Add support for Prometheus exporter

exporters/autoexport/go.mod

@@ -14,15 +14,23 @@ require (
 )
 
 require (
+	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/cenkalti/backoff/v4 v4.2.1 // indirect
+	github.com/cespare/xxhash/v2 v2.2.0 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/go-logr/logr v1.2.4 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/golang/protobuf v1.5.3 // indirect
 	github.com/grpc-ecosystem/grpc-gateway/v2 v2.16.0 // indirect
+	github.com/matttproud/golang_protobuf_extensions v1.0.4 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/prometheus/client_golang v1.16.0 // indirect
+	github.com/prometheus/client_model v0.4.0 // indirect
+	github.com/prometheus/common v0.42.0 // indirect
+	github.com/prometheus/procfs v0.10.1 // indirect
 	go.opentelemetry.io/otel v1.19.0 // indirect
 	go.opentelemetry.io/otel/exporters/otlp/otlpmetric v0.42.0 // indirect
+	go.opentelemetry.io/otel/exporters/prometheus v0.42.0
 	go.opentelemetry.io/otel/metric v1.19.0 // indirect
 	go.opentelemetry.io/otel/trace v1.19.0 // indirect
 	go.opentelemetry.io/proto/otlp v1.0.0 // indirect

exporters/autoexport/go.sum

@@ -1,5 +1,9 @@
+github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
+github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
 github.com/cenkalti/backoff/v4 v4.2.1 h1:y4OZtCnogmCPw98Zjyt5a6+QwPLGkiQsYW5oUqylYbM=
 github.com/cenkalti/backoff/v4 v4.2.1/go.mod h1:Y3VNntkOUPxTVeUxJ/G5vcM//AlwfmyYozVcomhLiZE=
+github.com/cespare/xxhash/v2 v2.2.0 h1:DC2CZ1Ep5Y4k3ZQ899DldepgrayRUGE6BBZ/cd9Cj44=
+github.com/cespare/xxhash/v2 v2.2.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/go-logr/logr v1.2.2/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbVz/1A=
@@ -8,6 +12,7 @@ github.com/go-logr/logr v1.2.4/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbV
 github.com/go-logr/stdr v1.2.2 h1:hSWxHoqTgW2S2qGc0LTAI563KZ5YKYRhT3MFKZMbjag=
 github.com/go-logr/stdr v1.2.2/go.mod h1:mMo/vtBO5dYbehREoey6XUKy/eSumjCCveDpRre4VKE=
 github.com/golang/glog v1.1.2 h1:DVjP2PbBOzHyzA+dn3WhHIq4NdVu3Q+pvivFICf/7fo=
+github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
 github.com/golang/protobuf v1.5.0/go.mod h1:FsONVRAS9T7sI+LIUmWTfcYkHO4aIWwzhcaSAoJOfIk=
 github.com/golang/protobuf v1.5.3 h1:KhyjKVUg7Usr/dYsdSqoFveMYd5ko72D+zANwlG1mmg=
 github.com/golang/protobuf v1.5.3/go.mod h1:XVQd3VNwM+JqD3oG2Ue2ip4fOMUkwXdXDdiuN0vRsmY=
@@ -17,8 +22,18 @@ github.com/grpc-ecosystem/grpc-gateway/v2 v2.16.0 h1:YBftPWNWd4WwGqtY2yeZL2ef8rH
 github.com/grpc-ecosystem/grpc-gateway/v2 v2.16.0/go.mod h1:YN5jB8ie0yfIUg6VvR9Kz84aCaG7AsGZnLjhHbUqwPg=
 github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
 github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
