VTEX Fetch Cache (SWR In-Memory)

Server-side SWR cache for all VTEX GET API responses. Ported from deco-cx/deco runtime/fetch/fetchCache.ts and adapted for @decocms/apps on TanStack Start.

When to Use This Skill

• Adding SWR caching to new VTEX API calls
• Understanding why a VTEX response is served stale
• Debugging cache hit/miss behavior
• Tuning TTL for specific endpoints
• Understanding the relationship between fetchWithCache, vtexCachedFetch, and createCachedLoader

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Architecture

Site Setup
  └→ createCachedLoader (loader-level SWR, 30-120s TTL)
       └→ vtexCachedFetch (HTTP-level SWR, 3min TTL)
            └→ fetchWithCache (core cache engine)
                 └→ _fetch (instrumented fetch)

Layer	File	Scope	TTL
createCachedLoader	deco-start/src/sdk/cachedLoader.ts	Loader result (parsed + transformed)	30-120s per loader
vtexCachedFetch	apps-start/vtex/client.ts	Raw HTTP JSON response	3 min (200), 10s (404)
fetchWithCache	apps-start/vtex/utils/fetchCache.ts	Core SWR + dedup engine	Status-based

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Core: fetchWithCache (vtex/utils/fetchCache.ts)

Features

• LRU eviction: Max 500 entries, oldest evicted first
• TTL by HTTP status: 200-299 → 3 min, 404 → 10s, 500+ → never cached
• In-flight deduplication: Concurrent calls for the same URL share one Promise
• Stale-while-revalidate: Stale entries served immediately, refreshed in background
• Custom TTL: Override per-call via opts.ttl

API

import { fetchWithCache, FetchCacheOptions } from "@decocms/apps/vtex/utils/fetchCache";

// Basic usage
const data = await fetchWithCache<ProductType>(
  fullUrl,                    // Cache key (typically the full URL)
  () => fetch(fullUrl, init), // Fetch callback (returns Response)
  { ttl: 60_000 },           // Optional: override TTL (1 min)
);

How SWR Works

Call fetchWithCache(key, doFetch)
  ├→ Entry exists & fresh? → return cached body
  ├→ Entry exists & stale? → return stale, fire background refresh
  ├→ Entry missing, inflight exists? → await inflight Promise
  └→ Entry missing, no inflight → execute doFetch(), cache result

TTL Configuration

const TTL_BY_STATUS: Record<string, number> = {
  "2xx": 180_000,  // 3 min — success responses
  "404": 10_000,   // 10s — not found (may become available)
  "5xx": 0,        // never cache server errors
};

Error Handling

Non-ok responses (status >= 400) throw an error. They are NOT cached. The error propagates to the caller, who should .catch() gracefully:

const data = await fetchWithCache<T>(url, doFetch).catch(() => fallback);

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Client Integration: vtexCachedFetch (vtex/client.ts)

Convenience wrapper that routes GET requests through fetchWithCache:

import { vtexCachedFetch } from "@decocms/apps/vtex";

// Automatically uses SWR cache for GET
const products = await vtexCachedFetch<Product[]>(
  `/api/catalog_system/pub/products/search/${slug}/p`,
);

// Non-GET falls through to regular vtexFetch
const result = await vtexCachedFetch<OrderForm>(
  `/api/checkout/pub/orderForms/simulation`,
  { method: "POST", body: JSON.stringify(items) },
);

Custom TTL per call

const pageType = await vtexCachedFetch<PageType>(
  `/api/catalog_system/pub/portal/pagetype/${term}`,
  undefined,
  { cacheTTL: 300_000 }, // 5 min for page types
);

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What Uses vtexCachedFetch (Current)

Module	Endpoint	Before	After
slugCache.ts	search/{slug}/p	Manual inflight Map + 5s timeout	vtexCachedFetch SWR 3min
relatedProducts.ts	crossselling/{type}/{id}	Manual crossSellingInflight Map	vtexCachedFetch SWR 3min
productDetailsPage.ts	Kit items search	Plain vtexFetch	vtexCachedFetch SWR 3min
client.ts cachedPageType	pagetype/{term}	Manual inflight Map	vtexCachedFetch SWR 3min

What Uses fetchWithCache Directly

Module	Endpoint	Notes
client.ts intelligentSearch	IS product_search, facets	Wrapped inline, uses default TTL

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Comparison with deco-cx/deco fetchCache.ts

Feature	deco-cx/deco	@decocms/apps
Storage	CacheStorage (Web Cache API)	In-memory Map (LRU)
Persistence	Disk-backed (Deno CacheStorage)	Process-lifetime only
Max entries	Unlimited (disk)	500 (memory)
TTL source	HTTP Cache-Control headers	Status-based defaults
SWR	stale-while-revalidate header parsing	Manual background refresh
Dedup	Separate singleFlight wrapper	Built into fetchWithCache
Redis/FS tiers	Yes (tiered.ts: LRU → FS → Redis)	No — single in-memory tier

Why In-Memory Only?

Cloudflare Workers don't have persistent storage APIs accessible during SSR. The Cache API (caches.default) is for edge HTTP responses, not arbitrary data. In-memory with LRU is the practical choice for Workers.

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Diagnostics

Check Cache Stats

import { getFetchCacheStats, clearFetchCache } from "@decocms/apps/vtex/utils/fetchCache";

console.log(getFetchCacheStats());
// { entries: 42, inflight: 0 }

Clear Cache

clearFetchCache(); // Useful after decofile hot-reload

Verify Cache Hits in Logs

With instrumented fetch (createInstrumentedFetch("vtex")), look for timing:

• Cache HIT: No [vtex] GET ... log appears (response served from cache)
• Cache MISS: [vtex] GET ... followed by [vtex] 200 GET ... Xms
• SWR refresh: [vtex] GET ... appears AFTER the response was already served

Common Issues

Stale data after CMS update: Wait 3 min for TTL to expire, or restart the dev server to clear in-memory cache.

Cache not working in dev: fetchWithCache works in both dev and prod. Unlike createCachedLoader which skips SWR in dev (only dedup), fetchWithCache always caches.

POST requests not cached: By design — vtexCachedFetch only caches GET. Use usePriceSimulationBatch for simulation POST optimization.

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Adding Cache to a New VTEX Endpoint

// Before — no cache
const data = await vtexFetch<MyType>(`/api/my-endpoint/${id}`);

// After — with SWR cache
const data = await vtexCachedFetch<MyType>(`/api/my-endpoint/${id}`);

// With custom TTL
const data = await vtexCachedFetch<MyType>(
  `/api/my-endpoint/${id}`,
  undefined,
  { cacheTTL: 60_000 }, // 1 min
);

For non-VTEX APIs, use fetchWithCache directly:

import { fetchWithCache } from "@decocms/apps/vtex/utils/fetchCache";

const data = await fetchWithCache<MyType>(url, () => fetch(url, init));

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Related Skills

Skill	Purpose
deco-api-call-dedup	Higher-level dedup patterns (slugCache, batching, PLP filtering)
deco-cms-layout-caching	Layout section caching (works on top of fetch cache)
deco-edge-caching	Cloudflare edge caching (HTTP level, outside the Worker)
deco-tanstack-storefront-patterns	General storefront patterns + createCachedLoader