monitoring: add monitoring package for Prometheus metric exports.

monitoring/log.go

@@ -0,0 +1,45 @@
+package monitoring
+
+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("PROM", 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
+}
+
+// logClosure is used to provide a closure over expensive logging operations so
+// don't have to be performed when the logging level doesn't warrant it.
+type logClosure func() string
+
+// String invokes the underlying function and returns the result.
+func (c logClosure) String() string {
+	return c()
+}
+
+// newLogClosure returns a new closure over a function that returns a string
+// which itself provides a Stringer interface so that it can be used with the
+// logging system.
+func newLogClosure(c func() string) logClosure {
+	return logClosure(c)
+}

monitoring/monitoring_off.go

@@ -0,0 +1,25 @@
+// +build !monitoring
+
+package monitoring
+
+import (
+	"fmt"
+
+	"google.golang.org/grpc"
+
+	"github.com/lightningnetwork/lnd/lncfg"
+)
+
+// GetPromInterceptors returns the set of interceptors for Prometheus
+// monitoring if monitoring is enabled, else empty slices. Monitoring is
+// currently disabled.
+func GetPromInterceptors() ([]grpc.UnaryServerInterceptor, []grpc.StreamServerInterceptor) {
+	return []grpc.UnaryServerInterceptor{}, []grpc.StreamServerInterceptor{}
+}
+
+// ExportPrometheusMetrics is required for lnd to compile so that Prometheus
+// metric exporting can be hidden behind a build tag.
+func ExportPrometheusMetrics(_ *grpc.Server, _ lncfg.Prometheus) error {
+	return fmt.Errorf("lnd must be built with the monitoring tag to " +
+		"enable exporting Prometheus metrics")
+}

monitoring/monitoring_on.go

@@ -0,0 +1,45 @@
+// +build monitoring
+
+package monitoring
+
+import (
+	"net/http"
+	"sync"
+
+	"google.golang.org/grpc"
+
+	"github.com/grpc-ecosystem/go-grpc-prometheus"
+	"github.com/lightningnetwork/lnd/lncfg"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+var started sync.Once
+
+// GetPromInterceptors returns the set of interceptors for Prometheus
+// monitoring.
+func GetPromInterceptors() ([]grpc.UnaryServerInterceptor, []grpc.StreamServerInterceptor) {
+	unaryInterceptors := []grpc.UnaryServerInterceptor{
+		grpc_prometheus.UnaryServerInterceptor,
+	}
+	streamInterceptors := []grpc.StreamServerInterceptor{
+		grpc_prometheus.StreamServerInterceptor,
+	}
+	return unaryInterceptors, streamInterceptors
+}
+
+// ExportPrometheusMetrics sets server options, registers gRPC metrics and
+// launches the Prometheus exporter on the specified address.
+func ExportPrometheusMetrics(grpcServer *grpc.Server, cfg lncfg.Prometheus) error {
+	started.Do(func() {
+		log.Infof("Prometheus exporter started on %v/metrics", cfg.Listen)
+
+		grpc_prometheus.Register(grpcServer)
+
+		http.Handle("/metrics", promhttp.Handler())
+		go func() {
+			http.ListenAndServe(cfg.Listen, nil)
+		}()
+	})
+
+	return nil
+}