Macro retry_async 

macro_rules! retry_async {
    ($f:expr, $timeout:expr, $delay:expr) => { ... };
    ($f:expr, $timeout:expr) => { ... };
    ($f:expr) => { ... };
}

Retrying async closures/functions holding mutable references is a pain in Rust. So, for now, we’ll have to use a macro to work that around.