all: add router client info detection

This commit add the ability for ctrld to gather client information,
including mac/ip/hostname, and send to Control-D server through a
config per upstream.

 - Add send_client_info upstream config.
 - Read/Watch dnsmasq leases files on supported platforms.
 - Add corresponding client info to DoH query header

All of these only apply for Control-D upstream, though.

internal/router/client_info.go

@@ -0,0 +1,88 @@
+package router
+
+import (
+	"bytes"
+	"log"
+	"os"
+	"time"
+
+	"github.com/fsnotify/fsnotify"
+	"tailscale.com/util/lineread"
+
+	"github.com/Control-D-Inc/ctrld"
+)
+
+var clientInfoFiles = []string{
+	"/tmp/dnsmasq.leases",                  // ddwrt
+	"/tmp/dhcp.leases",                     // openwrt
+	"/var/lib/misc/dnsmasq.leases",         // merlin
+	"/mnt/data/udapi-config/dnsmasq.lease", // UDM Pro
+	"/data/udapi-config/dnsmasq.lease",     // UDR
+}
+
+func (r *router) watchClientInfoTable() {
+	if r.watcher == nil {
+		return
+	}
+	timer := time.NewTicker(time.Minute * 5)
+	for {
+		select {
+		case <-timer.C:
+			for _, name := range r.watcher.WatchList() {
+				_ = readClientInfoFile(name)
+			}
+		case event, ok := <-r.watcher.Events:
+			if !ok {
+				return
+			}
+			if event.Has(fsnotify.Write) {
+				if err := readClientInfoFile(event.Name); err != nil && !os.IsNotExist(err) {
+					log.Println("could not read client info file:", err)
+				}
+			}
+		case err, ok := <-r.watcher.Errors:
+			if !ok {
+				return
+			}
+			log.Println("error:", err)
+		}
+	}
+}
+
+func Stop() error {
+	if Name() == "" {
+		return nil
+	}
+	r := routerPlatform.Load()
+	if r.watcher != nil {
+		if err := r.watcher.Close(); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func GetClientInfoByMac(mac string) *ctrld.ClientInfo {
+	if mac == "" {
+		return nil
+	}
+	_ = Name()
+	r := routerPlatform.Load()
+	val, ok := r.mac.Load(mac)
+	if !ok {
+		return nil
+	}
+	return val.(*ctrld.ClientInfo)
+}
+
+func readClientInfoFile(name string) error {
+	r := routerPlatform.Load()
+	return lineread.File(name, func(line []byte) error {
+		fields := bytes.Fields(line)
+		mac := string(fields[1])
+		ip := string(fields[2])
+		hostname := string(fields[3])
+		r.mac.Store(mac, &ctrld.ClientInfo{Mac: mac, IP: ip, Hostname: hostname})
+		return nil
+	})
+}

internal/router/ddwrt.go

@@ -20,9 +20,9 @@ https://wiki.dd-wrt.com/wiki/index.php/Journalling_Flash_File_System
 `)
 
 var nvramKeys = map[string]string{
-	"dns_dnsmasq":     "1",                  // Make dnsmasq running but disable DNS ability, ctrld will replace it.
-	"dnsmasq_options": dnsMasqConfigContent, // Configuration of dnsmasq set by ctrld.
-	"dns_crypt":       "0",                  // Disable DNSCrypt.
+	"dns_dnsmasq":     "1", // Make dnsmasq running but disable DNS ability, ctrld will replace it.
+	"dnsmasq_options": "",  // Configuration of dnsmasq set by ctrld, filled by setupDDWrt.
+	"dns_crypt":       "0", // Disable DNSCrypt.
 }
 
 func setupDDWrt() error {
@@ -31,6 +31,11 @@ func setupDDWrt() error {
 		return nil
 	}
 
+	data, err := dnsMasqConf()
+	if err != nil {
+		return err
+	}
+	nvramKeys["dnsmasq_options"] = data
 	// Backup current value, store ctrld's configs.
 	for key, value := range nvramKeys {
 		old, err := nvram("get", key)

internal/router/dnsmasq.go

@@ -1,14 +1,22 @@
 package router
 
-const dnsMasqConfigContent = `# GENERATED BY ctrld - DO NOT MODIFY
+import (
+	"strings"
+	"text/template"
+)
+
+const dnsMasqConfigContentTmpl = `# GENERATED BY ctrld - DO NOT MODIFY
 no-resolv
 server=127.0.0.1#5354
+{{- if .SendClientInfo}}
+add-mac
+{{- end}}
 `
 
 const merlinDNSMasqPostConfPath = "/jffs/scripts/dnsmasq.postconf"
 const merlinDNSMasqPostConfMarker = `# GENERATED BY ctrld - EOF`
 
-const merlinDNSMasqPostConf = `# GENERATED BY ctrld - DO NOT MODIFY
+const merlinDNSMasqPostConfTmpl = `# GENERATED BY ctrld - DO NOT MODIFY
 
 #!/bin/sh
 
@@ -20,7 +28,9 @@ if [ -n "$pid" ] && [ -f "/proc/${pid}/cmdline" ]; then
   pc_delete "servers-file" "$config_file"           # no WAN DNS settings
   pc_append "no-resolv" "$config_file"              # do not read /etc/resolv.conf
   pc_append "server=127.0.0.1#5354" "$config_file"  # use ctrld as upstream
-
+  {{- if .SendClientInfo}}
+  pc_append "add-mac" "$config_file"                 # add client mac
+  {{- end}}
 	
