Function http_connect 

pub async fn http_connect<IO, BodyIn, BodyConnection>(
    io: IO,
    req: Request<BodyIn>,
    exec: Executor,
) -> Result<EstablishedClientConnection<HttpClientService<BodyConnection>, Request<BodyIn>>, OpaqueError>
where
    IO: Io + Unpin + ExtensionsMut,
    BodyIn: Body + Unpin + Send + 'static,
    <BodyIn as Body>::Data: Send + 'static,
    <BodyIn as Body>::Error: Into<Box<dyn Error + Send + Sync>>,
    BodyConnection: Body + Unpin + Send + 'static,
    <BodyConnection as Body>::Data: Send + 'static,
    <BodyConnection as Body>::Error: Into<Box<dyn Error + Send + Sync>>,

Establish an HTTP connection on the pre-established IO (bytes) stream with the given http request as context for the initial setup.