Cherry-pick #18797 to 7.7: Fix panic on metricbeat test modules (#1…

…8853)

Since metricbeat light modules support processors (#15923), module
initialization requires a publisher in the beat so modules can attach
their processors. `metricbeat test modules` is not initializing as
normal metricbeat commands, and it is not initializing any output or
publisher pipeline, so metricbeat panics when trying to initialize
modules with the new method.

This change adds a dummy publisher for this case, and fixes also a
condition that was adding a `nil` module option, causing additional
panics. A test that reproduced the issues is also added.

(cherry picked from commit 25b8bf1)

Add nil pipeline from #16715, required for the fix.

(cherry picked from commit 7a1b524)

Co-authored-by: Steffen Siering <steffen.siering@elastic.co>

CHANGELOG.next.asciidoc

@@ -121,6 +121,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Fix storage metricset to allow config without region/zone. {issue}17623[17623] {pull}17624[17624]
 - Fix overflow on Prometheus rates when new buckets are added on the go. {pull}17753[17753]
 - Fix tags_filter for cloudwatch metricset in aws. {pull}18524[18524]
+- Fix panic on `metricbeat test modules` when modules are configured in `metricbeat.modules`. {issue}18789[18789] {pull}18797[18797]
 - Add missing network.sent_packets_count metric into compute metricset in googlecloud module. {pull}18802[18802]
 
 *Packetbeat*

libbeat/publisher/pipeline/nilpipeline.go

@@ -0,0 +1,83 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you 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 pipeline
+
+import "github.com/elastic/beats/v7/libbeat/beat"
+
+type nilPipeline struct{}
+
+type nilClient struct {
+	eventer      beat.ClientEventer
+	ackCount     func(int)
+	ackEvents    func([]interface{})
+	ackLastEvent func(interface{})
+}
+
+var _nilPipeline = (*nilPipeline)(nil)
+
+// NewNilPipeline returns a new pipeline that is compatible with
+// beats.PipelineConnector. The pipeline will discard all events that have been
+// published. Client ACK handlers will still be executed, but the callbacks
+// will be executed immediately when the event is published.
+func NewNilPipeline() beat.PipelineConnector { return _nilPipeline }
+
+func (p *nilPipeline) Connect() (beat.Client, error) {
+	return p.ConnectWith(beat.ClientConfig{})
+}
+
+func (p *nilPipeline) ConnectWith(cfg beat.ClientConfig) (beat.Client, error) {
+	return &nilClient{
+		eventer:      cfg.Events,
+		ackCount:     cfg.ACKCount,
+		ackEvents:    cfg.ACKEvents,
+		ackLastEvent: cfg.ACKLastEvent,
+	}, nil
+}
+
+func (c *nilClient) Publish(event beat.Event) {
+	c.PublishAll([]beat.Event{event})
+}
+
+func (c *nilClient) PublishAll(events []beat.Event) {
+	L := len(events)
+	if L == 0 {
+		return
+	}
+
+	if c.ackLastEvent != nil {
+		c.ackLastEvent(events[L-1].Private)
+	}
+	if c.ackEvents != nil {
+		tmp := make([]interface{}, L)
+		for i := range events {
+			tmp[i] = events[i].Private
+		}
+		c.ackEvents(tmp)
+	}
+	if c.ackCount != nil {
+		c.ackCount(L)
+	}
+}
+
+func (c *nilClient) Close() error {
+	if c.eventer != nil {
+		c.eventer.Closing()
+		c.eventer.Closed()
+	}
+	return nil
+}

metricbeat/cmd/test/modules.go

@@ -25,6 +25,7 @@ import (
 
 	"github.com/elastic/beats/v7/libbeat/beat"
 	"github.com/elastic/beats/v7/libbeat/cmd/instance"
+	"github.com/elastic/beats/v7/libbeat/publisher/pipeline"
 	"github.com/elastic/beats/v7/libbeat/testing"
 	"github.com/elastic/beats/v7/metricbeat/beater"
 )
@@ -49,6 +50,8 @@ func GenTestModulesCmd(name, beatVersion string, create beat.Creator) *cobra.Com
 				os.Exit(1)
 			}
 
+			// A publisher is needed for modules that add their own pipelines
+			b.Beat.Publisher = newPublisher()
 			mb, err := create(&b.Beat, b.Beat.BeatConfig)
 			if err != nil {
 				fmt.Fprintf(os.Stderr, "Error initializing metricbeat: %s\n", err)
@@ -78,3 +81,17 @@ func GenTestModulesCmd(name, beatVersion string, create beat.Creator) *cobra.Com
 		},
 	}
 }
+
+type publisher struct {
+	beat.PipelineConnector
+}
+
+// newPublisher returns a functional publisher that does nothing.
+func newPublisher() *publisher {
+	return &publisher{pipeline.NewNilPipeline()}
+}
+
+// SetACKHandler is a dummy implementation of the ack handler for the test publisher.
+func (*publisher) SetACKHandler(beat.PipelineACKHandler) error {
+	return nil
+}

metricbeat/mb/module/configuration.go

@@ -30,7 +30,7 @@ func ConfiguredModules(modulesData []*common.Config, configModulesData *common.C
 	var modules []*Wrapper
 
 	for _, moduleCfg := range modulesData {
-		module, err := NewWrapper(moduleCfg, mb.Registry, nil)
+		module, err := NewWrapper(moduleCfg, mb.Registry, moduleOptions...)
 		if err != nil {
 			return nil, err
 		}

metricbeat/tests/system/test_cmd.py

@@ -124,6 +124,21 @@ def test_modules_test(self):
         assert self.log_contains("cpu...OK")
         assert self.log_contains("memory...OK")
 
+    def test_modules_test_with_module_in_main_config(self):
+        self.render_config_template(reload=False, modules=[{
+            "name": "system",
+            "metricsets": ["cpu", "memory"],
+            "period": "10s",
+        }])
+
+        exit_code = self.run_beat(
+            logging_args=None,
+            extra_args=["test", "modules"])
+
+        assert exit_code == 0
+        assert self.log_contains("cpu...OK")
+        assert self.log_contains("memory...OK")
+
     def test_modules_test_error(self):
         """
         Test test modules command with an error result