</body>
+</html>`))
+
+// 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)
+	}
+}