L4 Development Memory#

Commands#

Development#

bun run dev          # Start local development server
bun run deploy       # Deploy to Cloudflare
bun run types        # Generate TypeScript types

Wrangler#

wrangler r2 bucket create l4-images     # Create R2 bucket
wrangler secret put AUTH_TOKEN          # Set auth token for API uploads
wrangler secret put SLACK_BOT_TOKEN     # Set Slack bot token
wrangler secret put SLACK_SIGNING_SECRET # Set Slack signing secret

Project Structure#

• /src/index.ts - Worker with Slack bot and upload endpoint
• /wrangler.toml - Cloudflare Workers configuration
• /manifest.yaml - Slack app manifest for easy setup

What It Does#

Slack CDN bot for Cloudflare Workers:

• Automatically uploads files posted in Slack to R2
• Returns public URLs in thread
• Uses custom emoji reactions for status (:spinny_fox: → :good_move: or :rac-concern:)
• Also supports direct API uploads with auth token
• Images served with transformations via Cloudflare's edge

Endpoints#

Public#

• GET /i/:key?w=800&h=600&f=webp&q=85&fit=scale-down - Serve image with transformations

Slack#

• POST /slack/events - Slack Events API endpoint
  • Listens for message events with files
  • Downloads files from Slack
  • Uploads to R2 with random filename
  • Posts URLs in thread

API (requires Authorization: Bearer <AUTH_TOKEN>)#

• POST /upload - Upload image (multipart form-data with file field)
  • Returns: {"success": true, "url": "https://.../i/xxx.jpg"}

Image URL Parameters#

• w - width
• h - height
• f - format (auto, webp, avif, jpeg)
• q - quality (1-100)
• fit - fit mode (scale-down, contain, cover, crop, pad)

Environment Variables#

Config (wrangler.toml):

• PUBLIC_URL - Public URL of the service (e.g., https://l4.dunkirk.sh)
• ALLOWED_CHANNELS - Comma-separated Slack channel IDs (e.g., "C12345,C67890"). Leave empty to allow all channels.

Secrets:

• AUTH_TOKEN - Auth token for API uploads
• SLACK_BOT_TOKEN - Slack bot user OAuth token
• SLACK_SIGNING_SECRET - Slack app signing secret

Bindings#

• IMAGES - R2 bucket for image storage

Slack Setup#

Option 1: Using Manifest (Easy)#

1. Go to api.slack.com/apps
2. Click "Create New App" → "From an app manifest"
3. Select your workspace
4. Paste contents of manifest.yaml
5. Update the request URL if needed
6. Install app to workspace
7. Copy "Bot User OAuth Token" and "Signing Secret"
8. Set secrets in Workers:

   wrangler secret put SLACK_BOT_TOKEN
   wrangler secret put SLACK_SIGNING_SECRET
   

Option 2: Manual Setup#

1. Create Slack app at api.slack.com/apps
2. Enable Event Subscriptions, set URL to https://l4.dunkirk.sh/slack/events
3. Subscribe to bot events: message.channels, message.groups, message.im, message.mpim
4. Add OAuth scopes: files:read, reactions:write, chat:write
5. Install app to workspace
6. Set secrets in Workers

Usage Examples#

# API upload
curl -X POST https://l4.dunkirk.sh/upload \
  -H "Authorization: Bearer YOUR_TOKEN" \
  -F "file=@image.jpg"

# Slack: Just post a file in a channel where the bot is invited

Emoji Reactions#

• :spinny_fox: - Uploading in progress
• :good_move: - Upload succeeded
• :rac-concern: - Upload failed