remove use of dynamic buffer

broker.go

@@ -1,7 +1,6 @@
 package sarama
 
 import (
-	"bytes"
 	"crypto/tls"
 	"encoding/binary"
 	"fmt"
@@ -488,23 +487,13 @@ func (b *Broker) responseReceiver() {
 // When credentials are invalid, Kafka closes the connection. This does not seem to be the ideal way
 // of responding to bad credentials but thats how its being done today.
 func (b *Broker) doSASLPlainAuth() error {
-	authBytes := []byte("\x00" + b.conf.Net.SASL.User + "\x00" + b.conf.Net.SASL.Password)
-	buf := new(bytes.Buffer)
-
-	err := binary.Write(buf, binary.BigEndian, int32(len(authBytes)))
-	if err != nil {
-		Logger.Printf("Failed to encode payload size (SASL credentials): %s", err.Error())
-		return err
-	}
-
-	err = binary.Write(buf, binary.BigEndian, authBytes)
-	if err != nil {
-		Logger.Printf("Failed to encode payload (SASL credentials): %s", err.Error())
-		return err
-	}
+	length := 1 + len(b.conf.Net.SASL.User) + 1 + len(b.conf.Net.SASL.Password)
+	authBytes := make([]byte, length + 4)  //4 byte length header + auth data
+	binary.BigEndian.PutUint32(authBytes, uint32(length))
+	copy(authBytes[4:], []byte("\x00" + b.conf.Net.SASL.User + "\x00" + b.conf.Net.SASL.Password))
 
 	b.conn.SetWriteDeadline(time.Now().Add(b.conf.Net.WriteTimeout))
-	b.conn.Write(buf.Bytes())
+	b.conn.Write(authBytes)
 
 	header := make([]byte, 4)
 	n, err := io.ReadFull(b.conn, header)