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>

2 files changed, 6 insertions, 10 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)