peernotifier: Add peer notifier package for peer online/offline events

This commit adds a peer notifier package which provides clients with
a subscription to peer online and offline events.

log.go

@@ -31,6 +31,7 @@ import (
 	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/monitoring"
 	"github.com/lightningnetwork/lnd/netann"
+	"github.com/lightningnetwork/lnd/peernotifier"
 	"github.com/lightningnetwork/lnd/routing"
 	"github.com/lightningnetwork/lnd/signal"
 	"github.com/lightningnetwork/lnd/sweep"
@@ -90,6 +91,7 @@ var (
 	chbuLog = build.NewSubLogger("CHBU", backendLog.Logger)
 	promLog = build.NewSubLogger("PROM", backendLog.Logger)
 	wtclLog = build.NewSubLogger("WTCL", backendLog.Logger)
+	prnfLog = build.NewSubLogger("PRNF", backendLog.Logger)
 )
 
 // Initialize package-global logger variables.
@@ -119,6 +121,7 @@ func init() {
 	chanbackup.UseLogger(chbuLog)
 	monitoring.UseLogger(promLog)
 	wtclient.UseLogger(wtclLog)
+	peernotifier.UseLogger(prnfLog)
 
 	addSubLogger(routerrpc.Subsystem, routerrpc.UseLogger)
 	addSubLogger(wtclientrpc.Subsystem, wtclientrpc.UseLogger)
@@ -165,6 +168,7 @@ var subsystemLoggers = map[string]btclog.Logger{
 	"CHBU": chbuLog,
 	"PROM": promLog,
 	"WTCL": wtclLog,
+	"PRNF": prnfLog,
 }
 
 // initLogRotator initializes the logging rotator to write logs to logFile and

peernotifier/log.go

@@ -0,0 +1,29 @@
+package peernotifier
+
+import (
+	"github.com/btcsuite/btclog"
+	"github.com/lightningnetwork/lnd/build"
+)
+
+// log is a logger that is initialized with no output filters.  This
+// means the package will not perform any logging by default until the caller
+// requests it.
+var log btclog.Logger
+
+// The default amount of logging is none.
+func init() {
+	UseLogger(build.NewSubLogger("PRNF", nil))
+}
+
+// DisableLog disables all library log output.  Logging output is disabled
+// by default until UseLogger is called.
+func DisableLog() {
+	UseLogger(btclog.Disabled)
+}
+
+// UseLogger uses a specified Logger to output package logging info.
+// This should be used in preference to SetLogWriter if the caller is also
+// using btclog.
+func UseLogger(logger btclog.Logger) {
+	log = logger
+}

peernotifier/peernotifier.go

@@ -0,0 +1,87 @@
+package peernotifier
+
+import (
+	"sync"
+
+	"github.com/lightningnetwork/lnd/subscribe"
+)
+
+// PeerNotifier is a subsystem which observes peer offline and online events.
+// It takes subscriptions for its events, and whenever it observes a new event
+// it notifies its subscribers over the proper channel.
+type PeerNotifier struct {
+	started sync.Once
+	stopped sync.Once
+
+	ntfnServer *subscribe.Server
+}
+
+// PeerOnlineEvent represents a new event where a peer comes online.
+type PeerOnlineEvent struct {
+	// PubKey is the peer's compressed public key.
+	PubKey [33]byte
+}
+
+// PeerOfflineEvent represents a new event where a peer goes offline.
+type PeerOfflineEvent struct {
+	// PubKey is the peer's compressed public key.
+	PubKey [33]byte
+}
+
+// New creates a new peer notifier which notifies clients of peer online
+// and offline events.
+func New() *PeerNotifier {
+	return &PeerNotifier{
+		ntfnServer: subscribe.NewServer(),
+	}
+}
+
+// Start starts the PeerNotifier's subscription server.
+func (p *PeerNotifier) Start() error {
+	var err error
+
+	p.started.Do(func() {
+		log.Info("PeerNotifier starting")
+		err = p.ntfnServer.Start()
+	})
+
+	return err
+}
+
+// Stop signals the notifier for a graceful shutdown.
+func (p *PeerNotifier) Stop() {
+	p.stopped.Do(func() {
+		log.Info("Stopping PeerNotifier")
+		p.ntfnServer.Stop()
+	})
+}
+
+// SubscribePeerEvents returns a subscribe.Client that will receive updates
+// any time the Server is informed of a peer event.
+func (p *PeerNotifier) SubscribePeerEvents() (*subscribe.Client, error) {
+	return p.ntfnServer.Subscribe()
+}
+
+// NotifyPeerOnline sends a peer online event to all clients subscribed to the
+// peer notifier.
+func (p *PeerNotifier) NotifyPeerOnline(pubKey [33]byte) {
+	event := PeerOnlineEvent{PubKey: pubKey}
+
+	log.Debugf("PeerNotifier notifying peer: %x online", pubKey)
+
+	if err := p.ntfnServer.SendUpdate(event); err != nil {
+		log.Warnf("Unable to send peer online update: %v", err)
+	}
+}
+
+// NotifyPeerOffline sends a peer offline event to all the clients subscribed
+// to the peer notifier.
+func (p *PeerNotifier) NotifyPeerOffline(pubKey [33]byte) {
+	event := PeerOfflineEvent{PubKey: pubKey}
+
+	log.Debugf("PeerNotifier notifying peer: %x offline", pubKey)
+
+	if err := p.ntfnServer.SendUpdate(event); err != nil {
+		log.Warnf("Unable to send peer offline update: %v", err)
+	}
+}

