edgeguard-native/internal/handlers/firewall.go

package handlers

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"net"
	"strconv"
	"strings"

	"github.com/gin-gonic/gin"

	"git.netcell-it.de/projekte/edgeguard-native/internal/handlers/response"
	"git.netcell-it.de/projekte/edgeguard-native/internal/models"
	"git.netcell-it.de/projekte/edgeguard-native/internal/services/audit"
	"git.netcell-it.de/projekte/edgeguard-native/internal/services/firewall"
)

// FirewallHandler exposes everything under /api/v1/firewall/*:
//
//	address-objects   — primitive Adress-Definitionen (host/network/range/fqdn)
//	address-groups    — Gruppen von address-objects (mit /members ops)
//	services          — proto+port (Builtins lassen sich nicht editieren)
//	service-groups    — Gruppen von services
//	rules             — v2-Policy: zone × addr × service × action
//	nat-rules         — separate Tabelle: dnat / snat / masquerade
//
// Validation lebt im Handler (DB lässt mehr zu als die Anwendung erlauben
// will — exactly-one-of-Constraints sind in Postgres mühsam).
type FirewallHandler struct {
	AddrObjects   *firewall.AddressObjectsRepo
	AddrGroups    *firewall.AddressGroupsRepo
	Services      *firewall.ServicesRepo
	ServiceGroups *firewall.ServiceGroupsRepo
	Rules         *firewall.RulesRepo
	NATRules      *firewall.NATRulesRepo
	Audit         *audit.Repo
	NodeID        string

	// Reloader regenerates and applies the nft ruleset. Called after
	// each mutation so the kernel ruleset is always in sync with the
	// DB. Errors are logged but don't fail the API call (the row is
	// already committed). Wire to internal/firewall.Generator.Render
	// in main.go; pass nil during tests.
	Reloader func(ctx context.Context) error
}

func NewFirewallHandler(
	ao *firewall.AddressObjectsRepo,
	ag *firewall.AddressGroupsRepo,
	sv *firewall.ServicesRepo,
	sg *firewall.ServiceGroupsRepo,
	rl *firewall.RulesRepo,
	nat *firewall.NATRulesRepo,
	a *audit.Repo,
	nodeID string,
	reloader func(ctx context.Context) error,
) *FirewallHandler {
	return &FirewallHandler{
		AddrObjects: ao, AddrGroups: ag,
		Services: sv, ServiceGroups: sg,
		Rules: rl, NATRules: nat,
		Audit: a, NodeID: nodeID,
		Reloader: reloader,
	}
}

// reload runs the configured Reloader (if any). Errors don't fail
// the surrounding API call — the DB row is already committed and
// the operator can re-trigger via `edgeguard-ctl render-config`.
func (h *FirewallHandler) reload(ctx context.Context, op string) {
	if h.Reloader == nil {
		return
	}
	if err := h.Reloader(ctx); err != nil {
		slog.Warn("firewall: nft reload failed",
			"op", op, "error", err)
	}
}

func (h *FirewallHandler) Register(rg *gin.RouterGroup) {
	g := rg.Group("/firewall")

	ao := g.Group("/address-objects")
	ao.GET("", h.ListAddrObj)
	ao.POST("", h.CreateAddrObj)
	ao.GET("/:id", h.GetAddrObj)
	ao.PUT("/:id", h.UpdateAddrObj)
	ao.DELETE("/:id", h.DeleteAddrObj)

	ag := g.Group("/address-groups")
	ag.GET("", h.ListAddrGrp)
	ag.POST("", h.CreateAddrGrp)
	ag.GET("/:id", h.GetAddrGrp)
	ag.PUT("/:id", h.UpdateAddrGrp)
	ag.DELETE("/:id", h.DeleteAddrGrp)

	sv := g.Group("/services")
	sv.GET("", h.ListService)
	sv.POST("", h.CreateService)
	sv.GET("/:id", h.GetService)
	sv.PUT("/:id", h.UpdateService)
	sv.DELETE("/:id", h.DeleteService)

