Fix socket_listener setting ReadBufferSize on TCP sockets (#3874)

CHANGELOG.md

@@ -87,6 +87,7 @@
 - [#1896](https://github.com/influxdata/telegraf/issues/1896): Fix various mysql data type conversions.
 - [#3810](https://github.com/influxdata/telegraf/issues/3810): Fix metric buffer limit in internal plugin after reload.
 - [#3801](https://github.com/influxdata/telegraf/issues/3801): Fix panic in http_response on invalid regex.
+- [#3973](https://github.com/influxdata/telegraf/issues/3873): Fix socket_listener setting ReadBufferSize on tcp sockets.
 
 ## v1.5.3 [unreleased]
 

plugins/inputs/socket_listener/socket_listener.go

@@ -26,6 +26,8 @@ type streamSocketListener struct {
 	net.Listener
 	*SocketListener
 
+	sockType string
+
 	connections    map[string]net.Conn
 	connectionsMtx sync.Mutex
 }
@@ -42,6 +44,14 @@ func (ssl *streamSocketListener) listen() {
 			break
 		}
 
+		if ssl.ReadBufferSize > 0 {
+			if srb, ok := c.(setReadBufferer); ok {
+				srb.SetReadBuffer(ssl.ReadBufferSize)
+			} else {
+				log.Printf("W! Unable to set read buffer on a %s socket", ssl.sockType)
+			}
+		}
+
 		ssl.connectionsMtx.Lock()
 		if ssl.MaxConnections > 0 && len(ssl.connections) >= ssl.MaxConnections {
 			ssl.connectionsMtx.Unlock()
@@ -237,17 +247,10 @@ func (sl *SocketListener) Start(acc telegraf.Accumulator) error {
 			return err
 		}
 
-		if sl.ReadBufferSize > 0 {
-			if srb, ok := l.(setReadBufferer); ok {
-				srb.SetReadBuffer(sl.ReadBufferSize)
-			} else {
-				log.Printf("W! Unable to set read buffer on a %s socket", spl[0])
-			}
-		}
-
 		ssl := &streamSocketListener{
 			Listener:       l,
 			SocketListener: sl,
+			sockType:       spl[0],
 		}
 
 		sl.Closer = ssl

plugins/inputs/socket_listener/socket_listener_test.go

@@ -1,6 +1,8 @@
 package socket_listener
 
 import (
+	"bytes"
+	"log"
 	"net"
 	"os"
 	"testing"
@@ -11,9 +13,24 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+// testEmptyLog is a helper function to ensure no data is written to log.
+// Should be called at the start of the test, and returns a function which should run at the end.
+func testEmptyLog(t *testing.T) func() {
+	buf := bytes.NewBuffer(nil)
+	log.SetOutput(buf)
+
+	return func() {
+		log.SetOutput(os.Stderr)
+		assert.Empty(t, string(buf.Bytes()), "log not empty")
+	}
+}
+
 func TestSocketListener_tcp(t *testing.T) {
+	defer testEmptyLog(t)()
+
 	sl := newSocketListener()
 	sl.ServiceAddress = "tcp://127.0.0.1:0"
+	sl.ReadBufferSize = 1024
 
 	acc := &testutil.Accumulator{}
 	err := sl.Start(acc)
@@ -27,8 +44,11 @@ func TestSocketListener_tcp(t *testing.T) {
 }
 
 func TestSocketListener_udp(t *testing.T) {
+	defer testEmptyLog(t)()
+
 	sl := newSocketListener()
 	sl.ServiceAddress = "udp://127.0.0.1:0"
+	sl.ReadBufferSize = 1024
 
 	acc := &testutil.Accumulator{}
 	err := sl.Start(acc)
@@ -42,9 +62,12 @@ func TestSocketListener_udp(t *testing.T) {
 }
 
 func TestSocketListener_unix(t *testing.T) {
+	defer testEmptyLog(t)()
+
 	os.Create("/tmp/telegraf_test.sock")
 	sl := newSocketListener()
 	sl.ServiceAddress = "unix:///tmp/telegraf_test.sock"
+	sl.ReadBufferSize = 1024
 
 	acc := &testutil.Accumulator{}
 	err := sl.Start(acc)
@@ -58,9 +81,12 @@ func TestSocketListener_unix(t *testing.T) {
 }
 
 func TestSocketListener_unixgram(t *testing.T) {
+	defer testEmptyLog(t)()
+
 	os.Create("/tmp/telegraf_test.sock")
 	sl := newSocketListener()
 	sl.ServiceAddress = "unixgram:///tmp/telegraf_test.sock"
+	sl.ReadBufferSize = 1024
 
 	acc := &testutil.Accumulator{}
 	err := sl.Start(acc)