作者:张富春(ahfuzhang)，转载时请注明作者和引用链接，谢谢！
做 profile 发现 url.QueryEscape 占用的 CPU 时间较多，于是搜索到了一个资料：net/url: optimize unescape and escape.
于是在这个代码的基础上改了FastQueryString的版本。
在 Macbook pro m2 上测试：
- url.QueryEscape() 281.5 ns/op
- FastQueryEscape() 38.40 ns/op， 快7.33 倍
具体代码如下：query_escape.go
package stringsutil
import (
"bytes"
"reflect"
"unsafe"
)
func shouldPathEscape(c byte) bool {
if 'A' <= c && c <= 'Z' || 'a' <= c && c <= 'z' || '0' <= c && c <= '9' {
return false
}
switch c {
case '-', '_', '.', '~': // = & ':', '@', '+', '$'
return false
}
return true
}
var (
shouldEscapeLUT [256]bool
)
func init() {
for i := 0; i < 256; i++ {
shouldEscapeLUT[i] = shouldPathEscape(byte(i))
}
}
// FastQueryEscape fast version
func FastQueryEscape(s string, buf *bytes.Buffer) []byte {
hexCount := 0
for i := 0; i < len(s); i++ {
if shouldEscapeLUT[s[i]] {
hexCount++
}
}
if hexCount == 0 {
return NoAllocBytes(s)
}
total := len(s) + 2*hexCount
if buf.Cap() < total {
buf.Grow(total * 2)
}
t := buf.Bytes()[:total]
j := 0
for i := 0; i < len(s); i++ {
c := s[i]
if shouldEscapeLUT[c] {
t[j] = '%'
t[j+1] = "0123456789ABCDEF"[c>>4]
t[j+2] = "0123456789ABCDEF"[c&15]
j += 3
} else {
t[j] = c
j++
}
}
return t
}
// copy from prometheus source code
// NoAllocString convert []byte to string
func NoAllocString(buf []byte) string {
return *(*string)(unsafe.Pointer(&buf))
}
// NoAllocBytes convert string to []byte
func NoAllocBytes(buf string) []byte {
// not safe: return *(*[]byte)(unsafe.Pointer(&buf))
x := (*reflect.StringHeader)(unsafe.Pointer(&buf))
h := reflect.SliceHeader{Data: x.Data, Len: x.Len, Cap: x.Len}
// nolint:all
return *(*[]byte)(unsafe.Pointer(&h))
}
使用的时候要重用 bytes.Buffer 对象。例如如下：
var testStr = "a=1&b=2&%%?_-/中文__-_.~:@+$"
// a%3D1%26b%3D2%26%25%25%3F_-%2F%E4%B8%AD%E6%96%87__-_.~%3A%40%2B%24
func TestFastQueryEscape(t *testing.T) {
s := url.QueryEscape(testStr)
t.Logf("%s", s)
target := &bytes.Buffer{}
target.Grow(1024)
out := FastQueryEscape(testStr, target)
t.Logf("%s", NoAllocString(out))
if s != NoAllocString(out) {
t.Error("not match")
}
}