PostHog Anonymous Logger Worker

A TypeScript Cloudflare Worker that provides anonymous event logging to PostHog with IP-based rate limiting for abuse prevention.

Features

• TypeScript: Full type safety and better developer experience
• Anonymous Event Logging: Strips personally identifiable information and forwards events to PostHog
• IP-Based Rate Limiting: Uses Durable Objects to prevent abuse (100 requests per minute per IP)
• CORS Support: Handles cross-origin requests for web applications
• Error Handling: Comprehensive error handling and response formatting
• Comprehensive Testing: Unit tests using Vitest and Cloudflare Workers testing framework

Setup

1. Install Dependencies:

   npm install

2. Configure PostHog API Key: Update the POSTHOG_PROJECT_API_KEY variable in wrangler.toml with your PostHog project API key.

3. Set up Rate Limiting (Optional): If you want to use the native Rate Limiting API instead of Durable Objects, update the namespace_id in the wrangler.toml file with your Cloudflare namespace ID.

4. Deploy:

   npm run deploy

Usage

Send POST requests to the worker endpoint with the following structure:

interface IncomingEvent {
  event?: string;
  properties?: Record<string, any>;
  anonymous_id?: string;
  timestamp?: string;
}

Example request:

{
  "event": "button_click",
  "properties": {
    "button_name": "signup",
    "page": "landing"
  },
  "anonymous_id": "optional-anonymous-id"
}

The worker will:

• Check rate limits based on client IP
• Strip any identifying information ($set, $set_once, distinct_id)
• Add anonymous identifiers ($ip, anonymous_id)
• Forward the event to PostHog

Rate Limiting

• Limit: 100 requests per minute per IP address
• Method: Sliding window using Durable Objects
• Response: 429 status with retry-after header when exceeded
• Cleanup: Automatically removes old rate limit windows

Testing

The project includes comprehensive tests using Vitest and Cloudflare Workers testing framework:

# Run tests once
npm run test

# Run tests in watch mode
npm run test:watch

# Type check
npm run type-check

Test Coverage

• CORS handling: Preflight requests and headers
• HTTP method validation: Only POST requests allowed
• Rate limiting: IP-based limits with Durable Objects
• Event processing: JSON parsing and PostHog forwarding
• Data sanitization: Removal of identifying information
• Error handling: Invalid JSON and network errors
• Edge cases: Concurrent requests, window boundaries, cleanup

Security Considerations

• IP-based rate limiting may affect users behind shared proxies
• No authentication required for anonymous logging
• Events are sanitized to remove identifying information
• CORS is enabled for all origins (consider restricting in production)
• All personally identifiable properties are stripped

Configuration

Environment Variables in wrangler.toml:

• POSTHOG_HOST: PostHog instance URL (default: https://app.posthog.com)
• POSTHOG_PROJECT_API_KEY: Your PostHog project API key

TypeScript Configuration:

• Target: ES2022
• Module: ES2022 with bundler resolution
• Strict mode: Enabled for type safety
• Workers Types: @cloudflare/workers-types included

Development

# Start local development server
npm run dev

# Build (dry run deploy)
npm run build

# Type check
npm run type-check

# Run tests
npm run test

# View logs
npm run tail

# Deploy to production
npm run deploy

File Structure

workers/
├── src/
│   └── index.ts           # Main worker code
├── test/
│   ├── index.test.ts      # Main worker tests
│   ├── rate-limiter.test.ts # Rate limiter specific tests
│   └── setup.ts           # Test setup and mocks
├── package.json           # Dependencies and scripts
├── tsconfig.json          # TypeScript configuration
├── vitest.config.ts       # Test configuration
├── wrangler.toml          # Cloudflare Workers configuration
└── README.md              # This file