net/http: use strings.FieldsFuncSeq to reduce memory allocations

net/http: use strings.FieldsFuncSeq to reduce memory allocations

After using strings.FieldsFuncSeq, the number of memory allocations has been reduced from 2 to 0.

The following is the complete benchamark code and results:

package main

import (
	"strings"
	"testing"
)

func isSlashRune(r rune) bool { return r == '/' || r == '\\' }

func containsDotDotLoop(v string) bool {
	if !strings.Contains(v, "..") {
		return false
	}
	for _, ent := range strings.FieldsFunc(v, isSlashRune) {
		if ent == ".." {
			return true
		}
	}
	return false
}

func containsDotDotSeq(v string) bool {
	if !strings.Contains(v, "..") {
		return false
	}
	for ent := range strings.FieldsFuncSeq(v, isSlashRune) {
		if ent == ".." {
			return true
		}
	}
	return false
}

func BenchmarkDotDot(b *testing.B) {
	testCases := []string{
		"/path/to/somewhere",
		"/path/../to/somewhere",
		"/really/long/path/with/many/segments",
		"../../../deep/path",
	}

	b.Run("Loop", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			for _, tc := range testCases {
				containsDotDotLoop(tc)
			}
		}
	})

	b.Run("Seq", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			for _, tc := range testCases {
				containsDotDotSeq(tc)
			}
		}
	})
}

go test -bench=. -benchmem

goos: darwin
goarch: arm64
pkg: bc
cpu: Apple M1
BenchmarkDotDot/Loop-8         	 6133270	       193.7 ns/op	     144 B/op	       2 allocs/op
BenchmarkDotDot/Seq-8          	23172360	        51.19 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	bc	2.633s

Change-Id: I529c296e701b22710e21b53877aa798799980a3b
Reviewed-on: https://go-review.googlesource.com/c/go/+/639536
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>