elmprodvpn/selective-vpn-api/app/traffic_mode.go

package app

import (
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/netip"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"time"
)

const (
	trafficRulePrefMarkDirect        = 11500
	trafficRulePrefMarkAppVPN        = 11510
	trafficRulePrefDirectSubnetStart = 11600
	trafficRulePrefDirectUIDStart    = 11680
	trafficRulePrefVPNSubnetStart    = 11720
	trafficRulePrefVPNUIDStart       = 11800
	trafficRulePrefFull              = 11900
	trafficRulePrefSelective         = 12000
	trafficRulePrefManagedMin        = 11500
	trafficRulePrefManagedMax        = 12099
	trafficRulePerKindLimit          = 70
	trafficAutoLocalDefault          = true
)

var cgnatPrefix = netip.MustParsePrefix("100.64.0.0/10")

const cgroupRootPath = "/sys/fs/cgroup"

// ---------------------------------------------------------------------
// traffic mode (selective / full_tunnel / direct)
// ---------------------------------------------------------------------

// EN: Controls route-policy behavior independently from DNS mode.
// EN: Uses a persisted desired state with runtime verification and rollback.
// RU: Управляет policy routing независимо от DNS-режима.
// RU: Использует сохраненное desired-state, runtime-проверку и откат.

func normalizeTrafficMode(raw TrafficMode) TrafficMode {
	switch strings.ToLower(strings.TrimSpace(string(raw))) {
	case string(TrafficModeFullTunnel):
		return TrafficModeFullTunnel
	case string(TrafficModeDirect):
		return TrafficModeDirect
	case string(TrafficModeSelective):
		return TrafficModeSelective
	default:
		return TrafficModeSelective
	}
}

func normalizePreferredIface(raw string) string {
	v := strings.TrimSpace(raw)
	l := strings.ToLower(v)
	if l == "" || l == "auto" || l == "-" || l == "default" {
		return ""
	}
	return v
}

func tokenizeList(raw []string) []string {
	repl := strings.NewReplacer(",", " ", ";", " ", "\n", " ", "\t", " ")
	out := make([]string, 0, len(raw))
	for _, line := range raw {
		for _, tok := range strings.Fields(repl.Replace(line)) {
			val := strings.TrimSpace(tok)
			if val != "" {
				out = append(out, val)
			}
		}
	}
	return out
}

func normalizeSubnetList(raw []string) []string {
	seen := map[string]struct{}{}
	out := make([]string, 0, len(raw))
	for _, tok := range tokenizeList(raw) {
		var cidr string
		if strings.Contains(tok, "/") {
			pfx, err := netip.ParsePrefix(tok)
			if err != nil || !pfx.Addr().Is4() {
				continue
			}
			cidr = pfx.Masked().String()
		} else {
			ip, err := netip.ParseAddr(tok)
			if err != nil || !ip.Is4() {
				continue
			}
			cidr = netip.PrefixFrom(ip, 32).String()
		}
		if _, ok := seen[cidr]; ok {
			continue
		}
		seen[cidr] = struct{}{}
		out = append(out, cidr)
	}
	sort.Strings(out)
	return out
}

func normalizeUIDToken(tok string) (string, bool) {
	t := strings.TrimSpace(tok)
	if t == "" {
		return "", false
	}
	parseOne := func(s string) (uint64, bool) {
		n, err := strconv.ParseUint(strings.TrimSpace(s), 10, 32)
		if err != nil {
			return 0, false
		}
		return n, true
	}
	if strings.Contains(t, "-") {
		parts := strings.SplitN(t, "-", 2)
		if len(parts) != 2 {
			return "", false
		}
		start, okA := parseOne(parts[0])
		end, okB := parseOne(parts[1])
		if !okA || !okB || end < start {
			return "", false
		}
		return fmt.Sprintf("%d-%d", start, end), true
	}
	n, ok := parseOne(t)
	if !ok {
		return "", false
	}
	return fmt.Sprintf("%d-%d", n, n), true
}

func normalizeUIDList(raw []string) []string {
	seen := map[string]struct{}{}
	out := make([]string, 0, len(raw))
	for _, tok := range tokenizeList(raw) {
		v, ok := normalizeUIDToken(tok)
		if !ok {
			continue
		}
		if _, exists := seen[v]; exists {
			continue
		}
		seen[v] = struct{}{}
		out = append(out, v)
	}
	sort.Strings(out)
	return out
}

func normalizeCgroupList(raw []string) []string {
	seen := map[string]struct{}{}
	out := make([]string, 0, len(raw))
	for _, tok := range tokenizeList(raw) {
		v := strings.TrimSpace(tok)
		if v == "" {
			continue
		}
		v = strings.TrimSuffix(v, "/")
		if v == "" {
			v = "/"
		}
		if _, exists := seen[v]; exists {
			continue
		}
		seen[v] = struct{}{}
		out = append(out, v)
	}
	sort.Strings(out)
	return out
}

