Add debug to Jolokia JMX metricset

CHANGELOG.asciidoc

@@ -63,6 +63,7 @@ https://github.com/elastic/beats/compare/v6.0.0-alpha1...master[Check the HEAD d
 - Add macOS implementation of the system diskio metricset. {issue}4144[4144]
 - Add process_summary metricset that records high level metrics about processes. {pull}4231[4231]
 - Add `kube-state-metrics` based metrics to `kubernetes` module {pull}4253[4253]
+- Add debug logging to Jolokia JMX metricset. {pull}4341[4341]
 
 *Packetbeat*
 

metricbeat/module/jolokia/jmx/config.go

@@ -38,12 +38,10 @@ type RequestBlock struct {
 }
 
 func buildRequestBodyAndMapping(mappings []JMXMapping) ([]byte, map[string]string, error) {
-
 	responseMapping := map[string]string{}
-	blocks := []RequestBlock{}
+	var blocks []RequestBlock
 
 	for _, mapping := range mappings {
-
 		rb := RequestBlock{
 			Type:  "read",
 			MBean: mapping.MBean,

metricbeat/module/jolokia/jmx/data.go

@@ -2,10 +2,10 @@ package jmx
 
 import (
 	"encoding/json"
-	"fmt"
 
 	"github.com/elastic/beats/libbeat/common"
 	"github.com/joeshaw/multierror"
+	"github.com/pkg/errors"
 )
 
 type Entry struct {
@@ -47,11 +47,9 @@ type Entry struct {
 //     }
 //  ]
 func eventMapping(content []byte, mapping map[string]string) (common.MapStr, error) {
-
 	var entries []Entry
-	err := json.Unmarshal(content, &entries)
-	if err != nil {
-		return nil, fmt.Errorf("Cannot unmarshal json response: %s", err)
+	if err := json.Unmarshal(content, &entries); err != nil {
+		return nil, errors.Wrapf(err, "failed to unmarshal jolokia JSON response '%v'", string(content))
 	}
 
 	event := common.MapStr{}
@@ -68,18 +66,21 @@ func eventMapping(content []byte, mapping map[string]string) (common.MapStr, err
 	}
 
 	return event, errs.Err()
-
 }
 
-func parseResponseEntry(mbeanName string, attributeName string, attibuteValue interface{},
-	event common.MapStr, mapping map[string]string) error {
-
-	//create metric name by merging mbean and attribute fields
+func parseResponseEntry(
+	mbeanName string,
+	attributeName string,
+	attibuteValue interface{},
+	event common.MapStr,
+	mapping map[string]string,
+) error {
+	// Create metric name by merging mbean and attribute fields.
 	var metricName = mbeanName + "_" + attributeName
 
 	key, exists := mapping[metricName]
 	if !exists {
-		return fmt.Errorf("No key found for metric: '%s', skipping...", metricName)
+		return errors.Errorf("metric key '%v' not found in response", key)
 	}
 
 	_, err := event.Put(key, attibuteValue)

metricbeat/module/jolokia/jmx/jmx.go

@@ -9,7 +9,9 @@ import (
 )
 
 var (
-	debugf = logp.MakeDebug("jolokia-jmx")
+	metricsetName = "jolokia.jmx"
+	logPrefix     = "[" + metricsetName + "]"
+	debugf        = logp.MakeDebug(metricsetName)
 )
 
 // init registers the MetricSet with the central registry.
@@ -67,6 +69,11 @@ func New(base mb.BaseMetricSet) (mb.MetricSet, error) {
 	http.SetMethod("POST")
 	http.SetBody(body)
 
+	if logp.IsDebug(metricsetName) {
+		debugf("%v The body for POST requests to jolokia host %v is: %v",
+			logPrefix, base.HostData().Host, string(body))
+	}
+
 	return &MetricSet{
 		BaseMetricSet: base,
 		mapping:       mapping,
@@ -83,12 +90,17 @@ func (m *MetricSet) Fetch() (common.MapStr, error) {
 		return nil, err
 	}
 
+	if logp.IsDebug(metricsetName) {
+		debugf("%v The response body from jolokia host %v is: %v",
+			logPrefix, m.HostData().Host, string(body))
+	}
+
 	event, err := eventMapping(body, m.mapping)
 	if err != nil {
 		return nil, err
 	}
 
-	// Set dynamic namespace
+	// Set dynamic namespace.
 	event[mb.NamespaceKey] = m.namespace
 
 	return event, nil