Exporting Google Docs Files in PDF format with Batch Requests using Google Apps Script

/**
 * Split byteArray by a search data.
 * @param {Array} baseData Input byteArray of base data.
 * @param {Array} searchData Input byteArray of search data using split.
 * @return {Array} An array including byteArray.
 */
function splitByteArrayBySearchData_(baseData, searchData) {
  if (!Array.isArray(baseData) || !Array.isArray(searchData)) {
    throw new Error("Please give byte array.");
  }
  const search = searchData.join("");
  const bLen = searchData.length;
  const res = [];
  let idx = 0;
  do {
    idx = baseData.findIndex(
      (_, i, a) => [...Array(bLen)].map((_, j) => a[j + i]).join("") == search
    );
    if (idx != -1) {
      res.push(baseData.splice(0, idx));
      baseData.splice(0, bLen);
    } else {
      res.push(baseData.splice(0));
    }
  } while (idx != -1);
  return res;
}

/**
 * Ref: https://cloud.google.com/blog/topics/developers-practitioners/efficient-file-management-using-batch-requests-google-apps-script
 * Create a request body of batch requests and request it.
 *
 * @param {Object} object Object for creating request body of batch requests.
 * @returns {Object} UrlFetchApp.HTTPResponse
 */
function batchRequests_(object) {
  const { batchPath, requests } = object;
  const boundary = "sampleBoundary12345";
  const lb = "\r\n";
  const payload = requests.reduce((r, e, i, a) => {
    r += `Content-Type: application/http${lb}`;
    r += `Content-ID: ${i + 1}${lb}${lb}`;
    r += `${e.method} ${e.endpoint}${lb}`;
    r += e.requestBody
      ? `Content-Type: application/json; charset=utf-8" ${lb}${lb}`
      : lb;
    r += e.requestBody ? `${JSON.stringify(e.requestBody)}${lb}` : "";
    r += `--${boundary}${i == a.length - 1 ? "--" : ""}${lb}`;
    return r;
  }, `--${boundary}${lb}`);
  const params = {
    muteHttpExceptions: true,
    method: "post",
    contentType: `multipart/mixed; boundary=${boundary}`,
    headers: { Authorization: "Bearer " + ScriptApp.getOAuthToken() },
    payload,
  };
  return UrlFetchApp.fetch(`https://www.googleapis.com/${batchPath}`, params);
}

// Please run this script.
function main() {
  const folderId = "###"; // Please set folder ID you want to put the files.
  const fileIds = ["###SpreadsheetID1###", "###DocumentID1###"]; // Please set Spreadsheet ID and Document IDs you want to export as PDF format.

  // Run batch requests. In this batch requests, as a sample, Google Docs files (Spreadsheet, Document and so on) are exported as PDF format.
  const requests = fileIds.map((id) => ({
    method: "GET",
    endpoint: `https://www.googleapis.com/drive/v3/files/${id}/export?mimeType=application/pdf`,
  }));
  const object = { batchPath: "batch/drive/v3", requests };
  const res = batchRequests_(object);
  if (res.getResponseCode() != 200) {
    throw new Error(res.getContentText());
  }

  // Parse data as binary data, and create the data as Blob.
  const check = res.getContentText().match(/--batch.*/);
  if (!check) {
    throw new Error("Valid response value is not returned.");
  }
  const search = check[0];
  const baseData = res.getContent();
  const searchData = Utilities.newBlob(search).getBytes();
  const res1 = splitByteArrayBySearchData_(baseData, searchData);
  res1.shift();
  res1.pop();
  const blobs = res1.map((e, i) => {
    const rrr = splitByteArrayBySearchData_(e, [13, 10, 13, 10]);
    const data = rrr.pop();
    const metadata = Utilities.newBlob(rrr.flat()).getDataAsString();
    const dataSize = Number(metadata.match(/Content-Length:(.*)/)[1]);
    return Utilities.newBlob(data.splice(0, dataSize)).setName(
      `sampleName${i + 1}`
    );
  });

  // Create blobs as the files in Google Drive.
  const folder = DriveApp.getFolderById(folderId);
  blobs.forEach((b) => {
    if (b) {
      console.log({ filename: b.getName(), fileSize: b.getBytes().length });
      folder.createFile(b);
    }
  });
}