validate_4.rs

// ...

impl Validator {

  // ...

  pub async fn is_valid(&self, key: String) -> bool {
      let result: bool = self
          .contract
          .query("isValid", (key.clone(),), None, Options::default(), None)
          .await
          .unwrap();
      log::debug!("{} is valid?: {}", key, result);
      result
  }

}