func normalizeTrafficModeState(st TrafficModeState) TrafficModeState {
	st.Mode = normalizeTrafficMode(st.Mode)
	st.PreferredIface = normalizePreferredIface(st.PreferredIface)
	st.ForceVPNSubnets = normalizeSubnetList(st.ForceVPNSubnets)
	st.ForceVPNUIDs = normalizeUIDList(st.ForceVPNUIDs)
	st.ForceVPNCGroups = normalizeCgroupList(st.ForceVPNCGroups)
	st.ForceDirectSubnets = normalizeSubnetList(st.ForceDirectSubnets)
	st.ForceDirectUIDs = normalizeUIDList(st.ForceDirectUIDs)
	st.ForceDirectCGroups = normalizeCgroupList(st.ForceDirectCGroups)
	return st
}

func loadTrafficModeState() TrafficModeState {
	data, err := os.ReadFile(trafficModePath)
	if err != nil {
		return inferTrafficModeState()
	}

	type diskState struct {
		Mode               TrafficMode `json:"mode"`
		PreferredIface     string      `json:"preferred_iface,omitempty"`
		AutoLocalBypass    *bool       `json:"auto_local_bypass,omitempty"`
		ForceVPNSubnets    []string    `json:"force_vpn_subnets,omitempty"`
		ForceVPNUIDs       []string    `json:"force_vpn_uids,omitempty"`
		ForceVPNCGroups    []string    `json:"force_vpn_cgroups,omitempty"`
		ForceDirectSubnets []string    `json:"force_direct_subnets,omitempty"`
		ForceDirectUIDs    []string    `json:"force_direct_uids,omitempty"`
		ForceDirectCGroups []string    `json:"force_direct_cgroups,omitempty"`
	}
	var raw diskState
	if err := json.Unmarshal(data, &raw); err != nil {
		return inferTrafficModeState()
	}
	st := TrafficModeState{
		Mode:               raw.Mode,
		PreferredIface:     raw.PreferredIface,
		AutoLocalBypass:    trafficAutoLocalDefault,
		ForceVPNSubnets:    append([]string(nil), raw.ForceVPNSubnets...),
		ForceVPNUIDs:       append([]string(nil), raw.ForceVPNUIDs...),
		ForceVPNCGroups:    append([]string(nil), raw.ForceVPNCGroups...),
		ForceDirectSubnets: append([]string(nil), raw.ForceDirectSubnets...),
		ForceDirectUIDs:    append([]string(nil), raw.ForceDirectUIDs...),
		ForceDirectCGroups: append([]string(nil), raw.ForceDirectCGroups...),
	}
	if raw.AutoLocalBypass != nil {
		st.AutoLocalBypass = *raw.AutoLocalBypass
	}
	return normalizeTrafficModeState(st)
}

func saveTrafficModeState(st TrafficModeState) error {
	st = normalizeTrafficModeState(st)
	st.UpdatedAt = time.Now().UTC().Format(time.RFC3339)

	data, err := json.MarshalIndent(st, "", "  ")
	if err != nil {
		return err
	}
	if err := os.MkdirAll(stateDir, 0o755); err != nil {
		return err
	}
	tmp := trafficModePath + ".tmp"
	if err := os.WriteFile(tmp, data, 0o644); err != nil {
		return err
	}
	return os.Rename(tmp, trafficModePath)
}

func inferTrafficModeState() TrafficModeState {
	rules := readTrafficRules()
	mode := detectAppliedTrafficMode(rules)
	iface, _ := resolveTrafficIface("")
	return normalizeTrafficModeState(TrafficModeState{
		Mode:               mode,
		PreferredIface:     iface,
		AutoLocalBypass:    trafficAutoLocalDefault,
		ForceVPNSubnets:    nil,
		ForceVPNUIDs:       nil,
		ForceVPNCGroups:    nil,
		ForceDirectSubnets: nil,
		ForceDirectUIDs:    nil,
		ForceDirectCGroups: nil,
	})
}

func ensureRoutesTableEntry() {
	data, _ := os.ReadFile("/etc/iproute2/rt_tables")
	want := fmt.Sprintf("%s %s", routesTableNum(), routesTableName())
	if strings.Contains(string(data), "\n"+want) || strings.HasPrefix(string(data), want) {
		return
	}
	f, err := os.OpenFile("/etc/iproute2/rt_tables", os.O_APPEND|os.O_WRONLY, 0o644)
	if err != nil {
		return
	}
	defer f.Close()
	_, _ = fmt.Fprintf(f, "%s\n", want)
}

func ifaceExists(iface string) bool {
	iface = strings.TrimSpace(iface)
	if iface == "" {
		return false
	}
	_, _, code, _ := runCommand("ip", "link", "show", iface)
	return code == 0
}

func statusIfaceFromFile() string {
	data, err := os.ReadFile(statusFilePath)
	if err != nil {
		return ""
	}
	var st Status
	if json.Unmarshal(data, &st) != nil {
		return ""
	}
	return strings.TrimSpace(st.Iface)
}

