Use new unsafe functions introduced in go 1.20

This eliminates usage of deprecated and error prone `reflect.SliceHeader` and `reflect.StringHeader`. Backwards compatibility saved with build tags

util_unsafe.go → util_unsafe_119.go

@@ -1,5 +1,5 @@
-//go:build !purego
-// +build !purego
+//go:build !purego && !go1.20
+// +build !purego,!go1.20
 
 package ws
 

util_unsafe_120.go

@@ -0,0 +1,14 @@
+//go:build !purego && go1.20
+// +build !purego,go1.20
+
+package ws
+
+import "unsafe"
+
+func strToBytes(str string) (bts []byte) {
+	return unsafe.Slice(unsafe.StringData(str), len(str))
+}
+
+func btsToString(bts []byte) (str string) {
+	return unsafe.String(&bts[0], len(bts))
+}

wsutil/util_go119_test.go

@@ -0,0 +1,12 @@
+//go:build go1.20
+// +build go1.20
+
+package wsutil
+
+import (
+	"unsafe"
+)
+
+func fakeMake(n int) []byte {
+	return unsafe.Slice((*byte)(nil), n) // len and cap are 'n'
+}

wsutil/util_go120_test.go

@@ -0,0 +1,18 @@
+//go:build !go1.20
+// +build !go1.20
+
+package wsutil
+
+import (
+	"reflect"
+	"unsafe"
+)
+
+func fakeMake(n int) (r []byte) {
+	rh := (*reflect.SliceHeader)(unsafe.Pointer(&r))
+	*rh = reflect.SliceHeader{
+		Len: n,
+		Cap: n,
+	}
+	return r
+}

wsutil/writer_test.go

@@ -8,7 +8,6 @@ import (
 	"reflect"
 	"strconv"
 	"testing"
-	"unsafe"
 
 	"github.com/gobwas/ws"
 )
@@ -131,15 +130,6 @@ func genReserveTestCases(s ws.State, n, m, exp int) []reserveTestCase {
 	return ret
 }
 
-func fakeMake(n int) (r []byte) {
-	rh := (*reflect.SliceHeader)(unsafe.Pointer(&r))
-	*rh = reflect.SliceHeader{
-		Len: n,
-		Cap: n,
-	}
-	return r
-}
-
 var reserveTestCases = []reserveTestCase{
 	{
 		name:      "len7",