01.get-public-ip.js

addEventListener('fetch', event => {
  const { request } = event;

  if (request.method === 'GET') {
    event.respondWith(getClientIP(request));
  } else {
    event.respondWith(sendErrorResponse(`Method not allowed: ${request.method}`, 405));
  }
});

async function getClientIP(request) {
  const clientIP = request.headers.get('CF-Connecting-IP') || 'IP not found';

  return new Response(clientIP, {
    status: 200,
    headers: {
      'Content-Type': 'text/plain; charset=utf-8',
      'Cache-Control': 'no-cache, no-store, must-revalidate',
      'X-Content-Type-Options': 'nosniff',
    }
  });
}

function sendErrorResponse(message, statusCode = 400) {
  const errorResponse = { error: message };

  return new Response(JSON.stringify(errorResponse), {
    status: statusCode,
    headers: {
      'Content-Type': 'application/json; charset=utf-8',
      'Cache-Control': 'no-cache, no-store, must-revalidate',
    }
  });
}