Improving Mac discovery

internal/clientinfo/dhcp.go

@@ -0,0 +1,256 @@
+package clientinfo
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"net"
+	"net/netip"
+	"os"
+	"strings"
+	"sync"
+
+	"github.com/Control-D-Inc/ctrld"
+	"tailscale.com/net/interfaces"
+	"tailscale.com/util/lineread"
+
+	"github.com/fsnotify/fsnotify"
+)
+
+type dhcp struct {
+	mac2name sync.Map // mac => name
+	ip2name  sync.Map // ip  => name
+	ip       sync.Map // mac => ip
+	mac      sync.Map // ip  => mac
+
+	watcher *fsnotify.Watcher
+}
+
+func (d *dhcp) refresh() error {
+	watcher, err := fsnotify.NewWatcher()
+	if err != nil {
+		return err
+	}
+	d.addSelf()
+	d.watcher = watcher
+	for file, format := range clientInfoFiles {
+		// Ignore errors for default lease files.
+		_ = d.addLeaseFile(file, format)
+	}
+	return nil
+}
+
+func (d *dhcp) watchChanges() {
+	if d.watcher == nil {
+		return
+	}
+	for {
+		select {
+		case event, ok := <-d.watcher.Events:
+			if !ok {
+				return
+			}
+			if event.Has(fsnotify.Write) {
+				format := clientInfoFiles[event.Name]
+				if err := d.readLeaseFile(event.Name, format); err != nil && !os.IsNotExist(err) {
+					ctrld.ProxyLog.Err(err).Str("file", event.Name).Msg("leases file changed but failed to update client info")
+				}
+			}
+		case err, ok := <-d.watcher.Errors:
+			if !ok {
+				return
+			}
+			ctrld.ProxyLog.Err(err).Msg("could not watch client info file")
+		}
+	}
+
+}
+
+func (d *dhcp) LookupIP(mac string) string {
+	val, ok := d.ip.Load(mac)
+	if !ok {
+		return ""
+	}
+	return val.(string)
+}
+
+func (d *dhcp) LookupMac(ip string) string {
+	val, ok := d.mac.Load(ip)
+	if !ok {
+		return ""
+	}
+	return val.(string)
+}
+
+func (d *dhcp) LookupHostnameByIP(ip string) string {
+	val, ok := d.ip2name.Load(ip)
+	if !ok {
+		return ""
+	}
+	return val.(string)
+}
+
+func (d *dhcp) LookupHostnameByMac(mac string) string {
+	val, ok := d.mac2name.Load(mac)
+	if !ok {
+		return ""
+	}
+	return val.(string)
+}
+
+// AddLeaseFile adds given lease file for reading/watching clients info.
+func (d *dhcp) addLeaseFile(name string, format ctrld.LeaseFileFormat) error {
+	if d.watcher == nil {
+		return nil
+	}
+	if err := d.readLeaseFile(name, format); err != nil {
+		return fmt.Errorf("could not read lease file: %w", err)
+	}
+	clientInfoFiles[name] = format
+	return d.watcher.Add(name)
+}
+
+// readLeaseFile reads the lease file with given format, saving client information to dhcp table.
+func (d *dhcp) readLeaseFile(name string, format ctrld.LeaseFileFormat) error {
+	switch format {
+	case ctrld.Dnsmasq:
+		return d.dnsmasqReadClientInfoFile(name)
+	case ctrld.IscDhcpd:
+		return d.iscDHCPReadClientInfoFile(name)
+	}
+	return fmt.Errorf("unsupported format: %s, file: %s", format, name)
+}
+
+// dnsmasqReadClientInfoFile populates dhcp table with client info reading from dnsmasq lease file.
+func (d *dhcp) dnsmasqReadClientInfoFile(name string) error {
+	f, err := os.Open(name)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	return d.dnsmasqReadClientInfoReader(f)
+
+}
+
+// dnsmasqReadClientInfoReader likes ctrld.Dnsmasq, but reading from an io.Reader instead of file.
