py/stream: Implement generic flush() method, in terms of C-level ioctl.

py/stream.c

@@ -477,6 +477,17 @@ STATIC mp_obj_t stream_tell(mp_obj_t self) {
 }
 MP_DEFINE_CONST_FUN_OBJ_1(mp_stream_tell_obj, stream_tell);
 
+STATIC mp_obj_t stream_flush(mp_obj_t self) {
+    const mp_stream_p_t *stream_p = mp_get_stream_raise(self, MP_STREAM_OP_IOCTL);
+    int error;
+    mp_uint_t res = stream_p->ioctl(self, MP_STREAM_FLUSH, 0, &error);
+    if (res == MP_STREAM_ERROR) {
+        nlr_raise(mp_obj_new_exception_arg1(&mp_type_OSError, MP_OBJ_NEW_SMALL_INT(error)));
+    }
+    return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_1(mp_stream_flush_obj, stream_flush);
+
 STATIC mp_obj_t stream_ioctl(size_t n_args, const mp_obj_t *args) {
     const mp_stream_p_t *stream_p = mp_get_stream_raise(args[0], MP_STREAM_OP_IOCTL);
 

py/stream.h

@@ -58,6 +58,7 @@ MP_DECLARE_CONST_FUN_OBJ(mp_stream_write_obj);
 MP_DECLARE_CONST_FUN_OBJ(mp_stream_write1_obj);
 MP_DECLARE_CONST_FUN_OBJ(mp_stream_seek_obj);
 MP_DECLARE_CONST_FUN_OBJ(mp_stream_tell_obj);
+MP_DECLARE_CONST_FUN_OBJ(mp_stream_flush_obj);
 MP_DECLARE_CONST_FUN_OBJ(mp_stream_ioctl_obj);
 
 // these are for mp_get_stream_raise and can be or'd together