Polling an API endpoint with timeout using channels

Question

I have written a simple API client for my app in Go. The client is very simple, it wraps http.Client and has some convenience methods.

The one method I am trying to get some feedback on, does endpoint polling with timeout. It blocks, and returns when either a timeout is reached or status returned by API is successful or in error.

My questions are in comments of the function itself. I have omitted some parts (structs, the "constructor method") that are not relevant to discussion.

caller (in main)

log.Printf("polling status, id: %d", sid)
status, err := api.PollStatus(sid, 1*time.Second, 5*time.Second)
if err != nil {
    log.Fatalf("PollStatus error: %+v", err)
}

log.Print(status)

the method

// PollStatus will keep 'pinging' the status API until timeout is reached or status returned is either sucesfull or in error.
// NOTES:
//   - this function will block the caller
// QUESTIONS:
//  - is the design/functionality of this method idiomatic Go or is there a better way?
//  - do I need to close ticker and timeout channels? If so how?
//  - is it safe to 'defer ticker.Stop()' at the start of goroutine or do I have to call it before each return?
func (client *APIClient) PollStatus(id int, pollInterval time.Duration, pollTimeout time.Duration) (*Status, error) {
    var status *Status
    var err error
    var wg sync.WaitGroup
    ticker := time.NewTicker(pollInterval)
    timeout := time.After(pollTimeout)
    tickerCounter := 0

    // increment the WaitGroup counter for number of goroutines to wait for...
    wg.Add(1)

    go func() {
        defer ticker.Stop()
        // decrement the counter when the goroutine completes.
        defer wg.Done()

        for {
            select {

            case tout := <-timeout:
                log.Printf("polling timeout of '%s' reached at '%s'...", pollTimeout, tout.Format(time.RFC3339))
                //ticker.Stop()
                return

            case tick := <-ticker.C:
                status, err = client.GetStatus(id)
                tickerCounter++
                if err != nil {
                    //ticker.Stop()
                    return
                }
                log.Printf("tick #%d at '%ss', %s", tickerCounter, tick.Format("05"), status)
                if status.IsErrorStatus() {
                    err = errors.New("error while polling for status")
                    //ticker.Stop()
                    return
                }
                if status.IsCompletedStatus() {
                    err = nil
                    //ticker.Stop()
                    return
                }

            }
        }
    }()

    // wait for polling to complete (or time out)
    wg.Wait()

    if err != nil {
        return nil, err
    }
    if status == nil {
        return nil, errors.New("unable to get status")
    }

    return status, nil
}

Answer 1

How about this? I used context.Context with the deadline which also gives control to the caller of poll if you want to cancel the poll before the deadline through CancelFunc. I do not have a full context of the problem here, but this should help you.

// PollStatus will keep 'pinging' the status API until timeout is reached or status returned is either successful or in error.
func (client *APIClient) PollStatus(ctx context.Context, id int, pollInterval time.Duration) (*Status, error) {
        ticker := time.NewTicker(pollInterval)
        defer ticker.Stop()
        tickerCounter := 0
        for {
            select {
            case <-ctx.Done():
                return nil, ctx.Err()

            case tick := <-ticker.C:
                status, err := client.GetStatus(id)
                tickerCounter++
                if err != nil {
                    return nil, err
                }

                log.Printf("tick #%d at '%ss', %s", tickerCounter, tick.Format("05"), status)
                if status.IsErrorStatus() {
                    return nil, errors.New("error while polling for status")
                }

                if status.IsCompletedStatus() {
                    return status, nil
                }

            }
        }

        return nil, errors.New("unable to get status")
  }

func someFunc() {
    log.Printf("polling status, id: %d", sid)
    ctx, cancelFunc := context.WithTimeout(context.Background(), 5*time.Second)
    // Having cancelFunc here gives control if you want to cancel the poll before deadline
    // but for this instance, I'm just gonna defer cancel it
    defer cancelFunc()
    status, err := api.PollStatus(ctx, sid, 1*time.Second)
    if err != nil {
        log.Fatalf("PollStatus error: %+v", err)
    }

    log.Print(status)
}