[Filebeat] Fix reference leak in TCP and Unix socket inputs (elastic#…

…19459)

The tcp and unix input sources were leaking references causing a memory leak.
When an accepted connection ended inputsource/common.Closer was
supposed to delete the pointer that it held to the connection, but due to a code
error `delete` was being called on the wrong map.

Instead of modifying the common.Closer I replaced it with a cancellable context.Context which
is designed to propagate signals from parent to children and requires less code.

(cherry picked from commit 61f4846)

CHANGELOG.next.asciidoc

@@ -231,6 +231,7 @@ field. You can revert this change by configuring tags for the module and omittin
 - Fix date and timestamp formats for fortigate module {pull}19316[19316]
 - Add missing `default_field: false` to aws filesets fields.yml. {pull}19568[19568]
 - Fix tls mapping in suricata module {issue}19492[19492] {pull}19494[19494]
+- Fix memory leak in tcp and unix input sources. {pull}19459[19459]
 
 *Heartbeat*
 

filebeat/inputsource/common/handler.go

@@ -19,6 +19,7 @@ package common
 
 import (
 	"bufio"
+	"context"
 	"net"
 
 	"github.com/pkg/errors"
@@ -31,15 +32,15 @@ import (
 type HandlerFactory func(config ListenerConfig) ConnectionHandler
 
 // ConnectionHandler interface provides mechanisms for handling of incoming connections
-type ConnectionHandler func(CloseRef, net.Conn) error
+type ConnectionHandler func(context.Context, net.Conn) error
 
 // MetadataFunc defines callback executed when a line is read from the split handler.
 type MetadataFunc func(net.Conn) inputsource.NetworkMetadata
 
 // SplitHandlerFactory allows creation of a handler that has splitting capabilities.
 func SplitHandlerFactory(family Family, logger *logp.Logger, metadataCallback MetadataFunc, callback inputsource.NetworkFunc, splitFunc bufio.SplitFunc) HandlerFactory {
 	return func(config ListenerConfig) ConnectionHandler {
-		return ConnectionHandler(func(closer CloseRef, conn net.Conn) error {
+		return ConnectionHandler(func(ctx context.Context, conn net.Conn) error {
 			metadata := metadataCallback(conn)
 			maxMessageSize := uint64(config.MaxMessageSize)
 
@@ -60,16 +61,11 @@ func SplitHandlerFactory(family Family, logger *logp.Logger, metadataCallback Me
 			scanner.Buffer(buffer, int(maxMessageSize))
 			for {
 				select {
-				case <-closer.Done():
+				case <-ctx.Done():
 					break
 				default:
 				}
 
-				// Ensure that if the Conn is already closed then dont attempt to scan again
-				if closer.Err() == ErrClosed {
-					break
-				}
-
 				if !scanner.Scan() {
 					break
 				}

filebeat/inputsource/common/listener.go

@@ -78,6 +78,14 @@ func (l *Listener) Start() error {
 		return err
 	}
 
+	l.ctx, l.cancel = context.WithCancel(context.Background())
+	go func() {
+		<-l.ctx.Done()
+		l.Listener.Close()
+	}()
+
+	l.log.Info("Started listening for " + l.family.String() + " connection")
+
 	l.wg.Add(1)
 	go func() {
 		defer l.wg.Done()