net/url: improve performance for resolvePath

benchmark compare results: benchmark old ns/op new ns/op delta BenchmarkResolvePath-12 297 141 -52.53% benchmark old allocs new allocs delta BenchmarkResolvePath-12 5 3 -40.00% benchmark old bytes new bytes delta BenchmarkResolvePath-12 181 24 -86.74% Change-Id: Ia69e9fb36abb5930ed49217b5219be62b57ec429 GitHub-Last-Rev: e16dd9f GitHub-Pull-Request: #42180 Reviewed-on: https://go-review.googlesource.com/c/go/+/264817 Run-TryBot: Emmanuel Odeke <emmanuel@orijtech.com> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org> Trust: Emmanuel Odeke <emmanuel@orijtech.com>
golang · Oct 28, 2020 · 49a210e · 49a210e
1 parent 07d206f
commit 49a210e
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Showing 2 changed files with 49 additions and 14 deletions.
diff --git a/src/net/url/url.go b/src/net/url/url.go
@@ -1000,25 +1000,52 @@ func resolvePath(base, ref string) string {
 	if full == "" {
 		return ""
 	}
-	src := strings.Split(full, "/")
-	dst := make([]string, 0, len(src))
-	for _, elem := range src {
-		switch elem {
-		case ".":
+
+	var (
+		last string
+		elem string
+		i    int
+		dst  strings.Builder
+	)
+	first := true
+	remaining := full
+	for i >= 0 {
+		i = strings.IndexByte(remaining, '/')
+		if i < 0 {
+			last, elem, remaining = remaining, remaining, ""
+		} else {
+			elem, remaining = remaining[:i], remaining[i+1:]
+		}
+		if elem == "." {
+			first = false
 			// drop
-		case "..":
-			if len(dst) > 0 {
-				dst = dst[:len(dst)-1]
+			continue
+		}
+
+		if elem == ".." {
+			str := dst.String()
+			index := strings.LastIndexByte(str, '/')
+
+			dst.Reset()
+			if index == -1 {
+				first = true
+			} else {
+				dst.WriteString(str[:index])
 			}
-		default:
-			dst = append(dst, elem)
+		} else {
+			if !first {
+				dst.WriteByte('/')
+			}
+			dst.WriteString(elem)
+			first = false
 		}
 	}
-	if last := src[len(src)-1]; last == "." || last == ".." {
-		// Add final slash to the joined path.
-		dst = append(dst, "")
+
+	if last == "." || last == ".." {
+		dst.WriteByte('/')
 	}
-	return "/" + strings.TrimPrefix(strings.Join(dst, "/"), "/")
+
+	return "/" + strings.TrimPrefix(dst.String(), "/")
 }
 
 // IsAbs reports whether the URL is absolute.

diff --git a/src/net/url/url_test.go b/src/net/url/url_test.go
@@ -1114,6 +1114,14 @@ func TestResolvePath(t *testing.T) {
 	}
 }
 
+func BenchmarkResolvePath(b *testing.B) {
+	b.ResetTimer()
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		resolvePath("a/b/c", ".././d")
+	}
+}
+
 var resolveReferenceTests = []struct {
 	base, rel, expected string
 }{