html/template: use strings.Builder

...and size initial buffers more accurately.

Easy pickings only. More might remain.

name                             old time/op    new time/op    delta
CSSEscaper-8                       1.17µs ± 1%    0.80µs ± 2%  -31.55%  (p=0.000 n=44+48)
CSSEscaperNoSpecials-8              205ns ± 2%     204ns ± 3%   -0.73%  (p=0.014 n=46+49)
DecodeCSS-8                         438ns ± 2%     436ns ± 2%     ~     (p=0.099 n=48+47)
DecodeCSSNoSpecials-8              6.11ns ± 3%    5.93ns ± 3%   -2.85%  (p=0.000 n=50+48)
CSSValueFilter-8                    149ns ± 0%     145ns ± 0%   -2.68%  (p=0.000 n=32+35)
CSSValueFilterOk-8                  238ns ± 2%     234ns ± 2%   -1.40%  (p=0.000 n=49+47)
EscapedExecute-8                   2.53µs ± 2%    2.55µs ± 1%   +0.87%  (p=0.000 n=48+49)
HTMLNospaceEscaper-8               1.35µs ± 2%    0.92µs ± 1%  -31.74%  (p=0.000 n=48+48)
HTMLNospaceEscaperNoSpecials-8      278ns ± 2%     263ns ± 2%   -5.17%  (p=0.000 n=47+49)
StripTags-8                         778ns ± 2%     786ns ± 1%   +0.96%  (p=0.000 n=46+47)
StripTagsNoSpecials-8              84.2ns ± 1%    84.1ns ± 1%     ~     (p=0.300 n=48+48)
JSValEscaperWithNum-8               506ns ± 2%     486ns ± 3%   -3.82%  (p=0.000 n=47+45)
JSValEscaperWithStr-8              1.61µs ± 1%    1.64µs ± 1%   +1.75%  (p=0.000 n=44+49)
JSValEscaperWithStrNoSpecials-8     548ns ± 2%     552ns ± 2%   +0.78%  (p=0.000 n=48+46)
JSValEscaperWithObj-8              1.91µs ± 2%    1.87µs ± 1%   -2.08%  (p=0.000 n=49+47)
JSValEscaperWithObjNoSpecials-8     735ns ± 2%     742ns ± 2%   +1.01%  (p=0.000 n=47+49)
JSStrEscaperNoSpecials-8            228ns ± 4%     211ns ± 3%   -7.53%  (p=0.000 n=50+49)
JSStrEscaper-8                     1.11µs ± 1%    0.78µs ± 1%  -29.94%  (p=0.000 n=48+48)
JSRegexpEscaperNoSpecials-8         214ns ± 2%     212ns ± 3%   -1.12%  (p=0.000 n=50+49)
JSRegexpEscaper-8                  1.17µs ± 0%    0.79µs ± 1%  -31.92%  (p=0.000 n=48+47)
TemplateSpecialTags-8               172µs ± 1%     172µs ± 1%     ~     (p=0.976 n=48+47)
URLEscaper-8                       1.88µs ± 2%    1.87µs ± 2%   -0.56%  (p=0.001 n=49+49)
URLEscaperNoSpecials-8              162ns ± 1%     169ns ± 1%   +3.76%  (p=0.000 n=49+50)
URLNormalizer-8                    1.29µs ± 3%    1.29µs ± 2%   -0.37%  (p=0.041 n=48+48)
URLNormalizerNoSpecials-8           185ns ± 1%     186ns ± 1%   +0.15%  (p=0.013 n=49+49)
SrcsetFilter-8                      616ns ± 1%     618ns ± 1%   +0.36%  (p=0.000 n=46+46)
SrcsetFilterNoSpecials-8            359ns ± 0%     352ns ± 0%   -1.93%  (p=0.000 n=40+43)
[Geo mean]                          560ns          525ns        -6.17%

