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), every failure is returned in an ErrorList, each dial failure with its address as context. The last failure is the primary one, so the error classifies as before: when that failure is classified (it carries a ConnectionError or a timeout), the returned error is a ConnectionError with that classification. A single unclassified failure is returned as itself.