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title	author	description	monikerRange	ms.author	ms.custom	ms.date	uid
Response Caching Middleware in ASP.NET Core	guardrex	Learn how to configure and use Response Caching Middleware in ASP.NET Core.	>= aspnetcore-2.1	riande	mvc	12/05/2019	performance/caching/middleware

Response Caching Middleware in ASP.NET Core

By Luke Latham and John Luo

View or download sample code (how to download)

This article explains how to configure Response Caching Middleware in an ASP.NET Core app. The middleware determines when responses are cacheable, stores responses, and serves responses from cache. For an introduction to HTTP caching and the [ResponseCache] attribute, see Response Caching.

Configuration

::: moniker range=">= aspnetcore-3.0"

Response Caching Middleware is implicitly available for ASP.NET Core apps via the shared framework.

In Startup.ConfigureServices, add the Response Caching Middleware to the service collection:

[!code-csharp]

Configure the app to use the middleware with the xref:Microsoft.AspNetCore.Builder.ResponseCachingExtensions.UseResponseCaching* extension method, which adds the middleware to the request processing pipeline in Startup.Configure:

[!code-csharp]

The sample app adds headers to control caching on subsequent requests:

Cache-Control – Caches cacheable responses for up to 10 seconds.
Vary – Configures the middleware to serve a cached response only if the Accept-Encoding header of subsequent requests matches that of the original request.

[!code-csharp]

Response Caching Middleware only caches server responses that result in a 200 (OK) status code. Any other responses, including error pages, are ignored by the middleware.

[!WARNING] Responses containing content for authenticated clients must be marked as not cacheable to prevent the middleware from storing and serving those responses. See Conditions for caching for details on how the middleware determines if a response is cacheable.

::: moniker-end

::: moniker range="< aspnetcore-3.0"

Use the Microsoft.AspNetCore.App metapackage or add a package reference to the Microsoft.AspNetCore.ResponseCaching package.

In Startup.ConfigureServices, add the Response Caching Middleware to the service collection:

[!code-csharp]

The sample app adds headers to control caching on subsequent requests:

Cache-Control – Caches cacheable responses for up to 10 seconds.
Vary – Configures the middleware to serve a cached response only if the Accept-Encoding header of subsequent requests matches that of the original request.

[!code-csharp]

Response Caching Middleware only caches server responses that result in a 200 (OK) status code. Any other responses, including error pages, are ignored by the middleware.

[!WARNING] Responses containing content for authenticated clients must be marked as not cacheable to prevent the middleware from storing and serving those responses. See Conditions for caching for details on how the middleware determines if a response is cacheable.

::: moniker-end

Options

Response caching options are shown in the following table.

Option	Description
xref:Microsoft.AspNetCore.ResponseCaching.ResponseCachingOptions.MaximumBodySize	The largest cacheable size for the response body in bytes. The default value is `64 * 1024 * 1024` (64 MB).
xref:Microsoft.AspNetCore.ResponseCaching.ResponseCachingOptions.SizeLimit	The size limit for the response cache middleware in bytes. The default value is `100 * 1024 * 1024` (100 MB).
xref:Microsoft.AspNetCore.ResponseCaching.ResponseCachingOptions.UseCaseSensitivePaths	Determines if responses are cached on case-sensitive paths. The default value is `false`.

The following example configures the middleware to:

Cache responses with a body size smaller than or equal to 1,024 bytes.
Store the responses by case-sensitive paths. For example, /page1 and /Page1 are stored separately.

services.AddResponseCaching(options =>
{
    options.MaximumBodySize = 1024;
    options.UseCaseSensitivePaths = true;
});

VaryByQueryKeys

When using MVC / web API controllers or Razor Pages page models, the [ResponseCache] attribute specifies the parameters necessary for setting the appropriate headers for response caching. The only parameter of the [ResponseCache] attribute that strictly requires the middleware is xref:Microsoft.AspNetCore.Mvc.ResponseCacheAttribute.VaryByQueryKeys, which doesn't correspond to an actual HTTP header. For more information, see xref:performance/caching/response#responsecache-attribute.

When not using the [ResponseCache] attribute, response caching can be varied with VaryByQueryKeys. Use the xref:Microsoft.AspNetCore.ResponseCaching.ResponseCachingFeature directly from the HttpContext.Features:

var responseCachingFeature = context.HttpContext.Features.Get<IResponseCachingFeature>();

if (responseCachingFeature != null)
{
    responseCachingFeature.VaryByQueryKeys = new[] { "MyKey" };
}

Using a single value equal to * in VaryByQueryKeys varies the cache by all request query parameters.

HTTP headers used by Response Caching Middleware

The following table provides information on HTTP headers that affect response caching.

