For administration purposes, I had to rework an uploaded CSV file, and stream it back to the user. I started wondering how I could test this uncommon response body type.

I knew about:

fixture_file_upload

which allows the simulation of a file upload, so I looked at the Rails source, in ActionController’s TestProcess class, where the method lies.

There I found the:

binary_content

method, which does the job by returning the entire streamed content in a string!

How it works

First, let’s take a look at the send_file sources:

...
render :status => options[:status], :text => Proc.new { |response, output|
  logger.info "Streaming file #{path}" unless logger.nil?
  len = options[:buffer_size] || 4096
  File.open(path, 'rb') do |file|
    while buf = file.read(len)
      output.write(buf)
    end
  end
}
...

We see that the response is returned as a Proc. All that binary_content has to do is to:

1. create an IO object,
2. call the proc and pass it the IO object
3. read the IO and return the content as a string

Here is the binary_content method:

def binary_content
  raise "Response body is not a Proc: #{body.inspect}" unless body.kind_of?(Proc)
  require 'stringio'
 
  sio = StringIO.new
  body.call(self, sio)
 
  sio.rewind
  sio.read
end

StringIO’s for the win!

Lazy loading has been a hot topic highly discussed over the internet recently. The amount of bandwidth for the average user has grown tenfold during the last few years, but the web itself has evolved a lot, and so have the contents of the temp folder.

This has created a need to dynamically load a piece of script (to make the host machine download it), instead of just forcing the user download everything from the very first load.

(more…)