self_request.rb

#!/usr/bin/env ruby

require 'rack'
require 'net/http'
require 'uri'

unused_port = -> do
  s = TCPServer.open(0)
  port = s.addr[1]
  s.close
  port
end.()

pid = fork do
  Rack::Handler::WEBrick.run \
    ->(env) { [200, {'Content-Type' => 'text/plain'}, ['Nyan!']] },
    Port:      unused_port,
    Logger:    WEBrick::Log.new("/dev/null"),
    AccessLog: []
end

sleep 1

begin
  puts Net::HTTP.get(URI.parse("http://localhost:#{unused_port}/"))
ensure
  Process.kill 'TERM', pid
end