func listUpIfaces() []string {
	out, _, code, _ := runCommand("ip", "-o", "link", "show", "up")
	if code != 0 {
		return nil
	}
	seen := map[string]struct{}{}
	var outIfaces []string
	for _, line := range strings.Split(out, "\n") {
		line = strings.TrimSpace(line)
		if line == "" {
			continue
		}
		parts := strings.SplitN(line, ":", 3)
		if len(parts) < 3 {
			continue
		}
		name := strings.TrimSpace(parts[1])
		name = strings.SplitN(name, "@", 2)[0]
		name = strings.TrimSpace(name)
		if name == "" || name == "lo" {
			continue
		}
		if _, ok := seen[name]; ok {
			continue
		}
		seen[name] = struct{}{}
		outIfaces = append(outIfaces, name)
	}
	return outIfaces
}

func listSelectableIfaces(preferred string) []string {
	up := listUpIfaces()
	seen := map[string]struct{}{}
	var vpnLike []string
	var other []string

	add := func(dst *[]string, iface string) {
		iface = strings.TrimSpace(iface)
		if iface == "" {
			return
		}
		if _, ok := seen[iface]; ok {
			return
		}
		seen[iface] = struct{}{}
		*dst = append(*dst, iface)
	}

	for _, iface := range up {
		if isVPNLikeIface(iface) {
			add(&vpnLike, iface)
		}
	}
	for _, iface := range up {
		if !isVPNLikeIface(iface) {
			add(&other, iface)
		}
	}
	sort.Strings(vpnLike)
	sort.Strings(other)

	selected := make([]string, 0, len(vpnLike)+len(other)+1)
	selected = append(selected, vpnLike...)
	selected = append(selected, other...)

	pref := normalizePreferredIface(preferred)
	if pref != "" {
		if _, ok := seen[pref]; !ok {
			selected = append([]string{pref}, selected...)
		}
	}
	return selected
}

func isVPNLikeIface(iface string) bool {
	l := strings.ToLower(strings.TrimSpace(iface))
	return strings.HasPrefix(l, "tun") ||
		strings.HasPrefix(l, "wg") ||
		strings.HasPrefix(l, "ppp") ||
		strings.HasPrefix(l, "tap") ||
		strings.HasPrefix(l, "utun") ||
		strings.HasPrefix(l, "vpn")
}

func resolveTrafficIface(preferred string) (string, string) {
	pref := normalizePreferredIface(preferred)
	if pref != "" && ifaceExists(pref) {
		return pref, "preferred"
	}

	statusIface := statusIfaceFromFile()
	if statusIface != "" && ifaceExists(statusIface) {
		return statusIface, "status"
	}

	for _, iface := range listUpIfaces() {
		if isVPNLikeIface(iface) {
			return iface, "auto-vpn-like"
		}
	}

	if pref != "" {
		return "", "preferred-not-found"
	}
	return "", "iface-not-found"
}

type autoLocalRoute struct {
	Dst string
	Dev string
}

func parseRouteDevice(fields []string) string {
	for i := 0; i+1 < len(fields); i++ {
		if fields[i] == "dev" {
			return strings.TrimSpace(fields[i+1])
		}
	}
	return ""
}

func isContainerIface(iface string) bool {
	l := strings.ToLower(strings.TrimSpace(iface))
	return strings.HasPrefix(l, "docker") ||
		strings.HasPrefix(l, "br-") ||
		strings.HasPrefix(l, "veth") ||
		strings.HasPrefix(l, "cni")
}

func isPrivateLikeAddr(a netip.Addr) bool {
	if !a.Is4() {
		return false
	}
	if a.IsPrivate() || a.IsLoopback() || a.IsLinkLocalUnicast() {
		return true
	}
	// Carrier-grade NAT block.
	return cgnatPrefix.Contains(a)
}

func isAutoBypassDestination(dst string) bool {
	dst = strings.TrimSpace(dst)
	if dst == "" || dst == "default" {
		return false
	}
	if strings.Contains(dst, "/") {
		pfx, err := netip.ParsePrefix(dst)
		if err != nil {
			return false
		}
		return isPrivateLikeAddr(pfx.Addr())
	}
	addr, err := netip.ParseAddr(dst)
	if err != nil {
		return false
	}
	return isPrivateLikeAddr(addr)
}

func detectAutoLocalBypassRoutes(vpnIface string) []autoLocalRoute {
	vpnIface = strings.TrimSpace(vpnIface)
	out, _, code, _ := runCommand("ip", "-4", "route", "show", "table", "main")
	if code != 0 {
		return nil
	}

	seen := map[string]struct{}{}
	routes := make([]autoLocalRoute, 0, 8)

