Performance - Caching - Response caching

In this article

• Enables caching server responses based on HTTP cache headers. Implements the standard HTTP caching semantics. Caches based on HTTP cache headers like proxies do.

• Is typically not beneficial for UI apps such as Razor Pages because browsers generally set request headers that prevent caching. Output caching, which is available in ASP.NET Core 7.0 and later, benefits UI apps. With output caching, configuration decides what should be cached independently of HTTP headers.

• May be beneficial for public GET or HEAD API requests from clients where the Conditions for caching are met.

HTTP-based response caching

Directive	Action
public	A cache may store the response.
private	The response must not be stored by a shared cache. A ```private``` cache may store and reuse the response.
max-age	The client doesn't accept a response whose age is greater than the specified number of seconds. Examples: max-age=60 (60 seconds), max-age=2592000 (1 month)
no-cache	On requests: A cache must not use a stored response to satisfy the request. The origin server regenerates the response for the client, and the middleware updates the stored response in its cache. On responses: The response must not be used for a subsequent request without validation on the origin server.
no-store	On requests: A cache must not store the request. On responses: A cache must not store any part of the response.

Header	Function
Age	An estimate of the amount of time in seconds since the response was generated or successfully validated at the origin server.
Expires	The time after which the response is considered stale.
Pragma	Exists for backwards compatibility with HTTP/1.0 caches for setting no-cache behavior. If the Cache-Control header is present, the Pragma header is ignored.
Vary	Specifies that a cached response must not be sent unless all of the Vary header fields match in both the cached response's original request and the new request.

HTTP-based caching respects request Cache-Control directives

ResponseCache attribute

Warning Disable caching for content that contains information for authenticated clients. Caching should only be enabled for content that doesn't change based on a user's identity or whether a user is signed in.

Request	Returned from
http://example.com?key1=value1	Server
http://example.com?key1=value1	Middleware
http://example.com?key1=NewValue	Server

• Removes any existing headers for Vary, Cache-Control, and Pragma.

• Writes out the appropriate headers based on the properties set in the ResponseCacheAttribute.

• Updates the response caching HTTP feature if VaryByQueryKeys is set.

Vary

[ApiController]
public class TimeController : ControllerBase
{
    [Route("api/[controller]")]
    [HttpGet]
    [ResponseCache(VaryByHeader = "User-Agent", Duration = 30)]
    public ContentResult GetTime() => Content(
                      DateTime.Now.Millisecond.ToString());

Cache-Control: public,max-age=30
Vary: User-Agent

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddControllers();
builder.Services.AddResponseCaching();

var app = builder.Build();

app.UseHttpsRedirection();

// UseCors must be called before UseResponseCaching
//app.UseCors();

app.UseResponseCaching();

app.UseAuthorization();

app.MapControllers();

app.Run();

NoStore and Location.None

• Cache-Control is set to no-store,no-cache.

• Pragma is set to no-cache.

[Route("api/[controller]/ticks")]
[HttpGet]
[ResponseCache(Location = ResponseCacheLocation.None, NoStore = true)]
public ContentResult GetTimeTicks() => Content(
                  DateTime.Now.Ticks.ToString());

builder.Services.AddControllersWithViews().AddMvcOptions(options => 
    options.Filters.Add(
        new ResponseCacheAttribute
        {
            NoStore = true, 
            Location = ResponseCacheLocation.None
        }));

Location and Duration

[Route("api/[controller]/ms")]
[HttpGet]
[ResponseCache(Duration = 10, Location = ResponseCacheLocation.Any, NoStore = false)]
public ContentResult GetTimeMS() => Content(
                  DateTime.Now.Millisecond.ToString());

Cache profiles

using Microsoft.AspNetCore.Mvc;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddResponseCaching();
builder.Services.AddControllers(options =>
{
    options.CacheProfiles.Add("Default30",
        new CacheProfile()
        {
            Duration = 30
        });
});

var app = builder.Build();

app.UseHttpsRedirection();

// UseCors must be called before UseResponseCaching
//app.UseCors();

app.UseResponseCaching();

app.UseAuthorization();

app.MapControllers();

app.Run();

[ApiController]
[ResponseCache(CacheProfileName = "Default30")]
public class Time2Controller : ControllerBase
{
    [Route("api/[controller]")]
    [HttpGet]
    public ContentResult GetTime() => Content(
                      DateTime.Now.Millisecond.ToString());

    [Route("api/[controller]/ticks")]
    [HttpGet]
    public ContentResult GetTimeTicks() => Content(
                      DateTime.Now.Ticks.ToString());
}

• Razor Pages: Attributes can't be applied to handler methods. Browsers used with UI apps prevent response caching.

• MVC controllers.

• MVC action methods: Method-level attributes override the settings specified in class-level attributes.

[ApiController]
[ResponseCache(VaryByHeader = "User-Agent", Duration = 30)]
public class Time4Controller : ControllerBase
{
    [Route("api/[controller]")]
    [HttpGet]
    public ContentResult GetTime() => Content(
                      DateTime.Now.Millisecond.ToString());

    [Route("api/[controller]/ticks")]
    [HttpGet]
    public ContentResult GetTimeTicks() => Content(
                  DateTime.Now.Ticks.ToString());

    [Route("api/[controller]/ms")]
    [HttpGet]
    [ResponseCache(Duration = 10, Location = ResponseCacheLocation.Any, NoStore = false)]
    public ContentResult GetTimeMS() => Content(
                      DateTime.Now.Millisecond.ToString());
}

Additional resources

• Storing Responses in Caches

• Cache-Control

• Cache in-memory in ASP.NET Core

• Distributed caching in ASP.NET Core

• Detect changes with change tokens in ASP.NET Core

• Response Caching Middleware in ASP.NET Core

• Cache Tag Helper in ASP.NET Core MVC

• Distributed Cache Tag Helper in ASP.NET Core

Ref: Response caching in ASP.NET Core