Set Content-Type on variant uploads

activestorage/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   The `Content-Type` header is set on image variants when they're uploaded to third-party storage services.
+
+    *Kyle Ribordy*
+
 *   Allow storage services to be configured per attachment
 
     ```ruby

activestorage/app/models/active_storage/variant.rb

@@ -98,7 +98,7 @@ class ActiveStorage::Variant
     def process
       blob.open do |input|
         variation.transform(input, format: format) do |output|
-          service.upload(key, output)
+          service.upload(key, output, content_type: content_type)
         end
       end
     end

activestorage/test/models/variant_test.rb

@@ -196,4 +196,16 @@ class ActiveStorage::VariantTest < ActiveSupport::TestCase
   ensure
     ActiveStorage.variant_processor = :mini_magick
   end
+
+  test "passes content_type on upload" do
+    blob = create_file_blob(filename: "racecar.jpg", content_type: "image/jpeg")
+
+    mock_upload = lambda do |_, _, options = {}|
+      assert_equal options[:content_type], "image/jpeg"
+    end
+
+    blob.service.stub(:upload, mock_upload) do
+      blob.variant(resize: "100x100").processed
+    end
+  end
 end