added StringIO support to json gem and okjson

lib/multi_json/engines/json_gem.rb

@@ -9,6 +9,7 @@ class JsonGem
       def self.decode(string, options = {}) #:nodoc:
         opts = {}
         opts[:symbolize_names] = options[:symbolize_keys]
+        string = string.read if string.respond_to?(:read)
         ::JSON.parse(string, opts)
       end
 

lib/multi_json/engines/json_pure.rb

@@ -9,6 +9,7 @@ class JsonPure
       def self.decode(string, options = {}) #:nodoc:
         opts = {}
         opts[:symbolize_names] = options[:symbolize_keys]
+        string = string.read if string.respond_to?(:read)
         ::JSON.parse(string, opts)
       end
 

lib/multi_json/engines/ok_json.rb

@@ -6,6 +6,7 @@ class OkJson
       ParseError = ::OkJson::Error
 
       def self.decode(string, options = {}) #:nodoc:
+        string = string.read if string.respond_to?(:read)
         result = ::OkJson.decode(string)
         options[:symbolize_keys] ? symbolize_keys(result) : result
       end

spec/multi_json_spec.rb

@@ -1,5 +1,6 @@
 require 'spec_helper'
-
+require 'stringio'
+
 class MockDecoder
   def self.decode(string, options = {})
     { 'abc' => 'def' }
@@ -75,6 +76,11 @@ def self.encode(string)
           encoded_json = MultiJson.encode(:a => 1, :b => {:c => 2})
           MultiJson.decode(encoded_json).should == { "a" => 1, "b" => { "c" => 2 } }
         end
+
+        it "properly decodes valid JSON in StringIOs" do
+          json = StringIO.new('{"abc":"def"}')
+          MultiJson.decode(json).should == { 'abc' => 'def' }
+        end
 
         it 'allows for symbolization of keys' do
           MultiJson.decode('{"abc":{"def":"hgi"}}', :symbolize_keys => true).should == { :abc => { :def => 'hgi' } }