	sg := g.Group("/service-groups")
	sg.GET("", h.ListSvcGrp)
	sg.POST("", h.CreateSvcGrp)
	sg.GET("/:id", h.GetSvcGrp)
	sg.PUT("/:id", h.UpdateSvcGrp)
	sg.DELETE("/:id", h.DeleteSvcGrp)

	rl := g.Group("/rules")
	rl.GET("", h.ListRule)
	rl.POST("", h.CreateRule)
	rl.GET("/:id", h.GetRule)
	rl.PUT("/:id", h.UpdateRule)
	rl.DELETE("/:id", h.DeleteRule)

	nat := g.Group("/nat-rules")
	nat.GET("", h.ListNAT)
	nat.POST("", h.CreateNAT)
	nat.GET("/:id", h.GetNAT)
	nat.PUT("/:id", h.UpdateNAT)
	nat.DELETE("/:id", h.DeleteNAT)
}

// ── Address Objects ────────────────────────────────────────────────────

func (h *FirewallHandler) ListAddrObj(c *gin.Context) {
	out, err := h.AddrObjects.List(c.Request.Context())
	if err != nil {
		response.Internal(c, err)
		return
	}
	response.OK(c, gin.H{"address_objects": out})
}

func (h *FirewallHandler) GetAddrObj(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	x, err := h.AddrObjects.Get(c.Request.Context(), id)
	if err != nil {
		if errors.Is(err, firewall.ErrAddressObjectNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	response.OK(c, x)
}

func (h *FirewallHandler) CreateAddrObj(c *gin.Context) {
	var req models.FirewallAddressObject
	if err := c.ShouldBindJSON(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	if err := validateAddrObjValue(req.Kind, req.Value); err != nil {
		response.BadRequest(c, err)
		return
	}
	out, err := h.AddrObjects.Create(c.Request.Context(), req)
	if err != nil {
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "fw.addr_obj.create", req.Name, out, h.NodeID)
	response.Created(c, out); h.reload(c.Request.Context(), "create")
}

func (h *FirewallHandler) UpdateAddrObj(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	var req models.FirewallAddressObject
	if err := c.ShouldBindJSON(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	if err := validateAddrObjValue(req.Kind, req.Value); err != nil {
		response.BadRequest(c, err)
		return
	}
	out, err := h.AddrObjects.Update(c.Request.Context(), id, req)
	if err != nil {
		if errors.Is(err, firewall.ErrAddressObjectNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "fw.addr_obj.update", req.Name, out, h.NodeID)
	response.OK(c, out); h.reload(c.Request.Context(), "update")
}

func (h *FirewallHandler) DeleteAddrObj(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	if err := h.AddrObjects.Delete(c.Request.Context(), id); err != nil {
		if errors.Is(err, firewall.ErrAddressObjectNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "fw.addr_obj.delete",
		strconv.FormatInt(id, 10), gin.H{"id": id}, h.NodeID)
	response.NoContent(c); h.reload(c.Request.Context(), "delete")
}

// ── Address Groups ─────────────────────────────────────────────────────

func (h *FirewallHandler) ListAddrGrp(c *gin.Context) {
	out, err := h.AddrGroups.List(c.Request.Context())
	if err != nil {
		response.Internal(c, err)
		return
	}
	response.OK(c, gin.H{"address_groups": out})
}

func (h *FirewallHandler) GetAddrGrp(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	x, err := h.AddrGroups.Get(c.Request.Context(), id)
	if err != nil {
		if errors.Is(err, firewall.ErrAddressGroupNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	response.OK(c, x)
}

func (h *FirewallHandler) CreateAddrGrp(c *gin.Context) {
	var req models.FirewallAddressGroup
	if err := c.ShouldBindJSON(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	out, err := h.AddrGroups.Create(c.Request.Context(), req)
	if err != nil {
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "fw.addr_grp.create", req.Name, out, h.NodeID)
	response.Created(c, out); h.reload(c.Request.Context(), "create")
}

func (h *FirewallHandler) UpdateAddrGrp(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	var req models.FirewallAddressGroup
	if err := c.ShouldBindJSON(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	out, err := h.AddrGroups.Update(c.Request.Context(), id, req)
	if err != nil {
		if errors.Is(err, firewall.ErrAddressGroupNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "fw.addr_grp.update", req.Name, out, h.NodeID)
	response.OK(c, out); h.reload(c.Request.Context(), "update")
}

func (h *FirewallHandler) DeleteAddrGrp(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	if err := h.AddrGroups.Delete(c.Request.Context(), id); err != nil {
		if errors.Is(err, firewall.ErrAddressGroupNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "fw.addr_grp.delete",
		strconv.FormatInt(id, 10), gin.H{"id": id}, h.NodeID)
	response.NoContent(c); h.reload(c.Request.Context(), "delete")
}

