Add Rack::NestedParams; based on Rails UrlEncodedPairParser

* Cleaned up whitespace errors [rtomayko]
* Added note to README [rtomayko]

README.rdoc

@@ -13,6 +13,8 @@ interface:
 * Rack::MailExceptions - Rescues exceptions raised from the app and
   sends a useful email with the exception, stacktrace, and contents of the
   environment.
+* Rack::NestedParams - parses form params with subscripts (e.g., * "post[title]=Hello")
+  into a nested/recursive Hash structure (based on Rails' implementation).
 * Rack::PostBodyContentTypeParser - Adds support for JSON request bodies. The
   Rack parameter hash is populated by deserializing the JSON data provided in
   the request body when the Content-Type is application/json.

lib/rack/contrib.rb

@@ -1,4 +1,5 @@
 require 'rack'
+
 module Rack
   module Contrib
     def self.release
@@ -20,4 +21,5 @@ def self.release
   autoload :TimeZone,                   "rack/contrib/time_zone"
   autoload :Evil,                       "rack/contrib/evil"
   autoload :Callbacks,                  "rack/contrib/callbacks"
+  autoload :NestedParams,               "rack/contrib/nested_params"
 end

lib/rack/contrib/nested_params.rb

@@ -0,0 +1,143 @@
+require 'cgi'
+require 'strscan'
+
+module Rack
+  # Rack middleware for parsing POST/PUT body data into nested parameters
+  class NestedParams
+
+    CONTENT_TYPE = 'CONTENT_TYPE'.freeze
+    POST_BODY = 'rack.input'.freeze
+    FORM_INPUT = 'rack.request.form_input'.freeze
+    FORM_HASH = 'rack.request.form_hash'.freeze
+    FORM_VARS = 'rack.request.form_vars'.freeze
+
+    # supported content type
+    URL_ENCODED = 'application/x-www-form-urlencoded'.freeze
+
+    def initialize(app)
+      @app = app
+    end
+
+    def call(env)
+      if form_vars = env[FORM_VARS]
+        env[FORM_HASH] = parse_query_parameters(form_vars)
+      elsif env[CONTENT_TYPE] == URL_ENCODED
+        post_body = env[POST_BODY]
+        env[FORM_INPUT] = post_body
+        env[FORM_HASH] = parse_query_parameters(post_body.read)
+        post_body.rewind if post_body.respond_to?(:rewind)
+      end
+      @app.call(env)
+    end
+
+    ## the rest is nabbed from Rails ##
+
+    def parse_query_parameters(query_string)
+      return {} if query_string.nil? or query_string.empty?
+
+      pairs = query_string.split('&').collect do |chunk|
+        next if chunk.empty?
+        key, value = chunk.split('=', 2)
+        next if key.empty?
+        value = value.nil? ? nil : CGI.unescape(value)
+        [ CGI.unescape(key), value ]
+      end.compact
+
+      UrlEncodedPairParser.new(pairs).result
+    end
+
+    class UrlEncodedPairParser < StringScanner
+      attr_reader :top, :parent, :result
+
+      def initialize(pairs = [])
+        super('')
+        @result = {}
+        pairs.each { |key, value| parse(key, value) }
+      end
+
+      KEY_REGEXP = %r{([^\[\]=&]+)}
+      BRACKETED_KEY_REGEXP = %r{\[([^\[\]=&]+)\]}
+
+      # Parse the query string
+      def parse(key, value)
+        self.string = key
+        @top, @parent = result, nil
+
+        # First scan the bare key
+        key = scan(KEY_REGEXP) or return
+        key = post_key_check(key)
+
+        # Then scan as many nestings as present
+        until eos?
+          r = scan(BRACKETED_KEY_REGEXP) or return
+          key = self[1]
+          key = post_key_check(key)
+        end
+
+        bind(key, value)
+      end
+
+      private
+        # After we see a key, we must look ahead to determine our next action. Cases:
+        #
+        #   [] follows the key. Then the value must be an array.
+        #   = follows the key. (A value comes next)
+        #   & or the end of string follows the key. Then the key is a flag.
+        #   otherwise, a hash follows the key.
+        def post_key_check(key)
+          if scan(/\[\]/) # a[b][] indicates that b is an array
+            container(key, Array)
+            nil
+          elsif check(/\[[^\]]/) # a[b] indicates that a is a hash
+            container(key, Hash)
+            nil
+          else # End of key? We do nothing.
+            key
+          end
+        end
+
+        # Add a container to the stack.
+        def container(key, klass)
+          type_conflict! klass, top[key] if top.is_a?(Hash) && top.key?(key) && ! top[key].is_a?(klass)
+          value = bind(key, klass.new)
+          type_conflict! klass, value unless value.is_a?(klass)
+          push(value)
+        end
+
+        # Push a value onto the 'stack', which is actually only the top 2 items.
+        def push(value)
+          @parent, @top = @top, value
+        end
+
+        # Bind a key (which may be nil for items in an array) to the provided value.
+        def bind(key, value)
+          if top.is_a? Array
+            if key
+              if top[-1].is_a?(Hash) && ! top[-1].key?(key)
+                top[-1][key] = value
+              else
+                top << {key => value}
+              end
+              push top.last
+              return top[key]
+            else
+              top << value
+              return value
+            end
+          elsif top.is_a? Hash
+            key = CGI.unescape(key)
+            parent << (@top = {}) if top.key?(key) && parent.is_a?(Array)
+            top[key] ||= value
+            return top[key]
+          else
+            raise ArgumentError, "Don't know what to do: top is #{top.inspect}"
+          end
+        end
+
+        def type_conflict!(klass, value)
+          raise TypeError, "Conflicting types for parameter containers. Expected an instance of #{klass} but found an instance of #{value.class}. This can be caused by colliding Array and Hash parameters like qs[]=value&qs[key]=value. (The parameters received were #{value.inspect}.)"
+        end
+    end
+
+  end
+end

