Custom cache

JavaScript

// Define configurable cache duration in seconds (default: 30 days)
const CACHE_DURATION_SECONDS = 30 * 24 * 60 * 60;

// Define which parts of the request to include in the cache key
const USE_PATH = true; // Include path in the cache key
const USE_QUERY_STRING = true; // Include query string in the cache key
const INCLUDE_HEADERS = ["User-Agent"]; // Headers to include in the cache key

export default {
  async fetch(request, env, ctx) {
    // Generate a custom cache key based on user preferences
    const cacheKey = createCacheKey(request);
    console.log(`Retrieving cache for: ${cacheKey.url}.`);

    // Access the default Cache API
    const cache = caches.default;

    // Attempt to retrieve the cached response
    let response = await cache.match(cacheKey);

    if (!response) {
      // Cache miss: Fetch the asset from the origin
      console.log(`Cache miss for: ${cacheKey.url}. Fetching from origin...`);
      response = await fetch(request);

      // Wrap the origin response for caching
      response = new Response(response.body, response);

      // Set Cache-Control headers to define the TTL
      response.headers.set(
        "Cache-Control",
        `s-maxage=${CACHE_DURATION_SECONDS}`,
      );
      response.headers.set("x-snippets-cache", "stored");

      // Store the response in the cache
      await cache.put(cacheKey, response.clone());
    } else {
      // Cache hit: Return the cached response
      console.log(`Cache hit for: ${cacheKey.url}.`);
      response = new Response(response.body, response);
      response.headers.set("x-snippets-cache", "hit");

      // Optionally check if the cache should expire based on age
      const ageHeader = response.headers.get("Age");
      if (ageHeader && parseInt(ageHeader, 10) > CACHE_DURATION_SECONDS) {
        console.log(
          `Cache expired for: ${cacheKey.url}. Deleting cached response...`,
        );
        await cache.delete(cacheKey);
        response.headers.set("x-snippets-cache", "deleted");
      }
    }

    // Return the response to the client
    return response;
  },
};

/**
 * Function to create a custom cache key based on request properties
 * @param {Request} request - The incoming request object
 * @returns {Request} - A valid cache key based on the URL
 */
function createCacheKey(request) {
  const url = new URL(request.url); // Use the request's base URL
  const cacheKey = new URL(url.origin); // Start with the origin (scheme + hostname)

  // Optionally include the path
  if (USE_PATH) {
    cacheKey.pathname = url.pathname;
  }

  // Optionally include the query string
  if (USE_QUERY_STRING) {
    cacheKey.search = url.search;
  }

  // Optionally include specific headers
  if (INCLUDE_HEADERS.length > 0) {
    const headerParts = INCLUDE_HEADERS.map(
      (header) => `${header}=${request.headers.get(header) || ""}`,
    ).join("&");
    cacheKey.searchParams.append("headers", headerParts);
  }

  // Return the constructed URL as the cache key
  return new Request(cacheKey.toString(), {
    method: "GET",
  });
}