diff --git a/lib/puma/io_buffer.rb b/lib/puma/io_buffer.rb
new file mode 100644
index 00000000..a7c4cbac
--- /dev/null
+++ b/lib/puma/io_buffer.rb
@@ -0,0 +1,33 @@
+module Puma
+  class IOBuffer
+    def initialize
+      @buf = ""
+    end
+
+    def reset
+      @buf = ""
+    end
+
+    def <<(str)
+      @buf << str
+    end
+
+    def append(*strs)
+      strs.each { |s| @buf << s }
+    end
+
+    def to_s
+      @buf
+    end
+
+    alias_method :to_str, :to_s
+
+    def used
+      @buf.size
+    end
+
+    def capacity
+      @buf.size
+    end
+  end
+end
diff --git a/lib/puma/server.rb b/lib/puma/server.rb
index 5a3e7274..90bd4959 100644
--- a/lib/puma/server.rb
+++ b/lib/puma/server.rb
@@ -14,6 +14,10 @@ require 'puma/accept_nonblock'
 
 require 'puma/puma_http11'
 
+unless Puma.const_defined? "IOBuffer"
+  require 'puma/io_buffer'
+end
+
 require 'socket'
 
 module Puma