Function setupWeightBasedFlushing

packages/core/src/client.ts:110–163

* Sets up weight-based flushing for logs or metrics. * This helper function encapsulates the common pattern of: * 1. Tracking accumulated weight of items * 2. Flushing when weight exceeds threshold (800KB) * 3. Flushing after timeout period from the first item * * Uses closure variables to tra

(
  client: Client,
  afterCaptureHook: AfterCaptureHook,
  flushHook: FlushHook,
  estimateSizeFn: (item: T) => number,
  flushFn: (client: Client) => void,
)

 * Uses closure variables to track weight and timeout state.
 */
function setupWeightBasedFlushing<
  T,
  AfterCaptureHook extends 'afterCaptureLog' | 'afterCaptureMetric',
  FlushHook extends 'flushLogs' | 'flushMetrics',
>(
  client: Client,
  afterCaptureHook: AfterCaptureHook,
  flushHook: FlushHook,
  estimateSizeFn: (item: T) => number,
  flushFn: (client: Client) => void,
): void {
  // Track weight and timeout in closure variables
  let weight = 0;
  let flushTimeout: ReturnType<typeof setTimeout> | undefined;
  let isTimerActive = false;

  // @ts-expect-error - TypeScript can't narrow generic hook types to match specific overloads, but we know this is type-safe
  client.on(flushHook, () => {
    weight = 0;
    clearTimeout(flushTimeout);
    isTimerActive = false;
  });

  // @ts-expect-error - TypeScript can't narrow generic hook types to match specific overloads, but we know this is type-safe
  client.on(afterCaptureHook, (item: T) => {
    weight += estimateSizeFn(item);

    // We flush the buffer if it exceeds 0.8 MB
    // The weight is a rough estimate, so we flush way before the payload gets too big.
    if (weight >= 800_000) {
      flushFn(client);
    } else if (!isTimerActive) {
      const flushInterval = client.getOptions()._flushInterval ?? DEFAULT_FLUSH_INTERVAL;
      if (flushInterval > 0) {
        // Only start timer if one isn't already running.
        // This prevents flushing being delayed by items that arrive close to the timeout limit
        // and thus resetting the flushing timeout and delaying items being flushed.
        isTimerActive = true;
        // Use safeUnref so the timer doesn't prevent the process from exiting
        flushTimeout = safeUnref(
          setTimeout(() => {
            flushFn(client);
            // Note: isTimerActive is reset by the flushHook handler above, not here,
            // to avoid race conditions when new items arrive during the flush.
          }, flushInterval),
        );
      }
    }
  });

  client.on('flush', () => {
    flushFn(client);
  });
}

/**
 * Base implementation for all JavaScript SDK clients.