net/url: avoid string concatenation in resolvePath

ame                  old time/op    new time/op    delta
String-12               8.09µs ± 7%    8.20µs ± 5%     ~     (p=0.347 n=20+19)
ResolvePath-12           223ns ± 8%     170ns ± 7%  -23.84%  (p=0.000 n=20+19)
QueryEscape/#00-12      72.9ns ± 5%    73.6ns ± 6%     ~     (p=0.337 n=20+20)
QueryEscape/#01-12       467ns ± 5%     467ns ± 7%     ~     (p=0.612 n=19+20)
QueryEscape/#02-12       257ns ± 8%     262ns ± 8%     ~     (p=0.080 n=20+20)
QueryEscape/#03-12       553ns ±12%     568ns ± 8%   +2.73%  (p=0.048 n=20+19)
QueryEscape/#04-12      4.45µs ± 7%    4.52µs ± 5%     ~     (p=0.163 n=20+20)
PathEscape/#00-12        119ns ± 9%     121ns ± 6%     ~     (p=0.140 n=20+20)
PathEscape/#01-12        458ns ± 7%     483ns ± 4%   +5.49%  (p=0.000 n=20+20)
PathEscape/#02-12        255ns ± 7%     257ns ± 7%     ~     (p=0.560 n=20+20)
PathEscape/#03-12        556ns ± 8%     559ns ± 8%     ~     (p=0.799 n=20+20)
PathEscape/#04-12       4.14µs ± 6%    4.28µs ± 8%   +3.30%  (p=0.003 n=20+20)
QueryUnescape/#00-12    72.2ns ± 8%    74.9ns ± 5%   +3.66%  (p=0.006 n=20+19)
QueryUnescape/#01-12     223ns ± 7%     230ns ± 8%   +2.84%  (p=0.016 n=20+20)
QueryUnescape/#02-12     200ns ± 7%     203ns ±10%     ~     (p=0.533 n=20+20)
QueryUnescape/#03-12     480ns ± 7%     500ns ± 8%   +4.15%  (p=0.006 n=20+20)
QueryUnescape/#04-12    2.61µs ± 8%    2.70µs ± 7%   +3.39%  (p=0.009 n=20+20)
PathUnescape/#00-12     74.6ns ± 6%    75.4ns ± 6%     ~     (p=0.425 n=20+20)
PathUnescape/#01-12      226ns ± 3%     227ns ± 8%     ~     (p=0.453 n=15+20)
PathUnescape/#02-12      202ns ±11%     202ns ± 6%     ~     (p=0.963 n=20+20)
PathUnescape/#03-12      484ns ± 9%     494ns ± 9%     ~     (p=0.078 n=20+19)
PathUnescape/#04-12     2.60µs ± 6%    2.61µs ± 8%     ~     (p=0.776 n=20+19)
Split-12                6.47ns ± 0%    6.47ns ± 0%     ~     (p=0.760 n=18+18)

name                  old alloc/op   new alloc/op   delta
String-12               1.50kB ± 0%    1.50kB ± 0%     ~     (all equal)
ResolvePath-12           24.0B ± 0%     16.0B ± 0%  -33.33%  (p=0.000 n=20+20)
QueryEscape/#00-12       8.00B ± 0%     8.00B ± 0%     ~     (all equal)
QueryEscape/#01-12       64.0B ± 0%     64.0B ± 0%     ~     (all equal)
QueryEscape/#02-12       32.0B ± 0%     32.0B ± 0%     ~     (all equal)
QueryEscape/#03-12       64.0B ± 0%     64.0B ± 0%     ~     (all equal)
QueryEscape/#04-12        832B ± 0%      832B ± 0%     ~     (all equal)
PathEscape/#00-12        16.0B ± 0%     16.0B ± 0%     ~     (all equal)
PathEscape/#01-12        64.0B ± 0%     64.0B ± 0%     ~     (all equal)
PathEscape/#02-12        32.0B ± 0%     32.0B ± 0%     ~     (all equal)
PathEscape/#03-12        64.0B ± 0%     64.0B ± 0%     ~     (all equal)
PathEscape/#04-12         704B ± 0%      704B ± 0%     ~     (all equal)
QueryUnescape/#00-12     8.00B ± 0%     8.00B ± 0%     ~     (all equal)
QueryUnescape/#01-12     24.0B ± 0%     24.0B ± 0%     ~     (all equal)
QueryUnescape/#02-12     24.0B ± 0%     24.0B ± 0%     ~     (all equal)
QueryUnescape/#03-12     64.0B ± 0%     64.0B ± 0%     ~     (all equal)
QueryUnescape/#04-12      320B ± 0%      320B ± 0%     ~     (all equal)
PathUnescape/#00-12      8.00B ± 0%     8.00B ± 0%     ~     (all equal)
PathUnescape/#01-12      24.0B ± 0%     24.0B ± 0%     ~     (all equal)
PathUnescape/#02-12      24.0B ± 0%     24.0B ± 0%     ~     (all equal)
PathUnescape/#03-12      64.0B ± 0%     64.0B ± 0%     ~     (all equal)
PathUnescape/#04-12       320B ± 0%      320B ± 0%     ~     (all equal)

