Ruby select socket server. An example of a single-threaded, event-driven (select) server.

client_example

$ irb -r ./select_server
>> client.puts "hi"
=> nil
>> client.puts "bye"
=> nil
>> client.close
=> nil
>> exit

select_server.rb

require 'socket'
if defined?(IRB)
  def self.client
    @client ||= TCPSocket.open("0.0.0.0", 4242)
  end
  client
else
  begin
    acceptor = TCPServer.open("0.0.0.0", 4242)
    fds = [acceptor]
    while true
      puts 'loop'
      if ios = select(fds, [], [], 10)
        reads = ios.first
        p reads
        reads.each do |client|
          if client == acceptor
            puts 'Someone connected to server. Adding socket to fds.'
            client, sockaddr = acceptor.accept
            fds << client
          elsif client.eof?
            puts "Client disconnected"
            fds.delete(client)
            client.close
          else
            # Perform a blocking-read until new-line is encountered.
            # We know the client is writing, so as long as it adheres to the
            # new-line protocol, we shouldn't block for very long.
            puts "Reading..."
            p client.gets("\n")
          end
        end
      end
    end
  ensure
    puts "Cleaning up"
    fds.each {|c| c.close}
  end
end

server_example

$ ruby select_server.rb
loop
[#<TCPServer:fd 3>]
Someone connected to server. Adding socket to fds.
loop
[#<TCPSocket:fd 4>]
Reading...
"hi\n"
loop
[#<TCPSocket:fd 4>]
Reading...
"bye\n"
loop
[#<TCPSocket:fd 4>]
Client disconnected
loop
loop
^Cuni.rb:12:in `select': Interrupt
	from uni.rb:12:in `<main>'