func Poll()

in origin/blobclient/cluster_client.go [268:307]
36 lines of code
9 McCabe index (conditional complexity)

func Poll(
	r ClientResolver, b backoff.BackOff, d core.Digest, makeRequest func(Client) error) error {

	// By looping over clients in order, we will always prefer the same origin
	// for making requests to loosely guarantee that only one origin needs to
	// fetch the file from remote backend.
	clients, err := r.Resolve(d)
	if err != nil {
		return fmt.Errorf("resolve clients: %s", err)
	}
	var errs []error
ORIGINS:
	for _, client := range clients {
		b.Reset()
	POLL:
		for {
			if err := makeRequest(client); err != nil {
				if serr, ok := err.(httputil.StatusError); ok {
					if serr.Status == http.StatusAccepted {
						d := b.NextBackOff()
						if d == backoff.Stop {
							break POLL // Backoff timed out.
						}
						time.Sleep(d)
						continue POLL
					}
					if serr.Status < 500 {
						return err
					}
				}
				errs = append(errs, fmt.Errorf("origin %s: %s", client.Addr(), err))
				continue ORIGINS
			}
			return nil // Success!
		}
		errs = append(errs,
			fmt.Errorf("origin %s: backoff timed out on 202 responses", client.Addr()))
	}
	return fmt.Errorf("all origins unavailable: %s", errutil.Join(errs))
}