Header	Details
`Authorization`	The response isn't cached if the header exists.
`Cache-Control`	The middleware only considers caching responses marked with the `public` cache directive. Control caching with the following parameters: max-age max-stale† min-fresh must-revalidate no-cache no-store only-if-cached private public s-maxage proxy-revalidate‡ †If no limit is specified to `max-stale`, the middleware takes no action. ‡`proxy-revalidate` has the same effect as `must-revalidate`. For more information, see RFC 7231: Request Cache-Control Directives.
`Pragma`	A `Pragma: no-cache` header in the request produces the same effect as `Cache-Control: no-cache`. This header is overridden by the relevant directives in the `Cache-Control` header, if present. Considered for backward compatibility with HTTP/1.0.
`Set-Cookie`	The response isn't cached if the header exists. Any middleware in the request processing pipeline that sets one or more cookies prevents the Response Caching Middleware from caching the response (for example, the cookie-based TempData provider).
`Vary`	The `Vary` header is used to vary the cached response by another header. For example, cache responses by encoding by including the `Vary: Accept-Encoding` header, which caches responses for requests with headers `Accept-Encoding: gzip` and `Accept-Encoding: text/plain` separately. A response with a header value of `*` is never stored.
`Expires`	A response deemed stale by this header isn't stored or retrieved unless overridden by other `Cache-Control` headers.
`If-None-Match`	The full response is served from cache if the value isn't `*` and the `ETag` of the response doesn't match any of the values provided. Otherwise, a 304 (Not Modified) response is served.
`If-Modified-Since`	If the `If-None-Match` header isn't present, a full response is served from cache if the cached response date is newer than the value provided. Otherwise, a 304 - Not Modified response is served.
`Date`	When serving from cache, the `Date` header is set by the middleware if it wasn't provided on the original response.
`Content-Length`	When serving from cache, the `Content-Length` header is set by the middleware if it wasn't provided on the original response.
`Age`	The `Age` header sent in the original response is ignored. The middleware computes a new value when serving a cached response.

Caching respects request Cache-Control directives

The middleware respects the rules of the HTTP 1.1 Caching specification. The rules require a cache to honor a valid Cache-Control header sent by the client. Under the specification, a client can make requests with a no-cache header value and force the server to generate a new response for every request. Currently, there's no developer control over this caching behavior when using the middleware because the middleware adheres to the official caching specification.

For more control over caching behavior, explore other caching features of ASP.NET Core. See the following topics:

Troubleshooting

If caching behavior isn't as expected, confirm that responses are cacheable and capable of being served from the cache. Examine the request's incoming headers and the response's outgoing headers. Enable logging to help with debugging.

When testing and troubleshooting caching behavior, a browser may set request headers that affect caching in undesirable ways. For example, a browser may set the Cache-Control header to no-cache or max-age=0 when refreshing a page. The following tools can explicitly set request headers and are preferred for testing caching:

Conditions for caching

The request must result in a server response with a 200 (OK) status code.
The request method must be GET or HEAD.
In Startup.Configure, Response Caching Middleware must be placed before middleware that require caching. For more information, see xref:fundamentals/middleware/index.
The Authorization header must not be present.
Cache-Control header parameters must be valid, and the response must be marked public and not marked private.
The Pragma: no-cache header must not be present if the Cache-Control header isn't present, as the Cache-Control header overrides the Pragma header when present.
The Set-Cookie header must not be present.
Vary header parameters must be valid and not equal to *.
The Content-Length header value (if set) must match the size of the response body.
The xref:Microsoft.AspNetCore.Http.Features.IHttpSendFileFeature isn't used.
The response must not be stale as specified by the Expires header and the max-age and s-maxage cache directives.
Response buffering must be successful. The size of the response must be smaller than the configured or default xref:Microsoft.AspNetCore.ResponseCaching.ResponseCachingOptions.SizeLimit. The body size of the response must be smaller than the configured or default xref:Microsoft.AspNetCore.ResponseCaching.ResponseCachingOptions.MaximumBodySize.
The response must be cacheable according to the RFC 7234 specifications. For example, the no-store directive must not exist in request or response header fields. See Section 3: Storing Responses in Caches of RFC 7234 for details.

[!NOTE] The Antiforgery system for generating secure tokens to prevent Cross-Site Request Forgery (CSRF) attacks sets the Cache-Control and Pragma headers to no-cache so that responses aren't cached. For information on how to disable antiforgery tokens for HTML form elements, see xref:security/anti-request-forgery#aspnet-core-antiforgery-configuration.

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Response Caching Middleware in ASP.NET Core

Configuration

Options

VaryByQueryKeys

HTTP headers used by Response Caching Middleware

Caching respects request Cache-Control directives

Troubleshooting

Conditions for caching

Additional resources

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