   # For John fork
   pc_delete "resolv-file" "$config_file"            # no WAN DNS settings
@@ -32,3 +42,24 @@ if [ -n "$pid" ] && [ -f "/proc/${pid}/cmdline" ]; then
   exit 0
 fi
 `
+
+func dnsMasqConf() (string, error) {
+	var sb strings.Builder
+	var tmplText string
+	switch Name() {
+	case DDWrt, OpenWrt, Ubios:
+		tmplText = dnsMasqConfigContentTmpl
+	case Merlin:
+		tmplText = merlinDNSMasqPostConfTmpl
+	}
+	tmpl := template.Must(template.New("").Parse(tmplText))
+	var to = &struct {
+		SendClientInfo bool
+	}{
+		routerPlatform.Load().sendClientInfo,
+	}
+	if err := tmpl.Execute(&sb, to); err != nil {
+		return "", err
+	}
+	return sb.String(), nil
+}

internal/router/merlin.go

@@ -19,6 +19,10 @@ func setupMerlin() error {
 		return err
 	}
 
+	merlinDNSMasqPostConf, err := dnsMasqConf()
+	if err != nil {
+		return err
+	}
 	data := strings.Join([]string{
 		merlinDNSMasqPostConf,
 		"\n",
@@ -38,7 +42,7 @@ func setupMerlin() error {
 }
 
 func cleanupMerlin() error {
-	buf, err := os.ReadFile(merlinDNSMasqPostConf)
+	buf, err := os.ReadFile(merlinDNSMasqPostConfPath)
 	if err != nil && !os.IsNotExist(err) {
 		return err
 	}

internal/router/merlin_test.go

@@ -9,7 +9,7 @@ import (
 func Test_merlinParsePostConf(t *testing.T) {
 	origContent := "# foo"
 	data := strings.Join([]string{
-		merlinDNSMasqPostConf,
+		merlinDNSMasqPostConfTmpl,
 		"\n",
 		merlinDNSMasqPostConfMarker,
 		"\n",

internal/router/openwrt.go

@@ -19,6 +19,10 @@ func setupOpenWrt() error {
 		return err
 	}
 	// Disable dnsmasq as DNS server.
+	dnsMasqConfigContent, err := dnsMasqConf()
+	if err != nil {
+		return err
+	}
 	if err := os.WriteFile(openwrtDNSMasqConfigPath, []byte(dnsMasqConfigContent), 0600); err != nil {
 		return err
 	}

internal/router/router.go

@@ -5,8 +5,10 @@ import (
 	"errors"
 	"os"
 	"os/exec"
+	"sync"
 	"sync/atomic"
 
+	"github.com/fsnotify/fsnotify"
 	"github.com/kardianos/service"
 
 	"github.com/Control-D-Inc/ctrld"
@@ -25,7 +27,10 @@ var ErrNotSupported = errors.New("unsupported platform")
 var routerPlatform atomic.Pointer[router]
 
 type router struct {
-	name string
+	name           string
+	sendClientInfo bool
+	mac            sync.Map
+	watcher        *fsnotify.Watcher
 }
 
 // SupportedPlatforms return all platforms that can be configured to run with ctrld.
@@ -33,18 +38,37 @@ func SupportedPlatforms() []string {
 	return []string{DDWrt, Merlin, OpenWrt, Ubios}
 }
 
+var configureFunc = map[string]func() error{
+	DDWrt:   setupDDWrt,
+	Merlin:  setupMerlin,
+	OpenWrt: setupOpenWrt,
+	Ubios:   setupUbiOS,
+}
+
 // Configure configures things for running ctrld on the router.
 func Configure(c *ctrld.Config) error {
 	name := Name()
 	switch name {
-	case DDWrt:
-		return setupDDWrt()
-	case Merlin:
-		return setupMerlin()
-	case OpenWrt:
-		return setupOpenWrt()
-	case Ubios:
-		return setupUbiOS()
+	case DDWrt, Merlin, OpenWrt, Ubios:
+		if c.HasUpstreamSendClientInfo() {
+			r := routerPlatform.Load()
+			r.sendClientInfo = true
+			watcher, err := fsnotify.NewWatcher()
+			if err != nil {
+				return err
+			}
+			r.watcher = watcher
+			go r.watchClientInfoTable()
+			for _, file := range clientInfoFiles {
+				_ = readClientInfoFile(file)
+				_ = r.watcher.Add(file)
+			}
+		}
+		configure := configureFunc[name]
+		if err := configure(); err != nil {
+			return err
+		}
+		return nil
 	default:
 		return ErrNotSupported
 	}

internal/router/ubios.go

@@ -12,6 +12,10 @@ const (
 
 func setupUbiOS() error {
 	// Disable dnsmasq as DNS server.
+	dnsMasqConfigContent, err := dnsMasqConf()
+	if err != nil {
+		return err
+	}
 	if err := os.WriteFile(ubiosDNSMasqConfigPath, []byte(dnsMasqConfigContent), 0600); err != nil {
 		return err
 	}