3 files changed, 47 insertions, 2 deletions
diff --git a/actionpack/lib/action_dispatch/http/content_disposition.rb b/actionpack/lib/action_dispatch/http/content_disposition.rb
new file mode 100644
index 0000000000..58164c1522
--- /dev/null
+++ b/actionpack/lib/action_dispatch/http/content_disposition.rb
@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+module ActionDispatch
+  module Http
+    class ContentDisposition # :nodoc:
+      def self.format(disposition:, filename:)
+        new(disposition: disposition, filename: filename).to_s
+      end
+
+      attr_reader :disposition, :filename
+
+      def initialize(disposition:, filename:)
+        @disposition = disposition
+        @filename = filename
+      end
+
+      TRADITIONAL_ESCAPED_CHAR = /[^ A-Za-z0-9!#$+.^_`|~-]/
+
+      def ascii_filename
+        'filename="' + percent_escape(I18n.transliterate(filename), TRADITIONAL_ESCAPED_CHAR) + '"'
+      end
+
+      RFC_5987_ESCAPED_CHAR = /[^A-Za-z0-9!#$&+.^_`|~-]/
+
+      def utf8_filename
+        "filename*=UTF-8''" + percent_escape(filename, RFC_5987_ESCAPED_CHAR)
+      end
+
+      def to_s
+        if filename
+          "#{disposition}; #{ascii_filename}; #{utf8_filename}"
+        else
+          "#{disposition}"
+        end
+      end
+
+      private
+        def percent_escape(string, pattern)
+          string.gsub(pattern) do |char|
+            char.bytes.map { |byte| "%%%02X" % byte }.join
+          end
+        end
+    end
+  end
+end
diff --git a/actionpack/lib/action_dispatch/http/response.rb b/actionpack/lib/action_dispatch/http/response.rb
index 885dc0ecba..f07be831d4 100644
--- a/actionpack/lib/action_dispatch/http/response.rb
+++ b/actionpack/lib/action_dispatch/http/response.rb
@@ -105,7 +105,7 @@ module ActionDispatch # :nodoc:
 
       def body
         @str_body ||= begin
-          buf = "".dup
+          buf = +""
           each { |chunk| buf << chunk }
           buf
         end
diff --git a/actionpack/lib/action_dispatch/http/url.rb b/actionpack/lib/action_dispatch/http/url.rb
index 35ba44005a..db6d8188d3 100644
--- a/actionpack/lib/action_dispatch/http/url.rb
+++ b/actionpack/lib/action_dispatch/http/url.rb
@@ -157,7 +157,7 @@ module ActionDispatch
           subdomain  = options.fetch :subdomain, true
           domain     = options[:domain]
 
-          host = "".dup
+          host = +""
           if subdomain == true
             return _host if domain.nil?