loki/pkg/querier/queryrange/queryrangebase/middleware.go

package queryrangebase

import (
	"net/http"

	"github.com/grafana/dskit/middleware"
	"github.com/grafana/dskit/tenant"
)

const (
	// ResultsCacheGenNumberHeaderName holds name of the header we want to set in http response
	ResultsCacheGenNumberHeaderName = "Results-Cache-Gen-Number"
)

func CacheGenNumberHeaderSetterMiddleware(cacheGenNumbersLoader CacheGenNumberLoader) middleware.Interface {
	return middleware.Func(func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			userIDs, err := tenant.TenantIDs(r.Context())
			if err != nil {
				http.Error(w, err.Error(), http.StatusUnauthorized)
				return
			}

			cacheGenNumber := cacheGenNumbersLoader.GetResultsCacheGenNumber(userIDs)

			w.Header().Set(ResultsCacheGenNumberHeaderName, cacheGenNumber)
			next.ServeHTTP(w, r)
		})
	})
}