+github.com/matttproud/golang_protobuf_extensions v1.0.4 h1:mmDVorXM7PCGKw94cs5zkfA9PSy5pEvNWRP0ET0TIVo=
+github.com/matttproud/golang_protobuf_extensions v1.0.4/go.mod h1:BSXmuO+STAnVfrANrmjBb36TMTDstsz7MSK+HVaYKv4=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/prometheus/client_golang v1.16.0 h1:yk/hx9hDbrGHovbci4BY+pRMfSuuat626eFsHb7tmT8=
+github.com/prometheus/client_golang v1.16.0/go.mod h1:Zsulrv/L9oM40tJ7T815tM89lFEugiJ9HzIqaAx4LKc=
+github.com/prometheus/client_model v0.4.0 h1:5lQXD3cAg1OXBf4Wq03gTrXHeaV0TQvGfUooCfx1yqY=
+github.com/prometheus/client_model v0.4.0/go.mod h1:oMQmHW1/JoDwqLtg57MGgP/Fb1CJEYF2imWWhWtMkYU=
+github.com/prometheus/common v0.42.0 h1:EKsfXEYo4JpWMHH5cg+KOUWeuJSov1Id8zGR8eeI1YM=
+github.com/prometheus/common v0.42.0/go.mod h1:xBwqVerjNdUDjgODMpudtOMwlOwf2SaTr1yjz4b7Zbc=
+github.com/prometheus/procfs v0.10.1 h1:kYK1Va/YMlutzCGazswoHKo//tZVlFpKYh+PymziUAg=
+github.com/prometheus/procfs v0.10.1/go.mod h1:nwNm2aOCAYw8uTR/9bWRREkZFxAUcWzPHWJq+XBB/FM=
 github.com/rogpeppe/go-internal v1.10.0 h1:TMyTOH3F/DB16zRVcYyreMH6GnZZrwQVAoYjRBZyWFQ=
 github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=
 github.com/stretchr/testify v1.8.4/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXlSw2iwfAo=
@@ -36,6 +51,8 @@ go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.19.0 h1:3d+S2
 go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.19.0/go.mod h1:0+KuTDyKL4gjKCF75pHOX4wuzYDUZYfAQdSu43o+Z2I=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.19.0 h1:IeMeyr1aBvBiPVYihXIaeIZba6b8E1bYp7lbdxK8CQg=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.19.0/go.mod h1:oVdCUtjq9MK9BlS7TtucsQwUcXcymNiEDjgDD2jMtZU=
+go.opentelemetry.io/otel/exporters/prometheus v0.42.0 h1:jwV9iQdvp38fxXi8ZC+lNpxjK16MRcZlpDYvbuO1FiA=
+go.opentelemetry.io/otel/exporters/prometheus v0.42.0/go.mod h1:f3bYiqNqhoPxkvI2LrXqQVC546K7BuRDL/kKuxkujhA=
 go.opentelemetry.io/otel/metric v1.19.0 h1:aTzpGtV0ar9wlV4Sna9sdJyII5jTVJEvKETPiOKwvpE=
 go.opentelemetry.io/otel/metric v1.19.0/go.mod h1:L5rUsV9kM1IxCj1MmSdS+JQAcVm319EUrDVLrt7jqt8=
 go.opentelemetry.io/otel/sdk v1.19.0 h1:6USY6zH+L8uMH8L3t1enZPR3WFEmSTADlqldyHtJi3o=
@@ -49,6 +66,7 @@ go.opentelemetry.io/proto/otlp v1.0.0/go.mod h1:Sy6pihPLfYHkr3NkUbEhGHFhINUSI/v8
 go.uber.org/goleak v1.2.1 h1:NBol2c7O1ZokfZ0LEU9K6Whx/KnwvepVetCUhtKja4A=
 golang.org/x/net v0.17.0 h1:pVaXccu2ozPjCXewfr1S7xza/zcXTity9cCdXQYSjIM=
 golang.org/x/net v0.17.0/go.mod h1:NxSsAGuq816PNPmqtQdLE42eU2Fs7NoRIZrHJAlaCOE=
+golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.13.0 h1:Af8nKPmuFypiUBjVoU9V20FiaFXOcuZI21p0ycVYYGE=
 golang.org/x/sys v0.13.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/text v0.13.0 h1:ablQoSUd0tRdKxZewP80B+BaqeKJuVhuRxj/dkrun3k=

