Add "components" Command

.chloggen/build-info-flag.yaml

@@ -0,0 +1,16 @@
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: service
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note:  Added build-info sub command which outputs components in collector distribution.
+
+# One or more tracking issues or pull requests related to the change
+issues: [4671]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:

service/README.md

@@ -36,6 +36,37 @@ For more technical details about how configuration is resolved you can read the
 
     `./otelcorecol --config=file:examples/local/otel-config.yaml --config="yaml:exporters::logging::loglevel: info"`
 
+
+## How to check components available in a distribution
+
+Use the sub command build-info. Below is an example:
+
+```bash
+   ./otelcorecol build-info
+```
+Sample output:
+
+```yaml
+
+buildinfo:
+   command: otelcorecol
+   description: Local OpenTelemetry Collector binary, testing only.
+   version: 0.62.1-dev
+receivers:
+   - otlp
+processors:
+   - memory_limiter
+   - batch
+exporters:
+   - otlp
+   - otlphttp
+   - logging
+extensions:
+   - zpages
+   - memory_ballast
+
+
+```
 ## How to override config properties?
 
 The `--set` flag allows to set arbitrary config property. The `--set` values are merged into the final configuration

service/command.go

@@ -53,7 +53,7 @@ func NewCommand(set CollectorSettings) *cobra.Command {
 			return col.Run(cmd.Context())
 		},
 	}
-
+	rootCmd.AddCommand(newBuildSubCommand(set))
 	rootCmd.Flags().AddGoFlagSet(flagSet)
 	return rootCmd
 }

service/command_build_info.go

@@ -0,0 +1,52 @@
+package service
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+	"gopkg.in/yaml.v3"
+
+	"go.opentelemetry.io/collector/component"
+	"go.opentelemetry.io/collector/config"
+)
+
+type componentsOutput struct {
+	BuildInfo  component.BuildInfo
+	Receivers  []config.Type
+	Processors []config.Type
+	Exporters  []config.Type
+	Extensions []config.Type
+}
+
+// newBuildSubCommand constructs a new cobra.Command sub command using the given CollectorSettings.
+func newBuildSubCommand(set CollectorSettings) *cobra.Command {
+	buildCmd := &cobra.Command{
+		Use:   "build-info",
+		Short: "Outputs available components in this collector distribution",
+		Args:  cobra.ExactArgs(0),
+		RunE: func(cmd *cobra.Command, args []string) error {
+
+			components := componentsOutput{}
+			for ext := range set.Factories.Extensions {
+				components.Extensions = append(components.Extensions, ext)
+			}
+			for prs := range set.Factories.Processors {
+				components.Processors = append(components.Processors, prs)
+			}
+			for rcv := range set.Factories.Receivers {
+				components.Receivers = append(components.Receivers, rcv)
+			}
+			for exp := range set.Factories.Exporters {
+				components.Exporters = append(components.Exporters, exp)
+			}
+			components.BuildInfo = set.BuildInfo
+			yamlData, err := yaml.Marshal(components)
+			if err != nil {
+				return err
+			}
+			fmt.Println(string(yamlData))
+			return nil
+		},
+	}
+	return buildCmd
+}

service/command_build_info_test.go

@@ -0,0 +1,71 @@
+package service
+
+import (
+	"bytes"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"gopkg.in/yaml.v3"
+
+	"go.opentelemetry.io/collector/component"
+	"go.opentelemetry.io/collector/component/componenttest"
+	"go.opentelemetry.io/collector/config"
+	"go.opentelemetry.io/collector/featuregate"
+)
+
+func TestNewBuildSubCommand(t *testing.T) {
+	factories, err := componenttest.NopFactories()
+	require.NoError(t, err)
+
+	cfgProvider, err := NewConfigProvider(newDefaultConfigProviderSettings([]string{filepath.Join("testdata", "otelcol-nop.yaml")}))
+	require.NoError(t, err)
+
+	set := CollectorSettings{
+		BuildInfo:      component.NewDefaultBuildInfo(),
+		Factories:      factories,
+		ConfigProvider: cfgProvider,
+		telemetry:      newColTelemetry(featuregate.NewRegistry()),
+	}
+	cmd := NewCommand(set)
+	cmd.SetArgs([]string{"build-info"})
+
+	ExpectedYamlStruct := componentsOutput{
+		BuildInfo:  component.NewDefaultBuildInfo(),
+		Receivers:  []config.Type{"nop"},
+		Processors: []config.Type{"nop"},
+		Exporters:  []config.Type{"nop"},
+		Extensions: []config.Type{"nop"},
+	}
+	ExpectedOutput, err := yaml.Marshal(ExpectedYamlStruct)
+	require.NoError(t, err)
+
+	// Obtaining StdOutput of cmd.Execute()
+	oldStdOut := os.Stdout
+	r, w, _ := os.Pipe()
+	os.Stdout = w // Write to os.StdOut
+
+	err = cmd.Execute()
+	require.NoError(t, err)
+
+	bufChan := make(chan string)
+
+	go func() {
+		var buf bytes.Buffer
+		_, err = io.Copy(&buf, r)
+		require.NoError(t, err)
+		bufChan <- buf.String()
+	}()
+
+	err = w.Close()
+	require.NoError(t, err)
+	defer func() { os.Stdout = oldStdOut }() // Restore os.Stdout to old value after test
+	output := <-bufChan
+	// Trim new line at the end of the two strings to make a better comparison as string() adds an extra new
+	// line that makes the test fail.
+	assert.Equal(t, strings.Trim(output, "\n"), strings.Trim(string(ExpectedOutput), "\n"))
+}