Empty mock response when using IO.copy_stream

[avlazarov]

I'm using the helper Sinatra::Streaming from the sinatra-contrib gem, where the yielded object of the stream method is meant to be IO-like. Hence I'm using IO.copy_stream to feed this IO-like object some data. All works fine when serving via Puma, however when testing the code with rack-test the response body is empty. I managed to pull the important parts from rack-test and got the minimal amount of code to reproduce the issue:

# app.rb
require 'sinatra'
require 'sinatra/streaming'

class App < Sinatra::Base
  helpers Sinatra::Streaming

  get '/copy_stream' do
    stream do |io|
      IO.copy_stream StringIO.new('ok'), io
    end
  end

  get '/write' do
    stream do |io|
      io.write 'ok'
    end
  end
end

# test.rb
require_relative 'app'

def body_for(path)
  env_hash = {
    'rack.test' => true,
    'REQUEST_METHOD' => 'GET',
  }
  env = Rack::MockRequest.env_for "http://localhost:3000/#{path}", env_hash

  status, headers, body = App.call(env).to_a
  response = Rack::MockResponse.new status, headers, body

  response.body
end

body_for('/copy_stream') => ""
body_for('/write') => "ok"

As you can see, just doing io.write 'ok' works fine, however IO.copy_stream for some reason results into an empty mock response body. Does not really matter if the first argument is StringIO, File, or whatever.

Any ideas?

Sinatra and contrib versions: 3.0.2
Rack version: 2.2.4
Ruby version: 3.0.3

[dentarg]

Converted this to a discussion because it isn't clear to me if something needs to be changed in Sinatra. I don't have any explanation, I think you need to dive deeper yourself. Have you read the rack-test source code?

[avlazarov]

@dentarg I'm not using rack-test in the example above, I've just mentioned it since it was where I first found the issue. Both Rack::MockRequest and Rack::MockResponse come from rack itself as the way to test without going through the whole stack. I'm expecting Sinatra's stream option to work with those two, but that does not seems to be the case when using IO.copy_stream.

I can look intro this in details when I have more time, but the fact that write works and IO.copy_steam (which invokes #responds_to?(:to_path) and #write on the source IO-like object) not, is odd.