Add do.Once protection to beater interface

CHANGELOG.next.asciidoc

@@ -116,6 +116,7 @@ https://github.com/elastic/beats/compare/v8.2.0\...main[Check the HEAD diff]
 - Added append Processor which will append concrete values or values from a field to target. {issue}29934[29934] {pull}33364[33364]
 - Add `add_formatted_index` processor that allows the resulting index for an event to be changed based on content from the event. {pull}33800[33800]
 - deps: Updated to github.com/elastic/go-sysinfo v1.9.0. {pull}33864[33864]
+- Fix panic due to close of already closed channel during shutdown {pull}33971[33971]
 
 *Auditbeat*
 

filebeat/beater/filebeat.go

@@ -21,6 +21,7 @@ import (
 	"flag"
 	"fmt"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/elastic/beats/v7/filebeat/channel"
@@ -67,6 +68,7 @@ type Filebeat struct {
 	moduleRegistry *fileset.ModuleRegistry
 	pluginFactory  PluginFactory
 	done           chan struct{}
+	stopOnce       sync.Once // wraps the Stop() method
 	pipeline       beat.PipelineConnector
 }
 
@@ -431,7 +433,7 @@ func (fb *Filebeat) Stop() {
 	logp.Info("Stopping filebeat")
 
 	// Stop Filebeat
-	close(fb.done)
+	fb.stopOnce.Do(func() { close(fb.done) })
 }
 
 // Create a new pipeline loader (es client) factory

heartbeat/beater/heartbeat.go

@@ -20,6 +20,7 @@ package beater
 import (
 	"errors"
 	"fmt"
+	"sync"
 
 	"syscall"
 	"time"
@@ -45,7 +46,8 @@ import (
 
 // Heartbeat represents the root datastructure of this beat.
 type Heartbeat struct {
-	done chan struct{}
+	done     chan struct{}
+	stopOnce sync.Once
 	// config is used for iterating over elements of the config.
 	config             config.Config
 	scheduler          *scheduler.Scheduler
@@ -257,7 +259,7 @@ func (bt *Heartbeat) makeAutodiscover(b *beat.Beat) (*autodiscover.Autodiscover,
 
 // Stop stops the beat.
 func (bt *Heartbeat) Stop() {
-	close(bt.done)
+	bt.stopOnce.Do(func() { close(bt.done) })
 }
 
 func makeStatesClient(cfg *conf.C, replace func(monitorstate.StateLoader), runFrom *config.LocationWithID) error {

metricbeat/beater/metricbeat.go

@@ -45,6 +45,7 @@ import (
 // Metricbeat implements the Beater interface for metricbeat.
 type Metricbeat struct {
 	done         chan struct{}   // Channel used to initiate shutdown.
+	stopOnce     sync.Once       // wraps the Stop() method
 	runners      []module.Runner // Active list of module runners.
 	config       Config
 	autodiscover *autodiscover.Autodiscover
@@ -272,7 +273,8 @@ func (bt *Metricbeat) Run(b *beat.Beat) error {
 // Stop should only be called a single time. Calling it more than once may
 // result in undefined behavior.
 func (bt *Metricbeat) Stop() {
-	close(bt.done)
+	bt.stopOnce.Do(func() { close(bt.done) })
+
 }
 
 // Modules return a list of all configured modules.

packetbeat/beater/packetbeat.go

@@ -19,6 +19,7 @@ package beater
 
 import (
 	"flag"
+	"sync"
 	"time"
 
 	"github.com/elastic/beats/v7/libbeat/beat"
@@ -77,9 +78,10 @@ func initialConfig() config.Config {
 
 // Beater object. Contains all objects needed to run the beat
 type packetbeat struct {
-	config  *conf.C
-	factory *processorFactory
-	done    chan struct{}
+	config   *conf.C
+	factory  *processorFactory
+	done     chan struct{}
+	stopOnce sync.Once
 }
 
 // New returns a new Packetbeat beat.Beater.
@@ -186,5 +188,5 @@ func (pb *packetbeat) runManaged(b *beat.Beat, factory *processorFactory) error
 // Called by the Beat stop function
 func (pb *packetbeat) Stop() {
 	logp.Info("Packetbeat send stop signal")
-	close(pb.done)
+	pb.stopOnce.Do(func() { close(pb.done) })
 }