metrics: add a very basic ConnectionTracer

metrics/connection_tracer.go

@@ -0,0 +1,114 @@
+package metrics
+
+import (
+	"context"
+	"errors"
+	"net"
+	"time"
+
+	"github.com/quic-go/quic-go/logging"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+var (
+	connStarted = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Namespace: metricNamespace,
+			Name:      "connections_started_total",
+			Help:      "Connections Started",
+		},
+		[]string{"dir"},
+	)
+	connClosed = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Namespace: metricNamespace,
+			Name:      "connections_closed_total",
+			Help:      "Connections Closed",
+		},
+		[]string{"dir"},
+	)
+	connDuration = prometheus.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Namespace: metricNamespace,
+			Name:      "connection_duration_seconds",
+			Help:      "Duration of a Connection",
+			Buckets:   prometheus.ExponentialBuckets(1.0/16, 2, 25), // up to 24 days
+		},
+		[]string{"dir"},
+	)
+)
+
+// DefaultTracer returns a callback that creates a metrics ConnectionTracer.
+// The ConnectionTracer returned can be set on the quic.Config for a new connection.
+// It should be reused across QUIC connections.
+func DefaultTracer() func(_ context.Context, p logging.Perspective, _ logging.ConnectionID) *logging.ConnectionTracer {
+	return DefaultTracerWithRegisterer(prometheus.DefaultRegisterer)
+}
+
+// DefaultTracerWithRegisterer returns a callback that creates a metrics ConnectionTracer
+// using a given Prometheus registerer.
+func DefaultTracerWithRegisterer(registerer prometheus.Registerer) func(_ context.Context, p logging.Perspective, _ logging.ConnectionID) *logging.ConnectionTracer {
+	return func(_ context.Context, p logging.Perspective, _ logging.ConnectionID) *logging.ConnectionTracer {
+		switch p {
+		case logging.PerspectiveClient:
+			return NewClientConnectionTracerWithRegisterer(registerer)
+		case logging.PerspectiveServer:
+			return NewServerConnectionTracerWithRegisterer(registerer)
+		default:
+			panic("invalid perspective")
+		}
+	}
+}
+
+// NewClientConnectionTracerWithRegisterer creates a new connection tracer for a connection
+// dialed on the client side with a given Prometheus registerer.
+func NewClientConnectionTracerWithRegisterer(registerer prometheus.Registerer) *logging.ConnectionTracer {
+	return newConnectionTracerWithRegisterer(registerer, true)
+}
+
+// NewServerConnectionTracerWithRegisterer creates a new connection tracer for a connection
+// accepted on the server side with a given Prometheus registerer.
+func NewServerConnectionTracerWithRegisterer(registerer prometheus.Registerer) *logging.ConnectionTracer {
+	return newConnectionTracerWithRegisterer(registerer, false)
+}
+
+func newConnectionTracerWithRegisterer(registerer prometheus.Registerer, isClient bool) *logging.ConnectionTracer {
+	for _, c := range [...]prometheus.Collector{
+		connStarted,
+		connClosed,
+		connDuration,
+	} {
+		if err := registerer.Register(c); err != nil {
+			if ok := errors.As(err, &prometheus.AlreadyRegisteredError{}); !ok {
+				panic(err)
+			}
+		}
+	}
+
+	direction := "incoming"
+	if isClient {
+		direction = "outgoing"
+	}
+
+	var startTime time.Time
+	return &logging.ConnectionTracer{
+		StartedConnection: func(_, _ net.Addr, _, _ logging.ConnectionID) {
+			tags := getStringSlice()
+			defer putStringSlice(tags)
+
+			startTime = time.Now()
+
+			*tags = append(*tags, direction)
+			connStarted.WithLabelValues(*tags...).Inc()
+		},
+		ClosedConnection: func(_ error) {
+			tags := getStringSlice()
+			defer putStringSlice(tags)
+
+			*tags = append(*tags, direction)
+			connDuration.WithLabelValues(*tags...).Observe(time.Since(startTime).Seconds())
+			connClosed.WithLabelValues(*tags...).Inc()
+		},
+	}
+}

metrics/dashboards/README.md

@@ -19,6 +19,18 @@ quic.Transport{
 
 When using multiple `Transport`s, it is recommended to use the metrics tracer struct for all of them.
 
+
+Set a metrics connection tracer on the `Config`:
+```go
+tracer := metrics.DefaultTracer()
+quic.Config{
+	Tracer: tracer,
+}
+```
+
+It is recommended to use the same connection tracer returned by `DefaultTracer` on the `Config`s for all connections.
+
+
 Running:
 ```shell
 docker-compose up

metrics/tracer.go

@@ -83,6 +83,11 @@ func NewTracerWithRegisterer(registerer prometheus.Registerer) *logging.Tracer {
 						break
 					}
 				}
+				// This should never happen. We only send Initials before creating the connection in order to
+				// reject a connection attempt.
+				if ccf == nil {
+					return
+				}
 				if ccf.IsApplicationError {
 					//nolint:exhaustive // Only a few error codes applicable.
 					switch qerr.TransportErrorCode(ccf.ErrorCode) {