pub trait Client: Errors {
fn subscribe<'a, S>(
&'a mut self,
topic: S,
qos: QoS
) -> Result<MessageId, Self::Error>
where
S: Into<Cow<'a, str>>;
fn unsubscribe<'a, S>(
&'a mut self,
topic: S
) -> Result<MessageId, Self::Error>
where
S: Into<Cow<'a, str>>;
}