Harden public asset endpoint against invalid payloads

Closes #143

test/music_library_web/controllers/asset_controller_test.exs

@@ -70,6 +70,33 @@ defmodule MusicLibraryWeb.AssetControllerTest do
       assert conn.resp_body == <<>>
     end
 
+    test "400s on invalid base64 payload", %{conn: conn} do
+      conn = get(conn, ~p"/assets/!!!invalid-base64!!!")
+      assert text_response(conn, 400) == "Bad request"
+    end
+
+    test "400s on valid base64 but invalid JSON payload", %{conn: conn} do
+      payload = Base.url_encode64("not json", padding: false)
+      conn = get(conn, ~p"/assets/#{payload}")
+      assert text_response(conn, 400) == "Bad request"
+    end
+
+    test "404s when payload has null hash", %{conn: conn} do
+      payload = Base.url_encode64(JSON.encode!(%{hash: nil, width: nil}), padding: false)
+      conn = get(conn, ~p"/assets/#{payload}")
+      assert text_response(conn, 404) == "Not found"
+    end
+
+    @tag :capture_log
+    test "404s when asset content is corrupt", %{conn: conn} do
+      {:ok, asset} = Assets.store(%{content: "not an image", format: "image/jpeg"})
+      transform = %Transform{hash: asset.hash, width: 480}
+      payload = Transform.encode!(transform)
+
+      conn = get(conn, ~p"/assets/#{payload}")
+      assert text_response(conn, 404) == "Not found"
+    end
+
     test "handles transforms with width", %{conn: conn, asset: asset} do
       transform = %Transform{hash: asset.hash, width: 480}
       payload = Transform.encode!(transform)