Bi-Directional Client

Problem

You want to a persistent service over a network, one which maintains an on-going connection with its clients.

Solution

Create a bi-directional TCP client.

In Node.js

net = require 'net'

domain = 'localhost'
port = 9001

ping = (socket, delay) ->
	console.log "Pinging server"
	socket.write "Ping"
	nextPing = -> ping(socket, delay)
	setTimeout nextPing, delay

connection = net.createConnection port, domain

connection.on 'connect', () ->
	console.log "Opened connection to #{domain}:#{port}"
	ping connection, 2000

connection.on 'data', (data) ->
	console.log "Received: #{data}"

connection.on 'end', (data) ->
	console.log "Connection closed"
	process.exit()

Example Usage

Accessing the Bi-Directional Server:

$ coffee bi-directional-client.coffee
Opened connection to localhost:9001
Pinging server
Received: You have 0 peers on this server
Pinging server
Received: You have 0 peers on this server
Pinging server
Received: You have 1 peer on this server
[...]
Connection closed

Discussion

This particular example initiates contact with the server and starts the conversation in the @connection.on ‘connect’@ handler. The bulk of the work in a real client, however, will lie in the @connection.on ‘data’@ handler, which processes output from the server. The @ping@ function only recurses in order to illustrate continuous communication with the server and can be removed from a real client.

See also the Bi-Directional Server, Basic Client, and Basic Server recipes.

Exercises

• Add support for choosing the target domain and port based on command-line arguments or from a configuration file.