Share file descriptors between processes on the same machine using unix domain sockets. Thanks to https://www.linuxquestions.org/questions/programming-9/how-to-share-socket-between-processes-289978/ for the inspiration.

1_README.md

Usage:

Open 2 terminals, run server.rb in one and client.rb in the other. The tcp socket file descriptor will be created in the client, passed to the server, and then used in the server to read from the HTTP server.

client.rb

#!/usr/bin/env ruby

require 'socket'

socket_path = File.expand_path(File.dirname(__FILE__), '.sock')

UNIXSocket.open(socket_path) { |c|
  # open a socket and pass the FD to the other process
  s = TCPSocket.new 'heroku.com', 80
  c.send_io STDOUT
  c.send_io s
  s.close # no longer needed here
  p s.fileno
}

server.rb

#!/usr/bin/env ruby

require 'socket'

socket_path = File.expand_path(File.dirname(__FILE__), '.sock')
File.delete(socket_path) if File.exist?(socket_path)

UNIXServer.open(socket_path) { |serv|
  s = serv.accept
  stdout = s.recv_io
  heroku = TCPSocket.for_fd(s.recv_io.fileno)

  p stdout.fileno
  p heroku.fileno
  p heroku.local_address
  p heroku.remote_address

  # Use the socket opened by client that we received above
  heroku.write "GET / HTTP/1.1\r\n"
  heroku.write "Host: heroku.com\r\n\r\n"

  while (line = heroku.gets)
    break if line.chomp == "0"
    puts line
  end
  heroku.close

  stdout.puts "done"
}