	add := func(dst, dev string) {
		dst = strings.TrimSpace(dst)
		dev = strings.TrimSpace(dev)
		if dst == "" || dev == "" {
			return
		}
		key := dst + "|" + dev
		if _, ok := seen[key]; ok {
			return
		}
		seen[key] = struct{}{}
		routes = append(routes, autoLocalRoute{Dst: dst, Dev: dev})
	}

	for _, raw := range strings.Split(out, "\n") {
		line := strings.TrimSpace(raw)
		if line == "" {
			continue
		}
		fields := strings.Fields(line)
		if len(fields) == 0 {
			continue
		}
		dst := strings.TrimSpace(fields[0])
		if dst == "" || dst == "default" {
			continue
		}
		dev := parseRouteDevice(fields)
		if dev == "" || dev == "lo" {
			continue
		}
		if vpnIface != "" && dev == vpnIface {
			continue
		}
		if isVPNLikeIface(dev) {
			continue
		}

		isScopeLink := strings.Contains(" "+line+" ", " scope link ")
		if isScopeLink || isContainerIface(dev) || isAutoBypassDestination(dst) {
			add(dst, dev)
		}
	}

	sort.Slice(routes, func(i, j int) bool {
		if routes[i].Dev == routes[j].Dev {
			return routes[i].Dst < routes[j].Dst
		}
		return routes[i].Dev < routes[j].Dev
	})
	return routes
}

func applyAutoLocalBypass(vpnIface string) {
	for _, rt := range detectAutoLocalBypassRoutes(vpnIface) {
		_, _, _, _ = runCommand(
			"ip", "-4", "route", "replace",
			rt.Dst, "dev", rt.Dev, "table", routesTableName(),
		)
	}
}

func prefStr(v int) string {
	return strconv.Itoa(v)
}

func removeTrafficRulesForTable() {
	out, _, _, _ := runCommand("ip", "rule", "show")
	for _, line := range strings.Split(out, "\n") {
		line = strings.TrimSpace(line)
		if line == "" {
			continue
		}
		fields := strings.Fields(line)
		if len(fields) == 0 {
			continue
		}
		pref := strings.TrimSuffix(fields[0], ":")
		if pref == "" {
			continue
		}
		prefNum, _ := strconv.Atoi(pref)
		low := strings.ToLower(line)
		managed := prefNum >= trafficRulePrefManagedMin && prefNum <= trafficRulePrefManagedMax
		legacy := strings.Contains(low, "lookup "+routesTableName())
		if !managed && !legacy {
			continue
		}
		_, _, _, _ = runCommand("ip", "rule", "del", "pref", pref)
	}
}

func cgroupCandidates(entry string) []string {
	v := strings.TrimSpace(entry)
	if v == "" {
		return nil
	}
	vc := filepath.Clean(v)
	vals := []string{}
	if filepath.IsAbs(vc) {
		if strings.HasPrefix(vc, cgroupRootPath) {
			vals = append(vals, vc)
		} else {
			vals = append(vals, filepath.Join(cgroupRootPath, strings.TrimPrefix(vc, "/")))
		}
	} else {
		vals = append(vals,
			filepath.Join(cgroupRootPath, strings.TrimPrefix(vc, "/")),
			filepath.Join(cgroupRootPath, "system.slice", strings.TrimPrefix(vc, "/")),
			filepath.Join(cgroupRootPath, "user.slice", strings.TrimPrefix(vc, "/")),
		)
	}
	seen := map[string]struct{}{}
	out := make([]string, 0, len(vals))
	for _, p := range vals {
		cp := filepath.Clean(p)
		if cp == "." || cp == "" {
			continue
		}
		if _, ok := seen[cp]; ok {
			continue
		}
		seen[cp] = struct{}{}
		out = append(out, cp)
	}
	return out
}

func resolveCgroupPath(entry string) (string, string) {
	for _, cand := range cgroupCandidates(entry) {
		fi, err := os.Stat(cand)
		if err != nil || !fi.IsDir() {
			continue
		}
		return cand, ""
	}
	return "", "cgroup not found: " + strings.TrimSpace(entry)
}

func collectPIDsFromCgroup(root string) (map[int]struct{}, string) {
	const (
		maxDirs = 5000
		maxPIDs = 50000
	)

	pids := map[int]struct{}{}
	dirs := 0
	warn := ""

