How I built Google Drive sync without a backend (and the 3 bugs that almost broke me)

Dean — Tue, 16 Jun 2026 14:35:12 +0000

When I started building PenPage — a privacy-first note app that
stores everything in IndexedDB — I made one assumption that cost me
three weeks of debugging:

"Google Drive sync will be the easy part."

It wasn't.

Here's what I learned building a sync engine entirely in the
browser, with no backend server.

## The core idea: one file to rule them all

Instead of syncing every note file individually, I built around
a single sync.json that stores all metadata:

  ppage-app/
  ├── sync.json        ← the source of truth
  ├── pages/
  │   └── page-*.md   ← actual note content
  └── images/

sync.json holds folder structure, page metadata, image metadata,
and device info — but NOT page content. On every sync:

Download sync.json (or skip if modifiedTime hasn't changed)
Compare local IndexedDB state vs Drive state
Upload/download only what changed
Upload the new sync.json

This keeps API calls to 2-3 per sync cycle instead of N×2 per file.

## Bug #1: The 404 that wasn't really a 404

Google Drive returns 404 when you try to access a folder that's
been deleted and recreated — even if a folder with the same name
exists now.

This hit me when implementing "Force Upload" (which recreates the
app folder from scratch). Device A would force upload, delete and
recreate the folder. Device B still had the old folder ID cached
— and every API call returned 404.

The fix: wrap every Drive operation in a recovery handler:

  private async withFolderRecovery<T>(
    operation: () => Promise<T>
  ): Promise<T> {
    try {
      return await operation()
    } catch (error) {
      if (error.message.includes('404')) {
        await this.reinitialize() // re-fetch all folder IDs
        return await operation()  // retry once
      }
      throw error
    }
  }

Any 404 triggers a full folder ID refresh, then retries. Simple,
but it took me a while to realize the root cause.

## Bug #2: The silent data corruption hiding in a sentinel value

Every sync, I run a cleanup step that repairs folder parentId
values. The check looked like this:

  // Intended: fix folders with wrong parentId
  if (isRootParentId(folder.parentId)) {
    repairFolder(folder)
  }

isRootParentId() returned true for both 'workspace' (the
actual sentinel for "orphaned folder") AND 'root' (the correct
value for top-level user folders).

Result: every sync, ALL top-level folders got their updatedAt
timestamp refreshed to Date.now(). The comparison logic saw
local as newer than Drive → uploaded everything → silently
overwrote changes from other devices.

The fix:

  // Only match the actual bad sentinel value
  if (folder.parentId === 'workspace') {
    repairFolder(folder)
  }

One character difference. Weeks of mysterious "my changes
disappeared" reports.

## Bug #3: IndexedDB index queries don't match undefined

Force Download is supposed to: clear local data → import from Drive.

But after Force Download, pages appeared blank. The root cause was
a chain of four silent failures:

clearAllData() queries IndexedDB by workspaceId: 'global'
Old records had workspaceId: undefined (pre-migration data)
IndexedDB index queries are exact match — undefined ≠ 'global'
Old records survived the clear
importAll() tried to create records with same IDs → store.add() silently fails on duplicate keys
New records never written → UI shows nothing

  // ❌ Misses orphan records where workspaceId is undefined
  const pages = await db.getAllPages({ workspaceId: 'global' })

  // ✅ Explicit orphan cleanup
  const allPages = await db.getAllPages()
  const orphans = allPages.filter(p => !p.workspaceId)
  await deleteAll(orphans)

Lesson: store.add() failure on duplicate keys is silent.
store.put() overwrites. Know which one you're using.

## What actually works well

Despite the bugs, the architecture held up:

modifiedTime as a proxy for "changed" — no polling, no webhooks, no server
Parallel uploads (5 concurrent) reduced sync time 80% for large note sets
Tombstones in sync.json for deleted pages — other devices learn about deletions without needing the deleted file

## Would I do it again?

Yes, but I'd budget 3× more time for edge cases. The Google Drive
API docs describe the happy path. The bugs live in:

Stale cached folder IDs
Silent IndexedDB failures
Sentinel value collisions in your own data model

If you're building anything with Google Drive API or browser-side
sync, happy to answer questions in the comments.

PenPage: https://penpage.com

I spent 5 months building a note app nobody asked me to build

Dean — Tue, 16 Jun 2026 14:28:05 +0000

Last November, I got fed up.

Every note-taking app I tried either locked my data in their cloud,
charged a subscription, or both. So I did what developers do —
I built my own.

Five months later, PenPage (penpage.com) is live: a privacy-first
WYSIWYG note app that stores everything in your browser's IndexedDB
and optionally syncs to your own Google Drive.

## The hardest part: Google Drive sync

I thought sync would take a weekend. It took three weeks.

The core problem: Google Drive has no real-time conflict detection.
When you edit on two devices, you get two versions with no merge
strategy. I ended up building a sync engine around modifiedTime
comparison + a single sync.json as the source of truth.

Edge cases I didn't expect:

Race conditions when auto-sync fires during manual sync
Google Drive returning 404 for files that technically still exist
Folder parentId returning 'root' vs the actual root folder ID (they mean different things)

## Lessons learned

Local-first is harder than it sounds — not the storage, but the sync
IndexedDB is powerful but needs a proper abstraction layer
PWA Service Workers will surprise you in production every time

If you're building anything with Google Drive API or IndexedDB,
happy to share more details in the comments.

PenPage: https://penpage.com

DEV Community: Dean

How I built Google Drive sync without a backend (and the 3 bugs that almost broke me)

I spent 5 months building a note app nobody asked me to build