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Add the internal experimental metric feature package (open-telemetry#…
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…4715)

* Add the internal experimental metric feature pkg

* Interpret empty envvar same as unset

* Test Exemplars and CardinalityLimit

* Fix empty test for CardinalityLimit

* Abstract common testing patterns

* Add test cases from review feedback

* Rename assertions based on review feedback

---------

Co-authored-by: Chester Cheung <[email protected]>
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MrAlias and hanyuancheung authored Dec 6, 2023
1 parent 9ccb0c6 commit d37d851
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93 changes: 93 additions & 0 deletions sdk/metric/internal/x/x.go
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// 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 x contains support for OTel metric SDK experimental features.
//
// This package should only be used for features defined in the specification.
// It should not be used for experiments or new project ideas.
package x // import "go.opentelemetry.io/otel/sdk/metric/internal/x"

import (
"os"
"strconv"
"strings"
)

var (
// Exemplars is an experimental feature flag that defines if exemplars
// should be recorded for metric data-points.
//
// To enable this feature set the OTEL_GO_X_EXEMPLAR environment variable
// to the case-insensitive string value of "true" (i.e. "True" and "TRUE"
// will also enable this).
Exemplars = newFeature("EXEMPLAR", func(v string) (string, bool) {
if strings.ToLower(v) == "true" {
return v, true
}
return "", false
})

// CardinalityLimit is an experimental feature flag that defines if
// cardinality limits should be applied to the recorded metric data-points.
//
// To enable this feature set the OTEL_GO_X_CARDINALITY_LIMIT environment
// variable to the integer limit value you want to use.
CardinalityLimit = newFeature("CARDINALITY_LIMIT", func(v string) (int, bool) {
n, err := strconv.Atoi(v)
if err != nil {
return 0, false
}
return n, true
})
)

// Feature is an experimental feature control flag. It provides a uniform way
// to interact with these feature flags and parse their values.
type Feature[T any] struct {
key string
parse func(v string) (T, bool)
}

func newFeature[T any](suffix string, parse func(string) (T, bool)) Feature[T] {
const envKeyRoot = "OTEL_GO_X_"
return Feature[T]{
key: envKeyRoot + suffix,
parse: parse,
}
}

// Key returns the environment variable key that needs to be set to enable the
// feature.
func (f Feature[T]) Key() string { return f.key }

// Lookup returns the user configured value for the feature and true if the
// user has enabled the feature. Otherwise, if the feature is not enabled, a
// zero-value and false are returned.
func (f Feature[T]) Lookup() (v T, ok bool) {
// https://github.com/open-telemetry/opentelemetry-specification/blob/62effed618589a0bec416a87e559c0a9d96289bb/specification/configuration/sdk-environment-variables.md#parsing-empty-value
//
// > The SDK MUST interpret an empty value of an environment variable the
// > same way as when the variable is unset.
vRaw := os.Getenv(f.key)
if vRaw == "" {
return v, ok
}
return f.parse(vRaw)
}

// Enabled returns if the feature is enabled.
func (f Feature[T]) Enabled() bool {
_, ok := f.Lookup()
return ok
}
81 changes: 81 additions & 0 deletions sdk/metric/internal/x/x_test.go
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// 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 x

import (
"testing"

"github.com/stretchr/testify/assert"
"github.com/stretchr/testify/require"
)

func TestExemplars(t *testing.T) {
const key = "OTEL_GO_X_EXEMPLAR"
require.Equal(t, key, Exemplars.Key())

t.Run("true", run(setenv(key, "true"), assertEnabled(Exemplars, "true")))
t.Run("True", run(setenv(key, "True"), assertEnabled(Exemplars, "True")))
t.Run("TRUE", run(setenv(key, "TRUE"), assertEnabled(Exemplars, "TRUE")))
t.Run("false", run(setenv(key, "false"), assertDisabled(Exemplars)))
t.Run("1", run(setenv(key, "1"), assertDisabled(Exemplars)))
t.Run("empty", run(assertDisabled(Exemplars)))
}

func TestCardinalityLimit(t *testing.T) {
const key = "OTEL_GO_X_CARDINALITY_LIMIT"
require.Equal(t, key, CardinalityLimit.Key())

t.Run("100", run(setenv(key, "100"), assertEnabled(CardinalityLimit, 100)))
t.Run("-1", run(setenv(key, "-1"), assertEnabled(CardinalityLimit, -1)))
t.Run("false", run(setenv(key, "false"), assertDisabled(CardinalityLimit)))
t.Run("empty", run(assertDisabled(CardinalityLimit)))
}

func run(steps ...func(*testing.T)) func(*testing.T) {
return func(t *testing.T) {
t.Helper()
for _, step := range steps {
step(t)
}
}
}

func setenv(k, v string) func(t *testing.T) {
return func(t *testing.T) { t.Setenv(k, v) }
}

func assertEnabled[T any](f Feature[T], want T) func(*testing.T) {
return func(t *testing.T) {
t.Helper()
assert.True(t, f.Enabled(), "not enabled")

v, ok := f.Lookup()
assert.True(t, ok, "Lookup state")
assert.Equal(t, want, v, "Lookup value")
}
}

func assertDisabled[T any](f Feature[T]) func(*testing.T) {
var zero T
return func(t *testing.T) {
t.Helper()

assert.False(t, f.Enabled(), "enabled")

v, ok := f.Lookup()
assert.False(t, ok, "Lookup state")
assert.Equal(t, zero, v, "Lookup value")
}
}

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