net/url: Reduce allocation on parsing URL func

Build result string via string.Builder to avoid allocation. As side effect some performance boots. name old time/op new time/op delta QueryUnescape/#00-4 114ns ± 0% 98ns ± 1% -13.89% (p=0.000 n=4+5) QueryUnescape/#1-4 401ns ± 2% 383ns ± 1% -4.54% (p=0.008 n=5+5) QueryUnescape/#2-4 300ns ± 2% 274ns ± 2% -8.66% (p=0.008 n=5+5) QueryUnescape/#3-4 564ns ± 2% 542ns ± 2% -4.04% (p=0.008 n=5+5) QueryUnescape/#4-4 3.27µs ± 2% 3.34µs ± 8% ~ (p=0.690 n=5+5) PathUnescape/#00-4 112ns ± 2% 99ns ± 3% -11.25% (p=0.008 n=5+5) PathUnescape/#1-4 392ns ± 2% 374ns ± 6% ~ (p=0.063 n=5+5) PathUnescape/#2-4 296ns ± 2% 274ns ± 2% -7.43% (p=0.008 n=5+5) PathUnescape/#3-4 556ns ± 2% 537ns ± 1% -3.45% (p=0.008 n=5+5) PathUnescape/#4-4 2.99µs ± 1% 3.00µs ± 1% ~ (p=0.690 n=5+5) name old allocs/op new allocs/op delta QueryUnescape/#00-4 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.008 n=5+5) QueryUnescape/#1-4 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.008 n=5+5) QueryUnescape/#2-4 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.008 n=5+5) QueryUnescape/#3-4 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.008 n=5+5) QueryUnescape/#4-4 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.008 n=5+5) PathUnescape/#00-4 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.008 n=5+5) PathUnescape/#1-4 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.008 n=5+5) PathUnescape/#2-4 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.008 n=5+5) PathUnescape/#3-4 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.008 n=5+5) PathUnescape/#4-4 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.008 n=5+5) Change-Id: I7cba5eb53bebef7b1fdd44598eed47241ce83167 Reviewed-on: https://go-review.googlesource.com/c/go/+/166463 Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org> Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>
golang · Apr 23, 2019 · 601eee3 · 601eee3
1 parent 24513d3
commit 601eee3
Showing 1 changed file with 9 additions and 14 deletions.
diff --git a/src/net/url/url.go b/src/net/url/url.go
@@ -250,29 +250,24 @@ func unescape(s string, mode encoding) (string, error) {
 		return s, nil
 	}
 
-	t := make([]byte, len(s)-2*n)
-	j := 0
-	for i := 0; i < len(s); {
+	var t strings.Builder
+	t.Grow(len(s) - 2*n)
+	for i := 0; i < len(s); i++ {
 		switch s[i] {
 		case '%':
-			t[j] = unhex(s[i+1])<<4 | unhex(s[i+2])
-			j++
-			i += 3
+			t.WriteByte(unhex(s[i+1])<<4 | unhex(s[i+2]))
+			i += 2
 		case '+':
 			if mode == encodeQueryComponent {
-				t[j] = ' '
+				t.WriteByte(' ')
 			} else {
-				t[j] = '+'
+				t.WriteByte('+')
 			}
-			j++
-			i++
 		default:
-			t[j] = s[i]
-			j++
-			i++
+			t.WriteByte(s[i])
 		}
 	}
-	return string(t), nil
+	return t.String(), nil
 }
 
 // QueryEscape escapes the string so it can be safely placed