Add option to emit metrics and logs when players connect to the router (#391)

README.md

@@ -78,6 +78,8 @@ Routes Minecraft client connections to backend servers based upon the requested
     	Indicates if the webhook will only be called if a user is connecting rather than just server list/ping (env WEBHOOK_REQUIRE_USER)
   -webhook-url string
     	If set, a POST request that contains connection status notifications will be sent to this HTTP address (env WEBHOOK_URL)
+  -record-logins
+      Log and generate metrics on player logins. Metrics only supported with influxdb or prometheus backend
 ```
 
 ## Docker Multi-Architecture Image

cmd/mc-router/main.go

@@ -54,6 +54,7 @@ type Config struct {
 	UseProxyProtocol      bool              `default:"false" usage:"Send PROXY protocol to backend servers"`
 	ReceiveProxyProtocol  bool              `default:"false" usage:"Receive PROXY protocol from backend servers, by default trusts every proxy header that it receives, combine with -trusted-proxies to specify a list of trusted proxies"`
 	TrustedProxies        []string          `usage:"Comma delimited list of CIDR notation IP blocks to trust when receiving PROXY protocol"`
+	RecordLogins          bool              `default:"false" usage:"Log and generate metrics on player logins. Metrics only supported with influxdb or prometheus backend"`
 	MetricsBackendConfig  MetricsBackendConfig
 	RoutesConfig          string `usage:"Name or full path to routes config file"`
 	NgrokToken            string `usage:"If set, an ngrok tunnel will be established. It is HIGHLY recommended to pass as an environment variable."`
@@ -142,7 +143,7 @@ func main() {
 		trustedIpNets = append(trustedIpNets, ipNet)
 	}
 
-	connector := server.NewConnector(metricsBuilder.BuildConnectorMetrics(), config.UseProxyProtocol, config.ReceiveProxyProtocol, trustedIpNets)
+	connector := server.NewConnector(metricsBuilder.BuildConnectorMetrics(), config.UseProxyProtocol, config.ReceiveProxyProtocol, trustedIpNets, config.RecordLogins)
 
 	clientFilter, err := server.NewClientFilter(config.ClientsToAllow, config.ClientsToDeny)
 	if err != nil {

cmd/mc-router/metrics.go

@@ -65,6 +65,8 @@ func (b expvarMetricsBuilder) BuildConnectorMetrics() *server.ConnectorMetrics {
 		ConnectionsFrontend: c,
 		ConnectionsBackend:  c,
 		ActiveConnections:   expvarMetrics.NewGauge("active_connections"),
+		ServerActivePlayer:  expvarMetrics.NewGauge("server_active_player"),
+		ServerLogins:        expvarMetrics.NewCounter("server_logins"),
 	}
 }
 
@@ -83,6 +85,8 @@ func (b discardMetricsBuilder) BuildConnectorMetrics() *server.ConnectorMetrics
 		ConnectionsFrontend: discardMetrics.NewCounter(),
 		ConnectionsBackend:  discardMetrics.NewCounter(),
 		ActiveConnections:   discardMetrics.NewGauge(),
+		ServerActivePlayer:  discardMetrics.NewGauge(),
+		ServerLogins:        discardMetrics.NewCounter(),
 	}
 }
 
@@ -132,6 +136,8 @@ func (b *influxMetricsBuilder) BuildConnectorMetrics() *server.ConnectorMetrics
 		ConnectionsFrontend: c.With("side", "frontend"),
 		ConnectionsBackend:  c.With("side", "backend"),
 		ActiveConnections:   metrics.NewGauge("mc_router_connections_active"),
+		ServerActivePlayer:  metrics.NewGauge("mc_router_server_player_active"),
+		ServerLogins:        metrics.NewCounter("mc_router_server_logins"),
 	}
 }
 
@@ -178,5 +184,15 @@ func (b prometheusMetricsBuilder) BuildConnectorMetrics() *server.ConnectorMetri
 			Name:      "active_connections",
 			Help:      "The number of active connections",
