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

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)
+	}
+}