[extension/zpages] Add an option to enable expvar

resolve open-telemetry#11081

Signed-off-by: Hong Chen <[email protected]>

extension/zpagesextension/README.md

@@ -33,7 +33,7 @@ extensions:
   zpages:
 ```
 
-The full list of settings exposed for this exporter are documented [here](./config.go)
+The full list of settings exposed for this extension are documented [here](./config.go)
 with detailed sample configurations [here](./testdata/config.yaml).
 
 ## Exposed zPages routes

extension/zpagesextension/config.go

@@ -13,6 +13,10 @@ import (
 // Config has the configuration for the extension enabling the zPages extension.
 type Config struct {
 	confighttp.ServerConfig `mapstructure:",squash"`
+
+	// EnableExpvar indicates whether to enable expvar service.
+	// (default = false)
+	EnableExpvar bool `mapstructure:"enable_expvar"`
 }
 
 var _ component.Config = (*Config)(nil)

extension/zpagesextension/config_test.go

@@ -37,5 +37,6 @@ func TestUnmarshalConfig(t *testing.T) {
 			ServerConfig: confighttp.ServerConfig{
 				Endpoint: "localhost:56888",
 			},
+			EnableExpvar: false,
 		}, cfg)
 }

extension/zpagesextension/factory.go

@@ -26,6 +26,7 @@ func createDefaultConfig() component.Config {
 		ServerConfig: confighttp.ServerConfig{
 			Endpoint: defaultEndpoint,
 		},
+		EnableExpvar: false,
 	}
 }
 

extension/zpagesextension/zpagesextension.go

@@ -6,6 +6,7 @@ package zpagesextension // import "go.opentelemetry.io/collector/extension/zpage
 import (
 	"context"
 	"errors"
+	"expvar"
 	"net/http"
 	"path"
 
@@ -18,7 +19,8 @@ import (
 )
 
 const (
-	tracezPath = "tracez"
+	tracezPath  = "tracez"
+	expvarzPath = "expvarz"
 )
 
 type zpagesExtension struct {
@@ -56,6 +58,11 @@ func (zpe *zpagesExtension) Start(ctx context.Context, host component.Host) erro
 		zpe.telemetry.Logger.Warn("zPages span processor registration is not available")
 	}
 
+	if zpe.config.EnableExpvar {
+		zPagesMux.Handle(path.Join("/debug", expvarzPath), expvar.Handler())
+		zpe.telemetry.Logger.Info("Registered zPages expvar handler")
+	}
+
 	hostZPages, ok := host.(interface {
 		RegisterZPages(mux *http.ServeMux, pathPrefix string)
 	})

extension/zpagesextension/zpagesextension_test.go

@@ -51,7 +51,7 @@ func newZpagesTelemetrySettings() component.TelemetrySettings {
 
 func TestZPagesExtensionUsage(t *testing.T) {
 	cfg := &Config{
-		confighttp.ServerConfig{
+		ServerConfig: confighttp.ServerConfig{
 			Endpoint: testutil.GetAvailableLocalAddress(t),
 		},
 	}
@@ -78,7 +78,7 @@ func TestZPagesExtensionUsage(t *testing.T) {
 
 func TestZPagesExtensionBadAuthExtension(t *testing.T) {
 	cfg := &Config{
-		confighttp.ServerConfig{
+		ServerConfig: confighttp.ServerConfig{
 			Endpoint: "localhost:0",
 			Auth: &confighttp.AuthConfig{
 				Authentication: configauth.Authentication{
@@ -98,7 +98,7 @@ func TestZPagesExtensionPortAlreadyInUse(t *testing.T) {
 	defer ln.Close()
 
 	cfg := &Config{
-		confighttp.ServerConfig{
+		ServerConfig: confighttp.ServerConfig{
 			Endpoint: endpoint,
 		},
 	}
@@ -110,7 +110,7 @@ func TestZPagesExtensionPortAlreadyInUse(t *testing.T) {
 
 func TestZPagesMultipleStarts(t *testing.T) {
 	cfg := &Config{
-		confighttp.ServerConfig{
+		ServerConfig: confighttp.ServerConfig{
 			Endpoint: testutil.GetAvailableLocalAddress(t),
 		},
 	}
@@ -127,7 +127,7 @@ func TestZPagesMultipleStarts(t *testing.T) {
 
 func TestZPagesMultipleShutdowns(t *testing.T) {
 	cfg := &Config{
-		confighttp.ServerConfig{
+		ServerConfig: confighttp.ServerConfig{
 			Endpoint: testutil.GetAvailableLocalAddress(t),
 		},
 	}
@@ -142,7 +142,7 @@ func TestZPagesMultipleShutdowns(t *testing.T) {
 
 func TestZPagesShutdownWithoutStart(t *testing.T) {
 	cfg := &Config{
-		confighttp.ServerConfig{
+		ServerConfig: confighttp.ServerConfig{
 			Endpoint: testutil.GetAvailableLocalAddress(t),
 		},
 	}
@@ -152,3 +152,31 @@ func TestZPagesShutdownWithoutStart(t *testing.T) {
 
 	require.NoError(t, zpagesExt.Shutdown(context.Background()))
 }
+
+func TestZPagesEnableExpvar(t *testing.T) {
+	cfg := &Config{
+		ServerConfig: confighttp.ServerConfig{
+			Endpoint: testutil.GetAvailableLocalAddress(t),
+		},
+		EnableExpvar: true,
+	}
+
+	zpagesExt := newServer(cfg, newZpagesTelemetrySettings())
+	require.NotNil(t, zpagesExt)
+
+	require.NoError(t, zpagesExt.Start(context.Background(), newZPagesHost()))
+	t.Cleanup(func() { require.NoError(t, zpagesExt.Shutdown(context.Background())) })
+
+	// Give a chance for the server goroutine to run.
+	runtime.Gosched()
+
+	_, zpagesPort, err := net.SplitHostPort(cfg.ServerConfig.Endpoint)
+	require.NoError(t, err)
+
+	client := &http.Client{}
+	resp, err := client.Get("http://localhost:" + zpagesPort + "/debug/expvarz")
+	require.NoError(t, err)
+	defer resp.Body.Close()
+
+	require.Equal(t, http.StatusOK, resp.StatusCode)
+}