server.go

@@ -44,6 +44,7 @@ import (
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/nat"
 	"github.com/lightningnetwork/lnd/netann"
+	"github.com/lightningnetwork/lnd/peernotifier"
 	"github.com/lightningnetwork/lnd/pool"
 	"github.com/lightningnetwork/lnd/routing"
 	"github.com/lightningnetwork/lnd/routing/route"
@@ -188,6 +189,8 @@ type server struct {
 
 	channelNotifier *channelnotifier.ChannelNotifier
 
+	peerNotifier *peernotifier.PeerNotifier
+
 	witnessBeacon contractcourt.WitnessBeacon
 
 	breachArbiter *breachArbiter
@@ -1081,6 +1084,10 @@ func newServer(listenAddrs []net.Addr, chanDB *channeldb.DB,
 		return nil, err
 	}
 
+	// Assemble a peer notifier which will provide clients with subscriptions
+	// to peer online and offline events.
+	s.peerNotifier = peernotifier.New()
+
 	if cfg.WtClient.Active {
 		policy := wtpolicy.DefaultPolicy()
 
@@ -1183,6 +1190,10 @@ func (s *server) Start() error {
 			startErr = err
 			return
 		}
+		if err := s.peerNotifier.Start(); err != nil {
+			startErr = err
+			return
+		}
 		if err := s.sphinx.Start(); err != nil {
 			startErr = err
 			return
@@ -1341,6 +1352,7 @@ func (s *server) Stop() error {
 		s.chainArb.Stop()
 		s.sweeper.Stop()
 		s.channelNotifier.Stop()
+		s.peerNotifier.Stop()
 		s.cc.wallet.Shutdown()
 		s.cc.chainView.Stop()
 		s.connMgr.Stop()
@@ -2713,7 +2725,8 @@ func (s *server) addPeer(p *peer) {
 	// TODO(roasbeef): pipe all requests through to the
 	// queryHandler/peerManager
 
-	pubStr := string(p.addr.IdentityKey.SerializeCompressed())
+	pubSer := p.addr.IdentityKey.SerializeCompressed()
+	pubStr := string(pubSer)
 
 	s.peersByPub[pubStr] = p
 
@@ -2722,6 +2735,13 @@ func (s *server) addPeer(p *peer) {
 	} else {
 		s.outboundPeers[pubStr] = p
 	}
+
+	// Inform the peer notifier of a peer online event so that it can be reported
+	// to clients listening for peer events.
+	var pubKey [33]byte
+	copy(pubKey[:], pubSer)
+
+	s.peerNotifier.NotifyPeerOnline(pubKey)
 }
 
 // peerInitializer asynchronously starts a newly connected peer after it has
@@ -2963,7 +2983,8 @@ func (s *server) removePeer(p *peer) {
 		return
 	}
 
-	pubStr := string(p.addr.IdentityKey.SerializeCompressed())
+	pubSer := p.addr.IdentityKey.SerializeCompressed()
+	pubStr := string(pubSer)
 
 	delete(s.peersByPub, pubStr)
 
@@ -2972,6 +2993,13 @@ func (s *server) removePeer(p *peer) {
 	} else {
 		delete(s.outboundPeers, pubStr)
 	}
+
+	// Inform the peer notifier of a peer offline event so that it can be
+	// reported to clients listening for peer events.
+	var pubKey [33]byte
+	copy(pubKey[:], pubSer)
+
+	s.peerNotifier.NotifyPeerOffline(pubKey)
 }
 
 // openChanReq is a message sent to the server in order to request the