Download all files in public dropbox folder (in dev console)

download.ts

async function retry(n, fn, ...args) {
  for (let i = 0; ; i++) {
    try {
      return await fn(...args);
    } catch (e) {
      if (i + 1 >= n) {
        throw e;
      }

      await new Promise(r => setTimeout(r, (2**i) * 1000));
    }
  }
}

async function getDownloadLink(t, url) {
  const res = await fetch("https://www.dropbox.com/sharing/fetch_user_content_link", {
    method: "POST",
    body: new URLSearchParams({
      is_xhr: "true",
      t,
      url,
    }),
  });
  if (!res.ok) {
    throw new Error(`Failed to get download link for ${url}: ${res.status} ${res.statusText}`);
  }

  return await res.text();
}

async function fetchAndDownloadToFile(url, fileHandle) {
  const w = await fileHandle.createWritable();
  try {
    const res = await fetch(url);
    if (!res.ok) {
      throw new Error(`Failed to download ${url}: ${res.status} ${res.statusText}`);
    }

    const reader = res.body.getReader();
    while (true) {
      const {done, value} = await reader.read();
      if (done) break;
      await w.write(value);
    }
  } finally {
    await w.close();
  }
}

async function fileExists(folderHandle, filename) {
  try {
    const h = await folderHandle.getFileHandle(filename);
    return (await h.getFile()).size > 0;
  } catch (e) {
    if (e.name === "NotFoundError") return false;
    throw e;
  }
}

async function downloadAndSaveLink(t, url, folderHandle) {
  const filename = decodeURIComponent(new URL(url).pathname).split("/").pop().replace(/[":?]/g, "_").replace(/\s+/g, " ") + ".zip";
  if (await fileExists(folderHandle, filename)) {
    console.log(`Skipping ${filename} because it already exists`);
    return;
  }

  const outFile = await folderHandle.getFileHandle(filename, { create: true });
  const realUrl = await retry(5, getDownloadLink, t, url);
  await retry(5, fetchAndDownloadToFile, realUrl, outFile);
}

async function* fetchFolderEntriesPage(t, link_key, rlkey) {
  let voucher = "";
  let more = true;
  while (more) {
    const body = {
      is_xhr: "true",
      t,
      link_key,
      link_type: "c",
      secure_hash: "h",
      sub_path: "",
      rlkey,
    };
    if (voucher) body.voucher = voucher;
    const { entries, has_more_entries, next_request_voucher, total_num_entries } = await (await fetch("https://www.dropbox.com/list_shared_link_folder_entries", {
      method: "POST",
      body: new URLSearchParams(body),
    })).json();

    yield [entries, total_num_entries];

    more = has_more_entries;
    voucher = next_request_voucher;
  }
}

function formatProgress(current, total) {
  return current.toString().padStart(Math.ceil(Math.log10(total + 1)), "0") + "/" + total;
}

function createPageByPageDownloader(t, link_key, rlkey, folder) {
  const pageIter = fetchFolderEntriesPage(t, link_key, rlkey);

  let allDownloadCount = 0;
  const progress = { value: [[], 0], pos: 0 };
  return async () => {
    try {
      if (progress.pos >= progress.value[0].length) {
        const { value, done } = await pageIter.next();
        if (done) {
          return false;
        }

        progress.value = value;
        progress.pos = 0;
      }

      const [entries, total_num_entries] = progress.value;
      for (; progress.pos < entries.length; progress.pos++) {
        const entry = entries[progress.pos];
        console.log(`${formatProgress(progress.pos, entries.length)} (${formatProgress(allDownloadCount + progress.pos, total_num_entries)}): downloading ${entry.filename}`);
        await downloadAndSaveLink(t, entry.href, folder);
      }

      allDownloadCount += entries.length;

      console.log(`${formatProgress(entries.length, entries.length)} (${formatProgress(allDownloadCount, total_num_entries)}): page done!`);

      return true;
    } finally {
      console.log("exited...", progress, allDownloadCount);
    }
  }
}

// USAGE:
//
// // Copy and paste into chrome dev tools console:
//
// const downloadNextPage = createPageByPageDownloader(
//   "session token", // look for `t` param from other requests in network tab
//   "link key",      // from url path segment
//   "rlkey",         // from url query string params
//   await window.showDirectoryPicker({ mode: "readwrite" }),
// );
//
// // THEN, TO DOWNLOAD PAGE BY PAGE (for testing):
//
// await downloadNextPage();
// await downloadNextPage();
// await downloadNextPage();
// ...
//
//
// // OR, TO SET AND FORGET (or after testing ok):
//
// while (await downloadNextPage());
//