mongocrypt_status_set requires null byte to be included in message_len, eg in Python this code prints '12' instead of '123':

msg = b"123"
lib.mongocrypt_status_set(
    status, lib.MONGOCRYPT_STATUS_ERROR_CLIENT, 1, msg, len(msg) + 1)
msg2 = _to_string(lib.mongocrypt_status_message(status, ffi.NULL))
print(msg2)

Other libmongocrypt functions (like mongocrypt_ctx_setopt_masterkey_aws) don't need the +1 for the null byte so I consider this a bug.