config.ru

require 'rack'
require 'rack/lobster'

class Streaming
  class Stream
    def each
      %w[a b c].each do |e|
        puts "Stream#each with #{e}"
        sleep 1
        yield e
      end
    end
  end

  def initialize(app)
    @app = app
  end

  def call(env)
    puts "call is called"
    @app.call(env)
    [
      200,
      {},
      Stream.new
    ]
  end
end

class Wrapper
  def initialize(app)
    @app = app
  end

  def call(env)
    puts "wrapper start"
    *res = @app.call(env)
    puts "wrapper end"
    res
  end
end

use Wrapper
use Streaming
run Rack::Lobster.new

response

$ curl -i 'http://localhost:9292'
HTTP/1.1 200 OK
Transfer-Encoding: chunked
Server: WEBrick/1.4.2 (Ruby/2.6.3/2019-04-16)
Date: Mon, 28 Oct 2019 03:54:59 GMT
Connection: Keep-Alive

abc%
$ curl --raw 'http://localhost:9292'
1
a
1
b
1
c
0

server

$ bundle exec rackup
[2019-10-28 15:23:25] INFO  WEBrick 1.4.2
[2019-10-28 15:23:25] INFO  ruby 2.6.3 (2019-04-16) [x86_64-darwin18]
[2019-10-28 15:23:25] INFO  WEBrick::HTTPServer#start: pid=11206 port=9292
wrapper start
call is called
wrapper end
Stream#each with a
Stream#each with b
Stream#each with c
::1 - - [28/Oct/2019:15:23:36 +0900] "GET / HTTP/1.1" 200 - 3.0114