Method downloadBlockWithRetry

internal/stream/pipe.go:245–289

downloadBlockWithRetry fetches a block with exponential backoff retry.

(offset int64)

// downloadBlockWithRetry fetches a block with exponential backoff retry.
func (p *StreamPipe) downloadBlockWithRetry(offset int64) ([]byte, error) {
	var lastErr error

	// TODO: make configurable later
	backoff := 100 * time.Millisecond   // initial backoff = 100ms
	const maxBackoff = 15 * time.Second // max backoff = 15s

	for attempt := 0; attempt < config.ValueOf.StreamMaxRetries; attempt++ {
		// check context before each attempt
		if p.ctx.Err() != nil {
			return nil, p.ctx.Err()
		}

		ctx, cancel := context.WithTimeout(p.ctx, time.Duration(config.ValueOf.StreamTimeoutSec)*time.Second)
		data, err := utils.TimeFuncWithResult(p.log, "downloadBlock", func() ([]byte, error) {
			return p.downloadBlock(ctx, offset)
		})
		cancel()

		if err == nil {
			return data, nil
		}

		lastErr = err

		// don't retry on context cancellation
		if p.ctx.Err() != nil {
			return nil, p.ctx.Err()
		}

		// exponential backoff
		select {
		case <-time.After(backoff):
			backoff *= 2
			// making sure backoff doesn't grow indefinitely in case of persistent failures
			if backoff > maxBackoff {
				backoff = maxBackoff
			}
		case <-p.ctx.Done():
			return nil, p.ctx.Err()
		}
	}

	return nil, fmt.Errorf("%w: %v", ErrMaxRetriesExceeded, lastErr)
}

// downloadBlock fetches a single block from Telegram.
func (p *StreamPipe) downloadBlock(ctx context.Context, offset int64) ([]byte, error) {