Override Rack method - ruby-on-rails-3

Question

My setup: Rails 3.0.9, Ruby 1.9.2
Due to a bug in Rack 1.2.3, I'm attempting to override Rack::Utils::Multipart.parse_multipart by creating a new file
rack_parse_multipart.rb
module Rack
module Utils
module Multipart
def self.parse_multipart(env)
...my changes...
end
end
end
end
Now I just need to figure out where I require this file, can someone point me in the right direction? Thanks in advance for your help.

Answer 1

For others having problems with this Rack 1.2.3 bug, there is a nice copy-paste solution here https://github.com/rack/rack/issues/186
goes in config/initializers
# -*- encoding: binary -*-
require 'rack/utils'
module Rack
module Utils
module Multipart
def self.parse_multipart(env)
unless env['CONTENT_TYPE'] =~
%r|\Amultipart/.*boundary=\"?([^\";,]+)\"?|n
nil
else
boundary = "--#{$1}"
params = {}
buf = ""
content_length = env['CONTENT_LENGTH'].to_i
input = env['rack.input']
input.rewind
boundary_size = Utils.bytesize(boundary) + EOL.size
bufsize = 16384
content_length -= boundary_size
read_buffer = ''
status = input.read(boundary_size, read_buffer)
raise EOFError, "bad content body" unless status == boundary + EOL
rx = /(?:#{EOL})?#{Regexp.quote boundary}(#{EOL}|--)/n
loop {
head = nil
body = ''
filename = content_type = name = nil
until head && buf =~ rx
if !head && i = buf.index(EOL+EOL)
head = buf.slice!(0, i+2) # First \r\n
buf.slice!(0, 2) # Second \r\n
token = /[^\s()<>,;:\\"\/\[\]?=]+/
condisp = /Content-Disposition:\s*#{token}\s*/i
dispparm = /;\s*(#{token})=("(?:\\"|[^"])*"|#{token})*/
rfc2183 = /^#{condisp}(#{dispparm})+$/i
broken_quoted = /^#{condisp}.*;\sfilename="(.*?)"(?:\s*$|\s*;\s*#{token}=)/i
broken_unquoted = /^#{condisp}.*;\sfilename=(#{token})/i
if head =~ rfc2183
filename = Hash[head.scan(dispparm)]['filename']
filename = $1 if filename and filename =~ /^"(.*)"$/
elsif head =~ broken_quoted
filename = $1
elsif head =~ broken_unquoted
filename = $1
end
if filename && filename !~ /\\[^\\"]/
filename = Utils.unescape(filename).gsub(/\\(.)/, '\1')
end
content_type = head[/Content-Type: (.*)#{EOL}/ni, 1]
name = head[/Content-Disposition:.*\s+name="?([^\";]*)"?/ni, 1] || head[/Content-ID:\s*([^#{EOL}]*)/ni, 1]
if filename
body = Tempfile.new("RackMultipart")
body.binmode if body.respond_to?(:binmode)
end
next
end
# Save the read body part.
if head && (boundary_size+4 < buf.size)
body << buf.slice!(0, buf.size - (boundary_size+4))
end
c = input.read(bufsize < content_length ? bufsize : content_length, read_buffer)
raise EOFError, "bad content body" if c.nil? || c.empty?
buf << c
content_length -= c.size
end
# Save the rest.
if i = buf.index(rx)
body << buf.slice!(0, i)
buf.slice!(0, boundary_size+2)
content_length = -1 if $1 == "--"
end
if filename == ""
# filename is blank which means no file has been selected
data = nil
elsif filename
body.rewind
# Take the basename of the upload's original filename.
# This handles the full Windows paths given by Internet Explorer
# (and perhaps other broken user agents) without affecting
# those which give the lone filename.
filename = filename.split(/[\/\\]/).last
data = {:filename => filename, :type => content_type,
:name => name, :tempfile => body, :head => head}
# elsif !filename && content_type
# body.rewind
#
# # Generic multipart cases, not coming from a form
# data = {:type => content_type,
# :name => name, :tempfile => body, :head => head}
else
data = body
end
Utils.normalize_params(params, name, data) unless data.nil?
# break if we're at the end of a buffer, but not if it is the end of a field
break if (buf.empty? && $1 != EOL) || content_length == -1
}
input.rewind
params
end
end
end
end
end

Answer 2

Don't do it like this, your file should be like this:
Rack::Utils::UploadedFile.class_eval do
def self.parse_multipart( env )
# add your code here
end
end
This file can be placed in a initializer file on your initializers folder.
The difference between doing the way you did and the way I'm showing is that when you're using module/class you might break the Rails autoload mechanism, as Rails could think you're defining the class (and not load the original class by itself) and the original class would never be loaded.
Whenever you're doing monkey patching like this make sure you use the class_eval solution so that Rails is forced to load the original class first and then runs your code.