	_ = filepath.WalkDir(root, func(path string, d os.DirEntry, err error) error {
		if err != nil || d == nil || !d.IsDir() {
			return nil
		}
		dirs++
		if dirs > maxDirs {
			warn = "cgroup scan truncated by directory limit"
			return filepath.SkipDir
		}
		data, err := os.ReadFile(filepath.Join(path, "cgroup.procs"))
		if err != nil {
			return nil
		}
		for _, ln := range strings.Split(string(data), "\n") {
			ln = strings.TrimSpace(ln)
			if ln == "" {
				continue
			}
			pid, err := strconv.Atoi(ln)
			if err != nil || pid <= 0 {
				continue
			}
			pids[pid] = struct{}{}
			if len(pids) > maxPIDs {
				warn = "cgroup scan truncated by pid limit"
				return filepath.SkipDir
			}
		}
		return nil
	})
	return pids, warn
}

func uidRangeForPID(pid int) (string, bool) {
	data, err := os.ReadFile(fmt.Sprintf("/proc/%d/status", pid))
	if err != nil {
		return "", false
	}
	for _, ln := range strings.Split(string(data), "\n") {
		ln = strings.TrimSpace(ln)
		if !strings.HasPrefix(ln, "Uid:") {
			continue
		}
		fields := strings.Fields(ln)
		if len(fields) < 2 {
			return "", false
		}
		v, ok := normalizeUIDToken(fields[1])
		return v, ok
	}
	return "", false
}

func resolveCgroupUIDRanges(entries []string) ([]string, string) {
	var uids []string
	var warnings []string

	for _, entry := range normalizeCgroupList(entries) {
		root, warn := resolveCgroupPath(entry)
		if root == "" {
			if warn != "" {
				warnings = append(warnings, warn)
			}
			continue
		}
		pids, scanWarn := collectPIDsFromCgroup(root)
		if scanWarn != "" {
			warnings = append(warnings, scanWarn)
		}
		if len(pids) == 0 {
			warnings = append(warnings, "cgroup has no processes: "+entry)
			continue
		}
		for pid := range pids {
			uidRange, ok := uidRangeForPID(pid)
			if !ok || uidRange == "" {
				continue
			}
			uids = append(uids, uidRange)
		}
	}
	seenWarn := map[string]struct{}{}
	uniqWarn := make([]string, 0, len(warnings))
	for _, w := range warnings {
		ww := strings.TrimSpace(w)
		if ww == "" {
			continue
		}
		if _, ok := seenWarn[ww]; ok {
			continue
		}
		seenWarn[ww] = struct{}{}
		uniqWarn = append(uniqWarn, ww)
	}
	return normalizeUIDList(uids), strings.Join(uniqWarn, "; ")
}

type effectiveTrafficOverrides struct {
	VPNSubnets         []string
	VPNUIDs            []string
	DirectSubnets      []string
	DirectUIDs         []string
	CgroupResolvedUIDs int
	CgroupWarning      string
}

func buildEffectiveOverrides(st TrafficModeState) effectiveTrafficOverrides {
	st = normalizeTrafficModeState(st)
	e := effectiveTrafficOverrides{
		VPNSubnets:    append([]string(nil), st.ForceVPNSubnets...),
		VPNUIDs:       append([]string(nil), st.ForceVPNUIDs...),
		DirectSubnets: append([]string(nil), st.ForceDirectSubnets...),
		DirectUIDs:    append([]string(nil), st.ForceDirectUIDs...),
	}

	vpnUIDsFromCG, warnVPN := resolveCgroupUIDRanges(st.ForceVPNCGroups)
	directUIDsFromCG, warnDirect := resolveCgroupUIDRanges(st.ForceDirectCGroups)
	e.CgroupResolvedUIDs = len(vpnUIDsFromCG) + len(directUIDsFromCG)
	e.VPNUIDs = normalizeUIDList(append(e.VPNUIDs, vpnUIDsFromCG...))
	e.DirectUIDs = normalizeUIDList(append(e.DirectUIDs, directUIDsFromCG...))
	warns := make([]string, 0, 2)
	if strings.TrimSpace(warnVPN) != "" {
		warns = append(warns, strings.TrimSpace(warnVPN))
	}
	if strings.TrimSpace(warnDirect) != "" {
		warns = append(warns, strings.TrimSpace(warnDirect))
	}
	e.CgroupWarning = strings.Join(warns, "; ")
	return e
}

func applyRule(pref int, args ...string) error {
	if pref <= 0 {
		return fmt.Errorf("invalid pref: %d", pref)
	}
	cmd := []string{"rule", "add"}
	cmd = append(cmd, args...)
	cmd = append(cmd, "pref", prefStr(pref))
	_, _, code, err := runCommand("ip", cmd...)
	if err != nil || code != 0 {
		if err == nil {
			err = fmt.Errorf("ip %s exited with %d", strings.Join(cmd, " "), code)
		}
		return err
	}
	return nil
}

func applyTrafficOverrides(e effectiveTrafficOverrides) (int, error) {
	applied := 0
	if len(e.DirectSubnets) > trafficRulePerKindLimit ||
		len(e.DirectUIDs) > trafficRulePerKindLimit ||
		len(e.VPNSubnets) > trafficRulePerKindLimit ||
		len(e.VPNUIDs) > trafficRulePerKindLimit {
		return 0, fmt.Errorf("override list too large (max %d entries per kind)", trafficRulePerKindLimit)
	}

