use Cache-Control for posts images

src/permap.ml

@@ -304,7 +304,14 @@ let get_post_image ~thumbnail request =
   | Ok image_opt -> (
     match image_opt with
     | None -> Dream.respond ~status:`Not_Found "Image does not exists"
-    | Some image -> Dream.respond ~headers:[ ("Content-Type", "image") ] image )
+    | Some image ->
+      (* posts images do not change so we cache them *)
+      Dream.respond
+        ~headers:
+          [ ("Cache-Control", "max-age=3628800, immutable")
+          ; ("Content-Type", "image")
+          ]
+        image )
 
 let get_avatar_image request =
   let nick = Dream.param request "user" in