Add env config map provider, read from environment variable (#4574)

Signed-off-by: Bogdan Drutu <bogdandrutu@gmail.com>

config/configmapprovider/env.go

@@ -0,0 +1,56 @@
+// 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 configmapprovider // import "go.opentelemetry.io/collector/config/configmapprovider"
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os"
+
+	"gopkg.in/yaml.v2"
+
+	"go.opentelemetry.io/collector/config"
+)
+
+type envMapProvider struct {
+	envName string
+}
+
+// NewEnv returns a new Provider that reads the configuration from the given environment variable.
+func NewEnv(envName string) Provider {
+	return &envMapProvider{
+		envName: envName,
+	}
+}
+
+func (emp *envMapProvider) Retrieve(_ context.Context, _ func(*ChangeEvent)) (Retrieved, error) {
+	if emp.envName == "" {
+		return nil, errors.New("config environment not specified")
+	}
+
+	content := os.Getenv(emp.envName)
+
+	var data map[string]interface{}
+	if err := yaml.Unmarshal([]byte(content), &data); err != nil {
+		return nil, fmt.Errorf("unable to parse yaml: %w", err)
+	}
+
+	return &simpleRetrieved{confMap: config.NewMapFromStringMap(data)}, nil
+}
+
+func (*envMapProvider) Shutdown(context.Context) error {
+	return nil
+}

config/configmapprovider/env_test.go

@@ -0,0 +1,68 @@
+// 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 configmapprovider
+
+import (
+	"context"
+	"os"
+	"path"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"go.opentelemetry.io/collector/config"
+)
+
+func TestEnv_EmptyName(t *testing.T) {
+	exp := NewEnv("")
+	_, err := exp.Retrieve(context.Background(), nil)
+	require.Error(t, err)
+}
+
+func TestEnv_InvalidYaml(t *testing.T) {
+	bytes, err := os.ReadFile(path.Join("testdata", "invalid-yaml.yaml"))
+	require.NoError(t, err)
+	const envName = "invalid-yaml"
+	require.NoError(t, os.Setenv(envName, string(bytes)))
+	t.Cleanup(func() {
+		require.NoError(t, os.Unsetenv(envName))
+	})
+	env := NewEnv(envName)
+	_, err = env.Retrieve(context.Background(), nil)
+	assert.Error(t, err)
+}
+
+func TestEnv(t *testing.T) {
+	bytes, err := os.ReadFile(path.Join("testdata", "default-config.yaml"))
+	require.NoError(t, err)
+	const envName = "default-config"
+	require.NoError(t, os.Setenv(envName, string(bytes)))
+	t.Cleanup(func() {
+		require.NoError(t, os.Unsetenv(envName))
+	})
+	env := NewEnv(envName)
+	ret, err := env.Retrieve(context.Background(), nil)
+	assert.NoError(t, err)
+	cfg, err := ret.Get(context.Background())
+	assert.NoError(t, err)
+	expectedMap := config.NewMapFromStringMap(map[string]interface{}{
+		"processors::batch":         nil,
+		"exporters::otlp::endpoint": "localhost:4317",
+	})
+	assert.Equal(t, expectedMap, cfg)
+	assert.NoError(t, ret.Close(context.Background()))
+	assert.NoError(t, env.Shutdown(context.Background()))
+}

config/configmapprovider/testdata/invalid-yaml.yaml

@@ -0,0 +1 @@
+processors