IO                              # The basis for all input and output in Ruby
└── BasicSocket                 # Abstract base class for all socket classes
    ├── IPSocket                # Super class for protocols using the Internet Protocol (AF_INET)
    │   ├── TCPSocket           # Class for Transmission Control Protocol (TCP) sockets
    │   │   ├── SOCKSSocket     # Helper class for building TCP socket servers applications
    │   │   └── TCPServer       # Helper class for building TCP socket servers
    │   └── UDPSocket           # Class for User Datagram Protocol (UDP) sockets
    ├── Socket                  # Base socket class that mimics that BSD Sockets API. It provides more operating system specific functionality
    └── UNIXSocket              # Class providing IPC using the UNIX domain protocol (AF_UNIX)
        └── UNIXServer          # Helper class for building UNIX domain protocol socket servers

Socket.new(domain, socktype [, protocol])

            Client        Server
              |             |                  
   socket     +             +      socket
              |             |
   connect    +--------,    +      bind
              |         |   |
   write ,--> +------,  |   +      listen
         |    |      |  |   |
   read  `----+ <--, |  `-> +      accept
              |    | |      |
   close      +--, | `----> + <--, read <--,
                 | |        |    |         |
                 | `--------+----' write   ٨
                 |                         |
                 `----->------>------->----`

require 'socket'
Socket.ip_address_list

Socket.gethostname

require 'socket'
​
server = TCPServer.new('0.0.0.0', 9911) # Server, binds/listens all interfaces on port 9911
client = server.accept                  # Wait for client to connect
rhost  = client.peeraddr.last           # peeraddr, returns remote [address_family, port, hostname, numeric_address(ip)]
client.puts "Hi TCP Client! #{rhost}"   # Send a message to the client once it connect
client.gets.chomp                       # Read incoming message from client
client.close                            # Close the client's connection
server.close                            # Close the TCP Server

require 'socket'
server = TCPServer.new('0.0.0.0', 0)
server.addr[1]    # Shows the picked port

require 'socket'
​
client = TCPSocket.new('127.0.0.1', 9911)   # Client, connects to server on port 9911
rhost  = client.peeraddr.last               # Get the remote server's IP address 
client.gets.chomp
client.puts "Hi, TCP Server #{rhost}"
client.close

timeval = [3, 0].pack("l_2")        # Time interval 3 seconds 
client.setsockopt Socket::SOL_SOCKET, Socket::SO_RCVTIMEO, timeval      # Set socket receiving time interval 
client.setsockopt Socket::SOL_SOCKET, Socket::SO_SNDTIMEO, timeval      # Set socket sending time interval
client.getsockopt(Socket::SOL_SOCKET, Socket::SO_RCVTIMEO).inspect      # Optional, Check if socket option has been set
client.getsockopt(Socket::SOL_SOCKET, Socket::SO_SNDTIMEO).inspect      # Optional, Check if socket option has been set

>> s = TCPSocket.new('0.0.0.0', 9911)
=> #<TCPSocket:fd 11>
>> s.method :puts
=> #<Method: TCPSocket(IO)#puts>
>> s.method :write
=> #<Method: TCPSocket(IO)#write>
>> s.method :send
=> #<Method: TCPSocket(BasicSocket)#send>

>> s = TCPSocket.new('0.0.0.0', 9911)
=> #<TCPSocket:fd 11>
>> s.method :gets
=> #<Method: TCPSocket(IO)#gets>
>> s.method :read
=> #<Method: TCPSocket(IO)#read>
>> s.method :recv
=> #<Method: TCPSocket(BasicSocket)#recv>

require 'socket'
​
server = UDPSocket.new                                  # Start UDP socket
server.bind('0.0.0.0', 9911)                            # Bind all interfaces to port 9911
mesg, addr = server.recvfrom(1024)                      # Receive 1024 bytes of the message and the sender IP
server puts "Hi, UDP Client #{addr}", addr[3], addr[1]  # Send a message to the client 
server.recv(1024)                                       # Receive 1024 bytes of the message

require 'socket'
client = UDPSocket.new
client.connect('localhost', 9911)       # Connect to server on port 991
client.puts "Hi, UDP Server!", 0        # Send message 
server.recv(1024)                       # Receive 1024 bytes of the server message

require 'gserver'
​
class HelloServer < GServer                 # Inherit GServer class
  def serve(io)
    io.puts("What's your name?")
    line = io.gets.chomp
    io.puts "Hi, #{line}!"
    self.stop if io.gets =~ /shutdown/      # Stop the server if you get shutdown string
  end
end
​
server = HelloServer.new(1234, '0.0.0.0')   # Start the server on port 1234
server.audit = true     # Enable logging
server.start            # Start the service 
server.join