net: use strings.Builder

Change-Id: I3861a73d6b9d1d454c42bec50099b916bf30f1cd
Reviewed-on: https://go-review.googlesource.com/c/go/+/428266
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Robert Griesemer <[email protected]>
Run-TryBot: xie cui <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Damien Neil <[email protected]>

Author: cuiweixie

src/net/lookup_test.go

@@ -7,7 +7,6 @@
 package net
 
 import (
-	"bytes"
 	"context"
 	"fmt"
 	"internal/testenv"
@@ -718,7 +717,7 @@ func testDots(t *testing.T, mode string) {
 }
 
 func mxString(mxs []*MX) string {
-	var buf bytes.Buffer
+	var buf strings.Builder
 	sep := ""
 	fmt.Fprintf(&buf, "[")
 	for _, mx := range mxs {
@@ -730,7 +729,7 @@ func mxString(mxs []*MX) string {
 }
 
 func nsString(nss []*NS) string {
-	var buf bytes.Buffer
+	var buf strings.Builder
 	sep := ""
 	fmt.Fprintf(&buf, "[")
 	for _, ns := range nss {
@@ -742,7 +741,7 @@ func nsString(nss []*NS) string {
 }
 
 func srvString(srvs []*SRV) string {
-	var buf bytes.Buffer
+	var buf strings.Builder
 	sep := ""
 	fmt.Fprintf(&buf, "[")
 	for _, srv := range srvs {

src/net/lookup_windows_test.go

@@ -5,7 +5,6 @@
 package net
 
 import (
-	"bytes"
 	"context"
 	"encoding/json"
 	"errors"
@@ -216,8 +215,8 @@ func (s byHost) Less(i, j int) bool { return s[i].Host < s[j].Host }
 func (s byHost) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
 
 func nslookup(qtype, name string) (string, error) {
-	var out bytes.Buffer
-	var err bytes.Buffer
+	var out strings.Builder
+	var err strings.Builder
 	cmd := exec.Command("nslookup", "-querytype="+qtype, name)
 	cmd.Stdout = &out
 	cmd.Stderr = &err