Problem posting multipart form data to Rails app.

home_controller.rb

# Rails 3.0.3 Controller. Just return the parameters as a string.

class HomeController < ApplicationController
  protect_from_forgery :except => :upload
  def upload
    render :text => params.to_s
  end
end

test.py

#!/usr/bin/env python

import requests

files = dict(avatar=open('avatar.jpg', 'rb'))
data = dict(name='A picture')

r = requests.post('http://localhost:4567/upload', data=data, files=files)
print r.text

test2.py

# This one monkey patches encode_multipart_formdata to omit the Content-Type header from non-binary parts. 
# See below for output from test.py and this one.

import requests

import codecs

try:
    from mimetools import choose_boundary
except ImportError:
    from requests.packages.urllib3.packages.mimetools_choose_boundary import choose_boundary

from io import BytesIO

from requests.packages.urllib3.packages import six
from requests.packages.urllib3.packages.six import b
from requests.packages.urllib3.filepost import get_content_type

writer = codecs.lookup('utf-8')[3]


def encode_multipart_formdata(fields, boundary=None):
    """Stop rails from doing stupid things by omitting the Content-Type header on non-binary parts."""
    body = BytesIO()
    if boundary is None:
        boundary = choose_boundary()
    for fieldname, value in six.iteritems(fields):
        body.write(b('--%s\r\n' % (boundary)))
        if isinstance(value, tuple):
            filename, data = value
            writer(body).write('Content-Disposition: form-data; name="%s"; '
                               'filename="%s"\r\n' % (fieldname, filename))
            body.write(b('Content-Type: %s\r\n\r\n' %
                         (get_content_type(filename))))
        else:
            data = value
            writer(body).write(
                'Content-Disposition: form-data; name="%s"\r\n\r\n' % (
                    fieldname))
        if isinstance(data, int):
            data = str(data)  # Backwards compatibility

        if isinstance(data, six.text_type):
            writer(body).write(data)
        else:
            body.write(data)

        body.write(b'\r\n')
    body.write(b('--%s--\r\n' % (boundary)))

    content_type = b('multipart/form-data; boundary=%s' % boundary)
    return body.getvalue(), content_type


requests.models.encode_multipart_formdata = encode_multipart_formdata

files = dict(avatar=open('avatar.jpg', 'rb'))
data = dict(name='A picture')

r = requests.post('http://localhost:4567/upload', data=data, files=files)
print r.text

test_one.sh

# running it with a recent version of requests / urllib3. Notice that Rails is parsing the non-binary part incorrectly
$ python test.py

{"name"=>#<ActionDispatch::Http::UploadedFile:0x007ff6b30d2670 @original_filename=nil, @content_type="text/plain", @headers="Content-Disposition: form-data; name=\"name\"\r\nContent-Type: text/plain\r\n", @tempfile=#<File:/var/folders/nb/httvyh1d7616jz77m4k1lxp40000gn/T/RackMultipart20120210-20637-6xlzo8>>, "avatar"=>#<ActionDispatch::Http::UploadedFile:0x007ff6b30d2530 @original_filename="avatar.jpg", @content_type="image/jpeg", @headers="Content-Disposition: form-data; name=\"avatar\"; filename=\"avatar.jpg\"\r\nContent-Type: image/jpeg\r\n", @tempfile=#<File:/var/folders/nb/httvyh1d7616jz77m4k1lxp40000gn/T/RackMultipart20120210-20637-4vziee>>, "action"=>"upload", "controller"=>"home"}

test_two.sh

# running another version with urllib3.filepost.encode_multipart_formdata monkey patched to *not* set a Content-Type header for non-binary parts of the form data (basically just removed https://github.com/shazow/urllib3/blob/master/urllib3/filepost.py#L58 and added the terminal '\r\n' to L57). 

$ python test2.py 
{"name"=>"A picture", "avatar"=>#<ActionDispatch::Http::UploadedFile:0x007ff6b54884c0 @original_filename="avatar.jpg", @content_type="image/jpeg", @headers="Content-Disposition: form-data; name=\"avatar\"; filename=\"avatar.jpg\"\r\nContent-Type: image/jpeg\r\n", @tempfile=#<File:/var/folders/nb/httvyh1d7616jz77m4k1lxp40000gn/T/RackMultipart20120210-20637-rh1v7e>>, "action"=>"upload", "controller"=>"home"}