Fix libbeat.output.*.bytes metrics of Elasticsearch output (elastic#2…

…1197)

## What does this PR do?

This PR passes a missing parameter to the constructor `elasticsearch.Client`.

## Why is it important?

The missing parameter prevented Beats from reporting the metrics `libbeat.output.write.bytes` and `libbeat.output.read.bytes` in case of Elasticsearch output.

## Related issues

Closes elastic#20752

CHANGELOG.next.asciidoc

@@ -172,6 +172,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Add missing country_name geo field in `add_host_metadata` and `add_observer_metadata` processors. {issue}20796[20796] {pull}20811[20811]
 - [Autodiscover] Handle input-not-finished errors in config reload. {pull}20915[20915]
 - Explicitly detect missing variables in autodiscover configuration, log them at the debug level. {issue}20568[20568] {pull}20898[20898]
+- Fix `libbeat.output.write.bytes` and `libbeat.output.read.bytes` metrics of the Elasticsearch output. {issue}20752[20752] {pull}21197[21197]
 
 *Auditbeat*
 

libbeat/outputs/elasticsearch/client.go

@@ -90,6 +90,7 @@ func NewClient(
 		Kerberos:         s.Kerberos,
 		Proxy:            s.Proxy,
 		ProxyDisable:     s.ProxyDisable,
+		Observer:         s.Observer,
 		Parameters:       s.Parameters,
 		CompressionLevel: s.CompressionLevel,
 		EscapeHTML:       s.EscapeHTML,

libbeat/outputs/elasticsearch/client_integration_test.go

@@ -40,6 +40,7 @@ import (
 	"github.com/elastic/beats/v7/libbeat/esleg/eslegtest"
 	"github.com/elastic/beats/v7/libbeat/idxmgmt"
 	"github.com/elastic/beats/v7/libbeat/logp"
+	"github.com/elastic/beats/v7/libbeat/monitoring"
 	"github.com/elastic/beats/v7/libbeat/outputs"
 	"github.com/elastic/beats/v7/libbeat/outputs/outest"
 )
@@ -78,7 +79,7 @@ func TestClientPublishEventKerberosAware(t *testing.T) {
 }
 
 func testPublishEvent(t *testing.T, index string, cfg map[string]interface{}) {
-	output, client := connectTestEs(t, cfg)
+	output, client := connectTestEsWithStats(t, cfg, index)
 
 	// drop old index preparing test
 	client.conn.Delete(index, "", "", nil)
@@ -107,6 +108,12 @@ func testPublishEvent(t *testing.T, index string, cfg map[string]interface{}) {
 	}
 
 	assert.Equal(t, 1, resp.Count)
+
+	outputSnapshot := monitoring.CollectFlatSnapshot(monitoring.Default.GetRegistry("output-"+index), monitoring.Full, true)
+	assert.Greater(t, outputSnapshot.Ints["write.bytes"], int64(0), "output.events.write.bytes must be greater than 0")
+	assert.Greater(t, outputSnapshot.Ints["read.bytes"], int64(0), "output.events.read.bytes must be greater than 0")
+	assert.Equal(t, int64(0), outputSnapshot.Ints["write.errors"])
+	assert.Equal(t, int64(0), outputSnapshot.Ints["read.errors"])
 }
 
 func TestClientPublishEventWithPipeline(t *testing.T) {
@@ -117,7 +124,7 @@ func TestClientPublishEventWithPipeline(t *testing.T) {
 	index := "beat-int-pub-single-with-pipeline"
 	pipeline := "beat-int-pub-single-pipeline"
 
-	output, client := connectTestEs(t, obj{
+	output, client := connectTestEsWithoutStats(t, obj{
 		"index":    index,
 		"pipeline": "%{[pipeline]}",
 	})
@@ -199,7 +206,7 @@ func TestClientBulkPublishEventsWithPipeline(t *testing.T) {
 	index := "beat-int-pub-bulk-with-pipeline"
 	pipeline := "beat-int-pub-bulk-pipeline"
 
-	output, client := connectTestEs(t, obj{
+	output, client := connectTestEsWithoutStats(t, obj{
 		"index":    index,
 		"pipeline": "%{[pipeline]}",
 	})
@@ -276,7 +283,7 @@ func TestClientBulkPublishEventsWithPipeline(t *testing.T) {
 
 func TestClientPublishTracer(t *testing.T) {
 	index := "beat-apm-tracer-test"
-	output, client := connectTestEs(t, map[string]interface{}{
+	output, client := connectTestEsWithoutStats(t, map[string]interface{}{
 		"index": index,
 	})
 
@@ -314,7 +321,17 @@ func TestClientPublishTracer(t *testing.T) {
 	assert.Equal(t, "/_bulk", secondSpan.Context.HTTP.URL.Path)
 }
 
-func connectTestEs(t *testing.T, cfg interface{}) (outputs.Client, *Client) {
+func connectTestEsWithStats(t *testing.T, cfg interface{}, suffix string) (outputs.Client, *Client) {
+	m := monitoring.Default.NewRegistry("output-" + suffix)
+	s := outputs.NewStats(m)
+	return connectTestEs(t, cfg, s)
+}
+
+func connectTestEsWithoutStats(t *testing.T, cfg interface{}) (outputs.Client, *Client) {
+	return connectTestEs(t, cfg, outputs.NewNilObserver())
+}
+
+func connectTestEs(t *testing.T, cfg interface{}, stats outputs.Observer) (outputs.Client, *Client) {
 	config, err := common.NewConfigFrom(map[string]interface{}{
 		"hosts":            eslegtest.GetEsHost(),
 		"username":         eslegtest.GetUser(),
@@ -337,7 +354,7 @@ func connectTestEs(t *testing.T, cfg interface{}) (outputs.Client, *Client) {
 
 	info := beat.Info{Beat: "libbeat"}
 	im, _ := idxmgmt.DefaultSupport(nil, info, nil)
-	output, err := makeES(im, info, outputs.NewNilObserver(), config)
+	output, err := makeES(im, info, stats, config)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -356,7 +373,7 @@ func connectTestEs(t *testing.T, cfg interface{}) (outputs.Client, *Client) {
 
 // setupRoleMapping sets up role mapping for the Kerberos user beats@ELASTIC
 func setupRoleMapping(t *testing.T, host string) error {
-	_, client := connectTestEs(t, map[string]interface{}{
+	_, client := connectTestEsWithoutStats(t, map[string]interface{}{
 		"hosts":    host,
 		"username": "elastic",
 		"password": "changeme",