Refactor table management to use a dedicated API and improve command handling.

internal/command/utils.go

@@ -0,0 +1,51 @@
+package command
+
+import (
+	"errors"
+	"fmt"
+	"os/exec"
+	"regexp"
+	"strings"
+)
+
+func checkingNFT(path string) error {
+	if path == "" {
+		return errors.New("path is empty")
+	}
+
+	cmd := exec.Command(path, "-V")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		return errors.New("nftables not found")
+	}
+
+	lines := regexp.MustCompile("\r?\n").Split(strings.TrimSpace(string(out)), -1)
+	json := false
+	for index, line := range lines {
+		line = strings.TrimSpace(line)
+
+		if index == 0 {
+			if !strings.HasPrefix(line, "nftables") {
+				return errors.New("nftables not found")
+			}
+			continue
+		}
+
+		if strings.HasPrefix(line, "json:") && strings.HasSuffix(line, "yes") {
+			json = true
+		}
+	}
+
+	if !json {
+		return errors.New("nftables disabled json")
+	}
+
+	cmd = exec.Command(path, "list", "ruleset")
+	out, err = cmd.CombinedOutput()
+
+	if err != nil {
+		return fmt.Errorf("nftables is not available or not supported by the kernel: %s", string(out))
+	}
+
+	return nil
+}