Use zero-copy approach to convert types between string and byte… (gin…

…-gonic#2206)

* Use zero-copy approach to convert types between string and byte slice

* Rename argument to a eligible one

Benchmark:

BenchmarkBytesConvBytesToStrRaw-4   	21003800	        70.9 ns/op	      96 B/op	       1 allocs/op
BenchmarkBytesConvBytesToStr-4      	1000000000	         0.333 ns/op	       0 B/op	       0 allocs/op
BenchmarkBytesConvStrToBytesRaw-4   	18478059	        59.3 ns/op	      96 B/op	       1 allocs/op
BenchmarkBytesConvStrToBytes-4      	1000000000	         0.373 ns/op	       0 B/op	       0 allocs/op


Co-authored-by: Bo-Yi Wu <appleboy.tw@gmail.com>

auth.go

@@ -8,6 +8,8 @@ import (
 	"encoding/base64"
 	"net/http"
 	"strconv"
+
+	"github.com/gin-gonic/gin/internal/bytesconv"
 )
 
 // AuthUserKey is the cookie name for user credential in basic auth.
@@ -83,5 +85,5 @@ func processAccounts(accounts Accounts) authPairs {
 
 func authorizationHeader(user, password string) string {
 	base := user + ":" + password
-	return "Basic " + base64.StdEncoding.EncodeToString([]byte(base))
+	return "Basic " + base64.StdEncoding.EncodeToString(bytesconv.StringToBytes(base))
 }

binding/form_mapping.go

@@ -12,6 +12,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/gin-gonic/gin/internal/bytesconv"
 	"github.com/gin-gonic/gin/internal/json"
 )
 
@@ -208,9 +209,9 @@ func setWithProperType(val string, value reflect.Value, field reflect.StructFiel
 		case time.Time:
 			return setTimeField(val, field, value)
 		}
-		return json.Unmarshal([]byte(val), value.Addr().Interface())
+		return json.Unmarshal(bytesconv.StringToBytes(val), value.Addr().Interface())
 	case reflect.Map:
-		return json.Unmarshal([]byte(val), value.Addr().Interface())
+		return json.Unmarshal(bytesconv.StringToBytes(val), value.Addr().Interface())
 	default:
 		return errUnknownType
 	}

gin.go

@@ -13,6 +13,7 @@ import (
 	"path"
 	"sync"
 
+	"github.com/gin-gonic/gin/internal/bytesconv"
 	"github.com/gin-gonic/gin/render"
 )
 
@@ -477,7 +478,7 @@ func redirectFixedPath(c *Context, root *node, trailingSlash bool) bool {
 	rPath := req.URL.Path
 
 	if fixedPath, ok := root.findCaseInsensitivePath(cleanPath(rPath), trailingSlash); ok {
-		req.URL.Path = string(fixedPath)
+		req.URL.Path = bytesconv.BytesToString(fixedPath)
 		redirectRequest(c)
 		return true
 	}

internal/bytesconv/bytesconv.go

@@ -0,0 +1,19 @@
+package bytesconv
+
+import (
+	"reflect"
+	"unsafe"
+)
+
+// StringToBytes converts string to byte slice without a memory allocation.
+func StringToBytes(s string) (b []byte) {
+	sh := *(*reflect.StringHeader)(unsafe.Pointer(&s))
+	bh := (*reflect.SliceHeader)(unsafe.Pointer(&b))
+	bh.Data, bh.Len, bh.Cap = sh.Data, sh.Len, sh.Len
+	return b
+}
+
+// BytesToString converts byte slice to string without a memory allocation.
+func BytesToString(b []byte) string {
+	return *(*string)(unsafe.Pointer(&b))
+}

