Enable aggressive caching for the images endpoint

lib/music_library_web/controllers/image_controller.ex

@@ -3,17 +3,27 @@ defmodule MusicLibraryWeb.ImageController do
 
   alias MusicLibrary.Records
 
-  def show(conn, %{"record_id" => record_id}) do
-    # TODO: better error handling
-    # TODO: serve correct caching headers
-    image_data = Records.get_image!(record_id)
+  @one_year 31_536_000
 
-    if image_data do
-      conn
-      |> put_resp_content_type("image/jpeg", "utf-8")
-      |> send_resp(200, image_data)
-    else
-      conn |> send_resp(404, "Not found")
+  def show(conn, %{"record_id" => record_id}) do
+    case Records.get_image!(record_id) do
+      nil ->
+        send_resp(conn, 404, "Not found")
+
+      image_data ->
+        # TODO: move hash result to database
+        etag = :crypto.hash(:sha256, image_data) |> Base.encode16()
+
+        case get_req_header(conn, "if-none-match") do
+          [^etag] ->
+            send_resp(conn, 304, "")
+
+          _ ->
+            conn
+            |> put_resp_content_type("image/jpeg", "utf-8")
+            |> put_resp_header("cache-control", "public, max-age=#{@one_year}")
+            |> send_resp(200, image_data)
+        end
     end
   end
 end