Cache transformations

lib/music_library/application.ex

@@ -5,8 +5,12 @@ defmodule MusicLibrary.Application do
 
   use Application
 
+  alias MusicLibrary.Assets
+
   @impl true
   def start(_type, _args) do
+    _ = Assets.Cache.new()
+
     children = [
       MusicLibraryWeb.Telemetry,
       MusicLibrary.Vault,

lib/music_library/assets/cache.ex

@@ -0,0 +1,16 @@
+defmodule MusicLibrary.Assets.Cache do
+  def new do
+    :ets.new(__MODULE__, [:named_table, :public, read_concurrency: true])
+  end
+
+  def set(payload, format, content) do
+    :ets.insert(__MODULE__, {{payload, format}, content})
+  end
+
+  def get(payload, format) do
+    case :ets.lookup(__MODULE__, {payload, format}) do
+      [{{^payload, ^format}, content}] -> {:found, content}
+      [] -> :not_found
+    end
+  end
+end

lib/music_library/records/cover.ex

@@ -6,18 +6,25 @@ defmodule MusicLibrary.Records.Cover do
 
   @external_resource fallback_path
 
-  @size 2000
+  @default_size 2000
+  @default_format "image/jpeg"
 
   def fallback_data, do: unquote(fallback_data)
 
-  def resize(cover_data, size \\ @size) do
+  def resize(cover_data, size \\ @default_size, format \\ @default_format) do
     {:ok, thumb} = Operation.thumbnail_buffer(cover_data, size)
-    Image.write_to_buffer(thumb, ".jpg")
+    Image.write_to_buffer(thumb, extension(format))
   end
 
-  def correct_size?(cover_data) do
-    {:ok, image} = Image.new_from_buffer(cover_data)
-
-    Image.width(image) == @size
+  def convert(cover_data, data_format, target_format) do
+    if data_format == target_format do
+      {:ok, cover_data}
+    else
+      {:ok, image} = Image.new_from_buffer(cover_data)
+      Image.write_to_buffer(image, extension(target_format))
+    end
   end
+
+  defp extension("image/jpeg"), do: ".jpg"
+  defp extension("image/webp"), do: ".webp"
 end

lib/music_library_web/controllers/cover_controller.ex

@@ -2,36 +2,58 @@ defmodule MusicLibraryWeb.CoverController do
   use MusicLibraryWeb, :controller
 
   alias MusicLibrary.Assets
-  alias MusicLibrary.Assets.Transform
+  alias MusicLibrary.Assets.{Cache, Transform}
   alias MusicLibrary.Records.Cover
 
   # 1 year in seconds
   @cache_duration 60 * 60 * 24 * 365
 
   def show(conn, %{"transform_payload" => payload}) do
+    format = pick_format(conn)
     transform = Transform.decode!(payload)
 
-    case Assets.get(transform.hash) do
+    case cached_get(payload, transform, format) do
       nil ->
         not_found(conn)
 
-      %{content: content} ->
-        image_data =
-          if transform.width do
-            # TODO: find a way to cache computation, or pre-compute thumb and store it
-            {:ok, thumb_data} = Cover.resize(content, transform.width)
-            thumb_data
-          else
-            content
-          end
-
+      content when is_binary(content) ->
         case get_req_header(conn, "if-none-match") do
           [^payload] -> extend_cache(conn)
-          _ -> respond_with_cache(conn, image_data, payload)
+          _ -> respond_with_cache(conn, content, format, payload)
         end
     end
   end
 
+  defp cached_get(payload, transform, format) do
+    case Cache.get(payload, format) do
+      :not_found ->
+        if asset = Assets.get(transform.hash) do
+          image_data =
+            if transform.width do
+              # TODO: find a way to cache computation, or pre-compute thumb and store it
+              {:ok, data} = Cover.resize(asset.content, transform.width, format)
+              data
+            else
+              {:ok, data} = Cover.convert(asset.content, asset.format, format)
+              data
+            end
+
+          Cache.set(payload, format, image_data)
+          image_data
+        end
+
+      {:found, content} ->
+        content
+    end
+  end
+
+  defp pick_format(conn) do
+    case get_req_header(conn, "accept") do
+      ["image/webp" <> _] -> "image/webp"
+      _ -> "image/jpeg"
+    end
+  end
+
   defp not_found(conn) do
     conn
     |> put_status(:not_found)
@@ -44,9 +66,9 @@ defmodule MusicLibraryWeb.CoverController do
     |> send_resp(304, "")
   end
 
-  defp respond_with_cache(conn, data, etag) do
+  defp respond_with_cache(conn, data, format, etag) do
     conn
-    |> put_resp_content_type("image/jpeg", "utf-8")
+    |> put_resp_content_type(format, "utf-8")
     |> put_resp_header("cache-control", "public, max-age=#{@cache_duration}")
     |> put_resp_header("etag", etag)
     |> send_resp(200, data)

test/music_library/records/cover_test.exs

@@ -11,7 +11,6 @@ defmodule MusicLibrary.Records.CoverTest do
       cover_data = marbles_cover_data()
       {:ok, resized_cover} = Cover.resize(cover_data)
       assert cover_data !== resized_cover
-      assert Cover.correct_size?(resized_cover)
     end
   end
 end

test/music_library_web/controllers/cover_controller_test.exs

@@ -12,7 +12,7 @@ defmodule MusicLibraryWeb.CoverControllerTest do
     %{asset: asset}
   end
 
-  describe "GET /covers/:hash" do
+  describe "GET /covers/:payload" do
     setup [:create_asset]
 
     test "404s when asset doesn't exist", %{conn: conn} do