Function race_connect 

pub async fn race_connect<S, C, F, Fut>(
    candidates: S,
    max_in_flight: usize,
    dial: F,
) -> Result<(SocketAddr, C), Box<dyn Error + Sync + Send>>
where
    S: Stream<Item = Result<SocketAddr, Box<dyn Error + Sync + Send>>>,
    F: Fn(SocketAddr) -> Fut + Sync,
    Fut: Future<Output = Result<C, Box<dyn Error + Sync + Send>>> + Send,
    C: Send,

Available on crate feature net only.

Race connection attempts over a stream of candidate SocketAddresses.

Pulls candidates from candidates in order (e.g. happy-eyeballs order from a ConnectorTargetStream), keeps up to max_in_flight dials racing concurrently via dial, and returns the first successful connection together with the address it connected to. If every candidate fails (to resolve or to connect), the last error is returned.