enforce constraints on the settings, store settings in the image

lib/labelmaker_web/constants.ex

@@ -1,6 +1,6 @@
 defmodule LabelmakerWeb.Constants do
   @defaults %{
-    "label" => "Labelmaker",
+    "label" => "64 character maximum",
     "font" => "Helvetica",
     "color" => "black",
     "size" => "24"
@@ -22,16 +22,19 @@ defmodule LabelmakerWeb.Constants do
          |> Enum.reject(&String.starts_with?(&1, "  Font: ."))
          |> Enum.map(&String.trim_leading(&1, "  Font: "))
 
+  @max_label_length 64
+
   @sizes 8..72
          |> Enum.to_list()
          |> Enum.take_every(4)
          |> Enum.map(&Integer.to_string/1)
 
-  def defaults, do: @defaults
-  def permitted_keys, do: @permitted_keys
   def colors, do: @colors
   def color_count, do: @colors |> length()
+  def defaults, do: @defaults
   def fonts, do: @fonts
   def font_count, do: @fonts |> length()
+  def max_label_length, do: @max_label_length
+  def permitted_keys, do: @permitted_keys
   def sizes, do: @sizes
 end

lib/labelmaker_web/controllers/label_controller.ex

@@ -6,10 +6,23 @@ defmodule LabelmakerWeb.LabelController do
   File.mkdir_p!(@label_dir)
 
   def show(conn, params) do
+    params =
+      params
+      |> Map.take(Constants.permitted_keys())
+      |> Enum.filter(fn {k, v} ->
+        case k do
+          "color" -> v in Constants.colors()
+          "font" -> v in Constants.fonts()
+          "label" -> String.length(v) <= Constants.max_label_length()
+          "size" -> v in Constants.sizes()
+          _ -> true
+        end
+      end)
+      |> Map.new()
+
     options =
       Constants.defaults()
       |> Map.merge(params)
-      |> Map.take(Constants.permitted_keys())
 
     filename =
       options
@@ -40,6 +53,9 @@ defmodule LabelmakerWeb.LabelController do
       "-font",
       options["font"],
       "label:#{options["label"]}",
+      "-set",
+      "comment",
+      inspect(options),
       filepath
     ]