example.rb

require "bundler/inline"

gemfile do
  source "https://rubygems.org"

  gem "iodine", "0.7.27"
  gem "puma", "3.12.1"
  gem "down", "4.6.1"
  gem "roda"
end

module EachChunk
  def each_chunk(chunk_size = 1024)
    yield read(chunk_size) until eof?
  end
end

app = Class.new(Roda) do
  plugin :streaming

  route do |r|
    data = StringIO.new("This is the data")

    input = Down::ChunkedIO.new(
      size: data.size,
      chunks: data.extend(EachChunk).enum_for(:each_chunk),
      data: {
        content_type: "text/plain"
      }
    )

    stream do |output|
      IO.copy_stream(input, output)
    end
  end
end

server = ARGV[0] or abort "Usage: #{$0} iodine|puma"
Rack::Server.start(app: app, server: server.to_sym, :Port => 9292)