Add HTTP Caching headers to links and thumbnails (#417)

* Add HTTP Caching headers to links and thumbnails

* remove extra newline

* update changelog

* Need to create the PR first to get a number

* Add todo-note that we'll surely not forget

Co-authored-by: Rasmus Karlsson <rasmus.karlsson@pajlada.com>

CHANGELOG.md

@@ -31,6 +31,7 @@
 - Dev: Resolve imgur.io links. (#365)
 - Dev: Don't use `stampede` for link resolver links. (#394)
 - Dev: Update to Twitter's v2 API. (#414)
+- Dev: Add HTTP Caching headers. (#417)
 
 ## 1.2.3
 

internal/resolvers/default/initialize.go

@@ -6,6 +6,7 @@ import (
 	"time"
 
 	"github.com/Chatterino/api/internal/db"
+	"github.com/Chatterino/api/pkg/cache"
 	"github.com/Chatterino/api/pkg/config"
 	"github.com/go-chi/chi/v5"
 	"github.com/go-chi/stampede"
@@ -34,7 +35,8 @@ func Initialize(ctx context.Context, cfg config.APIConfig, pool db.Pool, router
 	imageCached := stampede.Handler(256, 2*time.Second)
 	generatedValuesCached := stampede.Handler(256, 2*time.Second)
 
-	router.Get("/link_resolver/{url}", defaultLinkResolver.HandleRequest)
-	router.With(imageCached).Get("/thumbnail/{url}", defaultLinkResolver.HandleThumbnailRequest)
+	// TODO: Make the max age headers be applied based on the resolved link's configured cache timer
+	router.With(cache.MaxAgeHeaders(time.Minute*10)).Get("/link_resolver/{url}", defaultLinkResolver.HandleRequest)
+	router.With(cache.MaxAgeHeaders(time.Minute*10), imageCached).Get("/thumbnail/{url}", defaultLinkResolver.HandleThumbnailRequest)
 	router.With(generatedValuesCached).Get("/generated/{url}", defaultLinkResolver.HandleGeneratedValueRequest)
 }

pkg/cache/middleware.go

@@ -0,0 +1,17 @@
+package cache
+
+import (
+	"fmt"
+	"net/http"
+	"time"
+)
+
+// MaxAgeHeaders adds the Cache-Control: max-age=$TTL header to every response
+func MaxAgeHeaders(ttl time.Duration) func(next http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			w.Header().Add("Cache-Control", fmt.Sprintf("max-age=%.0f", ttl.Seconds()))
+			next.ServeHTTP(w, r)
+		})
+	}
+}