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/#01-4     401ns ± 2%     383ns ± 1%   -4.54%  (p=0.008 n=5+5)
QueryUnescape/#02-4     300ns ± 2%     274ns ± 2%   -8.66%  (p=0.008 n=5+5)
QueryUnescape/#03-4     564ns ± 2%     542ns ± 2%   -4.04%  (p=0.008 n=5+5)
QueryUnescape/#04-4    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/#01-4      392ns ± 2%     374ns ± 6%     ~     (p=0.063 n=5+5)
PathUnescape/#02-4      296ns ± 2%     274ns ± 2%   -7.43%  (p=0.008 n=5+5)
PathUnescape/#03-4      556ns ± 2%     537ns ± 1%   -3.45%  (p=0.008 n=5+5)
PathUnescape/#04-4     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/#01-4      2.00 ± 0%      1.00 ± 0%  -50.00%  (p=0.008 n=5+5)
QueryUnescape/#02-4      2.00 ± 0%      1.00 ± 0%  -50.00%  (p=0.008 n=5+5)
QueryUnescape/#03-4      2.00 ± 0%      1.00 ± 0%  -50.00%  (p=0.008 n=5+5)
QueryUnescape/#04-4      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/#01-4       2.00 ± 0%      1.00 ± 0%  -50.00%  (p=0.008 n=5+5)
PathUnescape/#02-4       2.00 ± 0%      1.00 ± 0%  -50.00%  (p=0.008 n=5+5)
PathUnescape/#03-4       2.00 ± 0%      1.00 ± 0%  -50.00%  (p=0.008 n=5+5)
PathUnescape/#04-4       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>

diff --git a/src/net/url/url.go b/src/net/url/url.go
index b60e2387814ef2229f5c91cf045a590c4d51a333..b7e8beec75acc43b92cae4d2430ad4aede84de72 100644 (file)
--- 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