tencent cloud

// Domain name request region and origin server group mapping table
const ROUTE_CLIENT_ORIGIN_MAP = {
  'example.com': {
    CN: 'cn',
    _DEFAULT_: 'sg',
  },
};

// Define the HTTP header name used to identify the original client region.
const ORIGIN_HEADER_NAME = 'X-Forwarded-For-Origin'; 
// Define the identifier of regions outside the Chinese mainland.
const OVERSEAS_AREA = '!CN'; 
// Define the identifier of the default region.
const DEFAULT_AREA = '_DEFAULT_'; 

addEventListener('fetch', (event) => {
  event.respondWith(handleEvent(event));
});

async function handleEvent(event) {
  const { request } = event; 
  // Delete the original client region identifier from the request header to avoid external interference.
  request.headers.delete(ORIGIN_HEADER_NAME); 

  let host = request.headers.get('host');

  // Attempt to obtain the country code from the geo location of the request, which is 'CN' in this example.
  let countryCodeAlpha2 = request.eo.geo?.countryCodeAlpha2; 

  // Obtain the mapping between the region and origin server group based on the host name, which is {CN:'cn',_DEFAULT_:'sg'} in this example.
  const clientOriginMap = ROUTE_CLIENT_ORIGIN_MAP[host]; 

  if (clientOriginMap) {
    // Attempt to obtain the origin server group name based on the country code, which is 'cn' in this example.
    const originName = clientOriginMap[countryCodeAlpha2]; 
    if (originName) {
      // Set the request header to identify the original client region.
      request.headers.set(ORIGIN_HEADER_NAME, originName); 
    } else if (clientOriginMap[OVERSEAS_AREA]) {
      // Set the request header to the identifier of regions outside the Chinese mainland.
      request.headers.set(ORIGIN_HEADER_NAME, clientOriginMap[OVERSEAS_AREA]); 
    } else if (clientOriginMap[DEFAULT_AREA]) { 
      // If no specific region is matched, use the default region, which is 'sg' in this example.
      request.headers.set(ORIGIN_HEADER_NAME, clientOriginMap[DEFAULT_AREA]); 
    }
  }

  return fetch(request); 
}