+func (d *dhcp) dnsmasqReadClientInfoReader(reader io.Reader) error {
+	return lineread.Reader(reader, func(line []byte) error {
+		fields := bytes.Fields(line)
+		if len(fields) < 4 {
+			return nil
+		}
+
+		mac := string(fields[1])
+		if _, err := net.ParseMAC(mac); err != nil {
+			// The second field is not a dhcp, skip.
+			return nil
+		}
+		ip := normalizeIP(string(fields[2]))
+		if net.ParseIP(ip) == nil {
+			ctrld.ProxyLog.Warn().Msgf("invalid ip address entry: %q", ip)
+			ip = ""
+		}
+
+		d.mac.Store(ip, mac)
+		d.ip.Store(mac, ip)
+		hostname := string(fields[3])
+		if hostname == "*" {
+			return nil
+		}
+		name := normalizeHostname(hostname)
+		d.mac2name.Store(mac, name)
+		d.ip2name.Store(ip, name)
+		return nil
+	})
+}
+
+// iscDHCPReadClientInfoFile populates dhcp table with client info reading from isc-dhcpd lease file.
+func (d *dhcp) iscDHCPReadClientInfoFile(name string) error {
+	f, err := os.Open(name)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	return d.iscDHCPReadClientInfoReader(f)
+}
+
+// iscDHCPReadClientInfoReader likes ctrld.IscDhcpd, but reading from an io.Reader instead of file.
+func (d *dhcp) iscDHCPReadClientInfoReader(reader io.Reader) error {
+	s := bufio.NewScanner(reader)
+	var ip, mac, hostname string
+	for s.Scan() {
+		line := s.Text()
+		if strings.HasPrefix(line, "}") {
+			d.mac.Store(ip, mac)
+			d.ip.Store(mac, ip)
+			if hostname != "" && hostname != "*" {
+				name := normalizeHostname(hostname)
+				d.mac2name.Store(mac, name)
+				d.ip2name.Store(ip, hostname)
+				ip, mac, hostname = "", "", ""
+			}
+			continue
+		}
+		fields := strings.Fields(line)
+		if len(fields) < 2 {
+			continue
+		}
+		switch fields[0] {
+		case "lease":
+			ip = normalizeIP(strings.ToLower(fields[1]))
+			if net.ParseIP(ip) == nil {
+				ctrld.ProxyLog.Warn().Msgf("invalid ip address entry: %q", ip)
+				ip = ""
+			}
+		case "hardware":
+			if len(fields) >= 3 {
+				mac = strings.ToLower(strings.TrimRight(fields[2], ";"))
+				if _, err := net.ParseMAC(mac); err != nil {
+					// Invalid dhcp, skip.
+					mac = ""
+				}
+			}
+		case "client-hostname":
+			hostname = strings.Trim(fields[1], `";`)
+		}
+	}
+	return nil
+}
+
+// addSelf populates current host info to dhcp, so queries from
+// the host itself can be attached with proper client info.
+func (d *dhcp) addSelf() {
+	hostname, err := os.Hostname()
+	if err != nil {
+		ctrld.ProxyLog.Err(err).Msg("could not get hostname")
+		return
+	}
+	hostname = normalizeHostname(hostname)
+	d.ip2name.Store("127.0.0.1", hostname)
+	d.ip2name.Store("::1", hostname)
+	interfaces.ForeachInterface(func(i interfaces.Interface, prefixes []netip.Prefix) {
+		mac := i.HardwareAddr.String()
+		// Skip loopback interfaces, info was stored above.
+		if mac == "" {
+			return
+		}
+		addrs, _ := i.Addrs()
+		for _, addr := range addrs {
+			ipNet, ok := addr.(*net.IPNet)
+			if !ok {
+				continue
+			}
+			ip := ipNet.IP
+			d.mac.Store(ip.String(), mac)
+			d.ip.Store(mac, ip.String())
+			if ip.To4() != nil {
+				d.mac.Store("127.0.0.1", mac)
+			} else {
+				d.mac.Store("::1", mac)
+			}
+			d.mac2name.Store(mac, hostname)
+			d.ip2name.Store(ip.String(), hostname)
+		}
+	})
+}