test/spec_rack_nested_params.rb

@@ -0,0 +1,45 @@
+require 'rack/mock'
+require 'rack/contrib/nested_params'
+require 'rack/methodoverride'
+
+context Rack::NestedParams do
+
+  App = lambda { |env| [200, {'Content-Type' => 'text/plain'}, Rack::Request.new(env)] }
+
+  def env_for_post_with_headers(path, headers, body)
+    Rack::MockRequest.env_for(path, {:method => "POST", :input => body}.merge(headers))
+  end
+
+  def form_post(params, content_type = 'application/x-www-form-urlencoded')
+    params = Rack::Utils.build_query(params) if Hash === params
+    env_for_post_with_headers('/', {'CONTENT_TYPE' => content_type}, params)
+  end
+
+  def middleware
+    Rack::NestedParams.new(App)
+  end
+
+  specify "should handle requests with POST body Content-Type of application/x-www-form-urlencoded" do
+    req = middleware.call(form_post({'foo[bar][baz]' => 'nested'})).last
+    req.POST.should.equal({"foo" => { "bar" => { "baz" => "nested" }}})
+  end
+
+  specify "should not parse requests with other Content-Type" do
+    req = middleware.call(form_post({'foo[bar][baz]' => 'nested'}, 'text/plain')).last
+    req.POST.should.equal({})
+  end
+
+  specify "should work even after another middleware already parsed the request" do
+    app = Rack::MethodOverride.new(middleware)
+    req = app.call(form_post({'_method' => 'put', 'foo[bar]' => 'nested'})).last
+    req.POST.should.equal({'_method' => 'put', "foo" => { "bar" => "nested" }})
+    req.put?.should.equal true
+  end
+
+  specify "should make first boolean have precedence even after request already parsed" do
+    app = Rack::MethodOverride.new(middleware)
+    req = app.call(form_post("foo=1&foo=0")).last
+    req.POST.should.equal({"foo" => '1'})
+  end
+
+end