Function createNodeTailSource

packages/node/src/streams/tail.ts:54–139

(
  filePath,
  options,
)

 * Node.js tail source factory for `useTail`.
 */
export const createNodeTailSource: TailSourceFactory<string> = (
  filePath,
  options,
): TailSource<string> => {
  const pollMs = normalizePositiveInteger(options.pollMs, DEFAULT_POLL_MS);
  const fromEnd = options.fromEnd;

  let closed = false;
  let sleepState: SleepState = { timer: null, resolve: null };

  const wakeSleep = (): void => {
    if (sleepState.timer !== null) {
      clearTimeout(sleepState.timer);
    }
    if (sleepState.resolve) {
      sleepState.resolve();
    }
    sleepState = { timer: null, resolve: null };
  };

  const sleep = async (ms: number): Promise<void> => {
    if (ms <= 0) return;

    await new Promise<void>((resolve) => {
      const timer = setTimeout(() => {
        sleepState = { timer: null, resolve: null };
        resolve();
      }, ms);
      sleepState = { timer, resolve };
    });
  };

  async function* iterator(): AsyncGenerator<string> {
    let initialized = false;
    let offset = 0;
    let carry = "";
    let decoder = new StringDecoder("utf8");

    while (!closed) {
      let fileSize: number;
      try {
        const stats = await stat(filePath);
        fileSize = Number(stats.size);
      } catch (error) {
        if (isNodeErrorWithCode(error) && error.code === "ENOENT") {
          await sleep(pollMs);
          continue;
        }
        throw error;
      }

      if (!initialized) {
        initialized = true;
        offset = fromEnd ? fileSize : 0;
      }

      if (fileSize < offset) {
        // File was truncated/rotated.