client.d

import std.stdio;
import std.socket;
import std.string;
import std.conv;
import std.random;
import std.outbuffer;
import core.thread;

int main() {
  auto s = new TcpSocket();
  // s.blocking(true);

  auto addr = new InternetAddress("localhost", 8111);
  s.connect(addr);

  // char [] data;
  // long r = s.send("hello");
  // writefln("send byte: %d", r);
  long r = s.send(cast(void[])"hello socket world");
  writefln("%d bytes sent.", r) ;

  Thread.sleep( dur!("seconds")( 1 ) );

  char [] data;
  r = s.receive(data);
  writefln("receive byte: %d", r);
  // writeln(data);

  s.close();
  return 0;
}

echo_server.rb

require 'socket'

gs = TCPServer.open(8111)
socks = [gs]
addr = gs.addr
addr.shift
puts "server is on #{addr.join(':')}"

while true
  nsock = select(socks)
  next if nsock == nil
  for s in nsock[0]
    if s == gs
      socks.push(s.accept)
      puts "#{s} is accepted"
    else
      begin
        if s.eof?
          puts "#{s} is gone"
          s.close
          socks.delete(s)
        else
          str = s.gets
          puts "received: #{str}"
          s.write(str)
          if str.strip == 'EOF'
            s.close
            socks.delete(s)
          end

        end
      rescue Exception => e
        puts "#{s} error: #{e.message}"
        s.close
        socks.delete(s)
      end
    end
  end
end

output

$ ruby echo_server.rb
server is on 8111:0.0.0.0:0.0.0.0
#<TCPServer:0x007ff2c989e310> is accepted
received: hello socket world
#<TCPSocket:0x007ff2c989d528> error: Connection reset by peer


$ rdmd client.d 127.0.0.1 8111
18 bytes sent.
receive byte: 0