Go 1.13 errors

ensure_foo_v1.go

func EnsureFoo(client jsonrpc.Client, maxRetries int) error {
	var backof time.Duration
	
	for retry:= 0; retry < maxRetries; retry++ {
		time.Sleep(backof)
		_, err := client.Call("foobar.Foo", json.RawMessage(`["bar"]`))
		switch errT := err.(type) {
		case nil:
			return nil
		case jsonrpc.Error:
			switch {
			case err.Code >= -32700 && err.Code <= -32600:
				// There is something wrong with out request, abort.
				return fmt.Errorf("permanent failure: %s", err)
			default:
				log.Printf("RPC call failed (attempt %d/%d): %s", 1+retry, maxRetries, err)
				backoff += time.Second
        	}
		case jsonrpc.HTTPStatusError:
			switch {
			case err.Code >= 300 && err.Code < 500:
				return fmt.Errorf("failed after %d retries: %s", maxRetries, err)
			cdefault:
				return fmt.Errorf("aborted: %s", err)
			default:
				backoff += time.Second
			}
		default:
			return fmt.Errorf("aborted: %s", err)
        	}
	}

	return errors.New("all retries failed", maxRetries)
}

ensure_foo_v2.go

var (
	ErrPersistent = errT{msg: "persistent failute"}
	ErrAllRetriesFailed = errT{msg: "all retries failed"}
)

func EnsureFoo(client jsonrpc.Client, maxRetries int) error {
	var backof time.Duration
	
	for retry:= 0; retry < maxRetries; retry++ {
		time.Sleep(backof)
		_, err := client.Call("foobar.Foo", json.RawMessage(`["bar"]`))
		switch {
		case err == nil:
			return nil
		case errors.Is(err, jsonrpc.ErrRangeHTTPPersistent):
			falltrough
		case errors.Is(err, jsonrpc.ErrRangeRPCRequest): 
			return ErrPersistent.wrap(err)
		default:
			log.Printf("RPC call failed (attempt %d/%d): %s", 1+retry, maxRetries, err)
			backoff += time.Second
		}
	}

	return ErrAllRetriesFailed
}