interface mqtt {
  /// Errors related to interacting with Mqtt
  variant error {
      /// An invalid address string
      invalid-address,
      /// There are too many open connections
      too-many-connections,
      /// Connection failure e.g. address not allowed.
      connection-failed(string),
      /// Some other error occurred
      other(string),
  }

  /// QoS for publishing Mqtt messages
     enum qos {
      at-most-once,
      at-least-once,
      exactly-once,
  }

  resource connection {
    /// Open a connection to the Mqtt instance at `address`.
    open: static func(address: string, username: string, password: string, keep-alive-interval-in-secs: u64) -> result<connection, error>;

    /// Publish an Mqtt message to the specified `topic`.
    publish: func(topic: string, payload: payload, qos: qos) -> result<_, error>;
  }

  /// The message payload.
  type payload = list<u8>;
}