BOUNDARY = "AaB03x"

uri = URI.parse("http://something.com/uploads")
file = "/path/to/your/testfile.txt"

post_body = []
post_body << "--#{BOUNDARY}\r\n"
post_body << "Content-Disposition: form-data; name=\"datafile\"; filename=\"#{File.basename(file)}\"\r\n"
post_body << "Content-Type: text/plain\r\n"
post_body << "\r\n"
post_body << File.read(file)
post_body << "\r\n--#{BOUNDARY}--\r\n"

http = Net::HTTP.new(uri.host, uri.port)
request = Net::HTTP::Post.new(uri.request_uri)
request.body = post_body.join
request["Content-Type"] = "multipart/form-data, boundary=#{BOUNDARY}"

http.request(request)

RestClient.post '/data', :myfile => File.new("/path/to/image.jpg", 'rb')