Book Cover Generator Worker

A Cloudflare Worker that retrieves book cover images using the Open Library API. Given a book title and author name, it searches for matching ISBNs and returns thumbnail cover images. If no cover is found, it generates a placeholder image with the book details.

Features

• Fetches book covers using ISBN lookup through Open Library
• Fallback to dynamically generated placeholder images
• Caches responses for improved performance
• Handles special characters and edge cases
• No API key required

Example Outputs

Successful Cover Retrievals

Book	Example URL	Result
The Great Gatsby	/?book_title=The Great Gatsby&author_name=F. Scott Fitzgerald
1984	/?book_title=1984&author_name=George Orwell

Fallback Placeholder

When a book cover isn't found, the service generates a placeholder with the book details:

Example	URL	Generated Placeholder
Non-existent Book	/?book_title=The Amazing Adventures of Nobody&author_name=John Smith

Setup

1. Install dependencies:

npm install

2. Configure your worker:

# Copy the example configuration
cp wrangler.example.toml wrangler.toml

# Edit wrangler.toml with your preferred settings
# Especially update the 'name' field to your desired worker name

KV Store Setup

1. Create a KV namespace in the Cloudflare dashboard:

   # Using Wrangler CLI
   wrangler kv:namespace create BOOK_COVERS
   
   # Also create a preview namespace for development
   wrangler kv:namespace create BOOK_COVERS --preview

2. Update your wrangler.toml with the KV namespace bindings:

   kv_namespaces = [
     { binding = "BOOK_COVERS", id = "xxx", preview_id = "yyy" }
   ]

3. Add required permissions:

   [[permissions]]
   type = "kv"
   target = "BOOK_COVERS"
   operation = ["read", "write", "delete"]

Development

Run the worker locally:

npm run dev

The worker will be available at http://localhost:8787. Test it using the example URLs shown in the Example Outputs section above.

Deployment

Deploy to Cloudflare Workers:

# Login to Cloudflare (first time only)
wrangler login

# Deploy your worker
npm run deploy

After deployment, your worker will be available at:

https://[worker-name].[your-subdomain].workers.dev

API Usage

Parameters

Parameter	Description	Required	Example
book_title	The title of the book	Yes	Pride and Prejudice
author_name	The name of the book's author	Yes	Jane Austen

Response Types

Scenario	Response Type	Example
Cover found	image/jpeg
No cover found	image/svg+xml

Cache Management

The worker implements a caching strategy to improve performance:

• Successful cover URLs are cached for 30 days
• Placeholder results are cached for 7 days
• Cache keys format: cover:${bookTitle}:${authorName}

Managing KV Store

View cached entries:

# List all keys
wrangler kv:key list --namespace-id=xxx

# Get specific value
wrangler kv:key get --namespace-id=xxx "your-key"

# Delete specific key
wrangler kv:key delete --namespace-id=xxx "your-key"

Resource Limits

• KV Store:
  • Keys: Maximum 512 bytes
  • Values: Maximum 25 MB
  • Read: ~1ms
  • Write: ~30ms
• Worker:
  • CPU: 10ms - 50ms per request
  • Memory: 128 MB
  • Environment Variables: 1 KB each
  • Subrequests: 50 per request

Performance Optimization

The worker implements several optimizations:

1. KV Caching:

   • Reduces API calls to Open Library
   • Improves response times for repeated requests
   • Handles both successful and fallback cases

2. Browser Caching:

   • Images are cached with Cache-Control: public, max-age=31536000, immutable
   • Reduces bandwidth usage and improves load times

3. Early Returns:

   • Returns cached results immediately when available
   • Avoids unnecessary API calls and processing

Error Handling Examples

Scenario	URL	Result
Empty parameters	/?book_title=&author_name=	Default placeholder
Missing author	/?book_title=NonExistentBook	Default placeholder
Special characters	/?book_title=L'Étranger&author_name=Albert Camus	Handles correctly

Monitoring

Viewing Logs

# View real-time logs
wrangler tail

# Filter logs by status
wrangler tail --status=error

# Filter logs by method
wrangler tail --method=GET

Key Metrics to Monitor

• Cache hit ratio
• Response times
• Error rates
• KV store usage

Common Issues

Issue	Solution
Placeholder instead of cover	Verify book title and author spelling
No image displayed	Check browser console for errors
Deployment fails	Ensure wrangler.toml is configured correctly

Example Test URLs

Try these URLs with your deployed worker:

https://[your-worker].[subdomain].workers.dev/?book_title=Pride%20and%20Prejudice&author_name=Jane%20Austen
https://[your-worker].[subdomain].workers.dev/?book_title=1984&author_name=George%20Orwell
https://[your-worker].[subdomain].workers.dev/?book_title=To%20Kill%20a%20Mockingbird&author_name=Harper%20Lee
https://[your-worker].[subdomain].workers.dev/?book_title=The%20Hunger%20Games&author_name=Suzanne%20Collins
https://[your-worker].[subdomain].workers.dev/?book_title=Harry%20Potter%20and%20the%20Sorcerer%27s%20Stone&author_name=J.K.%20Rowling

Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Add tests if applicable
5. Submit a pull request

License

MIT License

Credits

• Book cover images provided by Open Library
• Placeholder images generated using Placehold.co