param validators for encode processor

lib/dragonfly/image_magick/processors/encode.rb

@@ -4,11 +4,23 @@ module Dragonfly
   module ImageMagick
     module Processors
       class Encode
+        include ParamValidators
+
+        WHITELISTED_ARGS = %w(quality)
+
+        IS_IN_WHITELISTED_ARGS = ->(args_string) {
+          args_string.scan(/-\w+/).all? { |arg|
+            WHITELISTED_ARGS.include?(arg.sub("-", ""))
+          }
+        }
+
         def update_url(attrs, format, args = "")
           attrs.ext = format.to_s
         end
 
         def call(content, format, args = "")
+          validate!(format, &is_word)
+          validate!(args, &IS_IN_WHITELISTED_ARGS)
           Commands.convert(content, args, "format" => format)
         end
       end

spec/dragonfly/image_magick/processors/encode_spec.rb

@@ -0,0 +1,30 @@
+require "spec_helper"
+
+describe Dragonfly::ImageMagick::Processors::Encode do
+  let (:app) { test_imagemagick_app }
+  let (:image) { Dragonfly::Content.new(app, SAMPLES_DIR.join("beach.png")) } # 280x355
+  let (:processor) { Dragonfly::ImageMagick::Processors::Encode.new }
+
+  it "encodes to a different format" do
+    processor.call(image, "jpeg")
+    image.should have_format("jpeg")
+  end
+
+  describe "param validations" do
+    it "validates the format param" do
+      expect {
+        processor.call(image, "jpeg -write bad.png")
+      }.to raise_error(Dragonfly::ParamValidators::InvalidParameter)
+    end
+
+    it "allows good args" do
+      processor.call(image, "jpeg", "-quality 10")
+    end
+
+    it "disallows bad args" do
+      expect {
+        processor.call(image, "jpeg", "-write bad.png")
+      }.to raise_error(Dragonfly::ParamValidators::InvalidParameter)
+    end
+  end
+end