Add hosts file as source for hostname resolver

config.go

@@ -178,6 +178,7 @@ type ServiceConfig struct {
 	DiscoverARP           *bool  `mapstructure:"discover_arp" toml:"discover_dhcp,omitempty"`
 	DiscoverDHCP          *bool  `mapstructure:"discover_dhcp" toml:"discover_dhcp,omitempty"`
 	DiscoverPtr           *bool  `mapstructure:"discover_ptr" toml:"discover_ptr,omitempty"`
+	DiscoverHosts         *bool  `mapstructure:"discover_hosts" toml:"discover_hosts,omitempty"`
 	Daemon                bool   `mapstructure:"-" toml:"-"`
 	AllocateIP            bool   `mapstructure:"-" toml:"-"`
 }

docs/config.md

@@ -193,6 +193,13 @@ Perform LAN client discovery using PTR queries.
 - Required: no
 - Default: true
 
+### discover_hosts
+Perform LAN client discovery using hosts file.
+
+- Type: boolean
+- Required: no
+- Default: true
+
 ### dhcp_lease_file_path
 Relative or absolute path to a custom DHCP leases file location. 
 

go.mod

@@ -23,6 +23,7 @@ require (
 	github.com/spf13/pflag v1.0.5
 	github.com/spf13/viper v1.16.0
 	github.com/stretchr/testify v1.8.3
+	github.com/txn2/txeh v1.5.3
 	github.com/vishvananda/netlink v1.2.1-beta.2
 	go4.org/mem v0.0.0-20220726221520-4f986261bf13
 	golang.org/x/net v0.10.0

go.sum

@@ -270,6 +270,8 @@ github.com/stretchr/testify v1.8.3 h1:RP3t2pwF7cMEbC1dqtB6poj3niw/9gnV4Cjg5oW5gt
 github.com/stretchr/testify v1.8.3/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXlSw2iwfAo=
 github.com/subosito/gotenv v1.4.2 h1:X1TuBLAMDFbaTAChgCBLu3DU3UPyELpnF2jjJ2cz/S8=
 github.com/subosito/gotenv v1.4.2/go.mod h1:ayKnFf/c6rvx/2iiLrJUk1e6plDbT3edrFNGqEflhK0=
+github.com/txn2/txeh v1.5.3 h1:ZMgc3r+5/AFtE/ayCoICpvxj7xl/CYsZjnIGhozV/Kc=
+github.com/txn2/txeh v1.5.3/go.mod h1:qYzGG9kCzeVEI12geK4IlanHWY8X4uy/I3NcW7mk8g4=
 github.com/u-root/uio v0.0.0-20230305220412-3e8cd9d6bf63 h1:YcojQL98T/OO+rybuzn2+5KrD5dBwXIvYBvQ2cD3Avg=
 github.com/u-root/uio v0.0.0-20230305220412-3e8cd9d6bf63/go.mod h1:eLL9Nub3yfAho7qB0MzZizFhTU2QkLeoVsWdHtDW264=
 github.com/vishvananda/netlink v1.2.1-beta.2 h1:Llsql0lnQEbHj0I1OuKyp8otXp0r3q0mPkuhwHfStVs=

internal/clientinfo/client_info.go

@@ -73,6 +73,7 @@ type Table struct {
 	arp    *arpDiscover
 	ptr    *ptrDiscover
 	mdns   *mdns
+	hf     *hostsFile
 	cfg    *ctrld.Config
 	quitCh chan struct{}
 	selfIP string
@@ -134,6 +135,17 @@ func (t *Table) init() {
 			t.refreshers = append(t.refreshers, t.merlin)
 		}
 	}
+	if t.discoverHosts() {
+		t.hf = &hostsFile{}
+		ctrld.ProxyLogger.Load().Debug().Msg("start hosts file discovery")
+		if err := t.hf.init(); err != nil {
+			ctrld.ProxyLogger.Load().Error().Err(err).Msg("could not init hosts file discover")
+		} else {
+			t.hostnameResolvers = append(t.hostnameResolvers, t.hf)
+			t.refreshers = append(t.refreshers, t.hf)
+		}
+		go t.hf.watchChanges()
+	}
 	if t.discoverDHCP() {
 		t.dhcp = &dhcp{selfIP: t.selfIP}
 		ctrld.ProxyLogger.Load().Debug().Msg("start dhcp discovery")
@@ -328,6 +340,13 @@ func (t *Table) discoverPTR() bool {
 	return *t.cfg.Service.DiscoverPtr
 }
 
+func (t *Table) discoverHosts() bool {
+	if t.cfg.Service.DiscoverHosts == nil {
+		return true
+	}
+	return *t.cfg.Service.DiscoverHosts
+}
+
 // normalizeIP normalizes the ip parsed from dnsmasq/dhcpd lease file.
 func normalizeIP(in string) string {
 	// dnsmasq may put ip with interface index in lease file, strip it here.

internal/clientinfo/hostsfile.go

@@ -0,0 +1,86 @@
+package clientinfo
+
+import (
+	"os"
+
+	"github.com/fsnotify/fsnotify"
+	"github.com/txn2/txeh"
+
+	"github.com/Control-D-Inc/ctrld"
+)
+
+// hostsFile provides client discovery functionality using system hosts file.
+type hostsFile struct {
+	h       *txeh.Hosts
+	watcher *fsnotify.Watcher
+}
+
+// init performs initialization works, which is necessary before hostsFile can be fully operated.
+func (hf *hostsFile) init() error {
+	h, err := txeh.NewHostsDefault()
+	if err != nil {
+		return err
+	}
+	hf.h = h
+	watcher, err := fsnotify.NewWatcher()
+	if err != nil {
+		return err
+	}
+	hf.watcher = watcher
+	if err := hf.watcher.Add(hf.h.ReadFilePath); err != nil {
+		return err
+	}
+	return nil
+}
+
+// refresh reloads hosts file entries.
+func (hf *hostsFile) refresh() error {
+	return hf.h.Reload()
+}
+
+// watchChanges watches and updates hosts file data if any changes happens.
+func (hf *hostsFile) watchChanges() {
+	if hf.watcher == nil {
+		return
+	}
+	for {
+		select {
+		case event, ok := <-hf.watcher.Events:
+			if !ok {
+				return
+			}
+			if event.Has(fsnotify.Write) || event.Has(fsnotify.Rename) || event.Has(fsnotify.Chmod) || event.Has(fsnotify.Remove) {
+				if err := hf.refresh(); err != nil && !os.IsNotExist(err) {
+					ctrld.ProxyLogger.Load().Err(err).Msg("hosts file changed but failed to update client info")
+				}
+			}
+		case err, ok := <-hf.watcher.Errors:
+			if !ok {
+				return
+			}
+			ctrld.ProxyLogger.Load().Err(err).Msg("could not watch client info file")
+		}
+	}
+
+}
+
+// LookupHostnameByIP returns hostname for given IP from current hosts file entries.
+func (hf *hostsFile) LookupHostnameByIP(ip string) string {
+	hf.h.Lock()
+	defer hf.h.Unlock()
+
+	if names := hf.h.ListHostsByIP(ip); len(names) > 0 {
+		return names[0]
+	}
+	return ""
+}
+
+// LookupHostnameByMac returns hostname for given Mac from current hosts file entries.
+func (hf *hostsFile) LookupHostnameByMac(mac string) string {
+	return ""
+}
+
+// String returns human-readable format of hostsFile.
+func (hf *hostsFile) String() string {
+	return "hosts"
+}