name                             old alloc/op   new alloc/op   delta
CSSEscaper-8                         672B ± 0%      336B ± 0%  -50.00%  (p=0.000 n=50+50)
CSSEscaperNoSpecials-8              0.00B          0.00B          ~     (all equal)
DecodeCSS-8                          160B ± 0%      160B ± 0%     ~     (all equal)
DecodeCSSNoSpecials-8               0.00B          0.00B          ~     (all equal)
CSSValueFilter-8                    96.0B ± 0%     96.0B ± 0%     ~     (all equal)
CSSValueFilterOk-8                  48.0B ± 0%     48.0B ± 0%     ~     (all equal)
EscapedExecute-8                     688B ± 0%      624B ± 0%   -9.30%  (p=0.000 n=50+50)
HTMLNospaceEscaper-8                 752B ± 0%      368B ± 0%  -51.06%  (p=0.000 n=50+50)
HTMLNospaceEscaperNoSpecials-8      48.0B ± 0%     32.0B ± 0%  -33.33%  (p=0.000 n=50+50)
StripTags-8                          224B ± 0%      224B ± 0%     ~     (all equal)
StripTagsNoSpecials-8                112B ± 0%      112B ± 0%     ~     (all equal)
JSValEscaperWithNum-8               96.0B ± 0%     40.0B ± 0%  -58.33%  (p=0.000 n=50+50)
JSValEscaperWithStr-8                384B ± 0%      384B ± 0%     ~     (all equal)
JSValEscaperWithStrNoSpecials-8     96.0B ± 0%     96.0B ± 0%     ~     (all equal)
JSValEscaperWithObj-8                448B ± 0%      448B ± 0%     ~     (all equal)
JSValEscaperWithObjNoSpecials-8      160B ± 0%      160B ± 0%     ~     (all equal)
JSStrEscaperNoSpecials-8            0.00B          0.00B          ~     (all equal)
JSStrEscaper-8                       672B ± 0%      336B ± 0%  -50.00%  (p=0.000 n=50+50)
JSRegexpEscaperNoSpecials-8         0.00B          0.00B          ~     (all equal)
JSRegexpEscaper-8                    672B ± 0%      336B ± 0%  -50.00%  (p=0.000 n=50+50)
TemplateSpecialTags-8              48.0kB ± 0%    47.9kB ± 0%   -0.13%  (p=0.000 n=50+48)
URLEscaper-8                         336B ± 0%      336B ± 0%     ~     (all equal)
URLEscaperNoSpecials-8               112B ± 0%      112B ± 0%     ~     (all equal)
URLNormalizer-8                      176B ± 0%      176B ± 0%     ~     (all equal)
URLNormalizerNoSpecials-8            112B ± 0%      112B ± 0%     ~     (all equal)
SrcsetFilter-8                       160B ± 0%      160B ± 0%     ~     (all equal)
SrcsetFilterNoSpecials-8             160B ± 0%      160B ± 0%     ~     (all equal)
[Geo mean]                           259B           216B       -16.60%

name                             old allocs/op  new allocs/op  delta
CSSEscaper-8                         4.00 ± 0%      2.00 ± 0%  -50.00%  (p=0.000 n=50+50)
CSSEscaperNoSpecials-8               0.00           0.00          ~     (all equal)
DecodeCSS-8                          1.00 ± 0%      1.00 ± 0%     ~     (all equal)
DecodeCSSNoSpecials-8                0.00           0.00          ~     (all equal)
CSSValueFilter-8                     2.00 ± 0%      2.00 ± 0%     ~     (all equal)
CSSValueFilterOk-8                   3.00 ± 0%      3.00 ± 0%     ~     (all equal)
EscapedExecute-8                     18.0 ± 0%      18.0 ± 0%     ~     (all equal)
HTMLNospaceEscaper-8                 5.00 ± 0%      3.00 ± 0%  -40.00%  (p=0.000 n=50+50)
HTMLNospaceEscaperNoSpecials-8       1.00 ± 0%      1.00 ± 0%     ~     (all equal)
StripTags-8                          3.00 ± 0%      3.00 ± 0%     ~     (all equal)
StripTagsNoSpecials-8                2.00 ± 0%      2.00 ± 0%     ~     (all equal)
JSValEscaperWithNum-8                3.00 ± 0%      3.00 ± 0%     ~     (all equal)
JSValEscaperWithStr-8                2.00 ± 0%      2.00 ± 0%     ~     (all equal)
JSValEscaperWithStrNoSpecials-8      2.00 ± 0%      2.00 ± 0%     ~     (all equal)
JSValEscaperWithObj-8                3.00 ± 0%      3.00 ± 0%     ~     (all equal)
JSValEscaperWithObjNoSpecials-8      3.00 ± 0%      3.00 ± 0%     ~     (all equal)
JSStrEscaperNoSpecials-8             0.00           0.00          ~     (all equal)
JSStrEscaper-8                       4.00 ± 0%      2.00 ± 0%  -50.00%  (p=0.000 n=50+50)
JSRegexpEscaperNoSpecials-8          0.00           0.00          ~     (all equal)
JSRegexpEscaper-8                    4.00 ± 0%      2.00 ± 0%  -50.00%  (p=0.000 n=50+50)
TemplateSpecialTags-8                 185 ± 0%       185 ± 0%     ~     (all equal)
URLEscaper-8                         4.00 ± 0%      4.00 ± 0%     ~     (all equal)
URLEscaperNoSpecials-8               2.00 ± 0%      2.00 ± 0%     ~     (all equal)
URLNormalizer-8                      3.00 ± 0%      3.00 ± 0%     ~     (all equal)
URLNormalizerNoSpecials-8            2.00 ± 0%      2.00 ± 0%     ~     (all equal)
SrcsetFilter-8                       3.00 ± 0%      3.00 ± 0%     ~     (all equal)
SrcsetFilterNoSpecials-8             3.00 ± 0%      3.00 ± 0%     ~     (all equal)
[Geo mean]                           3.41           3.05       -10.65%

