/*The httpDo function runs the HTTP request and processes its response in a new goroutine. It cancels the request if ctx.Done is closed before the goroutine exits:*/

func httpDo(ctx context.Context, req *http.Request, f func(*http.Response, error) error) error {
    // Run the HTTP request in a goroutine and pass the response to f.
    c := make(chan error, 1)
    req = req.WithContext(ctx)
    go func() { c <- f(http.DefaultClient.Do(req)) }()
    select {
    case <-ctx.Done():
        <-c // Wait for f to return.
        return ctx.Err()
    case err := <-c:
        return err
    }
}