	for i, cidr := range e.DirectSubnets {
		if err := applyRule(trafficRulePrefDirectSubnetStart+i, "from", cidr, "lookup", "main"); err != nil {
			return applied, err
		}
		applied++
	}
	for i, uidr := range e.DirectUIDs {
		if err := applyRule(trafficRulePrefDirectUIDStart+i, "uidrange", uidr, "lookup", "main"); err != nil {
			return applied, err
		}
		applied++
	}
	for i, cidr := range e.VPNSubnets {
		if err := applyRule(trafficRulePrefVPNSubnetStart+i, "from", cidr, "lookup", routesTableName()); err != nil {
			return applied, err
		}
		applied++
	}
	for i, uidr := range e.VPNUIDs {
		if err := applyRule(trafficRulePrefVPNUIDStart+i, "uidrange", uidr, "lookup", routesTableName()); err != nil {
			return applied, err
		}
		applied++
	}
	return applied, nil
}

func ensureTrafficRouteBase(iface string, autoLocalBypass bool) error {
	iface = strings.TrimSpace(iface)
	if iface == "" {
		return fmt.Errorf("empty interface")
	}
	if !ifaceExists(iface) {
		return fmt.Errorf("interface not found: %s", iface)
	}

	ensureRoutesTableEntry()

	if _, _, code, err := runCommand("ip", "-4", "route", "replace", "default", "dev", iface, "table", routesTableName(), "mtu", policyRouteMTU); err != nil || code != 0 {
		if err == nil {
			err = fmt.Errorf("ip route replace default exited with %d", code)
		}
		return err
	}

	if autoLocalBypass {
		applyAutoLocalBypass(iface)
	}
	return nil
}

func applyTrafficMode(st TrafficModeState, iface string) error {
	st = normalizeTrafficModeState(st)
	eff := buildEffectiveOverrides(st)

	removeTrafficRulesForTable()

	// EN: Ensure the policy table name exists even in direct mode so mark-based rules can be installed.
	// RU: Гарантируем наличие имени policy-table даже в direct режиме, чтобы можно было ставить mark-правила.
	ensureRoutesTableEntry()

	needVPNTable := st.Mode != TrafficModeDirect || len(eff.VPNSubnets) > 0 || len(eff.VPNUIDs) > 0
	if needVPNTable {
		if err := ensureTrafficRouteBase(iface, st.AutoLocalBypass); err != nil {
			return err
		}
	}

	if _, err := applyTrafficOverrides(eff); err != nil {
		return err
	}

	// EN: Mark-based per-app routing support (cgroup-based marking in nftables).
	// EN: These rules are safe even when no packets are marked with MARK_APP/MARK_DIRECT.
	// RU: Поддержка per-app маршрутизации по mark (cgroup-based marking в nftables).
	// RU: Эти правила безопасны, если пакеты не помечаются MARK_APP/MARK_DIRECT.
	if err := applyRule(trafficRulePrefMarkDirect, "fwmark", MARK_DIRECT, "lookup", "main"); err != nil {
		return err
	}
	if err := applyRule(trafficRulePrefMarkAppVPN, "fwmark", MARK_APP, "lookup", routesTableName()); err != nil {
		return err
	}

	switch st.Mode {
	case TrafficModeFullTunnel:
		if err := applyRule(trafficRulePrefFull, "lookup", routesTableName()); err != nil {
			return err
		}
	case TrafficModeSelective:
		if err := applyRule(trafficRulePrefSelective, "fwmark", MARK, "lookup", routesTableName()); err != nil {
			return err
		}
	case TrafficModeDirect:
		// direct mode relies only on optional direct/vpn overrides.
	default:
		return fmt.Errorf("unknown traffic mode: %s", st.Mode)
	}

	return nil
}

type trafficRulesState struct {
	Mark bool
	Full bool
}

func readTrafficRules() trafficRulesState {
	out, _, _, _ := runCommand("ip", "rule", "show")
	var st trafficRulesState
	for _, line := range strings.Split(out, "\n") {
		l := strings.ToLower(strings.TrimSpace(line))
		if l == "" || !strings.Contains(l, "lookup "+routesTableName()) {
			continue
		}
		fields := strings.Fields(l)
		if len(fields) == 0 {
			continue
		}
		prefRaw := strings.TrimSuffix(fields[0], ":")
		pref, _ := strconv.Atoi(prefRaw)
		switch pref {
		case trafficRulePrefSelective:
			st.Mark = true
		case trafficRulePrefFull:
			st.Full = true
		}
	}
	return st
}

func detectAppliedTrafficMode(rules trafficRulesState) TrafficMode {
	if rules.Full {
		return TrafficModeFullTunnel
	}
	if rules.Mark {
		return TrafficModeSelective
	}
	return TrafficModeDirect
}

func probeTrafficMode(mode TrafficMode, iface string) (bool, string) {
	mode = normalizeTrafficMode(mode)
	iface = strings.TrimSpace(iface)

	args := []string{"-4", "route", "get", "1.1.1.1"}
	if mode == TrafficModeSelective {
		args = append(args, "mark", MARK)
	}

