Add ipadm: Go-Tool zur Verwaltung statischer DHCP/DNS-Hosts

tools/ipadm/dnsmasq.go

@@ -0,0 +1,85 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"sort"
+	"strings"
+)
+
+// renderDnsmasqConfig builds the content of the generated dnsmasq include
+// file from the current host list. Every host gets a host-record (forward +
+// reverse DNS). Hosts with a MAC additionally get a dhcp-host static lease.
+func renderDnsmasqConfig(hosts []Host) string {
+	sorted := make([]Host, len(hosts))
+	copy(sorted, hosts)
+	sort.Slice(sorted, func(i, j int) bool {
+		return strings.ToLower(sorted[i].Name) < strings.ToLower(sorted[j].Name)
+	})
+
+	var b strings.Builder
+	b.WriteString("# Generated by ipadm -u — DO NOT EDIT MANUALLY.\n")
+	b.WriteString("# Edit hosts with `ipadm` and re-run `ipadm -u` to regenerate this file.\n\n")
+	for _, h := range sorted {
+		if h.Comment != "" {
+			fmt.Fprintf(&b, "# %s: %s\n", h.Name, h.Comment)
+		}
+		fmt.Fprintf(&b, "host-record=%s,%s\n", h.Name, h.IP)
+		if h.MAC != "" {
+			fmt.Fprintf(&b, "dhcp-host=%s,%s,%s,infinite\n", h.MAC, h.IP, h.Name)
+		}
+		b.WriteString("\n")
+	}
+	return b.String()
+}
+
+// applyDnsmasqConfig writes the generated config to path, validates the full
+// dnsmasq configuration, and on success reloads the dnsmasq service. On
+// validation failure the previous file content is restored and the service
+// is left untouched.
+func applyDnsmasqConfig(path string, content string) error {
+	var backup []byte
+	hadFile := false
+	if b, err := os.ReadFile(path); err == nil {
+		backup = b
+		hadFile = true
+	} else if !os.IsNotExist(err) {
+		return fmt.Errorf("kann bestehende %s nicht lesen: %w", path, err)
+	}
+
+	if err := os.WriteFile(path, []byte(content), 0644); err != nil {
+		return fmt.Errorf("kann %s nicht schreiben: %w", path, err)
+	}
+
+	if err := runDnsmasqTest(); err != nil {
+		// roll back so a bad generated file never lingers
+		if hadFile {
+			os.WriteFile(path, backup, 0644)
+		} else {
+			os.Remove(path)
+		}
+		return fmt.Errorf("dnsmasq-Konfiguration ungültig, Änderung zurückgerollt: %w", err)
+	}
+
+	if err := reloadDnsmasq(); err != nil {
+		return fmt.Errorf("%s geschrieben, aber Reload fehlgeschlagen: %w", path, err)
+	}
+	return nil
+}
+
+func runDnsmasqTest() error {
+	out, err := exec.Command("dnsmasq", "--test").CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("%s", strings.TrimSpace(string(out)))
+	}
+	return nil
+}
+
+func reloadDnsmasq() error {
+	out, err := exec.Command("systemctl", "reload", "dnsmasq").CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("%s", strings.TrimSpace(string(out)))
+	}
+	return nil
+}