[6.2] Filebeat: Fix leak in log harvester (#6797)

CHANGELOG.asciidoc

@@ -38,6 +38,8 @@ https://github.com/elastic/beats/compare/v6.2.4...6.2[Check the HEAD diff]
 
 *Filebeat*
 
+- Fix memory leak in log prospector when files cannot be read. {issue}6797[6797]
+
 *Heartbeat*
 - Fix race due to updates of shared a map, that was not supposed to be shared between multiple go-routines. {issue}6616[6616]
 

filebeat/prospector/log/harvester.go

@@ -52,6 +52,9 @@ var (
 	ErrClosed       = errors.New("reader closed")
 )
 
+// OutletFactory provides an outlet for the harvester
+type OutletFactory func() channel.Outleter
+
 // Harvester contains all harvester related data
 type Harvester struct {
 	id     uuid.UUID
@@ -74,8 +77,8 @@ type Harvester struct {
 	encoding        encoding.Encoding
 
 	// event/state publishing
-	forwarder    *harvester.Forwarder
-	publishState func(*util.Data) bool
+	outletFactory OutletFactory
+	publishState  func(*util.Data) bool
 
 	onTerminate func()
 }
@@ -86,17 +89,18 @@ func NewHarvester(
 	state file.State,
 	states *file.States,
 	publishState func(*util.Data) bool,
-	outlet channel.Outleter,
+	outletFactory OutletFactory,
 ) (*Harvester, error) {
 
 	h := &Harvester{
-		config:       defaultConfig,
-		state:        state,
-		states:       states,
-		publishState: publishState,
-		done:         make(chan struct{}),
-		stopWg:       &sync.WaitGroup{},
-		id:           uuid.NewV4(),
+		config:        defaultConfig,
+		state:         state,
+		states:        states,
+		publishState:  publishState,
+		done:          make(chan struct{}),
+		stopWg:        &sync.WaitGroup{},
+		id:            uuid.NewV4(),
+		outletFactory: outletFactory,
 	}
 
 	if err := config.Unpack(&h.config); err != nil {
@@ -115,8 +119,6 @@ func NewHarvester(
 	}
 
 	// Add outlet signal so harvester can also stop itself
-	outlet = channel.CloseOnSignal(outlet, h.done)
-	h.forwarder = harvester.NewForwarder(outlet)
 	return h, nil
 }
 
@@ -163,6 +165,10 @@ func (h *Harvester) Run() error {
 	if h.onTerminate != nil {
 		defer h.onTerminate()
 	}
+
+	outlet := channel.CloseOnSignal(h.outletFactory(), h.done)
+	forwarder := harvester.NewForwarder(outlet)
+
 	// This is to make sure a harvester is not started anymore if stop was already
 	// called before the harvester was started. The waitgroup is not incremented afterwards
 	// as otherwise it could happened that between checking for the close channel and incrementing
@@ -302,7 +308,7 @@ func (h *Harvester) Run() error {
 
 		// Always send event to update state, also if lines was skipped
 		// Stop harvester in case of an error
-		if !h.sendEvent(data) {
+		if !h.sendEvent(data, forwarder) {
 			return nil
 		}
 
@@ -326,12 +332,12 @@ func (h *Harvester) Stop() {
 
 // sendEvent sends event to the spooler channel
 // Return false if event was not sent
-func (h *Harvester) sendEvent(data *util.Data) bool {
+func (h *Harvester) sendEvent(data *util.Data, forwarder *harvester.Forwarder) bool {
 	if h.source.HasState() {
 		h.states.Update(data.GetState())
 	}
 
-	err := h.forwarder.Send(data)
+	err := forwarder.Send(data)
 	return err == nil
 }
 

filebeat/prospector/log/prospector.go

@@ -572,18 +572,29 @@ func (p *Prospector) isCleanInactive(state file.State) bool {
 	return false
 }
 
+// subOutletWrap returns a factory method that will wrap the passed outlet
+// in a SubOutlet and memoize the result so the wrapping is done only once.
+func subOutletWrap(outlet channel.Outleter) func() channel.Outleter {
+	var subOutlet channel.Outleter
+	return func() channel.Outleter {
+		if subOutlet == nil {
+			subOutlet = channel.SubOutlet(outlet)
+		}
+		return subOutlet
+	}
+}
+
 // createHarvester creates a new harvester instance from the given state
 func (p *Prospector) createHarvester(state file.State, onTerminate func()) (*Harvester, error) {
 	// Each wraps the outlet, for closing the outlet individually
-	outlet := channel.SubOutlet(p.outlet)
 	h, err := NewHarvester(
 		p.cfg,
 		state,
 		p.states,
 		func(d *util.Data) bool {
 			return p.stateOutlet.OnEvent(d)
 		},
-		outlet,
+		subOutletWrap(p.outlet),
 	)
 	if err == nil {
 		h.onTerminate = onTerminate

filebeat/prospector/stdin/prospector.go

@@ -73,7 +73,9 @@ func (p *Prospector) createHarvester(state file.State) (*log.Harvester, error) {
 	h, err := log.NewHarvester(
 		p.cfg,
 		state, nil, nil,
-		p.outlet,
+		func() channel.Outleter {
+			return p.outlet
+		},
 	)
 
 	return h, err