name                  old allocs/op  new allocs/op  delta
String-12                 63.0 ± 0%      63.0 ± 0%     ~     (all equal)
ResolvePath-12            3.00 ± 0%      2.00 ± 0%  -33.33%  (p=0.000 n=20+20)
QueryEscape/#00-12        1.00 ± 0%      1.00 ± 0%     ~     (all equal)
QueryEscape/#01-12        1.00 ± 0%      1.00 ± 0%     ~     (all equal)
QueryEscape/#02-12        1.00 ± 0%      1.00 ± 0%     ~     (all equal)
QueryEscape/#03-12        1.00 ± 0%      1.00 ± 0%     ~     (all equal)
QueryEscape/#04-12        2.00 ± 0%      2.00 ± 0%     ~     (all equal)
PathEscape/#00-12         1.00 ± 0%      1.00 ± 0%     ~     (all equal)
PathEscape/#01-12         1.00 ± 0%      1.00 ± 0%     ~     (all equal)
PathEscape/#02-12         1.00 ± 0%      1.00 ± 0%     ~     (all equal)
PathEscape/#03-12         1.00 ± 0%      1.00 ± 0%     ~     (all equal)
PathEscape/#04-12         2.00 ± 0%      2.00 ± 0%     ~     (all equal)
QueryUnescape/#00-12      1.00 ± 0%      1.00 ± 0%     ~     (all equal)
QueryUnescape/#01-12      1.00 ± 0%      1.00 ± 0%     ~     (all equal)
QueryUnescape/#02-12      1.00 ± 0%      1.00 ± 0%     ~     (all equal)
QueryUnescape/#03-12      1.00 ± 0%      1.00 ± 0%     ~     (all equal)
QueryUnescape/#04-12      1.00 ± 0%      1.00 ± 0%     ~     (all equal)
PathUnescape/#00-12       1.00 ± 0%      1.00 ± 0%     ~     (all equal)
PathUnescape/#01-12       1.00 ± 0%      1.00 ± 0%     ~     (all equal)
PathUnescape/#02-12       1.00 ± 0%      1.00 ± 0%     ~     (all equal)
PathUnescape/#03-12       1.00 ± 0%      1.00 ± 0%     ~     (all equal)
PathUnescape/#04-12       1.00 ± 0%      1.00 ± 0%     ~     (all equal)

Fixes #43587

Change-Id: I66c47e78e92555180ce3554a2d4a21038362c41e
Reviewed-on: https://go-review.googlesource.com/c/go/+/282673
Trust: Ian Lance Taylor <iant@golang.org>
Trust: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>

diff --git a/src/net/url/url.go b/src/net/url/url.go
index a4d7c03a87d820e165f2050cfbb99e4346e08f67..73bef22e45614e16a4ee3ae3a596efe7e33e9045 100644 (file)
--- a/src/net/url/url.go
+++ b/src/net/url/url.go
@@ -1015,6 +1015,8 @@ func resolvePath(base, ref string) string {
        )
        first := true
        remaining := full
+       // We want to return a leading '/', so write it now.
+       dst.WriteByte('/')
        for i >= 0 {
                i = strings.IndexByte(remaining, '/')
                if i < 0 {
@@ -1029,10 +1031,12 @@ func resolvePath(base, ref string) string {
                }
 
                if elem == ".." {
-                       str := dst.String()
+                       // Ignore the leading '/' we already wrote.
+                       str := dst.String()[1:]
                        index := strings.LastIndexByte(str, '/')
 
                        dst.Reset()
+                       dst.WriteByte('/')
                        if index == -1 {
                                first = true
                        } else {
@@ -1051,7 +1055,12 @@ func resolvePath(base, ref string) string {
                dst.WriteByte('/')
        }
 
-       return "/" + strings.TrimPrefix(dst.String(), "/")
+       // We wrote an initial '/', but we don't want two.
+       r := dst.String()
+       if len(r) > 1 && r[1] == '/' {
+               r = r[1:]
+       }
+       return r
 }
 
 // IsAbs reports whether the URL is absolute.