all: implement router setup for openwrt

internal/router/openwrt.go

@@ -0,0 +1,74 @@
+package router
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+)
+
+var errUCIEntryNotFound = errors.New("uci: Entry not found")
+
+const openwrtDNSMasqConfigPath = "/tmp/dnsmasq.d/ctrld.conf"
+const openwrtDNSMasqConfigContent = `# GENERATED BY ctrld - DO NOT MODIFY
+port=0
+`
+
+func setupOpenWrt() error {
+	// Delete dnsmasq port if set.
+	if _, err := uci("delete", "dhcp.@dnsmasq[0].port"); err != nil && !errors.Is(err, errUCIEntryNotFound) {
+		return err
+	}
+	// Disable dnsmasq as DNS server.
+	if err := os.WriteFile(openwrtDNSMasqConfigPath, []byte(openwrtDNSMasqConfigContent), 0600); err != nil {
+		return err
+	}
+	// Commit.
+	if _, err := uci("commit"); err != nil {
+		return err
+	}
+	// Restart dnsmasq service.
+	if err := restartDNSMasq(); err != nil {
+		return err
+	}
+	return nil
+}
+
+func cleanupOpenWrt() error {
+	// Remove the custom dnsmasq config
+	if err := os.Remove(openwrtDNSMasqConfigPath); err != nil {
+		return err
+	}
+	// Restart dnsmasq service.
+	if err := restartDNSMasq(); err != nil {
+		return err
+	}
+	return nil
+}
+
+func postInstallOpenWrt() error {
+	return exec.Command("/etc/init.d/ctrld", "enable").Run()
+}
+
+func uci(args ...string) (string, error) {
+	cmd := exec.Command("uci", args...)
+	var stdout, stderr bytes.Buffer
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+	if err := cmd.Run(); err != nil {
+		if strings.HasPrefix(stderr.String(), errUCIEntryNotFound.Error()) {
+			return "", errUCIEntryNotFound
+		}
+		return "", fmt.Errorf("%s:%w", stderr.String(), err)
+	}
+	return strings.TrimSpace(stdout.String()), nil
+}
+
+func restartDNSMasq() error {
+	if out, err := exec.Command("/etc/init.d/dnsmasq", "restart").CombinedOutput(); err != nil {
+		return fmt.Errorf("%s: %w", string(out), err)
+	}
+	return nil
+}