gallery_server_client_s190js/middleware/waitForCastSegment.js

'use strict';

const fs = require('fs');
const path = require('path');

const SEGMENT_PATTERN =
  /^segment_[0-9]{5}\.ts$/;

const DEFAULT_TIMEOUT_MS =
  Number(
    process.env.CAST_SEGMENT_WAIT_TIMEOUT_MS ||
    300000
  );

const DEFAULT_POLL_MS =
  Number(
    process.env.CAST_SEGMENT_WAIT_POLL_MS ||
    100
  );

const DEFAULT_STABILITY_MS =
  Number(
    process.env.CAST_SEGMENT_STABILITY_MS ||
    50
  );


function sleep(ms) {
  return new Promise(resolve => {
    setTimeout(resolve, ms);
  });
}


async function getStableFileSize(
  filePath,
  stabilityMs
) {
  try {
    const first =
      await fs.promises.stat(filePath);

    if (
      !first.isFile() ||
      first.size <= 0
    ) {
      return null;
    }

    await sleep(stabilityMs);

    const second =
      await fs.promises.stat(filePath);

    if (
      !second.isFile() ||
      second.size <= 0 ||
      second.size !== first.size
    ) {
      return null;
    }

    return second.size;
  } catch {
    return null;
  }
}


function isInsideRoot(root, candidate) {
  const relative = path.relative(
    root,
    candidate
  );

  return (
    relative !== '' &&
    relative !== '..' &&
    !relative.startsWith(`..${path.sep}`) &&
    !path.isAbsolute(relative)
  );
}


function requestIsClosed(req, res) {
  return (
    req.destroyed ||
    res.destroyed ||
    res.writableEnded
  );
}


function createWaitForCastSegment({
  castRoot,
  timeoutMs = DEFAULT_TIMEOUT_MS,
  pollMs = DEFAULT_POLL_MS,
  stabilityMs = DEFAULT_STABILITY_MS
}) {
  const resolvedRoot =
    path.resolve(castRoot);

  return async function waitForCastSegment(
    req,
    res,
    next
  ) {
    try {
      if (
        req.method !== 'GET' &&
        req.method !== 'HEAD'
      ) {
        next();
        return;
      }

      let pathname;

      try {
        pathname = decodeURIComponent(
          req.path ||
          req.url.split('?')[0]
        );
      } catch {
        res
          .status(400)
          .end('Invalid URL');

        return;
      }

      const filename =
        path.basename(pathname);

      if (!SEGMENT_PATTERN.test(filename)) {
        next();
        return;
      }

      /*
       * Il middleware è montato su /cast.
       * req.path è quindi relativo a public/cast.
       */
      const relativePath =
        pathname.replace(/^\/+/, '');

      const filePath =
        path.resolve(
          resolvedRoot,
          relativePath
        );

      if (!isInsideRoot(
        resolvedRoot,
        filePath
      )) {
        res
          .status(403)
          .end('Forbidden');

        return;
      }

      /*
       * Se il segmento esiste già ed è stabile,
       * prosegue immediatamente verso express.static.
       */
      const initialSize =
        await getStableFileSize(
          filePath,
          stabilityMs
        );

      if (initialSize !== null) {
        next();
        return;
      }

      const startedAt = Date.now();
      const deadline =
        startedAt + timeoutMs;

      let lastProgressLogAt = 0;

      console.log(
        `[castSegmentWait] WAIT ` +
        `${relativePath} ` +
        `timeoutMs=${timeoutMs}`
      );

      while (Date.now() < deadline) {
        if (requestIsClosed(req, res)) {
          console.log(
            `[castSegmentWait] CLIENT_CLOSED ` +
            `${relativePath} ` +
            `waitedMs=${Date.now() - startedAt}`
          );

          return;
        }

        const size =
          await getStableFileSize(
            filePath,
            stabilityMs
          );

        if (size !== null) {
          console.log(
            `[castSegmentWait] READY ` +
            `${relativePath} ` +
            `waitedMs=${Date.now() - startedAt} ` +
            `size=${size}`
          );

          /*
           * Il file ora esiste ed è stabile.
           * express.static lo invierà al client.
           */
          next();
          return;
        }

        const now = Date.now();

        if (
          now - lastProgressLogAt >= 5000
        ) {
          console.log(
            `[castSegmentWait] STILL_WAITING ` +
            `${relativePath} ` +
            `elapsedMs=${now - startedAt}`
          );

          lastProgressLogAt = now;
        }

        await sleep(pollMs);
      }

      if (requestIsClosed(req, res)) {
        return;
      }

      console.warn(
        `[castSegmentWait] TIMEOUT ` +
        `${relativePath} ` +
        `waitedMs=${Date.now() - startedAt}`
      );

      res
        .status(503)
        .set({
          'Cache-Control':
            'no-store',
          'Retry-After':
            '1'
        })
        .end(
          'Segment not ready'
        );
    } catch (err) {
      /*
       * Chromecast può chiudere richieste speculative.
       * Non è un errore di transcodifica.
       */
      if (
        err &&
        (
          err.code === 'EPIPE' ||
          err.code === 'ECONNRESET'
        )
      ) {
        console.log(
          `[castSegmentWait] CLIENT_DISCONNECTED ` +
          `${req.originalUrl || req.url}`
        );

        return;
      }

      console.error(
        `[castSegmentWait] ERROR ` +
        `${req.originalUrl || req.url}: ` +
        `${err.stack || err.message}`
      );

      if (!requestIsClosed(req, res)) {
        next(err);
      }
    }
  };
}


module.exports = {
  createWaitForCastSegment
};