diff --git a/.gitea/workflows/release.yml b/.gitea/workflows/release.yml
new file mode 100644
index 0000000..20912ac
--- /dev/null
+++ b/.gitea/workflows/release.yml
@@ -0,0 +1,51 @@
+name: release-tag
+on:
+ push:
+ branches:
+ - 'main'
+jobs:
+ release-image:
+ runs-on: ubuntu-fast
+ env:
+ DOCKER_ORG: ${{ vars.DOCKER_ORG }}
+ DOCKER_LATEST: latest
+ RUNNER_TOOL_CACHE: /toolcache
+ steps:
+ - name: Checkout
+ uses: actions/checkout@v3
+
+ - name: Set up QEMU
+ uses: docker/setup-qemu-action@v2
+
+ - name: Set up Docker BuildX
+ uses: docker/setup-buildx-action@v2
+ with: # replace it with your local IP
+ config-inline: |
+ [registry."${{ vars.DOCKER_REGISTRY }}"]
+ http = true
+ insecure = true
+
+ - name: Login to DockerHub
+ uses: docker/login-action@v2
+ with:
+ registry: ${{ vars.DOCKER_REGISTRY }} # replace it with your local IP
+ username: ${{ secrets.DOCKER_USERNAME }}
+ password: ${{ secrets.DOCKER_PASSWORD }}
+
+ - name: Get Meta
+ id: meta
+ run: |
+ echo REPO_NAME=$(echo ${GITHUB_REPOSITORY} | awk -F"/" '{print $2}') >> $GITHUB_OUTPUT
+ echo REPO_VERSION=$(git describe --tags --always | sed 's/^v//') >> $GITHUB_OUTPUT
+
+ - name: Build and push
+ uses: docker/build-push-action@v4
+ with:
+ context: .
+ file: ./Dockerfile
+ platforms: |
+ linux/amd64
+ push: true
+ tags: | # replace it with your local IP and tags
+ ${{ vars.DOCKER_REGISTRY }}/${{ env.DOCKER_ORG }}/${{ steps.meta.outputs.REPO_NAME }}:${{ steps.meta.outputs.REPO_VERSION }}
+ ${{ vars.DOCKER_REGISTRY }}/${{ env.DOCKER_ORG }}/${{ steps.meta.outputs.REPO_NAME }}:${{ env.DOCKER_LATEST }}
\ No newline at end of file
diff --git a/Dockerfile b/Dockerfile
new file mode 100644
index 0000000..e206835
--- /dev/null
+++ b/Dockerfile
@@ -0,0 +1,8 @@
+FROM golang:1.24.1
+WORKDIR /app
+COPY go.mod ./
+RUN go mod download
+COPY *.go ./
+RUN CGO_ENABLED=0 GOOS=linux go build -o /goprg
+EXPOSE 8080
+CMD ["/goprg"]
\ No newline at end of file
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..1f0c71e
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module git.send.nrw/StadtHilden/ipv6calculator
+
+go 1.23.1
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..935c74c
--- /dev/null
+++ 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(`
+
+
+
+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)
+ }
+}