def post_validation(req: BaseRequest, *args) -> Tuple[dict, Optional[Error]]:
if req.method != "POST":
return {}, Error(405, "GET method is not allowed.")
if req.get_header("Content-Type") != "application/json":
return {}, Error(400, "HTTP request header `Content-Type` must be `application/json`.")
if req.body.getvalue().decode() == "":
return {}, Error(400, "Request body is empty.")
if not isinstance(req.json, dict):
return {}, Error(400, "Request body is not JSON string.")
for k in args:
if not req.json.get(k):
return {}, Error(400, f"The field {k} does not exist in the request body.")
return req.json, None
