C# Minimal API: Response Caching

#dotnet #minimalapis #performance #csharp

Response Caching

Response caching reduces the number of requests a client or proxy makes to a web server. Response caching also reduces the amount of work the web server performs to generate a response. Response caching is set in headers. (Microsoft Docs)

Response caching is configured using the Cache-Control header, which allows responses to be cached on the client or along the way, for example on a proxy.

Response Caching in Minimal APIs

In ASP.NET Core MVC, response caching is typically configured using the ResponseCache attribute in combination with the UseResponseCaching middleware, but this is purely an MVC concept.

For Minimal APIs, we can achieve similar behavior by adding an endpoint filter that sets the Cache-Control header after the request is processed.

RouteHandlerBuilder Caching Extension

The following extension method provides a simple way to apply response caching headers to Minimal API endpoints. The endpoint filter checks if the request is a GET or HEAD method, executes the endpoint, and then sets the Cache-Control header with the specified max age only if the response status code is 200 OK.

public static class HttpResponseCachingConfiguration
{
    public static RouteHandlerBuilder AddResponseCacheHeader(this RouteHandlerBuilder routeHandlerBuilder, int maxAgeInSeconds)
      => routeHandlerBuilder.AddEndpointFilter(async (context, next) =>
       {
         var isGetOrHeadRequest = HttpMethods.IsGet(context.HttpContext.Request.Method) || 
                                       HttpMethods.IsHead(context.HttpContext.Request.Method);
         if (!isGetOrHeadRequest)
         {
           return await next(context);
         }

         var result = await next(context);

         if (context.HttpContext.Response.StatusCode == StatusCodes.Status200OK)
         {
           context.HttpContext.Response.Headers.CacheControl = $"public,max-age={maxAgeInSeconds}";
         }

         return result;
      });
}

This extension makes it easy to attach caching headers to any Minimal API endpoint by chaining the extension method, as shown in the example below.

app.MapGet("/weatherforecast", () =>
{
    var forecast = Enumerable.Range(1, 5).Select(index =>
        new WeatherForecast
        (
            DateOnly.FromDateTime(DateTime.Now.AddDays(index)),
            Random.Shared.Next(-20, 55),
            summaries[Random.Shared.Next(summaries.Length)]
        ))
        .ToArray();
    return forecast;
})
.AddResponseCacheHeader(300);
.WithName("GetWeatherForecast");

Note: Client-side caching in browsers or proxies requires caching to be enabled. Once cached, the client or proxy serves the cached response automatically when appropriate.