// ── Services ───────────────────────────────────────────────────────────

func (h *FirewallHandler) ListService(c *gin.Context) {
	out, err := h.Services.List(c.Request.Context())
	if err != nil {
		response.Internal(c, err)
		return
	}
	response.OK(c, gin.H{"services": out})
}

func (h *FirewallHandler) GetService(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	x, err := h.Services.Get(c.Request.Context(), id)
	if err != nil {
		if errors.Is(err, firewall.ErrServiceNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	response.OK(c, x)
}

func (h *FirewallHandler) CreateService(c *gin.Context) {
	var req models.FirewallService
	if err := c.ShouldBindJSON(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	out, err := h.Services.Create(c.Request.Context(), req)
	if err != nil {
		response.BadRequest(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "fw.service.create", req.Name, out, h.NodeID)
	response.Created(c, out); h.reload(c.Request.Context(), "create")
}

func (h *FirewallHandler) UpdateService(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	var req models.FirewallService
	if err := c.ShouldBindJSON(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	out, err := h.Services.Update(c.Request.Context(), id, req)
	if err != nil {
		if errors.Is(err, firewall.ErrServiceNotFound) {
			response.NotFound(c, err)
			return
		}
		response.BadRequest(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "fw.service.update", req.Name, out, h.NodeID)
	response.OK(c, out); h.reload(c.Request.Context(), "update")
}

func (h *FirewallHandler) DeleteService(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	if err := h.Services.Delete(c.Request.Context(), id); err != nil {
		if errors.Is(err, firewall.ErrServiceNotFound) {
			response.NotFound(c, err)
			return
		}
		response.BadRequest(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "fw.service.delete",
		strconv.FormatInt(id, 10), gin.H{"id": id}, h.NodeID)
	response.NoContent(c); h.reload(c.Request.Context(), "delete")
}

// ── Service Groups ─────────────────────────────────────────────────────

func (h *FirewallHandler) ListSvcGrp(c *gin.Context) {
	out, err := h.ServiceGroups.List(c.Request.Context())
	if err != nil {
		response.Internal(c, err)
		return
	}
	response.OK(c, gin.H{"service_groups": out})
}

func (h *FirewallHandler) GetSvcGrp(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	x, err := h.ServiceGroups.Get(c.Request.Context(), id)
	if err != nil {
		if errors.Is(err, firewall.ErrServiceGroupNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	response.OK(c, x)
}

func (h *FirewallHandler) CreateSvcGrp(c *gin.Context) {
	var req models.FirewallServiceGroup
	if err := c.ShouldBindJSON(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	out, err := h.ServiceGroups.Create(c.Request.Context(), req)
	if err != nil {
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "fw.svc_grp.create", req.Name, out, h.NodeID)
	response.Created(c, out); h.reload(c.Request.Context(), "create")
}

func (h *FirewallHandler) UpdateSvcGrp(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	var req models.FirewallServiceGroup
	if err := c.ShouldBindJSON(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	out, err := h.ServiceGroups.Update(c.Request.Context(), id, req)
	if err != nil {
		if errors.Is(err, firewall.ErrServiceGroupNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "fw.svc_grp.update", req.Name, out, h.NodeID)
	response.OK(c, out); h.reload(c.Request.Context(), "update")
}

func (h *FirewallHandler) DeleteSvcGrp(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	if err := h.ServiceGroups.Delete(c.Request.Context(), id); err != nil {
		if errors.Is(err, firewall.ErrServiceGroupNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "fw.svc_grp.delete",
		strconv.FormatInt(id, 10), gin.H{"id": id}, h.NodeID)
	response.NoContent(c); h.reload(c.Request.Context(), "delete")
}

