Don't monkeypatch IO, Tempfile, StringIO.

For compatibility with Rails > 3.0.0.
(cherry picked from commit 2e6d3370553ef68aeb0deb2b08de3871616139a4)

lib/paperclip/attachment.rb

@@ -4,6 +4,7 @@ module Paperclip
   # when the model saves, deletes when the model is destroyed, and processes
   # the file upon assignment.
   class Attachment
+    include IOStream
 
     def self.default_options
       @default_options ||= {
@@ -88,7 +89,7 @@ module Paperclip
 
       return nil if uploaded_file.nil?
 
-      @queued_for_write[:original]   = uploaded_file.to_tempfile
+      @queued_for_write[:original]   = to_tempfile(uploaded_file)
       instance_write(:file_name,       uploaded_file.original_filename.strip)
       instance_write(:content_type,    uploaded_file.content_type.to_s.strip)
       instance_write(:file_size,       uploaded_file.size.to_i)

lib/paperclip/iostream.rb

 # Provides method that can be included on File-type objects (IO, StringIO, Tempfile, etc) to allow stream copying
 # and Tempfile conversion.
 module IOStream
-
   # Returns a Tempfile containing the contents of the readable object.
-  def to_tempfile
-    name = respond_to?(:original_filename) ? original_filename : (respond_to?(:path) ? path : "stream")
+  def to_tempfile(object)
+    return object.to_tempfile if object.respond_to?(:to_tempfile)
+    name = object.respond_to?(:original_filename) ? object.original_filename : (object.respond_to?(:path) ? object.path : "stream")
     tempfile = Paperclip::Tempfile.new(["stream", File.extname(name)])
     tempfile.binmode
-    self.stream_to(tempfile)
+    stream_to(object, tempfile)
   end
 
   # Copies one read-able object from one place to another in blocks, obviating the need to load
-  # the whole thing into memory. Defaults to 8k blocks. If this module is included in both
-  # StringIO and Tempfile, then either can have its data copied anywhere else without typing
-  # worries or memory overhead worries. Returns a File if a String is passed in as the destination
-  # and returns the IO or Tempfile as passed in if one is sent as the destination.
-  def stream_to path_or_file, in_blocks_of = 8192
+  # the whole thing into memory. Defaults to 8k blocks. Returns a File if a String is passed
+  # in as the destination and returns the IO or Tempfile as passed in if one is sent as the destination.
+  def stream_to object, path_or_file, in_blocks_of = 8192
     dstio = case path_or_file
             when String   then File.new(path_or_file, "wb+")
             when IO       then path_or_file
             when Tempfile then path_or_file
             end
     buffer = ""
-    self.rewind
-    while self.read(in_blocks_of, buffer) do
+    object.rewind
+    while object.read(in_blocks_of, buffer) do
       dstio.write(buffer)
     end
     dstio.rewind
@@ -31,18 +29,6 @@ module IOStream
   end
 end
 
-class IO #:nodoc:
-  include IOStream
-end
-
-%w( Tempfile StringIO ).each do |klass|
-  if Object.const_defined? klass
-    Object.const_get(klass).class_eval do
-      include IOStream
-    end
-  end
-end
-
 # Corrects a bug in Windows when asking for Tempfile size.
 if defined? Tempfile
   class Tempfile

test/iostream_test.rb

 require 'test/helper'
 
 class IOStreamTest < Test::Unit::TestCase
-  context "IOStream" do
-    should "be included in IO, File, Tempfile, and StringIO" do
-      [IO, File, Tempfile, StringIO].each do |klass|
-        assert klass.included_modules.include?(IOStream), "Not in #{klass}"
-      end
-    end
-  end
-
+  include IOStream
   context "A file" do
     setup do
       @file = File.new(File.join(File.dirname(__FILE__), "fixtures", "5k.png"), 'rb')
@@ -21,7 +14,7 @@ class IOStreamTest < Test::Unit::TestCase
       context "and given a String" do
         setup do
           FileUtils.mkdir_p(File.join(ROOT, 'tmp'))
-          assert @result = @file.stream_to(File.join(ROOT, 'tmp', 'iostream.string.test'))
+          assert @result = stream_to(@file, File.join(ROOT, 'tmp', 'iostream.string.test'))
         end
 
         should "return a File" do
@@ -38,7 +31,7 @@ class IOStreamTest < Test::Unit::TestCase
         setup do
           tempfile = Tempfile.new('iostream.test')
           tempfile.binmode
-          assert @result = @file.stream_to(tempfile)
+          assert @result = stream_to(@file, tempfile)
         end
 
         should "return a Tempfile" do
@@ -53,9 +46,9 @@ class IOStreamTest < Test::Unit::TestCase
 
     end
 
-    context "that is sent #to_tempfile" do
+    context "that is converted #to_tempfile" do
       setup do
-        assert @tempfile = @file.to_tempfile
+        assert @tempfile = to_tempfile(@file)
       end
 
       should "convert it to a Paperclip Tempfile" do