No-cache allows caches to store a response but requires them to revalidate it before reuse. If you want caches to always check for content updates while reusing stored content, no-cache is the directive to use. This usually means the response can be reused for subsequent requests, depending on request directives.
In such a case, you could address the caching needs by using a specific, numbered version of the library, and including the hash of the picture in its URL. Caches are encouraged to treat the value as if it were 0. Many browsers use this directive for reloading, as explained below. After the stale-if-error period passes, the client will receive any error generated. Afterwards, it becomes stale, but can be used for an extra 1 day (86400s) when an error is encountered. Here, an error is considered any response with a status code of 500, 502, 503, or 504.
- It can store and reuse personalized content for a single user.
- HTTP allows caches to reuse stale responses when they are disconnected from the origin server.
- The HTTP Cache-Control header carries directivescontrolling how browsers, proxies, and CDNs store andserve cached responses.
- Note that the major browsers do not support requests with max-stale.
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- The immutable response directive indicates that the response will not be updated while it’s fresh.
- Clients can use this header when the origin server is down or too slow and can accept cached responses from caches even if they are a bit old.
- This section lists directives that affect caching — both response directives and request directives.
- If the origin is unreachable, thecache returns a 504 instead of serving stalecontent.
The client indicates that an already-cached response should be returned. In the example above, the response is fresh for 7 days (604800s). Revalidation will make the cache be fresh again, so it appears to clients that it was always fresh during that period — effectively hiding the latency penalty of revalidation from them.
Folders and files
In some cases, this is undesirable for the content provider. For example, some convert images to reduce transfer size. Some intermediaries transform content for various reasons. If a cache doesn’t support must-understand, it will be ignored. Must-understand should be coupled with no-store for fallback behavior. You can use the public directive to unlock that restriction.
The Cache-Control header coordinates cachingacross browsers, proxies, and CDNs through a set ofcomposable directives. A page with a longmax-age is re-fetched less often, whileno-cache signals frequent content changes andwarrants more frequent crawling. Google’s crawling infrastructure implementsheuristic HTTP caching.The max-age directive helps Googlebotdetermine recrawl frequency. The browser and any sharedcache store this response for one year withoutrevalidation. Once the background revalidation completes, the cachereplaces the stale entry with the fresh response.
Installation and Usage
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Response Directives
If you don’t add a Cache-Control header because the response is not intended to be cached, that could cause an unexpected result. You can add a long max-age value and immutable because the content will never change. Note that the https://lopesezorzo.com/ major browsers do not support requests with min-fresh.
The must-revalidate directive allows caches to servethe response while fresh. The cachestill stores the response, enablingconditional requests withETag or Last-Modified. The no-store directive asks caches not to storethe request or the corresponding response. The table below shows which directives apply torequests, responses, or both. If you don’t want a response stored in caches, use the no-store directive. Clients can use this header when the origin server is down or too slow and can accept cached responses from caches even if they are a bit old.
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If /assets/ files are suitable for storing in a shared cache, you also need one of public, s-maxage or must-revalidate. Note that no-cache means “it can be stored but don’t reuse before validating” — so it’s not for preventing a response from being stored. If a cache has a stored response, even a stale one, it will be returned. For example, a request with the header above indicates that the browser will accept a stale response from the cache that has expired within the last hour. The must-understand response directive indicates that a cache should store the response only if it understands the requirements for caching based on status code. This means that the response is access-controlled for restricted users https://xolivi.com/ (who have accounts), and it’s fundamentally not shared-cacheable, even if it has max-age.
Cache directives
The public response directive indicates that the response can be stored in a shared cache. The private response directive indicates that the response can be stored only in a private cache (e.g., local caches in browsers). The no-store response directive indicates that any caches of any kind (private or shared) should not store this response. The proxy-revalidate response directive is the equivalent of must-revalidate, but specifically for shared caches only.
Installation and Usage
Cache storage is allowed to cache it heuristically — so if you have any requirements on caching, you should always indicate them explicitly, in the Cache-Control header. When you update the library or edit the picture, new content should have a new URL, and caches aren’t reused. Note that the major browsers do not support requests with max-stale. Browsers usually add no-cache to requests when users are force reloading a page. No-cache allows clients to request the most up-to-date response even if the cache has a fresh response. If no request happened during that period, the cache became stale and the next request will revalidate normally.
After freshnessexpires, caches serve the stale copy whilerevalidating in the background. The stale-while-revalidate directive extends theusability window of a stale response. The public directive is unnecessary whenmust-revalidate or s-maxage is already present.
Cache directives
Use a no-cache to make sure that the HTML response itself is not cached. When you build static assets with versioning/hashing mechanisms, adding a version/hash to the filename or query string is a good way to manage caching. In theory, if directives are conflicted, the most restrictive directive should be honored. If no cached response is available, a 504 Gateway Timeout response will be returned.
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The stale-if-error response directive indicates that the cache can reuse a stale response when an upstream server generates an error, or when the error is generated locally. The stale-while-revalidate response directive indicates that the cache could reuse a stale response while it revalidates it to a cache. If a request doesn’t have an Authorization header, or you are already using s-maxage or must-revalidate in the response, then you don’t need to use public.
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Sharedcaches such as CDNs and proxy servers discard theresponse. The private directive restricts storage to privatecaches, typically the end user’s browser. Once stale, the cachecontacts the origin to revalidate before serving theresponse again.
Directives
A request carrying no-cache requires the cache tovalidate the stored response with theorigin before serving the copy. The cache returns thestored copy only if the response will stay fresh forthe additional period. The max-stale directive signals acceptance of aresponse whose Age has exceeded the freshnesslifetime by up to the given number of seconds. Both requests and responses usethis header to coordinate Caching behavior acrossthe entire delivery chain.
The no-store directive prevents any cache fromstoring the response. This directive is useful when an originserver is temporarily unreachable and a slightly staleresponse is acceptable. Unrecognized directives are ignored by caches.This allows new directives to be introducedwithout breaking older implementations. Origins, intermediaries, and clients all rely onCache-Control to agree on when a stored responseremains usable and when a fresh copy is needed. Adding no-cache to the response causes revalidation to the server, so you can serve a fresh response every time — or if the client already has a new one, just respond 304 Not Modified.
Imagine that clients/caches store a fresh response for a path, with no request flight to the server. The no-cache request directive asks caches to validate the response with the origin server before reuse. If you forget to add private to a response with personalized content, then that response can be stored in a shared cache and end up being reused for multiple users, which can cause personal information to leak. HTTP allows caches to reuse stale responses when they are disconnected from the origin server. The cache stores the response for five minutesand revalidates before reuse once stale. The public directive marks a response as eligiblefor storage in shared caches.
The s-maxage (shared max-age) directive overridesmax-age for shared caches such as CDNs and proxyservers. After the hour elapses, caches treat theresponse as stale and either revalidate or fetch anew copy depending on other directives present. The min-fresh directive requests a stored responsewhose remaining freshness lifetime is at least thespecified number of seconds. The HTTP Cache-Control header carries directivescontrolling how browsers, proxies, and CDNs store andserve cached responses.
Clients can use this header when the user requires the response to not only be fresh, but also requires that it won’t be updated for a period of time. When you use a cache-busting pattern for resources and apply them to a long max-age, you can also add immutable to avoid revalidation. When a user reloads the browser, the browser will send conditional requests for validating to the origin server. The immutable response directive indicates that the response will not be updated while it’s fresh. No-transform indicates that any intermediary (regardless of whether it implements a cache) shouldn’t transform the response contents. If a cache supports must-understand, it stores the response with an understanding of cache requirements based on its status code.
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