Add back the stdoutmetric exporter

.github/dependabot.yml

@@ -127,6 +127,15 @@ updates:
     schedule:
       interval: weekly
       day: sunday
+  - package-ecosystem: gomod
+    directory: /exporters/stdout/stdoutmetric
+    labels:
+      - dependencies
+      - go
+      - Skip Changelog
+    schedule:
+      interval: weekly
+      day: sunday
   - package-ecosystem: gomod
     directory: /exporters/stdout/stdouttrace
     labels:

exporters/stdout/stdoutmetric/config.go

@@ -0,0 +1,66 @@
+// 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.
+
+//go:build go1.18
+// +build go1.18
+
+package stdoutmetric
+
+import (
+	"encoding/json"
+	"os"
+)
+
+// config contains options for the exporter.
+type config struct {
+	encoder *encoderHolder
+}
+
+// newConfig creates a validated config configured with options.
+func newConfig(options ...Option) (config, error) {
+	cfg := config{}
+	for _, opt := range options {
+		cfg = opt.apply(cfg)
+	}
+
+	if cfg.encoder == nil {
+		enc := json.NewEncoder(os.Stdout)
+		enc.SetIndent("", "\t")
+		cfg.encoder = &encoderHolder{encoder: enc}
+	}
+
+	return cfg, nil
+}
+
+// Option sets exporter option values.
+type Option interface {
+	apply(config) config
+}
+
+type optionFunc func(config) config
+
+func (o optionFunc) apply(c config) config {
+	return o(c)
+}
+
+// WithEncoder sets the exporter to use ecoder to encode all the metric
+// data-types to an output.
+func WithEncoder(encoder Encoder) Option {
+	return optionFunc(func(c config) config {
+		if encoder != nil {
+			c.encoder = &encoderHolder{encoder: encoder}
+		}
+		return c
+	})
+}

exporters/stdout/stdoutmetric/doc.go

@@ -0,0 +1,22 @@
+// 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 stdoutmetric provides an exporter for OpenTelemetry metric
+// telemetry.
+//
+// The exporter is intended to be used for testing and debugging. It is not an
+// exporter meant for production use. Additionally, it does not provide an
+// interchange format for OpenTelemetry that is supported with any stability
+// or compatibility guarantees. Please use the OTLP instead.
+package stdoutmetric // import "go.opentelemetry.io/otel/exporters/stdout/stdoutmetric"

exporters/stdout/stdoutmetric/encoder.go

@@ -0,0 +1,49 @@
+// 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.
+
+//go:build go1.18
+// +build go1.18
+
+package stdoutmetric
+
+import "errors"
+
+var ErrUnrecognized = errors.New("unrecognized metric data")
+
+// Encoder encodes and outputs OpenTelemetry metric data-types as human
+// readable text.
+type Encoder interface {
+	// Encode handles the encoding and writing OpenTelemetry metric data-types
+	// that the exporter will pass to it.
+	//
+	// Any data-type that is not recognized by the encoder and not output to
+	// the user, will have an ErrUnrecognized returned from Encode.
+	Encode(v any) error
+}
+
+// encoderHolder is the concrete type used to wrap an Encoder so it can be
+// used as a atomic.Value type.
+type encoderHolder struct {
+	encoder Encoder
+}
+
+func (e encoderHolder) Encode(v any) error { return e.encoder.Encode(v) }
+
+// shutdownEncoder is used when the exporter is shutdown. It always returns
+// errShutdown when Encode is called.
+type shutdownEncoder struct{}
+
+var errShutdown = errors.New("exporter shutdown")
+
+func (shutdownEncoder) Encode(any) error { return errShutdown }

