Pass file descriptors (FD) between unrelated processes via a unix socket

pass_fd_io.rb

    # PASS FD TO ANOTHER PROCESS VIA UNIX SOCKET
    def start_fd_listener
      @pass_fd = UNIXServer.new("/tmp/puma_fd.sock")
      ENV["PUMA_PASS_FD"] = @pass_fd.path
      Thread.new {
        begin

          while true do
              sock = @pass_fd.accept
              binder.listeners.each_with_index do |(bind,io),i|
                # puts "exporting #{bind} on FD #{io.to_i} to socket client"
                sock.puts(bind)
                sock.send_io(io)
              end
              sock.close
          end

        ensure
          # cleanup fd server
          File.unlink(@pass_fd.path)
        end
      }
    end
    
    
  # now to connect and receive the FD:
  UNIXSocket.open(ENV["PUMA_PASS_FD"]) do |sock|
    bind = sock.readline
    io = sock.recv_io()

    # add to binder
    tcp_io = TCPServer.for_fd(io.to_i)
  end