exporters/autoexport/metrics.go

@@ -16,10 +16,16 @@ package autoexport // import "go.opentelemetry.io/contrib/exporters/autoexport"
 
 import (
 	"context"
+	"log"
+	"net/http"
 	"os"
+	"time"
 
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc"
 	"go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp"
+	promexporter "go.opentelemetry.io/otel/exporters/prometheus"
 	"go.opentelemetry.io/otel/sdk/metric"
 )
 
@@ -94,4 +100,53 @@ func init() {
 	RegisterMetricReader("none", func(ctx context.Context) (metric.Reader, error) {
 		return newNoopMetricReader(), nil
 	})
+	RegisterMetricReader("prometheus", func(ctx context.Context) (metric.Reader, error) {
+		// variable names and defaults specified at https://opentelemetry.io/docs/specs/otel/configuration/sdk-environment-variables/#prometheus-exporter
+		host := getenv("OTEL_EXPORTER_PROMETHEUS_HOST", "localhost")
+		port := getenv("OTEL_EXPORTER_PROMETHEUS_PORT", "9464")
+
+		mux := http.NewServeMux()
+		reg := prometheus.NewRegistry()
+		mux.Handle("/metrics", promhttp.HandlerFor(reg, promhttp.HandlerOpts{Registry: reg}))
+
+		// Timeouts are necessary to make a server resilent to attacks, but
+		// ListenAndServe doesn't set any. We use timeout values from this example: https://blog.cloudflare.com/exposing-go-on-the-internet/#:~:text=There%20are%20three%20main%20timeouts
+		// TODO: find defaults with a better justification, and/or make these configurable
+		go serve(ctx, &http.Server{
+			Addr:         host + ":" + port,
+			ReadTimeout:  5 * time.Second,
+			WriteTimeout: 10 * time.Second,
+			IdleTimeout:  120 * time.Second,
+			Handler:      mux,
+		})
+
+		return promexporter.New(promexporter.WithRegisterer(reg))
+	})
+}
+
+func serve(ctx context.Context, server *http.Server) {
+	serverErr := make(chan error, 1)
+	go func() {
+		serverErr <- server.ListenAndServe()
+	}()
+
+	var err error
+	select {
+	case <-ctx.Done():
+		err = server.Close()
+	case err = <-serverErr:
+	}
+
+	if err != nil && err != http.ErrServerClosed {
+		log.Printf("error closing Prometheus HTTP server: %v", err)
+	}
+
+}
+
+func getenv(key, fallback string) string {
+	result := os.Getenv(key)
+	if result == "" {
+		return fallback
+	}
+	return result
 }

exporters/autoexport/metrics_test.go

@@ -17,9 +17,12 @@ package autoexport // import "go.opentelemetry.io/contrib/exporters/autoexport"
 import (
 	"context"
 	"fmt"
+	"io"
+	"net/http"
 	"reflect"
 	"testing"
 
+	"go.opentelemetry.io/otel/exporters/prometheus"
 	"go.opentelemetry.io/otel/sdk/metric"
 
 	"github.com/stretchr/testify/assert"
@@ -29,6 +32,9 @@ func TestMetricExporterNone(t *testing.T) {
 	t.Setenv("OTEL_METRICS_EXPORTER", "none")
 	got, err := NewMetricReader(context.Background())
 	assert.NoError(t, err)
+	t.Cleanup(func() {
+		assert.NoError(t, got.Shutdown(context.Background()))
+	})
 	assert.True(t, IsNoneMetricReader(got))
 }
 
@@ -47,6 +53,9 @@ func TestMetricExporterOTLP(t *testing.T) {
 
 			got, err := NewMetricReader(context.Background())
 			assert.NoError(t, err)
+			t.Cleanup(func() {
+				assert.NoError(t, got.Shutdown(context.Background()))
+			})
 			assert.IsType(t, &metric.PeriodicReader{}, got)
 
 			// Implementation detail hack. This may break when bumping OTLP exporter modules as it uses unexported API.
@@ -63,3 +72,24 @@ func TestMetricExporterOTLPOverInvalidProtocol(t *testing.T) {
 	_, err := NewMetricReader(context.Background())
 	assert.Error(t, err)
 }
+
+func TestMetricExporterPrometheus(t *testing.T) {
+	t.Setenv("OTEL_METRICS_EXPORTER", "prometheus")
+	t.Setenv("OTEL_EXPORTER_PROMETHEUS_PORT", "12345")
+
+	r, err := NewMetricReader(context.Background())
+	assert.NoError(t, err)
+	t.Cleanup(func() {
+		assert.NoError(t, r.Shutdown(context.Background()))
+	})
+
+	if _, ok := r.(*prometheus.Exporter); !ok {
+		t.Errorf("expected *prometheus.Exporter but got %v", r)
+	}
+
+	resp, err := http.Get("http://localhost:12345/metrics")
+	assert.NoError(t, err)
+	body, err := io.ReadAll(resp.Body)
+	assert.NoError(t, err)
+	assert.Contains(t, string(body), "# HELP")
+}

exporters/autoexport/spans_test.go

@@ -29,6 +29,9 @@ func TestSpanExporterNone(t *testing.T) {
 	t.Setenv("OTEL_TRACES_EXPORTER", "none")
 	got, err := NewSpanExporter(context.Background())
 	assert.NoError(t, err)
+	t.Cleanup(func() {
+		assert.NoError(t, got.Shutdown(context.Background()))
+	})
 	assert.True(t, IsNoneSpanExporter(got))
 }
 
@@ -47,6 +50,9 @@ func TestSpanExporterOTLP(t *testing.T) {
 
 			got, err := NewSpanExporter(context.Background())
 			assert.NoError(t, err)
+			t.Cleanup(func() {
+				assert.NoError(t, got.Shutdown(context.Background()))
+			})
 			assert.IsType(t, &otlptrace.Exporter{}, got)
 
 			// Implementation detail hack. This may break when bumping OTLP exporter modules as it uses unexported API.