	out, _, code, err := runCommand("ip", args...)
	if err != nil || code != 0 {
		if err == nil {
			err = fmt.Errorf("ip route get exited with %d", code)
		}
		return false, err.Error()
	}

	text := strings.ToLower(out)
	switch mode {
	case TrafficModeDirect:
		// direct mode must not be forced through agvpn rule table.
		if strings.Contains(text, " table "+strings.ToLower(routesTableName())) {
			return false, "route probe still uses agvpn table"
		}
		return true, "route probe direct path ok"
	case TrafficModeFullTunnel, TrafficModeSelective:
		if iface == "" {
			return false, "route probe has empty iface"
		}
		if !strings.Contains(text, "dev "+strings.ToLower(iface)) {
			return false, fmt.Sprintf("route probe mismatch: expected dev %s", iface)
		}
		return true, "route probe vpn path ok"
	default:
		return false, "route probe unknown mode"
	}
}

func evaluateTrafficMode(st TrafficModeState) TrafficModeStatusResponse {
	st = normalizeTrafficModeState(st)
	eff := buildEffectiveOverrides(st)
	hasVPN := len(eff.VPNSubnets) > 0 || len(eff.VPNUIDs) > 0
	iface, reason := resolveTrafficIface(st.PreferredIface)
	rules := readTrafficRules()
	applied := detectAppliedTrafficMode(rules)
	bypassCandidates := 0
	if st.AutoLocalBypass && (st.Mode != TrafficModeDirect || hasVPN) {
		bypassCandidates = len(detectAutoLocalBypassRoutes(iface))
	}

	overridesApplied := len(eff.VPNSubnets) + len(eff.VPNUIDs) + len(eff.DirectSubnets) + len(eff.DirectUIDs)

	tableDefault := false
	if iface != "" && (st.Mode != TrafficModeDirect || hasVPN) {
		ok, _ := checkPolicyRoute(iface, routesTableName())
		tableDefault = ok
	}

	res := TrafficModeStatusResponse{
		Mode:               st.Mode,
		DesiredMode:        st.Mode,
		AppliedMode:        applied,
		PreferredIface:     st.PreferredIface,
		AutoLocalBypass:    st.AutoLocalBypass,
		BypassCandidates:   bypassCandidates,
		ForceVPNSubnets:    append([]string(nil), st.ForceVPNSubnets...),
		ForceVPNUIDs:       append([]string(nil), st.ForceVPNUIDs...),
		ForceVPNCGroups:    append([]string(nil), st.ForceVPNCGroups...),
		ForceDirectSubnets: append([]string(nil), st.ForceDirectSubnets...),
		ForceDirectUIDs:    append([]string(nil), st.ForceDirectUIDs...),
		ForceDirectCGroups: append([]string(nil), st.ForceDirectCGroups...),
		OverridesApplied:   overridesApplied,
		CgroupResolvedUIDs: eff.CgroupResolvedUIDs,
		CgroupWarning:      eff.CgroupWarning,
		ActiveIface:        iface,
		IfaceReason:        reason,
		RuleMark:           rules.Mark,
		RuleFull:           rules.Full,
		TableDefault:       tableDefault,
	}

	res.ProbeOK, res.ProbeMessage = probeTrafficMode(st.Mode, iface)

	switch st.Mode {
	case TrafficModeDirect:
		// direct mode can still be healthy when vpn overrides exist
		// (base full/selective rules must be absent).
		if hasVPN {
			res.Healthy = !rules.Mark && !rules.Full && tableDefault && iface != "" && res.ProbeOK
		} else {
			res.Healthy = !rules.Mark && !rules.Full && res.ProbeOK
		}
	case TrafficModeFullTunnel:
		res.Healthy = rules.Full && !rules.Mark && tableDefault && iface != "" && res.ProbeOK
	case TrafficModeSelective:
		res.Healthy = rules.Mark && !rules.Full && tableDefault && iface != "" && res.ProbeOK
	default:
		res.Healthy = false
	}

	if res.Healthy {
		res.Message = "traffic mode applied"
		return res
	}
	if iface == "" && (st.Mode != TrafficModeDirect || hasVPN) {
		res.Message = "vpn interface not found"
		return res
	}
	if st.Mode != applied {
		res.Message = fmt.Sprintf("desired=%s applied=%s mismatch", st.Mode, applied)
		return res
	}
	if (st.Mode != TrafficModeDirect || hasVPN) && !tableDefault {
		res.Message = "policy table default route is missing"
		return res
	}
	if !res.ProbeOK {
		res.Message = res.ProbeMessage
		return res
	}
	if rules.Mark && rules.Full {
		res.Message = "conflicting traffic rules detected"
		return res
	}
	res.Message = "traffic mode check failed"
	return res
}

func handleTrafficInterfaces(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}

