Add prometheus bridge

.github/dependabot.yml

@@ -64,6 +64,15 @@ updates:
     schedule:
       interval: weekly
       day: sunday
+  - package-ecosystem: gomod
+    directory: /bridge/prometheus
+    labels:
+      - dependencies
+      - go
+      - Skip Changelog
+    schedule:
+      interval: weekly
+      day: sunday
   - package-ecosystem: gomod
     directory: /example/fib
     labels:
@@ -127,6 +136,15 @@ updates:
     schedule:
       interval: weekly
       day: sunday
+  - package-ecosystem: gomod
+    directory: /example/prometheusbridge
+    labels:
+      - dependencies
+      - go
+      - Skip Changelog
+    schedule:
+      interval: weekly
+      day: sunday
   - package-ecosystem: gomod
     directory: /example/view
     labels:

CHANGELOG.md

@@ -17,6 +17,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - OTLP Metrics Exporter now supports the `OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE` environment variable. (#4287)
 - Add `WithoutCounterSuffixes` option in `go.opentelemetry.io/otel/exporters/prometheus` to disable addition of `_total` suffixes. (#4306)
 - Add info and debug logging to the metric SDK. (#4315)
+- Add `go.opentelemetry.io/otel/bridge/prometheus` which can bridge metrics defined using the prometheus client library to OpenTelemetry. (#4351)
 
 ### Changed
 

bridge/prometheus/config.go

@@ -0,0 +1,58 @@
+// Copyright The OpenTelemetry Authors
+//
+// 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 prometheus // import "go.opentelemetry.io/otel/exporters/prometheus"
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+// config contains options for the exporter.
+type config struct {
+	gatherers []prometheus.Gatherer
+}
+
+// newConfig creates a validated config configured with options.
+func newConfig(opts ...Option) config {
+	cfg := config{}
+	for _, opt := range opts {
+		cfg = opt.apply(cfg)
+	}
+
+	if len(cfg.gatherers) == 0 {
+		cfg.gatherers = []prometheus.Gatherer{prometheus.DefaultGatherer}
+	}
+
+	return cfg
+}
+
+// Option sets exporter option values.
+type Option interface {
+	apply(config) config
+}
+
+type optionFunc func(config) config
+
+func (fn optionFunc) apply(cfg config) config {
+	return fn(cfg)
+}
+
+// WithGatherer configures which prometheus Gatherer the Bridge will gather
+// from. If no registerer is used the prometheus DefaultGatherer is used.
+func WithGatherer(gatherer prometheus.Gatherer) Option {
+	return optionFunc(func(cfg config) config {
+		cfg.gatherers = append(cfg.gatherers, gatherer)
+		return cfg
+	})
+}

bridge/prometheus/config_test.go

@@ -0,0 +1,60 @@
+// Copyright The OpenTelemetry Authors
+//
+// 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 prometheus // import "go.opentelemetry.io/otel/bridge/prometheus"
+
+import (
+	"testing"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNewConfig(t *testing.T) {
+	otherRegistry := prometheus.NewRegistry()
+
+	testCases := []struct {
+		name       string
+		options    []Option
+		wantConfig config
+	}{
+		{
+			name:    "Default",
+			options: nil,
+			wantConfig: config{
+				gatherers: []prometheus.Gatherer{prometheus.DefaultGatherer},
+			},
+		},
+		{
+			name:    "With a different gatherer",
+			options: []Option{WithGatherer(otherRegistry)},
+			wantConfig: config{
+				gatherers: []prometheus.Gatherer{otherRegistry},
+			},
+		},
+		{
+			name:    "Multiple gatherers",
+			options: []Option{WithGatherer(otherRegistry), WithGatherer(prometheus.DefaultGatherer)},
+			wantConfig: config{
+				gatherers: []prometheus.Gatherer{otherRegistry, prometheus.DefaultGatherer},
+			},
+		},
+	}
+	for _, tt := range testCases {
+		t.Run(tt.name, func(t *testing.T) {
+			cfg := newConfig(tt.options...)
+			assert.Equal(t, tt.wantConfig, cfg)
+		})
+	}
+}

bridge/prometheus/doc.go

@@ -0,0 +1,16 @@
+// Copyright The OpenTelemetry Authors
+//
+// 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 prometheus provides a bridge from Prometheus to OpenTelemetry.
+package prometheus // import "go.opentelemetry.io/otel/bridge/prometheus"

bridge/prometheus/go.mod

@@ -0,0 +1,40 @@
+module go.opentelemetry.io/otel/exporters/prometheus
+
+go 1.19
+
+require (
+	github.com/prometheus/client_golang v1.16.0
+	github.com/prometheus/client_model v0.4.1-0.20230719122841-95a0733b38a0
+	github.com/stretchr/testify v1.8.4
+	go.opentelemetry.io/otel v1.16.0
+	go.opentelemetry.io/otel/sdk v1.16.0
+	go.opentelemetry.io/otel/sdk/metric v0.39.0
+)
+
+require (
+	github.com/beorn7/perks v1.0.1 // 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/matttproud/golang_protobuf_extensions v1.0.4 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/prometheus/common v0.42.0 // indirect
+	github.com/prometheus/procfs v0.10.1 // indirect
+	go.opentelemetry.io/otel/metric v1.16.0 // indirect
+	go.opentelemetry.io/otel/trace v1.16.0 // indirect
+	golang.org/x/sys v0.10.0 // indirect
+	google.golang.org/protobuf v1.30.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)
+
+replace go.opentelemetry.io/otel => ../..
+
+replace go.opentelemetry.io/otel/sdk => ../../sdk
+
+replace go.opentelemetry.io/otel/sdk/metric => ../../sdk/metric
+
+replace go.opentelemetry.io/otel/trace => ../../trace
+
+replace go.opentelemetry.io/otel/metric => ../../metric

bridge/prometheus/go.sum

@@ -0,0 +1,46 @@
+github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
+github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
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+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
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+github.com/golang/protobuf v1.5.0/go.mod h1:FsONVRAS9T7sI+LIUmWTfcYkHO4aIWwzhcaSAoJOfIk=
+github.com/golang/protobuf v1.5.3 h1:KhyjKVUg7Usr/dYsdSqoFveMYd5ko72D+zANwlG1mmg=
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+github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
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