Use a singleton null object for empty request bodies

lib/puma/null_io.rb

@@ -0,0 +1,20 @@
+module Puma
+  class NullIO
+    def gets
+      nil
+    end
+
+    def each
+    end
+
+    def read(count)
+      nil
+    end
+
+    def rewind
+    end
+
+    def close
+    end
+  end
+end

lib/puma/server.rb

@@ -5,6 +5,7 @@ require 'stringio'
 require 'puma/thread_pool'
 require 'puma/const'
 require 'puma/events'
+require 'puma/null_io'
 
 require 'puma_http11'
 
@@ -249,8 +250,7 @@ module Puma
       env[REMOTE_ADDR] = client.peeraddr.last
     end
 
-    EmptyBinary = ""
-    EmptyBinary.force_encoding("BINARY") if EmptyBinary.respond_to? :force_encoding
+    EmptyBody = NullIO.new
 
     def handle_request(env, client, body, cl)
       normalize_env env, client
@@ -259,7 +259,7 @@ module Puma
         body = read_body env, client, body, cl
         return false unless body
       else
-        body = StringIO.new(EmptyBinary)
+        body = EmptyBody
       end
 
       env[RACK_INPUT] = body

test/test_persistent.rb

@@ -197,8 +197,8 @@ class TestPersistent < Test::Unit::TestCase
     assert_equal "HTTP/1.1 200 OK\r\nX-Header: Works\r\nContent-Length: #{sz}\r\n\r\n", lines(4)
     assert_equal "Hello", @client.read(5)
 
-    assert_equal "", @inputs[0].string
-    assert_equal "", @inputs[1].string
+    assert_kind_of Puma::NullIO, @inputs[0]
+    assert_kind_of Puma::NullIO, @inputs[1]
 
   end