Fix InfluxDB output UDP line splitting (#5439)

plugins/outputs/influxdb/udp.go

@@ -1,6 +1,8 @@
 package influxdb
 
 import (
+	"bufio"
+	"bytes"
 	"context"
 	"fmt"
 	"log"
@@ -45,9 +47,9 @@ func NewUDPClient(config *UDPConfig) (*udpClient, error) {
 	serializer := config.Serializer
 	if serializer == nil {
 		s := influx.NewSerializer()
-		s.SetMaxLineBytes(config.MaxPayloadSize)
 		serializer = s
 	}
+	serializer.SetMaxLineBytes(size)
 
 	dialer := config.Dialer
 	if dialer == nil {
@@ -96,7 +98,11 @@ func (c *udpClient) Write(ctx context.Context, metrics []telegraf.Metric) error
 			continue
 		}
 
-		_, err = c.conn.Write(octets)
+		scanner := bufio.NewScanner(bytes.NewReader(octets))
+		scanner.Split(scanLines)
+		for scanner.Scan() {
+			_, err = c.conn.Write(scanner.Bytes())
+		}
 		if err != nil {
 			c.conn.Close()
 			c.conn = nil
@@ -118,3 +124,15 @@ type netDialer struct {
 func (d *netDialer) DialContext(ctx context.Context, network, address string) (Conn, error) {
 	return d.Dialer.DialContext(ctx, network, address)
 }
+
+func scanLines(data []byte, atEOF bool) (advance int, token []byte, err error) {
+	if atEOF && len(data) == 0 {
+		return 0, nil, nil
+	}
+	if i := bytes.IndexByte(data, '\n'); i >= 0 {
+		// We have a full newline-terminated line.
+		return i + 1, data[0 : i+1], nil
+
+	}
+	return 0, nil, nil
+}