	st := loadTrafficModeState()
	active, reason := resolveTrafficIface(st.PreferredIface)
	resp := TrafficInterfacesResponse{
		Interfaces:     listSelectableIfaces(st.PreferredIface),
		PreferredIface: normalizePreferredIface(st.PreferredIface),
		ActiveIface:    active,
		IfaceReason:    reason,
	}
	writeJSON(w, http.StatusOK, resp)
}

func handleTrafficModeTest(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet && r.Method != http.MethodPost {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}
	st := loadTrafficModeState()
	writeJSON(w, http.StatusOK, evaluateTrafficMode(st))
}

func handleTrafficMode(w http.ResponseWriter, r *http.Request) {
	switch r.Method {
	case http.MethodGet:
		st := loadTrafficModeState()
		writeJSON(w, http.StatusOK, evaluateTrafficMode(st))
	case http.MethodPost:
		prev := loadTrafficModeState()
		next := prev

		var body TrafficModeRequest
		if r.Body != nil {
			defer r.Body.Close()
			if err := json.NewDecoder(io.LimitReader(r.Body, 1<<20)).Decode(&body); err != nil {
				http.Error(w, "bad json", http.StatusBadRequest)
				return
			}
		}

		if strings.TrimSpace(string(body.Mode)) != "" {
			next.Mode = normalizeTrafficMode(body.Mode)
		}
		if body.PreferredIface != nil {
			next.PreferredIface = normalizePreferredIface(*body.PreferredIface)
		}
		if body.AutoLocalBypass != nil {
			next.AutoLocalBypass = *body.AutoLocalBypass
		}
		if body.ForceVPNSubnets != nil {
			next.ForceVPNSubnets = append([]string(nil), (*body.ForceVPNSubnets)...)
		}
		if body.ForceVPNUIDs != nil {
			next.ForceVPNUIDs = append([]string(nil), (*body.ForceVPNUIDs)...)
		}
		if body.ForceVPNCGroups != nil {
			next.ForceVPNCGroups = append([]string(nil), (*body.ForceVPNCGroups)...)
		}
		if body.ForceDirectSubnets != nil {
			next.ForceDirectSubnets = append([]string(nil), (*body.ForceDirectSubnets)...)
		}
		if body.ForceDirectUIDs != nil {
			next.ForceDirectUIDs = append([]string(nil), (*body.ForceDirectUIDs)...)
		}
		if body.ForceDirectCGroups != nil {
			next.ForceDirectCGroups = append([]string(nil), (*body.ForceDirectCGroups)...)
		}

		next = normalizeTrafficModeState(next)
		prev = normalizeTrafficModeState(prev)

		nextIface, _ := resolveTrafficIface(next.PreferredIface)
		if err := applyTrafficMode(next, nextIface); err != nil {
			prevIface, _ := resolveTrafficIface(prev.PreferredIface)
			_ = applyTrafficMode(prev, prevIface)
			msg := evaluateTrafficMode(prev)
			msg.Message = "apply failed, rolled back: " + err.Error()
			writeJSON(w, http.StatusOK, msg)
			return
		}

		if err := saveTrafficModeState(next); err != nil {
			writeJSON(w, http.StatusOK, TrafficModeStatusResponse{
				Mode:               next.Mode,
				DesiredMode:        next.Mode,
				PreferredIface:     next.PreferredIface,
				AutoLocalBypass:    next.AutoLocalBypass,
				ForceVPNSubnets:    append([]string(nil), next.ForceVPNSubnets...),
				ForceVPNUIDs:       append([]string(nil), next.ForceVPNUIDs...),
				ForceVPNCGroups:    append([]string(nil), next.ForceVPNCGroups...),
				ForceDirectSubnets: append([]string(nil), next.ForceDirectSubnets...),
				ForceDirectUIDs:    append([]string(nil), next.ForceDirectUIDs...),
				ForceDirectCGroups: append([]string(nil), next.ForceDirectCGroups...),
				OverridesApplied:   len(next.ForceVPNSubnets) + len(next.ForceVPNUIDs) + len(next.ForceDirectSubnets) + len(next.ForceDirectUIDs),
				Healthy:            false,
				Message:            "state save failed: " + err.Error(),
			})
			return
		}

		res := evaluateTrafficMode(next)
		if !res.Healthy {
			prevIface, _ := resolveTrafficIface(prev.PreferredIface)
			_ = applyTrafficMode(prev, prevIface)
			_ = saveTrafficModeState(prev)
			rolled := evaluateTrafficMode(prev)
			rolled.Message = "verification failed, rolled back: " + res.Message
			writeJSON(w, http.StatusOK, rolled)
			return
		}

		events.push("traffic_mode_changed", map[string]any{
			"mode":              res.Mode,
			"applied":           res.AppliedMode,
			"active_iface":      res.ActiveIface,
			"healthy":           res.Healthy,
			"auto_local_bypass": res.AutoLocalBypass,
			"overrides_applied": res.OverridesApplied,
		})
		writeJSON(w, http.StatusOK, res)
	default:
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
	}
}