Change-Id: I809ea56495ce1881656af7e24621448ab64b449a
Reviewed-on: https://go-review.googlesource.com/c/155919
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/html/template/css.go

@@ -7,6 +7,7 @@ package template
 import (
 	"bytes"
 	"fmt"
+	"strings"
 	"unicode"
 	"unicode/utf8"
 )
@@ -156,7 +157,7 @@ func isCSSSpace(b byte) bool {
 // cssEscaper escapes HTML and CSS special characters using \<hex>+ escapes.
 func cssEscaper(args ...interface{}) string {
 	s, _ := stringify(args...)
-	var b bytes.Buffer
+	var b strings.Builder
 	r, w, written := rune(0), 0, 0
 	for i := 0; i < len(s); i += w {
 		// See comment in htmlEscaper.
@@ -168,6 +169,9 @@ func cssEscaper(args ...interface{}) string {
 		default:
 			continue
 		}
+		if written == 0 {
+			b.Grow(len(s))
+		}
 		b.WriteString(s[written:i])
 		b.WriteString(repl)
 		written = i + w

src/html/template/html.go

@@ -137,7 +137,7 @@ var htmlNospaceNormReplacementTable = []string{
 // htmlReplacer returns s with runes replaced according to replacementTable
 // and when badRunes is true, certain bad runes are allowed through unescaped.
 func htmlReplacer(s string, replacementTable []string, badRunes bool) string {
-	written, b := 0, new(bytes.Buffer)
+	written, b := 0, new(strings.Builder)
 	r, w := rune(0), 0
 	for i := 0; i < len(s); i += w {
 		// Cannot use 'for range s' because we need to preserve the width
@@ -146,6 +146,9 @@ func htmlReplacer(s string, replacementTable []string, badRunes bool) string {
 		r, w = utf8.DecodeRuneInString(s[i:])
 		if int(r) < len(replacementTable) {
 			if repl := replacementTable[r]; len(repl) != 0 {
+				if written == 0 {
+					b.Grow(len(s))
+				}
 				b.WriteString(s[written:i])
 				b.WriteString(repl)
 				written = i + w
@@ -154,6 +157,9 @@ func htmlReplacer(s string, replacementTable []string, badRunes bool) string {
 			// No-op.
 			// IE does not allow these ranges in unquoted attrs.
 		} else if 0xfdd0 <= r && r <= 0xfdef || 0xfff0 <= r && r <= 0xffff {
+			if written == 0 {
+				b.Grow(len(s))
+			}
 			fmt.Fprintf(b, "%s&#x%x;", s[written:i], r)
 			written = i + w
 		}

src/html/template/js.go

@@ -187,7 +187,7 @@ func jsValEscaper(args ...interface{}) string {
 	}
 	first, _ := utf8.DecodeRune(b)
 	last, _ := utf8.DecodeLastRune(b)
-	var buf bytes.Buffer
+	var buf strings.Builder
 	// Prevent IdentifierNames and NumericLiterals from running into
 	// keywords: in, instanceof, typeof, void
 	pad := isJSIdentPart(first) || isJSIdentPart(last)
@@ -217,7 +217,7 @@ func jsValEscaper(args ...interface{}) string {
 		if pad {
 			buf.WriteByte(' ')
 		}
-		b = buf.Bytes()
+		return buf.String()
 	}
 	return string(b)
 }
@@ -253,7 +253,7 @@ func jsRegexpEscaper(args ...interface{}) string {
 // It also replaces runes U+2028 and U+2029 with the raw strings `\u2028` and
 // `\u2029`.
 func replace(s string, replacementTable []string) string {
-	var b bytes.Buffer
+	var b strings.Builder
 	r, w, written := rune(0), 0, 0
 	for i := 0; i < len(s); i += w {
 		// See comment in htmlEscaper.
@@ -269,6 +269,9 @@ func replace(s string, replacementTable []string) string {
 		default:
 			continue
 		}
+		if written == 0 {
+			b.Grow(len(s))
+		}
 		b.WriteString(s[written:i])
 		b.WriteString(repl)
 		written = i + w