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How To: Build a Simple Server

Overview

In this guide we’re going to walk through the steps required to build a simple chat server. Users will connect using a standard telnet client and start chatting with other users that are connected.

Prerequisites

• Python
• circuits

Components Used

• Component
• TCPServer

Events Used

• Write

Step 1 - Setting up

Let’s start off by importing the components and events we’ll need.

#!/usr/bin/env python

from circuits import Component
from circuits.net.sockets import TCPServer, Write

Step 2 - Building the Server

Next let’s define our Server Component with a simple event handler that broadcasts all incoming messages to every connected client. We’ll keep a list of clients connected to our server in self._clients.

We need to define three event handlers.

1. An event handler to update our list of connected clients when a new client connects.
2. An event handler to update our list of connected clients when a client has disconnected.
3. An event handler to handle messages from connected clients and broadcast them to every other connected client.

class Server(Component):

    def __init__(self, host, port=8000):
        super(Server, self).__init__()

        self._clients = []

        TCPServer((host, port)).register(self)

    def connect(self, sock, host, port):
        self._clients.append(sock)

    def disconnect(self, sock):
        self._clients.remove(sock)

    def read(self, sock, data):
        for client in self._clients:
            if not client == sock:
                self.fire(Write(client, data.strip()))

Let’s walk through this in details:

1. Create a new Component called Server
2. Define its initialization arguments as (host, port=8000)
3. Call the super constructor of the underlying Component (This is important as all components need to be initialized properly)
4. Register a TCPServer Component and configure it.
5. Create Event Handlers for:
   • Dealing with new connecting clients.
   • Dealing with clients whom have disconnected.
   • Dealing with messages from connected clients.

Step 3 - Running the Server

The last step is simply to create an instance of the Server Component and run it (making sure to configure it with a host and port).

Server("localhost").run()

That’s it!

Using a standard telnet client try connecting to localhost on port 8000. Try connecting a second client and watch what happens in the 2nd client when you type text into the 1st.

Enjoy!

Source Code

#!/usr/bin/env python

from circuits import Component
from circuits.net.sockets import TCPServer, Write

class Server(Component):

    def __init__(self, host, port=8000):
        super(Server, self).__init__()

        self._clients = []

        TCPServer((host, port)).register(self)

    def connect(self, sock, host, port):
        self._clients.append(sock)

    def disconnect(self, sock):
        self._clients.remove(sock)

    def read(self, sock, data):
        for client in self._clients:
            if not client == sock:
                self.fire(Write(client, data.strip()))

Server("localhost").run()

Download simple_server.py

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