http_server.rb

require 'socket'
require 'rack'
require 'rack/lobster'

app = Rack::Lobster.new
server = TCPServer.new 5678

while session = server.accept
  request = session.gets
  puts request

  method, full_path = request.split(' ')
  path, query = full_path.split('?')

  status, headers, body = app.call({
    'REQUEST_METHOD' => method,
    'PATH_INFO' => path,
    'QUERY_STRING' => query
  })

  session.print "HTTP/1.1 #{status}\r\n"
  headers.each do |key, value|
    session.print "#{key}: #{value}\r\n"
  end
  session.print "\r\n"
  body.each do |part|
    session.print part
  end
  session.close
end

tcp_client.rb

require 'socket'
server = TCPSocket.new 'localhost', 5678

while line = server.gets
  puts line
end

server.close

tcp_server.rb

require 'socket'
server = TCPServer.new 5678

while session = server.accept
  session.print "Hello world! The time is #{Time.now}"
  session.close
end