Add CopyData and CopyDone messages support to Backend

backend.go

@@ -16,6 +16,8 @@ type Backend struct {
 	cancelRequest   CancelRequest
 	_close          Close
 	copyFail        CopyFail
+	copyData        CopyData
+	copyDone        CopyDone
 	describe        Describe
 	execute         Execute
 	flush           Flush
@@ -116,6 +118,10 @@ func (b *Backend) Receive() (FrontendMessage, error) {
 		msg = &b.execute
 	case 'f':
 		msg = &b.copyFail
+	case 'd':
+		msg = &b.copyData
+	case 'c':
+		msg = &b.copyDone
 	case 'H':
 		msg = &b.flush
 	case 'P':