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
+}