When parsing a multi-part POST, retain original pairs

lib/rack/constants.rb

@@ -54,6 +54,7 @@ module Rack
   RACK_RESPONSE_FINISHED              = 'rack.response_finished'
   RACK_REQUEST_FORM_INPUT             = 'rack.request.form_input'
   RACK_REQUEST_FORM_HASH              = 'rack.request.form_hash'
+  RACK_REQUEST_FORM_PAIRS             = 'rack.request.form_pairs'
   RACK_REQUEST_FORM_VARS              = 'rack.request.form_vars'
   RACK_REQUEST_FORM_ERROR             = 'rack.request.form_error'
   RACK_REQUEST_COOKIE_HASH            = 'rack.request.cookie_hash'

lib/rack/multipart.rb

@@ -19,6 +19,31 @@ class MissingInputError < StandardError
       include BadRequest
     end
 
+    # Accumulator for multipart form data, conforming to the QueryParser API.
+    # In future, the Parser could return the pair list directly, but that would
+    # change its API.
+    class ParamList # :nodoc:
+      def self.make_params
+        new
+      end
+
+      def self.normalize_params(params, key, value)
+        params << [key, value]
+      end
+
+      def initialize
+        @pairs = []
+      end
+
+      def <<(pair)
+        @pairs << pair
+      end
+
+      def to_params_hash
+        @pairs
+      end
+    end
+
     class << self
       def parse_multipart(env, params = Rack::Utils.default_query_parser)
         unless io = env[RACK_INPUT]

lib/rack/request.rb

@@ -516,7 +516,10 @@ def POST
             set_header RACK_REQUEST_FORM_INPUT, nil
             set_header(RACK_REQUEST_FORM_HASH, {})
           elsif form_data? || parseable_data?
-            unless set_header(RACK_REQUEST_FORM_HASH, parse_multipart)
+            if pairs = Rack::Multipart.parse_multipart(env, Rack::Multipart::ParamList)
+              set_header RACK_REQUEST_FORM_PAIRS, pairs
+              set_header RACK_REQUEST_FORM_HASH, expand_param_pairs(pairs)
+            else
               form_vars = get_header(RACK_INPUT).read
 
               # Fix for Safari Ajax postings that always append \0
@@ -672,6 +675,16 @@ def parse_multipart
         Rack::Multipart.extract_multipart(self, query_parser)
       end
 
+      def expand_param_pairs(pairs, query_parser = query_parser())
+        params = query_parser.make_params
+
+        pairs.each do |k, v|
+          query_parser.normalize_params(params, k, v)
+        end
+
+        params.to_params_hash
+      end
+
       def split_header(value)
         value ? value.strip.split(/[,\s]+/) : []
       end

test/spec_request.rb

@@ -1359,6 +1359,8 @@ def initialize(*)
     f[:filename].must_equal "dj.jpg"
     f.must_include :tempfile
     f[:tempfile].size.must_equal 76
+
+    req.env['rack.request.form_pairs'].must_equal [["reply", "yes"], ["fileupload", f]]
   end
 
   it "MultipartPartLimitError when request has too many multipart file parts if limit set" do