internal/bytesconv/bytesconv_test.go

@@ -0,0 +1,95 @@
+package bytesconv
+
+import (
+	"bytes"
+	"math/rand"
+	"strings"
+	"testing"
+	"time"
+)
+
+var testString = "Albert Einstein: Logic will get you from A to B. Imagination will take you everywhere."
+var testBytes = []byte(testString)
+
+func rawBytesToStr(b []byte) string {
+	return string(b)
+}
+
+func rawStrToBytes(s string) []byte {
+	return []byte(s)
+}
+
+// go test -v
+
+func TestBytesToString(t *testing.T) {
+	data := make([]byte, 1024)
+	for i := 0; i < 100; i++ {
+		rand.Read(data)
+		if rawBytesToStr(data) != BytesToString(data) {
+			t.Fatal("don't match")
+		}
+	}
+}
+
+const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+const (
+	letterIdxBits = 6                    // 6 bits to represent a letter index
+	letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits
+	letterIdxMax  = 63 / letterIdxBits   // # of letter indices fitting in 63 bits
+)
+
+var src = rand.NewSource(time.Now().UnixNano())
+
+func RandStringBytesMaskImprSrcSB(n int) string {
+	sb := strings.Builder{}
+	sb.Grow(n)
+	// A src.Int63() generates 63 random bits, enough for letterIdxMax characters!
+	for i, cache, remain := n-1, src.Int63(), letterIdxMax; i >= 0; {
+		if remain == 0 {
+			cache, remain = src.Int63(), letterIdxMax
+		}
+		if idx := int(cache & letterIdxMask); idx < len(letterBytes) {
+			sb.WriteByte(letterBytes[idx])
+			i--
+		}
+		cache >>= letterIdxBits
+		remain--
+	}
+
+	return sb.String()
+}
+
+func TestStringToBytes(t *testing.T) {
+	for i := 0; i < 100; i++ {
+		s := RandStringBytesMaskImprSrcSB(64)
+		if !bytes.Equal(rawStrToBytes(s), StringToBytes(s)) {
+			t.Fatal("don't match")
+		}
+	}
+}
+
+// go test -v -run=none -bench=^BenchmarkBytesConv -benchmem=true
+
+func BenchmarkBytesConvBytesToStrRaw(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		rawBytesToStr(testBytes)
+	}
+}
+
+func BenchmarkBytesConvBytesToStr(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		BytesToString(testBytes)
+	}
+}
+
+func BenchmarkBytesConvStrToBytesRaw(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		rawStrToBytes(testString)
+	}
+}
+
+func BenchmarkBytesConvStrToBytes(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		StringToBytes(testString)
+	}
+}

render/json.go

@@ -10,6 +10,7 @@ import (
 	"html/template"
 	"net/http"
 
+	"github.com/gin-gonic/gin/internal/bytesconv"
 	"github.com/gin-gonic/gin/internal/json"
 )
 
@@ -97,8 +98,9 @@ func (r SecureJSON) Render(w http.ResponseWriter) error {
 		return err
 	}
 	// if the jsonBytes is array values
-	if bytes.HasPrefix(jsonBytes, []byte("[")) && bytes.HasSuffix(jsonBytes, []byte("]")) {
-		_, err = w.Write([]byte(r.Prefix))
+	if bytes.HasPrefix(jsonBytes, bytesconv.StringToBytes("[")) && bytes.HasSuffix(jsonBytes,
+		bytesconv.StringToBytes("]")) {
+		_, err = w.Write(bytesconv.StringToBytes(r.Prefix))
 		if err != nil {
 			return err
 		}
@@ -126,19 +128,19 @@ func (r JsonpJSON) Render(w http.ResponseWriter) (err error) {
 	}
 
 	callback := template.JSEscapeString(r.Callback)
-	_, err = w.Write([]byte(callback))
+	_, err = w.Write(bytesconv.StringToBytes(callback))
 	if err != nil {
 		return err
 	}
-	_, err = w.Write([]byte("("))
+	_, err = w.Write(bytesconv.StringToBytes("("))
 	if err != nil {
 		return err
 	}
 	_, err = w.Write(ret)
 	if err != nil {
 		return err
 	}
-	_, err = w.Write([]byte(");"))
+	_, err = w.Write(bytesconv.StringToBytes(");"))
 	if err != nil {
 		return err
 	}
@@ -160,7 +162,7 @@ func (r AsciiJSON) Render(w http.ResponseWriter) (err error) {
 	}
 
 	var buffer bytes.Buffer
-	for _, r := range string(ret) {
+	for _, r := range bytesconv.BytesToString(ret) {
 		cvt := string(r)
 		if r >= 128 {
 			cvt = fmt.Sprintf("\\u%04x", int64(r))