config.ru

require 'rubygems'
require 'sinatra'

Sinatra::Default.set :run, false
Sinatra::Default.set :environment, ENV['RACK_ENV']

require 'test'
run Sinatra::Application

test.rb

require 'rubygems'
require 'sinatra'

post '/' do
  params['test'][:type] 
end

test.sh

#!/bin/bash
ruby -e "puts 'a' * 20000" > short
ruby -e "puts 'a' * 1000000" > long

# everything works fine without unicorn
ruby test.rb -p 8080 &

sleep 5

curl -v -F test=@short localhost:8080
curl -v -F test=@long localhost:8080

kill -9 $!

# the short test works, the long one doesn't
# EOFError: bad content body
#	/Users/vadim/.gem/ruby/1.8/gems/rack-1.0.0/lib/rack/utils.rb:347:in `parse_multipart'
#	/Users/vadim/.gem/ruby/1.8/gems/rack-1.0.0/lib/rack/utils.rb:319:in `loop'
#	/Users/vadim/.gem/ruby/1.8/gems/rack-1.0.0/lib/rack/utils.rb:319:in `parse_multipart'

unicorn &

sleep 5

curl -v -F test=@short localhost:8080
curl -v -F test=@long localhost:8080

kill -9 $!