3 files changed, 20 insertions, 3 deletions
diff --git a/actionpack/lib/action_dispatch/http/headers.rb b/actionpack/lib/action_dispatch/http/headers.rb
index 91c45767ef..d5eef2987d 100644
--- a/actionpack/lib/action_dispatch/http/headers.rb
+++ b/actionpack/lib/action_dispatch/http/headers.rb
@@ -3,7 +3,7 @@ module ActionDispatch
     # Provides access to the request's HTTP headers from the environment.
     #
     #   env     = { "CONTENT_TYPE" => "text/plain", "HTTP_USER_AGENT" => "curl/7.43.0" }
-    #   headers = ActionDispatch::Http::Headers.new(env)
+    #   headers = ActionDispatch::Http::Headers.from_hash(env)
     #   headers["Content-Type"] # => "text/plain"
     #   headers["User-Agent"] # => "curl/7.43.0"
     #
diff --git a/actionpack/lib/action_dispatch/http/parameters.rb b/actionpack/lib/action_dispatch/http/parameters.rb
index f25e50f9f3..31ef0af791 100644
--- a/actionpack/lib/action_dispatch/http/parameters.rb
+++ b/actionpack/lib/action_dispatch/http/parameters.rb
@@ -8,7 +8,7 @@ module ActionDispatch
       DEFAULT_PARSERS = {
         Mime[:json].symbol => -> (raw_post) {
           data = ActiveSupport::JSON.decode(raw_post)
-          data.is_a?(Hash) ? data : {_json: data}
+          data.is_a?(Hash) ? data : { _json: data }
         }
       }
 
@@ -37,6 +37,7 @@ module ActionDispatch
                    query_parameters.dup
                  end
         params.merge!(path_parameters)
+        params = set_custom_encoding(params)
         set_header("action_dispatch.request.parameters", params)
         params
       end
@@ -64,6 +65,21 @@ module ActionDispatch
 
       private
 
+        def set_custom_encoding(params)
+          action = params[:action]
+          params.each do |k, v|
+            if v.is_a?(String) && v.encoding != encoding_template(action, k)
+              params[k] = v.force_encoding(encoding_template(action, k))
+            end
+          end
+
+          params
+        end
+
+        def encoding_template(action, param)
+          controller_class.encoding_for_param(action, param)
+        end
+
         def parse_formatted_parameters(parsers)
           return yield if content_length.zero? || content_mime_type.nil?
 
diff --git a/actionpack/lib/action_dispatch/http/request.rb b/actionpack/lib/action_dispatch/http/request.rb
index 46409a325e..e4ef9783f3 100644
--- a/actionpack/lib/action_dispatch/http/request.rb
+++ b/actionpack/lib/action_dispatch/http/request.rb
@@ -68,7 +68,8 @@ module ActionDispatch
 
     PASS_NOT_FOUND = Class.new { # :nodoc:
       def self.action(_); self; end
-      def self.call(_); [404, {"X-Cascade" => "pass"}, []]; end
+      def self.call(_); [404, { "X-Cascade" => "pass" }, []]; end
+      def self.encoding_for_param(action, param); ::Encoding::UTF_8; end
     }
 
     def controller_class