exporters/stdout/stdoutmetric/example_test.go

@@ -0,0 +1,220 @@
+// 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.
+
+//go:build go1.18
+// +build go1.18
+
+package stdoutmetric_test
+
+import (
+	"context"
+	"encoding/json"
+	"os"
+	"time"
+
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/exporters/stdout/stdoutmetric"
+	"go.opentelemetry.io/otel/metric/unit"
+	"go.opentelemetry.io/otel/sdk/instrumentation"
+	"go.opentelemetry.io/otel/sdk/metric/metricdata"
+	"go.opentelemetry.io/otel/sdk/resource"
+	semconv "go.opentelemetry.io/otel/semconv/v1.10.0"
+)
+
+// Sat Jan 01 2000 00:00:00 GMT+0000.
+var now = time.Unix(946684800, 0)
+
+var mockData = metricdata.ResourceMetrics{
+	Resource: resource.NewSchemaless(semconv.ServiceNameKey.String("stdoutmetric-example")),
+	ScopeMetrics: []metricdata.ScopeMetrics{
+		{
+			Scope: instrumentation.Scope{
+				Name:    "example",
+				Version: "v0.0.1",
+			},
+			Metrics: []metricdata.Metrics{
+				{
+					Name:        "requests",
+					Description: "Number of requests received",
+					Unit:        unit.Dimensionless,
+					Data: metricdata.Sum[int64]{
+						IsMonotonic: true,
+						Temporality: metricdata.DeltaTemporality,
+						DataPoints: []metricdata.DataPoint[int64]{
+							{
+								Attributes: attribute.NewSet(attribute.String("server", "central")),
+								StartTime:  now,
+								Time:       now.Add(1 * time.Second),
+								Value:      5,
+							},
+						},
+					},
+				},
+				{
+					Name:        "latency",
+					Description: "Time spend processing received requests",
+					Unit:        unit.Milliseconds,
+					Data: metricdata.Histogram{
+						Temporality: metricdata.DeltaTemporality,
+						DataPoints: []metricdata.HistogramDataPoint{
+							{
+								Attributes:   attribute.NewSet(attribute.String("server", "central")),
+								StartTime:    now,
+								Time:         now.Add(1 * time.Second),
+								Count:        10,
+								Bounds:       []float64{1, 5, 10},
+								BucketCounts: []uint64{1, 3, 6, 0},
+								Sum:          57,
+							},
+						},
+					},
+				},
+				{
+					Name:        "temperature",
+					Description: "CPU global temperature",
+					Unit:        unit.Unit("cel(1 K)"),
+					Data: metricdata.Gauge[float64]{
+						DataPoints: []metricdata.DataPoint[float64]{
+							{
+								Attributes: attribute.NewSet(attribute.String("server", "central")),
+								Time:       now.Add(1 * time.Second),
+								Value:      32.4,
+							},
+						},
+					},
+				},
+			},
+		},
+	},
+}
+
+func Example() {
+	// Print with a JSON encoder that indents with two spaces.
+	enc := json.NewEncoder(os.Stdout)
+	enc.SetIndent("", "  ")
+	exp, err := stdoutmetric.New(stdoutmetric.WithEncoder(enc))
+	if err != nil {
+		panic(err)
+	}
+	// FIXME: The exporter should be registered with an SDK and the output
+	// should come from that.
+	exp.Export(context.Background(), mockData)
+
+	// Output:
+	// {
+	//   "Resource": [
+	//     {
+	//       "Key": "service.name",
+	//       "Value": {
+	//         "Type": "STRING",
+	//         "Value": "stdoutmetric-example"
+	//       }
+	//     }
+	//   ],
+	//   "ScopeMetrics": [
+	//     {
+	//       "Scope": {
+	//         "Name": "example",
+	//         "Version": "v0.0.1"
+	//       },
+	//       "Metrics": [
+	//         {
+	//           "Name": "requests",
+	//           "Description": "Number of requests received",
+	//           "Unit": "1",
+	//           "Data": {
+	//             "DataPoints": [
+	//               {
+	//                 "Attributes": [
+	//                   {
+	//                     "Key": "server",
+	//                     "Value": {
+	//                       "Type": "STRING",
+	//                       "Value": "central"
+	//                     }
+	//                   }
+	//                 ],
+	//                 "StartTime": "1999-12-31T16:00:00-08:00",
+	//                 "Time": "1999-12-31T16:00:01-08:00",
+	//                 "Value": 5
+	//               }
+	//             ],
+	//             "Temporality": "delta",
+	//             "IsMonotonic": true
+	//           }
+	//         },
+	//         {
+	//           "Name": "latency",
+	//           "Description": "Time spend processing received requests",
+	//           "Unit": "ms",
+	//           "Data": {
+	//             "DataPoints": [
+	//               {
+	//                 "Attributes": [
+	//                   {
+	//                     "Key": "server",
+	//                     "Value": {
+	//                       "Type": "STRING",
+	//                       "Value": "central"
+	//                     }
+	//                   }
+	//                 ],
+	//                 "StartTime": "1999-12-31T16:00:00-08:00",
+	//                 "Time": "1999-12-31T16:00:01-08:00",
+	//                 "Count": 10,
+	//                 "Bounds": [
+	//                   1,
+	//                   5,
+	//                   10
+	//                 ],
+	//                 "BucketCounts": [
+	//                   1,
+	//                   3,
+	//                   6,
+	//                   0
+	//                 ],
+	//                 "Sum": 57
+	//               }
+	//             ],
+	//             "Temporality": "delta"
+	//           }
+	//         },
+	//         {
+	//           "Name": "temperature",
+	//           "Description": "CPU global temperature",
+	//           "Unit": "cel(1 K)",
+	//           "Data": {
+	//             "DataPoints": [
+	//               {
+	//                 "Attributes": [
+	//                   {
+	//                     "Key": "server",
+	//                     "Value": {
+	//                       "Type": "STRING",
+	//                       "Value": "central"
+	//                     }
+	//                   }
+	//                 ],
+	//                 "StartTime": "0001-01-01T00:00:00Z",
+	//                 "Time": "1999-12-31T16:00:01-08:00",
+	//                 "Value": 32.4
+	//               }
+	//             ]
+	//           }
+	//         }
+	//       ]
+	//     }
+	//   ]
+	// }
+}