all: use strings.Builder instead of bytes.Buffer where appropriate

I grepped for "bytes.Buffer" and "buf.String" and mostly ignored test
files. I skipped a few on purpose and probably missed a few others,
but otherwise I think this should be most of them.

Updates #18990

Change-Id: I5a6ae4296b87b416d8da02d7bfaf981d8cc14774
Reviewed-on: https://go-review.googlesource.com/102479
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

4 files changed, 12 insertions, 17 deletions

diff --git a/src/net/http/cookie.go b/src/net/http/cookie.go
index 38b1b3630e..3e80cb659a 100644
--- a/src/net/http/cookie.go
+++ b/src/net/http/cookie.go
@@ -5,7 +5,6 @@
 package http
 
 import (
-	"bytes"
 	"log"
 	"net"
 	"strconv"
@@ -143,7 +142,7 @@ func (c *Cookie) String() string {
 	if c == nil || !isCookieNameValid(c.Name) {
 		return ""
 	}
-	var b bytes.Buffer
+	var b strings.Builder
 	b.WriteString(sanitizeCookieName(c.Name))
 	b.WriteRune('=')
 	b.WriteString(sanitizeCookieValue(c.Value))
@@ -168,17 +167,14 @@ func (c *Cookie) String() string {
 			log.Printf("net/http: invalid Cookie.Domain %q; dropping domain attribute", c.Domain)
 		}
 	}
+	var buf [len(TimeFormat)]byte
 	if validCookieExpires(c.Expires) {
 		b.WriteString("; Expires=")
-		b2 := b.Bytes()
-		b.Reset()
-		b.Write(c.Expires.UTC().AppendFormat(b2, TimeFormat))
+		b.Write(c.Expires.UTC().AppendFormat(buf[:0], TimeFormat))
 	}
 	if c.MaxAge > 0 {
 		b.WriteString("; Max-Age=")
-		b2 := b.Bytes()
-		b.Reset()
-		b.Write(strconv.AppendInt(b2, int64(c.MaxAge), 10))
+		b.Write(strconv.AppendInt(buf[:0], int64(c.MaxAge), 10))
 	} else if c.MaxAge < 0 {
 		b.WriteString("; Max-Age=0")
 	}
diff --git a/src/net/http/httptest/server.go b/src/net/http/httptest/server.go
index 6075397a26..ebafc9999c 100644
--- a/src/net/http/httptest/server.go
+++ b/src/net/http/httptest/server.go
@@ -7,7 +7,6 @@
 package httptest
 
 import (
-	"bytes"
 	"crypto/tls"
 	"crypto/x509"
 	"flag"
@@ -17,6 +16,7 @@ import (
 	"net/http"
 	"net/http/internal"
 	"os"
+	"strings"
 	"sync"
 	"time"
 )
@@ -224,7 +224,7 @@ func (s *Server) Close() {
 func (s *Server) logCloseHangDebugInfo() {
 	s.mu.Lock()
 	defer s.mu.Unlock()
-	var buf bytes.Buffer
+	var buf strings.Builder
 	buf.WriteString("httptest.Server blocked in Close after 5 seconds, waiting for connections:\n")
 	for c, st := range s.conns {
 		fmt.Fprintf(&buf, "  %T %p %v in state %v\n", c, c, c.RemoteAddr(), st)
diff --git a/src/net/mail/message.go b/src/net/mail/message.go
index 4f3184f3e8..5912b90334 100644
--- a/src/net/mail/message.go
+++ b/src/net/mail/message.go
@@ -19,7 +19,6 @@ package mail
 
 import (
 	"bufio"
-	"bytes"
 	"errors"
 	"fmt"
 	"io"
@@ -735,7 +734,7 @@ func isQtext(r rune) bool {
 
 // quoteString renders a string as an RFC 5322 quoted-string.
 func quoteString(s string) string {
-	var buf bytes.Buffer
+	var buf strings.Builder
 	buf.WriteByte('"')
 	for _, r := range s {
 		if isQtext(r) || isWSP(r) {
diff --git a/src/net/url/url.go b/src/net/url/url.go
index cc6c5e26e4..4a815148bf 100644
--- a/src/net/url/url.go
+++ b/src/net/url/url.go
@@ -11,7 +11,6 @@ package url
 // contain references to issue numbers with details.
 
 import (
-	"bytes"
 	"errors"
 	"fmt"
 	"sort"
@@ -737,7 +736,7 @@ func validOptionalPort(port string) bool {
 //	- if u.RawQuery is empty, ?query is omitted.
 //	- if u.Fragment is empty, #fragment is omitted.
 func (u *URL) String() string {
-	var buf bytes.Buffer
+	var buf strings.Builder
 	if u.Scheme != "" {
 		buf.WriteString(u.Scheme)
 		buf.WriteByte(':')
@@ -878,7 +877,7 @@ func (v Values) Encode() string {
 	if v == nil {
 		return ""
 	}
-	var buf bytes.Buffer
+	var buf strings.Builder
 	keys := make([]string, 0, len(v))
 	for k := range v {
 		keys = append(keys, k)
@@ -886,12 +885,13 @@ func (v Values) Encode() string {
 	sort.Strings(keys)
 	for _, k := range keys {
 		vs := v[k]
-		prefix := QueryEscape(k) + "="
+		keyEscaped := QueryEscape(k)
 		for _, v := range vs {
 			if buf.Len() > 0 {
 				buf.WriteByte('&')
 			}
-			buf.WriteString(prefix)
+			buf.WriteString(keyEscaped)
+			buf.WriteByte('=')
 			buf.WriteString(QueryEscape(v))
 		}
 	}