 		}, nil)),
+		ServerActivePlayer: prometheusMetrics.NewGauge(promauto.NewGaugeVec(prometheus.GaugeOpts{
+			Namespace: "mc_router",
+			Name:      "server_active_player",
+			Help:      "Player is active on server",
+		}, []string{"player_name", "player_uuid", "server_address"})),
+		ServerLogins: prometheusMetrics.NewCounter(promauto.NewCounterVec(prometheus.CounterOpts{
+			Namespace: "mc_router",
+			Name:      "server_logins",
+			Help:      "The total number of player logins",
+		}, []string{"player_name", "player_uuid", "server_address"})),
 	}
 }

mcproto/read.go

@@ -45,7 +45,8 @@ func ReadPacket(reader *bufio.Reader, addr net.Addr, state State) (*Packet, erro
 		return nil, err
 	}
 
-	packet := &Packet{Length: frame.Length}
+	// Packet length is frame length (bytes for packetID and data) plus bytes used to store the frame length data
+	packet := &Packet{Length: frame.Length + PacketLengthFieldBytes}
 
 	remainder := bytes.NewBuffer(frame.Payload)
 

mcproto/types.go

@@ -80,3 +80,7 @@ type LegacyServerListPing struct {
 type ByteReader interface {
 	ReadByte() (byte, error)
 }
+
+const (
+	PacketLengthFieldBytes = 1
+)

server/connector.go

@@ -34,6 +34,8 @@ type ConnectorMetrics struct {
 	ConnectionsFrontend metrics.Counter
 	ConnectionsBackend  metrics.Counter
 	ActiveConnections   metrics.Gauge
+	ServerActivePlayer  metrics.Gauge
+	ServerLogins        metrics.Counter
 }
 
 type ClientInfo struct {
@@ -57,13 +59,14 @@ type PlayerInfo struct {
 	Uuid uuid.UUID `json:"uuid"`
 }
 
-func NewConnector(metrics *ConnectorMetrics, sendProxyProto bool, receiveProxyProto bool, trustedProxyNets []*net.IPNet) *Connector {
+func NewConnector(metrics *ConnectorMetrics, sendProxyProto bool, receiveProxyProto bool, trustedProxyNets []*net.IPNet, recordLogins bool) *Connector {
 	return &Connector{
 		metrics:           metrics,
 		sendProxyProto:    sendProxyProto,
 		connectionsCond:   sync.NewCond(&sync.Mutex{}),
 		receiveProxyProto: receiveProxyProto,
 		trustedProxyNets:  trustedProxyNets,
+		recordLogins:      recordLogins,
 	}
 }
 
@@ -72,6 +75,7 @@ type Connector struct {
 	metrics           *ConnectorMetrics
 	sendProxyProto    bool
 	receiveProxyProto bool
+	recordLogins      bool
 	trustedProxyNets  []*net.IPNet
 
 	activeConnections int32
@@ -383,9 +387,37 @@ func (c *Connector) findAndConnectBackend(ctx context.Context, frontendConn net.
 
 	c.metrics.ActiveConnections.Set(float64(
 		atomic.AddInt32(&c.activeConnections, 1)))
+	if c.recordLogins && userInfo != nil {
+		logrus.
+			WithField("client", clientAddr).
+			WithField("playerName", userInfo.Name).
+			WithField("playerUUID", userInfo.Uuid).
+			WithField("serverAddress", serverAddress).
+			Info("Player attempted to login to server")
+
+		c.metrics.ServerActivePlayer.
+			With("player_name", userInfo.Name).
+			With("player_uuid", userInfo.Uuid.String()).
+			With("server_address", serverAddress).
+			Set(1)
+
+		c.metrics.ServerLogins.
+			With("player_name", userInfo.Name).
+			With("player_uuid", userInfo.Uuid.String()).
+			With("server_address", serverAddress).
+			Add(1)
+	}
+
 	defer func() {
 		c.metrics.ActiveConnections.Set(float64(
 			atomic.AddInt32(&c.activeConnections, -1)))
+		if c.recordLogins && userInfo != nil {
+			c.metrics.ServerActivePlayer.
+				With("player_name", userInfo.Name).
+				With("player_uuid", userInfo.Uuid.String()).
+				With("server_address", serverAddress).
+				Set(0)
+		}
 		c.connectionsCond.Signal()
 	}()