quic: add a WithMetrics option (#1716)

p2p/transport/quic/options.go

@@ -4,6 +4,7 @@ type Option func(opts *config) error
 
 type config struct {
 	disableReuseport bool
+	metrics          bool
 }
 
 func (cfg *config) apply(opts ...Option) error {
@@ -22,3 +23,11 @@ func DisableReuseport() Option {
 		return nil
 	}
 }
+
+// WithMetrics enables Prometheus metrics collection.
+func WithMetrics() Option {
+	return func(cfg *config) error {
+		cfg.metrics = true
+		return nil
+	}
+}

p2p/transport/quic/tracer.go

@@ -13,16 +13,12 @@ import (
 	"github.com/lucas-clemente/quic-go/qlog"
 )
 
-var tracer logging.Tracer
+var qlogTracer logging.Tracer
 
 func init() {
-	tracers := []logging.Tracer{&metricsTracer{}}
 	if qlogDir := os.Getenv("QLOGDIR"); len(qlogDir) > 0 {
-		if qlogger := initQlogger(qlogDir); qlogger != nil {
-			tracers = append(tracers, qlogger)
-		}
+		qlogTracer = initQlogger(qlogDir)
 	}
-	tracer = logging.NewMultiplexedTracer(tracers...)
 }
 
 func initQlogger(qlogDir string) logging.Tracer {

p2p/transport/quic/transport.go

@@ -26,6 +26,7 @@ import (
 
 	logging "github.com/ipfs/go-log/v2"
 	"github.com/lucas-clemente/quic-go"
+	quiclogging "github.com/lucas-clemente/quic-go/logging"
 	"github.com/minio/sha256-simd"
 )
 
@@ -199,7 +200,16 @@ func NewTransport(key ic.PrivKey, psk pnet.PSK, gater connmgr.ConnectionGater, r
 	if _, err := io.ReadFull(keyReader, qconfig.StatelessResetKey); err != nil {
 		return nil, err
 	}
-	qconfig.Tracer = tracer
+	var tracers []quiclogging.Tracer
+	if qlogTracer != nil {
+		tracers = append(tracers, qlogTracer)
+	}
+	if cfg.metrics {
+		tracers = append(tracers, &metricsTracer{})
+	}
+	if len(tracers) > 0 {
+		qconfig.Tracer = quiclogging.NewMultiplexedTracer(tracers...)
+	}
 
 	tr := &transport{
 		privKey:      key,