// ── Rules ──────────────────────────────────────────────────────────────

func (h *FirewallHandler) ListRule(c *gin.Context) {
	out, err := h.Rules.List(c.Request.Context())
	if err != nil {
		response.Internal(c, err)
		return
	}
	response.OK(c, gin.H{"rules": out})
}

func (h *FirewallHandler) GetRule(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	x, err := h.Rules.Get(c.Request.Context(), id)
	if err != nil {
		if errors.Is(err, firewall.ErrRuleNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	response.OK(c, x)
}

func (h *FirewallHandler) CreateRule(c *gin.Context) {
	var req models.FirewallRule
	if err := c.ShouldBindJSON(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	if err := validateRule(req); err != nil {
		response.BadRequest(c, err)
		return
	}
	out, err := h.Rules.Create(c.Request.Context(), req)
	if err != nil {
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "fw.rule.create", strconv.FormatInt(out.ID, 10), out, h.NodeID)
	response.Created(c, out); h.reload(c.Request.Context(), "create")
}

func (h *FirewallHandler) UpdateRule(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	var req models.FirewallRule
	if err := c.ShouldBindJSON(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	if err := validateRule(req); err != nil {
		response.BadRequest(c, err)
		return
	}
	out, err := h.Rules.Update(c.Request.Context(), id, req)
	if err != nil {
		if errors.Is(err, firewall.ErrRuleNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "fw.rule.update", strconv.FormatInt(id, 10), out, h.NodeID)
	response.OK(c, out); h.reload(c.Request.Context(), "update")
}

func (h *FirewallHandler) DeleteRule(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	if err := h.Rules.Delete(c.Request.Context(), id); err != nil {
		if errors.Is(err, firewall.ErrRuleNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "fw.rule.delete",
		strconv.FormatInt(id, 10), gin.H{"id": id}, h.NodeID)
	response.NoContent(c); h.reload(c.Request.Context(), "delete")
}

// ── NAT Rules ──────────────────────────────────────────────────────────

func (h *FirewallHandler) ListNAT(c *gin.Context) {
	out, err := h.NATRules.List(c.Request.Context())
	if err != nil {
		response.Internal(c, err)
		return
	}
	response.OK(c, gin.H{"nat_rules": out})
}

func (h *FirewallHandler) GetNAT(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	x, err := h.NATRules.Get(c.Request.Context(), id)
	if err != nil {
		if errors.Is(err, firewall.ErrNATRuleNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	response.OK(c, x)
}

func (h *FirewallHandler) CreateNAT(c *gin.Context) {
	var req models.FirewallNATRule
	if err := c.ShouldBindJSON(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	if err := validateNAT(req); err != nil {
		response.BadRequest(c, err)
		return
	}
	out, err := h.NATRules.Create(c.Request.Context(), req)
	if err != nil {
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "fw.nat.create", strconv.FormatInt(out.ID, 10), out, h.NodeID)
	response.Created(c, out); h.reload(c.Request.Context(), "create")
}

func (h *FirewallHandler) UpdateNAT(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	var req models.FirewallNATRule
	if err := c.ShouldBindJSON(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	if err := validateNAT(req); err != nil {
		response.BadRequest(c, err)
		return
	}
	out, err := h.NATRules.Update(c.Request.Context(), id, req)
	if err != nil {
		if errors.Is(err, firewall.ErrNATRuleNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "fw.nat.update", strconv.FormatInt(id, 10), out, h.NodeID)
	response.OK(c, out); h.reload(c.Request.Context(), "update")
}

func (h *FirewallHandler) DeleteNAT(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	if err := h.NATRules.Delete(c.Request.Context(), id); err != nil {
		if errors.Is(err, firewall.ErrNATRuleNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "fw.nat.delete",
		strconv.FormatInt(id, 10), gin.H{"id": id}, h.NodeID)
	response.NoContent(c); h.reload(c.Request.Context(), "delete")
}

