app/eth2wrap: implement eth2 wrapper for metrics and errors (#359)

Add a `app/eth2wrap` package the contains a `Service` type that wraps `eth2http.Service` by adding prometheus metrics and error wrapping (for proper stack traces). It uses code generation.

category: feature
ticket: #362

app/app.go

@@ -35,6 +35,7 @@ import (
 	"go.uber.org/automaxprocs/maxprocs"
 
 	"github.com/obolnetwork/charon/app/errors"
+	"github.com/obolnetwork/charon/app/eth2wrap"
 	"github.com/obolnetwork/charon/app/lifecycle"
 	"github.com/obolnetwork/charon/app/log"
 	"github.com/obolnetwork/charon/app/retry"
@@ -254,12 +255,13 @@ func wireCoreWorkflow(ctx context.Context, life *lifecycle.Manager, conf Config,
 		if err != nil {
 			return err
 		}
+
 		conf.BeaconNodeAddr = bmock.HTTPAddr()
 		eth2Cl = bmock
 		life.RegisterStop(lifecycle.StopBeaconMock, lifecycle.HookFuncErr(bmock.Close))
 	} else {
 		var err error
-		eth2Cl, err = eth2http.New(ctx,
+		eth2Cl, err = eth2wrap.NewHTTPService(ctx,
 			eth2http.WithLogLevel(1),
 			eth2http.WithAddress(conf.BeaconNodeAddr),
 		)

app/eth2wrap/eth2wrap.go

@@ -0,0 +1,80 @@
+// Copyright © 2021 Obol Technologies Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package eth2wrap provides a wrapper for eth2http.Service adding prometheus metrics and error wrapping.
+package eth2wrap
+
+import (
+	"context"
+	"time"
+
+	eth2http "github.com/attestantio/go-eth2-client/http"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+
+	"github.com/obolnetwork/charon/app/errors"
+)
+
+//go:generate go run genwrap/genwrap.go
+
+var (
+	latencyHist = promauto.NewHistogramVec(prometheus.HistogramOpts{
+		Namespace: "core",
+		Subsystem: "eth2",
+		Name:      "latency_seconds",
+		Help:      "Latency in seconds for eth2 beacon node requests",
+	}, []string{"endpoint"})
+
+	errorCount = promauto.NewCounterVec(prometheus.CounterOpts{
+		Namespace: "core",
+		Subsystem: "eth2",
+		Name:      "errors_total",
+		Help:      "Total number of errors returned by eth2 beacon node requests",
+	}, []string{"endpoint"})
+)
+
+// NewHTTPService returns a new instrumented eth2 http service.
+func NewHTTPService(ctx context.Context, params ...eth2http.Parameter) (*Service, error) {
+	eth2Svc, err := eth2http.New(ctx, params...)
+	if err != nil {
+		return nil, errors.Wrap(err, "new et2http")
+	}
+
+	eth2Cl, ok := eth2Svc.(*eth2http.Service)
+	if !ok {
+		return nil, errors.New("invalid eth2http service")
+	}
+
+	return &Service{Service: eth2Cl}, nil
+}
+
+// Service wraps an eth2http.Service adding prometheus metrics and error wrapping.
+type Service struct {
+	*eth2http.Service
+}
+
+// latency measures endpoint latency.
+// Usage:
+//  defer latency("endpoint")()
+func latency(endpoint string) func() {
+	t0 := time.Now()
+	return func() {
+		latencyHist.WithLabelValues(endpoint).Observe(time.Since(t0).Seconds())
+	}
+}
+
+// incError increments the error counter.
+func incError(endpoint string) {
+	errorCount.WithLabelValues(endpoint).Inc()
+}