// ── Validators ─────────────────────────────────────────────────────────

func validateAddrObjValue(kind, value string) error {
	switch kind {
	case "host":
		if net.ParseIP(value) == nil {
			return fmt.Errorf("host: %q is not a valid IPv4/IPv6 address", value)
		}
	case "network":
		if _, _, err := net.ParseCIDR(value); err != nil {
			return fmt.Errorf("network: %q is not a valid CIDR (%w)", value, err)
		}
	case "range":
		parts := strings.SplitN(value, "-", 2)
		if len(parts) != 2 ||
			net.ParseIP(strings.TrimSpace(parts[0])) == nil ||
			net.ParseIP(strings.TrimSpace(parts[1])) == nil {
			return fmt.Errorf("range: %q must be 'IP-IP'", value)
		}
	case "fqdn":
		if !looksLikeFQDN(value) {
			return fmt.Errorf("fqdn: %q does not look like a hostname", value)
		}
	default:
		return fmt.Errorf("unknown address-object kind %q", kind)
	}
	return nil
}

func looksLikeFQDN(s string) bool {
	s = strings.TrimSuffix(strings.TrimSpace(s), ".")
	if s == "" || len(s) > 253 || !strings.Contains(s, ".") {
		return false
	}
	for _, label := range strings.Split(s, ".") {
		if len(label) == 0 || len(label) > 63 {
			return false
		}
		for _, r := range label {
			ok := r == '-' || (r >= '0' && r <= '9') ||
				(r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z')
			if !ok {
				return false
			}
		}
		if label[0] == '-' || label[len(label)-1] == '-' {
			return false
		}
	}
	return true
}

// validateRule enforces "exactly one or zero" of the three address
// pointers per side, and "exactly one or zero" service references.
func validateRule(r models.FirewallRule) error {
	if r.Action == "" {
		return errors.New("action is required")
	}
	if got := countNonNil(r.SrcAddressObjectID, r.SrcAddressGroupID, optStr(r.SrcCIDR)); got > 1 {
		return errors.New("source: at most one of src_address_object_id / src_address_group_id / src_cidr")
	}
	if got := countNonNil(r.DstAddressObjectID, r.DstAddressGroupID, optStr(r.DstCIDR)); got > 1 {
		return errors.New("destination: at most one of dst_address_object_id / dst_address_group_id / dst_cidr")
	}
	if r.ServiceObjectID != nil && r.ServiceGroupID != nil {
		return errors.New("service: at most one of service_object_id / service_group_id")
	}
	if r.SrcCIDR != nil {
		if _, _, err := net.ParseCIDR(*r.SrcCIDR); err != nil {
			return fmt.Errorf("src_cidr: %w", err)
		}
	}
	if r.DstCIDR != nil {
		if _, _, err := net.ParseCIDR(*r.DstCIDR); err != nil {
			return fmt.Errorf("dst_cidr: %w", err)
		}
	}
	return nil
}

func validateNAT(n models.FirewallNATRule) error {
	switch n.Kind {
	case "dnat":
		if n.TargetAddr == nil || *n.TargetAddr == "" {
			return errors.New("dnat: target_addr is required")
		}
		if n.MatchDPortStart == nil {
			return errors.New("dnat: match_dport_start is required (which incoming port to forward)")
		}
	case "snat":
		if n.TargetAddr == nil || *n.TargetAddr == "" {
			return errors.New("snat: target_addr is required (the address to rewrite to)")
		}
	case "masquerade":
		if n.OutZone == nil || *n.OutZone == "" {
			return errors.New("masquerade: out_zone is required (which interface group's IP to use)")
		}
		if n.TargetAddr != nil && *n.TargetAddr != "" {
			return errors.New("masquerade: target_addr must be empty (uses out-iface IP)")
		}
	default:
		return fmt.Errorf("unknown NAT kind %q", n.Kind)
	}
	return nil
}

// countNonNil counts how many of the supplied pointers are non-nil
// (and, for *string, non-empty). Used by validateRule.
func countNonNil(args ...any) int {
	n := 0
	for _, a := range args {
		switch v := a.(type) {
		case *int64:
			if v != nil {
				n++
			}
		case *string:
			if v != nil && *v != "" {
				n++
			}
		case nil:
			// skip
		default:
			n++
		}
	}
	return n
}

func optStr(p *string) *string { return p }